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مباحث عمومی هواشناسی
- شروع کننده موضوع Amir Mohsen
- تاریخ شروع
- وضعیت
در آخرین یافته هایی که در انجمن ها و بلاگهای هواشناسی خارجی منتشر شده زمستان 2013- 2014 در شباهت بسیار زیادی با زمستان 1962-1963 برآورد شده!!!!
سلام محسن جان
اون کاهش ارتفاع روی اروپا خیلی هیجان‌انگیز به نظر میاد!
زمستان 1962-1963 هم خیلی خوب بود برای اینجا
این نمودارهای ارتفاع برف روی زمین، دمای کمینه و دمای بیشینه از 18 نوامبر ( 1 آذر) هست تا 10 مارس (20 اسفند).
از اول دی تا 15 اسفند ارتفاع برف روی زمین از 20 سانت بیشتر بود.
کمینه مطلق 24- بود
و روزهای متوالی در زمستان دمای بیشینه زیر 8- ثبت شد
من دیشب داشتم به نقش ناهمواری‌های منطقه‌ی خاورمیانه و فلات تبت در شکل‌گیری پرارتفاع‌های داغ! فکر می‌کردم. اینکه کم‌فشارهای گرمایی تشکیل شده در مناطق مرتفع، نقش اساسی رو در افزایش دما در ترازهای بالاتر ایفا میکنند. توی مقاله‌ای که برای ویکیپدیای فارسی در مورد تروپوفاز ترجمه کرده بودم، ارتفاع تروپوفاز عاملی از دماهای زیرینش معرفی شده بود، نه معلولش.اما سوال خودت
شاید چون تروپوسفر در مناطق نزدیک به استوا ضخیمتره و دما با افزایش ارتفاع دیرتر کاهش پیدا می کنه . صعود هوای گرم و ارتفاعات خیلی بلند هم در دمای تراز ۵۰۰ موثرند. در البته مرکز پر ارتفاع جنب حاره ای نزول هوا رو داریم و در تراز میانی جو هوای اطراف رو با همگرایی درون خودش می مکه و میده پایین. شاید اگه یک مرکز پر ارتفاع نزدیکتر به استوا باشه هوای گرمتری به درون خودش می کشه.
دمای تراز ۵۰۰ هکتوپاسکال:
ارتفاع Tropopause:
تروپوفاز از دمای تمام لایه‌های زیرین خود تاثیر می‌پذیرد٬ بنابراین در مناطق استوایی به بیشترین ارتفاع و در نقاط قطبی به کمترین ارتفاع خود می‌رسد. به همین دلیل٬ سردترین لایه در جو٬ در ارتفاع ۱۷ کیلومتری از سطح زمین بر فراز استوا قرار دارد. به دلیل تفاوت ارتفاع نقاط مختلف تروپوفاز٬ بیشترین و کمترین ارتفاع‌های این لایه با نام‌های تروپوفاز استوایی و تروپوفاز قطبی شناخته می‌شود
درود بر امیر محسن عزیز این زمستون 62-63همون زمستونی نیست که میگن همدان توش رکورد زده؟در آخرین یافته هایی که در انجمن ها و بلاگهای هواشناسی خارجی منتشر شده زمستان 2013- 2014 در شباهت بسیار زیادی با زمستان 1962-1963 برآورد شده!!!!
سلام محسن جان
اون کاهش ارتفاع روی اروپا خیلی هیجان‌انگیز به نظر میاد!
زمستان 1962-1963 هم خیلی خوب بود برای اینجا
این نمودارهای ارتفاع برف روی زمین، دمای کمینه و دمای بیشینه از 18 نوامبر ( 1 آذر) هست تا 10 مارس (20 اسفند).
از اول دی تا 15 اسفند ارتفاع برف روی زمین از 20 سانت بیشتر بود.
کمینه مطلق 24- بود
و روزهای متوالی در زمستان دمای بیشینه زیر 8- ثبت شد
درود ماهان جان
اروپا با منطقه ما الاکلنگ هستند، اگر مرکز اروپا اینطوری بوده پس ما باید زمستان گرم و خشکی داشته باشیم؟
والا آرش جان من نمی‌دونم این پیش‌بینی که امیرمحسن گذاشتن تا چه حد به وقوع می‌پیونده. ولی زمستان 1963 در ژانویه و فوریه دمای رشت 4 درجه بالای نرمال بود، از پارسال هم بدتر بود یعنی!! این دو ماه حتا یک روز یخبندان نداشت و فقط سه روز در ماه مارس بارش برف ثبت شد. اگه توی اون نمودارها نگاه کنین از 10 مارس اینجا افزایش ناگهانی دما داشت. البته بارش رشت در حد نرمال بود.
Amir Mohsen
متخصص بخش هواشناسی
درود آرش جان و پوزش بابت تاخیر در پاسخ چون واسه انجام کاری بیرون بودم.
والا در این پیش بینی اذعان شده که در اوایل زمستان ما وارد دوره النیو خفیف با تمایل به متوسط خواهیم شد. و شاخص NAO بعنی همون نوسان اقیانوس اطلس شمالی هم در فاز منفی قوی قرار خواهد گرفت!! اما در ارتباط با سرما و تقویت پرفشار سیبری همه چیز بر میگرده به روند شاخص AO یعنی اقیانوس منجد شمالی و اگه اون مثبت باشه که این مهم محقق خواهد شد.
ماهان جان سلام
والا واسه اروپا که مطابق با این پیش بینی هوای سردی پیش بینی شده ولی بنظر شدت سرما بیشتر در اروپای شرقی خواهد بود.
انشاء الله در پست بعدی متن و جزئیات کامل این پیش بینی که زمستان بسیار سختی رو برای شرق آسیا و شرق و جنوب شرق آمریکا در نظر گرفته رو در همینجا به زبان اصلی واسه استفاده دوستان عزیز خواهم گذاشت
محمد رضا جان
خیلی ممنون. اگه میزان بارش اکتبر تا دسامبر سال 1962 میلادی رو هم برای سال 1963 میلادی در نظر بگیرم، و در صورت تحقق سال پر خیر و پرکتی واسه ما مشهدی ها خواهد بود.
جزئیات دمایی مشهد در اون ایام چطوره؟
درود دوست خوبم
والا اینو فکر میکنم محمد رضا و محمد عزیز باید اعلام کنند که تخصص بینظیر در تهیه آمار جوی کشور دارند.:گل:
والا در این پیش بینی اذعان شده که در اوایل زمستان ما وارد دوره النیو خفیف با تمایل به متوسط خواهیم شد. و شاخص NAO بعنی همون نوسان اقیانوس اطلس شمالی هم در فاز منفی قوی قرار خواهد گرفت!! اما در ارتباط با سرما و تقویت پرفشار سیبری همه چیز بر میگرده به روند شاخص AO یعنی اقیانوس منجد شمالی و اگه اون مثبت باشه که این مهم محقق خواهد شد.
ماهان جان سلام
والا واسه اروپا که مطابق با این پیش بینی هوای سردی پیش بینی شده ولی بنظر شدت سرما بیشتر در اروپای شرقی خواهد بود.
انشاء الله در پست بعدی متن و جزئیات کامل این پیش بینی که زمستان بسیار سختی رو برای شرق آسیا و شرق و جنوب شرق آمریکا در نظر گرفته رو در همینجا به زبان اصلی واسه استفاده دوستان عزیز خواهم گذاشت
سلام محسن جان
اون کاهش ارتفاع روی اروپا خیلی هیجان‌انگیز به نظر میاد!
زمستان 1962-1963 هم خیلی خوب بود برای اینجا
این نمودارهای ارتفاع برف روی زمین، دمای کمینه و دمای بیشینه از 18 نوامبر ( 1 آذر) هست تا 10 مارس (20 اسفند).
از اول دی تا 15 اسفند ارتفاع برف روی زمین از 20 سانت بیشتر بود.
کمینه مطلق 24- بود
و روزهای متوالی در زمستان دمای بیشینه زیر 8- ثبت شد
محمد رضا جان
خیلی ممنون. اگه میزان بارش اکتبر تا دسامبر سال 1962 میلادی رو هم برای سال 1963 میلادی در نظر بگیرم، و در صورت تحقق سال پر خیر و پرکتی واسه ما مشهدی ها خواهد بود.
جزئیات دمایی مشهد در اون ایام چطوره؟
درود دوست خوبم
والا اینو فکر میکنم محمد رضا و محمد عزیز باید اعلام کنند که تخصص بینظیر در تهیه آمار جوی کشور دارند.:گل:
Amir Mohsen
متخصص بخش هواشناسی
پیش بینی چشم انداز وضعیت جوی زمستان 2013-2014 - بخش اول
Amir Mohsen
متخصص بخش هواشناسی
پیش بینی چشم انداز وضعیت جوی زمستان 2013-2014 - بخش دوم
Amir Mohsen
متخصص بخش هواشناسی
تو یک بخش از این پیش بینی اومده که این احتمال بسیار زیاده که امسال ورتکس قطبی به عرضهای پایین تر جغرافیایی کشیده بشه:
-The polar vortex may be at lower latitudes this winter. -
-The polar vortex may be at lower latitudes this winter. -
البته محسن جان نکنه اینا از روی جوگیری پیش‌بینی می‌کنن؟ مثلن ما با دیدن یه نقشه نوسان اطلس شمالی گاهی می‌گیم که چه خوب می‌شه امسال بشه مث 1386 و اینا بجای 1386 میگن مثل 1963؟؟
)Amir Mohsen
متخصص بخش هواشناسی
حالا باید تا 15 جولای صبر کنیم تا جدیدترین پیش بینی زمستان 2013-2014 منتشر بشه
Amir Mohsen
متخصص بخش هواشناسی
البته محسن جان نکنه اینا از روی جوگیری پیش‌بینی می‌کنن؟ مثلن ما با دیدن یه نقشه نوسان اطلس شمالی گاهی می‌گیم که چه خوب می‌شه امسال بشه مث 1386 و اینا بجای 1386 میگن مثل 1963؟؟
حالا ماهان جان
اون زمستون برای آمریکایی ها خیلی رویایی بوده و برف و سرمای شدیدی داشتند:تعجب2:
Amir Mohsen
متخصص بخش هواشناسی
این پیش بینی امروز صبح دیگه چی چی میگه؟!!!!!!!!!!!!!!!
Amir Mohsen
متخصص بخش هواشناسی
خلاصه ای از وضعیت جوی ایستگاه فرودگاه مشهد در سال 2012 میلادی
Historical Weather For 2012 in Mashhad, Iran
Location
This report describes the historical weather record at the Mashhad International Airport (Shahid Hashemi Nejad Airport) (Mashhad, Iran) during 2012. This station has records back to March 1949.
Mashhad has a cold semi-arid steppe climate. The area within 40 km of this station is covered by shrublands (67%), grasslands (21%), and croplands (11%)
Calendar
Daylight saving time (DST) was observed at Mashhad during 2012. There were two time changes during 2012:
2012 was a leap year and thus has 366 days rather than the normal 365. Leap years occur every fourth year and the extra day is always February 29th. In 2012 February 29th falls on a Wednesday.
The summer and winter solstices and the spring and fall equinoxes mark the passing of the seasons. They fall on nearly the same day each year, with differences of a day or two depending on the year. In 2012 they occurred on:
Temperature
The hottest day of 2012 was July 10, with a high temperature of 40°C. For reference, on that day the average high temperature is 35°C and the high temperature exceeds 38°C only one day in ten. The hottest month of 2012 was July with an average daily high temperature of 36°C.
Relative to the average, the hottest day was November 11. The high temperature that day was 33°C, compared to the average of 16°C, a difference of 17°C. In relative terms the warmest month was April, with an average high temperature of 24°C, compared to an typical value of 22°C.
The longest warm spell was from March 30 to April 19, constituting 21 consecutive days with warmer than average high temperatures. The month of July had the largest fraction of warmer than average days with 74% days with higher than average high temperatures.
Temperature
The daily low (blue) and high (red) temperature during 2012 with the area between them shaded gray and superimposed over the corresponding averages (thick lines), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile). The bar at the top of the graph is red where both the daily high and low are above average, blue where they are both below average, and white otherwise.
The coldest day of 2012 was December 28, with a low temperature of -17°C. For reference, on that day the average low temperature is -1°C and the low temperature drops below -6°C only one day in ten. The coldest month of 2012 was January with an average daily low temperature of -4°C.
Relative to the average, the coldest day was December 28. The low temperature that day was -17°C, compared to the average of -1°C, a difference of 16°C. In relative terms the coldest month was February, with an average low temperature of -2°C, compared to an typical value of 0°C.
The longest cold spell was from March 4 to March 15, constituting 12 consecutive days with cooler than average low temperatures. The month of February had the largest fraction of cooler than average days with 72% days with lower than average low temperatures.
Hourly Temperature Bands
The full year of hourly temperature reports with the days of the year on the horizontal and the hours of the day on the vertical. The hourly temperature measurement is color coded into meaningful temperature bands: frigid is purple (below -9°C), freezing is blue (-9°C to 0°C), cold is dark green (0°C to 10°C), cool is light green (10°C to 18°C), comfortable is yellow (18°C to 24°C), warm is light red (24°C to 29°C), hot is medium red (29°C to 38°C), sweltering is dark red (above 38°C), and missing data is pink.
Clouds
The clearest month of 2012 was August, with 100% of days being more clear than cloudy. The longest spell of clear weather was from July 26 to September 29, constituting 66 consecutive days that were clearer than they were cloudy.
Cloud Coverage
The fraction of time spent in each of the five sky cover categories over the course of 2012 on a daily basis. From top (most blue) to bottom (most gray), the categories are clear, mostly clear, partly cloudy, mostly cloudy, and overcast. Pink indicates missing data. Outside of the United States clear skies are often reported ambiguously, leading them to be lumped in with the missing data. The bar at the top of the graph is gray if the sky was cloudy or mostly cloudy for more than half the day, blue if it is clear or mostly clear for more than half the day, and blue-gray otherwise.
The cloudiest month of 2012 was November, with 30% of days being more cloudy than clear. The longest spell of cloudy weather was from December 12 to December 19, constituting 8 consecutive days that were cloudier than they were clear.
Hourly Cloud Coverage
The full year of hourly cloud coverage reports with the days of the year on the horizontal and the hours of the day on the vertical. The sky cover is color coded: from most blue to most gray, the categories are clear, mostly clear, partly cloudy, mostly cloudy, and overcast. Pink indicates missing data. Outside of the United States clear skies are often reported ambiguously, leading them to be lumped in with the missing data.
Precipitation
This station provides hourly reports of significant weather events at and around the station, but does not report the quantity of precipitation at the station itself. This is common for weather stations located outside of the United States, and for a small subset of stations in the United States that are located at lesser used and smaller airports.
Present Weather Reports
This station reports when significant weather events (including precipitation) are visually observed at or near the station. Such events do not always correspond to measured quantities of liquid equivalent precipitation, such as when the event is near by not at the station, or in the case of solid precipitation that does not melt in the collection basin.
The day in 2012 with the most precipitation observations was January 14. There were 24 hourly weather reports that day (out of a maximum of 24) in which some form of precipitation was observated at or near the station. The month with the most precipitation observations was December, with 108 hourly present weather reports involving some form of precipitation.
Precipitation Reports
The daily number of hourly observed precipitation reports during 2012, color coded according to precipitation type, and stacked in order of severity. From the bottom up, the categories are thunderstorms (orange); heavy, moderate, and light snow (dark to light blue); heavy, moderate, and light rain (dark to light green); and drizzle (lightest green). Not all categories are necessarily present in this particular graph. The faint shaded areas indicate climate normals. The bar at the top of the graph is green if any precipitation was observed that day and white otherwise.
As determined by the present weather reports, the longest dry spell was from June 22 to September 29, constituting 100 consecutive days with no observed precipitation. The months July and August were completely without observed precipitation.
The month with the largest fraction of days with at least some observed precipitation was May, with 55% of days reporting some observed precipitation.
Hourly Weather Reports
The full year of hourly present weather reports with the days of the year on the horizontal and the hours of the day on the vertical. The color-coded categories are thunderstorms (orange); heavy, moderate, and light snow (dark to light blue); heavy, moderate, and light rain (dark to light green); drizzle (lightest green); freezing rain and sleet (light and dark cyan); snow grains (lightest blue); hail (red); fog (gray); and haze (brownish gray).
Liquid Precipitation Reports
In this section we consider only those weather reports that indicate liquid precipitation. For the purposes of this analysis, we include thunderstorms even though some thunderstorms are not accompanied by liquid precipitation.
The month of 2012 with the largest number of those reports was May, with a total of 64 reports. The day with the largest number of those reports was December 12, with a total of 20 reports.
Liquid Precipitation Reports
The daily number of hourly observed liquid precipitation reports (including thunderstorms) during 2012, with climate normals (faint shaded areas). The bar at the top of the graph is green if any liquid precipitation was observed that day and white otherwise.
Snow
This station reports both when snow is observed to be falling and the measured depth of the snow on the ground. Both are subject to erroneous reports, but the latter is significantly less reliable. Please bear this in mind when reading this section.
Reports
In this section we consider hourly weather reports that contain an observation of falling snow. These reports do not necessarily correspond to accumulation.
The first reported snow fall in 2012 was on December 15; the last was on March 19. The month of 2012 with the largest number of those reports was December, with a total of 79 reports. The day with the largest number of those reports was December 26, with a total of 24 reports.
Snow Reports
The daily number of hourly observed snow reports during 2012, with climate normals (faint shaded areas). The bar at the top of the graph is blue if there was snow fall observed that day and white otherwise.
Depth
Snow depth on the ground is an optional and inconsistently reported part of standard weather reports. It is rarely reported more often than every six hours, it is often skipped, it is often reported erroneously, and a snow depth of zero is normally not distinguished from a missing report. These issues (particularly the last one) make it hard to collect statistics on snow depth with any confidence. To overcome this issue, we base our statistics on only those reports with present non-zero measurements of snow depth. Reports that fail to mention snow that is present, and reports that do not report snow depth because there is no snow on the ground are excluded because they cannot be distinguished from one another.
The first reported accumulation in 2012 was on December 17. The last day of the snow season with snow reported on the ground was March 20. The day with the deepest snow depth was December 27, with an average snow depth of 29.0 cm over the course of the day. The longest stretch of time during which there was always snow on the ground was from January 4 to January 11 (8 consecutive days).
Snow Depth
Snow depth on the ground (thick blue line) during 2012 with median value of non-zero reports from previous years (thick faint gray line), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile). The bar at the top of the graph is blue if there was snow on the ground that day and white otherwise.
Humidity
Humidity is an important factor in determining how weather conditions feel to a person experiencing them. Hot and humid days feel even hotter than hot and dry days because the high level of water content in humid air discourages the evaporation of sweat from a person's skin.
When reading the graph below, keep in mind that the hottest part of the day tends to be the least humid, so the daily low (brown) traces are more relevant for understanding daytime comfort than the daily high (blue) traces, which typically occur during the night. Applying that observation, the least humid month of 2012 was August with an average daily low humidity of 10%, and the most humid month was January with an average daily low humidity of 54%.
But it is important to keep in mind that humidity does not tell the whole picture and the dew point is often a better measure of how comfortable a person will find a given set of weather conditions. Please see the next section for continued discussion of this point.
Humidity
The daily low (brown) and high (blue) relative humidity during 2012 with the area between them shaded gray and superimposed over the corresponding averages (thick lines), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).
Dew Point
Dew point is the temperature below which water vapor will condense into liquid water. It is therefore also related to the rate of evaporation of liquid water. Since the evaporation of sweat is an important cooling mechanism for the human body, the dew point is an important measurement for understanding how dry, comfortable, or humid a given set of weather conditions will feel.
Generally speaking, dew points below 10°C will feel a bit dry to some people, but comfortable to people accustomed to dry conditions; dew points from 10°C to 20°C are fairly comfortable to most people, and dew points above 20°C are increasingly uncomfortable, becoming oppressive around 25°C.
To take some examples, and basing our categorization on the daily high dew point in 2012, January had 31 dry days, no comfortable days, and no humid days; April had 15 dry days, 15 comfortable days, and no humid days; July had 24 dry days, 7 comfortable days, and no humid days; and October had 27 dry days, 4 comfortable days, and no humid days.
Dew Point
The daily low (blue) and high (red) dew point during 2012 with the area between them shaded gray and superimposed over the corresponding averages (thick lines), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).
Wind
The highest sustained wind speed was 21 m/s, occurring on May 5; the highest daily mean wind speed was 10 m/s (February 12); and the highest wind gust speed was 10 m/s (March 23).
The windiest month was July, with an average wind speed of 5 m/s. The least windy month was January, with an average wind speed of 2 m/s.
Wind Speed
The daily low and high wind speed (light gray area) and the maximum daily wind gust speed (tiny blue dashes).
Visibility
Visibility is the maximum distance at which a given reference object or light can be clearly discerned. In the United States, visibilities that are greater than or equal to 10 miles are typically reported as 10 miles.
The day of 2012 with the lowest average visibility was December 26, with an average visibility of 0.9 km. The month with the lowest average visibility was December, with an average visibility of 5.9 km. With an average visibility of 11.1 km, the month of August had the highest average visibility.
Visibility
The daily average visibility, depicted as gray bars encroaching down from the top of the graph.
Cloud Ceiling
The cloud ceiling is the altitude of the lowest layer of clouds that are at categorized as broken (mostly cloudy) or overcast (cloudy). If no such cloud layer exists then the ceiling is unlimited and no value is reported.
The day of 2012 with the lowest average cloud ceiling was December 20, with an average cloud ceiling of 24 m. The month with the lowest average cloud ceiling was January, with an average cloud ceiling of 1500 m. The month of May has the highest average cloud ceiling, with an average cloud ceiling of 4125 m.
Cloud Ceiling
The daily average cloud ceiling, depicted as gray bars encroaching down from the top of the graph. Missing data or days with insufficient clouds to define a cloud ceiling are shown as white columns.
Location
This report describes the historical weather record at the Mashhad International Airport (Shahid Hashemi Nejad Airport) (Mashhad, Iran) during 2012. This station has records back to March 1949.
Mashhad has a cold semi-arid steppe climate. The area within 40 km of this station is covered by shrublands (67%), grasslands (21%), and croplands (11%)
Calendar
Daylight saving time (DST) was observed at Mashhad during 2012. There were two time changes during 2012:
- DST started on Wednesday March 21, 2012 at 1:00 am, from IRST (GMT+3.5) to IRDT (GMT+4.5).
- DST ended on Thursday September 20, 2012 at 23:00 pm, from IRDT (GMT+4.5) to IRST (GMT+3.5).
2012 was a leap year and thus has 366 days rather than the normal 365. Leap years occur every fourth year and the extra day is always February 29th. In 2012 February 29th falls on a Wednesday.
The summer and winter solstices and the spring and fall equinoxes mark the passing of the seasons. They fall on nearly the same day each year, with differences of a day or two depending on the year. In 2012 they occurred on:
| Spring Equinox | Tuesday, 20 March 2012. |
|---|---|
| Summer Solstice | Wednesday, 20 June 2012. |
| Fall Equinox | Saturday, 22 September 2012. |
| Winter Solstice | Friday, 21 December 2012. |
Temperature
The hottest day of 2012 was July 10, with a high temperature of 40°C. For reference, on that day the average high temperature is 35°C and the high temperature exceeds 38°C only one day in ten. The hottest month of 2012 was July with an average daily high temperature of 36°C.
Relative to the average, the hottest day was November 11. The high temperature that day was 33°C, compared to the average of 16°C, a difference of 17°C. In relative terms the warmest month was April, with an average high temperature of 24°C, compared to an typical value of 22°C.
The longest warm spell was from March 30 to April 19, constituting 21 consecutive days with warmer than average high temperatures. The month of July had the largest fraction of warmer than average days with 74% days with higher than average high temperatures.
Temperature
The daily low (blue) and high (red) temperature during 2012 with the area between them shaded gray and superimposed over the corresponding averages (thick lines), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile). The bar at the top of the graph is red where both the daily high and low are above average, blue where they are both below average, and white otherwise.
The coldest day of 2012 was December 28, with a low temperature of -17°C. For reference, on that day the average low temperature is -1°C and the low temperature drops below -6°C only one day in ten. The coldest month of 2012 was January with an average daily low temperature of -4°C.
Relative to the average, the coldest day was December 28. The low temperature that day was -17°C, compared to the average of -1°C, a difference of 16°C. In relative terms the coldest month was February, with an average low temperature of -2°C, compared to an typical value of 0°C.
The longest cold spell was from March 4 to March 15, constituting 12 consecutive days with cooler than average low temperatures. The month of February had the largest fraction of cooler than average days with 72% days with lower than average low temperatures.
Hourly Temperature Bands
The full year of hourly temperature reports with the days of the year on the horizontal and the hours of the day on the vertical. The hourly temperature measurement is color coded into meaningful temperature bands: frigid is purple (below -9°C), freezing is blue (-9°C to 0°C), cold is dark green (0°C to 10°C), cool is light green (10°C to 18°C), comfortable is yellow (18°C to 24°C), warm is light red (24°C to 29°C), hot is medium red (29°C to 38°C), sweltering is dark red (above 38°C), and missing data is pink.
Clouds
The clearest month of 2012 was August, with 100% of days being more clear than cloudy. The longest spell of clear weather was from July 26 to September 29, constituting 66 consecutive days that were clearer than they were cloudy.
Cloud Coverage
The fraction of time spent in each of the five sky cover categories over the course of 2012 on a daily basis. From top (most blue) to bottom (most gray), the categories are clear, mostly clear, partly cloudy, mostly cloudy, and overcast. Pink indicates missing data. Outside of the United States clear skies are often reported ambiguously, leading them to be lumped in with the missing data. The bar at the top of the graph is gray if the sky was cloudy or mostly cloudy for more than half the day, blue if it is clear or mostly clear for more than half the day, and blue-gray otherwise.
The cloudiest month of 2012 was November, with 30% of days being more cloudy than clear. The longest spell of cloudy weather was from December 12 to December 19, constituting 8 consecutive days that were cloudier than they were clear.
Hourly Cloud Coverage
The full year of hourly cloud coverage reports with the days of the year on the horizontal and the hours of the day on the vertical. The sky cover is color coded: from most blue to most gray, the categories are clear, mostly clear, partly cloudy, mostly cloudy, and overcast. Pink indicates missing data. Outside of the United States clear skies are often reported ambiguously, leading them to be lumped in with the missing data.
Precipitation
This station provides hourly reports of significant weather events at and around the station, but does not report the quantity of precipitation at the station itself. This is common for weather stations located outside of the United States, and for a small subset of stations in the United States that are located at lesser used and smaller airports.
Present Weather Reports
This station reports when significant weather events (including precipitation) are visually observed at or near the station. Such events do not always correspond to measured quantities of liquid equivalent precipitation, such as when the event is near by not at the station, or in the case of solid precipitation that does not melt in the collection basin.
The day in 2012 with the most precipitation observations was January 14. There were 24 hourly weather reports that day (out of a maximum of 24) in which some form of precipitation was observated at or near the station. The month with the most precipitation observations was December, with 108 hourly present weather reports involving some form of precipitation.
Precipitation Reports
The daily number of hourly observed precipitation reports during 2012, color coded according to precipitation type, and stacked in order of severity. From the bottom up, the categories are thunderstorms (orange); heavy, moderate, and light snow (dark to light blue); heavy, moderate, and light rain (dark to light green); and drizzle (lightest green). Not all categories are necessarily present in this particular graph. The faint shaded areas indicate climate normals. The bar at the top of the graph is green if any precipitation was observed that day and white otherwise.
As determined by the present weather reports, the longest dry spell was from June 22 to September 29, constituting 100 consecutive days with no observed precipitation. The months July and August were completely without observed precipitation.
The month with the largest fraction of days with at least some observed precipitation was May, with 55% of days reporting some observed precipitation.
Hourly Weather Reports
The full year of hourly present weather reports with the days of the year on the horizontal and the hours of the day on the vertical. The color-coded categories are thunderstorms (orange); heavy, moderate, and light snow (dark to light blue); heavy, moderate, and light rain (dark to light green); drizzle (lightest green); freezing rain and sleet (light and dark cyan); snow grains (lightest blue); hail (red); fog (gray); and haze (brownish gray).
Liquid Precipitation Reports
In this section we consider only those weather reports that indicate liquid precipitation. For the purposes of this analysis, we include thunderstorms even though some thunderstorms are not accompanied by liquid precipitation.
The month of 2012 with the largest number of those reports was May, with a total of 64 reports. The day with the largest number of those reports was December 12, with a total of 20 reports.
Liquid Precipitation Reports
The daily number of hourly observed liquid precipitation reports (including thunderstorms) during 2012, with climate normals (faint shaded areas). The bar at the top of the graph is green if any liquid precipitation was observed that day and white otherwise.
Snow
This station reports both when snow is observed to be falling and the measured depth of the snow on the ground. Both are subject to erroneous reports, but the latter is significantly less reliable. Please bear this in mind when reading this section.
Reports
In this section we consider hourly weather reports that contain an observation of falling snow. These reports do not necessarily correspond to accumulation.
The first reported snow fall in 2012 was on December 15; the last was on March 19. The month of 2012 with the largest number of those reports was December, with a total of 79 reports. The day with the largest number of those reports was December 26, with a total of 24 reports.
Snow Reports
The daily number of hourly observed snow reports during 2012, with climate normals (faint shaded areas). The bar at the top of the graph is blue if there was snow fall observed that day and white otherwise.
Depth
Snow depth on the ground is an optional and inconsistently reported part of standard weather reports. It is rarely reported more often than every six hours, it is often skipped, it is often reported erroneously, and a snow depth of zero is normally not distinguished from a missing report. These issues (particularly the last one) make it hard to collect statistics on snow depth with any confidence. To overcome this issue, we base our statistics on only those reports with present non-zero measurements of snow depth. Reports that fail to mention snow that is present, and reports that do not report snow depth because there is no snow on the ground are excluded because they cannot be distinguished from one another.
The first reported accumulation in 2012 was on December 17. The last day of the snow season with snow reported on the ground was March 20. The day with the deepest snow depth was December 27, with an average snow depth of 29.0 cm over the course of the day. The longest stretch of time during which there was always snow on the ground was from January 4 to January 11 (8 consecutive days).
Snow Depth
Snow depth on the ground (thick blue line) during 2012 with median value of non-zero reports from previous years (thick faint gray line), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile). The bar at the top of the graph is blue if there was snow on the ground that day and white otherwise.
Humidity
Humidity is an important factor in determining how weather conditions feel to a person experiencing them. Hot and humid days feel even hotter than hot and dry days because the high level of water content in humid air discourages the evaporation of sweat from a person's skin.
When reading the graph below, keep in mind that the hottest part of the day tends to be the least humid, so the daily low (brown) traces are more relevant for understanding daytime comfort than the daily high (blue) traces, which typically occur during the night. Applying that observation, the least humid month of 2012 was August with an average daily low humidity of 10%, and the most humid month was January with an average daily low humidity of 54%.
But it is important to keep in mind that humidity does not tell the whole picture and the dew point is often a better measure of how comfortable a person will find a given set of weather conditions. Please see the next section for continued discussion of this point.
Humidity
The daily low (brown) and high (blue) relative humidity during 2012 with the area between them shaded gray and superimposed over the corresponding averages (thick lines), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).
Dew Point
Dew point is the temperature below which water vapor will condense into liquid water. It is therefore also related to the rate of evaporation of liquid water. Since the evaporation of sweat is an important cooling mechanism for the human body, the dew point is an important measurement for understanding how dry, comfortable, or humid a given set of weather conditions will feel.
Generally speaking, dew points below 10°C will feel a bit dry to some people, but comfortable to people accustomed to dry conditions; dew points from 10°C to 20°C are fairly comfortable to most people, and dew points above 20°C are increasingly uncomfortable, becoming oppressive around 25°C.
To take some examples, and basing our categorization on the daily high dew point in 2012, January had 31 dry days, no comfortable days, and no humid days; April had 15 dry days, 15 comfortable days, and no humid days; July had 24 dry days, 7 comfortable days, and no humid days; and October had 27 dry days, 4 comfortable days, and no humid days.
Dew Point
The daily low (blue) and high (red) dew point during 2012 with the area between them shaded gray and superimposed over the corresponding averages (thick lines), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).
Wind
The highest sustained wind speed was 21 m/s, occurring on May 5; the highest daily mean wind speed was 10 m/s (February 12); and the highest wind gust speed was 10 m/s (March 23).
The windiest month was July, with an average wind speed of 5 m/s. The least windy month was January, with an average wind speed of 2 m/s.
Wind Speed
The daily low and high wind speed (light gray area) and the maximum daily wind gust speed (tiny blue dashes).
Visibility
Visibility is the maximum distance at which a given reference object or light can be clearly discerned. In the United States, visibilities that are greater than or equal to 10 miles are typically reported as 10 miles.
The day of 2012 with the lowest average visibility was December 26, with an average visibility of 0.9 km. The month with the lowest average visibility was December, with an average visibility of 5.9 km. With an average visibility of 11.1 km, the month of August had the highest average visibility.
Visibility
The daily average visibility, depicted as gray bars encroaching down from the top of the graph.
Cloud Ceiling
The cloud ceiling is the altitude of the lowest layer of clouds that are at categorized as broken (mostly cloudy) or overcast (cloudy). If no such cloud layer exists then the ceiling is unlimited and no value is reported.
The day of 2012 with the lowest average cloud ceiling was December 20, with an average cloud ceiling of 24 m. The month with the lowest average cloud ceiling was January, with an average cloud ceiling of 1500 m. The month of May has the highest average cloud ceiling, with an average cloud ceiling of 4125 m.
Cloud Ceiling
The daily average cloud ceiling, depicted as gray bars encroaching down from the top of the graph. Missing data or days with insufficient clouds to define a cloud ceiling are shown as white columns.
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