July 2012 hottest month in US history.. extends warmest 12 month period on record

July 2012 has finished as the hottest month in the contiguous US since national records started in 1895, according to recent figures from the National Climatic Data Center. The national monthly average of 77.6F in July 2012 was 0.2F warmer than the previous hottest month of July 1936, set during the great Dust Bowl era.  The month was dominated by hot and dry conditions over most of the US, with the heat mainly centered over the Great Plains through the midwest and Ohio Valley into the mid Atlantic seaboard.  Seven states recorded their 2nd warmest July on record on a statewide average.

The record hot month extended the persistent warmth that began last summer, with the last 12 months now standing as the warmest 12 month period in the US since 1895. The average US national temperature over the last 12 months has been 56.1F (13C), or about 3.3F above normal. Previous to this year, the warmest 12 month period was Nov 1999 to Oct 2000 which averaged 2.7F above normal at 55.5F. The record warmth has also been occurring north of the border as well. Winnipeg has recorded 13 consecutive months above normal dating back to July 2011, and the last 12 months (August 2011-July 2012) have been the warmest 12 month period on record since records began in Winnipeg in 1872. Prior to this year, the warmest 12 month period in the city was from Nov 1877 to Oct 1878, thanks to the record warm El Nino winter of 1877-1878 (still the warmest winter on record in Winnipeg)  

Graph of national US temperature
anomalies since 1895.   Note how much
warmer 2012 has been to date, warmer
than any other similar period since 1895.

In addition, the year to date average of 56.4F so far in 2012 is the warmest Jan-July period ever recorded in the US, easily beating the previous warmest Jan-July period of 1998 (at 54.5F) The graph left shows how dramatically warmer this year has been to date, especially with the warm winter and spring that has made this year warmer than any other corresponding period in US history (since 1895 anyways)  In Winnipeg, our year to date average through the end of July 2012 is 4.0C, tying 1987 for the warmest year through July. (1987 stands as Winnipeg's warmest calendar year with an average of 5.4C.)  For more details on the exceptional warmth of July 2012 and the past year, see blog entries from Dr Jeff Masters and climate historian Chris Burt.              

Pleasant week ahead..

Generally dry and warm weather is expected through the upcoming week with little in the way of weather systems affecting Winnipeg and the Red River valley. Models are indicating a weak system tracking from southern Saskatchewan into North Dakota Tuesday night into Wednesday that may bring some scattered showers and thunderstorms over southwest MB, but the bulk of precipitation with that system is expected to remain south of the border. Other than that, it looks like mainly sunny and seasonably warm weather this week with temperatures in the mid to upper 20s, along with comfortable humidity levels and generally light winds.  Enjoy!

Wet start to the holiday weekend.. showers and thunderstorms developing today with locally heavy rain possible

A pair of low pressure systems, one over southwest MB this morning and another in the Dakotas, will slowly push eastward today, triggering showers and a few thunderstorms this afternoon into this evening over southern MB.  Depending on how much sunshine we get today, some of these thunderstorms may be strong to possibly severe, with large hail and heavy rain possible.  This system will slowly push into NW Ontario overnight into Saturday, with cooler and showery weather over southern Manitoba behind the system. In all, about 15-25 mm of rain is possible today into Saturday over southern MB including Winnipeg and the RRV, with locally heavier amounts of 25-50 mm possible with stronger or more persistent thunderstorms. Sunnier and warmer weather is expected for the latter half of the holiday weekend.

RAINFALL SUMMARY - Rainfall amounts Aug 3-4, 2012
 

Location            amount

Gimli               42.3 mm
Fisher Branch       37.2 mm
Steinbach           35.5 mm
Birtle              32.9 mm
Swan valley         32.8 mm
Portage la Prairie  32.0 mm
Starbuck            30.6 mm
Brandon             30.2 mm

Winnipeg locations

East st. Paul       50.0 mm
St. Vital           46.0 mm
The forks           35.4 mm
Whyte ridge         32.8 mm
Charleswood         30.5 mm
Airport             26.5 mm

Another 30c day to cap off warm July... More thunderstorms possible this evening

The hot July of 2012 will end with another round of hot and potentially stormy weather, as daytime highs rise into the low 30s once again this afternoon. This will mark the 14th day this month with highs of 30c or more at Winnipeg airport, the most since July 2006 which had 16 days. (record is 17 days of 30c or more in July 1936). July will end up with a monthly average just over 22c, over 2.5C above the normal July mean of 19.5C, and our 13th consecutive month that has averaged above normal. Today's hot weather will also lead to the potential for another round of strong thunderstorms later today into this evening as a disturbance tracks across southern Manitoba. The greatest threat will be over southwest MB late today with storms possibly spreading into the Red River valley this evening.

UPDATE: July 2012 ended with a monthly mean of 22.3C at YWG airport, 5th warmest July on record in Winnipeg since records began in 1872.  It was the city's hottest July since 1936, our hottest July on record at 24.2C.  It was also only 0.1C from being Winnipeg's second hottest July on record.

Top 5 warmest Julys in Winnipeg (since 1872) 

1. 1936 .... 24.2C 
2. 1935 .... 22.4C 
    1916 .... 22.4C  
    1914 .... 22.4C  
5. 2012 .... 22.3C 

July 2012 was also the hottest month on record in the contiguous United States, beating the former record holder of July 1936.

Summer pattern continues..

Temperature graph for Winnipeg
over the past 12 months showing
persistent warmth since last summer.
The past 12 months have been the
warmest 12 month period in
Winnipeg history.

The warm and generally dry weather pattern of the past month continues this week, with temperatures in the upper 20s under mostly fair conditions.  Thunderstorm potential will be limited this week, with a slight chance of storms overnight into Sunday morning over the RRV, and a better chance later in the week in the Wednesday-Thursday time frame.  Precipitation this July has varied greatly across the Red River valley with some localities receiving fairly generous rainfall amounts of 30-50 mm or more this month, while other places have been quite dry, including much of Winnipeg (only 15 mm so far this month at YWG airport)  Conditions have been drier south of the border with drought conditions starting to spread northward across much of North Dakota and Minnesota from the central plains.  Temperatures in Winnipeg so far this month are averaging some 2-3C above normal for July, with a mean temperature so far this month of 22.2C (normal = 19.5C) This is on pace for a top 10 ten warmest July based on current trends, and would also be a staggering 13th consecutive month with monthly temperatures that have averaged above normal in Winnipeg. The 12 month period of July 2011-June 2012 is the warmest 12 month period on record in Winnipeg at 5.9C, beating the previous warmest 12 month period of Dec 1877-Nov 1878 (5.6C)  Weather records in the city began 140 years ago in 1872.

UPDATE:  With an average of +6.0C, Aug 2011 - Jul 2012 is now the warmest 12 month period on record in Winnipeg. That 's almost 3.5C above the normal annual average of +2.6C.  This has also been the warmest 12 month period across most of the United States.