Another hot humid day... severe thunderstorms developing

July 2007 ended on another hot and humid day over southern MB with temperatures of 33-36C and dewpoints in the 22-26C range to produce humidex values of 43-48C. A cold front approaching from the northwest is producing a few intense thunderstorms mainly northwest of Winnipeg. The cell north of Gimli even showed signs of tornadic potential. Additional storms are likely through this evening and tonight as the front moves through southern MB. Some of these storms will be severe with strong winds, hail and torrential rain. The front will usher in less humid and more comfortable conditions across southern Mb for Wednesday.

West is burning

This satellite image taken Monday evening July 30 shows large smoke plumes from Montana forest fires spreading into southern SK and southern MB. Residents may have noticed a hazy appearance to the sky today, as well as a redder than usual sunset or sunrise. This is due to the presence of smoke particles spreading through a layer in the mid atmosphere, about 10000 ft or so. The smoke layer will likely persist over southern MB on Tuesday before a northwest flow clears out the smoke layer on Wednesday.

Note also several other smoke plumes from forest fires over western Montana and the BC/Alberta border.. a result of several weeks of hot dry weather that has baked the upper Rockies and western Prairies. Forest fires have also been a problem over northern MB as well this month.

Heat rebuilding across southern Prairies

After a couple of days reprieve, hot weather is again returning to much of the southern Prairies this weekend, including southern MB. Temperatures in southern MB will hit the 30c mark again today with even hotter temperatures of 35c for Sunday into Tuesday. Fortunately, it looks like the humidity levels will not be as oppressive as last week's heat wave which saw dewpoints climb into the mid to upper twenties. Dewpoints over the next few days should be in the more moderate 15-20c range which combined with 35c temperatures will still make for uncomfortable conditions, with afternoon humidex readings in the 40-43c range. However, local areas such as the western Red River valley may once again see higher humidex values due to humidity input from crops (especially corn)

Record hot and humid day over Southern MB

Special weather statement from Environment Canada, Winnipeg - July 25 2007.. (graph showing heat index and dewpoints from Rob's Obs)

HOT AND MOIST AIR FROM THE CENTRAL UNITED STATES CONTINUED TO FLOW INTO SOUTHERN MANITOBA ON WEDNESDAY. THE HIGH TEMPERATURES COMBINING WITH THE EXTREME HUMIDITY LED TO RECORD HIGH TEMPERATURES AND RECORD HIGH HUMIDEX VALUES OVER SOUTHERN MANITOBA TODAY. WINNIPEG SET AN ALL TIME RECORD FOR THE HIGHEST HUMIDEX READING EVER RECORDED AT THE WINNIPEG AIRPORT. HUMIDEX VALUES PEAKED AT 47 LATE THIS AFTERNOON BREAKING THE ALL TIME WINNIPEG RECORD OF 46.1 SET BACK ON JUNE 27, 1996. AS WELL CARMAN, MANITOBA UNOFFICIALLY SET AN ALL TIME CANADIAN RECORD HIGH HUMIDEX WHEN VALUES CLIMBED TO 53 LATE THIS AFTERNOON, BREAKING THE RECORD PREVIOUSLY HELD BY WINDSOR, ONTARIO OF 52.1 SET ON JUNE 20, 1953.

THE HUMIDEX IS AN INDEX (A COMPUTED VALUE AS OPPOSED TO SOMETHING MEASURED) DEVISED TO DESCRIBE HOW HOT OR HUMID WEATHER FEELS TO THE AVERAGE PERSON. THE HUMIDEX COMBINES THE TEMPERATURE AND HUMIDITY INTO ONE NUMBER TO REFLECT THE PERCEIVED TEMPERATURE. IT TAKES INTO ACCOUNT THESE TWO IMPORTANT FACTORS TO BETTER DESCRIBE HOW STIFLING THE AIR FEELS THAN EITHER TEMPERATURE OR HUMIDITY ALONE.

THE FOLLOWING ARE THE UNOFFICIAL NEW MAXIMUM TEMPERATURE RECORDS AS OF 5:00 P.M. WEDNESDAY JULY 25.

GILLAM 28.8 28.1 1983
PINAWA 34.3 34.0 1989
GRETNA 33.2 32.2 1961
CARMAN 34.0 28.1 1997

THE FOLLOWING ARE LOCATIONS THAT CAME CLOSE TO BREAKING THEIR MAXIMUM TEMPERATURE RECORDS.

GIMLI 32.1 33.1 1989
ISLAND LAKE 29.6 29.7 1989
THOMPSON 27.4 28.7 1989
CHURCHILL 28.2 30.0 1929
FISHER BRANCH 30.5 32.2 2003
WINNIPEG 35.3 36.7 1931

Severe thunderstorm approaching Winnipeg

At 4:30 pm radar displayed a rapidly developing thunderstorm approaching Winnipeg from the southwest. A severe thunderstorm warning has been issued for this cell. Radar indicates possible rotation with this storm which may indicate tornadic potential. Very strong downdraft winds and torrential downpours are likely. This storm has developed right along the cold front which is just approaching Winnipeg as of 4:30 pm.

Another scorcher - but relief on the way

It's another scorcher over the Red River valley, with 1 pm temperatures of 33C in Winnipeg and a humidex of 45C.. the steamiest day of the heat wave so far. But relief is on the way as a cold front approaches from the west. As of 1 pm, the front was just about through Brandon with showers and thunderstorms west of the front. Temperatures drop significantly behind the front with values near 20C near the SK border as of 1 pm. The front should be moving through Winnipeg later this afternoon with noticeably cooler conditions and some rain moving in this evening.

Another sultry night.. relief coming Wednesday

We got to 34.8C at Winnipeg airport today, just 0.2C off the record high for today with humidex values peaking at43C. And after today's steamy weather, there won't be much relief tonight. It will be another very warm night across southern MB, especially here in Winnipeg and the Red River valley where gusty southerly winds will persist tonight, keeping temperatures from dropping much. As a result, temperatures will remain above 30 well into the evening, gradually dropping to an overnight low of only 26C. That would be Winnipeg's second warmest low temperature on record, behind only July 12 1936 when a low of 28.3C was recorded. That will mean a very uncomfortable night for sleeping for those without A/C.

Relief however is on the way on Wednesday. A heat-wave ending cold front will be coming through by midday or early afternoon. So after another warm and muggy morning with temperatures peaking at 32C by midday, winds will shift into the northwest in the afternoon sending temperatures and humidex values down. By evening, temperatures will likely be down to the 25C mark, and 20c by midnight with lows of 16C by morning. In addition, the cold front will likely be accompanied by showers and thunderstorms that could bring locally heavy rainfall and possibly some severe winds or hail. Look for more comfortable conditions and seasonably warm temperatures for Thursday into the weekend.

Heat Wave - Day 3

It's already 27C at Winnipeg airport as of 8 am, after an overnight low of only 24C, a record warm night for July 24th (and one of the warmest minimum temperatures on record in Winnipeg). I think we have a good shot at hitting 35C today provided we stay sunny all day. With dewpoints of 23c, that will give peak humidex values of 45 this afternoon, the steamiest day of the heat wave so far.

Tonight will be another warm one.. with a low of only 25C, maybe even 26 or 27C as we get a southerly breeze all night. If so, that will be Winnipeg's second warmest minimum temperature on record (warmest minimum was an amazing low of 28.3C on July 12 1936 following Winnipeg's hottest day ever of 42.2 on July 11) However, that low of 25C will likely not be the minimum for Wednesday. The heat-wave ending cold front will be coming through by midday, so temperatures will be dropping noticeably in the evening, likely below 25C by midnight.

Heat Wave - Day 2

After a sizzling Sunday, it's a meltdown Monday as the hot and humid airmass persists over southern MB. As of 11 am, humidex values had already surpassed the 40 degree mark over many localities thanks to some very high dewpoints today.. including an unbelievable 28C dewpoint reading at Carman. (I suspect this value is erroneously high, as the dewpoint at Carman always seems to be a couple of degrees too moist compared to neighbouring sites.) Nonetheless, dewpoints across southern MB are in the 22-25c range today which will make today's 35C temperatures feel oppressive. Take it easy out there.

By the way, I replaced the barometric graph plot on my main page with a dewpoint/heat index plot to better gauge how sticky it is over the next few days.

The heat is on!..

It was a sizzling Sunday across southern Manitoba with temperatures of 32 to 33C and humidex values of 40 to 44C. As they say, it wasn't the heat.. it was the humidity, or more accurately, the dewpoints which were in the 21 to 24C range across southern MB. These dewpoints are in the uncomfortable range, and makes it more difficult for the body to cool off by evaporation. (see graph from my weather station showing dewpoint and heat index from today. Notice how the dewpoints dropped late in the day!)

And it looks like the hot humid weather will continue for the next 2 to 3 days before a cold front brings more comfortable conditions by Wednesday evening. Until then, expect more of the same as today with afternoon temperatures of 32 to 35C, and humidex values of 40 to 45C. Stay cool!

By the way, you may notice that my weather station displays "heat index" rather than the humidex. The "Heat Index" as shown on my station is an equivalent temperature based on air temperature and humidity (or more accurately, the dew point). It is similar to but NOT the same as the Canadian "humidex" value, which employs a slightly different equation and gives different results than the American "Heat Index". Generally the Heat index will register about 3-5C lower than the humidex. My station can only display heat index. A simple way of calculating the humidex is to add the temperature and dewpoint (in C) then subtract 13. For example, if the air temperature is 32C and the dewpoint is 22C then the humidex is 41C (32 + 22 - 13 = 41C) Environment Canada issues humidex advisories when humidex values of 40C or greater are expected. Whatever the case, both indeces are designed to tell you how hot it "really" feels based on the moisture content of the airmass. The basis for this is that when it's humid, it becomes harder for the body to cool since evaporation from the skin (i.e sweating) is less efficient. Thus, 30C with 60% humidity will feel "hotter" than 30C with 30% humidity because the body will not be able to cool as quickly at higher humidity levels. In reality, it's not any hotter, it's just more uncomfortable.

The dew point is the best indicator of how humid or "sticky" an airmass is. The following table gives a rough idea of dewpoint and comfort of an airmass..

DewPoint
< 10C ..............dry
10-14C ............comfortable
15-17C ............moderately humid, still comfortable for most people
18-21C ............humid, uncomfortable for most people
22-24C ............very humid, uncomfortable for everyone
>24C ..............oppressive, stifling

In our latitudes, dewpoints above 24C are rare although they do occur sometimes in southern MB in the growing season due to contribution from evapotranspiration from plants and crops. Dewpoints of 27C or more are usually only found in tropical areas near warm oceans.

Western heat wave spreading east this weekend

The heat wave that has gripped the western Prairies for the past week with temperatures in the mid to upper thirties will be spreading east over southern Manitoba beginning this weekend. A ridge of high pressure over southern Manitoba on Thursday will move east into the Great Lakes by Friday. A return southerly flow west of the ridge will draw increasingly warm air from the western U.S. and Canada into southern MB over the weekend, with temperatures expected to climb into the low to mid thirties by Sunday. The hot weather is expected to continue through much of next week with temperatures likely persisting in the thirties most of the week. Little precipitation is expected over the period, except for a possibility of some showers or thunderstorms Tuesday and Wednesday as a weak cold front tries to move through southern MB.

Officially, a heat wave is defined as a period of at least 3 consecutive days with maximum temperatures of 32C or greater. This is a throwback from the Fahrenheit days when we used 90F (32C) to define a "hot" day. Unofficially, we have started to define a heat wave in Canada as a period of 3 days or more with maximum temperatures of 30C or more. It's a nice round number, and it's a good threshold for most Canadians to define as a "hot" day. Either way you slice it, it looks like an extended period of hot weather is coming to southern MB!

Rainfall Summary

A LOW PRESSURE SYSTEM PASSING SOUTH OF MANITOBA BROUGHT SIGNIFICANT AMOUNTS OF RAIN TO PARTS OF SOUTHERN MANITOBA OVERNIGHT...WITH THE HEAVIEST RAIN FALLING SOUTH OF THE CITY OF WINNIPEG. THE FOLLOWING ARE SOME RAINFALL TOTALS FROM THE EVENT AS OF 7 AM THIS MORNING.

PILOT MOUND............ 57.2 MM
EMERSON................ 52.0 MM
GRETNA................. 50.6 MM
MORDEN................. 45.8 MM
STEINBACH.............. 36.6 MM
CARMAN................. 29.4 MM
SPRAGUE................ 27.0 MM

WINNIPEG (ST VITAL)...... 26.2 MM
Whyte Ridge ............. 20.4 MM
Charleswood (Rob's Obs).. 16.5 MM
WINNIPEG (AIRPORT)....... 10.5 MM

Steamy Saturday

Whew.. it's a sweltering one out there today. As of 2 pm, my weather station is showing 29C with a 23C dewpoint giving a humidex of 39C. Very uncomfortable. (A trick to estimate humidex.. add the temperature and dewpoint in C, then subtract 13). Even more oppressive down to our south with Emerson checking in with a 42C humidex as of 2 pm (temp 32C dewpoint 23c) The hot and humid airmass will trigger a few thunderstorms this afternoon as a cold front approaches from the northwest. A few of thes storms may become severe, with large hail and damaging winds being the main threats. Isolated tornadoes are also possible given the extreme instability today. EC has issued a severe thunderstorm watch this afternoon for much of southern Manitoba including Winnipeg. Stay tuned and keep an eye to the sky if you're out and about today.

River Heights weather site joins Winnipeg mesonet

Another personal weather station (PWS) has come online in the Winnipeg area.. this one from River Heights (click here for data) This station came online a couple of days ago, and uses a Davis Vantage Pro 2 for data collection (very good quality station) Winnipeg now has at least 11 PWS sites around the city reporting real time data online to augment the official weather observations from Winnipeg Airport and Winnipeg Forks. Great to see, and welcome to the Winnipeg mesonet! Data from these sites are automatically plotted on my city temperature map, and included on the Winnipeg area PWS table as well as on a Google map.

Personal weather stations (PWS) are becoming more and more popular, where private citizens or organizations are purchasing their own weather stations, and posting their data automatically to the web for anyone to see in real time. It's a growing hobby, and one that is fast gaining interest from many users who rely on quick and reliable real time weather information from more and more sites. This is especially important for rainfall measurements which can vary widely even within a city itself. (as we've seen these past few weeks..)

Heat building across western Prairies

A building ridge of high pressure in the upper atmosphere over western Canada will bring sunshine and increasingly hot temperatures this week over the Prairies.. especially over southern Alberta and Saskatchewan. Temperatures are expected to hit the 30 degree mark today and soar into the mid to upper 30s by mid to late week. In fact, it's possible that some areas of southeastern Alberta and southwest Saskatchewan may hit the 40 degree mark by Friday. (watch out for Val Marie, SK on Friday.. they could hit 42C if the models are right..)

Southern MB will not be quite as hot as we'll be on the eastern edge of the building heat wave. However, it does look like we'll be hitting the 30 degree mark by the end of the week into the weekend. Most of the week looks dry, although models hint at some instability the next couple of days which could produce isolated pop-up thunderstorms in the afternoon and evening. Most areas however should remain rain free this week.. a welcome change from the unsettled stormy pattern of the past few weeks.

JUNE 2007 HIGHLIGHTS..

AVERAGE TEMP: 18.9 C ( 1.3C above normal)
RAINFALL: 118.9 mm (29.6 mm above normal)
(* Rob's Obs stats)

...WET AND WILD..

June 2007 will be remembered for its wet and often stormy weather that produced heavy rainfall and some of the most severe weather seen in southern Manitoba in many years. Rainfall for the month totalled 119 mm at my site, about 30 mm above normal, with even heavier rainfall amounts of 150 mm or more in other parts of the city (official airport total : 125 mm). Frequent thunderstorm activity was responsible for the heavy precipitation amounts, with at least 7 days with thunderstorms during the month. It was particularly stormy during the third week of June when thunderstorms were recorded on 6 of 7 days between the 18th and 26th. This period included a memorable severe weather outbreak on the 22nd and 23rd of June that produced at least 5 tornadoes across southern Manitoba, including an F4 that hit Elie, MB on the 22nd, and two F3s that hit southwest MB on the 23rd. The severe outbreak also produced damaging winds on the night of the 23rd causing widespread damage through the Whiteshell cottage area, with a gust of 107 km/h at the Winnipeg airport. Large hail was also recorded early on the 24th in north Winnipeg. The stormy wet weather has made it a challenging season for area farmers who have had to deal with wet fields, as well as wind and hail damage to crops.

The wet weather this June is in sharp contrast to the record dry weather last year. Consider that this year's rainfall in June alone was more than all of May, June, July and August combined last year (114 mm total) In addition, the 2 month total of 203 mm this May and June is equivalent to the entire rainfall recorded in all of 2006! (at my location) The stormy weather pattern this year is due to a storm track that has set up through the Dakotas with weather systems coming in every few days tapping warm moist air to the south and bringing showers and thunderstorms across southern MB. This is highlighted by the fact that the longest rain-free period during June 2007 was only 3 days.

Temperatures for the month were generally near to slightly above normal, with variable spells of warm and cool weather offsetting each other. Temperatures ranged from a high of 31C on the 12th to a cool 2c on the 5th, when patchy frost was recorded around the city.

All in all.. a wet and wild month.