Monday, September 29, 2008

Getting better and better this week

A massive upper ridge of high pressure will be building over western Canada this week, bringing some superb late summerlike weather over AB and Saskatchewan this week. Daily highs will be in the 25-29C range all week in southern AB and southwest SK with sunny clear skies through Friday. Here in southern MB, we will be on the eastern flank of the upper ridge much of the week, which will keep us cooler than the western Prairies. Still, after some cloudy and cool conditions to start the week, the rest of the week should be getting progressively better with daily highs approaching the 20 degree mark by mid to late week. That should lead us into a nice warm weekend with highs over 20 degrees as the upper ridge moves east over southern MB. All in all, it's looking like a nice start to October!     

Friday, September 26, 2008

Nice stretch of weather coming up..

Looks like some pleasant fall weather coming up over the next few days into next week as a large upper ridge begins to build over western Canada early next week. This upper ridge will bring sunny warm and dry conditions to Alberta and Saskatchewan much of next week, with some of that weather moving into southern MB by Tuesday.

In the meantime, skies have cleared across southern MB today behind a weak cold front that moved across the region this morning. High pressure will build into southern MB tonight giving clear skies and diminishing winds.. with some patchy frost possible by early Saturday.  This high pressure system will bring ideal fall weather on Saturday with plenty of sunshine and light winds, making those afternoon highs of 17 degrees feel even warmer.  On Sunday a low pressure system moving through the Interlake regions will spread an area of cloud and scattered showers across central and southern MB. This system is now forecast to move further north than earlier expected, thus the threat of rain will be lower for Winnipeg and areas south. As a result, we may get by with a rainfree weekend here.  

Once this system passes to our east, clearing skies and seasonable temperatures are expected over southern MB for Monday and Tuesday with more sunshine and even warmer temperatures likely by Wednesday as the western ridge builds east.  Some models are indicating that this ridge will collapse over the eastern Prairies by late next week allowing cooler air to return over us again, while the Cdn GLB model keeps us dry and warm right through next week.  It's still a long way off to say one way or another.. but in the meantime, enjoy the fine stretch of weather coming up!        

Tuesday, September 23, 2008

Strong thunderstorms bring heavy rain, high winds

The first official day of fall was marked by strong thunderstorms last night that brought a swath of heavy rain over the Red River valley, as well as some severe wind gusts along the US border. Thunderstorms developed over northern North Dakota late Monday, and pushed into southern MB during the evening. As the storms crossed the border into Manitoba, they produced torrential rain and wind gusts to 106 km/h (57 knots) at Emerson at 10:43 pm, and an unverified gust of 165 km/h (89 knots) at Gretna at 10:42 pm. Although possible, the Gretna gust seems suspiciously high since there would have been damage reported with such wind gusts, and no reports of damage have been received so far. The storms were accompanied by 29 mm of rain within one hour at Gretna, and 34 mm of rain within one hour at Emerson between 10 and 11 pm.

The storms continued to move to the northeast through the night bringing a swath of heavy rain mainly from the Gretna/Emerson areas through Letellier/Dominion City to St Pierre up to the Landmark area just east of Winnipeg. Rainfall in this swath totalled 50-90 mm from overnight thunderstorms. The heavy rain area just clipped the east side of Winnipeg with Deacons Corners (Hwy 1/Perimeter) reporting 46 mm of rain since midnight, while the west end of the city only had 15-20 mm including Winnipeg airport and my site in Charleswood.

Some rainfall amounts recorded since late yesterday include.

Dominion City… 91 mm (spotter report)
Landmark………78 mm (including 44 mm 9 pm - midnight)
St Pierre………..72 mm (MB Ag-wx)
Emerson………. 65 mm (EC)
Morris…………. 62 mm (MB Ag-wx)
Winkler………… 58 mm (MB Ag-Wx)
Dugald………….53 mm (MB Ag-Wx)
Steinbach………46 mm (MB Ag-Wx)
Gretna…………..46 mm (EC)
Wpg - Deacons Corners…46 mm (CWB)

Winnipeg Forks…. 22 mm (EC)
Winnipeg Arpt….. 17 mm (EC)

Sunday, September 21, 2008

Nice end to summer.. unsettled start to fall

It was a beautiful end to summer over southern MB with sunny skies, balmy southeast breezes and temperatures in the 25C range. Fall officially arrives Monday morning at 10:44 am, and will be greeted with some unsettled weather in the form of showers and possible thunderstorms. The unsettled weather will come in two waves. The first wave of precipitation is expected overnight as a band of showers and scattered thunderstorms over North Dakota moves northward into the Red River valley. These showers may bring 5 to 15 mm of rain to Winnipeg overnight, although heavier amounts of 25-35 mm are possible in thunderstorm activity over portions of southern MB by early Monday morning. There should be a break in the shower activity through midday Monday which will allow temperatures to warm into the 20s along with dewpoints in the midteens. This will set the stage for another round of showers and thunderstorms to develop by late afternoon over southern MB ahead of a cold front. This line of activity may be accompanied by severe thunderstorms late Monday into Monday evening with heavy downpours (giving local rainfall amounts of 30-50 mm), strong winds, and possibly large hail. There may even be the threat of isolated tornadoes with some supercell storms early in the evening. Stay tuned as Mother Nature may be ushering in fall on a stormy note.

Wednesday, September 17, 2008

Late summer weather before fall arrives Monday

Some nice weather is on tap for Southern MB over the next couple of days as Mother Nature gives us some late summer weather before the official start of fall on Monday. Thursday will see brisk southerly winds of 40 to 60 km/h developing in the Red River valley as a warm front moves through southern MB. Afternoon temperatures will climb into the 24-27C range along with plenty of sunshine. Friday will see a weak cool front push through from the Interlake, but temperatures should remain above normal Friday with highs of 25C or so before cooling off in the afternoon or evening as northerly winds develop. Saturday will likely see cooler temperatures as we get northeast outflow winds from a cool high pressure area over northern MB. Current advertised highs of 25C are likely over-optimistic for Saturday, with highs of 17-20c more likely in the cooler airmass. There could also be considerable cloudiness around along with areas of dense fog as that frontal boundary remains stalled over southern MB separating warm air to our south from cooler air to the north. (in fact, Saturday's weather may be much like today's.. overcast and cool) By Sunday we should be getting back into south or southeast winds which would boost temperatures back into the low to mid 20s (current advertised high of 27C still likely about 5c too high for Winnipeg and areas to the north and east) So although the bulk of the weekend is expected to remain dry, I don't think it's going to be as warm or as sunny as current forecasts indicate.

Fall officially arrives at 10:44 am Monday morning but current models are suggesting we'll be staying with above normal temperatures in the low to mid 20s through Tuesday before more fall-like temperatures return by mid to late week.

Monday, September 15, 2008

Ike damage

Hurricane Ike has brought incredible devastation on the Bolivar Peninsula just east of Galveston along the Gulf Of Mexico. This area was the hardest hit being on the east side of Ike's eyewall. Communities of Crystal Beach and Gilchrist have been wiped off the map by Ike's winds and storm surge which likely topped 15 feet over this unprotected peninsula.The image on the left shows a single home standing in what used to be the beachside town of Gilchrist. Satellite images show the extensive damage brought to the Texas Gulf coast, including the destruction of Crystal Beach.

Sunday, September 07, 2008

Lake effect season is here

This morning is providing a good example of a common phenomenon in southern MB in the fall - lake effect precipitation. Lake effect precipitation develops when you have cool air aloft moving over the relatively warm lake waters, creating narrow bands of instability precipitation to the lee of the lakes. You need at least a 13C difference between the lake water and the temperature at 850 mb, and winds need to be well aligned in the lowest 10000 feet (i.e. little directional shear) to form these narrow bands. This morning we have 850 temperatures of +2C over 18C lake waters, along with low level winds aligned in a 330-340 degree orientation giving lake precipitation to the southeast of Lakes Manitoba and Winnipeg. Typically these lake effect bands form in the cool air behind a cyclonic storm system and will dissipate as subsidence moves in with an approaching ridge of high pressure.

Early in the season, these precipitation bands are in the form of rainshowers. As we get further into the fall with colder temperatures aloft (i.e. 850 temps of -5C or colder), these lake effect bands will produce narrow swaths of snow to the lee of the lakes.. sometimes quite heavy. See an example from October 11, 2006 for an early season lake effect snow event over southern MB.. notice that the lake effect bands from that case are oriented virtually identical to those this morning (except it's rain today, not snow!) Lake effect bands off Lake Manitoba commonly set up between Portage and Elie, but can come into Winnipeg if the low level flow is in the right direction, from around 300 degrees, as seen in this example from last September.

Thursday, September 04, 2008

Some rain on the way

A weak low pressure system over North Dakota will be tracking slowly east over the next 24 hours, bringing an area of rain to southern MB. The leading edge of the rain shield is just spreading up to the MB border from the south as of midday, and should continue edging north this afternoon likely reaching Winnipeg by mid to late afternoon. Rain amounts are expected to be in the 5 to 15 mm range, most of it falling south of Winnipeg closer to the international border. Here in Winnipeg, look for about 5 mm from late afternoon through tonight. Cool unsettled weather is expected behind this system for Friday through the weekend.