Tuesday, September 13, 2011
Falling temperatures, lake effect precipitation and frost.. fall weather pushing into southern Manitoba today..
A cold front through central Manitoba this morning will push south today, ushering in a flow of unseasonably cold air from Northern Manitoba southward. This front will be accompanied by a few showers as it moves across southern Manitoba around midday today, followed by gusty northerly winds and falling temperatures this afternoon. The flow of colder air over the warm lake waters of the Manitoba lakes will likely set up some heavier bands of rainshowers off Lake Winnipeg and Lake Manitoba later today into tonight, with narrow bands of locally heavy precipitation possible mainly east and west of Winnipeg. Strong northerly winds of 50-70 km/h will also cause large waves and rising water levels along the south shores of the lakes today into tonight. Things should settle down Wednesday as high pressure drifts across southern Manitoba easing winds and weakening lake effect precipitation. This area of high pressure however will likely produce the season's first widespread frost across southern Manitoba Thursday morning with temperatures of 0 to -3C likely in many areas including the Red River valley.
Posted by rob at 10:32 AM
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Does the speed of the Surface winds have any effect on how intense or how far the lake effect bands travel???ReplyDelete
Absolutely.. the stronger the winds, the longer the lake effect bands will be and the further away the regions that will be impacted. Strong winds can also affect the intensity.. sometimes, strong winds can break up the bands and cause weaker multibanded streamers, rather than single intense bands.ReplyDelete
How much rain are we talking about in these lake streamers?ReplyDelete
If you believe the GEM, it's calling for a narrow axis of 50-100 mm off the north basin of Lake Winnipeg through the eastcentral Interlake area north of Arborg, with about 15-30 mm off the south end of Lake Winnipeg, and 5-15 mm off Lake Manitoba. These amounts could be overdone with convective feedback from the models, but I wouldn't be surprised to see localized amounts of 30-50 mm in the north, and 10-25 mm in the south. This would mean a stretch of about 12 hours with an average rate of 2-5 mm/hr within the bands, sometimes heavier, sometimes lighter. Again, these amounts will be localized within narrow bands some 10-20 km wide, particularly when the bands become more consolidated at night. (they tend to be more cellular and disjointed during the day)ReplyDelete
Note that you can already see evidence on satellite and radar imagery of some vigorous lake effect bands developing off the north basin of Lake Winnipeg and Lake Winnipegosis this afternoon. Look for these bands to set up shortly off the south basins as well.
Are the winds ever gusting here in Winnipeg!!!72 km/h at the airport!
Winds just howling here! Some small tree branches getting broken off!!!ReplyDelete
Is it possible on a day like today for some of the passing showers to drag down some stronger wind gusts compared to what is occuring over other parts of the city??? I think that's what happened here!!
Possibly.. Doppler indicating max wind speeds aloft of around 45 kt (85 km/h) so it's possible some of those gusts are reaching the ground. Note also that it's easier to have tree damage when leaves are still on the tress to capture the wind.ReplyDelete
Reports of snowflurries this afternoon in Riding Mtn Park between Wasagaming and Dauphin.ReplyDelete
Thanks for that explanation!ReplyDelete
Look at the temperature drop from 12 C (3:00) to 8 C (3:38) with that quick rainshower! I guess that rain will quickly cool an airmass down with such a low dewpoint!
CWB Weatherbug sites reporting max gusts of 92 km/h at Brady landfill, and 85 km/h in South St Vital.. so some stronger gusts being recorded in parts of the city.ReplyDelete
I agree with the overnite of 1 C for the city.. flow at 925 hPa becomes more northerly at 30-40 kts right off the N basin up to 7 AM. This should allow for at least partly cloudy skies and bursts of mixing keeping temps above zero (Mixing down from 925 hPa yields around 5 C). There is a chance that winds may decouple briefly and allow some spots to temporarily drop below zero, but duration should be short (the YWG recording station is notorious for that). There is a better chance for that happening in some of the sheltered valleys in the hillier terrain of SE Manitoba and N Minnesota if clouds are not present.ReplyDelete
Further west look for a very cold nite from Llyodminster all the way down to Bismarck N Dakota under the ridge. Calm winds thru a farily deep layer of the lower atmosphere and very low dewpoints of -6 C will allow for strong radiational cooling. I would not rule out the odd -5 to -7 C reading in some colder spots by dawn.
Attention then turns to Wednesday overnite. Question will be how warm we get tomorrow afternoon and how fast temps drop off in the early evening. Most models develop a SW downslope flow by 11PM over the city. Temps may drop below zero early in some spots (YWG) but then stabilize or even slowly rise.. so I would not expect a widespread freeze for Winnipeg. Best chance for that would be SE Manitoba down towards Fargo.
Ec had a risk of frost in this mornings forecast for Winnipeg tonight...now nothing!ReplyDelete
I don't know folks....this will be a close one!!
Ahhh....EC changed their forecast @ 4:17 to add back in the risk of frost!!!ReplyDelete
Skies are clearing quite rapidly and winds have really dropped off here in Winnipeg!ReplyDelete
Dewpoints in Brandon are really low at -6C. They will get quite the freeze. Here in Winnipeg...I'm sure will touch 0C at sometime overnight!
Winnipeg airport already down to
Does anyone see any clouds upstream to prevent this plummet of temps???
Winds decoupling and temps dropping quickly over portions of RRV.. a bit surprising how fast its happening with main ridge well off to the west.ReplyDelete
There two main clouds bands off L Manitoba and Winnipeg and we are currently between them. Flow at 925 hPa is depicted as veering somewhat to NNW by dawn.. NAM hints at the L Winnipeg band weakening but steering more over head by 5-7 AM. Upstream dewpoints in central Manitoba in the 0-2 C range and a few areas of clouds still. Having said that.. temps may well drop below zero at YWG for at least some time and fluctuate thru the nite..
Portage La Prairie is sitting at 7C under that cloud patch and bit of a breeze!ReplyDelete
Winnipeg's temperature continues to surprise with it at 0.6C now!
Really quite amazing that we were baking in the heat a few days ago!!
I would love to see some snow flurries tonight so that I could say that I saw snow in September....or on seconds thoughts If that did come true there would be a lot of people that would be in a state of shock!ReplyDelete
At this time of year, that heatwave is, ironically, slightly responsible for the sudden fall in temperatures. The ground dries out, reducing its innate moderating effect and it cannot contribute to increasing the dewpoint of the Arctic air mass.ReplyDelete
The -1.1 at YWG is the coldest location in the entire RRV looking at all the Environment Canada, Manitoba Ag-wx and CWB weatherbug stations.. therefore that reading needs to be taken with a grain of salt.ReplyDelete
Other stations outside the city will catch up however unless clouds move in. Currently the L Winnipeg streamer has aligned itself more or less north to south but is not quite reaching the city. The edge of clouds and radar returns appear to be about 70 km north of Winnipeg. Lets hope it can make a push further south before below freezing temperatures become more widespread..
Nice lake effect bands off the lakes this morning, with a streamer off Lake Manitoba extending from just east of Delta Beach through Oakville and Elm Creek down to Sperling. About 5-10 mm of rain reported since midnight in the Elm Creek area under the band. Another streamer off southern Lake Winnipeg extends through Pine Falls into the Lac Du Bonnet/Pinawa area. Also lake effect showers off the north basin mainly north of Arborg.ReplyDelete
Bands should be fairly stationary this morning before ridge builds in this afternoon and weakens streamers, first off Lake Manitoba and later off Lake Winnipeg.
First frost of the season at YWG airport last night, but as Daniel noted, it wasn't widespread through the city with most sites remaining above zero overnight (+1.3C at my place) Frost is more extensive just south and east of the city through St Adolphe/Dugald/Steinbach areas.. and then widespread over SW Manitoba and all of southern SK under the ridge. That will be us tomorow morning.
Click on my name for a nice radar image from Weather Underground overlaid on a Google map background to show exactly where the lake effect streamers are. To view the radar images, under NEXRAD options, select 00Q (world base reflectivities) to get a drop on Woodlands hi-res Doppler reflectivity data. You can animate up to 6 images. Blue circles are weather underground stations showing precip amounts in cm. Unfortunately, the Lake Winnipeg streamer is out of Doppler range unless it moves closer to Beausejour.ReplyDelete
Dont forget, if you are able come down to NWS Grand Forks this Saturday for our open house...ReplyDelete
Time 10-3 I will be there with many other staff members.
Link to info and map on my name
Some freezing rain looks to be moving south in very scattered areas in the interlakes. I expect it could be here around 9:15. Also there is a nice band of rain and mixed precip streaming off Lake Manitoba. It was quite cold when I got up to leave for my day, frost on the ground first time in years wev'e seen a temperature of -1C at the airport. the calmer the winds at night the colder it gets, that was a reality last night.ReplyDelete
First time in years we've seen a temperature of -1C at the airport??? Not following that one...ReplyDelete
Thanks for the invite Dan GF!!!ReplyDelete
I would love to go....(now I have to find a way to get off work)
Anyone else from this blog considering going down????
Last freeze at YWG airport was actually May 26th when we hit -3.7C, for a total growing season of 110 days this year. Of course, our last freeze was way back when we didn't have a Jets team.. maybe that's what confused Mike ;)ReplyDelete
And there isn't any threat of freezing rain off the lakes.. any off lake activity will be occurring with temperatures above freezing thanks to modification from the 19C lake waters. Off lake streamers are plain rain, possibly mixed with wet snowflurries in some areas.
For the record, Winnipeg airport's average first fall frost is around Sept 22nd, with an average frost free season of 121 days. So this year's first frost was about a week or so earlier than usual, and the official growing season was about 1.5 weeks shorter than normal. Last year, first fall frost was on Sept 19th with a growing season of 132 days.ReplyDelete
Daniel, I'm planning to go down to visit, I may not go if my plans change.ReplyDelete
I'm moving in a few weeks, so I started going through some books that I wanted to give away/throw out.
Well I found a hidden jem of a weather book I forget that I had.
It's called "The Climates of Canada" written by Environment Canada!(1990)
I wonder if that book is worth millions???? Any offers??? Going once....Going twice.....
Strange night.. winds decoupled very early allowing for a very lite WNW flow at the surface before some of those stronger NNW winds from 925 hPa mixed down after midnight. Almost seems like a mesoscale bubble of high pressure formed between the two main streamers well east of the synoptic ridge. Still, the low at the YWG does not jive with the surrounding CWB weatherbugs or MB Ag-Wx stations. Open country locations at route 90 and the perimeter, headingly, fermor and perimeter, oak bluff, Rosser, Meadows, East St Paul, and Stonewall remained above zero. Only Grosse Isle dipped just below the freezing mark. The coldest temps locally were as Rob mentioned off to our SE with Glenlea, Landmark, St Adolphe, Dugald dropping to around -1 or -2 C.ReplyDelete
There needs to better quality control around that site to ensure it is situated in a location that receives adequate drainage of cold air. The data should not be used to derive growing season statistics for our area. At the very least EC could start putting out forecasts for the city in addition to the airport. This is done in Edmonton.. why can't it be done here?
That lake-effect cloud band finally moved in this morning. Question will be how quickly it dissapates tonite and if any cloud cover can survive. NAM has consistently been showing approx 70% RH at 850 and 925 hPa until at least 4 AM.. will that translate necessarily into stratus clouds? Currently, clouds in the band look very cellular. Models also show flow turning SSW from the surface up thru 925 hPa.
Expect a rapid drop in temperature if we are clear in the early evening (esp YWG). Temps would likely stabilize there as the station gets a fetch off the city.. coldest readings would be in the south and west end of Winnipeg by dawn. I would prepare for the worst, and hope that things don't get too cold..