Thursday, May 27, 2010
Wet weekend on the way..
It looks like May will be ending on a wet note as a slow moving low pressure system tracks across the Dakotas and southern Manitoba this weekend. This system will tap very warm and humid air over the central Plains producing several waves of showers and thunderstorms that have already spread into southwest Manitoba today. Additional showers and thunderstorms are likely tonight which will track across southern Manitoba overnight into Friday as a warm front settles along the international border. This front will mark the leading edge of very warm and moist air over the Dakotas with cooler air over the central Prairies. There will be a sharp temperature gradient across this front Friday with temperatures of 30C or more along and south of the US border, and only in the teens through the Manitoba Interlake. On Saturday the low pressure system and associated frontal trough will slowly move across southern Manitoba generating more showers and thunderstorms Saturday through Sunday. Rainfall could be heavy at times with local amounts of 50 to 75 mm possible across portions of southern and central Manitoba by Sunday evening. Cooler and unsettled weather will follow in the wake of the system early next week.
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Time for a precip poll! How much rain will Winnipeg get this weekend (7 pm Friday night to 7 am Monday morning) Ensembles are indicating a 50% chance of at least 30 mm for Winnipeg this weekend, with a 25% chance of 55 mm or more. But the precipitation mode will be convective and amounts could be highly variable depending on where it develops and how it tracks. Will Winnipeg miss most of it? Will we be deluged this weekend? Cast your vote and let us know what you think!
ReplyDeleteLooks wet this weekend. TWN is leaning on the greater amount of precip. to hit Winnipeg.
ReplyDeleteOn a bright note TWN issued their summer forecast and are calling for above normal temps. and precip. What I hope this means is warm and humid during the day with plenty of nocturnal t-storms.
Correct me if I'm wrong, but I think TWN forecasted an above normal summer last year and we all know how that turned out.
Here's to hoping they are correct.
Rob!
ReplyDeleteI'm heading down to Minneapolis this weekend...
By the sounds of it I'll be needing the sunscreen!!!
Definitely a good set up for heavy rain with persistent LLJ over-running stalled front. Main question is how far SE precip band will set up tonite. Best convergnece from LLJ will intensify and shift NE over Winnipeg area. However models show complex forming farther north where frontogenetic forcing and temp gradient is strongest. Given that highest moisture/instability at 850hPa will be further south.. I suspect precip will build back into theta e ridge that will remain anchored to our SW and affect Northern RRV/ Winnipeg. Convection forming downwind of a stationary moisture axis is a signature of extreme rain events.. so careful attention must be paid to evolution of precip tonite.
ReplyDeleteThings will simmer down by tomorrow morning with elevated mixed layer spreading NE from central rockies. With warm mid-level temps providing cap and front lifting NW, focus for convection will be further NW. Will have to see where warm sector sets-up on Saturday as main low moves in and erodes cap. Another line of storms (likely elevated on cold side of front) will be triggered and possibly stall out. Brad or Rob.. what is your take?
Daniel..
ReplyDeleteLatest radar confirms what models had been predicting... namely an elongated west-east band of convective rainfall through west central MB through the Interlake.. which should remain relatively stationary or move slowly north tonight into Friday. This will result in a band of 20-30 mm through this area according to the GEM which looks reasonable. Further west, we have some strong thunderstorms developing over SE SK associated with the LLJ over the western Dakotas overriding the sharp warm front over northern ND. Nice cell there this evening could be producing near severe hail. I would expect more storms over SE SK and SW MB as the LLJ increases and taps substantial low level moisture south of the border. You're correct in noting concern for heavy rainfall with this setup.. a slow moving LLJ over a stationary warm front can lead to backbuilding storms and very heavy rain as cells train over the same area.
The big question for us is how much of this activity will spread eastward into the rest of southern MB overnight into Friday and will it reach the RRV? It looks like much of southwest MB will be primed to see elevated convection tonight into Friday as the LLJ moves east, with the possibility of some of that shower/tstm activity riding along the thickness ribbon into Winnipeg/northern RRV during the day Friday.
Things get interesting Saturday as main low moves across northern ND with overunning showers/tstms over southern MB and risk of severe storms over eastern Dakotas ahead of cold frontal trough. Latest NAM has gone insane with rainfall amounts over southern MB Saturday with 2-4 inches (50-100 mm) indicated across northern RRV into Whiteshell areas. Latest GEM not as crazy with amounts, more like 10-20 mm. Best we can say at this point is that the potential for heavy rain is there.. but still too early to say exactly where or how much.
Its sure getting stormy out there to start the day today =D
ReplyDeleteSome intriguing cloud-to-ground lightning at times, and very loud thunder! =D
Storm season starting on a good note
Quite the downpour we're getting here in Charleswood right now. My station is only showing 0.8 mm but I think that's an error.. the gauge may be blocked by leaves, I'll have to check. PJ school a few blocks from me is up to 6 mm so far..
ReplyDeleteCheck out HPC's precipitation outlook for Saturday .. 80 mm bullseye over Winnipeg! I guess they're going with the NAM.. other models not as heavy. In fact, latest ensembles have reduced amounts over Winnipeg to only about 10-15 mm for tomorrow. Ahh, the joys of convective rainfall forecasting!
ReplyDeleteBTW, just checked my stand alone backyard rain gauge.. 11.4 mm so far. So ignore the 3 mm that my online station shows.. it obviously has underrecorded the rainfall amount from this morning's downpour, possibly due to blockage.
Another 10 mm past half hour.. up to 21 mm now and still pouring. I see they've upped the rainfall amounts in the forecast from 5-10 mm to 10-20 mm. Do I hear 20-30 mm?!
ReplyDeleteYa no kidding Rob, looks like we could be getting lots of more storms right? I hope so =D Lots more to the west.
ReplyDeleteYou must be getting targeted Rob, only been showers here in south end. 1 or 2 brief downpours, that's it.
I got pea to marble sized hail this morning with the leading edge of the thunderstorms.
ReplyDeleteLooks like some juicy storms in the Brandon area and still no warnings! Anyways looks like more storms on the way in the next couple hours for Winnipeg. Nice to finally see some storms hitting us.
ReplyDeleteI'm up to 25 mm total so far this morning, with one more heavy band to come through before morning activity finishes up. Note training line of heavy cells along Hwy 2 towards St Claude-Elm Creek area.. watch out for torrential rain down there..
ReplyDeleteAnother 5 mm her ein Charlewsood.. 30 mm total so far. 35 mm over Ft Garry. Unofficial amounts of 40-50 mm from St Claude through Elm Creek and Starbuck to Sanford along that training line of heavy cells.
ReplyDeleteAnd this isn't even the main event yet! (supposedly) Are we looking another another 50 mm on top of all this over the weekend? Local flooding concerns likely if we get the heavy rainfall this weekend.
50-60 mm rain totals so far over the Hwy 2-3 corridors south of the city including Elm Creek, Starbuck, Sanford and La Salle.. and the line continues through the area with rainfall rates of 10-25 mm/hr. Could be seeing 70-80 mm totals through that area this morning.. WOW!
ReplyDeleteRob Is that a typo in your poll☁☂？
ReplyDeleteDid you mean 7pm Thursday ？☺
28 May 1000am 41.4mm so far at Silver Heights. Peak rainfall rate went just over 150mm/hr at the worst of it this morning - same time when I had to run from my house to my garage. Totally soaked!
ReplyDeleteJim.. no, that wasn't a typo.. I meant starting 7 pm tonight. I wasn't expecting this much rain today from the convective activity upstream to count in the poll. Now it looks like that may be heaviest part of the event! Hopefully the heaviest rainfall this weekend doesn't occur over the same areas as today, otherwise we'll be looking at some local flooding concerns.
ReplyDeleteI'm a little foreign to these events, being an Alberta native, but if there's one thing I know: don't trust the models in convective situations in the southern Prairies (beyond it might happen). I'm not paying to much attention today (saving it up for tomorrow for when I have to), but it definitely looks like elevated stuff will be the biggest concern. To my eyes, tonight looks relatively quiet unless some elevated stuff initiates again (which based on the flow, would probably head right over YWG again), and then main rain starting tomorrow with approach of low. I think that the GEM-REG may be underdoing tomorrow with only 10-15mm of rain; positioning of warm front and overrunning LLJ will be absolutely crucial in precip. forecasting over the next few days.
ReplyDeleteThat being said, with the warm front continuing to be relatively QS, any nocturnal event that does initiate will probably have heavy rainfall as it's most "high risk" aspect. Rob is definitely right in saying that if we get repeat of last night, there will likely be local flooding.
NWS and MB Flood forecasts posted on Wednesday with rises of 12 to 15 feet at GFKs and Oslo NWS Flood Briefing
ReplyDeleteIn Manitoba rises of 3 to 8 feet from Wpg James to Emerson based on Last weekends rainfall. at Manitoba Flood Reports
Updates to include these Noah like rains will be posted at these locations.☺
The 3 foot rise has occurred.
ReplyDeleteThose docks on the Red and Assiniboine may be at risk.
The Forks Assiniboine Walkway is once again underwater.