Sunday, September 06, 2009
Showers and thunderstorms Monday night into Tuesday.. locally heavy rain possible
Our stretch of dry warm weather will come to end Monday night into Tuesday as a slow moving cold front crosses southern MB. This front will trigger a band of showers and thunderstorms that will move into southwest MB by Monday evening, reaching the Red River valley overnight Monday into Tuesday morning. In general, most localities in southern MB should be seeing 10-20 mm of rain Monday night through Tuesday as this front crosses through. However, models are indicating that some of the rainfall could be heavy, with local rainfall amounts of 50 mm or more possible especially across SW MB into the Interlake area. The showers are expected to move east of the RRV Tuesday evening, with drier and slightly cooler weather for the rest of the week.
Posted by rob at 7:06 AM
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After intense scrutiny, I have determined that there is a slight severe thunderstorm risk tomorrow. It is mainly in western Manitoba, but the risk does extend a sliver into SE SK and a bit into NW ND.ReplyDelete
A cold front will be near the MB/SK border around the 18-21Z time frame. The front then pushes into MB and cools the 700mb temperatures by 4-5C. The front weakens the strong capping over the region to manageable levels. It will also serve as a focus for thunderstorm development. Shortwave(s) will be sitting over Central SK and Central MT during this time.
Early evening temperatures over Western MB will be in the high twenties, with tds around 18 to 20C. Moisture depth is good, with 850mb tds of 12 to 14C. This yields CAPE values around 1500J/kg.
Possible limiting factor to this risk is the slow entry of the upper trough. Winds of 65kts reside at 500mb and 90kts at 250mb. The jet streak is over central SK, but the trough digs into western MB by 00Z. A strong belt of 850mb southerlies is present over Lake Manitoba during the afternoon hours, which could give a slight tornado risk should storms fire earlier than expected. My magic number for bulk shear is generally 40kts. The line of 40kt shear just edges over the MB/SK border by 00Z. This could be problematic.
I see strong potential for severe storms around the riding mountains at 00Z. This is due to additional lifting provided by the increased elevation, general weakness in the cap over the area and maximization of CAPE and shear. If the cap weakens as expected, we could see a variety of severe modes. On the other hand, if the models are wrong on dissolving the cap, we may see nothing. There may also be a case to be made for some kind of MCS for the RRV by 12Z, but I'm not prepared to make that case.
Has anybody calculated the ods of cywg or cybr or southern MB west of the riding mntn being hit with Tornadic activity as the cold front goes thru??ReplyDelete
The tornado risk is very low overall. With a strong cap only forecast to break down by early evening, I think that supercells are highly unlikely. The upper jet doesn't intersect the lower level winds in a favourable area to promote tornado development. Besides, with the cap being as strong as it is, we may not see anything at all.ReplyDelete
I see like the Riding Mountain region by late afternoon.
Have you noticed that the dewpoint at Winnipeg airport has really dropped off this afternoon???
As of 5:00 pm it is only 9.5 !
Meanwhile at Portage it is 15.5!
Maybe a error with the readings????
Cap is still holding strong over Western Manitoba. The RUC does show weakening around the Turtle Mountain region, extending north to about the Riding Mountains.ReplyDelete
If the cap continues to deteriorate, then we should see some multicell storms this evening. I would watch the turtle mountain area for storms attm. The riding mountains could become active as well if the cap weakens farther north.
Bentornato Rob. I am glad you had some time to enjoy the warm climate and warm culture of the Mediterranean region... makes me wonder sometimes how we can tolerate life on the Canadian Prairies *sigh*.ReplyDelete
Too much cloud cover ahead of trough to get surface based convection going. Convection taking on an elevated character now following weakening LLJ up into interlake. Watch for redevelopment as upper low closes off and becomes better organized over N Dakota towards dawn. Resurgent LLJ will ramp up by the mid morning hours ahead of the distrubance... expect convection to form along nose of LLJ and wrap around under upper low giving possibly high precip totals. I think some models are over estimating the amount of QPF in the deformation zone and bullseye may end up being a bit further SE in the unstable warm advection regime/LLJ (ie RRV). Will be interesting to see what happens. Ciao.
Narrow but locally heavy band of rain training north of McCreary this evening. Local CWB Weatherbug site near Ste Rose Du Lac has picked up 52 mm of rain this evening, with 28-38 mm at 2 nearby sites. Not much elsewhere. I agree with Daniel that there should be redevelopment of showers/local thunderstorms over southern MB along LLJ overnight into Tuesday..ReplyDelete
Nice line of showers and thunderstorms to the west of Winnipeg this morning.. should move into the city between 9-10 am if it holds together. Heavier rain over southwest MB behind cold front where showers and thunderstorms are merging in favoured northwest flank of upper low. Rainfall rates of 30 mm or more per hour being observed here hence heavy rainfall warning issued over SW MB possibly extending into the Interlake.ReplyDelete
SPC and EC mentioning risk of severe storms this afternoon over extreme SE MB ahead of cold front, but this will be contingent on how much of the extensive cloud cover over southern MB can dissipate to allow sufficient heating for storm initiation. Severe threat will be suppressed further to our south and east if clouds hang in..
In Steinbach, the first week of September had an average high of 26.5C. The mean is currently 20.4C.
Too bad those figures won't last.
At 200PM today TWN forecast Radar has Steinbach as the midpoint in a trailing line of Severe Stms moving ENE from Pembina to RicherReplyDelete
NOW 12PM At each update TWN speeds up the arrival time .ReplyDelete
We had a good burst of rain at around 0930hrs this morning. We lost sight of the runway from the School of Meteorology during the worst of it. 8.2mm of rain fell in less than 15 minutes from the first wave of cells and it came with an impressive 5mb plunge and rebound as the CBs passed by. In total, 11.8mm of rain fell at Silver Heights (2km SW of the School of Met) as of 5pm. Not quite the deluge they got in Western MB, but still enough to water my lawn.ReplyDelete
Unofficial report of up to 275 mm (11") of rain in the Cayer area.. in the Lake Manitoba narrows region northeast of McCreary. They supposedly had 5" of rain in one hour last evening (9-10 pm) then another 4" overnight and another 2" today. Not surprisingly, flooded roads and fields in the area.. Not sure about how accurate that report is, but radar does show heaviest rain axis through that area. Most other reports are coming in the 50-80 mm range through southwestern MB.ReplyDelete
Storm total of 40mm in Steinbach (at my place)...quite a bit more than I was expecting.ReplyDelete
At the Steinbach airport, 48mm was recorded, a sure sign of thunderstorm activity.
Tomorrow looks rather interesting for severe storms in SE MB. CAPE values of 2000 to 2500J/kg, along with 40kts of bulk shear. Storm focus will be a cold front moving through in the evening. Capping doesn't look to be a problem, with 700mb temperatures only around 4C. Surface temperatures are forecast to be around 28C, with tds of 17 to 20C.ReplyDelete
SPC has northern North Dakota in a "slight risk" for tomorrow evening!!ReplyDelete
Do you see the potential for some severe storm to make into the Red River Valley tomorrow night???
Or will they fall apart before they make it across the border?
To me, it looks like better dynamics and moisture for possible severe storms will be south of the border in North Dakota Thursday night. Some storms may track across the border into southern RRV and SE MB overnight Thursday into early Friday morning.. but they will likely weaken overnight.ReplyDelete