Sunday, July 12, 2009

Nice today and Monday.. more showers/tstorms Tuesday and Wednesday

We've got some nice weather to enjoy today and tomorrow with sunshine, light winds and temperatures in the low to mid 20s. Things will get more unsettled Tuesday as another storm system pushes into the Northern Plains bringing a band of showers and thunderstorms into southern MB by Tuesday morning. Conditions are favourable for some severe thunderstorms to develop over Montana and western ND Monday evening, pushing into southern MB as a band of locally heavy thunderstorms overnight Monday into Tuesday morning. Models are indicating the potential for locally heavy rainfall with these storms over portions of southern MB overnight Monday into Tuesday morning, with local amounts of 30-50 mm possible. Additional showers and thunderstorms are likely Tuesday afternoon with
more showers expected Wednesday across southern MB as the storm system moves east.

33 comments:

  1. Rob!

    It seems like this spring/summer so far has turned out about as foul as last year!

    Just barely hit 30 C in June....if not for that day we might have made a run for another very late "first" 30 C for the year!

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  2. Here's some pleasant news.

    If next Wednesday is a few degrees cooler than the models predict, there is a chance of wet flurries around Lake Winnipeg. Although highly unlikely, I suppose it's still possible for flurries in July given a very strange pattern.

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  3. Well the models have come to their senses on the snow idea. While I never actually thought we had a chance at flurries, it was a funny sidenote.

    On a more reasonable note, it looks like we will be transitioning into another above-normal phase starting this weekend. I would like to see a few more model runs that are consistent with this idea, but the solution doesn't seem out of whack attm.

    Severe weather chances for tomorrow are still unclear. The models bring good moisture into S MB (tds +16 to +20C), but daytime heating could be an issue. If we can get temperatures into the 22 to 25C range, CAPE values will come close to 2000J/kg. If thunderstorms form before 18Z, the RRV and SE MB can take advantage of a strong SLY LLJ, after that the strong core of the SLY winds move into NW ON. For the most part the shear will be unidirectional, but somewhat strange, with a SLY 250mb jet. 0-6km bulk shear won't exceed 40 knots, which takes away the supercell risk (although still possible, not likely).

    Overall severe risk/type isn't very certain. Could be similar to last Thursday...?

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  4. Thanks for the city rain gauge info Rob. Given the observed radar returns and that the rain was nearly horizontal, I imagine there was undercatch at most gauges for the afternoon convection...

    We have been in a semi-blocking pattern recently. Hudson Bay Vortex periodically weakens/ opens up as trough and shifts east... this allows for upper lows to move in from Pacific Northwest and re-form the vortex over N Manitoba, starting the whole process over again.

    LLJ develops ahead of upper low with attendant isentropic ascent destabilizing the airmass. Looks like initially precipitation will focused into two areas (similar to the last system):

    1)around main upper low
    2)along main instability/theta e gradient

    By morning, forcing more or less merges producing a generalized area of showers/Tstorms along LLJ. I would expect main activity to be between 7 and 11 AM. Chance for severe convection dependent on amount of mid level drying working in behind the system. Models show a lot of clouds hanging around limiting instability.

    Btw, NAM still depcited 850 hPa temps of 2 C over the Bissett region. Heat transfer off the lakes would be enough to keep everything rain however, even if 850 hPa temps were cold enough.

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  5. Looks like some heavy thunderstorms could be forming this afternoon if the skies will clear a little according to EC morning discussion!

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  6. With a "high" of only 15 C the next few days could there be frost if the skies clear one of those nights??????

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  7. Good downpour coming down now in Charleswoood along with thunder and lightning. 5 mm rain past 10 minutes.. 60 mm/hr rain rate..

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  8. Some minor street flooding in my area of the city across the river in St James!!

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  9. Rob!

    PASAC discussion is mentioning a risk of severe storms this afternoon if skies can clear

    The overcast is very thick!
    Could we clear out????

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  10. Yeah.. good lightning noted. This is still elevated convection associated with LLJ. RUC not very aggressive with drying behind 850 hPa trough... maybe hinting at a few clear breaks.

    Some convection may yet form along surface trough in N Dakota. This would rotate in but weaken, giving us another round of rain later this evening.

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  11. Another 22 mm here today.. on top of the 50 mm deluge last Thursday. Ground can't absorb too much more.

    More thunderstorms firing up in the dry slot over southwest MB. CAPES not that impressive, but could get marginally severe hail and wind gusts out of them, as noted by latest SPC mesoscale discussion.

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  12. Grand Forks office is stating that on Wednesday the 850 mb temperatures will only be + 4C !

    Now that is cold for July......I can't believe that for this time of year!

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  13. Just east of Lake Winnipeg, the models are showing 850mb temps below freezing! With surface temperatures between +5 and +8, there could be a flake of snow! Although that remains unlikely, it is not a pleasant idea to think about.

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  14. Rob!
    Look to your south!
    Some nice towering cumulus are starting to fire in the clear break!!!

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  15. Storms are really starting to take off within the last 10 minutes!

    Looks like Winnipeg and area could get another intense downpour!

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  16. Line of convection about set to move into southern Winnipeg... seems like instability is advecting in with the storms from the southwest.

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  17. Very black skies to the west of the city!!

    I have not seen skies that dark in a long time!!

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  18. Very heavy rain in west Winnipeg.. another 10 mm in 10 minutes.. rain rate of 155 mm/hr. Over 30 mm for the day now..

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  19. I intercepted line of cells at Assiniboine park... absolutely torrential rain...blinding in fact with street flooding noted. Very strong straight line winds. Severe tstorm warning necessary. Cells appear to be training and somewhat slow moving heightening potential for heavy rain...

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  20. We simply need better resolution radar... there are severe flare ups within the general line that show up only as red or scarlet pixels. Impossible to gauge from weather office severity of these small localized cells. I wish I had my laptop with me.. I could have posted from the Starbuck's at Roblyn and Moray. It was in the parking lot that I experienced the downburst of very strong winds. In fact I started wondering if there was a rain-wrapped tornado!

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  21. Street flooding and ditches at bank-full in Charleswood.. west end of Winnipeg appears to have got the heaviest rainfall withtis last band. My station recorded 42 mm past hour.. with 65 mm for the day. I'll have to check my standard gauge in the backyard to verify this, but no doubt, we've had quite the rain here. Over 100 mm now in the past 5 days. No more please!

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  22. Btw.. my intention is not to second guess or criticize the meteorologists at the weather office. I am simply trying to provide additional feedback. I have the suspicion (and that is all since I have no experience or access) that the algorithms used to detect severe phenomena within the radar data are not able to detect smaller scale, localized events. One is just left with one or two scarlet pixels or proverbial blips on the radar... hard to say what is happening unless you have a weather spotter right there.

    Looks like the area between St Francis Xavier and Rosser was pummeled by heavy rain.. will be interesting to see rain fall totals from there and also in the vicinity of western Assiniboine park. There also appears to be a strong cell just NW of Treherne.

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  23. Agreed Daniel. We need to make live radar available to the public, not just on the news at 6 or noon. It would help a lot for regular civilians in the city to know ahead of time especially for outdoor sports like baseball or soccer. Coaches would instantly know when to cancel or postpone a game/practice session. Either live radar or 5 minute updates would help greatly. As for the possibility of a rain-wrapped tornado, it would be unlikely because EC would likely issue a severe thunderstorm warning or a tornado watch. These cells just fired up out of nowhere about 3 hours ago. That would also be a reason why EC probably didn't issue a warning because they were weakening every image update.

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  24. You're right Connor (not sure if thats your name lol).. it was almost certainly a high precip microburst. Deep moisture and very high relative humidities (we barely heated out at all ahead of there storms), and instability likely produced a favorable environment for such an occurence. LCLs were likely very low giving the clouds a particularly nasty, dark appearance as daniel P noted earlier. I just wanted to stress how intense the winds were at that particular moment and time.

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  25. Incredible... another line of intense cells developing from Dominion City NW to Long Plain first nation (SW of Portage) moving due east. How does the atmosphere have enough 'juice' left?

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  26. Picked up 62 mm in the standard gauge.. with 42 mm of that falling in the evening deluge between 6:30 and 7:30 pm. So my Davis weather station is not all that far off.. although I still wonder if my gauges pick up additional rainfall from nearby trees and roofs during exceptionally heavy downpours. Again.. I'll have to check with the city network to make a valid comparison.

    Airport picked up 25 mm between 7-8 pm, and 44 mm for the day. Forks had 20 mm in the evening downpour, and 32 mm for the day.

    Higher resolution Doppler radar images showed west end of Winnipeg had heavier rain from a mesoscale comma head associated with the convective band moving through in the evening. Such small scale temporal features are impossible to predict with any useful lead time. Note that the rest of the city had half the amounts of the west end..

    Higher resolution radar data is available from the U of M chase page.. link to my name. Highly recommend it over the very basic and inadequate radar images from Weatheroffice.

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  27. Cell north of Carman looking interesting..

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  28. It would appear to be helpful if EC Winnipeg had this type of DATA Collection, Radar and Warning capability..???

    NATIONAL WEATHER SERVICE DULUTH MN
    751 PM CDT TUE JUL 14 2009

    THE NATIONAL WEATHER SERVICE IN DULUTH MN HAS ISSUED A

    * FLASH FLOOD WARNING FOR...
    CENTRAL AITKIN COUNTY IN EAST CENTRAL MINNESOTA...
    CROW WING COUNTY IN EAST CENTRAL MINNESOTA...
    THIS INCLUDES THE CITY OF BRAINERD...
    SOUTHERN CASS COUNTY IN NORTH CENTRAL MINNESOTA...

    * UNTIL 1145 PM CDT

    * AT 744 PM CDT...TRAINED WEATHER SPOTTERS REPORTED AREAS OF FLASH
    FLOODING IN AN AREA FROM NEAR MOTLEY AND CASINO...THROUGH
    NISSWA...BRAINERD...IRONTON...DEERWOOD...AITKIN AND MCGREGOR.
    AT 715 PM...WEATHER SPOTTERS REPORTED 6 INCHES OF RAIN IN AN
    AREA BETWEEN DEERWOOD AND AITKIN WITH SEVERAL REPORTS OF 4 OR
    MORE INCHES ELSEWHERE IN THIS AREA.

    * LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO ARTHYDE...
    WOODROW...WOLFORD...WEALTHWOOD...WAUKENABO...WALDECK...TROM
    MALD...TAMARACK...SHESHEBEE...ROSSBURG...RIVERTON...POPLAR...PINE
    KNOLL...PEQUOT LAKES...PALISADE...NISSWA...MISSION...MERRIFIELD...
    MCGREGOR...LITTLE PINE...LIBBY...LEGIONVILLE...LEADER...LAWLER...
    LAKE SHORE...LAKE HUBERT...KIMBERLY...JENKINS...IRONTON...
    HASSMAN...GLORY...GLEN...ESTERDY...EAST GULL LAKE...DEERWOOD...
    CUYUNA...CROSSLAKE...CROSBY...CASINO...BREEZY POINT...BALSAM...
    BAIN AND AITKIN.

    THE VAST MAJORITY OF THE THUNDERSTORMS SHOULD MOVE EAST OF THE
    WARNING AREA BY 9 PM...BUT IT WILL TAKE SOME TIME FOR THE STORM WATER RUNOFF EFFECTS TO TAKE FULL HOLD. AS A RESULT...FLOODING COULD
    CONTINUE OR EVEN BECOME MORE SUBSTANTIAL THROUGH THE EVENING HOURS
    AND THE FLASH FLOOD WARNING HAS BEEN EXTENDED FOR THIS AREA THROUGH
    MIDNIGHT.

    PRECAUTIONARY/PREPAREDNESS ACTIONS........

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  29. Thanks for posting that link again... For some reason I thought it was only for american radar data lol

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  30. Another small line of thunderstorms approaching from the west.. heaviest core near Starbuck moving east towards the southwest part of Winnipeg before midnight. Just what we don't need.. more rain! Should be a relatively quick shot though..maybe 5-10 mm.

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  31. Lots of areas of the city need a couple days to dry off.... to bad the forecast looks cool (no....cold)
    and wet!

    I looking at that weekend forecast thinking.....I'll believe it when I see it!!!!

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  32. Rob!

    Go to "cjob.com"

    and click on the "winnipeg get drenched"

    They got some great photos from the charleswood area !!!

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  33. Yeah I saw those.. posted on new entry.

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