Wednesday, April 23, 2008

Messy mix for the Thursday morning commute

A winter storm watch has been issued for much of southern MB as a low pressure system from the Dakotas spreads an area of precipitation up from the south beginning tonight. The precipitation will start off as band of rain (with possible thunderstorms) near the international border this evening spreading north through the evening. As it moves north, it will encounter colder air aloft and rain will change to snow over southwest MB and the northern Red River valley by midnight continuing overnight into Thursday morning. Precipitation will likely stay mostly as rain over southeast MB tonight before changing to wet snow early Thursday. In between the rain and snow areas, there may be a band of freezing rain and ice pellets cutting though the Red River valley including Winnipeg overnight.

Snow accumulations with this system will be highly dependent on elevation and the position of the rain/snow line.. but at this point, it appears areas north and west of Winnipeg will see around 10 cm of snow overnight with up to 20 cm possible over higher elevations west of the Red River valley. Areas south and east of Winnipeg will see more rain at first before the changeover to snow, so snow amounts in these areas will only be in the coating to 5 cm range. Here in Winnipeg, snow amounts will be a tough call since we'll be right on the rain/snow line much of tonight, but as a first guess, 5 to 10 cm are possible by midday Thursday, although some of that will melt initially due to the warm ground. Note that this system has the potential for heavy precipitation rates due to elevated convection, thus snow or freezing rain could be heavy at times overnight into Thursday morning. In areas that are cold enough for snow, this will mean very poor visibilities in heavy snow, with snowfall rates of 2 to 3 cm/hr possible at times. All in all, a messy commute to work and school Thursday.. be prepared for anything!

41 comments:

  1. Rob!
    you think the snowfall rates will be heavy enough, so that we could even get some THUNDER-SNOW???
    I mean the thunderstorms that are south of the border could move into the cold air and produce heavy snowfall rates!
    Man I'm glad that I do not have to drive the transit bus tomorrow!!
    It could be crazy on the roads tomorrow morning!

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  2. This system has a good setup for elevated thunderstorms overnight into Thursday morning.. although I think the greater potential for thunderstorms will be further south of Winnipeg, over northern ND where the precipitation will be in the form of rain. However, if the instability gets transported far enough north, thundersnow (or even worse, thunder-freezing rain!) is a possibility for parts of southern MB! Should be an interesting 24 hours coming up..

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  3. According to Environment Canada's discussion it would seem that the rain/snow line would be running right through Winnipeg.
    It will be interesting to see how they make a call on this one!

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  4. Models really blowing up the QPF for tonight and Thursday over southern MB.. indicating rapid and intense precipitation development tonight due to elevated convection along the international border. This will compound an already difficult forecast for Winnipeg area. Trying to forecast convective-induced QPF along a precipitation phase boundary is as challenging as it gets in this business. Big potential for bust forecasts in Winnipeg area not only for precip amounts but for precip phase as well. Based on current trends, I'm leaning to more of a snow and/or ice pellet mix for Winnipeg with rain to the southeast.. but precip amounts will be a wild card based on how much convection gets going tonight. 5 to 10 cm still looks like a reasonable first guess for Winnipeg (if snow is reasonable at this time of year :)...but we could see anywhere from just a coating to 20+ cm depending on how everything lines up. Stay tuned..

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  5. Winter storm watch has been upgraded to a winter storm warning.. although the warning is saying pretty much what the watch was saying. Same thinking as previous.. rain southeast, snow northwest.. Winnipeg in the transition zone of snow and ice. Note thunderstorms starting to fire up in North Dakota as of 4 pm. Let the games begin!

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  6. Winter Storm warning for most of Southern Manitoba, including the Interlake!

    Not much has changed from the previous watch in terms of what to expect, but as Rob mentioned higher amounts of precipitation are now being forecast! I am excited to see what happens too. I wonder if we will see any highway/school closures due to freezing rain and/or snow!

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  7. Lovely evening out there.. partly sunny, +7C, no wind, enjoying a nice BBQ out on the deck. Hard to believe that within 12 hrs that deck may be covered with snow, ice, or being pelted with ice pellets.

    Still a lot of very dry air over southern MB with dewpoints in the -8 to -12 range. Zero degree dewpoints spreading into southeast ND now with convective precipitation growing over central ND.

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  8. Rob!
    I think all that dry air
    (low dewpoint) is a good thing if you want heavy snow!
    With a heavy rain falling in that dry air it will cool the lower layers of the atmosphere changing that rain over to snow if the temp. is hovering around borderline 0 C !!!

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  9. There is a heavy band of precip. heading very quickly up to the north.
    It looked like it was going to hit the Steinbach area but last second is starting to make more of a north turn.
    Winnipeg should be getting this heavy precip in a hour of so!!

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  11. Ice pellets here in Steinbach as of 10:20 p.m. on Wednesday. It is like a "mini hailstorm" out there and sounds like one too!

    A heavy band of precipitation is rolling through. Looks to be the remains of what was once a thunderstorm in North Dakota, so I wouldn't be surprised to see lightning stroke or two.

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  12. Precipitation coming in as rain over the southern Red river valley this evening with Winkler, Dominion, Altona, and Vita reporting 0.4-2 mm of rain past hour and temperatures above zero. Precip likely falling as wet snow west of the Red River such as in Pilot Mound, Manitou, Killarney, Boissevain, etc. where temperatures have dropped close to freezing.

    I suspect the band of precipitation will move into Winnipeg by midnight as rain then quickly change to snow as the low level temperatures cool.

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  13. Thanks for the report Scott.. nothing here in Winnipeg yet. Bright banding on radar south of here indicating presence of ice pellets or freezing rain aloft. I guess it's making it down to the surface now! Rain or ice pellets should be moving into Winnipeg within the hour..

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  14. Hmm...two Daniels, this could get confusing.

    The first band of precip having a hard time overcoming the very dry atmosphere. Hallock only reported 3 one hundredths of an inch of precip (rain). Their dewpoint did come up nicely to 1 C so it is at least saturating the airmass.

    Still a bone dry airmass up in Winnipeg. An impressive 50+ knot low level jet noses into SE N Dakota closer to midnight. There will be copious moisture transport down there and warm air advection supporting strong elevated storms as mentioned already.

    However most of that forcing remains off to our southeast... it's not clear how far northwest the deformation band will set up with such a dry airmass in place. Let's see what happens.

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  15. So when are we going to know if it will snow or not? Are we actully going to have to wait minute by minute. It could be a very long night for me if I have to stay up all night to see if I have to call the guys in to man the machines.

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  16. Daryl.. Precipitation will be moving into Winnipeg shortly from the south.. likely as ice pellets or a rain/wet snow mix as temperatures remain above zero. Then it should change to all snow or a snow/ice pellet mix shortly thereafter as temperatures fall closer to the freezing mark. Any snow will likely be melting at first since the ground is relatively warm.. but we could see snow start accumulating by 1 or 2 am I suspect. Still.. it's a tricky call since temperatures at the surface and aloft are so close to that melting/freezing point. Personally though, I'd lean more towards snow than rain in Winnipeg..

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  17. Ice pellets falling in Charleswood as of 11:20 pm.

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  18. we started as snow and ice pellets here in winnipeg at about 11:20 pm. we're launching a 06z sonde to better determine precip typing through the night.
    dave

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  19. A midnight sounding.. cool!

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  20. Wow I surprised that it is ice pellets falling right now with the temp. at 4 C
    The radar returns are so weak over Winnipeg right now yet the ice pellets are coming down at a good clip!
    The radar is also filling in nicely over north Dakota !

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  21. Well..that's it for me tonight.. we'll see what the morning will bring. Good luck all!

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  22. Well its about 2:15 am. So far we have had some rain a little bit of freezing rain and some ice pellets. The temperture is about 0 right now but the winds have really picked up from the north. Radar at the moment is showing precipatation as very light or stopping for the next while in the Winnipeg area but looks like could redevelop again in several hours. Have to wait and see if it changes to snow as of right now it looks more like a rain with some ice. A little further north looks more like snow. Anyways with the wind picking up from the north the roads will be slippery.

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  23. It's about 4:15am and so far nothing has really happened. It's still around 0. A freezing rain warning has just been issued. Radar shows a heavier band of mixed precipitation around the border moving north towards the Winnipeg area. It looks like Portage La Praire and Morden have got most of the action so far.

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  24. 6:15 AM - Whoa! A winter wonderland out there! Snow, strong winds, poor visibility in Winnipeg.. just a coating on the ground so far, but we should get a good (or is that bad) 5-10 cm at this rate!

    Looks like we dodged a bullet with the first wave of precipitation last night (just some ice pellets/rain), but not so lucky with this second wave! Careful driving out there this morning!

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  25. 7:00 am - 1-2 cm of snow in Charleswood, with snow now mixing with ice pellets. Visibility has improved a bit.. temperature -1.7C.

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  26. Environment Canada Changed to freezing rain warning and then changed it back AGAIN to winter storm warning!
    A forecasting nightmare!!
    LOL

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  27. "A forecasting nightmare!!"

    you said it, daniel.
    dave

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  28. Forecasting nightmare is right.. still getting reports of rain in the east parts of the city this morning, with snow and ice pellets west. Rain/snow line still right over the city this morning.

    Further west, climate observer from Portage La Prairie reports 17 cm of snow overnight!

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  29. Straight ice pellets and freezing rain now in Charleswood.. no snow falling at the moment. Temperature -1.3C. The battle between warm and cold continues..

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  30. Freezing rain is building up on the trees here. The roads currently have no ice due to the warmer ground. The temperature has gradually fallen all morning, and it now at 0C. I would expect further ice accumulations until the surface temperature starts climbing again.

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  31. Power bumps and some power outages in Charleswood due to wet snow/freezing rain/winds.

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  32. Quite the event here in Steinbach. We haven't seen any snow, just rain and freezing rain. Trees and power lines are coated with ice. a couple millimetres of ice cover everything, except the ground. If you touch a tree branch all you hear is ice cracking. It actually looks like a beautiful winter scene out there with the tree-buds covered in ice. So much ice has built up my anemometer is stuck, so my wind reads 0, even though it is 20 to 30km/h.

    The Steinbach rain gauge reads 16.1mm as of 12:00 p.m. and mine reads 13.5mm. The temperature is now -0.4, so any rain that falls will easily freeze to anything! When the freezing rain started the temperature was 0.5 to 0C, so now things are even better for ice build-up. It is still raining as of 12:10 p.m. Thursday, and the power has flickered here too. At our house we saw one hour without power this morning.

    I posted some images of the ice build-up here:

    http://members.shaw.ca/sdk1/pages/pictures.htm

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  33. Scott.. that's a good buildup of ice down there. Lucky it was above freezing at first, otherwise there could have been some serious tree damage.

    As for me, I ended up with 15.4 mm of melted slop in my standard rain gauge (melted snow, ice, and rain) Ended up being about 3 cm of actual snow on the ground, the rest a mix of ice pellets and freezing rain. Station anemometer is frozen up here as well.. stopped recording just after 8 am due to ice build-up.. will have to wait for some sun, or the temperature to climb above zero for those cups to start spinning again!

    Kudos to the people who picked 2-5 cm in the snow pool! You get a gold star for such a tricky forecast!

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  34. Speaking of iced up anemometers the Steinbach Weather station (MB AG) has been reading winds of around 7km/h for the last 6 hours. The Woodlawn school meter is reading 11km/h winds, so I guess that one is iced over too!

    The wind is actually around 30km/h gusting to 50km/h.

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  35. Interesting storm to say the least.
    I was surprised how easily the atmosphere saturated with even low dbz values on the radar. Must have a fairly shallow dry layer just near the surface?

    A somewhat complex precipitation pattern evolved last night also. Seems like the low level jet did not become the dominant player as the system unfolded. They were expecting possibly up to 50 mm of precip in tstroms down in SE N Dakota and WC Minnesota. Although there were storms these high amounts did not materialize.

    Had those storms been larger and more widespread, might they have cut off mositrue supply to the frontogenic (or is it frontogenetic ... I never remember) band/forcing that set up farther north?

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