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January 24-25th Potential Winter Weather Event


dmc76

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Unless I'm reading the map wrong, it looks decent for northeast Scarborough.

 

WRF and the 4km NAM are pushing the band further inland than I would have thought. Actually those models are hitting the east side of the city hardest, with l'il ole me here in Etobicoke on the fringes. Seems they're liking more of a SE/SSE flow rather than E/ESE. 

 

Actually, the more I look at it, the more I'm thinking that where the LES doesn't pan out, only a dusting or thin coating might fall. Looking more like an all or nothing event.

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Noticed the NAM hard trended to the GFS in terms of QPF locally here. Around .2" I would say it has pretty good credence too looking at the soundings. DGZ over 250mb deep for 8 or 9 hours. If we saturate like both the NAM and GFS show now, could be a pretty good hit, maybe in the 3-4" range.

Does the DGZ over 250mb deep mean good flake size (and ratios)? DTX and MKX both cited 20-1 ratios. A good average of qpf for DTW is 0.15", so that should be a solid 2-3" snowfal, maybe 4". Some models have closer to 0.20". Good old fashioned clipper incoming!

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LOT not changing their thinking on snowfall accumulations.

 

MAIN FORECAST CONCERNS TODAY INCLUDE ACCUMULATING LIGHT SNOW TONIGHTAND A VERY MESSY WINTRY MIX POSSIBLE ON SUNDAY.WILL ISSUE AN SPS FOR SNOW TONIGHT INTO FRIDAY LIKELY HAVING ANIMPACT ON THE FRIDAY MORNING COMMUTE.LATE TONIGHT INTO FRIDAY...STILL EXPECT A RELATIVELY FAST MOVING BAND OF ACCUMULATING LIGHTSNOW IS EXPECTED FROM A CLIPPER SYSTEM PASSING TO OUR NORTH AND INTOCENTRAL GREAT LAKES ON FRIDAY. THIS EVENT WILL BE DRIVEN BYISENTROPIC LIFT...FRONTOGENESIS AND PVA FROM A VORT MAX PUSHING OVERTHE AREA. THUS THERE COULD BE SOME MODERATE TO EVEN HEAVY SNOWFALLRATES FOR A FEW HOURS ONCE SATURATION OCCURS. EVALUATING 12ZGUIDANCE...THE NAM HAS COME AROUND TO THE IDEA OF PRECIPITATIONOCCURRING WITH THIS SYSTEM UNLIKE YESTERDAY MORNINGS RUN...WHILE THEGFS HAS COME IN A BIT DRIER THAN ITS LAST SEVERAL CYCLES AND THEECMWF ACTUALLY A HAIR MORE QPF. THIS STILL YIELDS THE SAME GENERALIDEA OF A RANGE OF .05 TO .15 LIQUID EQUIVALENT WITH THISSYSTEM...LESS IN THE SOUTHWEST CWA AND MOST IN THE NORTHEAST.ACCOUNTING FOR THE COLD AIR MASS AND GOOD SATURATION AND LIFTTHROUGH TWO DENDRITIC GROWTH LAYERS...A FLUFFY HIGH RATIO SNOW ISEXPECTED. GIVEN EXPECTED QPF AMOUNTS...SNOWFALL TOTALS SHOULD RANGEFROM JUST UNDER AN INCH/UP TO 1 INCH IN THE FAR SOUTHWEST CWA TO UPTO 3 INCHES IN THE NORTHEAST CWA.DUE TO THE LARGE DRY LAYER BETWEEN 900 AND 700 MB SEEN MOSTPROMINENTLY ON THE 12Z ILX RAOB...HAVE SCALED BACK POPS SOME UNTILLATE IN THE OVERNIGHT...WITH ONLY LIKELIES IN THE NORTHWEST FROM 6ZTO 9Z. HOWEVER SINCE WE ARE NOT LOOKING AT A SITUATION WITH DRYEASTERLY FLOW AND ADVECTING IN DRIER AIR...BUT INSTEAD A WARMADVECTION PATTERN...THE GOOD FORCING WILL BE ABLE TO OVERCOME THEINITIALLY DRY LAYER ALOFT. SO ONCE TO LATE IN THE OVERNIGHT TOWARDDAYBREAK...HAD ENOUGH CONFIDENCE TO GO WITH CATEGORICALPOPS...TAPERING FROM WEST TO EAST BY MID MORNING.AFTER A LIKELY LULL IN PRECIP IN THE EARLY AFTERNOON...WHERE IINCLUDED LOW POPS FOR POSSIBLY SOME LIGHT SNOW OR FLURRIES IN THECYCLONIC FLOW ALOFT...THE NAM IN PARTICULAR IS SHOWING A STRONGPUSH OF COLD AIR BEHIND THE COLD FRONT TRAILING FROM THE CLIPPERMID/LATE FRIDAY AFTERNOON. THIS COULD RESULT IN SOMESCATTERED...POSSIBLY BRIEFLY INTENSE SNOW SHOWERS SIMILAR TOWEDNESDAY EVENING DUE TO STEEPENING OF LOW LEVEL LAPSE RATES. WITHTHE OTHER GUIDANCE NOT SHOWING AS STRONG A COLD AIR PUSH BEHIND THECOLD FRONT...CONFIDENCE IS NOT OVERLY HIGH IN THIS SCENARIOOCCURRING. BUT TO ACCOUNT FOR THE NAM SCENARIO...BUMPED UP MIDAFTERNOON POPS TO HIGH CHANCE IN THE NORTH AND NORTHEAST PORTION OFTHE CWA. SOME SCATTERED LIGHT ADDITIONAL ACCUMULATIONS ARE POSSIBLEBY EARLY FRIDAY EVENING. HIGHS WILL BE IN THE MID AND UPPER20S...WITH BREEZY SOUTHWEST WINDS VEERING WESTERLY DURING THEAFTERNOON WITH APPROACH OF COLD FRONT.
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From Environment Canada:

 

WOCN11 CWTO 242303
Special weather statement
Issued by Environment Canada
At 6:03 PM EST Thursday 24 January 2013.
---------------------------------------------------------------------
Special weather statement for:
=new= City of Toronto
=new= Pickering - Oshawa - Southern Durham Region
=new= Cobourg - Colborne - Western Northumberland County.

      Some snow Friday with the added risk of a Lake Ontario snow
      Squall.

---------------------------------------------------------------------
==discussion==
An Alberta clipper tracking southeastwards towards the Lower Great
Lakes will give a fairly minor snowfall to much of Southern Ontario
on Friday. However, light southeast winds ahead of the low will
develop during the day and are expected to help steer a fairly strong
Lake Ontario snow squall towards the north shore of Lake Ontario.
This squall will most likely intensify over the lake in the morning
then slowly meander towards the shoreline from near Toronto eastwards
to Cobourg by afternoon. Some locales along this corridor may be
impacted with one or two periods of heavier snow if this squall
brushes the area. It may linger into the evening as well.

Snowfall totals may be in the 5 to locally 10 cm range from the
combination of the Alberta clipper and snow squall. But localized
amounts may surpass this. A snow squall warning is not anticipated
At this time but cannot be ruled out.

Winds are expected to be light thus blowing snow would not be an
issue with the squall if it materializes. However, visibilities may
be very low with a few centimetres of accumulation in a short time.
Commuters and travellers should be prepared for potentially hazardous
conditions should the snow squall develop.

The public is advised to monitor future forecasts and warnings as
warnings may be required.

Please monitor the latest forecasts and warnings from Environment
Canada at www.weatheroffice.gc.ca

END/OSPC

 

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From Environment Canada:

 

WOCN11 CWTO 242303

Special weather statement

Issued by Environment Canada

At 6:03 PM EST Thursday 24 January 2013.

---------------------------------------------------------------------

Special weather statement for:

=new= City of Toronto

=new= Pickering - Oshawa - Southern Durham Region

=new= Cobourg - Colborne - Western Northumberland County.

      Some snow Friday with the added risk of a Lake Ontario snow

      Squall.

---------------------------------------------------------------------

==discussion==

An Alberta clipper tracking southeastwards towards the Lower Great

Lakes will give a fairly minor snowfall to much of Southern Ontario

on Friday. However, light southeast winds ahead of the low will

develop during the day and are expected to help steer a fairly strong

Lake Ontario snow squall towards the north shore of Lake Ontario.

This squall will most likely intensify over the lake in the morning

then slowly meander towards the shoreline from near Toronto eastwards

to Cobourg by afternoon. Some locales along this corridor may be

impacted with one or two periods of heavier snow if this squall

brushes the area. It may linger into the evening as well.

Snowfall totals may be in the 5 to locally 10 cm range from the

combination of the Alberta clipper and snow squall. But localized

amounts may surpass this. A snow squall warning is not anticipated

At this time but cannot be ruled out.

Winds are expected to be light thus blowing snow would not be an

issue with the squall if it materializes. However, visibilities may

be very low with a few centimetres of accumulation in a short time.

Commuters and travellers should be prepared for potentially hazardous

conditions should the snow squall develop.

The public is advised to monitor future forecasts and warnings as

warnings may be required.

Please monitor the latest forecasts and warnings from Environment

Canada at www.weatheroffice.gc.ca

END/OSPC

 

 

From what I'm seeing, the 18z NAM/RGEM/WRF don't turn the winds easterly at all. We get a 150 flow that goes to calm later tomorrow night and then shifts to the north on Saturday as the coastal storm takes charge. It's going to be tough for Toronto, aside from Scarborough, to really get into the good stuff if the winds stay SSE. That's extremely unfortunate because some of those models actually are hinting at a single dominant band despite the wind shear. That band could produce well in excess of 4". But right now Oshawa to me seems like it'll be the sweet spot.

 

It's close enough that we're going to have to keep an eye on it though.  

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I hope this ends up like that one clipper back in 2005 (correct me if I'm wrong), when we were expecting 3-5" 4"-7" with very high ratios, ended up with almost a foot of snow, especially around the M59/94 areas where heavy bands developed... Does anyone remember that one?  Started off very lightly in the am, picked up drastically, 1-2" per hour for 6 hours. Looked like a blizzard outside. Great storm!

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I hope this ends up like that one clipper back in 2005 (correct me if I'm wrong), when we were expecting 3-5" 4"-7" with very high ratios, ended up with almost a foot of snow, especially around the M59/94 areas where heavy bands developed... Does anyone remember that one?  Started off very lightly in the am, picked up drastically, 1-2" per hour for 6 hours. Looked like a blizzard outside. Great storm!

 

That was the January 22, 2005 clipper and I have a better chance of banging Anne Hathaway on the moon than a redux of that super clipper happening tomorrow.

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