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Potential of Widespread Snow/ Mixed Precipitation 2/25


sferic
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Man, those New England guys bicker like a bunch of grumpy old men and grannies. When they go at it, they go at it. Back and forth...back and forth. We tease each other on here...and I'm grateful we don't get as intense with one another as they do. (Besides debates about which Upstate city is bigger or has better ratios.)

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This afternoon an elongated surface high pressure is located across
Ontario and Quebec, producing a northeasterly flow across our
region. A shortwave is crossing the desert Southwest this afternoon.

This upstream shortwave will develop and deepen a storm system...one
that will advance from the southern Mississippi Valley tonight to
sneaking just into WNY around daybreak tomorrow.

The dynamics of this storm system are coming together to produce a
period of snow (with a mix towards the south). Initial snow
formation will be upon isentropic upglide motion, with a 40 to 50
knot LLJ to our south enhancing the overall lift. Aloft several jet
streaks at 300 hPa will bring pockets of deeper lift, along with a
tightening 700-850 hPa circulation that will pass over our region.
Snow will reach our Southern Tier late this evening and quickly
spread towards the Lake Ontario region just past midnight. Snow,
though only a few inches at the start of rush hour will likely slow
the morning commute with snow slicken roads.

The surface low will be tracking towards the Southern Tier by early
Friday morning. A warm nose ahead of this low will reach into at
least the southern two tiers of counties transitioning the snow over
to sleet and freezing rain. Will side with a more northward push of
the warm nose with the surface high now off to our northeast. The
mixed precipitation looks to be in about a 6-9 hour window from late
tonight through late tomorrow morning. Thereafter the surface low
will track to our east with cold air returning.

Snow will end from west to east with the passing of the upper level
shortwave a weakening deformation band of snow. The widespread snow
will eventually contract back towards the lake belts with a north-
northwest flow continuing lake enhanced snows through the late
afternoon hours. This north-northwest wind will gust towards 25 to
30 mph tomorrow afternoon behind the front, bringing some blowing
snow to the southern shoreline of Lake Ontario.

Overall will have snow amounts through Friday within the advisory
range for this system south of Lake Ontario, with possible higher
amounts east of Lake Ontario where snow ratios should be higher with
the surface high to the north and a period of higher snowfall rates
through the afternoon hours under the deformation band.

Sleet and any freezing rain to the south will hold snow amounts down
across the Southern Tier.

 

Cold advection on northwesterly flow starts the period out with lake
responses being the biggest player in the forecast. While inversion
heights are far from impressive, saturation within the dendritic
layer and unstable lapse rates are likely to allow for efficient ice
nucleation. This will result in decent coverage of snow showers to
the SE of both lakes on Friday night. Better fetch and more open
water over Lake Ontario will yield a better response there, however
there is ample open water on Lake Erie to allow for a response there
too. It seems model guidance is far overplaying ice cover on
Lake Erie and minimizing latent heat flux as well as moisture
flux off the lake as a result. As usual, only the Canadian model
really has any handle at all on this, and it was heavily leaned
upon for the forecast.

Flow turns from northwesterly to westerly and eventually WSW as cold
advection ebbs Saturday into Saturday night. This allows for
minimal lake response to continue in the form of very light
accumulating snow showers as lake bands lift northward and
become more disorganized. This results in further impetus for
lake responses to become less robust by Saturday night, as 850
hPa temperatures start to increase from -16C to around -10C,
reducing lake-induced instability, especially over Lake Erie, as
modest warm advection starts to take hold ahead of the next
system to affect the area in the long term forecast.
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