Current SPC mesoanalysis in the upper levels
continues to indicate a slightly stronger shortwave than was originally
forecasted by the mesoscale models. This could have strong implications,
especially in regards to the amount of snowfall, and
its duration. Generally, a stronger clipper in a NW flow pattern will
generally head slightly farther south, given all other variables are
constant, due to the fact that northwest flow patterns are highly
conducive to mid and upper level frontogenesis. Sometimes, especially in
highly mesoscale events, this can lead to a phenomena known as
"foldogenesis", which is what can occur in intense cyclogenesis events.
While this event is not related to any strong storm system, mesoscale
areas of intense frontogenesis and folding of the tropopause could lead
to precipitation banding at times, especially by the early morning
tomorrow (6-10 a.m.) across the area. Also, precipitable water values
are currently increasing to near 0.5 across parts of the Northern
Plains, which will eventually be drawn into the system itself. If it is
drawn into the clipper system, we may see higher snowfall totals than
what the NAM is currently forecasting. Frankly, the mesoscale models
neither handled Saturday or Today's snow events all that accurately,
especially farther west, and so I would like to give lower credence to
their forecasts.
Even though conditions do seem slightly ideal for this event, there are some caveats to a much heavier snowfall than 2-5 inches across the area. One.) The presence of a strong dry air mass will likely impede much heavier or widespread snowfall from developing (unless the system ingests the 0.4 to 0.5 PW values over the Northern Plains, which is entirely possible given the fact that a stronger surface cyclone is currently noted on surface analysis across the Plains.). Two.) Lack of widespread upper level forcing will also limit coverage of snowfall (though conditions are slightly more ideal than they were for Saturday's clipper system). The main forcing mechanisms involved will be whether areas of strong low level frontogenesis and upper level frontogenesis can couple with each other, producing a strong ageostrophic circulation along the warm frontal boundary, which could in itself not only strengthen the surface storm, but also the coverage and intensity of precipitation bands. This, we are already seeing across parts of the Upper Midwest.
In other words, there is the possibility that some areas, especially north of Route 30, see isolated higher amounts over 2-4 inches due to mesoscale banding. Anywhere south of the Route 30 corridor will likely see around an inch or two of snow. The snow event will likely start around 3 or 4 a.m. tomorrow morning, possibly later due to the presence of strong low level dry air.
Even though conditions do seem slightly ideal for this event, there are some caveats to a much heavier snowfall than 2-5 inches across the area. One.) The presence of a strong dry air mass will likely impede much heavier or widespread snowfall from developing (unless the system ingests the 0.4 to 0.5 PW values over the Northern Plains, which is entirely possible given the fact that a stronger surface cyclone is currently noted on surface analysis across the Plains.). Two.) Lack of widespread upper level forcing will also limit coverage of snowfall (though conditions are slightly more ideal than they were for Saturday's clipper system). The main forcing mechanisms involved will be whether areas of strong low level frontogenesis and upper level frontogenesis can couple with each other, producing a strong ageostrophic circulation along the warm frontal boundary, which could in itself not only strengthen the surface storm, but also the coverage and intensity of precipitation bands. This, we are already seeing across parts of the Upper Midwest.
In other words, there is the possibility that some areas, especially north of Route 30, see isolated higher amounts over 2-4 inches due to mesoscale banding. Anywhere south of the Route 30 corridor will likely see around an inch or two of snow. The snow event will likely start around 3 or 4 a.m. tomorrow morning, possibly later due to the presence of strong low level dry air.
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