Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
528 PM EDT Sat Apr 11 2020

Valid 00Z Sun Apr 12 2020 - 00Z Wed Apr 15 2020


...Wyoming Rockies to the Central/Northern Plains/Upper MS
Valley/Upper Great Lakes...

Days 1-3 ...

A 700 mb shortwave pressing east southeast out of MT and across WY
and SD/NE and MN Sun is preceded by a mid level convergence and
frontogenesis maxima, and a 300 mb divergence maxima. Additional
snows of 6-10 inches are expected
in the ranges of northern and central WY to the SD Black Hills
east across southern South Dakota, northeast Nebraska, northwest
Iowa, southeast MN, western WI, and the UP of MI.  Amounts locally
to a foot are possible in the mountains of WY and the SD Black
Hills, with amounts of 1-2 feet expected in the western Upper
Peninsula of Michigan.  The continuing higher confidence is the
heavier snows in the upper peninsula of MI as the northern and
southern streams phase to form a rapidly deepening low that
produces both the ascent with the low, followed by post-front lake
enhanced and lake effect snow in the UP of MI. 

Guidance still has variability to resolve, with the high res
windows, NAM/NAM Nest heavier with QPF and snow amounts and a bit
further north than the GFS/ECMWF in southeast SD to southern
MN/western WI.  WPC forecasts show moderate probabilities for
accumulations of 8 inches across much of southern South Dakota to
northeast Nebraska, northwest Iowa, and southern MN, becoming a
high probabilities across western to northern WI and the UP of
Michigan.

...CO/NM Rockies to the Southern High Plains...
Days 1-3...
Models show a longwave trough covering much of the contiguous U.S.
early next week.  Mid level energy moving into the base of the
trough along with a developing upper jet couplet is expected to
support an area of moisture and lift moving south from Wyoming
across the ranges of Colorado on Sunday and then into New Mexico
Sunday night-Monday.
Snows are expected to focus on the front range of both states. 
The highest amounts are expected to be 8 to 12 inches across the
CO front range.

As a 700 mb wave moves east across southeast CO and northeast NM,
enhanced theta-e advection along the low level jet supports snow
extending east across the high Plains of southeast CO/northeast NM
and then moving east into the Texas/OK Panhandles Monday night
into Tuesday morning.
The chances of snow decrease further east in OK/TX as near surface
temperatures become too warm for snow.
Drier air aloft moving out of the southern Rockies into the high
plains should bring the snow to and end late Tue or Tue evening.

For Days 1-3, the probability of significant icing (0.25 inches or
greater) is less than 10 percent.

Petersen