Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
413 AM EDT Fri Apr 12 2019

Valid 12Z Fri Apr 12 2019 - 12Z Mon Apr 15 2019


...Northern Plains and Upper Midwest...

The deep low that is currently impacting the region will continue
to weaken before accelerating to the northeast later today into
Ontario.  This will bring an end to the heavy snow threat across
the region, with WPC probabilities continuing to show only a
Slight Risk for additional accumulations of 4-inches or more
across portions of northern Minnesota after 12Z today.

...Central and Southern Rockies into the High Plains...

Energy diving through the West will continue to amplify a trough
over the Southwest later today.  Cold air aloft along with a
period of upslope flow will promote snow showers along the
Colorado Front Range and the Sangre de Cristos Mountains. 
Widespread heavy accumulations are not expected, with WPC
probabilities only showing a Slight Risk for amounts of 8-inches
or greater over a small portion of the Sangre de Cristos Mountains
on Day 1. 

Models show the upper trough continuing to amplify as it moves
farther east, assuming a slight negative tilt with a well-defined
surface cyclone developing over Texas on Saturday.  Rain changing
to snow is possible along the northwest extent of the associated
comma-head.  While favorable upper jet forcing along with low to
mid level frontogenesis are expected to support heavier
precipitation rates and the potential for accumulating snows
across portions of the High Plains, the NAM and some of the SREF
members continue to be cold outliers with amounts heavier than the
overnight model consensus.  WPC probabilities remain generally
unchanged, with a Slight Risk for accumulations of 4-inches or
more centered over the Texas Panhandle on Day 2.

...Mid Mississippi valley to the Great Lakes...

System over the southern Plains on Saturday is forecast to lift to
the northeast across the Mississippi and into the lower Ohio
valley on Sunday.  Strong upper jet forcing and low to mid level
frontogenesis will continue to support steady precipitation on the
northwest side of the low, with rain mixing with or changing to
wet snow at times.  Again, believe the NAM is too cold and its
solid stripe of accumulating snows from central Missouri to the
Great Lakes on Sunday is likely overdone.  However, there is
broader model agreement for accumulating snows Sunday evening from
the eastern Iowa border to northern Michigan, with WPC
probabilities indicating a Slight Risk for accumulations of
4-inches or more across the area on Day 3.

...Pacific Northwest to the Northern Rockies...

An upper trough and its associated surface low are forecast to
move into British Columbia on Saturday.  Falling snow levels
behind the trailing cold front pushing across the Northwest
Saturday evening may support some locally heavy totals across
portions of the northern Cascades, with WPC probabilities
continuing to show a Slight Risk for accumulations of the 8-inches
or more along some of the western slopes.  This frontal boundary
will drop into and remain across western Wyoming on Sunday.  This
along with an approaching shortwave is expected to raise the
potential for locally heavy snows within the northwestern Wyoming
ranges.

Pereira