Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
344 AM EST Thu Jan 10 2019

Valid 12Z Thu Jan 10 2019 - 12Z Sun Jan 13 2019


...Colorado/New Mexico to mid-lower MS Valley and lower Ohio
Valley and Mid-Atlantic...
...Days 2-3...

A southern stream trough develops with the 500 mb wave crossing
CO/NM on Friday onto the central and southern Plains Fri
night-early Sat. Snow develops in the front range and Sangre De
Cristo Mountains and adjacent high plains of CO and NM as 700 mb
convergence is forecast in the region in concert with the
developing lee low. Several inches of snow are possible at the
higher elevations of the Sangre de Cristos, WPC probabilities are
moderately high for 8 inches.

The circulation causes low-mid level warm/moisture advection out
of OK across AR/MO Fri night-Sat, with snow and then mixed precip
types in northern AR and then southern MO.
On Sat the snow expands northeast across the rest of eastern MO
and southern IL/KY/southern IN. Surface low cyclogenesis is
delayed until the Carolina coast Saturday night, so the focus is
on low and mid-level forcing (in addition to jet dynamics) in the
elongated trough. The continuing southerly component of flow east
of the 700 mb trough produces a precip type transition zone across
southern MO to southern KY and northern TN.

The shifting of the trough from a positive to neutral tilt snow
produces the greatest potential for heavy snow across east central
MO to southern IL, left of the 850 mb circulation track. On the
north end, a tight QPF gradient in southeast NE, southern IA, and
central IL with the 00Z 3km NAM and ECMWF farther south than the
00Z GFS/UKMET. Day 2 WPC probabilities are low to mid for 8 inches
across much of MO.

The jet increases and becomes zonal through Day 3 with a stripe of
moderately high probabilities of 4 inches across the OH valley and
central Appalachians.


...Southwest...
...Day 3...

A deep trough pushes east across southern CA to AZ Saturday
through Saturday night. Pacific moisture spreads in with high
elevation snow over the southern Sierra, high terrain outside the
LA basin and the Mogollon Rim (snow elevation around 6000ft).

The probability of a quarter inch of freezing rain is less than 10
percent days 1-3.

Jackson