Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
418 AM EST Mon Jan 30 2023

Valid 12Z Mon Jan 30 2023 - 12Z Thu Feb 02 2023

...Significant and Long-Duration Ice Storm For Portions of Texas
and Oklahoma through the Mid-South...

...West-Central Texas through the Mid-South...
Days 1-3...

Low pressure stalling/slowly drifting from the Southern CA coast
to the northern Baja peninsula today through Tuesday will direct
tropical Pacific moisture across Mexico which will combine with
increasing moisture from the western Gulf as broad ridging over
the Southeast amplifies a bit. Arctic-sourced cold air currently
spilling down the southern Plains across Texas and the Mid-South
will maintain a large area of Texas below freezing through Tuesday
night as a 1040mb surface high pressure lingers over the central
Plains before shifting east Wednesday. Overrunning precip with a
very strong warm nose will begin today from a weak impulse with
areas of light freezing over much of central/east-central/North
Texas and mostly sleet showers over Oklahoma into Arkansas,
expanding east across Mid-South tonight. Broad overrunning flow
tonight looks to produce freezing drizzle of much of central/North
Texas tonight. Day 1 ice probabilities are moderate for a tenth
inch of north Texas, southeast Oklahoma, the northern half of
Arkansas, western Tennessee through the Bootheel of Missouri and
southwest Kentucky.

Increasing moisture advection will reinvigorate waves of locally
moderate precip over Texas, southeast Oklahoma, and the Mid-South
Tuesday and even heavier on Wednesday. The question of how trapped
the air will be by Wednesday is a large question mark as surface
flow should become southerly in return flow as the surface high
center shifts east to the Midwest - a particularly difficult
question given the increased precip rates/freezing rain potential
for areas that retain subfreezing air. The northwest portion of
the precip shield looks to be over deep enough cold air to allow
sleet over west-central Texas into central Oklahoma. The Canadian
Regional and NAM models have consistent been colder over a larger
area while the GFS and EC continue to struggle to push cold air
farther through central and especially east-central Texas. Thermal
preference has been given to the CMCreg and NAM, though it is
noted that the NAM remains much drier than other guidance.
However, given the depth and strength of converging moisture,
significant precip is expected. High Day 2 probabilities for a
tenth inch ice are across west-central, central, North, and
east-central Texas (where there are moderate probabilities for a
quarter inch), with moderate probabilities over southeast
Oklahoma, central Arkansas, and the western half of Tennessee into
northwest Mississippi. Day 3 ice probabilities are similar in
intensity to Day 2, just shifted just a bit north and west.


...Southwest to the Colorado Rockies...
Day 1...

A closed mid-level low over the central CA coast stalls off the
southern CA coast today, driving height anomalies to -2 standard
deviations below the climo mean at 500mb and 700mb according to
NAEFS ensemble tables. The peak amplitude of this low is expected
to occur today, before it slowly fills as it drifts to the
northern Baja Peninsula through Tuesday. Moisture advects inland
today south of the positively-tilted trough of which the low is at
the end of, bring mountain snow (snow levels around 3500ft) to
SoCal ranges, northern AZ/southern UT and most CO ranges west of
the divide where Day 1 snow probabilities of 6"+ are moderate
(high in the higher CO Rockies). The moisture plume shifts well
south into Mexico tonight, cutting off appreciable snow Tuesday
morning as snow levels continue to drop over southwest AZ.


...Northern Great Lakes..
Days 1-2...

Periods of moderate to heavy lake effect snow (LES) are likely,
especially in the westerly flow snow belt areas off Lakes
Superior, Huron, and Ontario as shortwave energy rounding a deep
gyre over northern Hudson Bay through Tuesday night. Steep lapse
rates are expected in the particularly cold (near or lower than
the DGZ) air over lake temperatures well above average and nearing
record highs for early February according to GLERL. Efficient snow
rates are therefore possible with both Days 1 and 2 WPC
probabilities for 4"+ moderate across the Keweenaw Peninsula and
near Whitefish Point in the U.P. and the southern Tug Hill off
Lake Ontario.


Jackson