Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
442 PM EDT Sun Mar 26 2023
Valid 00Z Mon Mar 27 2023 - 00Z Thu Mar 30 2023
...Great Lakes and Northeast...
Days 1/2 and 3...
Vort lobe that caused a narrow stripe of heavy snow over Neb/IA
last night into today will redevelop this evening as it crosses
into the L.P. of MI until it is replaced by a following impulse
currently over the OK Panhandle crossing the Midwest late tonight
and over the Northeast Monday before shifting off the northern
Mid-Atlantic coast Monday evening. The availability of some
Gulf-sourced moisture with these impulses will allow some moderate
precip rates. Dynamic banding north of a weak surface low allows
some localized heavy snow tonight over the L.P. of MI with a risk
for moderate snow late tonight over the eastern Great Lakes
including in the Buffalo metro. The developing coastal low over
the Mid-Atlantic Monday allows broader precip development, though
the majority of precip is during the max diurnal which here in
late March usually greatly limits accumulation potential, though
areas at elevation in PA/NY with the Day 1.5 snow probs for 4"+ 20
to 30 percent over western NY as well as the Catskills and the
southern Adirondacks with further low probs in the Greens of
southern VT into the Berkshires of western Mass.
On Tuesday night, a shortwave trough rotating around a deep low
centered over western Hudson Bay swings from western Ontario and
crosses the northern Great Lakes on Wednesday. Continental air
with this wave looks to limit precip, though LES develops in NWly
flow raising low probabilities for 4"+ over the U.P. and
northwestern L.P. of MI. The upper trough begins to eject east
Monday evening with a consensus for snow to weaken as it crosses
KS into MO Monday night.
...Northern Rockies, Central High Plains...
An upper low over WY this afternoon opens into a trough tonight,
dipping into CO late tonight before slowly shifting onto the
central High Plains Monday. Upslope flow around the Bighorns and
Red Lodge continues tonight where there are moderately-high probs
for 4"+ additional snow. A lee side trough develops over the High
Plains of CO tonight with moderate to locally heavy snow
developing across northeastern CO where there are moderate probs
for 4"+ snowfall which extends over the borders into WY/Neb/KS.
...Oregon/California and Great Basin...
Potent upper low shifting south off the BC coast will remain
offshore, but a reinforcing trough Monday causes it to shift
toward the OR/CA coast Monday night before tracking south down the
CA coast through Wednesday night. Plume of moisture will surge
ahead of the low pressure and cold front into NorCal and southern
OR Monday night as precipitable water values rise to between +1 to
+2 sigma. Low snow levels around 2000ft will rise to 4000-5000ft
for the CA coastal ranges in the milder/humid air ahead of the
cold front with snow levels around 4000ft expected for the Sierra
Nevada. Heavy snow is expected for the higher terrain with
snowfall rates 1-2"/hr shifting southeast from the Klamath Monday
night through the Sierra Nevada Tuesday/Tuesday night as the
moisture plumes sinks southeastward. WPC probabilities for at
least 12 inches of snow are high on Day 2 over the Klamath/Shasta
Siskiyou and northern/central Sierra Nevada and then high over the
southern Sierra on Day 3. The initial wave of heavy precip crosses
SoCal Wednesday with snow levels there 5000-6000ft with Day 3 snow
probabilities for 6"+ limited to the highest terrain there.
The probability of significant icing Days 1-3 is less than 5%.