Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
452 AM EST Thu Feb 24 2022

Valid 12Z Thu Feb 24 2022 - 12Z Sun Feb 27 2022

...Southern Plains through the Mid-Mississippi Valley and Great
Lakes...
Day 1...

Strong upper trough over the southern Rockies this morning will
turn northeastward over the Plains this afternoon/evening and lift
into Lower Michigan by 12Z Fri. Concurrently, subtropical jet will
increase to ~170kts promoting broad scale lift from the Lower MS
Valley northeastward to the tail of another jet streak over New
England. Surface low pressure will organize in response to the
strong dynamics and ride along the frontal boundary with
precipitation overrunning cold low levels yielding a wintry mix
from sleet and freezing rain to snow north of the front. Moisture
will be more than sufficient with SW flow off the western Gulf and
PW values near 1 inch in the warmer air mass decreasing toward
0.50 inch in the mixed precip zone. Precipitation should intensify
this afternoon as ingredients come together over the region.
Farther north, height falls from the approaching shortwave into
the Corn Belt will support light to modest snow eastward into
Lower Michigan as the low pressure-induced precip shield moves
northeastward early Fri morning. Broad southwest flow will keep
the system progressive once it forms in a final wave of
precipitation through the central states.

WPC probabilities for at least 4 inches of snow were focused west
of Lake Michigan and over Lower Michigan with some lake
enhancement and added lift on the NW side of low pressure,
respectively. To the south, WPC probabilities of at least 0.10
inch freezing rain are moderate to high centered over northern
Arkansas into southern Missouri.


...Ohio Valley, Mid-Atlantic, and New England...
Days 1-2...

Surface low will continue to deepen and move along the Ohio River
Day 1 into Day 2 with surface high pressure squeezed/pinched to
the north over Quebec. Strong mid-level frontogenesis suggests a
burgeoning area of moderate to heavy snow along the PA/NY border
at precip onset as a new area of low pressure develops east of
Delaware Bay along the oceanic boundary, eventually becoming the
dominant center as the primary low pressure weakens over central
NY Fri morning. The surge in southerly flow aloft will bring a
mixed precip zone from southwest to northeast but disrupted by
local topography, creating a headache for p-type
transition/amounts as the models keep wavering on how far north to
bring in milder air (and to what depth). NAM would typically
handle narrow warm noses better than the GFS but it has wavered on
how far north in recent runs, but have taken a probabilistic
approach toward a slightly milder solution within the confines of
the National Blend of Models p-type guidance.

To the north, in the all snow zone, strong FGEN will support a
period of at least 1"/hr rates (supported by the CAM guidance
snowband tool) over northern NY across central New England.
Profiles suggest strong lift at times into the DGZ (perhaps not a
large depth but quite sufficient) with higher SLRs ~20:1 closer to
the Canadian border. There, snowfall should maximize just north of
the QPF maximum where some mixing will be possible up toward the
CT/MA border. Column will cool as the coastal low deepens and
winds back to northerly as the precip starts to exit Friday
afternoon/evening. WPC probabilities of at least eight inches of
snow are moderate to high over much of eastern NY north of I-84
eastward into central New England and along I-90.

To the south, there could be a zone of sleet before a transition
to freezing rain from central Ohio eastward into PA then a more
expansive southward extension east of the Appalachians into
northern MD northeastward into the Poconos. Colder air in
sheltered areas will support a longer duration of freezing rain in
excess of a tenth of an inch to over a quarter of an inch. WPC
probabilities for at least a quarter inch of ice are high (>50%)
across the Laurel Highlands and Allegheny Mountains of SW PA and
far W MD (a well-known prolonged icing area in cold air damming).
Low probabilities of a quarter inch of freezing rain extend
eastward along the PA Turnpike as well as far northern MD.


...Pacific Northwest...
Day 3...
Shortwave in the Pacific will move northeastward into WA/OR late
Sat into early Sun, driving a cold front into western WA with a
plume of moisture (+1 to +1.5 sigma) on southerly flow. Snow
levels will rise in advance of the front but linger around
2000-3000ft along the Cascades with several inches likely at pass
levels around that altitude.


Fracasso



Key Messages:

 - A significant winter storm will bring a variety of winter
hazards from the Southern Plains through the Ohio Valley today and
into the Northeast through Friday.

 - Significant total ice accumulations greater than 0.25†are
likely across the Ozarks and southeast Missouri. Locally, damaging
ice of 0.50†or more is possible which could lead to scattered
power outages, tree damage, and dangerous travel.

 - Another area of freezing rain is likely from the eastern Ohio
Valley through the Mid-Atlantic states. Significant ice
accumulations are possible across south-central Pennsylvania and
western Maryland, with hazardous travel possible.

 - Heavy snow is expected across Upstate New York and New England
on Friday with six inches or more likely. Snowfall rates may
eclipse 1â€/hr at times. Travel will be difficult.