Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
224 PM EDT Thu Apr 10 2025

Valid 00Z Fri Apr 11 2025 - 00Z Mon Apr 14 2025


...Northern Mid-Atlantic to New England...
Days 1-2...

Two rounds of mostly elevation-dependent spring snow are forecast
to impact areas from northeast PA and far northern NJ through
Upstate NY and into New England through Saturday. The first wave of
precipitation is already moving into the Northeast this afternoon
ahead of a weak surface wave and leading upper shortwave trough.
Current surface 0 degree C wet-bulb temp is confined to the
Adirondacks and northern New England, which depicts the marginal
boundary layer thermals. These marginal temperatures will remain,
although dynamically cooling beneath heavier precipitation and
850mb temps ranging from +1C to -2C, through the weekend and lead
to a typical distribution of accumulating mid- April snowfall.
Amounts through Friday morning are expected to add up to around 1-4
inches across the Catskills, Adirondacks, and southern New England
Mts, with a dusting or conversational flakes possible down to the
I-95 corridor of CT/RI/MA.

The next round of precipitation is expected to enter the region
Friday night into Saturday as the large scale eastern U.S. trough
consolidates into a closed low and strengthens over the Mid-
Atlantic and gradually slides east. More uncertainty with the
details of this system remain, but have consolidated on the
southernmost cluster of solutions from prior forecasts. This leads
to potentially moderate snow reaching as far south as the Poconos,
northern NJ, and the Litchfield Hills of western CT as 850mb temps
drop below 0C near and just northwest of strengthening 700mb FGEN.
However, temperatures will still be marginal, and any axis of
notable accumulating snowfall will probably be rather narrow on the
northern periphery of the precipitation axis. Additionally,
approachable QPF amounts might not reach as far north and
therefore lowering the potential for heavy snow from the
Adirondacks through the northern Greens and Whites. Snowfall
amounts on Day 2 (00z Sat to 00z Sun) are generally expected once
again to range between 1-4 inches, with low chances (<10%) for >4
inches outside of the tallest peaks of the Catskills.


...Cascades to Northern Rockies...
Day 1-3..

Periods of light to moderate snow area expected over the Cascades
tonight through Saturday, with snow levels lowering over time.
Some accumulating snowfall is likely as low as around 2,000 feet,
with total snowfall over 4-6" expected in the more favored terrain
areas.

After a quick-moving cold front moves across the northern Cascades
tonight with a brief burst of snowfall above 3,000-4,000ft, a
strong mid level shortwave moving across the Northwest will spread
the snow threat into the Northern Rockies by Saturday. Southerly
flow ahead of this shortwave will result in a warm system
initially, with most snow falling above 6,000 feet. However behind
the shortwave temperatures will rapidly drop, resulting in lowering
snow levels and bringing the threat of some accumulating snowfall
to more of central MT. More uncertainty with this lower elevation
snowfall as model differences in the low track and strength will
impact the amount of precipitation on the cold side of the system,
with most trends leaning towards lower QPF amounts. So the greater
confidence for accumulating snowfall remains over the higher
terrain over 6,000 feet, with probabilities of exceeding 6" through
00z Sun as high as 40-60% over the Little Belt Mountains, northern
Absarokas, as well as the Lewis and Swan Ranges of northwest MT.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Snell