Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
432 PM EDT Thu Apr 27 2023

Valid 00Z Fri Apr 28 2023 - 00Z Mon May 01 2023

...Southern Rockies...
Day 1...

A shortwave trough digging over the MT Rockies this afternoon will
continue shifting south, crossing NM Friday with the left exit
region of the associated trough over the Rockies through this
time. Heavy snow will remain confined to the higher elevations of
the Front Range and central to southern CO Rockies where Day 1
snow probs for >6" are moderately high. Lighter snows adding up to
a few inches are expected over the Palmer Divide and Raton Mesa
which should result in some localized impacts to those portions of
I-25 late tonight.


...Western Lake Superior...
Days 2/3...

A shortwave trough digging southeast out of Saskatchewan tonight
within large scale troughing across the eastern half of the CONUS
will amplify into a closed low near the northern MN/WI border
Saturday. While there remains some spread in the placement and
timing of this feature, the guidance is in good agreement that
this closed low will pivot slowly east to northern MI through
Sunday. The overlap of associated height falls with a modest, but
increasingly coupled, jet structure will result in surface low
development near/over northern Lake Michigan Saturday and as
features become vertically stacked later that day, this low should
stall/retrograde before being absorbed into an eastern U.S. low
Sunday night. Overall forcing appears modest for precipitation,
but spokes of vorticity rotating around the closed low combining
with waves of mid-level deformation will provide periods of
enhanced ascent. This should result in precipitation pivoting
around the low, and despite a marginal thermal structure, some
light to moderate snowfall is likely, especially W/NW of the
surface low at at elevation off the western shores of Lake
Superior. With northerly flow, there will be some lake enhanced
snowfall over northern WI/the U.P. of MI. Day 2 snow probs for >4"
are limited to the Arrowhead of MN with Day 3 featuring moderate
probs for >4" centered near Ironwood, MI and the Porcupine Mtns of
MI and the Whitecap Mtns of WI.

The probability of significant icing greater than 0.25" is less
than 10 percent.


Jackson