Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
419 PM EDT Tue Mar 12 2024

Valid 00Z Wed Mar 13 2024 - 00Z Sat Mar 16 2024


...Northwest...
Day 1...

Shortwave trough energy currently moving through the Intermountain
West will amplify as it reaches the Great Basin later tonight into
Wednesday before closing off Wednesday night. A final push of
forcing for ascent will be driven primarily via height falls and
PVA associated with this shortwave, but a modest 90kt Pacific jet
streak is also likely to orient WNW to ESE, driving favorable LFQ
difluence into the area as well. This synoptic flow along with
upslope flow will produce heavy snowfall as moisture surges ahead
of the best ascent. As a result, additional snowfall for the Day 1
period (00Z Wed-00Z Thur) will be locally heavy for the higher
elevations of the OR/WA Cascades as well as eastward including
portions of the Northern Rockies, in the NW WY ranges, and south
to the Ruby Mountains and along the Wasatch of UT.

...Central Rockies, Southern Rockies, & Central High Plains...
Days 1-3...

***Significant and long lasting winter storm to produce heavy
 snow across much of the terrain of the Central and Southern
 Rockies, with impactful snowfall likely into the lower elevations
 of the High Plains as well.***

An amplifying and digging shortwave trough will elongate as it
approaches the Intermountain West and Rockies Wednesday and
Wednesday night in response to a rapidly strengthening eastern
Pacific ridge axis where height anomalies approach +4 sigma by the
end of the week. The shortwave energy is then expected to close
off and settle southward into the Four Corners region by Thursday
morning. In response, an area of low pressure will develop in the
lee of the Rockies and a classic northeasterly upslope event will
begin to take shape Wednesday night through Friday. Impressive
dynamics, characterized by the height falls, strengthening low
pressure, and left exit lift from a 90-115 kt jet streak
positioned across NM through MO will all come together to produce
a longer duration precipitation event.

Precipitation is expected to begin more steadily during Day 1, but
it's Day 2 where the greatest potential for significant upslope
precipitation exists along the CO Front Range Mountains and into
the lower elevations including the I-25 urban corridor. While
there remains some uncertainty in the placement (north/south) of
the greatest QPF and also the available moisture, the latest WPC
snow probabilities are above 50 percent for at least 1 foot for
much of the WY and CO mountain areas, and locally exceed 70% for 1
foot for the Big Horns south into the Laramies, across the CO
Front Range Mountains and south into the Palmer Divide through the
Sangre de Cristos. Localized higher amounts in excess of 2 feet
will be possible, particularly for the Front Range Mountains. In
the lower elevations including the I-25 corridor, confidence is
increasing in a significant snowfall event and probabilities for
at least 8 inches are high (>70%) with a slight (20-30%) chance of
totals exceeding 12 inches.

As the first phase of the storm winds down, a second phase begins
to develop over the Four Corners region and southern CO Rockies
as the closed low settles southwestward over Arizona by Friday.
This will push a favorable fetch of moisture and lift over the
Four Corners northeast into the southern CO Rockies with waves of
precipitation likely. Snow levels will initially be high, but a
backdoor cold front pushing through NM will lead to a favorable
northeasterly flow event for significant snowfall where WPC snow
probabilities for 6 inches during Day 3 are high (>70%) across
along/north of the Mogollon Rim, the White Mountains of AZ,
southern Wasatch and into the San Juans and localized totals in
excess of a foot are possible (30-50% probability).

The probability of receiving at least 0.1" ice is less than 10%
across the CONUS through Day 3.


Weiss/Taylor

**Key Messages for March 13-16 Winter Storm have been started and
 can be found on our website at https://www.wpc.ncep.noaa.gov**