New CTP disco. I’ve never heard if the “classic Colorado low” hah
SHORT TERM /7 PM THIS EVENING THROUGH MONDAY NIGHT/...
A classic Colorado low storm type will bring a swath of
moderate to heavy snow across the Middle Atlantic late this
evening into the day on Monday. Snow arrives late this evening
across the southwest and overspreads east and north early Monday
into Monday afternoon. Snow ends from west to east by Tuesday
evening, so it will be a quick-hitting (less than 24 hour)
storm. Travel impacts are likely for the Monday morning and
Monday evening commutes, with the most significant impacts
favored along and south of the PA Turnpike.
Still quite a bit of uncertainty with 18 hours or less until
first flakes. The ECMWF and Regional Canadian models are on the
lower end of the snowfall total spectrum. Part of the reason
for this might be that they both develop a stronger midlevel low
pressure system over northern New England late Monday from a
shortwave trough originating east of Hudson Bay at 00z Sunday.
This could act as a kicker to bring in drier air more quickly
and shorten the window for moisture advection early Monday
before the Mid Atl coastal system gets nudged offshore. This
shortwave trough is outside the domain of the hires models (HRRR
and 3km NAM) and will remain so until the 00z Monday runs.
Given that the HRRR and 3km NAM together make up about 1/3 of
the NBM weighting in this time period, IF this Hudson Bay
feature is indeed responsible for the lower snow totals in the
ECMWF and Canadian models, it`s certainly possible that we see a
shift south in snowfall totals over the next 24 hours. That
said, the HRRR does represent the worst case scenario, with
warning criteria (6+ inches) across much of central PA from I-80
southward, which can not completely be ruled out at this point.
Regardless, the isentropic ascent and favorable upper jet
dynamics do look to be over central PA between midnight Sunday
night and at least early morning on Monday. The main period of
snow will start over the Laurels right around midnight Sun
night, and spread NE through sunrise, struggling to get too far
past I-80 as it encounters drier low-mid levels. By the
afternoon, the precip may be tapering off over the I-80
counties, and by sunset, many models have little or nothing
falling over the bulk of the CWA. The places that we continue
higher PoPs Mon night are the far NW where lake effect-
favorable flow returns and in the SW where the snow may not end
for another 2 days thanks to another shortwave trough coming
down Tue night - Wed.
No worries for p-type (all snow) even though the precip will be
falling during the daylight hours on Mon. Profiles show no warm
nose whatsoever, even along the MD border. SLRs will generally
range from 11:1 to 14:1. 1"+ per hour snowfall rates are
possible in the Laurel Highlands and extreme southern PA on
Monday morning. The most likely snow totals at this time range
from a coating to 2 inches along the I-80 corridor, little if
anything to the north, about 3-6 inches in the Lower Susq, and
4-8 inches in the Laurels.
Have issued Winter Storm Warnings for the southern stripe of
counties over to Adams and Winter Weather Advisories for the
rest of the Lower Susquehanna Valley along with Huntingdon,
Blair, and Cambria County. The 4" snowfall contour currently
runs along 22 in Cambria County and then extends east southeast
through southern Cumberland County, York city and just south of
Lancaster. We`ll be monitoring for shifts in the track of this
storm along with any suppression from the aforementioned
midlevel low over New England. Think we are in pretty good shape
if the suppressed solution verifies, but a northern shift would
likely require upgrades and/or expansion of products farther
north.
