.DISCUSSION...
KEY MESSAGE 1...
The Winter Storm Warning continues. Significant snow
accumulations are still forecast, but sleet and freezing rain
chances have increased in the ridges, particularly in northern
West Virginia.
The large-scale pattern as advertised by the model suite has
not changed significantly with the upcoming winter storm. An
Arctic cold front currently dropping across the region with a
thin band of snow showers will have the main impact of
introducing a very cold air mass back to the region. Upstream,
shortwaves originating over the northern Plains and southern
Rockies will begin to phase as they approach the Mississippi
River Valley Sunday/Sunday night. Surface low pressure develops
along the Gulf Coast Saturday night and lifts northeastward on
Sunday, eventually handing off to a developing Atlantic Coast
low by Monday morning. Inverted troughing pokes northward into
the Middle and Upper Ohio Valley Saturday night and Sunday. On
the eastern side of this, southeast flow and a decent southerly
850mb jet will support warming aloft mainly to the south and
east of Pittsburgh on Sunday. With increased confidence in this,
greater coverage and amounts of freezing rain and sleet have
been introduced. This is particularly true in the higher
terrain of northern West Virginia, where one to two tenths of
ice accretion may occur, along with a period of sleet. This has
cut down the snow accumulations in this region.
Overall, moisture and lift remain impressive overall with this
system. We still expect a coupled upper jet structure, layered
frontogenesis, and the inverted trough to support strong lift.
Precipitable water is forecast to reach around the 90th
percentile level as compared to late January climatology as
well. So, overall liquid equivalent totals of 1 to 2 inches are
still a good bet. With the further northward extent of warm air
aloft, snow-to-liquid ratios have trended down slightly, which
was the main factor in lowering storm total snowfall amounts.
Nevertheless, a widespread significant snowfall is still
forecast across the region with high confidence.
Here are the latest 48-hour ensemble-based probabilities for
48-hour snow totals through 7 AM Monday. They are similar to
previous model runs overall, but probabilities for the higher-
end accumulations have decreased slightly:
15":10-50%
12":50-80%
8": 75-95%
6": 85-100%
4": 95-100%
Given the lower expected SLRs, there remains a decent chance of
a heavier, wetter snow, especially near and south of Pittsburgh.
Also, given low SLRs and increased chances for freezing rain,
the chance of power outage impacts is increasing in the higher
elevations, particularly in northern West Virginia. We will
need to continue to monitor precipitation-type trends and
adjust accordingly. However, there is high confidence in Winter
Storm Warning-level impacts in any case. The timing of the
heaviest snow still appears to be during Sunday morning south of
I-70, and late morning Sunday through Sunday evening north of
I-70. Cold northwesterly flow and the crossing parent upper
trough could result in lingering snow into Monday.
Continue to monitor the latest forecasts as this system
approaches, as widespread impacts to travel and daily life are
highly likely Sunday into Monday.