FXUS61 KLWX 220815
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
315 AM EST Fri Feb 22 2019
.SYNOPSIS...A front will stall across the Carolinas through
tonight as high pressure builds to the north toward New
England. Low pressure developing over the middle Mississippi
River Valley will strengthen as it moves northeastward across
the Great Lakes into Canada this weekend. High pressure will
build from the northern Great Plains toward the Great Lakes and
eventually into the northeast through the first half of next
week. Low pressure developing over the Tennessee Valley could
approach the region during the middle of next week.
.NEAR TERM /THROUGH TONIGHT/...
The dew point gradient is the best way to discern a subtle boundary
moving southward across the Mid-Atlantic early this morning. The
main surface front/temperature gradient is draped across central
North Carolina. Both of these boundaries will sink southward and
stall through the day today.
A weak wave of low pressure passing to our south will likely
continue to force a bit of light rain across central Virginia and
far southern Maryland until about mid morning, after which time
northerly winds should push rain to the south, limiting to the I-64
corridor through the rest of the day.
Lots of mid and high level clouds are expected today in overrunning
well north of the stalling surface boundary, and should keep highs
generally in the lower to middle 40s.
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Surface high pressure will be building to the north over upstate New
York and into New England tonight (~1035 mb). This is an ideal spot
to lock in some cold air near the surface, but the antecedent
airmass isn't abundantly cold. Temperatures are expected to fall to
around freezing for elevations above 1500 feet tonight, and across
northern Maryland, the eastern West Virginia panhandle and
Precipitation likely holds off until after daybreak Saturday, except
perhaps across west-central Virginia, which should allow
temperatures to rise some. Still, freezing rain seems likely at
least across the ridgetops along and west of the Blue Ridge and into
western Maryland, possibly the eastern West Virginia panhandle
Saturday morning through about midday. This is as precipitation
develops in strengthening overrunning ahead of a deepening surface
low over the Midwest.
Continued warm advection should push temperatures above freezing
Saturday afternoon, though some hi-res guidance like the 00Z NAM
Nest wants to hold onto freezing temperatures over the ridges until
Saturday evening. Lower elevations should see all rain (except
perhaps over northern Maryland near the Pennsylvania border).
The latest guidance has trended southward a bit with the heaviest
precipitation amounts Saturday night, likely in part due to high
pressure to the north nosing some drier low-level air into the
region. Strong warm air advection may overcome this some, but the
best upper jet forcing is displaced to our northwest closer to the
parent surface low (likely to track over Lake Michigan Saturday
night). This could help keep rainfall amounts near or a little under
one inch, but even that could result in minor flooding given
saturated ground and recent snowmelt, particularly over eastern West
Virginia this weekend.
There may be a few heavier showers along the approaching cold front
early Sunday morning. I could see the warm front never truly making
it fully through the area given the high to the north and the parent
low being so far west, but Sunday is still expected to be very mild
since appreciable cold air advection lags well behind the surface
front, and downsloping westerly flow/compressional warming should
push highs well into the 60s. Winds will likely be very gusty Sunday
with a strong pressure gradient behind the front, possibly reaching
or exceeding advisory criteria (greater than 45 MPH).
.LONG TERM /MONDAY THROUGH THURSDAY/...
The weather pattern will be largely dominated by a broad trough
aloft across eastern North America and strong Canadian high
pressure at the surface. As a result, temperatures will stay
cooler than normal and it will be much drier than it has been
lately. On Monday, a tight pressure gradient will still exist
over the region associated with a deep cyclone over Atlantic
Canada, but the winds will not be as strong like on Sunday, but
still windy nonetheless. Overall, fair weather is expected much
of next week but on the chilly side.
.AVIATION /07Z FRIDAY THROUGH TUESDAY/...
Mainly VFR today. MVFR INVOF CHO should lift around mid morning,
though spotty -RA may linger into this afternoon. CIGs expected to
lower to IFR by late Saturday as a warm front slowly approaches from
the south, with rain overspreading the area Saturday afternoon. Some
freezing rain is possible near MRB Saturday morning, if
precipitation moves in quickly enough while temperatures are still
near or below freezing. Winds will generally be N to NE AOB 10 kts.
VFR likely returns by Sunday afternoon with gusty W winds 35+
Still windy on Monday with gusts likely in the 25-35 kt range.
Winds diminish further on Tue but still breezy with gusts in
the 15-25 kt range.
A subtle uptick in northerly winds is possible early this morning
behind a weak moisture boundary pressing southward. An isolated 18
knot gust is possible during this time. Otherwise, generally light
north to northeast flow is expected through Saturday night.
Rain is expected to overspread the waters Saturday into Saturday
night as the aforementioned boundary returns north as a warm front.
Whether or not the warm front makes it through the waters before a
cold front approaches from the west by Sunday morning remains to be
seen, but there is moderately high confidence in gale force winds
later Sunday into Sunday night in westerly flow behind the
Marginal gales will still be possible on Mon. Otherwise, strong
SCA conditions Mon-Mon evening. SCA conditions possible again on
Tue and Wed.
Given recent snowmelt and saturated ground, three quarters of an
inch to around an inch of rain may be enough to result in minor
flooding issues this weekend, particularly over eastern West
Virginia. The overall trend has been for slightly less rain, but not
so much less to completely avoid a flood threat. Despite the
slightly lower QPF totals in the 00Z model suite, MMEFS still
indicates >50% chance of minor flood at several river forecast
points later this weekend.
VA...Winter Weather Advisory until 10 AM EST this morning for
WV...Winter Weather Advisory until 10 AM EST this morning for