Area Forecast Discussion
Issued by NWS Sterling, VA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KLWX 100901
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
401 AM EST Sat Dec 10 2016
High pressure over the center of the continent builds east today
before moving off the Mid-Atlantic coast Sunday morning. A warm
front develops over the area and lifts north Sunday before a cold
front crosses Monday. A reinforcing cold front crosses Wednesday
before cold high pressure builds back into the area.
.NEAR TERM /THROUGH TONIGHT/...
Northwest flow continues across the Mid-Atlantic as high pressure
approaches the region from the west. Light snow showers are
tapering off across the Allegheny Front and no additional
accumulation is expected this morning. High pressure will move
overhead late today and tonight. Max temps will range from the 20s
at higher elevations to the 30s elsewhere. Clear and calm
conditions will result in another cool night with temperatures
dropping into the teens/20s tonight.
Mid-high level clouds will increase from the west late tonight as
low pressure moves into the Central Plains. Warm air advection
will begin across the Ohio Valley and light snow showers are
possible across the northern Allegheny Front and Potomac Highlands
late tonight. Little to no accumulation is expected through Sunday
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Moisture advection will spread across the Mid-Atlantic region
Sunday. Snow showers are expected to spread eastward but hug the
MD/PA border as the area of best mid-level convergence shifts
northward into PA. High pressure will be off the Mid-Atlantic
coast by Sunday afternoon and southerly flow will increase across
the region. Temperatures will still be on the cool side due to
cloud cover across much of the region especially across the north.
An area of lower pressure will move northward along the SE U.S.
coast Sunday afternoon associated with Atlantic moisture. Rain
showers are possible across the Tidewater region and Southern MD
into Sunday night and amts will be light.
Low pressure will move into the Great Lakes region Sunday night
and warm air advection aloft will continue... 850mb temperatures
will cross 0 deg and keep rising into Monday morning. Sfc
temperatures are expected to drop into the low to mid 30s across
the region with warmer temperatures along and east of I-95. This
will make for multiple p-types across the region Sunday night into
Monday morning. Guidance shows sfc temperatures rising overnight
into Mon morning and after analysis of boundary layer winds it may
actually occur as SW winds will be 10-20kts. This can be a flaw in
model guidance as they can overestimate sfc warm air advection. A
wintry mix is expected across the region as precipitation moves
into the west Sunday night. Snow will likely change to sleet and
then freezing rain for places below freezing. As precipitation
moves eastward by Monday morning...SN/IP will change to rain.
Temperatures will climb into the 50s Monday and rain is definitely
expected. Overall...a brief period of ice accumulation is possible
mainly across the Alleghany Front and Potomac Highlands Sunday
night into Monday. Confidence is low at this time to issue any
Decent gulf moisture associated with the advancing cold front
Monday will result in 0.25-0.5 of rainfall through Monday.
Clearing will occur by Monday night with snow showers ending along
the Allegheny Front. High pressure will move overhead Monday
.LONG TERM /TUESDAY THROUGH FRIDAY/...
Guidance is in somewhat better agreement through the long term
period of the forecast than it was last night. We start out on
Tuesday with a weak area of high pressure over the region which
looks to keep the weather dry with near normal temperatures. It
looks like Tuesday night stays mostly dry ahead of an approaching
cold front. On Wednesday however, latest guidance is notably in
better agreement regarding an approaching shortwave and vort max
helping to initiate cyclogenesis along the front as it crosses the
area, which could lead to a period of mixed precipitation or snow.
Still a long way out but we continue to watch this potential
closely. By Thursday, this system is long gone and we end up with
arctic high pressure and temps struggling to reach the freezing
point even in the warm spots. The arctic high settles right
overhead on Friday with continued very cold conditions.
.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions expected through tonight. -SN may move into MRB
late tonight into Sun morning and may result in vsby restrictions
however confidence is low. -SN will move out of MRB by Sunday
afternoon and VFR conditions expected Sunday at all terminals.
Sub-vfr conditions expected Sunday night into Monday as moisture
advection occurs. -SN/IP/FZRA is possible at MRB during this time.
-SN/IP possible at other terminals however activity should become
-RA early Monday. RA expected at all terminals Monday. VFR
conditions expected Monday night-Tuesday. Sub VFR conditions
possible Wednesday as a storm may try to bring rain or snow to the
region again just ahead of the next arctic surge.
Northwest winds continue on the waters this morning and SCA will
continue across most zones with the exception of the upper Tidal
Potomac. Enough pressure gradient remains across northern portions
of the Bay to warrant another SCA today. Lighter winds expected
with high pressure Saturday night into early Sunday. Increasing
southerly flow ahead of the next storm system looks to warrant
another SCA by Sunday evening.
SCA level winds expected Monday...dropping off Tuesday before
possibly redeveloping Wednesday.
MARINE...Small Craft Advisory until 6 PM EST this evening for
Small Craft Advisory until 9 AM EST this morning for ANZ533-