Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
341 PM EST Friday Dec 6 2013
a wave of low pressure will continue move across the region into
the overnight hours...moving off the coast by early Saturday.
High pressure will briefly build overhead Saturday...though
another low pressure system will quickly develop and approach from
the southwest Saturday night into early Sunday. This system will
impact the area with wintry precipitation for the early part of
next week. An upper-level disturbance will pass through the area
Tuesday and Canadian high pressure will build overhead during the
middle of next week.
Near term /through Saturday/...
headline update...Winter Storm Watch expanded to include the
remainder of the County Warning Area - minus St. Marys & Calvert Colorado. The initial
segment for the areas west of the Blue Ridge has a slight timing
difference...beginning a few hours earlier and ending a few hours
later than the new eastern segment. See wbcwswlwx for further details.
This watch encompasses the expected complex wintry event for much
of Sunday into Monday morning/early afternoon. This is a separate low
pressure system than the one currently affecting the area...though
it is expected to develop on the heels of the widespread precipitation
region that currently stretches from the Southern Plains to New
England. ... be discussed further in the short term portion...
This evening and tonight...
separate waves of low pressure have been making their way across
the region since late last night. The last couple have brought
some localized batches of light to moderate rain across portions
of the area. The southern periphery of the latest one had enough
elevated instability to push a few weak batches of convection over
southern Maryland and the lower northern Virginia Piedmont. The dynamics for this
activity have moved well of the area. Over the next few hours...the
current light rain will dissipate from south-to-north west/ a few hour
period of a relative lull for at least the southern half of the County Warning Area west/
scattered rain continuing for the Potomac Highlands/northern shen valley.
Heading into the late night hours...yet another and likely last
upper wave will push through - taking the remainder of the precipitation
directly across the County Warning Area and head toward the coast by the predawn
hours. A bulk of this activity will occur toward midnight and the
few hours following...then a gradual dissipation from west-to-east.
Some of the colder air working in on the backside of the exiting
precipitation will bring some brief wintry precipitation - mainly snow to the
higher terrain of the Potomac Highlands.
a brief break in the action as one system leaves and another gears
up to our southwest. Toward daybreak Sat morning...an upper shortwave
that is currently sliding over the middle MS valley will swing by to our
north and push the rest of the precipitation off the middle Atlantic coast.
Precipitation will be ending gradually from west to east but fairly
quickly during the Post-dawn hours. Clouds will be a couple of hours
behind in terms of clearing out but the process of drying out and
cooling down the area will be well underway.
During this time...a potent high over the northern plains/upper
Midwest - the same one in control of the widespread frigid temperatures
over a large part of the country will begin to push its eastern
periphery over the central Appalachians and filter down into the middle Atlantic.
Breezy northwesterly winds will be helping to mix out the moist and
relatively warm conditions from today...bringing in dewpoints
10-20 degree lower than today and setting the stage for the next wave
of precipitation and wintry conditions. Highs across the I-95 corridor
will peak near the 40 degree mark...barely above freezing for the
mountains and generally M-u30s for the remainder of the County Warning Area.
Short term /Saturday night through Monday/...
Arctic high pressure will filter into the area Saturday night. Min
temperatures is the middle 20s are expected Sunday morning with warmer temperatures
near 30 degrees near the Bay and Potomac River. Further
south...cyclogenesis will form along the front that moved through
our region today as an upper level trough moves eastward from The
Rockies. Shortwave energy will move across the region in the
midlevels and a warm 40-60kt jet will start to nose into the central
foothills...northern Virginia and northern Piedmont Sunday morning. Before the warm
nose reaches the middle Atlantic precipitation will begin as all snow.
This snow will accumulate as surface temperatures will be below freezing. As
the warm nose moves northward snow will start to mix with sleet.
Shortwaves will move over the region and enhance precipitation at
times. The axis of the ridge across our area will be strong and GFS
and European model (ecmwf) both Show Low pressure splitting around the surface ridge. Low
pressure moving to our east will enhance the northerly flow into the
region and enhance the cold air.
Warm air aloft will increase in size and a switch over to freezing
rain is expected. The confidence of all freezing rain GOES from high
to medium confidence moving from west to east across the lookout area.
Temperatures will be subfreezing due to the filtering of the
northerly flow around low pressure to our east and the high to our
north. The lower confidence is mainly along and east of I-95 due to
warmer marine air mixing in to the area. Warm moist air aloft will
continue to move into the region from the S-SW Sunday afternoon and
evening and freezing rain is expected to continue. A Winter Storm Watch is in
effect Sunday morning through Monday morning... please check
wswlwx for more details. Areas west of the Blue Ridge including
I-81 and valley locations are expected to see significant ice
accretion of a quarter inch or more Sunday and Sunday night. This
will produce hazardous travel conditions...tree damage and power
Synoptic features move northward including low pressure to our west
and east and the high pressure wedged across our region as the
trough over The Rockies moves eastward. The warm nose will descend to
the surface Sunday night and eventually take over the surface late Monday
morning. Temperatures below freezing will lift northward and exit west
central Maryland by late Monday morning. Total liquid forecast amount of
around an inch are expected for the event.
Rain will move out of the region Monday night and even linger into
Tuesday as a cold front moves through and helps scour out moisture.
Cold air will move in and rain may switch to snow but no
accumulation is expected at this time.
Long term /Monday night through Friday/...
a brisk week is ahead as high pressure moves into the region and
Canadian air continues to filter into the region. Below normal
temperatures are expected. A shortwave trough will pass over the middle
Atlantic Thursday and may squeeze out some snow showers. No hazards
expected through the long term.
Aviation /20z Friday through Wednesday/...
much of the area has seen conditions wavering in-and-out of solid
MVFR to periodic IFR. This will continue over the next several
hours...as a lull period in the precipitation is coming but a final wave of
precipitation will move through overnight. As the precipitation dissipates...a few
hours of sub-IFR ceilings should occur across much of the area around
the predawn hours Sat. The conditions will quickly improve after
sunrise...W/ drier air sliding in from the north and mixing out
these lower ceilings. Breezy northwest winds will take over on Sat
afternoon...clearing skies out for at least the daytime hours.
Snow and sleet are expected across the terminals Sunday morning
before changing to freezing rain Sunday afternoon. Freezing rain will continue through
Sunday night for cho-mrb-iad-dca. Lower confidence in constant freezing rain
for BWI-mrb due to temperature moderating. MVFR/IFR conditions are possible
during this time. High pressure moves into the region Tuesday and
continues through the middle of the week.
winds have largely dropped off to a 10kt breeze or less over the
waters this afternoon. This will continue into the late night hours
before the next and final cold front for the current low pressure
system moves through. Several lesser boundaries have moved across
the waters in the past day...reinforcing the higher winds from
earlier. But now conditions have slackened. Expecting the next
wave of gusty winds late tonight...as the cold front moves through
and behind it will be several hours of solid Small Craft Advisory conditions during
the daytime hours Sat.
Snow and sleet are expected Sunday morning before changing over a
mix of freezing rain-sleet-rain Sunday afternoon. Ice accumulation is
possible mainly near the land as water temperatures are still in the middle
40s. Northerly winds will be 5 to 10 kts through this time. High
pressure moves over the waters next week. Small Craft Advisory conditions possible
middle week with north-northwest flow over the waters.
District of Columbia...Winter Storm Watch from Sunday morning through Monday morning
Maryland...Winter Storm Watch from Sunday morning through Monday morning
Winter Storm Watch from Sunday morning through Monday morning
Virginia...Winter Storm Watch from Sunday morning through Monday morning
Winter Storm Watch from Sunday morning through Monday morning
WV...Winter Storm Watch from Sunday morning through Monday morning
Marine...Small Craft Advisory from midnight tonight to 6 PM EST
Saturday for anz530>543.