Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 080900
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
400 AM EST Thu Dec 8 2016

.SYNOPSIS...
Cold front moves through the Mid-Atlantic through the day today.
High pressure returns to the area Friday into the weekend. Another
cold front crosses the area Monday followed by another reinforcing
cold front Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Tricky forecast through early morning...Nearly all guidance failed
to capture radiational cooling overnight...which allowed many
locations to drop below freezing. Having said that, cloud cover has
finally arrived and sites are beginning to slowly warm (e.g., IAD
went from 29F-33F over last hour). Main question then becomes
will...and more importantly where...will any precipitation be
through mid-morning as potent jet max approaches the area. High-res
guidance continues to show low-end possibility of light
precipitation developing a few hours on either side of daybreak.
With low wet-bulb zero heights and only a very shallow low level
inversion, expectation is that anything that falls would either be
snow/rain/drizzle. Question then becomes...what will surface
temperatures be where it precipitates. While very low
probability...there is a non-zero possibility of some isolated light
glaze on area roads (outside of immediate DC/Balt metros) coinciding
with rush hour where air/road temperatures are below freezing. Will
be watching this very closely to see how things evolve over the next
few hours. Overall, best chance of precipitation will be across S MD
after sunrise...where plain rain showers are most likely.

Any precipitation moves east by midday...with some gusty winds up to
25 mph developing by afternoon. Highs today peak in the
M/U40s...before tumbling tonight behind cold front. Westerly flow
will promote the development of upslope snow showers beginning
overnight.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
On Friday...Mid-Atlantic will be sandwiched between Canadian high
pressure building into the area from the central CONUS and trough of
low pressure departing the NE CONUS...with a strong cold air
advection pattern. Thus, expect a blustery and cold day...with wind
gusts up to 25-30 mph and highs AOB 40F. Additionally, wind chills
expected to be AOB freezing all day.

Strong low-level upslope component through a moist layer will allow
snow showers to continue Friday into Saturday morning. While low-end
advisory level snowfall remains possible...current forecast keeps
storm total amounts between 2-3 inches for the entire event (roughly
24 hours).

High pressure continues to build overhead Friday night through
Saturday night...with cold weather continuing. Lows Saturday and
Sunday morning AOB 30F. Highs Saturday similar to Friday...with most
places AOB 40F...though winds expected to be lighter as high
pressure is overhead by afternoon.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
The long term is a bit active, continuing the recent trend started
at the end of November. Starting on Sunday, we have a fast zonal
flow aloft. We`ll have a stationary front in the area with perhaps
a little overruning precipitation, most likely north of the CWA.
Any precipitation that makes it into the CWA may be wintry, at
least partly, given a cold atmosphere, but a lot of uncertainty on
this. Highs will be chilly, 30s north and 40s further south.

The fast zonal flow aloft buckles just slightly as a shortwave
moves across the region later on Monday. At the surface, a wave of
low pressure will ride across the area, but it looks like it will
cross to our north. While the odds of wintry precipitation will
still exist Sunday night, by Monday it appears the low pushes a
warm front north of the area and most of our CWA will likely end
up rain. Highs will rise into the 40s to lower 50s. After a short
break Monday night into Tuesday, another disturbance is progged to
move late Tuesday and Wednesday next week. By this time however,
guidance gets into some significant disagreement, with varying
strength of the next trough. GFS has a signficant storm, though we
stay on the warm side until it passes, while EC is much weaker
with little precip. Either way, we end up cold late next week, but
temps middle of next week are highly uncertain.

&&

.AVIATION /09Z THURSDAY THROUGH MONDAY/...
VFR conditions tonight with light flow. A cold front crosses the
area from the west today with MVFR cigs and rain/snow chances mainly
SE of DC metros/southern MD. Gusty NW winds expected this afternoon
through Friday...along with the possibility of some low level
turbulence.

VFR conditions prevail Saturday through Saturday night...with
relatively light winds as high pressure builds over the area. Sub
VFR possible Sunday night and Monday with another storm system
moving through.

&&

.MARINE...
Light and variable flow through sunrise under high pressure. A cold
front moves through the waters later this morning with west-
northwest winds increasing to gusts up to 30 kt through the
afternoon. Bumped up current SCA headline a little bit temporally
based on BUFKIT soundings and HRRR wind gust output. Thus, SCA now
begins at 10 AM for most waters...and 2 PM for southern MD waters.
SCA then continues for all waters through Friday and will likely
need to be extended for at least a few hours Friday night into
Saturday morning. While a few isolated gale force wind gusts are
possible late tonight into Friday...most areas should just have
solid SCA conditions. Winds begin to diminish Saturday morning as
high pressure builds into the area.

Relatively light winds Saturday and Saturday night as high pressure
resides over the area. Winds may increase Sunday and Monday as
another system approaches.

&&

.TIDES/COASTAL FLOODING...
Anomalies have increased markedly in the last 12 hours. Flow over
the waters was light during this time and we are not near a full
or new moon, so best guess is that this may be related to the
lowering pressure combined with slosh back. Really, not sure, but
bottom line is that we currently expect some very minor flooding
at high tide in St. Mary`s county this morning before stronger NW
winds start to lower anomalies this afternoon. Elsewhere, think we
reach action stage in some spots but should stay below minor, and
anomalies as mentioned should drop thereafter. Will need to
monitor the other sites however as there will be some spots which
come close.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Coastal Flood Advisory until noon EST today for MDZ017.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 10 AM this morning to 6 PM EST
     Friday for ANZ530>533-535-536-538>541.
     Small Craft Advisory from 2 PM this afternoon to 6 PM EST
     Friday for ANZ534-537-542-543.

&&

$$
SYNOPSIS...MSE
NEAR TERM...MSE
SHORT TERM...MSE
LONG TERM...RCM
AVIATION...MSE/RCM
MARINE...MSE/RCM
TIDES/COASTAL FLOODING...RCM


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