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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
356 am EST Thursday Jan 29 2015

high pressure will move off the coast this morning. A cold front
will swing through the region late today into tonight. A strong
pressure gradient ahead of high pressure will bring windy and cold
conditions Friday into Friday night. High pressure will build over
the area Saturday...but low pressure may impact the area later
Sunday into Monday. Cold high pressure will return for the middle
portion of next week.


Near term /through tonight/...
surface high pressure remains over the region early this morning.
The combination of light winds...dry air and only a thin deck of
high clouds has allowed for radiational cooling.
will be quite cold early this morning with temperatures in the teens for
most areas...but middle to upper 20s in downtown Washington and

The high will move off the coast later this morning and low
pressure will track through the Great Lakes this afternoon and the
cold front associated with this system will approach our area from
the west. Moisture will be limited with this system...despite a
southerly flow ahead of it. However...there should be enough
forcing from a potent upper-level disturbance that will track
through the region this afternoon into this evening. This will
cause a period of light precipitation. Strong warm advection aloft
from the southerly flow combined with cold and dry air near the
surface poses a threat for mixed precipitation. Precipitation
amounts will be light and the duration of precipitation will be
about one to two hours. However...some of that precipitation is
expected to fall in the from of freezing rain across portions of
western and northern Maryland...northern Virginia and the eastern
Panhandle of West Virginia. Given the recent cold conditions...any
freezing rain that does fall will likely freeze on untreated
surfaces even if the surface temperatures are slightly above freezing.
This will impact the evening rush. Therefore...a Winter Weather
Advisory is in effect for these areas.

Farther south and east across central Virginia...southern
Maryland...and the Washington metropolitan areas surface temperatures
will be a bit warmer. Some sleet may mix in with rain...but
confidence in freezing rain is low at this time. However...will
have to monitor pavement temperatures today because rain may freeze on
some surfaces even with temperatures a little above freezing.

Across the Blue Ridge mountains into the Potomac
Highlands...freezing rain is possible but confidence in
precipitation is too low at this time to warrant an advisory.

Precipitation will move away from most areas this evening and the
cold front is expected to pass through overnight. Gusty northwest
winds are possible late tonight...especially along the ridges. Upslope
snow showers are expected tonight along and west of the Allegheny
Front. A Winter Weather Advisory is in effect for these areas.


Short term /Friday through Friday night/...
low pressure will intensify over New England Friday while high
pressure approaches from the Midwest. The pressure gradient
between these systems will be quite strong...resulting in gusty
northwest winds. Wind gusts around 45 to 50 miles per hour are possible and a
Wind Advisory may be needed for portions of the area. The strong
northwest winds will usher in cold conditions. In fact...temperatures may
hold steady or even fall throughout the day. Temperatures Friday
afternoon will range from the single digits in Allegheny Highlands
to the lower and middle 30s in southern Maryland. More upslope
snow showers are expected along and west of the Allegheny Front.
The Winter Weather Advisory continues until noon...but snow
showers are possible during the afternoon as well.

For locations east of the Allegheny Front...a few snow showers are
possible Friday as another potent upper-level disturbance swings
through the area. Most areas will not see accumulating snow...but
there will be enough instability to combine with strong cold
advection for the possibility of a few bursts of heavier snow
showers. This could leave a quick coating in spots and with sudden
changes in visibility that could have a significant impact on
travel...although it would be localized. The best chance for the
heavier snow showers will be across northern Maryland...eastern
West Virginia and northern Virginia.

Cold and dry conditions Friday night as surface high pressure builds south
and east. Lingering snow showers over the Allegheny Front Friday
evening expected to diminish as the northwest flow injects much drier air.
Main concern for Friday night will be the well below normal
temperatures...almost 10-15 degrees below. Combining with northwest winds with
gusts 20-30 kts...and in higher elevations 30-35 kts...wind chills
forecasted to drop to around -10 degrees celsius Potomac
Highlands...negative single digits along the Mason-Dixon line...and
positive single digits the remainder of the area. Will continue to
highlight the Wind Chill Advisory potential in the severe weather potential statement...mainly for
the far western areas. Used a blend of adjmetbc/mosbc which has been
trending well for overnight temperatures.


Long term /Saturday through Wednesday/...
center of the high slips southeast into the southeast US Sat while a near
zonal flow sets up during the day...and weak ridging builds Sat
night-Sun morning. The pattern keeps the area dry though cold through
Sat with temperatures still running below normal. Warming trend by Sat
night as winds back to SW flow...with 850mb temperatures warming to around
-5 degrees celsius.

Next chance for precipitation sun-Monday with surface low developing over gom and
riding a near stationary front to our south. Some question remains
on precipitation timing and intensity...and as such then p-type. GFS/CMC
stronger solutions with the low development as upper level trough digs
deeper south...and picks up shortwave energy riding the southern
stream...while the European model (ecmwf) keeps more of a separation. Went with
likely probability of precipitation by Sun afternoon over western areas to highlight the higher
confidence of precipitation...then spreading the likely probability of precipitation to the east for
Sun night-Mon. Concerning precipitation type...maintained mainly a snow
event...with possible transition to rain during the afternoon sun over just
the far southern areas of the County Warning Area. Higher confidence any precipitation on
Monday remains all snow with 850mb temperatures dropping -10 to -15 degrees
celsius during the day. As the low becomes clearer on subsequent
shifts...will be able to have a better handle on p-type and amts at
the onset.

Precipitation clears the area by Tuesday morning...with surface high bringing
another period of dry and cold temperatures. Trended colder with highs Tuesday
and lows Tuesday night as a result. Model divergence by middle week on the
handling of the next low pressure system...with precipitation possible once again
late Wed-thurs.


Aviation /08z Thursday through Monday/...
southerly winds are expected today. A brief period of wintry
precipitation is possible late this afternoon into early this
evening. Drier conditions will return tonight. Strong northwest
winds are expected Friday with a couple snow showers possible.
Northwest winds will gust around 35 to 40 knots Friday.

Friday night-Sat night...VFR likely...possible sub-VFR late Sat night.
Gusty northwest winds 15-20 kts with gusts to 25 kts Friday night...becoming less
than 10 kts by Sat afternoon. Possible low level wind shear Friday night with 2kft winds 40-50

Sun-Mon...sub-VFR likely with precipitation...possible sub-IFR Sun night/Monday
morning. Wintry mix possible. Increasing northwest winds Monday...gusts to 20 kts.

Monday night-Tuesday night...VFR likely.

Wednesday-Wednesday night...sub-VFR possible with precipitation.


southerly winds are expected ahead of a cold front today. The cold
front will pass through tonight and gusty northwest winds are
expected behind the front Friday. A Small Craft Advisory is in
effect for portions of the waters through tonight. A Gale Warning
is in effect for the waters Friday.

Gales likely at least first half of Friday night on Chesapeake
Bay...and possibly on the upper Potomac. Occasional gales may linger till
daybreak Sat on the Bay. Winds subside Sat but remaining 15-20 kts
during the day. Winds diminish Sat night...and remain sub-Small Craft Advisory
through Sunday. Depending on the track of the low Sun
night-Mon...Small Craft Advisory conditions will become possible again. Sub-Small Craft Advisory
conditions return for middle week.


Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...Winter Weather Advisory from 1 PM this afternoon to noon EST
Friday for mdz501.
Winter Weather Advisory from 1 PM this afternoon to 7 PM EST
this evening for mdz003-502.
Winter Weather Advisory from 3 PM this afternoon to 9 PM EST
this evening for mdz004-005-503-505.
Virginia...Winter Weather Advisory from 7 PM this evening to noon EST
Friday for vaz503.
Winter Weather Advisory from 1 PM this afternoon to 7 PM EST
this evening for vaz028-031.
Winter Weather Advisory from 3 PM this afternoon to 9 PM EST
this evening for vaz505.
WV...Winter Weather Advisory from 1 PM this afternoon to noon EST
Friday for wvz503.
Winter Weather Advisory from 7 PM this evening to noon EST
Friday for wvz501-505.
Winter Weather Advisory from 1 PM this afternoon to 7 PM EST
this evening for wvz050>053-504.
Marine...Small Craft Advisory from 1 PM this afternoon to 6 am EST
Friday for anz530>534-537>543.
Gale Warning from 6 am to 6 PM EST Friday for anz530>543.
Small Craft Advisory from 1 PM this afternoon to 6 PM EST this
evening for anz535-536.


near term...bjl
short term...bjl/Sears
long term...Sears

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