Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
616 PM EDT Tuesday Oct 21 2014

Synopsis...
a cold front will move through the middle Atlantic region this
evening. Low pressure will persist along the coast through Thursday.
High pressure will return for the end of the workweek and into the
weekend.

&&

Near term /through Wednesday/...
update...pressure surge moving across the middle-Atlantic and towards
the waters late this afternoon. See marine section.

Developing surface low pressure will move through the region late
this afternoon and evening...then offshore overnight. Broad closed
upper low over the lower Great Lakes will also drop into the middle-
Atlantic region by this evening...and become better organized as
it moves into the Tidewater region overnight.

Combination of cool air aloft...an approaching cold front and
marginal surface instability is producing scattered rain and
showers over the Shenandoah Valley...Potomac Highlands and
upstream across WV/PA and Ohio late this afternoon. With around
500 j/kg of SBCAPE...will have enough instability for some
isolated heavier showers and perhaps a few thunderstorms late this
afternoon and evening. Afternoon high temperatures are primarily in the
60s...with a few 70s noted in the Virginia Piedmont. Cooler temperatures over
the mountains where cloud cover and rain is keeping temperatures in the
upper 50s.

Rain will continue overnight as the surface and upper lows move
just to the east and southeast of the forecast area. Basin wide
rain amounts will likely be a quarter of an inch or less
overnight...but some local areas may see higher amounts with
localized periods of more moderate rainfall. Steady breeze around
5-10kt from the northwest continues as the pressure gradient around the
back side of the surface low increases. Lows tonight range from
the low 40s in The Highlands to the low 50s along and east of
I-95.

&&

Short term /Wednesday night/...
surface low pressure moves offshore and begins to strengthen as it
reaches the Gulf Stream. Winds strengthen to around 15-20 miles per hour with
higher gusts as the pressure gradient between the strengthening
low and high pressure over the Ohio Valley. Wraparound rainfall
likely at times over eastern Maryland and portions of Virginia. Upslope rain
will develop over the Potomac Highlands and continue Wednesday
night. Looks like overnight temperatures will favor liquid rain over most
of The Highlands...but the highest elevations in Grant...Pendleton
and Highland may see snow mixed in. Low temperatures in the 40s across
most of the forecast area.

&&

Long term /Thursday through Tuesday/...
blustery conditions will continue into the day Thursday as surface
low pressure slowly slides up the New England coast. Downsloping of
northeasterly winds will eliminate probability of precipitation locally during the day
Thursday everywhere except the Potomac Highlands...where upslope
rain is possible...and the far northeastern portion of the County Warning Area along
the Chesapeake Bay.

High pressure will begin to fill in Thursday night and winds will be
weaker Friday. The rest of the long term period will see quiet/dry
weather as broad surface high pressure moves overhead and upper
level ridging keeps plenty of sunshine across the area. Expect temperatures
this weekend to be right around normal...with highs mostly in the
mid-60s...and temperatures early next week to be just a few degrees above
normal.

&&

Aviation /22z Tuesday through Sunday/...
scattered areas of rain are developing to the west...and will move
into the Washington/Baltimore terminals by this evening. Periods
of MVFR visibilities likely with rain. Ceilings lower to MVFR tonight.
Periods of IFR possible as well as low pressure moves across the
region bringing additional rainfall. Light westerly winds this
afternoon and evening...becg northwest and increasing to around 10kt
overnight. Lower ceilings expected to persist Wednesday...and periodic
rainfall will be possible. Gusty northwest winds expected...up to 20-25kt
by the afternoon.

Thursday...VFR. Northwest winds gusting to 20-25kt.

Friday...VFR. Northwest winds around 1okt.

Confidence is low in the occurrence of aviation hazards over the
weekend as high pressure builds in.



Cloudy Wednesday night but ceilings expeceted to be VFR. Brzy northwest winds expeceted Wednesday night
and Thursday. VFR/no probs Friday and Sat.

&&

Marine...
update...pressure surge heading towards the waters as a cold front
moves through the I-95 corridor. Northwest winds behind the front have resulted
in gusts around 20kts. A tight pressure gradient will move into
the region tonight. A Small Craft Advisory is now in effect for the waters.

Previous discussion...
rain will move into the waters late this afternoon and
evening...with potential for a few thunderstorms. Winds become
north-northwest and increase overnight...with Small Craft Advisory gusts likely by early
Wednesday morning. Potential continues for gales Wednesday night
as low pressure strengthens off the New Jersey/Delaware-Maryland-Virginia shore. Model
forecasts are marginal for gales...so for now opted to extend Small Craft Advisory
through Wednesday night with gusts likely to reach 30kt in some
parts of ches Bay at least.

A Small Craft Advisory will likely be needed Thursday through Friday
and possibly into Friday night in gusty northeasterly winds as low
pressure moves up the northeast coast. Winds may approach gale force
Thursday afternoon over the waters...though currently think they
will stay mostly in the middle to upper 20 knot range.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory from 11 PM this evening to 6 am EDT
Thursday for anz530>534-538>543.
Small Craft Advisory until 6 am EDT Thursday for anz535>537.

&&

$$
Update...has
synopsis...Kansas
near term...Kansas
short term...Kansas
long term...ceb
aviation...KS/ceb
marine...KS/ceb

National Weather Service Glossary of Abbreviations