Area Forecast Discussion


693 
FXUS61 KLWX 230901
AFDLWX
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
401 AM EST Thu Feb 23 2017
.SYNOPSIS...High pressure will remain south of the area through
Friday. A cold front will pass through the area on Saturday. 
High pressure builds over the area during the early part of next
week. Another cold front will move through the area around the
middle part of next week.
&&
.NEAR TERM /THROUGH TONIGHT/...Light southeast flow and moisture
advection has resulted in widespread stratus and areas of dense
fog along the western shore of Baltimore and Harford counties.
Short-term guidance suggests stratus layer will continue to
expand next few hours with fog becoming an issue over northeast
MD. Will continue to monitor obs for possible expansion of dense
fog advisory. 
After low clouds/fog mix out later this morning, it will become 
very warm with highs reaching into the mid 70s. There will
actually be sufficient instability (200-400 J/KG of CAPE) for
pop-up scattered showers and isolated thunderstorms mainly
between 20z-02z over the nrn Shenandoah valley, ern WV panhandle
and north cntrl MD. Showers will dissipate with loss of heating
later in the evening. More low clouds and/or fog tonight as area
remains in warm sector.  
&&
.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...500 mb ridge
crests over the area around 00Z Sat with sfc temps rising
another 1-4F degs. An elevated mixed layer also advects 
northward into the area keeping atmosphere capped. Won't rule a
few spots hitting 80F. Very warm Fri night with record high
minimums likely. Fog not likely to be a problem as winds
strengthen, but low clouds still possible. 
Attention then turns to sharp cold front fcst to move through 
the area Sat. SPC DY3 Otlk now has entire area under marginal 
risk. Simulated cloud imagery from GFS shows convection 
remaining strong possibly severe as it moves across ern OH, wrn
PA, and wrn MD between 12Z-15Z then weakening/becoming 
shallower after 15Z as it crosses the rest of the fcst area.
Based on this, it appears any severe threat would be confined to
morning hours as strongest forcing stays north over PA. Cdfnt
clears the Chesapeake Bay by 00Z Sun, then turning much cooler
and windy.
&&
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
High pressure will be building overhead on Sunday. While temperature 
departures will be some 15-20 degrees lower from Saturday, highs 
will still be near or slightly above normal. Outlying areas could 
fall below freezing Sunday night.
The remainder of the extended period becomes much more uncertain. 
The upper level pattern will feature mean troughing in the western 
US and a building ridge over Florida and the Caribbean. With fast 
WSW flow aloft, any cold air intrusions are unlikely, with 
temperatures likely remaining above normal for the remainder of the 
forecast period. 
The tricky part will be timing in shortwave troughs within the fast 
flow, with the possibility of a front remaining somewhere near the 
area. If the GFS low pressure solution arrives early enough Monday, 
there could be a little wintry precipitation in the mountains, but 
this is far from certain. Otherwise, the forecast will carry a low 
chance of showers for each period due to the wide spread of model 
solutions. There is a little better agreement on more substantial 
troughing arriving late Wednesday or Thursday...which would 
represent a more targeted opportunity for rainfall.
&&
.AVIATION /09Z THURSDAY THROUGH MONDAY/...MVFR/IFR Cigs at KIAD,
DCA, and BWI through 14Z then mixing out. Another repeat tonight
with more low clouds. Sharp cdfnt to move through the area Sat
with showers and gusty shifting winds.
VFR with high pressure Sunday into Sunday night. There are a wide 
range of model solutions regarding the timing and strength of the 
next low pressure system arriving Monday (or later), thus confidence 
on impacts is low.
&&
.MARINE...Small craft advisory conditions likely Sat through
Sun. Showers Sat afternoon may require SMWs.
Winds will likely diminish through the day Sunday as high pressure 
moves into the area, but SCA conditions may continue for a time. The 
high will quickly move offshore Monday, but models differ on how 
strong southerly winds will become, depending on the strength of low 
pressure to the west. Will mention possible SCA conditions in the 
marine synopsis.
&&
.CLIMATE...
Warmest Februaries (average temperature)
   DCA           BWI           IAD
1. 46.9 (1976)   44.0 (1976)   42.1 (1990)
2. 45.2 (1990)   43.9 (1949)   41.1 (1976)
3. 44.7 (1997)   43.3 (1890)   41.0 (1998)
4. 44.3 (2012)   42.7 (1932)   40.9 (2012)
5. 43.9 (1949)   42.6 (1909)   40.5 (1997)
Feb 2017 (through the 21st)
DCA: 45.1  BWI: 41.6   IAD: 42.1
Warmest Winters (Dec 1-Feb 28/29)
   DCA              BWI              IAD
1. 44.7 (1931-32)   45.3 (1931-32)   40.0 (2011-12)
2. 44.3 (1889-90)   44.4 (1889-90)   39.7 (2001-02)
3. 43.3 (2011-12)   42.4 (1948-49)   39.4 (1997-98)
4. 43.2 (2001-02)   41.9 (1949-50)   39.0 (2015-16)
5. 42.8 (1949-50)   41.3 (1879-80)   38.3 (1990-91)
Winter 2016-17 (through Feb 21)
DCA: 43.0   BWI: 39.6   IAD: 39.9
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Dense Fog Advisory until 8 AM EST this morning for MDZ011-508.
VA...None.
WV...None.
MARINE...None.
&&
$$
SYNOPSIS...LFR
NEAR TERM...LFR
SHORT TERM...LFR
LONG TERM...ADS
AVIATION...ADS/LFR
MARINE...ADS/LFR
CLIMATE...DFH