Area Forecast Discussion


248 
FXUS61 KLWX 230125
AFDLWX
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
925 PM EDT Sun Oct 22 2017
.SYNOPSIS...
High pressure will push eastward into the northwest Atlantic 
through Monday. Low pressure will move up the Appalachians 
Monday night into Tuesday. Upper troughing will remain over the 
region through the second half of the week.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Like last night, blow-off cirrus overspreading the forecast area
this evening. Unlike last night though, anticipate the shield 
to get thicker overnight, with a strong possibility of low 
clouds working inland as well across the Baltimore metro area 
toward morning...and maybe reaching metro DC too. These clouds 
in turn will keep temperatures higher than previous nights. Also
at play will be a continuing south wind, which actually is 
quite strong (close to 20 kt) just off the deck per 00z LWX 
RAOB. RAP/NAM model sounding both suggest that this low level 
jet will remain most of the night. So, skies should be mostly
cloudy, and radiational cooling looks unlikely. Therefore, 
believe that low temperatures likely won't dip lower than the 
50s.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
Low clouds mix out during the late morning, but mid-high clouds
thicken through the day with showers developing over the 
Appalachians and spreading east Mon night as moisture deepens in
response to strengthening low-level jet. Models indicate a thin
convective line will move quickly across the area with potential
for gusty winds of 35-40 mph as strong 850mb low-level jet of
50-60 kts mixes down with the showers. The pre-frontal convective
line should be east of the Chesapeake Bay by 18Z Tue but light
showers will remain possible Tue-Tue night as actual cdfnt 
moves through and upper trough remains still to the west.
Rainfall amounts of 0.5 to 0.75 inches are expected except
higher over the Appalachians and Blue Ridge mountains. Given
progressive nature of front and dry antecedent conditions, no
flooding is anticipated.
&&
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
The cold front will be well off the eastern seaboard 12Z 
Wednesday as weak high pressure builds. Moderate 850 hPa cold 
advection on Wednesday afternoon in NW flow should bring a fair 
amount of strato-cumulus cloudiness across the area which will hold 
down temperatures during the afternoon. 12Z/GFS shows 850 hPa 
temperatures falling to at or just below 0 degC overnight Wed into 
Thursday, but quickly start to rebound by 12Z Thursday. Along 
upslope mountain areas Wednesday night, there could be some a few 
showers, with temps fall aloft to below freezing...some wet snow 
could mix with rain after midnight.
Thursday...high pressure builds across the southeast and into our 
region...and will be in control with dry weather and seasonal 
temperatures. Morning temperatures will probably be the coldest of 
the week...but nothing unseasonably cold.
Friday...the center of the high will move off the southeast coast 
during the day...allowing a return of warmer readings to commence on 
Friday under clear skies.
Weekend...Saturday...the center of high will be over New 
England...and temperatures will once again rebound to above seasonal 
normals. Dry weather is expected on Saturday. By Sunday, more 
uncertainty in the forecast associated with the timing of a cold 
front extending from a low centered over the northern Great Lakes, 
that is expected to cross the area. The new 12Z GFS is faster 
brining in the colder air in on Sunday compared to the slower 
00Z/ECMWF ensemble guidance. Looks like this is the next best chance 
for widespread wetting precipitation.
&&
.AVIATION /01Z MONDAY THROUGH FRIDAY/...
VFR conditions expected through late this evening. A southerly flow 
will allow for increasing moisture to get trapped underneath the 
nocturnal inversion late tonight into Monday morning. Did allow for 
a period of IFR cigs and MVFR vsbys during this time. There is still 
some guidance that keeps VFR conditions in place but as of now there 
appears to be a better chance for low clouds and patchy fog given 
the fact that most of the guidance is forecasting this and dewpoints 
are climbing due to the light southerly flow. 
Any low clouds will burn off by mid to late morning and it will turn 
out breezy Monday afternoon with gusts around 15 to 20 knots from 
the south and southeast. Showers are expected Monday night ahead of 
a cold front. Some showers may contain gusty winds...especially 
overnight along the frontal boundary as it passes through. Gusts 
around 30 to 40 mph are possible. LLWS is expected with southerly 
winds around 45 knots are most likely around 2000 feet. 
However...should more winds mix down to the surface it may be more 
turbulence instead of LLWS. Confidence in that is low. Conditions 
will improve behind the front early Tuesday morning. 
Expect VFR conditions through the extended. Possibly on Friday there 
could be locally IFR visibilities in early morning fog at IAD/MRB 
terminals.
&&
.MARINE...
A southerly low level jet resides just above the waters tonight.
If these winds were to mix down, then 20 kt gusts would be 
realized. However, with water temperatures in the upper 60s, 
think that an inversion will hold. Have included gusts in the 
mid teens across most of the waters.
Winds are expected to strengthen Mon afternoon and night. Have 
issued a gale warning for much of the Chesapeake Bay and lower 
Potomac for Mon night in anticipation of a convective line to 
move across the area when a 850-mb jet of 50+kt is expected to 
spread the area. 
Small craft winds possible Wednesday. As high pressure builds in on 
Thursday, expect winds/waves to remain below small craft advisory 
levels for the remainder of the week.
&&
.TIDES/COASTAL FLOODING...
Water levels are expected to rise rapidly Mon night as strong
srly low-level flow develops with minor coastal flooding
expected at most of the sensitive locations.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 11 AM to 6 PM EDT Monday for 
     ANZ531>534-537-539>541-543.
     Gale Warning from 6 PM Monday to 6 AM EDT Tuesday for 
     ANZ531>534-537-539>541-543.
     Small Craft Advisory from 11 AM Monday to 6 AM EDT Tuesday for 
     ANZ538-542.
     Small Craft Advisory from 6 PM Monday to 6 AM EDT Tuesday for 
     ANZ530-535-536.
&&
$$
SYNOPSIS...LFR
NEAR TERM...HTS
SHORT TERM...LFR
LONG TERM...SMZ
AVIATION...BJL/SMZ
MARINE...HTS/LFR/SMZ 
TIDES/COASTAL FLOODING...LFR