Area Forecast Discussion

FXUS61 KLWX 160758
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
358 AM EDT Mon Jul 16 2018
High pressure will remain over the Atlantic through tonight. A
cold front will approach the area Tuesday before passing through
Tuesday night. High pressure will return for Wednesday and
Thursday before moving offshore Friday. Low pressure may impact
the area during the weekend.
Clearing skies observed this morning as showers and storms last 
evening have pressed south of our region. Areas of patchy fog
being observed on satellite and surface observations, with 
those areas that received rainfall yesterday being the favored 
locations. Still seeing some mid to high level clouds along our 
southern zones this morning as shortwave energy moves off to our
south. These areas will continue to see clearing this morning. 
Temperatures are in the upper 60s to lower 70s, and dewpoints 
are creeping upwards from the middle 60s to near 70 degrees, 
indicating increasing moisture across the area. 
Looking for showers and storms to form once again this afternoon 
over the mountains, with the bulk of the activity residing mostly 
along and west of the Blue Ridge, much like today. Do expect a bit 
more sun today than yesterday, which will allow temperatures to 
extend in to the lower to middle 90s. Coupled with dewpoints 
hovering in the lower 70s, we will see heat indices approach the
100 degree mark east of the Blue Ridge, maybe a couple degrees
higher than that. As such, am not forecasting heat advisory 
criteria being met today. That being said, it will be 
unseasonably hot and humid, so ensure to consume plenty of 
fluids and take frequent breaks in the shade if spending time 
outdoors today.
Showers and thunderstorms will decrease in coverage this evening
and overnight, as winds favor a southwesterly trajectory at 5 
to 10 mph. This will maintain muggy conditions overnight, and 
lows will range in the 70s area wide, with upper 70s likely 
along and east of the I- 95 corridor. 
The cold front currently over the upper Midwest and western
Great Lakes region will be knocking on our doorstep on 
Tuesday. Expect widespread showers and storms, favoring Tuesday 
afternoon and the evening hours as the front crosses the area. 
Precipitable water values will be in excess of two inches, which
will support at least an isolated threat for localized flash 
flooding despite the dry conditions observed over the last few 
weeks. There is some indication of the potential for strong to 
severe storms, particularly over portions of north central 
Maryland where a Marginal Risk of severe storms has been 
highlighted by the Storm Prediction Center (SPC). Moderate to 
high CAPE values ahead of the front will range in the 2000-3000 
J/Kg range, with some modest 0-6km shear will support the chance
for damaging wind gusts. Again, this looks to be an elevated 
threat for severe and/or flash flooding, but not a significant 
threat at this time.
Model guidance is in general agreement of the front moving east of 
the region by around midnight, with drier conditions winning out
in its wake. Lows Tuesday night will range from the upper 50s 
over the Allegheny Front to near 70 degrees in the cities. 
Canadian high pressure will build in behind the front, 
delivering cooler and less humid conditions area wide. Highs on 
Wednesday will top out in the lower to middle 80s, with 
dewpoints in the upper 50s to near 60 degrees. Lows Wednesday 
night will be in the 60s with no threat of rain Wednesday or 
Wednesday night.
High pressure will build remain overhead for Thursday, bringing
dry and seasonably warm conditions, but with low humidity.
Dry and mild conditions are expected Thursday night with high
pressure remaining in control. 
The high will move offshore Friday and low pressure both at the
surface and upper-levels will cutoff from the jetstream over the
Great Lakes. A return flow will result in slightly more humid
conditions. A warm front associated with the low will remain to
our south, so although a stray shower or thunderstorm is
possible it appears that most areas will be dry on the stable
side of the warm front. 
The cutoff upper-level and surface low is expected to remain
nearby over the Great Lakes Friday night through the weekend.
This will allow for the warm front to lift north through our
area. Also, there may even be a coastal low that develops due to
jet dynamics interacting with the Mid-Atlantic Coast. Details
still remain highly uncertain, but with an anamolous upper- 
level low to our west and deep moisture advection it does appear
that there will be at least an increasing chance for showers 
and thunderstorms during the weekend. 
Generally VFR flying conditions this morning at all terminals. One 
exception is MRB where fog has developed, producing mainly MVFR 
visibilities. CHO could join in on reduced visibilities due to fog, 
but confidence is lower here as cloud coverage is greater there. 
Winds this morning will trend calm to light, favoring a southerly 
Afternoon showers and storms will ignite once again over the 
mountains, with MRB seeing the highest chance of sub VFR VIS/CIGs. A 
shower or thunderstorm could impact terminals further east, but best 
chances will reside along and west of the Blue Ridge, thus no 
mention of SHRA or VCTS for the eastern terminals at this time. Any 
impact will produce brief periods of MVFR/IFR VIS, with CIGs 
remaining AOA FL050.
Cold front will approach and cross the terminals Tuesday, 
delivering widespread showers and storms, and periods of 
MVFR/IFR VIS/CIGs. Favored time period of impact will be Tuesday
afternoon and early evening, with strong gusty winds a 
possibility with any stronger thunderstorms. Winds will turn 
northwesterly behind the front Tuesday evening, and high 
pressure will build over the terminals through Wednesday, 
resulting in a return to VFR flying conditions.
High pressure will remain over the terminals Thursday before
moving offshore Friday. VFR conditions are expected during this
SCA conditions failed to materialize early this morning, thus
went ahead and cancelled the advisory for the remainder of the
morning. Light southerly flow will persist today before 
increasing this evening and overnight. This will bring a better 
likelihood for SCA wind gusts over portions of the Bay and lower
Tidal Potomac. As such, an SCA will go in to effect from early 
this evening into early Tuesday morning. A cold front will 
approach and cross the waters Tuesday afternoon and evening, 
with showers and thunderstorms expected to impact the waters. 
Some storms could be strong, producing gusty winds and the need 
for Special Marine Warnings. Be sure to have your weather radio 
handy to receive alerts should warnings be issued.
In the wake of the front Tuesday night, wind gusts will near SCA 
criteria as winds turn northwesterly. High pressure will build
in behind the front on Wednesday, promoting lighter northerly 
breezes and likely sub SCA conditions.
High pressure will remain over the waters Thursday through
Thursday night before moving offshore Friday. Low pressure may
impact the waters during the weekend. Winds may approach SCA
criteria later Friday into the weekend. 
A southerly flow will continue to bring elevated water levels
through Tuesday. The flow will be just west of south most of the
time so most high tides should be around caution stage. However,
water levels near minor flood stage are possible for sensitive
areas this morning, and again tonight into Tuesday morning 
during the higher of the two high tides. 
MARINE...Small Craft Advisory until 8 AM EDT this morning for