Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
1047 am EDT Thursday may 28 2015
high pressure will remain offshore through Friday. A southerly
flow will bring warm humid conditions to the middle-Atlantic through
Saturday. Showers and thunderstorms will be possible each
afternoon and evening as a series of cold fronts approach and then
dissipate. A stronger cold front will arrive Sunday.
Near term /this afternoon/...
Warm/moist air continues over the middle Atlantic courtesy of high pressure off
the NC CST. A weak cold fnt stretches across northwestern PA/eastern Ohio. Morning iad
sndg modified for afternoon heating shows ample cape...but winds were
missing in sndg. However BUFKIT soundings show little-to-no wind field.
Most likely scenario would be for rain shower/thunderstorm to develop over the mountains this
afternoon and slowly track east. Sndg precipitable water was not as high as yesterday but it
is still possible that a slow moving cell could produce an inch of rafl.
Another day of temperatures in the 80s and dew points into the 60s.
Short term /tonight through Friday night/...
Showers and thunderstorms continue this evening with still enough
instability lingering...but also now aided by a passing weak
shortwave. The precipitation tapers off by the second half of the night
with the loss of the boundary...instability and upper level forcing.
Dry period then through daybreak before yet another round of precipitation.
Another sinking cold front nears the region...though weakening as
it settles along the Mason Dixon line with the surface high and ridge
aloft stalling any forward progression. Have slight chance probability of precipitation in
the morning to account for any development along this frontal
boundary...then increased to chance for the afternoon as a passing
shortwave could trigger scattered activity. Thinking the better chance on
Friday will be for western areas closer to the forcing aloft. Loss of
daytime heating and forcing should keep things mainly dry Friday
night...especially by the second half of the night.
Long term /Saturday through Wednesday/...
County warning forecast area will be well within the warm sector Sat as strong ridging surface-500 mb
resides off the eastern Seaboard. MDT-high instability values/lapse rates
will be sliding up the back side of the ridge...which mainly will
encompass the ptmc Highlands but the eastern periphery may include the
blurdg. Wind fields lclly will be incrsg...which may support a few
stronger thunderstorms. In addition...the moisture plume will be coming off the
Gulf of Mexico west/ precipitable water at or above 1.5 inches...so any storm could be a heavy rainer as
The ridge will begin to break down Sat night...and will continue to do so through
sun. This will be enough to allow cold front to sag into County warning forecast area. Since northern
stream support will eject well into the Canadian Maritimes...orientation
of the fnt will permit training cells. Think the rafl will become the
bigger deal...but GFS/European model (ecmwf) still depicting spread of solutions...so
confidence low on specifics. Enough evidence for likely probability of precipitation though.
Model spread manifests itself more Mon-Tue. Hipres ridging southward from Quebec will
carry cool air west/ it...and would support maritime flow for County warning forecast area.
Meanwhile...frontal boundary should be nearby and provide some overrunning.
Temperature forecast for Monday quite a bit cooler because of this. Further...have
removed mention of thunder as air mass should have stabilized. Confidence
rather low on the magnitude of the cold air advection.
500 mb height pttn across the Continental U.S. For the week ahead features broad ridging but
west/ a cutoff low meadering across the southeast. Am unsure of impact...but
range of psbltys reluctantly suggests probability of precipitation need to stay in place.
Aviation /15z Thursday through Monday/...
VFR conditions today.
Chance for afternoon showers and thunderstorms at all taf sites. Have included with
vcsh for now due to the scattered nature and the high uncertainty of exact
timing and placement of the storms. Not expecting severe levels...but
cannot rule out gusty winds and brief heavy rainfall dropping visible
to sub-VFR. Any precipitation threat ends overnight...with another round of
precipitation possible on Friday.
Winds generally light and vrb through tonight. Ely to southeasterly flow
Brief flgt restrictions possible Sat PM in vicinity of thunderstorms and rain. Mrb has best chance at
being affected. Cold front will drop southward sun providing a greater risk of
thunderstorms and rain areawide. Sporadic restrictions continue into Monday. IFR possible if
marine air mass spreads inland.
sub-Small Craft Advisory conditions now expected on all waters through Friday night. Chance
of thunderstorms this afternoon and then again Friday afternoon could bring a period of
Southwesterly flow increases Sat-Sat night...providing the next potential round
of Small Craft Advisory conds. A few strong thunderstorms and rain will be possible during the afternoon-
evening...but storms will be more numerous Sunday. Strong sustained winds will
be replaced by lclly strong gusts at that time.
District of Columbia...none.