Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
344 am EST Sat Nov 22 2014
high pressure will shift offshore today. A deepening low pressure
system over the Great Lakes will lift a warm front through the
area Sunday night. An associated cold front is expected to move
through Monday night. The front stalls just offshore as high
pressure builds across the area Tuesday.
Near term /until 6 PM this evening/...
surface hipres atop County warning forecast area Ely this morning. West/ clear skies and little/no wind...
temperatures would have an opportunity to drop to dewpoints in the teens. However...
warm air advection seems to be hvg an influence as temperatures have lvld off past few hours.
Surface high will move offshore today...providing southwesterly flow to County warning forecast area. As
such...warm air advection will increase. 800 mb temperatures should be in the neighborhood of 6c
by days end. Hence...am reflecting a sharp warm up in maxt...near
mav/met/ecs blend. /Ecs solution a compromise of the other two anyway./
Only wrinkle will be isent lift inducing some cldcvr...especially during
the afternoon. Seems like any decent lift remains confined northwest of County warning forecast area...
so will keep forecast dry.
Short term /6 PM this evening through 6 PM Sunday/...
ridging will protect County warning forecast area tonight as well. Will have disturbances along the northwestern
perhiphery as well as approaching from the S. Should have clouds nak/dca/shd
northward...but otherwise none of this will affect area. Will be able to radiate
after dark...but suspect we/ll keep a pinch of southwesterly flow as well...so it
wont be able to get all that cold /spcly on the rdgtops/. Changes from
going forecast not that significant.
By sun...positive vorticity advection from southern stream will begin to affect area...especially during
the afternoon hours. Will start the day mosun...but clouds will overspread hours
midday/Ely afternoon and will bring precipitation northeastward after 18z. Am most confident on
rain toward/after sunset due to continued influence of surface ridging and need to
saturate llvls first. Maxt once again a blend of MOS.
Long term /Sunday night through Friday/...
warm front will move through the forecast area Sunday night into
early Monday morning. Models continue to indicate very strong low level jet
moving across the region...on the order of 50-70kts at 850mb.
Isentropic lift...the low level jet and precipitable waters peaking around 1.5 inches will
support a period of moderate to heavy rainfall for most of the
area...with otherwise steady light rain. Basin wide quantitative precipitation forecast expected to
be less than an inch...but locally higher amounts of rain possible.
Low temperatures Sunday night will be in the 40s...with low 50s in some
spots along and east of I-95.
Warm front is expected to be across PA by 12z Monday morning...with
a cold front approaching from the Ohio Valley. Pressure gradient
both surface and aloft will be strong enough for a breezy day...with
S-SW winds gusting to around 20-25 miles per hour. Some model output suggests
scattered or isolated showers over portions of the area...but kept
probability of precipitation correspondingly low. Warm airmass will bring a brief return to
mild temperatures...with highs around 70 east of the Blue Ridge and
in the middle to upper 60s across the valleys west of the Blue Ridge.
Cold front moves through Monday evening. 00z NAM suggests potential
for organized showers...but is not supported by GFS or European model (ecmwf). Winds
will shift to the northwest behind the front. Lows primarily in the
40s...with some 30s in the Shenandoah Valley and Highlands.
Confidence decreases with synoptic setup from Tuesday Onward.
General scenario is that high pressure attemps to build in from the
west...but a coastal low develops off the Carolina coast and moves
through the offshore waters. 00z GFS and European model (ecmwf) differ in
timing...location and strength of the low. Forecast at this point calls
for potential showers Tuesday east of I-95...followed by light rain
or a rain/snow mix Tuesday night. Precipitation potential includes
most of the County Warning Area Wednesday into Wednesday night. High temperatures Wednesday
should be in the 40s...so any precipitation should be liquid. Wednesday
night temperatures start above freezing and drop below late at night for
most of the County Warning Area...so a period of snow or a rain/snow mix possible.
However...with County Warning Area being on the backside of the low...precipitation amounts
will be highly dependent on the exact track of the storm.
By late week...model divergence increases with European model (ecmwf) favoring an
upper low dropping into the Great Lakes while GFS favors the upper
low further north and a cold frontal passage across the mid-Atlantic. High
pressure builds in for the start of the weekend.
Aviation /09z Saturday through Wednesday/...
VFR tda-tngt. Most clouds will be mid-deck.
Will have lowering ceilings Sun afternoon as precipitation approaches. No restrictions expeceted
during most of the day...but deteriorating conds will be apprchg from
the SW...potentially affecting afternoon push.
MVFR/IFR conditions expected Sunday night with rain...with potential
for a period of heavy rain. Conditions improve to VFR Monday
morning...with gusty S-SW winds. Flight conditions uncertain midweek
with potential for some precipitation from a coastal system.
will have southerly winds on the waters this weekend. While there will periods west/
decent flow...mixing will be quite poor over Lower-Middle 40s water temperatures.
Have capped winds at or below 15 knots.
Small craft conditions likely Sunday night through Monday as a
warm front moves through...followed by a cold front Monday
evening. Gusty winds possible midweek with a coastal low...but
strength and track of the system is uncertain at this time.
still have water levels 1/2 to 1 feet below astro tides. Winds will become
southerly after daybreak...which will bring water back to normal levels. May
even be a pinch above normal by this evening.
District of Columbia...none.