Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
943 PM EDT sun Mar 29 2015

Synopsis...
high pressure pushes offshore tonight with a cold front crossing
through the region on Monday. A reinforcing clipper low will pass
over the region on Tuesday. The high pressure that follows will
slide to our southeast Thursday and Friday allowing for warm
temperatures. Another cold front is expected at the end of the
week.

&&

Near term /through Monday/...
01z observation has surface high to the south off the Carolina coast...with
approaching frontal system back over Ohio. With the high
positioned to the south...southerly flow now over the
area...working to inject in more moisture rich air. A very dry
airmass needs to be overcome though...as evident with dew points
still hovering in the single digits across much of the area.
Thinking the stronger surge of more moist air...as well as warm air advection...will
come with the low level jet increasing after midnight tonight...with SW
winds between 40-50 kts.

Looking upstream...there are a few spots reporting light rain with
dew pt depressions of almost 20. As such...have very light rain
mentioned through 07z for only extreme western areas...then thinking
with more moisture advection should see the airmass saturate
enough for light rain to occur. Tricky situation when relating to
temperatures...as forecasted temperatures have dropped this evening...but are
expected to remain near steady around midnight then increase
toward dawn with the warm air advection. Despite the low dew points...the precipitation is
expected to remain light enough so not anticipating wet bulbing.
So have mainly light rain mentioned...with isolated spots that
could drop to the lower 30s potentially seeing some snowflakes mix
in with the rain. After having a day with highs in the 40s and
lower 50s...not anticipating sfcs to drop to or below freezing for
long enough to be concerned with ice...especially with Road temperatures
currently showing in the 40s and 50s (as of 01z). The exception to
this forecast will be the western slopes of the alleghenies which
should see a period of snow showers...and possible up to a couple
tenths of an inch accumulate.

The fnt itself will be rather moisture starved. Therefore expect most of the
precipitation ahead of the fnt...and thus have precipitation ending by midday as cold front passage
will occur by noon areawide. Cold air advection may result in a quick chgover to
shsn on the western slopes of the mountains prior to a rapid precipitation /and
cldcvr/ decrease. At the same time...winds will be increasing...and
the compressional warming may yield maxt warmer than today. It
appears as though the core of higher winds will be at the top /or just
above/ the mixed layer...W/ clouds present to interfere west/ deep layer
mixing. Therefore am keeping gusts 20-25 knots.

&&

Short term /Monday night through Wednesday/...
in a relatively short amount of time after the exit of the gusty
Monday system...the next upper level disturbance will be right on
the doorstep to our northwest. This feature will be much more compact and
therefore affecting much less area...also being driven by a more
compact advection pattern - tightly wound around the system. Ahead
of and behind this next upper wave some wind...mainly around 5-10kt
but generally the system will pass west/o the day-long period of strong
winds behind it.

The next question is about precipitation and ptype. The past few runs of
all main guidance suites have been wavering back/forth about the surface
low trekking directly over the County Warning Area...a hundred miles to the
north...or somewhere in between. The 12z NAM is going west/ the Mason-
Dixon line solution...but in terms of precipitation - that means very little
for areas S of the surface low. Much of the precipitation is carried along
north of the low...as it is for the Euro and GFS but their
deterministic 12z runs have the low further south - between the I-70
and I-66 corridor of the County Warning Area. Ahead of the feature...southwesterly low level
winds will increase and so will surface temperatures - into 40s/50s from S to
north. Although a rain/snow mix is possible early Tuesday morning over the
extreme northwest quadrant of the County Warning Area as precipitation arrives...precipitation expected to be
all rain for the daytime hours and much of it will spread across the
northern half of the County Warning Area. Kept a high chance and some liklies in for
these areas. On the immediate back end of the low's passage is still
somewhat in question. The cold air west/ the feature will again be
compact and close into the back end of the system. There may be
enough over northestern Maryland for a brief period and the cold front swings
through to mix in some snow but also the precipitation may be well east of the
area by that time.

As west/ a typical upper wave passage...the day after will be a
moderated version of the previous day in terms of temperatures and dry. Surface
winds will be a steady northwest and drier breeze but not all that strong
and highs will be allowed to reach the 50s across much of the
area...near 60 across the south.

&&

Long term /Wednesday night through Sunday/...
high pressure...moving offshore the East Coast...will sponsor dry
conditions and near normal temperatures Wednesday night. An
increased southerly flow will develop Wednesday night and Thursday
ahead of an approaching cold front. Highs are expected to approach
70 degrees across much of the region Thursday with a chance of rain
showers across the western half of the region.

The cold front should push across the region Thursday night
into Friday before stalling to the south Friday night.
Additional rain showers and perhaps a thunderstorm or two could
develop in lieu of the passing front. Temperatures should remain
mild Thursday night and Friday with highs reaching the upper
60s to near 70 Friday.

The stalled front should meander north and south Friday night
and Saturday...only to remain the focal zone for additional
rain showers or rumbles of thunder and cooler temperatures. A
low pressure system is expected to develop along this front before
pushing to the East Coast later Saturday into Saturday night.

High pressure will bring drier conditions and reinforcing cooler air
into the middle Atlantic for Sunday.

&&

Aviation /02z Monday through Friday/...
mainly VFR conditions through Monday. Possible MVFR ceilings with light rain
tonight...mainly between 08-12z. Have included -ra at the metropolitan
terminals for 3 hour blocks...the precipitation could very well end up more
occasional in nature. Light S flow tonight...thoguh with incrsng SW flow
aloft...have included low level wind shear mention through 08/09z.

No precipitation concerns Monday...but incrsng west-northwest flow during the
day...with gusts 25-30 kts. Winds will diminish Monday night.

Yet another quick-moving upper level low will swing by the area on
Tuesday...mainly during the daytime hours. Any precipitation is expected to be
rain...W/ warmer temperatures working into the southern end of the system as
it passes by. Brief MVFR ceilings could result from this system during
the daytime hours...but quickly improving Tuesday night into Wednesday as
skies clear out.

VFR conditions Wednesday night. Light southeast winds will become
southerly. VFR conditions at all terminals Thursday night into Friday...except
for mrb and perhaps iad where MVFR could evolve due to spotty rain
showers in the area. South winds becoming southwest and gusting
around 15 knots.

&&

Marine...
with winds around 17 kts over the northern Chesapeake Bay...have
gone ahead and begun the Small Craft Advisory there. Remaining waters have the Small Craft Advisory
starting at midnight...then all waters go through the day Monday as
winds increase behind a passing cold front. Expecting solid Small Craft Advisory
conditions...with possible higher gusts with strong winds aloft.
However...BUFKIT soundings look to restrict mixing to these
strongest winds and think the Small Craft Advisory will be sufficient. Sub-Small Craft Advisory
conditions then expected Monday night.

A cold front will cross the region late Tuesday...W/ a period of low-end
Small Craft Advisory gusts possible from SW winds ahead of the front. High pressure will
clear out the clouds/precipitation Tuesday night. Low-end Small Craft Advisory winds behind this
feature will pick up again over the waters during the daytime hours
Wednesday.

No marine hazards expected Wednesday night and Thursday. Winds
generally around 5 knots Wednesday night...becoming south to
southwest at 10 knots with occasional gusts around 15 knots.

&&

Tides/coastal flooding...
water levels running a foot to a foot and a half below astro
predictions due to recent blowout winds. Levels should normalize
somewhat tonight in southerly flow. Blowout tides will return Monday afternoon
as northwest winds resume.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory until 8 PM EDT Monday for anz530-531-538-
539.
Small Craft Advisory until 8 PM EDT Monday for anz532>534-537-
540>543.
Small Craft Advisory from 9 am to 8 PM EDT Monday for anz535-
536.

&&

$$
Synopsis...heights
near term...Sears/hts
short term...gms
long term...klw
aviation...Sears/gms/hts/klw
marine...Sears/gms/hts/klw
tides/coastal flooding...

National Weather Service Glossary of Abbreviations