Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
250 PM EDT sun Jul 13 2014
Bermuda high will keep southerly flow across the middle-Atlantic into
Tuesday. A cold front will approach the area tonight and stall
over the area Monday before pushing east late Tuesday. Canadian
high pressure will build across the eastern states Wednesday
through Thursday night.
Near term /until 6 am Monday morning/...
as of 18z...the Bermuda high has set up with southerly flow across the
area. Dewpoints have risen a couple degrees to around 70f since
daybreak. A cold front is over the Midwest...extending west-southwest from the
eastern Great Lakes through Indianapolis. Scattered thunderstorms have
broken out along this boundary. These will be the focus of the most
significant weather for the area through tonight. Tonight is a good
operative word as the 15z hrrr has this activity reaching the
Potomac Highlands around 6pm and spreading east into the area after
that. 6pm to 2am is the anticipated timeframe for thunderstorms to
enter the area and reach the balt-wash metropolitan. The cold front will
stall or even retrograde tonight. This will make for an active
Increasing moisture is making for an unstable afternoon. Rap
estimates from Storm Prediction Center mesoanalysis Page depicts 1500 to 3000 j/kg south
of District of Columbia. This is mainly due to the sunshine that has been strong
southeast of District of Columbia. Areas south and southeast should see some thunderstorm
development late this afternoon (though the cumulus field currently seems
to be struggling to take hold). With bulk shear 20 knots or less this
would be pulse activity. Otherwise...it is a waiting game for the
Ohio activity which continues to increase since 18z.
Tonight...bulk shear increases as the cold front approaches allowing
multi-cell clusters. Precipitable waters approaching 2in will allow for heavy
rain...so a flash flood threat exists for tonight. Clouds and southerly
flow keep min temperatures up...generally low to middle 70s.
Short term /6 am Monday morning through Tuesday/...
Monday and Tuesday...secondary lobe of deep low north of the Great
Lakes swings down into the Great Lakes Monday...amplifying the
trough over the Midwest states into Tuesday. Meanwhile the stalled
front will be the focus of development for over 24 hours. There should
be a diurnal Ebb and flow of activity with Monday evening (across
the cwa) and Tuesday afternoon/evening (east of the blue ridge)
being the most high impact times. Slight risk for Monday. Low level
shear profiles still look too weak to provide a tornado threat.
Heavy rain and damaging winds are the main threats. Storm Prediction Center day 2 update
does mention the potential for surface low development along the front.
This would provide at least some tornado threat...so that threat
will need to be followed by subsequent forecast shifts.
Above normal temperatures persist through Tuesday ahead of the cold
Long term /Tuesday night through Sunday/...
high pressure will usher in stable air Wednesday into Wednesday
night. There is a chance that a shower or perhaps a rumble of
thunder will linger across parts of southern Maryland and the
Chesapeake Bay...mainly early Wednesday. Temperatures will be cooler
than normal for the middle of July. A pleasant night Wednesday night
with temperatures a few degrees below normal.
A few pop-up showers could develop Thursday into Thursday evening as
a weak piece of energy pivots across the region. Most of the
activity would develop in the Potomac Highlands and Shenandoah
Valley where it would become slightly less stable than the
metropolitan and Chesapeake Bay areas. Temperatures should remain
A stronger piece of upper level energy riding along the Ohio Valley
Friday into Friday night will bring a better chance of showers and
even a couple of thunderstorms anywhere across the region. The GFS
model wants to slow down the northeastward progress of this energy
Saturday and Saturday night. Both the Euro and GFS show this type of
active pattern Friday through Saturday night. We kept chance of
showers and thunderstorms Saturday and Saturday night as well.
Temperatures Friday should be slightly below normal or near normal.
If there is a large and persistent coverage of showers and
thunderstorms Saturday...then temperatures could remain below
normal. If showers and thunderstorms develop in lieu of daytime
heating later in the afternoon and evening...then temperatures could
turn out to be a few degrees above normal.
With one piece of energy following another Sunday...we left chances
of showers and thunderstorms for now. There appears to be no big
pattern change toward the latter part of next weekend.
Aviation /19z Sunday through Friday/...
VFR prevails into this evening ahead of thunderstorms along a cold
front approaching from the Midwest. IFR in heavy thunderstorms and rain. Otherwise southerly
flow 10-15kt. Thunderstorms on tap for Monday evening and Tuesday
afternoon/into the evening as the cold front stalls for
Monday...then pushes east Tuesday.
MVFR or IFR conditions are possible for mountain...BWI and perhaps dca
Wednesday with some shower or thunderstorm activity in the
vicinity...mainly early in the day. All other terminals should have
VFR conditions. Winds will be northwest Wednesday veering around to
the north later Wednesday less than 10 knots. Winds may be stronger
in showers or thunderstorms early Wednesday at the mountain...BWI and dca
MVFR or IFR conditions may occur at the cho or iad terminals due to
pop-up showers and thunderstorms possibly around Thursday.
Otherwise...VFR conditions elsewhere.
southerly flow 15-20 knots up the Maryland portion of the Bay and lower tidal
Potomac into late tonight...with Maryland waters south of Sandy Point in
an Small Craft Advisory into Monday morning. Gusts to around 22 knots. Southerly flow
generally 10-15kt Monday afternoon and night. However...gusty
thunderstorms and special marine warning are possible both Monday
and Tuesday. Cold front moves east from the waters Tuesday night.
No hazard marine conditions expected Wednesday through Thursday.
water levels have increased to three quarters of a foot above a full
moon normal this afternoon and may increase more as southerly flow
increases this evening. The preferred morning high tide Monday
should be more impactful than this morning's high tide that simply
reached the minor flooding threshold of 2.40 feet. Expect a coastal
Flood Advisory for Anne Arundel...Washington District of Columbia...and possibly
District of Columbia...none.
Marine...Small Craft Advisory until 2 am EDT Monday for anz530-531-539.
Small Craft Advisory until 10 am EDT Monday for anz532>534-540-
Small Craft Advisory until 10 am EDT Monday for anz537.