Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...updated 
National Weather Service Baltimore Maryland/Washington District of Columbia
442 am EDT sun Apr 19 2015

high pressure centered over Ontario will track toward the East
Coast today. Low pressure developing in the Gulf of Mexico will
track northeast into the middle Atlantic tonight. A cold front will
move through the area late Monday. An upper low brings cooler than
normal temperatures to the northeastern states for the middle and
late portion of the week.


Near term /through tonight/...
surface high pressure centered over Ontario early this morning. A
backdoor front is slipping through the area...with the most
noticeable marker being a wind shift to the N/NE.

The high will move off to the east today as middle/upper level
troughing digs into the nation/S middle section and a surface low takes
shape over the middle MS valley. Moisture will begin to overrun the dry
airmass currently in place. Expect rain to approach central Virginia by
the midday hours. This will probably be light initially as the
airmass saturates.

As the low deepens into the Great Lakes...a
strong southeast low level jet will develop by this evening...transporting
copious moisture into the region. Precipitable waters will climb to near maximum
climatology values for this time of year (upwards of 1.5 inches) and warm
cloud depths are forecast to at or above 3 km...especially east of the Blue
Ridge. Combined with the upslope component...expect highest rain
totals approaching 2 inches to be focused near the central Blue
Ridge. Will be raising a Flood Watch in this area as 6 hour ffg is
around 1.5 inches in spots. However the entire area will get a good
soaking rain as the warm frontal band lifts through tonight...with
many spots topping an inch. Will allow the dayshift to assess the
need to expand the watch...with the most likely candidates being
into the urban areas. However...would expect ponding of water would
be the main concern.

Increasing clouds today limit temperatures to the upper 50s/lower 60s.
Temperatures hold steady or perhaps rise a little in eastern areas tonight
with the rain. Lows in the 50s.


Short term /Monday through Monday night/...
after the warm frontal band passes early Monday morning...there may
be a fairly prolonged break into the midday hours as the area
becomes warm sectored...and there may be a cap in place as well.
Temperatures will warm into the 70s...and fairly good agreement on
60s dew points especially east of Blue Ridge. Decent probs of
MUCAPE greater than 1000 j/kg and deep layer shear at or above 30 knots. Hi-
res guidance suggest storms first fire along the mountains near a
pre- frontal trough...with additional storms along the cold front
to the west. Storm Prediction Center has highlighted most of the area for a slight
risk of severe storms. Unidirectional winds suggest potential for
linear features. Given some middle level drying and steep low level lapse
rates...think damage winds will be more likely than large hail.

Cold front sweeps offshore overnight...bringing an end to any
showers and thunderstorms from west to east...likely by around
midnight. Slight chance a few showers linger near the Bay into the
wee hours of the morning Tuesday. Otherwise...breezy and drier
overnight behind the front.

Pressure surge behind the cold front could bring down strong gusty
winds near advisory levels especially over the ridgelines Monday


Long term /Tuesday through Saturday/...
a large and deep upper-level low pressure system will dive out of
Canada and set up shop across the northeastern Continental U.S. For much of
the middle and later part of the week. A reinforcing cold front
will move across the area Wednesday. Moisture may be somewhat
limited so kept probability of precipitation at chance for now. Seems like a scattered
shower/isolated thunderstorm day enhanced over terrain
areas...more isolated further east.

Behind this front will come a much cooler and drier during the
second half of the week. Temperatures will be around 10 degrees
below normal...with highs struggling to get out of the 50s Thursday
through next weekend.


Aviation /09z Sunday through Thursday/...
VFR conditions through most of the day with NE winds becoming
easterly. Rain will spread S to north this afternoon and evening...with
flight conditions deteriorating first at cho. As the rain spreads
through tonight...MDT to locally heavy rain is possible. IFR or
lower ceilings and IFR visibilities are likely. Conditions will improve Monday
morning as the rain exits and winds become southerly. Thunderstorms
will be possible Monday afternoon and evening ahead of an
approaching cold front. Strong wind gusts and brief ceiling/visibility
reductions possible.

Winds turn westerly behind cold front Monday night...10-20 knots west/
VFR likely by around midnight. Gusty Tuesday in continued westerly flow and
VFR. Southwesterly flow 10-15 knots Tuesday night-Wed...W/ sub-VFR possible in isolated
shower/tstm...highest probability n&w of Blue Ridge Wednesday PM. VFR Thursday
westerly flow 10 knots.


cold front has moved through the waters bringing north winds. Will leave
Small Craft Advisory in effect as a few higher gusts may reach the waters. After
daybreak expect east winds to increase...with Small Craft Advisory for all waters
through tonight. Winds shift to the S early Monday morning. Have
extended Small Craft Advisory for Bay/lower Potomac due to channeling.

Moderate to heavy rain tonight. Possible a few strong gusts mix
down. Break possible through early Monday afternoon...but then
thunderstorms possible with a chance of strong wind gusts and

Small Craft Advisory conditions likely in westerly surge Monday night into
Tuesday...with gale gusts possible during this time. Small Craft Advisory gusts
possible again Wednesday ahead of a secondary cold front.


Tides/coastal flooding...
easterly flow increases today...then southeasterly tonight. Water levels
will increase across the Bay...particularly tonight. Minor
coastal flooding is possible by the high tides early Monday.


Saturday was the warmest day of 2015 so far at our
three major climate sites.

Washington District of Columbia /Reagan National Airport...dca/ had a high temperature
of 84 degrees...the warmest reading since September 27 2014 when the
high temperature was 85.

Baltimore Maryland /Baltimore-Washington thurgood Marshall international
Airport...BWI/ had a high temperature of 80 degrees...the warmest
reading and first 80-degree day since October 28 2014 when the high
temperature was also 80.

Dulles international Airport /iad/ had a high temperature of 80
degrees...the warmest reading and first 80-degree day since October
28 2014 when the high temperature was 82 degrees.


audio degradation at the National oceanic and atmospheric administration weather radio Charlottesville
transmitter is expected to continue through this weekend.
Technicians are scheduled to perform maintenance at the
transmitter site Monday.


Lwx watches/warnings/advisories...
District of Columbia...none.
Virginia...Flood Watch from 2 PM EDT this afternoon through late tonight
for vaz025-026-029-036>040-507-508.
Marine...Small Craft Advisory until 6 PM EDT Monday for anz530>534-
Small Craft Advisory from 8 am this morning to 8 am EDT Monday
for anz535.
Small Craft Advisory until 8 am EDT Monday for anz536.


long term...dfh

National Weather Service Glossary of Abbreviations