Severe Thunderstorm Warning 46, NWS Baltimore/Washington

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
225 PM EDT MON MAY 23 2016

.SYNOPSIS...
Upper level low pressure system near Norfolk this
afternoon will move northeastward towards New England and the
Canadian Maritimes tonight and Tuesday. High pressure over the
Midwest today will then slide southeastward into the western
Atlantic on Tuesday, where it will remain through the rest of the
week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Closed upper level low remains stationed near Norfolk VA this
afternoon and will slowly lift northeastward through tonight. The
breaks of sun that formed today across northern VA, eastern WV,
and into MD have allowed for temperatures to rise into the upper
60s and low 70s. The warming, coupled with lingering low level
moisture, and cold temperatures aloft under the upper low have led to
the development of some instability (seeing ML CAPE values
between 300-800 J/KG), and in turn convective showers and a few
thunderstorms. Severe weather is not expected, but with low
freezing heights (7000-8000 feet AGL), could see some gusty winds
and small hail in any of the stronger storms.

Showers and a few thunderstorms will persist through the evening,
but will decrease in coverage and intensity after sunset. Will
also begin to see more clearing working into the region. This
combined with lingering low level moisture and wet soils will
lead to the development of some patchy fog across the area as
temperatures cool. There will be some wind remaining in the
boundary layer, so that and some lingering clouds should preclude
a more widespread dense fog situation. Will see lows in the 50s
for most, with some 40s north/west.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Upper low will continue pulling away on Tuesday, and we will see
drier air wrapping in behind it. This should lead to more sun than
today with some scattered instability cumulus and some cirrus.
Could also see an isolated instability shower or sprinkle, but
coverage will be spotty at best. Temperatures will be much warmer
than recent days with highs in the upper 70s to around 80 degrees.

Upper ridge builds into the region on Wednesday ushering in more
summer-like weather. The surface high will slide south of the
region, allowing for a warm southerly flow to develop. Wednesday
should remain dry for much of the region with highs in the 80s
area-wide. With dew points hovering in the 50s, should be quite
nice, with relatively low humidity. Not expecting much in the way
of shower/thunderstorm activity either, except for an isolated
one or two possible in the mountains as a weak ripple moves
through aloft.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Summer-like pattern begins Thursday, with Bermuda high promoting
warm/moist advection across the Mid-Atlantic. Increasing moisture
will lead to typical summertime diurnal thunderstorm activity
Thursday and Friday, with the best chances over the higher terrain
and fairly low chances east of the Blue Ridge. While instability
will be in the moderate range during peak heating, rather anemic
wind field keeps effective bulk shear generally less than 20 kts,
suggesting pulse-type thunderstorms. Highs Thursday and Friday
generally in the M/U80s, though a few 90s are possible, especially
in areas bereft of thunderstorm activity.

Mid-level heights begin to rise Saturday, which leads to poor
mid- level lapse rates. As such, guidance has really backed off on
QPF Saturday.

Model spread increases by Sunday, so will take a blended approach
for now until better agreement can be reached.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
VFR at most sites at most times through the rest of today and
into this evening. Have seen the development of scattered showers
and a few thunderstorms which may lead to brief reductions to
MVFR/IFR at times this afternoon and into the evening. Later
tonight, as showers end and skies begin to clear, may see the
development of some patchy fog and Sub-VFR conditions. Will show
with a 5-6SM and BR for now, as coverage and density is
questionable with amount of cloud cover and residual winds in the
boundary layer.

VFR returns Tuesday and should persist for most
through at least Wednesday night.

Winds will be light (less than 10 knots) and generally
west/northwesterly through tonight and into Tuesday. Some gusts up
to about 15 knots likely Tuesday afternoon. Light southwest flow
then develops by Wednesday.

While most of Thursday through Saturday will end up VFR, a few
afternoon thunderstorms are possible.

&&

.MARINE...
Winds locally variable and less than 10 knots this afternoon and
evening with scattered showers and few thunderstorms, which may
create some isolated gusts to 20 knots. Plan to cover with Marine
Weather Statements for now. Winds will increase out of the
west/northwest Tuesday around departing low, but should stay below
SCA criteria. Southwest winds then develop Wednesday, but should
also remain sub- SCA.

While flow remains sub-SCA, a low chance of an afternoon
thunderstorms exists over the waters Thursday and Friday.

&&

.TIDES/COASTAL FLOODING...
12Z ESTOFS indicates potential for minor coastal flooding at
Annapolis Tuesday morning. High tide there is at 746 AM. Big
discrepancy between ESTOFS and ETSS surge but ESTOFS initialized
much better.

&&

.CLIMATE...
We put together some records (preliminary) of how this month compares
to rainy Mays on record for our area.

Washington, DC (records since 1871)
Most days in May with at least a trace: 25 (in 1952
and 1943) So far in 2016 (through the 23rd): 19

Most days in May with at least 0.01": 20 (in 2003)
So far in 2016 (through the 23rd): 18

Highest May monthly rainfall: 10.69" (in 1953 and 1889)
So far in 2016 (through noon on the 23rd): 5.12"

Baltimore, MD (records since 1870)
Most days in May with at least a trace: 25 (in 2003)
So far in 2016 (through the 23rd): 19

Most days in May with at least 0.01": 21 (in 1882)
So far in 2016 (through the 23rd): 15

Highest May monthly rainfall: 8.71" (in 1989)
So far in 2016 (through noon on the 23rd): 4.48"

Dulles, VA
Most days in May with at least a trace: 23 (in 2003)
So far in 2016 (through the 23rd): 20

Most days in May with at least 0.01": 21 (in 2003)
So far in 2016 (through the 23rd): 16

Highest May monthly rainfall: 10.26" (in 2009 and 1988)
So far in 2016 (through noon on the 23rd): 5.62"

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

SYNOPSIS...MM
NEAR TERM...MM
SHORT TERM...MM
LONG TERM...MSE
AVIATION...MM/MSE
MARINE...MM/MSE
TIDES/COASTAL FLOODING...LFR
CLIMATE...DFH

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