Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
1000 PM EDT Wednesday Jul 29 2015
a cold front will cross the area late Thursday. High pressure will
build for the weekend and hold through early next week.
Near term /through Thursday/...
precipitation covering has been much spottier...and lighter...than this time
yesterday. Warm layer between h6-4 on 00z lwx radiosonde observation likely the reason why. Radar
trends seem to have been captured by the hrrr quite well. Storms east
of the blurdg have dsptd...W/ only a few cells in the ptmc
Highlands. If latest cycle output verifies...even this activity will
erode before midngt...W/ not much going on until new cells approach
the Appalachians predawn. Have adapted grids toward this direction...but have
held onto low probability of precipitation in the mountains that can be reevaluated.
Not nearly as much wet grnd as past cpl ngts. However a fair amount of
clear skies and dewpoints in the Lower-Middle 70s suggests there will once again
be potl for fog development. Have kept it patchy and not dense due to
reasons mentioned above...situated along/west of blurdg as well as
across northern Maryland.
Cold front currently moving through the Midwest will enter the forecast
area around 18z Thursday and should clear the forecast area by 03z Friday.
Front will be losing much of its punch but it appears there could
be a quick band of -shra/thunderstorms and rain right along or just behind the
Short term /Thursday night through Saturday/...
12z model suite has the cold front placed just southeast of the
County Warning Area by 12z Friday. Any lingering precipitation with the front should remain
to the south as the frontal boundary stalls and eventually
dissipates over the weekend. Surface high pressure builds in from the
west in the wake. The region will remain at the southern fringe of
broad closed low over Canada...with the shortwave energy rounding
the low remaining well to the north. As such...expecting dry weather
Friday and Friday night. 12z GFS suggesting light precipitation over northeastern
areas of the County Warning Area Sat afternoon with a shortwave just to the north. Will
keep things dry for now though during this time with lack of surface
forcing currently noted.
Quick shot of cold air advection in the wake of the front on Friday drop 850mb
temperatures to around 15 degrees celsius...resulting in highs generally in
the 80s. The cooler airmass will be short lived as the high builds
in...with 850mb temperatures rebounding back to near 20 degrees celsius by
Sat afternoon. Lows Friday near normal...with highs nearing 90 on
Saturday. Dew points in the 60s Sat should keep heat indices well below
Long term /Saturday night through Wednesday/...
quiet weather pattern for sun into Monday with high press dominating
conditions behind a cold front. The front lingers off the Delaware-Maryland-Virginia
coast as it weakens... therefore cannot rule out some showers to
the southeast and east of our County Warning Area. Shortwave trough could bring some afternoon
showers on Monday and Tuesday... but confidence with it is low at this time... so
have kept low probability of precipitation. Another front approaches on Wednesday increasing the
chance of showers and thunderstorms for this day. Temperatures will near normal
sun and gradually increasing into he low 90s for Wednesday.
Aviation /02z Thursday through Monday/...
VFR conds across the terminals at this time. Setup seems favorable for fog
development once again between midngt-dawn. However not as much wet grnd as
past ngts...which is countered by higher dewpoints/low level humidity.
Unsure exactly how these two factors will balance each other. Have
opted to keep prolonged MVFR conds overnight at mrb...IFR at cho
where rain showers was recvd...and only brief MVFR at sunrise iad/mtn. Do
not have high confidence at this time. Could see flgt conds worse than forecast
but was hesitant on offering up prolonged restrictions.
Flgt restrictions for the morning push will erode by middle morning. A cold front
will cross the terminals during the afternoon...affecting that push as
well. Scattered-numerous rain showers/thunderstorms and rain will be found along/ahead of the fnt. Think
there will be some diurnal strengthening...and am carrying thunderstorms in the vicinity for
District of Columbia/balt terminals as a result. Would not completely rule out impact
at cho/mrb but probability is less. In the event of a direct hit
brief at or below IFR can be anticipated. Timing/spatial uncertanties
preclude carrying any specific mention at this time. Wind shift near 18z at
mrb...spreading east to 21-22z dca/BWI.
VFR conditions Friday and Saturday. Winds generally 10 kts or
less...shifting from the northwest Friday to a westerly flow Sat.
southerly winds sustained 10-15 knots at this time. However...southerly channeling forecast tonight
over the Maryland Bay/lower ptmc. Marginal winds /maybe just shy of advisory/
forecast to continue through the day Thursday...especially ahead of cold front. Small Craft Advisory already in
place. Looks solid tonight...and do not have confidence to remove it
for tmrw at this juncture.
Brief period of Small Craft Advisory gusts early Friday morning on the Chesapeake
Bay...with all waters becoming sub-Small Craft Advisory by Friday after. Sub-Small Craft Advisory conditions
then lasting into the weekend.
water levels running about a half foot above astro normals this evening.
However...there is strong consensus amongst water level models that the
upcoming high tide will eclipse the minor flood threshold at
Annapolis...which has been supported by latest runs. Only a slight
increase in the current departure would be sufficient to bear this
out. Have opted to issue advisory for aa County. High tide at apam2
No other site in jeopardy at this time...although Baltimore City/County and
wasd2 will get awfully close. The Baltimore high tide runs between
6-8 am. At SW District of Columbia high tide is approx 730 am.
The PM tide will be the lower of the two astronomically. Northwest winds
thereafter suggest the upcoming tide will be the only one to watch
District of Columbia...none.
Maryland...coastal Flood Advisory from 2 am to 8 am EDT Thursday for
Marine...Small Craft Advisory until 7 PM EDT Thursday for anz530>534-