Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
915 PM EDT Tuesday Jul 7 2015
a cold front will slide southeast into the area tonight and
Wednesday. The front will stall in the area Wednesday night and a
low pressure will ride eastward along the front on Thursday. The
front will slide south of the area Friday and weaken. High pressure
will dominate over the weekend.
Near term /through Wednesday night/...
shortwave energy has supported thunderstorms and rain crossing wva and into the County warning forecast area. Air mass
ahead of line has sufficient instability...although that level diminishes
further east. /2000+ j/kg cape from rnk sndg but less than 1000
j/kg at iad./ Shear profiles not that great...plus diurnal heating
has been lost with the setting sun. Overall...expect thunderstorms and rain to be
non- severe...and weakening through the evening. Some gusty winds /30-40 knots/
possible next hour or two. Have bumped probability of precipitation upwd west of the blurdg once
already...and based on latest trends suspect I/ll be doing it yet
again. Rap runs suggest it may make it to District of Columbia...although latest rap less
emphatic than prvs cycles.
Cold front approaches the region Wednesday morning...with incrsg
coverage of precipitation out ahead of the system. As it seems to be with
cold fronts this Summer...the flow aloft becomes nearly
zonal...resulting in the front taking a more east- west position
than NE-SW. With this set up as well...the front will have minimal
progression to the south...with it stalling near the Mason-Dixon
Wednesday-Wednesday night. Instability looks to be marginal for most of the
day...but enough to warrant thunderstorms in the forecast. Overall
dynamics would keep any severe threat minimal.
Despite the cloud cover...high temperatures on Wednesday expected into the
upper 80s to lower 90s. Heat indices will remain below the century
Short term /Thursday through Friday night/...
wave of low pressure will ride along the front to our north on
Thursday. This will allow warm air to remain and highs may once
again reach the 90s across much of the area. Most of the upper level
energy with this wave appears to stay north of US...but suggest a
decent amount of shear and cape...so a stray severe thunderstorm
doesnt look impossible. As the low passes to the north the cold
front will slide southeast across our area Thursday
night...putting an end to the 90s for a day or two. Humidity will
also lower and the chance of showers and thunderstorms appears
pretty low on Friday...but did not completely remove them from the
forecast just yet in case future modeling is slower in dragging
the front through.
Long term /Saturday through Tuesday/...
cold front weakens and moves away from the region Friday night as a
high pressure builds in for Sat. Upper flow transitions to northwest into sun
as a frontal boundary lifts later that day. Upper level disturbances
affects the area Monday into Tuesday. Best chance for precipitation appears to
be sun through Tuesday. Temperatures will be close to normal.
Aviation /01z Wednesday through Sunday/...
generally VFR conditions through the night. Line of thunderstorms and rain crossing the
Appalachians at this time. Expect a bit of a weakening trend...but a few storms
likely will make it to the blurdg. Low confidence what will hppn
thereafter. Mrb nearest storms...and added MVFR tempo group to
taf. However...a break has developed in the line...and its possible that even
mrb may miss this activity. Am withholding any mention District of Columbia/balt
metros at this time since confidence too low. Worst case scenario would be
for brief at or below IFR west/ gusty winds 30-40 knots. Based on current
speed...extrapolation brings precipitation to mrb between 02-03z...cho/iad
between 03-04z...and elsewhere aftr 04z /assuming it survives/.
The better chance for precipitation impacting the terminals tomorrow. Could
see precipitation as early as 12z...but incrsg chance aftr 15/16z...lasting
through the afternoon...tapering off Wednesday evening. Sub-VFR conditions possible
in any storm.
Winds S-SW this afternoon 8-12 kts...becoming S 5 kts or less tonight.
Winds will increase again from the SW aftr 12z Wednesday...becoming
light/vrb Wednesday night as the front stalls over the region. Depending
on where the boundary aligns...could see sub-VFR conditions with
Main concern Thursday is potential for a gusty thunderstorm during
the afternoon and evening. Conditions should otherwise be VFR with
southwesterly winds becoming northwesterly on Friday.
VFR conditions expected for Friday night through the weekend.
sub-Small Craft Advisory conditions on the waters at this time. As the front nears
tonight...could see incrsg southerly flow...resulting in channeling on
the Chesapeake Bay. Will maintain the Small Craft Advisory for now...but will be
reevaluating it shortly. As the winds veer to the SW Wednesday...sub-
Small Craft Advisory conditions.
Low pressure passing to the north may bring some Small Craft Advisory-level winds to
the waters on Thursday. Winds appear to diminish by Friday afternoon
after the system has passed our area. Thunderstorms will also remain
a concern Thursday.
Sub-Small Craft Advisory conditions expected for Friday night and Sat.
District of Columbia...none.
Marine...Small Craft Advisory until 8 am EDT Wednesday for anz533-534-