Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
338 am EDT Monday may 4 2015
high pressure off the Carolina coast will settle offshore through
tonight. A cold front approaches late Tuesday...stalling across
the middle Atlantic through midweek. High pressure is expected to
return to the region late in the week while low pressure develops
off the Carolina coast.
Near term /until 6 PM this evening/...
surface high pressure currently off the Carolina coast will push
offshore today...settling to the east by tonight. As the region
remains on the western periphery of the high...S-SW flow will be
persistent. Warm air advection on this flow will result in a good warm up for the
area...with most of the area reaching the 80s...the exception
being the higher elevations of the Potomac Highlands.
All mesoscale models suggesting isolated precipitation development over the far
southwestern corner of the County Warning Area late in the day/during the
evening...with the suggestion of a surface trough extending across
eastern WV. Have inclusion of low end slight chance probability of precipitation to account for
any development that makes if over the ridge line. Anything that
does form will be very light in nature and short lived.
Short term /6 PM this evening through Tuesday night/...
any lingering precipitation this evening will quickly diminish with loss
of daytime heating. Dry weather then expected through most of the night.
Low pressure trekking through southern Canada will drag its
associated cold front close to the region tonight...with the front
straddling PA by 12z Tuesday. Will introduce probability of precipitation around daybreak
near the Mason-Dixon line of western Maryland to account for the fronts
placement as well as a weak shortwave/vorticity maximum expected to move
through Tuesday morning.
The cold front nudges south during the day...eventually stalling
just south of the Mason-Dixon line through Tuesday night. Near zonal flow
sets up aloft...so expecting any precipitation development Tuesday to be
confined near the frontal boundary with the best surface convergence.
Have chance probability of precipitation in over northern areas...tapering off to the
south...with potential for some areas of the Piedmont to remain dry
through the period. With highs pushing into the 80s yet again...and SW
flow injecting in more moist air...minimal instability is possible.
Shear and lapse rates are on the weaker side...but enough with the
instability to trigger an isolated thunderstorm. So will have thunder mention for
Tuesday afternoon. With the loss of daytime heating...will keep thunder
mention out for Tuesday night. Probability of precipitation decrease second half of Tuesday
Long term /Wednesday through Sunday/...
cold front will continue to sag into and perhaps through County warning forecast area Wednesday...which will
provide southern counties with a better chance at seeing precipitation. However...the fnt
will be bumping into the 500 mb ridge...so not only will southern progress be slow
but also suspect there will be a weakening trend. Therefore will not be
going west/ probability of precipitation higher than chance. Such a baroclinic zone in a Summer air mass
will yield a little instability...but that will be undercut by Ely surface flow. Am
keeping schc thunder in grids but do not believe any storms will be a
really big deal. Tapered maxt back a pinch due to the maritime
influence... but timing of not just the fnt but also the winds and
any precipitation will unlimately determine the maxt outcome.
Fnt looks to wash out Thursday...W/ ridging maintaining its influence through
Sat. Dry forecast. Temperatures on the warm side...and reflects addtl warming
daily. There will be more clouds on Thursday due to residual moisture...but will be
ptsun at worst for central Virginia/southern Maryland. Otherwise...mosun-sunny through the
period. Next fnt may arrive by Sunday.
Aviation /08z Monday through Friday/...
VFR conditions for the taf period. Occasional gusts possible this
afternoon...mainly kiad/kbwi/kmtn...though staying generally less than
20 kts. Southerly flow will become SW-west by Tuesday morning.
Any precipitation today/tonight should remain well west of the taf sites.
Incrsg chance of showers and maybe an isolated thunderstorm on Tuesday...mainly aftr
18z for all sites except kcho.
Local flgt restrictions possible in vicinity of rain showers Wednesday...otherwise VFR through the end of
sub-Small Craft Advisory conditions initially this morning. Incrsg southerly flow today
should result in enough of a tunneling effect to produce gusts to
20 kts for the Chesapeake Bay and lower tidal Potomac waters. Small Craft Advisory
in effect for these zones beginning this afternoon to account for this.
For tonight...winds expected to diminish to sub-Small Craft Advisory over the
northern Chesapeake Bay...and then the lower tidal Potomac by
tomorrow morning. Will continue Small Craft Advisory for the middle Chesapeake zone
through Tuesday morning...with possible extension into Tuesday if winds are
slow to shift to a west component. Sub-Small Craft Advisory conditions all waters
for Tuesday night.
Ely flow bhd a cold front dropping slowly southward Wednesday. May have a breif surge
in wind spds...but mixing shudnt be that great. Will be capping winds
at 15 knots. After that...winds will be on the lighter side once again
/aob 10 knots/ under a ridge axis.
one of the warmest airmasses so far this year is expected
to move over the area during the first half of the upcoming week.
Below is a list of the last time a high temperature of 85 degrees or
higher was observed.
Site..last 85+ degree day...
dca...September 27th 2014...
BWI...September 11th 2014...
iad...September 11th 2014...
cho...September 21st 2014...
dmh...September 11th 2014...
hgr...September 6th 2014....
mrb...September 21st 2014...
District of Columbia...none.
Marine...Small Craft Advisory from 4 PM this afternoon to 6 am EDT
Tuesday for anz531>534-537-540-541-543.