Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
903 PM EDT Tuesday Sep 30 2014
low pressure over the Great Lakes will track east across the
middle Atlantic region tonight and Wednesday. High pressure will
return to the East Coast later Wednesday and remain in place until a
cold front approaches the area Friday. A cooler and drier airmass
will follow for the weekend and early next week.
Near term /through Wednesday/...
Shortwave ejecting from 500 mb low spinning over upper ohvly spreading rain showers and
a few thunderstorms and rain across County warning forecast area. The more vigorous thunderstorms and rain/higher rafl rates seem
to be in southern PA extending into Maryland. There was a hail threat erlr. Due
to lower sun angle and sunset prior to 7pm...heavy rain and wind gusts
15-25 miles per hour will mark the top end of activity. Hrrr has been doing a
decent job tracking activity...although prvs cpl runs may have been a
little bit slow. Latest run has accounted for this...and takes activity
east of County warning forecast area by/soon after midngt. Will adjust database accrdgly.
Bigger story overnight may be the potential for fog development.
PM rain showers/thunderstorms and rain will add to the low level moisture in place. The question
is whether clouds will part enough for radiation to take place. Infrared
satpix across wva casts some doubt on that. Will continue west/ the overall
concept of patchy fog aftr midngt and areas of fog pre-dawn.
/There should be some breaks in overcast./ However...have raised visibilities up a little. /Its
a bias of most guidance./ Am not at all confident on dense fog at this time.
Upper low will pull away to the north and east on Wednesday. Fog
and low clouds will mix out by late morning/midday with a few
afternoon showers possible especially over the high terrain.
Afternoon highs from the lower to middle 70s can be expected.
Short term /Wednesday night through Thursday night/...
high pressure to the north nosing into the region will keep an
easterly low-level wind fetch in place Wednesday night into
Thursday. This will result in more clouds than clear sky through the
period...especially east of the Blue Ridge mountains.
As the high pressure moves out into the northern Atlantic...mid- and
high-level clouds approaching from the west will lower and thicken
in advance of an approaching trough Thursday night. A couple of
showers preceding this trough could approach the western slopes by
daybreak Friday...but the bulk of precipitation is expected to hold
off until Friday afternoon and night.
Long term /Friday through Tuesday/...
a seasonably strong upper trough and cold front will move towards
the middle-Atlantic Friday. Widespread clouds will continue to lower
and thicken through the day...with a band of showers preceding the
front expecting to move across the area during the afternoon and
into the overnight. Most areas east of the Blue Ridge mountains
should remain predominantly dry during the day. Models are still
divergent on timing/strength of the trough which will determine
exactly who gets how much rain and when. Forcing with the trough is
strong but there is not much instability to work with...so while a
few rumbles of thunder cannot be ruled out the current thinking is
that widespread thunder is unlikely. Brief heavy downpours and
perhaps gusty winds in stronger/heavier bands of rain could be
realized especially if the trough ends up being on the stronger side.
Models are in better agreement by later Saturday after the front
moves through. A much cooler and drier airmass will move into the
region and stick around for the remainder of the weekend...with
temperatures falling to several degrees below normal...perhaps
isolated freezing temperature readings along the western ridges
Saturday night if winds slacken a tad quicker than guidance is
The next storm system approaches the area from the west early next
week but models are highly divergent on when it and its impacts
reach the area.
Aviation /01z Wednesday through Sunday/...
VFR conds across all terminals at this time. A line of rain showers/thunderstorms and rain aligned west/
blurdg at this time will track eastward across hubs through 03z. Stability marginal.
Suspect activity will weaken further as it approaches. Brief flgt
restrictions likely during its passage...mostly MVFR. Will attempt to
place 1 hour tempos in tafs shortly.
Low ceilings and fog a good bet overnight....mixing out by late
morning or midday Wednesday. Went a touch more optimistic thatn
prvs forecast cycle...but still have sub-IFR ceilings for morning push.
Ceiling and possible visibility restrictions late Wednesday night-Thursday am and again Thursday
night into Friday am with moist onshore flow portrayed in all the
guidance. Climatology is favorable for fog/stratus this time of the year
so that lends to moderate confidence. Showers/isolated thunderstorms in one or more
bands ahead of a cold front possible west/ gusty winds Friday-Friday night. VFR
Sat as winds turn out of the west or northwest.
winds are expected to remain below Small Craft Advisory criteria the remainder of
today through Thursday.
Solid Small Craft Advisory conditions looking increasingly likely late this week into
this weekend both ahead of /southerly flow/ and behind
/northwesterly flow/ a seasonably strong cold front. Winds/seas
gradually abate as the weekend progresses.
District of Columbia...none.