Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
350 am EDT Thursday may 7 2015
high pressure will build over the northern middle-Atlantic today.
Low pressure off the Carolina coast will approach the coastline
Friday before gradually eroding this weekend. A cold front looks
to move into the region Tuesday.
Near term /through tonight/...
latest surface analy depicts a broad region of hipres over the northestern quadrant of
the Continental U.S....while lopres resides S of the NC/SC brdr. The nearest
frontal boundary west of the MS river. Ridging also dominates the height pttn aloft.
Fortunately there is a fair amount of blowoff cloud from the coastal low.
Areas of fog have developed...especially where it rained last night. Suspect we
would be dealing with a lot more fog...include some dense fog...if it
werent for the clouds. Continued Ely winds keeping atmos mixed...and
dewpoints have dropped back into the 50s. Both of these items helping
as well. At this point...do not believe a dense fog advisory will be
ncsry...but will be monitoring in case one reqd.
Ridging will be the primary synoptic feature through the day into the evening.
That should keep the air mass east of the Appalachians rather stable. Guidance is bringing
cape up the rdgs /aplcns and central blurdg/. Combined with terrain
circulations...think there is a decent chance that isolate-scattered cnvctn will
develop in these areas taftn. Will be maintaining a dry forecast for the I-95
crrdr as well as north-centrl Maryland...but cumulus will be developing areawide.
Any rain showers/thunderstorms and rain should end upon sunset...as instability predicated on daytime
heating. Dewpoints dont drop much...so patchy fog once again will need to
be a consideration.
Temperatures still above climatology. No big outliers noted...and blended gndc
sources for temperature forecasts.
Short term /Friday through Friday night/...
County warning forecast area will be in the ridge axis again Friday...but that axis will begin to be
squeezed on both sides...from the coastal low and from instability spreading
northward ahead of a surface fnt. Still...there shudnt be much precipitation...and dry
probability of precipitation /10 percent/ dominate forecast.
There remains a little uncertainty as to how to hndl potl precipitation ahead of
tropical/subtropical low. At the very least...have incrsd cldcvr from S
to north Friday night. Will entertain a schc of a rain showers spreading north too...though
confidence on that quite low.
Maxt a cpl degf warmer than Thursday. Continuity maintained for min-T Friday
Long term /Saturday through Wednesday/...
an upper level ridge persists across the eastern Seaboard this
weekend while a surface low spins off the SC coast. S-southeast flow will
continue to usher in warm moist air across the region Saturday and
Sunday. This will continue the diurnal thunderstorm chances in the
afternoon Saturday and Sunday. The wind field is weak and therefore
any thunderstorms that form should be sub-severe.
By Monday morning...the surface low should move into NC as an upper
level trough to the west moves eastward. The surface low will pick up
speed and move near the mouth of the Chesapeake Monday night.
S winds will increase Monday and warm moist conditions will continue
with the chance of afternoon showers and thunderstorms. A cold
front should cross the region Tuesday. Depending on the timing of
the front...temperatures expected to be highest Tuesday M/u 80s. This
coupled with moisture and a Lee trough may produce slightly
stronger thunderstorms across the region Tuesday afternoon and
evening. Dry air moves into the region Wednesday and Thursday.
Aviation /08z Thursday through Monday/...
areas of fog have developed across the region. At this point..mrb/cho the only
two terminals affected. Visibility conds have been quite variable...fluctuating
between 1sm and 5sm. Have employed tempos to attempt to cover range of
psbltys. Tafs do not reflect any sub-IFR yet. Think may have to do
that before night is out. Elsewhere...dropped iad into MVFR due to
climatology/wet grnd from erlr precipitation. Kept dca/BWI at VFR.
Any morning fog will burn off by 13 UTC... +/- an hour. Expect diurnal clouds
to develop taftn...sct-bkn covering west/ bases near 4 or 5 kft. While chance of
precipitation not zero...think it should be confined in the hills/mountains and not
Anthr rnd of fog possible lt tonight into Friday morning. Will be assessing extent
of flgt restrictions shortly. Would think that restrictions limited to
the climatology preferred terminals. VFR will otherwise prevail through nightfall.
-Shra/-tsra possible in the afternoon Sat-tues. Coverage should
be isolated/scattered where a brief sub-VFR conditions is possible.
Ely flow less than 10 knots across the waters. Will be spending the next cpl
days under a ridge axis...so light winds will prevail. Ely flow should
become southerly Friday...but still at or below 10 knots.
S-southeast flow will continue Sat-sun as a surface low persists along the SC
coast. Showers and thunderstorms possible this weekend mainly in the
District of Columbia...none.