Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
311 PM EDT Sat may 30 2015
high pressure will persist offshore through tonight with warm and
humid conditions in the mid-Atlantic. A cold front will enter
the region late Sunday and stall over the region into Tuesday.
High pressure is expected to slide into the region for the middle
and latter portions of next week.
Near term /through Sunday/...
persistent ridge of high pressure remains off the coast this
afternoon. Several shortwave troughs are evident in WV imagery over
the MS and Ohio Valley...while more organized frontal system over
Ontario. This system will play a role in our weather the next
several days as it suppresses the ridge.
There is also a small impulse around the back side of the ridge into
wva...which combined with daytime instability and terrain has produced a
broken line of convection. The main impact with these will be
locally heavy rain in an environment of 1.5 inch precipitable waters . However
stronger cells could produce isolated damaging wind gusts and small
hail...with middle level lapse rates being the limiting factor. Per
mesoa...higher cape values over the northern shen valley...so some storms
may pulse up. Have also seen some very small showers along the Blue
Ridge. Not out of the question a couple of these could sneak east
late this afternoon.
Frontal zone associated with northern stream system slips into
southern Great Lakes tonight...but will be held up by ridge and wave
of low pressure over Ohio Valley. Convection should generally taper
off after sunset...but a few showers may sneak down toward the M-d
line late tonight. With high dew points...min temperature will once again
be relegated to 60s-a70.
With continued slower frontal progression...much of the favorable
forcing will remain north of the area through much of the day and
the area remains firmly in the warm sector. Probability of precipitation have been trimmed a
bit further in space and time. In fact Sunday may not look too much
differently than today...although there may be a little better
coverage of storms in the northwest County Warning Area as heights lower. A lot of the southeast
County Warning Area may escape most of the day dry. Deep layer shear may increase a
little with the middle level disturbances to our north...but still
looks to be on the weak end of the spectrum. Storm Prediction Center has placed much of
the area under a marginal risk of severe weather. With little change to
atmos moisture...locally heavy rain will also be possible. Temperatures
will be able to warm into the 80s across much of the area.
Short term /Sunday night through Monday night/...
with better forcing in place to our north...convection may persist
longer into Sunday night. Some implications that there is a higher
chance of storms moving across northern Maryland overnight and have
adjusted probability of precipitation up accordingly. No longer looks like there will be any
cold air advection through Sunday night...so lows will again be in the 60s-a70.
A cold front will remain stalled out to our north over
Pennsylvania while an upper-level ridge continues to slowly side
farther south and east away from the area. A southerly flow ahead
of the front will continue to usher in warm and very humid
conditions during this time. The heat and humidity will lead to
more showers and thunderstorms. Convection coverage should be
widespread due to moderate amounts of instability...little to no
inversion...and a surface trough acting as a lifting mechanism.
Shear profiles remain marginal...but with moderate amounts of
instability a few thunderstorms may be capable of becoming severe.
Thunderstorms will also contain heavy rainfall and localized flash
flooding cannot be ruled out. The best chance for the stronger
storms will be Monday afternoon and evening.
Long term /Tuesday through Saturday/...
cold front will be slow to sag south of the area...and stalls near
the region during the middle part of the week. Expecting possibly
another flare up of showers and a few thunderstorms Tuesday
afternoon...mainly across central Virginia/southern Maryland. Somewhat cooler
airmass filters into the region behind the front...but guidance has
really backed off on anomalously cooler air...so at this time
expect temperatures to be near normal during the middle of the week.
Warmer and more humid conditions return by the end of the week as
southerly flow gradually takes over again. Chance for showers and
possibly thunderstorms increases again as well...and several
ensemble members of both ec and gefs have an area of low pressure
drifting up the coast by next weekend which could further enhance
rain chances depending on track/evolution.
Aviation /18z Saturday through Thursday/...
overall VFR conditions through this evening with scattered-broken cumulus around 5
kft. Scattered-numerous thunderstorms develop over the western mountains.
Will amend mrb as timing and impacts become more evident...but will
otherwise carry broad brushed thunderstorms in the vicinity. Other terminals have very slim
chance of storm so will not carry mention. Southerly flow 10-15 knots.
Some fog may develop late tonight again with cho and mrb favored.
Have limited to MVFR for now. Mrb may have a better chance of
dropping lower...especially if they get a decent amount of rain.
Slower frontal timing means Sunday may not be too dissimilar to
today. Mrb will have the highest chance of afternoon
storms...difference being that these could eventually spread into
the metropolitan tafs during the evening. Questions remain how much linger
overnight. Winds remain S or SW.
Showers and thunderstorms are expected Monday and Monday night.
Convection will be most widespread during the afternoon and
evening. Thunderstorms may contain gusty winds and heavy rainfall
that reduces ceilings/visibilities briefly to IFR levels.
Northerly flow at or below 10 knots...sub-VFR possible in -shra Tuesday. Northeasterly 10
knots Tuesday night-Wednesday west/ VFR expected.
southerly flow over the waters with offshore high pressure. Small Craft Advisory
conditions occurring over the Bay and are expected to continue
through this evening. Once mixing increases Sunday...a similar
situation is expected to unfold. Have therefore extended Small Craft Advisory through
Sunday evening. Possible this may need to be extended a bit further.
A little better chance of thunderstorms Sunday vs this afternoon.
Northern portions of the Bay would be favored toward Sunday evening.
An smw not out of the question.
A southerly flow will continue Monday through Monday night ahead
of a cold front that will be located to the north. A Small Craft
Advisory may be needed for portions of the waters during this
time. Showers and thunderstorms are expected...with the most
widespread coverage during the afternoon and evening hours. Gusty
winds are possible in thunderstorms...and locally heavy rainfall
may reduce visibilities briefly below one mile at times.
Small Craft Advisory gusts possible in northerly flow into Tuesday...then subsides Tuesday PM-
District of Columbia...none.
Marine...Small Craft Advisory until 2 am EDT Sunday for anz530>534-
Small Craft Advisory from 2 PM Sunday to 2 am EDT Monday for