Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
320 PM EDT Wednesday may 22 2013
Synopsis...
high pressure persisting over the Atlantic with warm and humid
conditions until a cold front Thursday night. An upper trough
will linger over the area Friday with high pressure building
through Saturday. A frontal boundary stalls out across the middle-
Atlantic Sunday night through early next week.
&&
Near term /through tonight/...
Hipres remains in the western Atlantic while lopres resides over the
Great Lakes. Southerly flow across Middle Atlantic States creating a warm unstable air mass.
Thunderstorms and rain developing along the wva aplchns...where dewpoints higher and temperatures
aloft a pinch cooler. Orographic uplift also assisting in thunderstorm
development. This initiation in line west/ what mesoscale guidance has
suggested. Now that the cap has been broken...there/S plenty of
instability to feed off of...but features for organization slightly
lacking. Still do need to monitor the upper ohvly where heights lower as
this area ripe for development. That poses a situation where these
storms may propagate into area. Am keeping a lineup where likely
probability of precipitation confined to the mountains and chance/schc along I-95. There is a
threat for locally damaging wind gusts and large hail in any
thunderstorms that do develop due to the high instability.
Convection will likely dissipate later this evening due to the loss
of daytime heating. However...an upper-level disturbance is expected
to pass through the region late tonight as the upper-level trough
continues to slide closer to our area. Plenty of moisture and
forcing from the upper-level disturbance may result in scattered
showers/T-storms toward morning. Raised aplchns to likely. Min temperatures
tonight will range from the 50s in the mountains to the lower and
middle 70s in downtown Washington/Baltimore.
&&
Short term /Thursday through Friday/...
heights continue to drop Thursday as cold front approaches. Although instability will be
lower...shear will be greater. There may be two rounds of weather...first
coming midday with the disturbance and ribbon of instability...and then
second nearer the cold front and diurnal heating. Have raised probability of precipitation into
the def range rather quickly...and holding it there throughout the day.
Cold front passage Thursday night. Will scale back probability of precipitation and transition from thunderstorms and rain to rain showers in
the evening. After frontal passage...only lingering rain showers will remain.
Friday...upper trough drifts east over the area with back edge of
clouds slow to come in the afternoon. Gusty northwesterly flow Friday
continues as high pressure builds through Saturday.
&&
Long term /Friday night through Wednesday/...
shortwave from Tennessee Valley on Sunday now looks to expand east across the
southern-central mid-Atlantic. Convergence along this boundary would
set off showers. Pattern is stalled into middle next week...so a
prolonged cloudy/rainy period is possible. This would result in
below normal temperatures.
&&
Aviation /18z Wednesday through Monday/...
showers and thunderstorms developing...but staying west of the terminals
at this time. Concerned that these storms may drift closer...especially for
cho/mrb. Have thunderstorms in the vicinity in all tafs for the evening due to instability present...
which may lead to addtl storms developing. Some of the thunderstorms
will be capable of producing gusty winds and large hail.
Will have a respite lt evening as diurnal component lost. However...another
disturbance will be moving in toward morning...leading to potentially
anthr round of thunderstorms. IFR conds possible in the heaviest activity.
Threat for storms continue until cold front passage Thursday night. Northwesterly flow with
gusts 25 to possibly 30 knots with middle level ceilings Friday. Northwesterly flow
continues through Saturday as high pressure builds.
&&
Marine...
high pressure will remain over the Atlantic Ocean through tonight. A
southerly flow will continue over the waters during this time. A
Small Craft Advisory remains in effect for portions of the waters
through tonight. Scattered showers and thunderstorms are possible
later this afternoon and evening. Any thunderstorms that do
develop will be capable of producing gusty winds and hail.
Southerly flow ahead of a late Thursday night cold front. Small Craft Advisory expanded
through Thursday. Expect an extension Thursday night for prefrontal
southerly flow...then northwesterly flow around 25 knots Friday through Saturday as
high pressure builds.
&&
Tides/coastal flooding...
a southerly flow will continue over the waters through Thursday
night...but the flow may remain just west of south. Tidal anomalies
will likely increase a little...but with the flow remaining west of
south the water levels should remain below thresholds for minor
coastal flooding. The closest water levels will come to minor
flooding thresholds will be during the high tide cycle late Wednesday
night and late Thursday night...the higher of the two high tides.
Tidal anomalies will decrease Friday behind a cold front.
&&
Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory from 9 PM this evening to 6 PM EDT
Thursday for anz530-531-539.
Small Craft Advisory from 9 am to 6 PM EDT Thursday for anz535-
538.
Small Craft Advisory until 6 PM EDT Thursday for anz532-536-
540-542.
Small Craft Advisory until 6 PM EDT Thursday for anz533-534-
537-541-543.
&&
$$
