Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
810 PM EDT Sat may 18 2013
Synopsis...
a warm front over the central Appalachians and southern middle-Atlantic
will drift north across the area through Sunday night as surface
high pressure build off the northern middle-Atlantic coast. High
pressure will build into the region during midweek.
&&
Near term /through Sunday/...
blocked pattern this weekend with an upper trough drifting east to the
northern Great Plains and an amplifying trough over the Canadian
Maritimes and a ridge in between over the Midwest. At the surface...high
pressure continues to build off the northern middle-Atlantic coast with the
stalled boundary drifting north as a warm front over southern Virginia.
Onshore flow will persist in the middle Atlantic through Sunday
night. Rain/dz will spread northeast across the balt- wash metropolitan
late this evening/overnight as moist southerly low level flow expands across
the County Warning Area. Min temperatures in the upper 50s to low 60s.
Sunday is a wedge day with onshore flow...low clouds...and
widespread precipitation. Only flood threat is where northwest moving activity
stalls and repeats over the same area. This would most likely be
over the southwestern zones where thunderstorms are once again expected to
be limited to (far SW of dc). Went a couple degrees under
guidance to have maximum temperatures around 70f.
&&
Short term /Sunday night through Tuesday night/...
warm front will cross the area Sun night...bringing favorable moisture inflow and
good upglide. Should be a wet evening...but any instability should be limited
and elevated. Gnly stayed west/ rain showers instead of thunderstorms and rain.
500 mb East Coast ridging will be maintained Mon-Tue...which will keep the
quasistationary/warm front north of the County warning forecast area. Therefore the air mass across Maryland/Virginia will be warm
and at least marginally unstable. Since there will be a little middle-level positive vorticity advection
around and perhaps temperatures slightly cooler...areal covering of thunderstorms and rain should be a
bit better Monday vs Tuesday. However...both days trends should favor diurnally
driven cnvctn. Also added a pinch of an orographic component on the
Tuesday PM activity.
&&
Long term /Wednesday through Saturday/...
trough/cutoff 500 mb low in The Rockies will gradually migrate eastward for the 2nd
half of the weak...pushing a surface cold front into and eventually through County warning forecast area.
Thunderstorms and rain Wednesday will once again be diurnally-driven with a fair terrain-based
component. Maxt middle-upper 80s...but a few 90f readings not out of the
qstn.
Details on precipitation timing gets harder to distinguish Thu-Fri...although
frontal passage itself should be on/near Friday. Will need to see how subsequent runs
shake out. Fnt should be able to clear area before stalling out Sat...
but it/ll be awfully close and attaining an east-west orientation with respect to
middle-level flow. Gotta keep probability of precipitation going at this pt...but maxt will be back
into the 70s.
&&
Aviation /00z Sunday through Thursday/...
IFR ceilings spread northeast across the District of Columbia metros this evening as
coverage of showers...along with drizzle...increases. LIFR by late
tonight continuing into Sunday with little condition improvement
through tomorrow. East/southeast flow 5-10 knots. Any thunder chances look to be
this evening in vicinity of kcho and Sunday afternoon again by kcho.
Stability from the onshore flow is expected to keep thunder
southwest of the District of Columbia metros through the rest of the weekend.
Outlook...
flgt restrictions likely sun evening due to precipitation/residual moisture in vicinity of
warm front. At or below IFR quite possible...especially in vicinity of BWI/mtn.
VFR should prevail for a majority of the time Mon-Thu...with two
exceptions...
1...diurnally driven thunderstorms and rain will result in brief IFR restrictions
when/where they occur.
2...there may be patches of Ely morning MVFR due to fog.
&&
Marine...
Small Craft Advisory in effect for the lower ptmc and lower ches Bay overnight.
Southerly flow will prevail for most of the outlook period. Channeling will
result in Small Craft Advisory conds sun aftn-eve. Low level jet should continue beyond that...but am
having doubts whether it/ll make it to the Waters Edge. Similarly...
should have another southerly channeling event Monday night.
&&
Tides/coastal flooding...
departures remain half to 3/4 foot above astro prediction through
this evening. No flooding is expected. Flow slackens over night
through Sunday morning...so no increases are expected. Southerly flow
increases Sunday late afternoon...will have to watch that high
tide for possible minor inundation at sensitive sites...but as of
now no coastal flooding is anticipated.
&&
Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory from 6 PM Sunday to midnight EDT Sunday
night for anz531-532-539-540.
Small Craft Advisory until 10 PM EDT this evening for anz533-
534-536-537-543.
Small Craft Advisory from 3 PM Sunday to midnight EDT Sunday
night for anz533-534-537-541-543.
&&
$$
Update...Woody!
Prvs...bjl/hts
