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Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
937 am EDT sun may 19 2013
a stationary boundary will remain south of the area through
tonight before lifting north of the area Monday. A weak middle-level
trough will move through Monday. High pressure builds over the
western Atlantic midweek...with southerly return flow providing
warm temperatures to the region. A cold front will approach from
the Great Lakes late this week.
Near term /through tonight/...
nearly stationary boundary along the coastal Virginia/North Carolina
border was snaking its way westward through the central Appalachians
and into the Ohio Valley. Meanwhile...high pressure was located
over the North Atlantic.
There hasnt been much change to synoptic features thus far today...and
really dont anticipate rapid change taftn. Morning lwx radiosonde observation stable and
satd below h9. While rnk sndg a little less stable...its not exactly
unstable either. Changed precipitation character to radz for the mrng/midday.
Radr presentation unimpressive...and have/will scale back probability of precipitation. Do
think that a few holes will develop in overcast...and that will aide in rain showers
development lt today. Maybe a thunderstorms and rain too...but that/S looking rather slim.
Think model cape/Li fields overdone.
For tonight...models are suggestive that the stationary front will
start to make its way north. Even if low level flow turns more to
the south...am not convinced that enough wind in the boundary layer
will be able to push the front this far to the north. Therefore
forecast reflects this boundary remaining south of the County Warning Area...keeping
low cloud cover over the County Warning Area. North of the boundary...lift enhanced
by a shortwave at 500 mb is likely to bring at least scattered
showers over the County Warning Area. Stayed close to bias corrected mav/met for
Short term /Monday through Wednesday/...
low level ridge will amplify over the western Atlantic during the first half
of the work week. Broad southerly return flow on the western periphery of the
high will keep whatever is left of the remnant surface warm front north
of the area during this time. South of this front...a warm and a
modestly humid airmass will be in place. Maximum temperatures in the 80s each
day although clouds may inhibit temperatures from reaching 80f in some
locations on Monday.
Both the 00z NAM/GFS forecast a middle-level shortwave trough that is
currently over the Tennessee Valley to slowly move wd through the middle-Atlantic
region on Monday. Lift/moisture ahead of the trough in conjunction with
daytime heating will support diurnal convection over the County Warning Area. Probability of precipitation
highest toward central Virginia/southern Maryland but still in chance range.
Middle-level ridge builds overhead Tuesday and Wednesday after the shortwave
trough exits the area. Coverage of showers and storms will be low
Tuesday and Wednesday due to an absence of organized lift and a
strengthening subsidence inversion. Kept forecast dry for most of the
I-95 corridor and chesepeake Bay as weak steering flow will limit how
far east convection propagates once initiated over the mts.
Long term /Wednesday night through Saturday/...
shortwave trough and associated cold front will approach from the
Great Lakes/Midwest regions Wednesday night and Thursday before passing through
the area on Friday. Chances for showers and storms will accordingly
increase late in the week and will be highest with frontal passage. Above
normal temperatures ahead of the cold front will trend much cooler in
wake of frontal passage Friday into the weekend.
Aviation /14z Sunday through Thursday/...
with moist onshore flow in place...confidence is high in the
presence of IFR/LIFR flight restrictions through this morning.
Confidence lowers to moderate regarding the ending time of these
flight restrictions. Have favored lamp guidance on keeping IFR until
17-18z. Despite high sun angle...these conditions could linger
longer given easterly flow. Any improvement that occurs later this
afternoon is expected to be brief as a stalled frontal boundary is
forecast to remain to the south of the area tonight. Even if
easterly flow becomes more south-southeast...a degradation to
IFR/LIFR conditions is expected overnight per guidance. The only taf
site with the inclusion of thunder in the grids is cho...rest of the
sites are expected to be too stable for thunder and only rain showers was
mentioned in tafs.
IFR conditions likely to start the day Monday before morning stratus/
fog mix out from west to east. Predominately VFR conditions expected Monday
afternoon although brief restrictions in rain showers/thunderstorms and rain are possible.
Diurnal fog/low clouds possible at night and early in the morning each
day in the midweek. Chances for rain showers/thunderstorms and rain will be low during this
easterly flow starts to become southeast later this afternoon and
evening. Models forecast winds to increase...and southeast winds
tend to be enhanced over the lower tidal Potomac River and up the
Bay. Small Craft Advisory in effect this afternoon/evening for these areas. Its
possible that the Small Craft Advisory could need to be extended into the overnight
for some of these areas.
Light southerly flow early in the week will strengthen later in the week. Small Craft Advisory
conditions possible by Thursday...when a cold front approaches from the
departures have decreased to a half foot or less. If these
anomalies remain the same...no flooding should occur with the
upcoming high tide cycle. However...as winds turn more to the
southeast and then south...departures may increase Monday
increasing the risk for minor tidal flooding at sensitive
Water levels should tick upward early next week with southerly flow
persisting and a waxing gibbous moon. This far out...still some
uncertainty if positive anomalies increase enough to reach minor
District of Columbia...none.
Marine...Small Craft Advisory from 6 PM this evening to midnight EDT
tonight for anz531-532-539-540.
Small Craft Advisory from 3 PM this afternoon to midnight EDT
tonight for anz533-534-537-541-543.
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