Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
357 am EDT Monday Jul 14 2014
Bermuda high pressure will keep very warm and humid conditions
across the middle-Atlantic into Tuesday. A cold front will cross the
area Tuesday night. Canadian high pressure will build across the
eastern states Wednesday through Thursday night.
Near term /through tonight/...
zone of convergence/lift from central West Virginia northeast
through northern Maryland continues to maintain scattered
showers/isolated thunderstorms overnight. While there is no severe
risk for the remainder of the night it looks like this general area
will continue to experience episodes of light to moderate rainfall.
Hrrr and lwx wfr-arw suggest there may be somewhat less coverage by
daybreak...but given radar trends will continue with high chance to
likely probability of precipitation in this area through then...transitioning to no mention
of weather further south into the central Virginia Piedmont/lower southern
Synoptically...the frontal boundary that will eventually move across
the County Warning Area late Tuesday into Tuesday night still resides over the Great
Lakes. A Lee trough exists over the County Warning Area...and this will be in place
today/tonight and couple with a middle-level vorticity maximum to produce
numerous showers and thunderstorms.
Models continue to advertise a very moist environment...with
dewpoints within a couple degrees of 70 degrees and precipitable
water values around 2 inches. This combined with occasional morning
breaks in the clouds should contribute to 1k-2k j/kg of cape by
afternoon. At the same time...NAM suggests 0-6 km shear increases to
or above 30 knots thus providing the expectation for organized strong
to severe convection /multicells and line segments/. Primary risk
will be damaging winds however later in the afternoon isolated
tornadoes can/T be ruled out.
In addition to the severe risk...high precipitable water values
raise the concern for heavy rainfall and flash flooding. At this
time...expectation is for convection to acquire sufficient eastward
storm motion where flash flooding would be localized and found
within areas of lower flash flood guidance and/or areas that
experience localized training. Severe weather potential statement will continue to mention these
Organized convection/severe risk should diminish/move out of the County Warning Area
this evening...but generalized broad lift continues across the County Warning Area
so will continue with chance probability of precipitation through the overnight.
Used a blend of bias corrected srefs/adjmav for maxima and bias
corrected srefs/adjmet for minima.
Short term /Tuesday through Tuesday night/...
moist/unstable environment persists over the County Warning Area on Tuesday...with
an axis of high precipitable water/Theta-E air east of the Blue
Ridge. Some convection will likely be ongoing Tuesday morning...
increasing in coverage again for the afternoon as a cold front
approaches from the west and as heights lower in advance of an
approaching upper trough.
Severe weather /damaging wind gusts/ and flash flooding will again
be possible by afternoon...especially within the aforementioned axis
of moisture coinciding with the best instability /east of the Blue
Cold front starts to push eastward through the County Warning Area in the
evening...likely residing east of the Interstate 95 corridor by
daybreak Wednesday. Trend will be for lowering probability of precipitation from west to
east through the night as Post-frontal northwest winds begin to
bring drier air into the County Warning Area.
Long term /Wednesday through Sunday/...
may have a lingering clouds/a rain showers of two east of I-95 at the start of
Wednesday...but cooler and particularly drier air will be advecting eastward
throughout the day...which will coax unsettled conds toward the Delaware-Maryland-Virginia.
Anomalously sharp 500 mb low will pivot toward County warning forecast area Wednesday...and that could be a
concern in terms of either stalling cold front or providing steep enough
lapse rates to reinvirogate diurnal cumulus if not a pop-up rain showers. Will be
taking the optimistic rte at this time...banking on upper level energy keeping
fnt somewhat progressive and downslope flow to inhibit cloud growth.
It appears as though the trough axis itself will recede back into cnda
west/o crossing middle Atlantic...so wont be dropping temperatures tremendously.
Actually...raised Wednesday maxt by a cpl...but temperatures in the upper 70s-lower
80s /lwr-middle 70s in the mountains/ with dewpoints dropping through the 50s
isnt a common occurence.
Surface hipres will build bhd fnt...and will most directly affect County warning forecast area Wednesday night
through Thursday night. Mosun/mostly clear and dry weather throughout. Thursday maxt comparable to
Wednesday. Min-T both ngts in the 50s to lower 60s.
Friday into the weekend...shortwave energy ejects eastward from the center of the
Continental U.S. Toward the middle Atlantic. Exactly how that transpires will determine the
forecast outcome. However...need to include probability of precipitation in the forecast for the period. Will
hold back significant temperature increases...but that could hppn if a warm front can
actually make it through.
Aviation /08z Monday through Friday/...
zone of lift will continue to bring episodes of MVFR -shra to mrb
this morning. Southern fringe may sink far enough south for -shra to
affect the iad to BWI/mountain corridor by 12z...although high resolution
guidance also suggests less coverage by then. For the rest of the
day...expect Lee trough and moist/unstable atmosphere to instigate
numerous rain showers/thunderstorms and rain by afternoon...some with heavy rain/strong
winds. Convection should diminish in coverage after dark...but a few
showers will remain possible overnight.
Thunderstorms are likely again Tuesday afternoon/evening...then a
cold front moves through with a wind shift to the northwest /and
drying/ Tuesday night.
Wed-Thu...VFR under hipres.
Friday...should be VFR too...but there is an outside chance at a shra/tsra.
will continue with Small Craft Advisory up the Bay into early this morning...with
some spots gusting in the 18-20 knots range through then. Winds should
diminish below Small Craft Advisory thresholds thereafter...however strong gusty
winds may accompany thunderstorms this afternoon/evening and again
on Tuesday. Cold front is expected to approach the Chesapeake Bay
late Tuesday night.
Cooler and drier air overspreads waters Wednesday. However...guidance suggests
that winds wont exceed Small Craft Advisory criteria. Since theres a little uncertainty
as to whether cold front may get hung up near the waters...will keep gusts
capped at 15 knots.
Hipres crests over waters Thursday and mvs offshr Friday. Northwest winds lessen and
a cpl rounds of thunderstorms sun evening pushed a Little Water away from the western
shore of the Bay. While its only a matter of a few inches...thats
enough of a margin to suggest that high tide at Annapolis will come in
just under minor criteria. Water levels at or below a half-foot above astro
predictions at this time...and Hight ide shouldnt be a problem this morning.
Perhaps the only other site to watch is SW District of Columbia...but do not have the
confidence to issue advisories anywhere at this time.
District of Columbia...none.
Marine...Small Craft Advisory until 10 am EDT this morning for