Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
904 PM EDT sun Jul 5 2015
a stationary front will remain to the south through tonight before
lifting north as a warm front Monday. A weak cold front will
approach the region Wednesday...then linger over our area through
Near term /through Monday night/...
an upper level low is located over Kentucky with an embedded shortwave
trough entering WV. A stationary front is draped across the NC/Virginia
border this evening. Showers and thunderstorms have been ongoing
across southern Virginia this afternoon and early evening in vicinity of
the front and upper low. The steering flow is weak and oriented
S-swto north-NE and activity is slow moving. The middle- Atlantic is
starting to see activity move into the central foothills and
Piedmont this evening. Very heavy rain is expected overnight as
precipitable waters range from 1.5-2.0 across Virginia. Expect this trend to continue
as the shortwave trough apporaches tonight. Heavy showers with
isolated thunderstorms will spread the region by Monday morning.
At this time...Flash Flood Watch continues across Highland and
Pendleton counties where ffg is low. Further east and near the
central foothills...localized flooding is possible as multiple
rounds of showers begin to move into the area. Coverage will be
weak and therefore no Flash Flood Watch extension was done. Around 1 inch
is expected in heavy showers with the potential of 2 inches in
areas that see training this evening.
the stationary front will eventually begin
to lift north as a warm front tonight...eventually pushing north
of the area by Monday night. Thinking the front will provide the
needed forcing to trigger showers east of the Blue Ridge as the
shortwave energy looks to stay more to the west. As such...have
higher probability of precipitation west first half of the night...then pushing east
second half of the night. Some question as to how long the precipitation
lingers in the morning...though general idea would be some
clearing Monday morning before the next round of convection then Monday
afternoon as the warm front lifts through and the next shortwave moves
through. This shortwave looks to be further east...so the threat
of of thunderstorms encompasses the entire area Monday aftn/evening. Severe
threat looks to be more marginal as instability is currently
limited. However...if we can scatter out more in the
morning...could see better instability. Shear is stronger on
Monday...though still not completely selling on severe. Backing winds
with the warm front could hint at possible tornados threat...but still on
the low end. Will highlight that heavy rain will be a threat again
Monday afternoon as precipitable waters stay well above normal...especially over eastern areas.
Precipitation will slowly taper off Monday night as the front clears to the
Short term /Tuesday through Wednesday night/...
middle/upper level low starts pulling away from our area Tuesday
morning...as it is sheared apart...and is ingested into main belt of
westerlies associated with the northern stream. Most of Tuesday appears
to be relatively dry under subsidence from departing low and little
in the way of lifting mechanisms in the area. Although...cannot
entirely rule out an isolated afternoon thunderstorm with surface heating combined
with mesoscale features (subtle boundaries...terrain)...though at this time
chances appear very low. Guidance has been trending higher with
temperatures...likely due to more insolation...so nudged them up a bit with
temperatures in the u80s across the region. Light southwesterly winds usher in some
drier air...which keep heat indices in l90s.
Weak cold front approaches the region Wednesday. Increased probability of precipitation somewhat
in the afternoon...as quantitative precipitation forecast signal is becoming more consistent. Deep layer
flow remains rather weak through the period and instability is also
rather limited...so expecting most activity to be unorganized. Temperatures
increase slightly under continued airmass modification...but should
only be a few degrees above climatology norms.
Long term /Thursday through Sunday/...
cold front moves over the County Warning Area Wednesday night and lingers through the
weekend. Instability from this system will allow for the risk of
isolated/scattered showers and/or thunderstorms each day. Temperatures will be
near normal for this time of the year.
Aviation /01z Monday through Friday/...
VFR/MVFR conditions expected this evening before becoming MVFR/IFR
by Monday morning. Rain showers will move into the terminals from S to north
impacting cho already. Visibilities may drop to IFR/sub-IFR in rain showers/thunderstorms and rain but
main impact will be low ceilings into Monday morning. Isolated ts
expected tonight and confidence is low to put in tafs.
VFR conditions return Monday morning as the precipitation tapers off. Another
round of showers and thunderstorms likely Monday afternoon which once again will
result in sub-VFR conditions.
Winds generally 10 kts or less from the southeast through Monday. Any thunderstorm
could produce sporadic gusts up to 40 kts.
Expect VFR conds Tuesday...as middle/upper low departs our area and we are
in region of subsidence. At this time very low chance for afternoon thunderstorm Tuesday with
localized sub-VFR conds if they occur. Better chances for
shwrs/tstms...and localized sub-VFR conds on Wednesday as cold front
approaches the region.
VFR conditions expected for
Wednesday night and Thursday. Sub-VFR conditions possible due to showers and/or
sub-Small Craft Advisory conditions on all waters through Monday morning. Have issued a
Small Craft Advisory for the lower tidal Potomac and Chesapeake Bay Monday afternoon and
evening for increasing southerly flow resulting in gusts up to 20 kts. Sub-
Small Craft Advisory conditions return for all waters Monday night.
Winds expected to subside Tuesday morning as pressure gradient relaxes
and region is under subsidence from departing low. Winds expected to
remain below Small Craft Advisory criteria through Wednesday...though mariners should watch
out for thunderstorm chances Wednesday afternoon.
Sub-Small Craft Advisory conditions expected for Wednesday night and Thursday. Possible showers
and thunderstorms across the waters during this period.
District of Columbia...none.
Virginia...Flash Flood Watch until 6 am EDT Monday for vaz503-504.
WV...Flash Flood Watch until 6 am EDT Monday for wvz505-506.
Marine...Small Craft Advisory from 2 PM Monday to 2 am EDT Tuesday for