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fxus61 klwx 241903 

Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
303 PM EDT Wed may 24 2017

low pressure will approach the area tonight before passing
through Thursday. The cold front associated with the low will
move through Thursday night and high pressure will return for
later Friday into Friday night. The high will move offshore
Saturday and a warm front will stall over the region for later
Saturday through Sunday. A stronger cold front may pass through
the area Monday.


Near term /through tonight/...
cutoff low pressure continues to develop over the Ohio Valley
this afternoon. High pressure is moving off the New England
coast and an easterly flow has ushered in unusually cool
conditions for this time of year. Max temps will hold in the 60s
for most locations...with perhaps some areas across northern
Maryland reaching the lower 70s where there have been a few
breaks of sun.

The warm front associated with the low will move into the area
tonight. A strengthening low-level jet will cause moisture to
overrun the surface cooler air in place causing rain to
overspread the area from southwest to northeast this evening.
Increased frontogenetical forcing from the strengthening low-
level jet and shortwave energy rotating around the upper-level
enhance rainfall rates at times. Therefore...a soaking rain is
expected this evening into the overnight hours. The dry slot
will move in from south to north late tonight diminishing
rainfall rates. Since the dry slot is expected to move in
quickly late tonight...this will keep rainfall amounts down a
bit. However...widespread rainfall amounts around one inch are
expected. Localized rainfall amounts around 2 inches are
possible...especially along the eastern slopes of the Blue Ridge
mountains and Potomac Highlands. Despite stable air near the
surface...there still will be elevated instability so a few
rumbles of thunder are also possible. Severe weather is not
expected since thunderstorms will not be rooted within the
boundary layer. Localized flooding is a concern...especially
along the Blue Ridge mountains into the central Shenandoah
Valley where ffg values are lower due to rainfall from last
night. Still leaned against a watch for now thinking that
rainfall will be spaced out over 6 to 12 hours and the fast
moving dry slot will cause rainfall rates to diminish late
tonight. Min temps will be in the 50s for most locations.


Short term /Thursday through Friday night/...
the dry slot will cause rain to dissipate for a period Thursday
morning...but surface low pressure will build overhead Thursday.
The cutoff upper-level low will also move overhead Thursday. A
southerly flow ahead of the low will allow for moderate amounts
of instability. Popup showers and thunderstorms are expected to
develop later Thursday morning and afternoon. Thunderstorms may
contain gusty winds and hail due to colder air aloft associated
with the upper-level low.

The low pressure will move away from the area Thursday night and
the cold front associated with this system will pass through
Thursday evening before moving off to the east and northeast
Thursday night.

Low pressure will continue to move up the New England coast
Friday. Breezy conditions are expected behind the low. A popup
shower cannot be ruled out...but most of the time will be dry
seasonable. High pressure will briefly build overhead Friday


Long term /Saturday through Wednesday/...
brief dry period expected Saturday morning. An upper level
shortwave trough could increases pops Saturday afternoon into
the evening before a boundary settles near/over our County Warning Area Saturday
night into Sunday. A cold front then slowly moves across Sunday
night into Monday. Showers and thunderstorms possible during
this period. Conditions begins to dry out on Tuesday before
another -weaker- front approaches on Wednesday.

High temperatures will be in the 70s and low 80s... some 60s at
higher elevations.


Aviation /19z Wednesday through Monday/...
a soaking rain is expected to overspread the terminals this
evening. Cigs/vsbys will continue to deteriorate and IFR
conditions are expected this evening through late tonight.
Steady rain will end toward Thursday morning. Cigs/vsbys will
improve later Thursday...but popup showers and thunderstorms
are expected later Thursday morning into Thursday night.

VFR conditions are expected Friday and Friday night as high
pressure builds in from the west.

VFR conditions expected early on Saturday. Then sub-
VFR conditions return Saturday afternoon and into Monday with
rounds of showers and thunderstorms moving through our region
with a boundaries stalled/moving through our region.


an onshore flow will strengthen ahead of low pressure tonight. A
Small Craft Advisory is in effect for the waters. Low pressure
will move overhead Thursday and the gradient may weaken a bit.
However...low pressure and its associated cold front will move
away from the waters Thursday night. A Small Craft Advisory is
in effect for portions of the waters Thursday night and it will
likely be needed Friday into Friday night.

Dry conditions early on Saturday before periods of
showers and thunderstorms move through Saturday night into
Monday as front stalls and moves across our region. Winds will
be below the Small Craft Advisory threshold Saturday into Monday.


Tides/coastal flooding...
an onshore flow will strengthen tonight and tidal anomalies
will increase. The next high tide will be the higher of the two
and the lunar phase is at a new minor flooding is
likely during the high tide cycle later tonight into Thursday
morning. A coastal flood advisory is in effect for many
locations along the western shore of the Chesapeake Bay and the
upper tidal Potomac River.

The flow will weaken and turn to the south Thursday before
turning southwest Thursday night and eventually to the west and
northwest Friday. Significant blowout should not occur until
later minor tidal flooding is possible during the
high tide cycles Thursday through Thursday night.


Lwx watches/warnings/advisories...
District of Columbia...coastal flood advisory from 6 PM this evening to 11 am EDT
Thursday for dcz001.
Maryland...coastal flood advisory from midnight tonight to 8 am EDT
Thursday for mdz014-018.
Coastal flood advisory from 11 PM this evening to 6 am EDT
Thursday for mdz016-017.
Coastal flood advisory from 4 am to 10 am EDT Thursday for
Virginia...coastal flood advisory from 11 PM this evening to 6 am EDT
Thursday for vaz057.
Coastal flood advisory from 6 PM this evening to 11 am EDT
Thursday for vaz054.
Marine...Small Craft Advisory from 6 PM this evening to 9 am EDT
Thursday for anz530>534-537>543.
Small Craft Advisory from 6 PM Thursday to 6 am EDT Friday for
Small Craft Advisory from 6 PM this evening to 6 am EDT
Thursday for anz535-536.


near term...bjl
short term...bjl

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