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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
854 PM EDT Monday Oct 20 2014

a cold front will approach from the west tonight and move through
the region Tuesday. Low pressure will persist near the middle-
Atlantic coast into Thursday. High pressure will return for the
end of the workweek and into the weekend.


Near term /through Tuesday/...
a upper level trough will move across the Great Lakes and New
England tonight. Low pressure and an associated cold front will
approach the region tonight.

An area of vorticity advection is moving ahead of an advancing
shortwave trough this evening. Showers have moved across the
Potomac Highlands and Blue Ridge and will continue to move
eastward. These showers are moving into a dry airmass and only
hundredths are expected in places that recieve rain this evening.
A cold front across the Ohio Valley will also continue to move
eastward tonight. Showers are expected taper off overnight and
into Tuesday morning with the exception of The Highlands. Westerly
flow against the mountains will lead to enhanced lift and showers are expected
through Tuesday. Forecast min temperatures are in the 40s and near 50 in the

The cold front is expected to cross the region Tuesday as the
upper low moves over head. Cold air aloft will lead to steepening lapse
rates and therefore some instability. Added isolated thunderstorms to
areas east of the Blue Ridge Tuesday afternoon. Little wind field
will limit gusty winds Tuesday afternoon. Forecast maximum temperatures are in
the 60s Tuesday afternoon.


Short term /Tuesday night through Wednesday/...
upper level low pressure will remain occluded and strengthen near
the middle-Atlantic through the day Wednesday and Wednesday night. The
associated surface low will deepen due to baroclinic enhancement as
it moves over relatively warm ocean waters off of the middle-Atlantic
coast during this time. Probability of precipitation will remain focused over the
northeastern half of the County Warning Area as storms precipitation shields slowly
staggers northeastward with the low. We should see a respectable quantitative precipitation forecast
gradient with the areas along and just west of the Bay receiving
only a couple of tenths of an inch of rainfall while locations on
the the Delaware-Maryland-Virginia peninsula will see significantly more due to their
proximity ot the low.


Long term /Wednesday night through Monday/...
the major forecast challenge on the backside of the low is the
upslope precipitation threat. The highest elevations along the Potomac
Highlands will see low temperatures that may dip into the middle 30s
Wednesday night...and given the fetch of the northerly winds over
the Great Lakes upstream of the Allegheny Front the option to
include snow as a precipitation type was tempting. But it looks like the
layer of above-freezing air near the surface will be a bit too
thick for any snowfall. This may change in upcoming forecasts as
confidence in low temperatures increases...but even if a few flakes do
fall no accumulation will occur.

High pressure centered over the southeastern United States will nose
into the area Friday and continue to strengthen through the weekend.
Overall...Saturday and Sunday should be beautiful fall days with dry
conditions and highs in the mid-60s. High pressure will begin to
shift off of the middle-Atlantic coast early next workweek and our next
threat for adverse weather should not present itself until the
middle of next week.


Aviation /01z Tuesday through Saturday/...
a cold front will approach from the west tonight and move through
the region Tuesday. Periodic showers and sub-VFR possible...but
confidence too low to include at the end of the taf period at this
time. Light west winds Tuesday.

Confidence is low in the occurrence of aviation hazards through the
long term period.


southerly channeling will continue across the Maryland Chesapeake Bay
south of Pooles Island/Tangier Sound and lower tidal Potomac
until 2 am. Westerly flow Tuesday as low pressure approaches from the
northwest. Light S winds expected late tonight...trending towards
the west and eventually northwest during the day Tuesday.

A Small Craft Advisory will likely be needed Wednesday and Wednesday
night as low pressure deepens just off of the middle-Atlantic coast. A
Small Craft Advisory may also be needed Thursday through Friday
night as breezy northerly winds fill in behind low pressure
departing off to the northeast.


Tides/coastal flooding...
anomalies back on the rise...approaching 1 feet tonight under
southerly winds. Forecasts for Washington Channel...Baltimore and
Annapolis show likelihood to reach action stages in the next two
high tide cycles tonight and overnight...but at this time fall
short of minor inundation.


Lwx watches/warnings/advisories...
District of Columbia...none.
Marine...Small Craft Advisory until 2 am EDT Tuesday for anz531>534-537-


near term...has
short term...Kansas
tides/coastal flooding...

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