Scientific Forecaster Discussion

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Area forecast discussion...updated 
National Weather Service Baltimore Maryland/Washington District of Columbia
934 PM EDT Thursday Apr 17 2014

high pressure over New England will stretch southward toward the
middle-Atlantic coast through the remainder of the week. An area of
low pressure and cold front may affect the area Saturday. A second
cold front looks to move through the region Tuesday.


Near term /through Friday/...
cad regime continues over the middle Atlantic as 1042 mb high
holds in place just off the New England coast. Persistent easterly
fetch has developed with low level moisture advection slowly
pushing west across the Bay. Will see increasing clouds overnight
into Friday morning especially along and east of I-95 as marine
layer settles in. Big question remains how far west the marine
layer pushes. Thinking it could clip District of Columbia and Baltimore metropolitan areas
bringing stratus deck by dawn. Further west...drier air with only
some cirrus will help radiational cooling processes and falling
temperatures in the lower to middle 30s. Frost advisory will continue for
the same counties.

High pressure begins to nudge a little east on Friday as a weak cold
front approaches from the west. We/ll likely have more cloud cover
on Friday compared to today...but forecast will be dry. Maxima
similar or slightly above today.


Short term /Friday night through Sunday night/...
northern and southern stream lows will split the area over the
weekend. In the northern stream...low pressure north of the Great
Lakes will produce a weak cold front that will deteriorate as it
moves over the Appalachian Mountains. This front will be dry by the
time it reaches our area Saturday morning...though it could provide
a bit of a reinforcement of cool air for the day on Saturday.

The feature that will have a stronger influence on the middle Atlantic
weather will be a southern stream low that will cut off from the
upper level flow over the Gulf states Friday night and move into the
Atlantic Ocean near the Georgia/Florida border early Saturday morning. The
primary model divergence at this time is with the track of this low
and the size of the precipitation shield associated with it. European model (ecmwf)
and NAM keep US dry through the weekend while the GFS is wetter
overall...with precipitation covering the southern portions of the
County Warning Area through the day on Saturday. Have left any chance of probability of precipitation out of
the forecast given that the GFS is clearly the outlier.

Expect pleanty of sunshine to reach the ground between some daytime
cumulus clouds this weekend everywhere except for the most southerly
tier of counties in the County Warning Area as stratus clouds associated with the
low stay mostly to our south and east. With the low to our south and
high pressure to the north some cold air wedging is possible over
the weekend...but with north to nerly 850 mb flow a strong cad event
is not expected...mostly just a weak influx of cool air at the
surface which should be easily overcome by daytime heating. Highs
will be in the middle to upper 60s Sat and sun and weak nwrly flow will
keep nights cold...with Sat and sun lows near 40 everywhere except
the cities...where middle to upper 40s are expected.


Long term /Monday through Thursday/...
an axis of high pressure will remain anchored along the eastern
Seaboard into early next week as an area of low pressure drifts off
the Georgia/Florida coast and east towards Bermuda...well south of the area. A
generally light easterly flow will persist across the area between
these two features. Temperatures will be near normal Sunday night
into Monday night...with daytime highs at or above 70 for most of
the area /warmest west away from the cooler water/ and overnight
lows in the 40s to around 50.

The latest GFS/European model (ecmwf) and their respective ensemble members have a
cold front crossing the area from west to east on Tuesday with
varying intensity. This front will bring a chance of rain showers to
the area...and could be accompanied by a few thunderstorms depending
on the exact timing of the frontal passage and the amount of
moisture/instability return ahead of the front.

High pressure will build towards the area from the northern plains
and Great Lakes with briefly cooler temperatures expected Wednesday.
Temperatures look to start warming again by next Thursday as the
high pushes to the east.


Aviation /02z Friday through Tuesday/...
confidence increasing for sub VFR conditions between 09-13z
Friday. Persistent easterly wind will aid in stratus development
overnight...affecting terminals east of the Blue Ridge. IFR
possible...especially kbwi/kmtn/kdca. Stratus will lift by middle
morning with cirrus and VFR thereafter.

Outlook...VFR conditions in easterly flow of 5 to 10 knots is
forecast through early next week.


Small Craft Advisory continues for much of the waters overnight. Current forecasts
are for winds under Small Craft Advisory criteria Friday.

A Small Craft Advisory may be necessary for the lower Maryland
Chesapeake Bay Sunday night as low pressure moves away from the middle
Atlantic Seaboard. Sub-Small Craft Advisory conditions are
expected in generally light easterly flow around high pressure
Sunday night through Monday night...then modest southerly ahead of
a cold front by Tuesday. Small Craft Advisory level winds are
possible Wednesday in gusty northwest flow behind departing cold
front and ahead of approaching high pressure.


Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...frost advisory from 2 am to 8 am EDT Friday for mdz004>007-
Virginia...frost advisory from 2 am to 8 am EDT Friday for vaz036>040-042-
Marine...Small Craft Advisory until 3 am EDT Friday for anz531>534-


near term...krw
long term...dfh