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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
914 am EST Wednesday Mar 4 2015

Synopsis...
a cold front will cross the region today and tonight. High
pressure builds overhead Friday...then persists through the
weekend.

&&

Near term /until 6 PM this evening/...
surface analy depicts a cpl of boundaries in the pressure fields this morning.
The first one runs from balt/District of Columbia to cho...then heads west-southwestward across Tennessee to
Arkansas. This boundary has low level thermal support. The latter
stretches across northwest PA and Northern Ohio. The upper jet dynamics lie here.

Regional radar this morning already shows the dynamical...high
moisture content frontal zone sagging our way. Theres plenty of
moisture west of the Appalachians at this time...and will need to monitor how much of
this can hop the mountains

In short...today will feature occasional rounds of rain...most
prevalent across the northern half of the County Warning Area. Will keep an eye on
rain totals...especially in The Highlands where temperatures have
warmed and the heaviest rain will fall.

In-situ wedge will hold temperatures in the 40s across much of
area. Going forecast has good lamp support. No temperature changes anticipated
at this time.

&&

Short term /6 PM this evening through Friday/...
synoptic pttn from latest guidance runs seem to be simlr to those yesterday.
Only adjustments based on subtle thermal diffs. Key factors are a
slightly slower timing and higher quantitative precipitation forecast value. Based on that...the
midnight shift transitioned the Winter Storm Watch to a warning
for most of the County warning forecast area. The southern fringe of the area is the exception
due to a longer period of time in rain and sleet.

The boundaries /mdl guidance doesnt do a good job distinctly resolving
both of them/ will continue slide southward tonight...allowing the Arctic air mass from
the Great Lakes to overspread the area. Meanwhile...a satd moisture stream
will continue spreading east-northeastward...overriding the colder air mass. Dynamics will
be fueled by the rrq of the upper jetmax as well as low level
baroclinicity. All of this supports a transition from rain to pl and
then to snow.

Forecast based on an ensemble approach...which suggests a period of favorable
dendritic growth as well as fgen forcing in a corridor bhd the
snow/pl transition. Thats the justification for raising snow ttls
across north-central Maryland/eastern wva/northern shen valley...as these features will
coincide west/ snowfall the longest. Sufficient cold air to support snow
will reach the southern edge of the County warning forecast area by afternoon. Will be making the
warning/advisory decision for the srnmost 5 counties once 12z guidance arrives.

Tail end of snow Thursday evening is a few more tenths inch
for southern Maryland before tapering off. Skies clear late in the night with
high pressure quickly building overhead. Gusty northwest flow (around 20
mph) follows the cold front. Wind chills reach zero across the County Warning Area
with wind chill advisories likely over portions west of Interstate
95. Areas west of Interstate 95 should decouple before sunrise which
will allow for single digit min temperatures...teens east.

Sunny Friday under high pressure with tranquil conditions and maximum
temperatures middle to upper 20s due to little mixing and fresh snow.

&&

Long term /Friday night through Tuesday/...
one of the longest consistent warming patterns in awhile
Saturday through middle of next week as very broad East Coast trough
slowly deamplifies. Welcome calm weather pattern as the subtropical
ridge builds into the southeastern Continental U.S.. a few degrees warmer on maximum temperatures
each day in southwesterly flow...low 40s for Saturday...50s by
Monday...60s...mainly south of District of Columbia Monday through Wednesday.
Uncertainty due to cloud cover in the middle of next week prevented
a bolder forecast of middle 60s south/middle 50s north by Wednesday...as
of now it is around 60f south and around 50 north.

&&

Aviation /14z Wednesday through Sunday/...
VFR conds prevalent across the terminals at this time...but west/ patches of
IFR. Solid flgt restrictions will arrive for the afternoon push...W/
consistent at or below IFR coincient west/ a transition to snow aftr midngt.
At or below IFR should continue through the day Thursday.

Conds quickly improve to VFR Thursday evening from northwest to southeast
with northwest gusts around 20 knots. Single digits min temperatures that night for
most of the area. High pressure builds overhead Friday with
VFR/tranquil conds. Southwesterly flow and more high pressure then through
the weekend.

&&

Marine...
all winds at or below 10 knots at this time. A transition to north-northwesterly flow will occur later
today or tonight. Winds will increase thereaftr...W/ Small Craft Advisory conds foer the
latter part of the night into Thursday night.

Small Craft Advisory likely to extend into Friday before high pressure builds
overhead. High pressure then through the weekend with southwesterly flow
developing Friday night.

&&

Hydrology...
there has been noteable snowmelt across the area thus far. Add in
rainfall up to a half-inch...and rivers in the upper ptmc basin have
experienced significant west/in bank rises. Still do not expect flooding...
but will continue to monitor closely. At this rate...rainfall may reach
1-2 inches.

Some complicating factors to keep in mind...if the changeover from
rain to wintry precipitation this evening occurs later than expected...
concerns may become heightened. Trends have been suggesting a later
changeover. Also many of our area streams are covered with ice or
even partially frozen. These effects will have to be monitored for
a potential role in affecting runoff.

Lastly...as we saw with the recent rain/ice/minor snowmelt...any
amount of liquid precipitation stands a good chance of causing minor
poor drainage flooding...as normal drainage patterns may be blocked
by plowed snow.

&&

Lwx watches/warnings/advisories...
District of Columbia...Winter Storm Warning from midnight tonight to 9 PM EST
Thursday for dcz001.
Maryland...Winter Storm Warning from 7 PM this evening to 7 PM EST
Thursday for mdz003-501-502.
Winter Storm Warning from 10 PM this evening to 7 PM EST
Thursday for mdz004>006-011-503>508.
Winter Storm Warning from midnight tonight to 9 PM EST
Thursday for mdz013-014-016-018.
Winter Storm Watch from late tonight through Thursday evening
for mdz017.
Virginia...Winter Storm Warning from 7 PM this evening to 7 PM EST
Thursday for vaz028-503-504.
Winter Storm Warning from 10 PM this evening to 7 PM EST
Thursday for vaz025>027-029>031-040-501-505>508.
Winter Storm Warning from midnight tonight to 9 PM EST
Thursday for vaz038-039-050>055-502.
Winter Storm Watch from late tonight through Thursday evening
for vaz036-037-056-057.
WV...Winter Storm Warning from 7 PM this evening to 7 PM EST
Thursday for wvz050>052-055-501>506.
Winter Storm Warning from 10 PM this evening to 7 PM EST
Thursday for wvz053.
Marine...Small Craft Advisory from 1 am Thursday to 6 am EST Friday for
anz530>543.

&&

$$
Synopsis...baj/ads/hts
near term...ads/hts
short term...hts/baj
long term...baj
aviation...hts/baj
marine...hts/baj
hydrology...hts/je

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