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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
305 PM EST sun Mar 1 2015

Synopsis...
a cold front will cross the area tonight. High pressure builds on
Monday and continues through Tuesday. A warm front will cross the
area Tuesday night. Then a strong cold front will cross the region
late Wednesday as cold high pressure builds in for Thursday and
continues into the weekend.

&&

Near term /through Monday/...
the winter headlines continue into early this evening for central
Virginia and portions of the Potomac Highlands. The winter
headlines continue into late tonight for the eastern West
Virginia Panhandle...most of Maryland...as well as the Washington
and Baltimore metropolitan areas. Low pressure will pass by to our
west this afternoon into tonight while high pressure remains off
the New England coast. The southerly flow has overrun the surface
cold air in place...resulting in precipitation breaking out across
the area. The main ptype this afternoon has been freezing rain
with warmer air aloft moving in while surface temperatures remain below
freezing. Ice accumulations will average around one tenth of an
inch where winter weather advisories are in effect. Ice
accumulations will average around one-quarter inch where warnings
are in effect. Travel will be dangerous into this evening.
Numerous reports of icy conditions have been received.

The precipitation will end late this afternoon across central
Virginia..and this evening across the Washington and Baltimore
metropolitan areas into northern Maryland. However...areas of
freezing drizzle may hang around into late tonight. Temperatures
will hover around the freezing mark for most valleys...with
warmer temperatures in the higher elevations above 1kft.

The cold front associated with the low will pass through late
tonight into early Monday morning. A dry northwest flow is
expected behind the front. There will be enough sunshine and
downsloping winds for milder conditions. Maximum temperatures will range from
the 20s in the Allegheny Highlands...to the lower 40s near
Washington and Baltimore...to the upper 40s/near 50 in central
Virginia.

&&

Short term /Monday night through Wednesday/...
high pressure over the Ohio Valley will move eastward toward New
England by Monday night. With dewpoints dropping into the teens and
light winds...temperatures should fall well into the 20s...setting
the stage for yet another wintry precipitation threat.

Tuesday morning should be fine...with precipitation just beginning to
spread northward into western Virginia and wva. At this point...model
solutions have some similarity to today...with vertical profiles
from the NAM and GFS showing precipitation in The Highlands starting as
snow in the morning...followed by a changeover to sleet and freezing
rain during the day. Looking back through several previous model
runs...forecast soundings have varied in p-type...so rather than
carrying the full gamut of p-type on day 3...have elected to keep
the wording as rain-or-sleet at this time as those appear the more
likely two.

P-type should be all rain by sunset...but as the surface high shifts
offshore and warm air advection surges north...temperatures should actually rise
overnight...with most areas at least approaching 40 and communities
west of the Blue Ridge possibly pushing 50 by daybreak. Kept a brief
period of freezing rain in the evening for areas that may stay near freezing
longer.

The cold front will be slow to approach...allowing warm air advection to continue
and highs to reach into the 50s or perhaps even lower 60s on
Wednesday. Model solutions differ on frontal passage timing...so I took a
middle ground close to the GFS. See hydrology section for additional
information on rain/snowmelt/river ice.

&&

Long term /Wednesday night through Sunday/...
cold air advection increases after frontal passage Wednesday night with much
cooler/drier air moving in. Some guidance has been consistently
indicating anafrontal quantitative precipitation forecast overnight Wednesday and through the day on
Thursday. If this were to occur...would expect a quick transition
from rain to sleet to snow as the thermal column quickly cools in
the strong cold air advection.

High pressure settles into the region overnight Thursday...and with
strong radiational cooling...expect lows Friday morning to be very
cold. Airmass modification begins Friday with warm air advection over the area.
Next cold front approaches the region Saturday...at this point it
appears to pass through dry.

&&

Aviation /19z Sunday through Friday/...
freezing rain will taper off late this afternoon across kcho and
this evening between 23z and 02z for the rest of the terminals.
However...areas of freezing drizzle are possible behind the main
precipitation shield tonight. IFR ceilings/visibilities are expected through
this evening. There may be enough drier air to erode the low
clouds late tonight...but the forecast still shows low clouds
hanging on through 12z due to low-level moisture being trapped
underneath the subsidence inversion.

Winds will shift to the northwest Monday morning. Ceilings/visibilities will
improve to VFR levels and northwest winds will gust around 20 to
25 knots late Monday morning and afternoon.

Visibility/ceiling restrictions expected Tuesday afternoon through Wednesday
with precipitation. Gusty southerly winds also expected on
Wednesday.

Sub-VFR conditions possible Thursday in any regions of
precipitation.

&&

Marine...
southerly winds are expected through this evening. Winds will
shift to the northwest toward Monday morning behind a cold front.
A Small Craft Advisory is in effect Monday for northwest winds
gusting around 20 to 25 knots.

Small Craft Advisory conditions possible Tuesday night and Wednesday ahead of an
approaching cold front.

Possibility of Small Craft Advisory Wednesday night through Thursday in the cold air advection
behind the cold front.

&&

Hydrology...
we have been advertising the potential of midweek flooding in the
hazardous weather outlook. Liquid precipitation forecast from wpc puts much of
the forecast area in a minima for amounts...around an inch or less in
many areas. With temperatures expected to rise into the 50s on
Wednesday...there will be some...possibly a lot of...melting of the
existing snowpack...which computer models and observations indicate
contains anywhere from 3/4 inch to 2 inches of snow water
equivalent. This combination may lead to minor flooding as the rain
falls on Wednesday.

Although river ice is not especially thick...it will have to be
monitored for potential role in affecting runoff. Also...plowed snow
is likely covering some of the drains out there...which could cause
more poor drainage flooding than would otherwise usually be
expected.

Worth noting...current forecast rain totals are on the lower side of
the ensemble suites of the gefs and sref. Please continue to monitor
the forecast for udpates as the event gets closer.

&&

Lwx watches/warnings/advisories...
District of Columbia...Winter Storm Warning until 3 am EST Monday for dcz001.
Maryland...Winter Weather Advisory until 6 am EST Monday for mdz501.
Winter Weather Advisory until 3 am EST Monday for mdz003-502.
Winter Storm Warning until 3 am EST Monday for mdz004>006-011-
013-014-016>018-503>508.
Virginia...Winter Weather Advisory until 6 am EST Monday for vaz503.
Winter Weather Advisory until 7 PM EST this evening for
vaz025>027-029-030-036>040-050-051-056-501-502-504-507-
508.
Winter Weather Advisory until 3 am EST Monday for vaz028-031.
Winter Storm Warning until 3 am EST Monday for vaz052>055-057-
505-506.
WV...Winter Weather Advisory until 6 am EST Monday for wvz501-503-
505.
Winter Weather Advisory until 7 PM EST this evening for wvz055-
502-506.
Winter Weather Advisory until 3 am EST Monday for wvz050>053-
504.
Marine...Small Craft Advisory from 9 am to 6 PM EST Monday for
anz530>543.

&&

$$
Synopsis...bjl
near term...bjl
short term...jce
long term...ME
aviation...jce/bjl/ME
marine...jce/bjl/has/ME

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