Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Baltimore Maryland/Washington District of Columbia
711 PM EST Monday Nov 24 2014
low pressure intensifying over the Great Lakes will bring an
associated cold front through the middle-Atlantic late this afternoon
and early this evening. Low pressure is expected to track north
along the coast Wednesday. High pressure will return for Thursday
Near term /through Tuesday/...
intermediate update...cancelled wind adzy for the western Highlands
and periphery zones of the current small craft adzy for the
From previous disc...cold front will push east across the area this
evening with a wind shift and drying of the airmass. Temperatures
will be a bit slower to fall as the colder air is blocked by the
mountains. Lows will generally be in the 40s with upper 30s in
high elevations and lower 50s near the Bay. Some patchy fog or
stratus may develop in southern Maryland as the front slows and low
level moisture pools along it.
Tuesday will be dry with high pressure nosing in from the lower
Mississippi Valley. Increasing middle and high level clouds through the
day as the front remains just offshore and the low pressure system
begins to take shape over northern Florida. Despite being much cooler
than today... the coldest air stays poised over the Great Lakes and
highs will be near climatology in the 50s. Shaded southeast County Warning Area a little
cooler due to the increasing clouds.
Short term /Tuesday night through Wednesday night/...
a potent jetmax/shortwave will track through the Gulf Coast states
Tuesday night and this will cause coastal low pressure to develop
off the southeast coast. At the same time...high pressure will
build to our north allowing for colder and drier air to filter
into the region. High and middle-level clouds will increase ahead of
this system Tuesday night...but much of the time will turn out dry
with the system remaining to our south and west.
However...precipitation is expected to overspread the area quickly
early Wednesday morning as the coastal low tracks northeast
toward Cape Hatteras. The low will intensify as it tracks
northeast...and this will allow for moisture from the Atlantic and
Gulf of Mexico to get wrapped into the storm.
Therefore...precipitation will be moderate to locally heavy at
times during the day Wednesday. The main question is how much
cold air will work its way into the region...causing the threat
for snow. As of now...it appears that there will be enough cooling
from the wet-bulb effect and dynamical cooling for any rain or
mixed precipitation to quickly change to snow for locations near
the Mason-Dixon line and also near and west of the Blue Ridge
mountains. The heaviest snow accumulation is most likely to fall
in the mountains...but there is a potential for several inches of
snow across most of these areas so a watch has been issued.
For locations closer to Interstate 95...there may be enough warm
air for precipitation to start out as rain...but even across these
areas precipitation will likely change to snow due to the cooling
affects previously mentioned. However...surface temperatures will hover
close to or perhaps even a couple degrees above freezing and this
may make it difficult for snow to stick. The highest degree of
uncertainty is in these areas so please stay tuned to the latest
forecasts for updates. For locations south and east of
I-95...mostly rain is expected...but there is a potential for
snow to mix in Wednesday afternoon.
Precipitation will end from southwest to northeast later Wednesday
afternoon into Wednesday evening. Exact timing is still uncertain
but the forecast leans a bit toward the more progressive guidance
since this should be a fast moving system and it is not expected
to phase with the northern branch until after it is off to our
north. Temperatures will dip below freezing Wednesday night as conditions
dry out. Therefore...any wet or slushy roads may freeze up.
Long term /Thursday through Monday/...
low pressure departs into the Canadian Maritimes Thursday.
Meanwhile...500 mb northern stream trough moves across the area.
Snow showers possible over the western ridges but trajectories not
favorable for prolonged upslope. Cannot rule out a few flurries east
of the ridges as the trough axis passes but mostly just expecting
passing clouds in a breezy west flow. Highs should make it to around
40 degrees Thursday afternoon.
Colder temperatures at 850 mb accompany the northern stream wave...so below
normal temperatures are expected later this week. Surface high pressure
moves across Friday into Friday night...then moves offshore for the
weekend accompanied by a gradual warmup to near normal temperatures.
A front may approach the area by the beginning of next week.
Aviation /00z Tuesday through Saturday/...
VFR conditions are expected through the taf period. Southerly wind
gust approx 25kt will continue through this afternoon...diminishing
with sunset. Cold frontal passage will occur this evening with a
wind shift to the southwest...which could vary within a couple hours
of what is currently in the tafs. Winds gradually become more
westerly by late tonight. Winds around 10kt or less through Tuesday.
VFR conditions are expected Tuesday night. A rain and snow mix
will overspread the terminals early Wednesday morning.
Precipitation will change to all snow Wednesday and IFR conditions
are expected. The low will move away from the area Wednesday night
and conditions will improve to VFR levels. Gusty north-northwest
winds are possible Wednesday into early Wednesday evening.
Mainly VFR expected Thursday-Thursday night west/ west wind 10-15 kts. VFR into next
weekend...winds become light/variable as high pressure moves
overhead Friday-Friday night...then S around 10 kts Sat.
strong southerly wind gusts will continue on the waters through this
afternoon. Winds will shift to the southwest this evening with a
cold front passage then gradually diminish while becoming westerly.
Not a strong surge of cold air...so gusts should taper off despite
the frontal passage. Have kept the Small Craft Advisory the
same...ending at 8 PM for the middle/upper tidal Potomac and at 1 am
for the rest of the waters. Westerly winds through the day Tuesday
at less than 15kt.
Low pressure will develop off the southeast coast Tuesday night. A
Small Craft Advisory is in effect late Tuesday night for the
Maryland Chesapeake Bay from Sandy Point to Smith Point and for
the lower tidal Potomac River from Cobb Island to Smith Point.
The low will move up the middle-Atlantic coast Wednesday and it will
intensify as it moves off to our northeast Wednesday night. A
Small Craft Advisory will likely be needed for the waters
Wednesday into Wednesday evening. A Gale Warning may be needed for
portions of the waters Wednesday.
Gusty west winds between departing/deepening low pressure and
approaching high pressure will likely breach Small Craft Advisory
criteria Thursday night into Friday. Winds will lighten as high
pressure moves overhead Friday afternoon and night...then southerly
channeling looks to bring a return to higher gusts Saturday
a southerly flow has caused tidal anomalies to increase this
afternoon. However...the astronomical norms are relatively low.
Therefore...minor coastal flooding is not expected with the high
tide cycle this evening. Anomalies will decrease behind a cold
front later tonight.
high temperatures today for dca/iad/BWI will all come very near
current records. Here are the record highs and the year they
Dca...74 in 1958. ..officially tied..
iad...74 in 1979.
BWI...73 in 1979.
District of Columbia...none.
Maryland...Winter Storm Watch from Wednesday morning through Wednesday
afternoon for mdz003>007-501-502.
Virginia...Winter Storm Watch from Wednesday morning through Wednesday
afternoon for vaz025>031-036>040-042-501-503-504.
WV...Winter Storm Watch from Wednesday morning through Wednesday
afternoon for wvz050>053-055-501>506.
Marine...Small Craft Advisory until 1 am EST Tuesday for anz532>534-537-
Small Craft Advisory from 1 am to 6 am EST Wednesday for