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Area forecast discussion...corrected
National Weather Service Baltimore Maryland/Washington District of Columbia
400 am EST Fri Dec 6 2019

Synopsis...
high pressure will move offshore from the Carolinas today. A
cold front will cross the area this evening. High pressure will
follow for the weekend, before a stronger area of low pressure
develops over the mid-Mississippi Valley and tracks
northeastward toward the eastern Great Lakes early next week.

&&

Near term /through tonight/...
high pressure is situated along the southeastern coast this
morning, and areas of low pressure are over Michigan and the
arklatex, connected by a cold front. An area of mountain wave
cirrus developed last evening and has slowly been eroding,
although any clear skies will be replaced by mid/high clouds
advancing ahead of the next system.

Moisture ahead of the southern low will intersect the
Appalachians by this afternoon, but westerly (downsloping) flow
at 850 mb and above will likely mean precipitation will be
focused along the appalachian crest. Warm advection will result
in temperatures in the upper 40s to mid 50s, and even on the
ridgetops, temperatures should be well above freezing with most
of the precipitation being rain. As the cold front sinks
southeastward across the area late this afternoon and evening, a
few very light showers could be found along it. Used sprinkle
wording east of the mountains since the chance of measurable
precipitation looks very low in The Lowlands.

As cold air advances behind the front, precipitation could end as a
little snow on the Allegheny Front. There also could be freezing
drizzle as inversion heights crash, but it would be a very brief
window and thus didn't put it in the forecast. Skies will clear late
tonight with lows in the upper 20s to mid 30s.

&&

Short term /Saturday through Sunday night/...
a large/strong area of high pressure originating from Canada will
quickly build east Saturday and be overhead by Saturday evening.
Cold advection will result in highs in the 40s.
Favorable radiational cooling on Saturday night will lead to
widespread low to mid 20s, except lower 30s in the cities and by
the Bay. The high will move offshore Sunday. Return flow will be
offset by increasing clouds and poor mixing, with highs
remaining below 50 for most.

A shortwave trough will be approaching from the nation's
midsection Sunday night with low pressure developing over the mid
Mississippi Valley. Moisture will stream into the area ahead of this
system, and there could be additional focus of moisture along an
inverted trough along the coast. Chances for rain will increase
during the second half of the night. Low temperatures will be above
freezing for most areas. However, some of the mountainous areas
could be near freezing as the precipitation arrives, so a few
pockets of wintry mix are within the realm of possibility if warm
advection isn't fast/strong enough.

&&

Long term /Monday through Thursday/...
high pressure will be centered over the western Atlantic on Monday.
Low pressure will be moving NE from the Midwest into the Great Lakes
Monday into Monday night as IR deepens. Southerly flow will advect
warm and moist air into our region. This will increase the chance
for showers over area for Monday.

The cold front associated to this low pressure will be approaching
our region Monday night and will move across on Tuesday. Chance of
showers will continue during this time and into Tuesday night. Cold
air advection and residual moisture behind the front could allow for
snow showers over parts of or County Warning Area Tuesday night. Trough axis aloft
will move across on Wednesday while surface high pressure starts
building east and remains in control through the end of the
week.

&&

Aviation /09z Friday through Tuesday/...
mainly mid/high level clouds today with southwest flow ahead of
an approaching cold front. There could be lower ceilings (around
5kft) and a few light showers or sprinkles as the front passes
late this afternoon/early evening, but no visibility issues are
expected. Winds will shift out of the northwest behind the front
and could be briefly gusty to 20-25 kt.

No significant weather Saturday and Sunday with high pressure.
Next weather system approaches Sunday night with lowering
ceilings (possibly sub-vfr) and a chance of rain.

Chance of precipitation Monday through Tuesday night could bring sub-
VFR conditions over the terminals as low pressure and cold front
impact our area. Conditions should improve Wednesday when high
pressure builds into our region.

&&

Marine...
high pressure will move offshore today with southwest flow
increasing. Have not changed the start times of the small craft
advisories, which will be in effect for all waters by noon.
Worth noting mixing may be poor and gusts sporadic. There could be a
brief lull in winds early this evening with decoupling, but then a
cold front will pass, winds will shift to the northwest and become
gusty. Thus extended the advisory for all waters until 2 am. Then
winds will start diminishing from north to south through Saturday
morning as high pressure builds.

Light winds expected Saturday afternoon through Sunday as high
pressure builds across the area. Southerly flow may increase a
bit Sunday night as the high departs, but looks to be sub-
advisory at this time.

Sub-Small Craft Advisory conditions expected Monday into Monday night over the
waters. Small Craft Advisory may be needed on Tuesday through Wednesday behind a
cold front that will move across our area.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory from noon today to 6 am EST Saturday
for anz531-538-539.
Small Craft Advisory from 9 am this morning to noon EST
Saturday for anz533-534-537-541>543.
Small Craft Advisory from noon today to 2 am EST Saturday for
anz530-535-536.
Small Craft Advisory from 9 am this morning to 6 am EST
Saturday for anz532-540.

&&

$$
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