Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 180745
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
345 AM EDT Mon Oct 18 2021

.SYNOPSIS...
High pressure is expected to slowly build eastward to our south
through the middle of the week. A cold front will likely cross
the region late in the week.

&&

.NEAR TERM /THROUGH TUESDAY/...
Latest analysis shows high pressure finally pushing eastward,
now centered over the lower Mississippi valley. Upper trough is
now centered over western New England, continuing to slowly move
eastward as well. For our region, this will mainly result in
less cloud cover today, though the gusty breeze will continue
and temperatures will remain chilly... chilly compared to
recent weather this month, at least, not really that chilly
compared to normal.

High pressure will be centered over the southern Appalachians
tonight. Not quite close enough for ideal radiational cooling,
but certainly better positioned than it is presently. Have some
patchy frost in the forecast for the colder spots, but not
widespread enough for an advisory. That is also unusual for so
late in the season.

High pressure becomes centered over the Carolinas on Tuesday,
with westerly downslope flow and warm advection riding over the
top of the high allowing surface temps to warm a bit compared to
today. Winds will also be a bit lighter as the gradient relaxes.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
High pressure will mostly remain in place Tuesday night into
Wednesday, positioned to our south over the Carolinas, allowing
lighter westerly flow to bring warmer air northward around the
periphery of the high. Thus expect both periods to nudge upwards
in the temperature department, but no radical changes are
expected, and winds should remain comparatively light.

Wednesday night, the next frontal system, currently (as of early
Monday) located over northern California, will approach from the
west as it moves into the Great Lakes. This will result in a
stronger southerly flow and increased cloud cover, but still
expect it to remain dry. Temperatures will moderate further.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
High pressure that is overhead of our region through the early
parts of this week will shift off-shore on Thursday. As the high
shifts off-shore, a weak return flow is forecast to form
leading to weak warm air advection. Weak ridging to the north of
our region will start to breakdown by the end of this week as a
shortwave trough moves over the Great Lakes region up through
the NE US. A surface low associated with this disturbance is
forecast to remain situated to the north of our region over
Michigan. A weak front associated with the low will pass through
our region sometime late Thursday into Friday. This frontal
passage will likely be moisture starved as the main forcing will
remain well to the north of our region. Model ensembles suggest
there could be close to 45 knots of shear with the frontal
passage but the main forcing will remain to the north and little
to no CAPE is expected. I expect the main threat from this
frontal passage will be some scattered showers. Ahead of the
first frontal passage, afternoon temperatures will be warm in
the mid 70s with overnight lows in the 50s.

Another shortwave may drive a secondary cold front through our
region Friday evening into Saturday but this front will be
weaker than the previous front. The secondary front will cool
down daytime highs into the 60s once again with overnight lows
dropping down into the 40s with few areas potential reach the
30s. High pressure is forecast to build over our region during
this weekend bringing continued seasonable conditions along with
our first chances for frost and freeze weather. Another
shortwave may impact the region late Sunday into Monday but
there remains a lot of uncertainty between model solutions.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
VFR through Wednesday night. Gusty NW winds reaching 20-25 knots
expected again today, but should be mostly sub-20 knots on
Tuesday, and mostly below 15 knots Wednesday. No cig or vsby
issues anticipated.

High pressure will shift off-shore leading to winds become more
south to southwesterly on Thursday. Showers will be possible at
terminals on Thursday due to a frontal passage but VFR
conditions expected at this time. Another front may bring
another chance for showers Friday into early Saturday but VFR
conditions are still expected. Cooler and drier conditions
return for Saturday with winds become more west to
northwesterly.

&&

.MARINE...
Brisk northwesterly flow will only gradually wane over the next
36 hours. SCA returns to all waters by midday today, then slowly
wanes for good starting this evening, but sporadic SCA gusts
likely continue until late Tuesday afternoon. Sub-SCA winds
likely prevail Tuesday night through Wednesday night.

A cold front will pass through our marine areas on Thursday and
then again on Friday. A strong southwesterly flow may require
Small Craft Advisories Thursday into Friday morning. Near SCA
conditions will be possible again Friday into Saturday due to a
channeling northwesterly flow.

&&

.TIDES/COASTAL FLOODING...
Persistent brisk northwesterly flow may lead to near blow out
tides today.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 7 AM EDT Tuesday for ANZ531-532-539-
     540.
     Small Craft Advisory from 7 AM this morning to 8 PM EDT this
     evening for ANZ530-538-542.
     Small Craft Advisory until 6 PM EDT Tuesday for ANZ534-543.
     Small Craft Advisory until 11 AM EDT Tuesday for ANZ533-537-
     541.
     Small Craft Advisory from 10 AM this morning to 8 PM EDT this
     evening for ANZ535-536.

&&

$$
SYNOPSIS...RCM/JMG
NEAR TERM...RCM
SHORT TERM...RCM
LONG TERM...JMG
AVIATION...RCM/JMG
MARINE...RCM/JMG
TIDES/COASTAL FLOODING...DHOF


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