Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 131801
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
201 PM EDT Sat Aug 13 2022

.SYNOPSIS...
High pressure will remains overhead tonight, before progressing
offshore on Sunday. An upper level low will move overhead early
in the week, bringing a return to unsettled weather. A less
active weather pattern may return towards the end of the week
with a more seasonable weather pattern.

&&

.NEAR TERM /THROUGH TONIGHT/...
Dry and mostly clear for the rest of the afternoon as our region
remains under the influence of high pressure. Aloft, a trough
remains anchored over the eastern CONUS, putting our are in NW
flow aloft. This all leads to the below average temperatures we
are seeing today, as well as the low humidity.

With high pressure settling overhead this evening, conditions
will be prime for radiational cooling for a time. High clouds
will eventually begin to stream in aloft later in the overnight,
but prior to that, temperatures may fall quickly back into the
50s, with urban centers holding in the lower to middle 60s. Have
even dropped temperatures a few degrees for this forecast
package to nudge a bit closer to some of the cooler guidance.
Wasn`t quite confident enough to fully lock onto a colder
solution, but felt that nudging it towards it was a good
compromise.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
The upper troug remains overhead on Sunday with a potent
vort max riding around the periphery and moving over head later
in the day. This will likely spark some showers out west by
late afternoon, spreading eastward by the overnight hours. There
will be just enough instability to perhaps get a few rumbles of
thunder as well, but no severe threat at this time. Temperatures
will be even cooler on Sunday with highs struggling to get out
of the 70s for most (even the mid 60s in the higher elevations).

These chances for showers and potentially a few thunderstorms
will continue through the day Monday and into Monday night as
the trough over the East Coast deepens and then eventually cuts
off nearby. As a result, temperatures on Monday will be well
below average, perhaps only getting into the low to mid 70s.

As is often the case with developing upper lows, there is still a
considerable amount of spread amongst various forecast models
with respect to the finer scale details of how things pan out.
Most solutions depict well below normal temperatures beneath
thick low overcast on Monday, with temperatures struggling to
get out of the low-mid 70s. Instability appears to be weak, so
the threat for thunderstorms will be low, but non-zero. Severe
thunderstorms are not expected given the weak instability
present. Some solutions (such as the NAM) develop a low-level
circulation across the area by later Monday into Monday night.
If this were to occur, heavy rainfall and a few instances of
flooding may be possible. However, there are also plenty of
solutions that develop the low well offshore and impact portions
of New England moreso than us. Will have to continue to monitor
trends to see if models try to converge on a solution.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
On Tuesday, a broad upper low remains a fixture over the
northeastern U.S. with anomalies running around 2 sigma below
average for mid-August. This system is set to wobble toward the
northeast during subsequent days before settling in the vicinity of
northern Maine by Thursday. Eventually the longwave pattern becomes
more progressive by week`s end. Global ensembles do maintain general
troughing east of the Rockies with subtropical ridging over Florida
and into the subtropical Atlantic.

Heading down to the surface, a wavy frontal zone will sit over the
Carolinas as waves of low pressure ride along this boundary. Ample
lift within the cool sector will dump light/moderate rain showers
across the Mid-Atlantic region. Forecast amounts are quite variable
depending on the guidance, but on average, totals run between 0.25-
0.50". The persistent northeasterly flow combined with the showers
and enhanced cloud cover will make for a rather raw summer day.
Highs may only rise into the low/mid 70s with 60s possible from the
Blue Ridge westward. The primary forcing from this trough and
associated surface features begin to exit by mid-week. Thus, do
expect a trend toward drier conditions by some time Wednesday. Multi-
model ensembles favor a warming trend back into the low to possibly
mid 80s by the conclusion of the work week. This is in response to a
shift to more of a southerly warm advection pattern. Any discernible
precipitation chances do not arrive until the beginning of next
weekend.

&&

.AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions and northerly winds are expected today. Winds go
light but VFR conditions continue tonight. Largely VFR again
tomorrow in southerly flow, but MVFR conditions and showers may
be possible by late in the day as an upper-level disturbance
approaches from the northwest. Sub-VFR conditions become
increasingly likely through the night on Sunday and especially
on Monday.

An unsettled pattern within the northeasterly flow regime will favor
lengthy periods of sub-VFR conditions on Tuesday. Improvements can
be expected by Wednesday as precipitation exits the region. Wind
fields generally waver between north to northeasterly through mid-
week.

&&

.MARINE...
Gusty northerly winds will continue through much of the day
today, but should be sub-SCA for the remainder of the afternoon.
Winds will subside overnight as high pressure moves overhead.

Winds will turn southerly on Sunday, and then southeasterly on
Monday, but are expected to remain sub-SCA in nature. Showers
are expected by Sunday evening and will continue throughout the
day Monday, but shouldn`t be hazardous from a boating
perspective.

Prevailing north to northeasterly winds are expected for Tuesday and
Wednesday as a frontal zone and waves of low pressure pass off to
the south. Such winds may approach Small Craft Advisory levels by
Tuesday night into portions of Wednesday.

&&

.TIDES/COASTAL FLOODING...
Tidal anomalies are forecast to run slightly high over the next
couple of days, but should not cause any minor flooding. Flow
turns southerly by Sunday though, which will raise anomalies
more. Some of the more sensitive sites (Annapolis, Straits, and
DC) could experience minor tidal flooding by early next week.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until noon EDT today for ANZ530>534-
     537>541-543.

&&

$$
SYNOPSIS...CJL
NEAR TERM...CJL
SHORT TERM...CJL/KJP
LONG TERM...BRO
AVIATION...BRO/CJL
MARINE...BRO/CJL
TIDES/COASTAL FLOODING...CJL


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