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fxus61 klwx 231356 
afdlwx

Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
956 am EDT Mon Apr 23 2018

Synopsis...
high pressure will move offshore today. A low pressure system
will bring unsettled weather to the region tonight through the
middle of next week. A brief ridge ridge of high pressure will
build in later in the week, ahead of the next low pressure
system toward the weekend.

&&

Near term /through tonight/...
high pressure will move off of the East Coast today as a cut-
off low pressure system moves through the southern United States
and towards the mid-Atlantic states. High clouds of varying
thickness will stream overhead through the day today, with a
general increase/thickening trend, especially later this
afternoon. Rain will eventually spread northeastward and into
the southern Shenandoah Valley, Blue Ridge, and Allegheny
Highlands late this afternoon, and especially this evening.
High temperatures will reach the upper 60s to near 70f for most
locations, except mid 60s where clouds/rain chance increase
first.

Overnight tonight rain probabilities increase from southwest to
northeast as moist/warm air advection continues and closed low
gradually approaches. Rain should be falling by sunrise from the
District of Columbia Metro area South/West. Further northeastward, locations
may remain dry through the night.

&&

Short term /Tuesday through Wednesday night/...
as the cut-off low and a couple of pieces of upper level energy move
into the mid-Atlantic region Tuesday, additional rounds of light to
moderate rain will develop and overspread most of the region. This
rain should gradually taper to showers Tuesday night and end from
southwest to northeast. However, the ending time may be delayed as
the next upper level disturbance will be quick on the heels of the
Monday night and Tuesday low pressure system. Temperatures will be
about 5 to 10 degrees cooler Tuesday due to cloud cover and rainfall
and about 5 to 10 degrees milder Tuesday night due to the same two
factors.

Low pressure will be moving northeast away from the area Wednesday
morning, leaving a chance for some residual showers in its wake.
Another quick moving shortwave will move through Wednesday evening
into Thursday morning. Some showers will be possible with this
system as well, especially Wednesday night. Temperatures Wednesday
will be below average, thanks to the cloud cover and precipitation
expected over the area.

&&

Long term /Thursday through Sunday/...
the area of low pressure will depart off to the northeast on
Thursday leading to dry conditions and slightly below normal
temperatures.

The forecast becomes much more uncertain for Friday. Several
different shortwave disturbances will interact as they move across
the Continental U.S. Between now and Friday. The high number of these complex
interactions lend themselves to high uncertainty in the forecast for
Friday through Sunday. The GFS forms a surface low in the southeast
Thursday night out ahead of a compact shortwave, and then proceeds
to track that low up the East Coast on Friday giving US a round of
rain. On the other hand, the Euro keeps the shortwave and attendant
area of low pressure suppressed to the south and weaker in nature.
Roughly half of the members in the 00z gefs give US over a tenth of
an inch of rain, and only a few members of the 12z eps gave US over
a tenth of an inch with this system. So, to summarize...there's at
least a chance for rainfall on Friday, but it's an uncertain
forecast to say the least.

Another upper-level trough and associated weakening cold front will
approach the area from the west this weekend. Most model guidance
keeps US dry with the passage of this front, but some light
precipitation can't be ruled out. Temperatures this weekend are
expected to remain slightly below average.

&&

Aviation /14z Monday through Friday/...
VFR conditions expected through this evening with winds
southeast around 10 knots or so. MVFR conditions then become
possible at cho overnight tonight as light rain approaches from
the southwest. Chances for MVFR conditions then increase at all
terminals Tuesday and especially Tuesday night due to low
ceilings and light to moderate rain. A period of IFR is also
possible Tuesday night into early Wednesday morning. Clouds and
showers will persist for much of the day on Wednesday with
potential for sub-VFR conditions continuing.

VFR conditions are likely on Thursday. Conditions
could potentially drop to sub-VFR on Friday if a coastal low were to
develop, but the forecast is highly uncertain at this point.
Conditions will likely return to VFR for the weekend.

&&

Marine...
Small Craft Advisory GOES into effect for all waters this
afternoon as southerly flow increases ahead of an approaching
low pressure system. The advisory continues tonight through
Tuesday with gusty south/southeast winds 20-25 knots. An
extension through Tuesday night may be needed.

As the area of low pressure exits Wednesday morning, some gusty
winds are possible across the marine areas, with Small Craft Advisory criteria
winds possible during that time. No marine hazards are expected
Thursday through Sunday at this time.

&&

Hydrology...
while the area saw significant rain a week ago, its been
relatively dry since then. That said, 1-2 inches of rain appears
likely across the region tonight through Wednesday, which could
lead to some minor hydrology issues and cause river and stream
rises, potentially nearing flood stages. Will be closely
monitoring this for potential need of any flood watches over the
next day or so.

&&

Tides/coastal flooding...
as low pressure approaches the waters from the southeastern U.S.
Late Monday into Tuesday, a persistent onshore flow will
develop. This will yield increasing tidal anomalies, and the
possibility of coastal flooding toward the middle part of the
week.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory from 1 PM this afternoon to 6 PM EDT
Tuesday for anz530>543.

&&

$$
Synopsis...klw
near term...mm/klw
short term...klw

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