Scientific Forecaster Discussion
fxus61 klwx 271922
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
322 PM EDT Sat may 27 2017
weak low pressure will shift east the area this evening. A
trailing frontal boundary linger south of the area into Sunday
morning. A weakening cold front will move east through the area
Monday morning. Upper level low pressure will linger north of
the Great Lakes Monday night through the remainder of the week
with persistent weak high pressure over the mid-Atlantic.
Near term /until 6 am Sunday morning/...
as of 2pm, a weak upper level shortwave trough is over the
northeastern Continental U.S. With a 1011mb surface low stretching from
Ohio to central Virginia. A weak ridge over the Midwest will continue
to shunt this low east which will reach the coast late tonight.
Areas south of this area of low pressure have had at least
partly sunny skies today with temperatures in the low 80s.
Persistent mid level clouds and patchy rain have kept
temperatures in the upper 60s north of the low with 70s in
between. GOES imagery depicts a transition from stable wave
clouds to unstable cloud streets over central Virginia this afternoon.
Greatest threat for thunderstorms is central Virginia and west through
sunset. Bulk shear is decreasing as from a weak jet streak
south of the shortwave shifting east. Expect SBCAPE values of
1500 j/kg or so in southern areas of the County Warning Area through the rest of
the afternoon. Isolated at best risk for severe thunderstorms
3-7pm down there with hail and damaging winds as main threats.
Farther north, thunderstorm chances decrease as you move north
into cooler/cloudier conditions. This activity will shift east
with the pattern late this evening.
Tonight, low pressure moves off with onshore flow filling in
behind from high pressure centered over New England. This should
allow low clouds to develop across the area with patchy fog west
of I-95. Humid, but cool tonight with min temps near 60f.
Short term /6 am Sunday morning through Monday night/...
deep upper level low pressure approaches Lake Superior Sunday
with a broad warm sector ahead. The cold/occluded front will
push east across the Midwest Sunday. Low pressure looks to
develop over in Sunday afternoon and lift NE over the eastern
Great Lakes Sunday night. This should keep most of the heavy
rain potential north of the area. However, will stay the course
with a heavy rain mention in the severe weather potential statement for Sunday late
afternoon/night as ingredients of pwats of 1.5in and
convergence from the wave approaching from the west.
The front crosses the area Monday/Memorial Day morning with
precip generally ending by midday. Increasing sunshine and 15c
850mb temps mixing down in westerly flow should allow Max temps
in the low to mid 80s.
Long term /Tuesday through Saturday/...
dry conditions expected Tuesday before a weak cold
front moves through Tuesday night into early Wednesday. Some
scattered showers and a few thunderstorm possible over our area but
mainly dry conditions overall.
Another cold front moves through Wednesday night into Thursday. This
boundary could bring a chance of showers and thunderstorms Wednesday
into Thursday, but ensemble spread leaning towards a drier solution.
There is higher uncertainty into Friday and Saturday as models
disagree, but again, the ensemble spread looks mostly dry. So
overall during this period, we are looking into mostly dry
conditions with periods of showers and maybe a thunderstorm.
High temperatures will be in the 70s and 80s... some 60s at higher
elevations. Low temperatures in the 50s and 60s, with some 40s.
Aviation /20z Saturday through Thursday/...
low pressure over the area shifts east through tonight.
Thunderstorms generally over kcho and south of the District of Columbia metros.
Onshore flow in the wake of the low will allow low/IFR cigs by
late tonight western District of Columbia metros.
A cold front crosses the area Monday morning with thunderstorms
mainly west of the District of Columbia metros Sunday night.
Mostly dry/VFR conditions expected Tuesday into
Thursday with sub-VFR conditions at times with boundaries moving
through. Gusty winds expected on Wednesday afternoon/evening, up to
sub-Small Craft Advisory southerly flow backs to onshore as low pressure shifts
east over the area tonight. Flow shifts back to southerly but
remains sub-Small Craft Advisory Sunday ahead of a weak cold front that crosses
Mostly dry conditions expected Tuesday into Thursday
with some showers and maybe a thunderstorm at times with boundaries
moving through. Gusty winds expected on Wednesday afternoon/evening,
up to 20 kt... a Small Craft Advisory may be needed.
water levels hanging around a half-foot to one foot above
astronomical normals this afternoon. Do not anticipate an
appreciable change through evening. Fortunately, this is the
lower of the two astronomical tides, so we believe that tides
will come in under critical thresholds. The more sensitive sites
likely to hit action stage, however. St George Island will come
the closest. High tide at 4pm; latest indication suggest tide
will peak an inch or two short.
Onshore flow will begin to mark an increase late tonight into
tomorrow. St George Island will be the most susceptible site
(for minor flooding) early Sunday morning, although Solomons may
come close. Widespread action stage at high tide elsewhere.
Will issue the advisory for St. Mary's County, and hold off
elsewhere. By early Monday morning, most sites should reach the
minor threshold. That's too far removed for an advisory at this
On the upper tidal Potomac, etss and hec-Ras both suggest that
high tide tonight will be just under minor threshold, with the
subsequent tide cycles flirting with minor flood. Will not
raise any headlines at this time.
District of Columbia...none.
Maryland...coastal flood advisory from 1 am to 9 am EDT Sunday for mdz017.