Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Wakefield Virginia
104 am EST Thu Nov 14 2019
Canadian high pressure settles over the mid-Atlantic region
tonight into Thursday. Low pressure develops off the southeast
coast Friday and tracks off the Carolina coast into Saturday
while strong high pressure builds in from the Great Lakes this
Near term /until 6 am this morning/...
as of 925 PM EST Wednesday...
Cold sfc hi pres has settled over the local area this evening.
Most temperatures have fallen into the 20s under mainly sky clear.
A cold/mainly sky clear night is expected W/ lgt-vrb winds. Nudged low
temperatures down a couple of degs f most places (based on
trends and hi res near term guidance). Lows in the teens to
l20s inland to the M-u20s in far southeast Virginia- coastal NE NC.
Short term /6 am this morning through Saturday night/...
as of 330 PM EST Wednesday...
Clouds increase on Thursday as a low pressure system begins to
organize over the deep south. Precip will be well north and east of
the system. Some of this moisture may try to reach the far southern
portions of the forecast area by late Thursday but expect much of
the day to be dry. Temps will remain below average on Thursday with
highs in the 40s west of I-95 and in the 50s east.
Low pressure is expected to get organized over the southeast coast
on Friday along a stationary boundary. While this system is forecast
to drift northeast, the precip shield will extend well north of the
center and rain showers will impact the southeast portions of the forecast
area throughout the day. A secondary low pressure system is expected
to develop off the southeast coast on Saturday and also drift
northeast. Once again, the bulk of the precip should be across the
southeast portions of the forecast area. Meanwhile, a strong high pressure
system builds into the Great Lakes area Friday and Saturday which
will drag drier and cooler air in from the north. There will likely
be a large dewpoint spread from northwest to se, with dewpoints around 30
northwest to around 50 southeast where there will be more influence from the low
pressure systems off the coast. Through at least Saturday, there
doesn't appear to be any p-type issues as long as the bulk of the
precip remains over the southeast portions of the area. If that precip
advances further north into the colder air, some mixed precip is a
low probability. High temps Friday likely to remain cool under cloud
cover and precip, expect mid to upper 40s west to near 60 along the
coast. Saturday will be a bit colder as cooler air filters in from
the north, expect highs mainly in the 40s with lower 50s along the
coast. Min temps Friday and Saturday range from the 30s northwest to 40s
Biggest concern Saturday may end up being the winds. Strong pressure
gradient develops as the strong high pressure shifts east over the
Great Lakes and low pressure remains off the coast. Gusty north/NE winds
will develop and will be strongest along the coast where 35-45 mph
gusts are possible beginning early Saturday.
Long term /Sunday through Wednesday/...
as of 315 PM EST Wednesday...
The main models are still in agreement with an area of low pressure
developing off the southeast coast Saturday, and then eventually lifting to
the north-northeast late Sunday into Monday. There is however disagreement on
how much precipitation is brought into the region from this system.
The GFS remains a little further west with precipitation shield,
while the European model (ecmwf) keeps the majority of the precipitation across the
far E/offshore. For now, took a blend of the two solutions with
chance pops mainly east of I-95 and increasing towards the coast and
slight chance pops to no pops west of I-95. Due to the cold air that
will remain in place across the west Saturday night, did introduce a
slight chance of rain/snow - mainly along/west of I-95. Any wintry
precip that does develop may be more of the freezing rain or ice pellets variety rather
than just pure rain/snow due to warmer air aloft. However,
confidence for wintry weather remains fairly low at this time and
impacts appear relatively minimal. Any wintry precip changes to rain
during the day Sunday, with rain chances generally decreasing from
SW to NE. The coastal low will continue to lift to the north-northeast Monday
while another shortwave digs into the Gulf states, potentially
developing another coastal low by the middle of next week.
Temperatures remain below average on both Sunday and Monday, before
a gradual warming trend Tuesday and Wednesday when temperatures
climb closer to normal.
Aviation /06z Thursday through Monday/...
as of 100 am EST Thursday...
Sfc high pressure currently over the region will slide offshore
this afternoon. VFR conditions are expected through 03z Friday.
A weak surface low will slide into the region from the
southwest bringing increased pops for light rain and potential
MVFR conditions after 03z Friday for ecg, orf, and phf.
A coastal low will linger off the southeast coast Fri/sun bringing the
potential for rain and degraded flight conditions (esp at the
coast) through the weekend.
as of 330 PM EST Wednesday...
Afternoon surface analysis shows high pressure centered over Virginia just
west of the waters. Winds have finally subsided below Small Craft Advisory criteria
in the mouth of the ches Bay, with north winds averaging 10-15 kt
elsewhere. Seas are still 5-7 ft over the srn Virginia/NE NC coastal
waters, with 3-4 ft seas north of Parramore Island. Will allow scas for
the mouth of the Bay/nrn coastal waters to expire at 4 PM. Will keep
other Small Craft Advisory headlines in place, as seas will be slow to diminish this
evening over the srn coastal waters (especially S of the Virginia-NC
border). Winds diminish to below below 10 kt tonight as high
pressure builds over the waters. Seas should fall below 5 ft in the
NE NC coastal waters by 06-09z Thu.
The area of sfc high pressure moves offshore Thursday into early
Friday for a period of sub-Small Craft Advisory conditions. Marine conditions start
to deteriorate during the second half of the day on Friday as an
area of low pressure starts to deepen off the Carolina coast while
~1035 mb high pressure builds into the nwrn Great Lakes. The
resulting pressure gradient will allow north winds to increase to 20-25
kt by 00z Sat (with gusts up to 30 kt). While most of the guidance
has this first low tracking well to our south/east, the 12z/13 NAM
has the low tracking offshore of NE NC (which would bring gale
conditions to the ocean/lower ches Bay on fri). Will disregard the
NAM solution for now, given that it is an outlier.
Another (stronger) area of low pressure then deepens off the
Carolina coast late Saturday-Sunday morning as the strong high
becomes centered over New England. An extended period of adverse
marine conditions appears very likely from Fri night-Sunday with a
very good likelihood of widespread gale conditions and the potential
for storm conditions for at least our southern coastal waters. Even
the rivers (especially the lower james) could experience a period of
frequent gale force gusts. The most likely onset of gale conditions
looks to be late Friday evening-early Saturday morning (local wind
probabilities show probs of gale force gusts ramping up to 70-90%
during this timeframe over the ocean/lower ches bay). Winds during
the period of gales this weekend look to be out of the N-NE. There's
still some uncertainty in the models regarding the strength/overall
timing of the two coastal lows, but the 12z/13 suite of guidance has
come into better agreement with respect to the track of the two
lows. Seas are forecast to build to 12-16 ft offshore with waves in
the ches Bay up to 4-7 ft (perhaps up to 8 ft at the mouth). Winds
are expected to diminish to below gale criteria late Sun night-early
Mon am, before falling below Small Craft Advisory criteria during the late Mon-Mon
night timeframe. However, seas likely remain elevated through early
as of 355 PM EST Wednesday...
Coastal low pressure will produce strong and persistent onshore
flow beginning Friday night and lasting through the weekend.
Minor to locally moderate coastal flooding will be possible for
several high tide cycles. The highest threat for locally moderate
coastal flooding (at least through sun am) looks to be in areas
near the lower ches Bay, James River, and srn coastal waters.
a strong cold front will cross the region today, with the
coldest air of the season spreading across the area tonight
through Thursday. Record low and low Max temperatures for
Wednesday 11/13 are below:
location low (11/13) year
------- -------- ------
Richmond 20 1941
Norfolk 27 1934
Salisbury 19 2001
location (11/13) year
-------- ------ ----
Richmond 37 1911
Norfolk 42 1920
Salisbury 42 1977