Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
311 PM EST Sat Nov 28 2015
high pressure shifts southward today as it slowly weakens. A cold
front sags south through the middle Atlantic region late tonight
through Sunday...stalling across the Carolinas Sunday night into
early next week. The next cold front is expected to cross the
region on Wednesday.
Near term /through tonight/...
this middle and high clouds continue to stream across the area from
the west with enough breaks allowing temperatures this afternoon
to reach the upper 60s to lower 70s. Clouds will increase tonight
and thicken ahead of a cold front. The slow moving cold front was
dropping south into West Virginia and Kentucky late this afternoon. The
front does not push south across the area until later on Sunday.
Rain chances will hold off for at least the first part of tonight.
As the front approached Maryland and northern Virginia scattered showers
will be possible during the early morning areas primarily in the
north and over Maryland. Any rain would be rather light and not
widespread. Have gone with chance probability of precipitation in the extreme northern
and northwest portions of the area. Temperatures remain well above
normal tonight generally in the lower to even some middle 50s close
to the coast and Bay. This is about 10-15 degrees above normal for
Short term /Sunday through Tuesday/...
the cold front sags southward into lower Maryland by Sunday morning...then
into central Virginia by early afternoon and NC middle afternoon. The front
will stall over the Carolinas Sun night into early next week as
the parent high remains well to north over eastern Canada. Rain is
not expected to begin across far northwest-north counties and lower Maryland
until the early morning hours on sun. As the front drops through
the area...rainfall (light and scattered in nature in the morning)
will slowly spread southward and become a little more widespread Sun
afternoon. Scattered light rain may not push into southeast Virginia
until late Sunday afternoon into Sunday evening.
A better chance for more widespread rain in expected late Sunday
night into Monday as better dynamics aloft enhance precipitation
generation. Meanwhile...high pressure slides across southeast Canada into
northern New England during this timeframe extending down into the Middle
Atlantic States. This will create a cold air wedge on the leeside
of the Appalachians into central Virginia reinforcing the seasonably cool
air. Rain chances will continue into Monday/Monday night...but models
have backed off on the amount of overrunning with the cooler wedge
in place. Best probability of precipitation remain over the southern half of the forecast
area where isentropic lift is expected. Pop forecasts for this
period will likely chance as the models have been somewhat
inconsistent handling moisture Monday afternoon into Tuesday.
Overall quantitative precipitation forecast amounts remain fairly light (0.10 inches or less in
any given 6 hour period) with forecast total rainfall averaging
0.30-0.40 inches mainly across the south. Temperatures will be
highly variable on sun as the front drops through the area.
Currently anticipating highs in the middle- upper 50s north to middle-
upper 60s south through temperatures will fall in the late afternoon
across portions of the area. Lows Sun night in the 40s
inland/lower 50s far southeast Virginia and NE NC. Effects of the cad
wedge will be felt on Monday with highs in the middle-upper 40s
along/west of Interstate 95 and in the 50s eastward. Temperatures likely to
hold nearly steady Monday night. Lows in the 40s inland/lower 50s
along the coast.
Rain chances increased again on Tuesday as the shallow cad
remains in place and low pressure develops along the stalled
front just off the coast. The cad does look to slowly erode
Tuesday allowing high inland to get into the lower to middle 50s with
lower 60s closer to the coast and Bay.
Long term /Tuesday night through Friday/...
going with a blend of the 12z GFS/European model (ecmwf) for the extended period.
There is uncertainty with the timing/passage of the cold front on
Wednesday...and how close low pressure tracks toward the southeast and middle Atlantic CST Friday
into Sat. So...cool hi pressure wedge and overrunning will result in
40%-60% probability of precipitation for rain Monday night into Tuesday night...then 30%-50% probability of precipitation for
rain or rain showers with cold front during Wednesday. Dry weather Wednesday night
and Thursday...as hi pressure builds in from the west. At this time...going in
between the GFS and European model (ecmwf) for Friday with regard to low pressure moving off
the southeast CST. So...have 30%-40% probability of precipitation mainly over southeast Virginia and NE NC.
Lows in the 40s to lower 50s Tuesday morng...in the middle 40s to lower 50s
Wednesday morng...in the upper 30s to middle 40s Thursday morng...and in the middle
30s to middle 40s Friday morng. Highs in the middle 50s to middle 60s Tuesday and
Wednesday...and in the lower to middle 50s Thursday and Friday.
Aviation /20z Saturday through Thursday/...
high pressure remains in place through this afternoon...with
considerable middle/hi clouds across the region ahead of the enxt
cold front sagging southeastward through southern New England and the central
Appalachians. The front will reach sby between 6z and 9z...then
continue southeastward on Sunday. The front is not expected to reach kecg
until near the end of the 18z taf period. For tonight...have kept
fog out of all tafs except kecg...due to increasing cloud cover
and some mixing. Kecg should experience only hi cloud cover until
late tonight...which should allow for sufficient radiational
cooling and shallow ground fog to develop...much as has been the
case the last 2 nights. Any fog should burn off by 13z.
As the cold front sags southeastward...ceilings should lower...with most
sites having ceilings in the 4kft to 6kft range by the end of the
taf period. At ksby...ceilings should lower to MVFR Sunday
morning...with some light rain possible during the last few hours
of the taf period.
Outlook...a cold front stalls over the Carolinas Sunday night and
Monday. With cool high pressure building into the region...a cold
air damming situation is expected to develop Monday into Tuesday.
Expect periods of rain and MVFR/IFR conditions at times Sunday
night through at least Tuesday. Next cold front crosses the region
1 PM update...have cancelled Small Craft Advisory for the northern 3 ocean
zones...as seas have dropped below 5 feet. No other changes.
Early morning discussion...the period begins with high
pressure over the waters this morning. The persistent northeast
flow that has been in place most of the week has produced a
consistent swell that has had wave heights between 4 - 6 in the
coastal zones and 2 to 3 in the mouth of the Bay. However...with
the surface high reforming over the Carolinas on Friday...the
surface flow has turned more to the SW over all the waters except
for near Duck NC. As a result...the seas have diminished some over
the northern waters as buoy 9 is down to 4 to 5 feet.
As the surface high weakens today and the front to the northwest
approaches will see the winds turn more SW...but not expecting
them to increase above 10 knots. For now have kept seas around 5 feet
in the outer most portion of the coastal zones...but allowed the
nrshore waves to drop to 3 to 4 feet. So will keep the Small Craft
Advisory in place for now...but will need to monitor whether it
can be dropped early...especially for the northern coastal zones.
The cold front...which has been slowing in each model run over the
last few days should finally push across the waters late Sat night
or Sunday. Initially...not seeing much push as the surface high is
way up in eastern Canada. But by Monday...that high drops southeast into New
England and noses down the coast. This should allow the winds to
increase especially in the coastal zones to around 20 knots on Monday
and Monday night with seas getting back to around 5 - 6 feet. This
could lead to another small craft period. On the Bay and Currituck
Sound however...not anticipating Small Craft Advisory conditions...but will need to
watch the mouth of the Bay for a slight increase in seas .
The wedging high retreats on Tuesday as the strong surface low lifts
into the Great Lakes and the flow in advance of the storm becomes
SW again. The SW flow should again allow the seas to relax some as
the winds also weaken. The cold front crosses the region on
Wednesday and the winds could increase as much colder air moves
into the area.
forecast highs versus record highs for November 28:
location high high year
-------- -------- ------ ----
Richmond 72 76 1990
Salisbury 71 76 1990
Marine...Small Craft Advisory until 7 am EST Sunday for anz656-658.