Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
738 PM EDT Thursday Sep 18 2014
a weak cold front will push south of the area tonight. High
pressure from southeast Canada builds into New England from Friday
into the upcoming weekend.
Near term /through Friday/...
weak surface cold front settles through the forecast area this evening...then is S of the
region by after mdngt as middle level short wave exits off the CST. Ongoing isolated
rain showers in vicinity of the Maryland Eastern Shore (dorchester county) and Farmville
in the eastern Piedmont are expected to shift S-SW the remainder
of this evening. Radar returns are very light and any precipitation
accumulations will be around 0.01 inches at best. Otherwise...most
areas across interior Virginia and the Maryland/Virginia Eastern Shore will be
cloudy to mostly cloudy...partly cloudy across southeast Virginia and NE NC.
Winds vrb and mainly light this evening...becoming north-northeast after mdngt...and a
little breezy near the CST (esp lt). Low temperatures tonight from the M/u50s inland
to l60s right near the CST in southeast Virginia/NE NC.
Short term /Friday night through Sunday/...
another period of onshore winds from Friday into sun as large surface hi pressure
builds from southeast Canada across new eng. Along west/ the NE winds (breezy at
the cst) will be periods of cloudiness...especially Friday through Sat morning. While
no trigger for precipitation across the region...not ruling out isolated rain showers or
drizzle due to the east-northeast surface winds.
By Sat afternoon...the maritime flow weakens...ptntlly allowing drying
over the forecast area. However...surface low pressure developing off the Georgia/Florida CST Friday
night...is forecast to slowly track NE off the southeast Continental U.S. CST. Some
timing differences in the models with respect to this surface low (nam slower than
GFS west/ its eventual movement). Right now...ECMWF/GFS/NAM keep bulk
of that systems moisture to the east. Will bring incrsg cloudiness to coastal
sections of the forecast area beginning Sat...while keeping other places at
worst pcldy. By sun...the low expected to track away from the
CST...resulting in dry/seasonably warm conds over the forecast area.
Hi temperatures Friday mainly in the M/u70s. Low temperatures Friday night from the m50s to
l60s. Hi temperatures Sat from the u70s at the CST to l/m80s inland. Hi
temperatures sun ranging through the 80s.
Long term /Sunday night through Thursday/...
a reinforcing cold front will usher in below normal temperatures through
the extended as cool Canadian high pressure builds over the the NE.
Medium range guidance in fairly good agreement over the eastern Continental U.S.
With the evolving amplified upper air pattern. Amplified pattern
will feature a longwave trough over the eastern Continental U.S. To begin the
period. An associated secondary/reinforcing cold front will sweep
through the region Sunday night-Monday morning. Moisture will be
rather limited along the front (pwats ~1.5 inches)...but height
falls and increasing winds aloft (jet streak rounding the base of
the upper trough) will provide forcing for ascent over the region.
Should be enough for slight chance/isolated probability of precipitation...with the best
coverage over the northern local area. The bigger headline with the front
will be the dry air and cold air advection Post frontal as high
pressure builds in from the W-NW. Monday will be a transition day as
the coolest/driest air lags behind the front. Reinforcing shortwave
crosses the Great Lakes-NE states Tuesday as the trough axis pushes off
the eastern Seaboard. Meanwhile...mid-level ridge will progress eastward over
the Central Plains and into the eastern Continental U.S. Tues-weds. Cool Canadian
high pressure prognosticated to build over New England Wednesday. Upper/surface high
pressure remains over the region Thursday. The result will be continued
dry conditions and below normal temperatures.
Highs will be below average through the period...with Tuesday and Wednesday being
the coldest days at nearly -1 Standard dev (low-middle 70s). Went a little
above wpc guidance as low level thicknesses yield slightly warmer
temperatures under mostly sunny skies. Lows generally in the low-middle 50s
inland to low 60s near the coast. Few locales in the Piedmont may
drop into the upper 40s at night.
Aviation /00z Friday through Tuesday/...
as of 23z...VFR should hold for the 00z taf period. Broken-overcast clouds
with bases from 5 to 8 kft were over most of the area except the far
southeast. A couple of spotty light showers were present but should not
affect the taf sites. Widely scattered showers are expected again
across northern and western sections with a slight chance for a shower at
sby and ric. Winds will continue from an easterly direction becoming
primarily NE on Friday. Winds will be light overnight and around 10
knots on Friday.
Outlook...mainly VFR and dry weather are expected to continue into
early next week. High pressure will prevail though a weak cold front
crosses the area on Sunday night to early Monday.
weak cold front crosses/dissipates over the waters this evening as
high pressure builds over southeast Canada and the NE states. Weak pressure
gradient has produced Ely winds over the water...average 5-10 knots. Waves
generally 1-2 feet (locally up to 3 in the mouth of the bay) and seas
3-4 feet. Flow becomes northeasterly tonight and Friday as high pressure builds
over New England. Gradient will strengthen...with speeds reaching 20
knots over the coastal waters Friday afternoon. Combination of strong surface
high pressure...NE flow and warm waters may result in Small Craft Advisory winds over
the coastal waters. Capped at 20 knots for now. However...seas will
build to 4-5 feet late Friday...first in the northern waters...then spreading
southward over the remaining coastal waters Friday evening-night. Small Craft Advisory
headlines have been hoisted for the coastal waters late Friday through Friday
night (third period). If flow is stronger than forecast...6-7 feet
seas will be possible. 4 feet waves also possible at the mouth of the
High pressure will begin to slowly push off the NE coast Sat as low
pressure develops along a stalled boundary off the southeast coast. The low
will lift along the boundary through the weekend...locating off the
middle-Atlantic coast sometime late this weekend. Small Craft Advisory conditions are
not anticipated at this time based on the gradient winds...but spatial and
timing differences with respect to low pressure lend little confidence. Seas
will likely remain elevated (4-5 ft) through Sat...but flow will
briefly become S-southeasterly late Sat-Sat night as the surface ridge breaks
down over the water. This will allow seas to drop below Small Craft Advisory conds.
Surface low lifts NE off the coast late in the weekend with a cold front
forecast to cross the region Sun night-Monday morning. Below normal
temperatures early next week over warm waters may produce periods of Small Craft Advisory
conds through the middle of next week.
Maryland...moderate rip current risk through Friday evening for mdz025.
NC...moderate rip current risk through Friday evening for ncz102.
Virginia...moderate rip current risk through Friday evening for
Marine...Small Craft Advisory from 4 PM Friday to 6 am EDT Saturday for