Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
401 PM EDT Sat Jul 12 2014
high pressure remains off the coast through the weekend. Low pressure
moves across the Great Lakes region with the trailing cold front approaching
from the northwest early next week. The front is expected to slowly
push through the local area late Tuesday into Wednesday.
Near term /until 6 am Sunday morning/...
latest analysis showing weak surface high pressure centered off the
middle Atlantic coast...with low pressure deepening across the middle/upper
MS valley. Flow aloft is west-northwest. Radar showing some isolated/widely
scattered thunderstorms over the Appalachians and an isolated shower
briefly went through Fluvanna County over the past hour. Latest Storm Prediction Center
mesoanalysis Page showing a band of ml convective available potential energy on the order of 1000
j/kg along the mountains so will continue to maintain a 20% pop along
with scattered/broken cloud cover across the northwest counties through 9 PM.
Elsewhere scattered cumulus will generally give way to mainly clear skies after
sunset with seasonable temperatures. Lows tonight mainly in the
upper 60s to lower 70s. Overall...expect less fog than past 2
nights as low level flow shifts more to the S/SW overnight (some
patchy fog possible mainly over interior southeast Virginia/NE nc).
Short term /6 am Sunday morning through Tuesday/...
combination of high pressure off the coast and a deepening low
pressure system tracking through the Great Lakes and eastern Canada
will allow winds to shift to the south-southwest. Temperatures will warm a few
degrees over today's readings...with Lower-Middle 90s along/west of
the I-95 corridor...to upper 80s to lower 90s farther east. Bulk
of forcing for showers/thunderstorms looks to stay north of akq County Warning Area for the
most part so will favor the drier GFS over the wetter NAM
solution. Will carry a 30% pop over the far north...with 20% probability of precipitation
into central Virginia and dry across approximately the southern 1/2 of the
County Warning Area.
Deep upper low over Manitoba looks to push a strong shortwave
southeast through the upper Midwest into the western lakes on Monday. This
allows low level flow from the SW to increase further. Storm Prediction Center has northwest
1/3 of County Warning Area outlined for slight risk for severe thunderstorms although much
uncertainty remains given this is 2 days out. A strong SW flow in
boundary layer often dries akq County Warning Area out (especially southeast Virginia/NE nc).
For now...will maintain high chance probability of precipitation developing by Monday afternoon over
the northwest counties tapered to only 20% probability of precipitation in southeast Virginia/NE NC (think GFS
depiction of am showers in the southeast is overdone). Highs lower to middle
90s most areas (upper 80s to lower 90s at the beaches). Probability of precipitation
actually may increase somewhat Monday evening all the way to the
coast so will have at least 30% probability of precipitation all zones. Warm/humid Monday
night west/ lows mainly 70-75 f. By Tuesday...cold front moves closer to
the region and upper level support including rrq forcing from the
upper jet arrives. Will carry likely probability of precipitation by afternoon all zones...some
severe potential will tend to transition to mainly a heavy rain
threat Tuesday night. Highs in the upper 80s to lower 90s.
Long term /Tuesday night through Saturday/...
as an anomalous trough develops over the eastern Continental U.S....height falls
and increasing winds aloft will result in better forcing for ascent
over the local area. Strong speed maximum rounds the deep closed low
over the Great Lakes Tuesday...ejecting the low northeastward into southeast Canada.
The cold front drops into the region Tuesday night. Strongest dynamics
lift well north of the region with the closed low...but height falls
and perturbations in the west-southwest flow will result in scattered-numerous
showers/thunderstorms. Strong to severe thunderstorms also possible
as models depict marginal shear and MLCAPE > 2000 j/kg. Anomalous
trough will push the southern portion of the front into the deep
south...but the eastern portion likely stalling over/off the
middle-Atlantic coast as an anomalous upper ridge remains parked over
the western Atlantic. Will maintain elevated probability of precipitation Wednesday across the southeast as
the front will likely linger over the region. Highs expected in the
low to middle 80s for the week after frontal passage. Surface high
pressure will be slow to build into the region in wake of the front
as upper trough remains over the eastern Continental U.S.. model guidance depicting
the high ridging south across the middle-Atlantic creating NE/east-northeast
winds. This setup can cause daytime temperatures to be below climatology with
cloudy conditions. The stalled frontal boundary remains across the
southeast through the weekend and with a passing shortwave trough...showers
and thunderstorms may be possible Sat night into sun.
Aviation /20z Saturday through Thursday/...
surface high pressure continues to dominate the region with VFR conds
and light east-southeast winds. Expect VFR conds through the afternoon and evening
with no expected flight hazards. There is the slight chance of an
isolated thunderstorm developing west of ric in the higher elevations during
the late afternoon/evening hours. Winds will shift to the S-SW by early
Sunday as the high moves offshore. Shifting winds and good sun today
will reduce chance of dense fog in the morning although there is a chance
for patchy MVFR fog in the early morning.
Dry weather continues into Sunday with the high offshore and low
pressure tracking well northwest of the local area. A cold front will bring
the potential for rain showers/thunderstorms and rain Monday and Tuesday.
calm conditions will continue today as a stationary boundary remains
south of the akq marine waters. Meanwhile...broad area of high
pressure stretches from New England through the southeast Continental U.S. Today. Flow
returns to the south late Sat night and sun as the high slides
offshore...increasing slightly to 10-15 knots gusting to 18-20 knots
Sunday evening. Southerly flow persists through early next week. A cold
front will approach the waters late Monday...crossing the waters Wednesday
morning. Persistent southerly flow may push seas to 5-6 feet across the
northern waters by Monday night. High pressure builds in Post front
briefly turning winds to the NE with the winds becoming weak and
variable as the high building east and an area of low pressure forms
along the stalled frontal boundary across the southeast.