Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
130 am EDT Tuesday Sep 1 2015
low pressure slides off the Carolina coast overnight. Weak high
pressure then persists over the area through the end of the week
with occasional weak troughs of low pressure.
Near term /until 6 am this morning/...
latest radar mosaic indicating showers have diminished in areal
coverage largely as expected...although dual-pol differential
reflectivity data (zdr) indicating there are still some spotty
rain showers over the southeastern third of the area. Will hold onto
wording accounting for a slight chance for a shower or two overnight
across this area. Expect dry weather will prevail for most overnight as
surface high pressure nudges into the area from the west. Noting some
clearing occurring a bit quicker than previously expected across
the Piedmont and northern Virginia. Have accounted for some fog late
tonight over much of the area, with the best chance mainly
west/southwest of Richmond where majority of recent rainfall has
occurred coincident with aforementioned partial clearing and light
winds overnight. Also nudged min temperatures down a degree out west, but
otherwise quite similar to the going forecast...with lows in the
upper 60s to lower 70s.
Short term /6 am this morning through Thursday/...
short term period will be characterized by weak surface hi pressure on average
with an occasional weak trough of low pressure developing over the middle
Atlantic. For Tuesday...decreasing moisture profiles and weak forcing for
ascent will yield mainly dry conds...with at best a slight chance
of a rain showers/thunderstorm over southern portions of the forecast area. With rising middle-level
thicknesses...temperatures will be warmer than the previous few days and
maximum out near 90 in most areas...about five degrees above normal.
A weakening middle-level shortwave trough approaching from the west Wednesday afternoon
will lead to a slight chance-chance of shras/tstms...with the best
chance over western areas. Moisture profiles do not favor widespread
heavy precipitation. Similar probability of precipitation into Thursday with a weak surface trough over the
region and little upper-level support. Temperatures maximum out in the low 90s
most areas Wednesday and thug...mid/upr 80s near the CST. Overnight low
temperatures in the upper 60s to lower 70s.
Long term /Thursday night through Monday/...
extended period begins with a backdoor front moving across the area
on Friday...resulting in surface high pressure over the NE US
ridging south. The ridging will help to moderate temperature and
humidity through the weekend due to the NE to east flow. Weak middle level
troughing off the southeast will help generate showers and thunderstorms to
our south...but as the ridge at the surface and aloft builds over
the area...precipitation will be suppressed to the south of the akq
Forecast highs in the middle 80s inland and lower 80s near the coast
Sat through Monday. Low temperatures will range from the middle 60s to upper 60s
across the area.
Aviation /06z Tuesday through Saturday/...
models not picking up on the IFR stratus that is overspreading
the Piedmont Erly this morning...but is picking up on the MVFR
stratus across the southeastern taf sites. Given not much wind prognosticated
over the next 6 hours and the current GOES IFR Sat loop...decided to
keep the IFR St at ric through 12z with MVFR 1-3k feet at orf/phf/ecg
(basically the areas which received rain ystrdy). Sby problematic
for the 06z taf given sky clear there now. Still think sby will see St
develop before sunrise. Also added vcsh to ecg given the showers currently
moving NE across NE NC.
Expect the St/ patchy fog to burn off before 15z with scattered-broken cumulus
(arnd 5k ft) dvlpng drng the late morning/afternoon hours. This cumulus dspts
before 00z with sky clear after that. Variable winds at or below 10 kts today as high
prs moves ovrhead.
Outlook through Saturday...mainly dry with VFR conds. Xcptn being
the possiblity of patchy fog for a few hours near sunrise.
weak area of high pressure remains over the local waters with the
center of the high offshore. The result is southerly flow at or below 10 knots.
Seas 2 feet in the north and 2-3 feet south. Waves across the Bay 1-2
feet. A slight strengthening of the gradient tonight will push speeds
to 10-15 knots. Weak area of low pressure forms off the Carolina coast
on Tuesday resulting in variable wind directions through Wednesday. Seas
generally 2 feet and waves 1-2 feet. High pressure weakens over the
region Friday...as another area of high pressure builds southward over New
England. Prolonged NE flow may bring potential Small Craft Advisory conditions during
the upcoming weekend as seas could build 4 to 5ft.