Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
939 PM EDT Tuesday Jun 30 2015
cold front approaches the area from the northwest late this
afternoon into tonight. The front will stall across the region
Wednesday through Saturday...with low pressure tracking along the
front later Thursday afternoon into Thursday night.
Near term /until 6 am Wednesday morning/...
Severe Thunderstorm Watch 378 is in effect until 10 PM EDT for
the eastern Virginia Piedmont and portions of central and eastern Virginia. Also for
Dorchester County Maryland and Northampton County NC.
Latest GOES visible imagery depicts expanding cumulus field over the
local area. Isolated to widely scattered showers/thunderstorms have
developed along a line from South Hill to Richmond and the Northern
Neck in vic of the Lee/thermal trough. Beginning to see lightning
activity increasing in these cells...but they will continue to
fight the warm air aloft and modest middle-level lapse rates. Expect
convection to continue in this region through the afternoon...as
locations to the east fight the ridge over the subtropical western
Atlantic. Storm Prediction Center mesoanalysis depicts 1000-1500 j/kg MLCAPE along
with 40-50 knots effective shear. The main threat will be damaging
wind gusts due to strong shear in a region of steep low-level
lapse rates and a well mixed bl. Brief heavy rainfall also
expected. Have maintained 30-40 probability of precipitation this afternoon as convection
Another area of convection associated with the
approaching/weakening front will approach from the west late through
the afternoon. Better height falls/uvm also arrive this evening.
Pv anomaly and increasing winds aloft prognosticated to develop a wave of
low pressure along the thermal trough. Thunderstorms prognosticated to
lifts into the Piedmont from the west...spreading eastward across the
local area. Continued influence from the western Atlantic ridge
expected to suppress activity as it reaches the coast due to warm
temperatures aloft. Low level jet also kicks in this evening...advecting better
moisture into the region. Damaging wind threat continues into the
Probability of precipitation taper off after midnight with partial clearing late
(especially w). May be a few showers lingering eastern Virginia. Low tonight
are forecast to range from the upper 60s to middle 70s.
Short term /6 am Wednesday morning through Friday/...
the frontal boundary settles immediately north of the region Wednesday
as shortwave energy exits the NE coast. Overall...there is little
forcing in deep layer westerly flow. Surface trough also locates along the
immediate coast. Will retain slight chance probability of precipitation for most of the
area...with the exception of low end chance probability of precipitation closer to the
coast where low-level moisture will interact with the surface trough.
Highs forecast in the upper 80s to low 90s. Partly cloudy and dry
conditions are expected Wednesday night with lows in the upper 60s to
The front sags southward into the region by Thursday.
Meanwhile...shortwave energy is expected to track into the central
Appalachians by Thursday afternoon. Shortwave will develop a wave
of low pressure over eastern NC as another stronger area of low
pressure associated with a stronger upper wave locates over the
middle MS valley. 20-30 probability of precipitation Thursday morning increase to 40-50 probability of precipitation
Thursday afternoon and evening...and continuing through the overnight.
Precipitable waters prognosticated to increase to 2+ inches Thursday night in deep layer
southwesterly flow. Anomalous moisture in concert with shortwave energy
lifting along the front will result in periods of moderate to
heavy rainfall Thursday night. Due to the recent rainfall (up to 600
percent of normal this past week)...minor flooding is possible and has
been headlined in the severe weather potential statement. 72 hour rainfall totals (including today)
range from over an inch from the Piedmont into central Virginia to
three quarters of an inch near the coast. Localized higher amounts
are expected. Highs Thursday in the middle-upper 80s. Lows Thursday night
in the middle- upper 60s north to low 70s south.
Boundary and anomalous moisture remain over the region Friday as the
aforementioned middle MS valley low approaches from the west. Will
maintain solid chance probability of precipitation Friday as several waves continue to spread
over the region. Highs Friday in the low-middle 80s (upper 70s far nw)
under mostly cloudy-cloudy skies.
Long term /Friday night through Tuesday/...
upstream blocking pattern results in little movement of overall
synoptic features through the Holiday weekend / medium range period.
Models stall wavy frontal boundary across the middle atlntc region Sat.
GFS wants to push this boundary into North Carolina sun as weak high
prs builds into the region from the north while European model (ecmwf) keeps the
boundary nearly stationary across the region. The boundary prognosticated to lift north
as a warm front Monday with a trough lingering across the area Tuesday.
Thus look for chance probability of precipitation each day as timing of any one disturbance
rather problematic this far out.
Highs Sat / sun in the M-u80s...85-90 Monday / Tuesday. Lows u60s-m70s.
Aviation /02z Wednesday through Sunday/...
VFR conds are expected for the 00z taf period. S/SW winds will
continue as the cold front will remain northwest of the area. Will need to
monitor for scattered thunderstorms this evening. Thunderstorms are possible again Wednesday afternoon
and evening though not as widespread as today.
Outlook...a frontal systm will linger over the area through
Sunday. Mainly VFR conds will prevail outside convection. There
will be chances for afternoon/eveng rain showers/thunderstorms each day with the
highest chances on Thursday and Friday.
will keep current Small Craft Advisory headlines up for the ches Bay tonight as prs
gradient tightens enough for marginal (15-20 kt) winds. Gradient relaxes
Wednesday morning keeping a weaker southerly/southwesterly flow (10-15 kt) through Wednesday night
ahead of an approaching cold front. The front drops into the area from
the northwest on Thursday...with winds becoming light and variable as the front stalls
the lifts back north as a warm front Thursday night and Friday. Waves avgg
1-2 feet and seas avgg 2-4 feet through the weekend.
Marine...Small Craft Advisory until 4 am EDT Wednesday for anz630>632-