Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
1055 am EDT Monday Jul 14 2014
low pressure moves across the Great Lakes region today with a
trailing cold front approaching the local area from the northwest
tonight into Tuesday morning. The front is expected to slowly
push through the local area Tuesday afternoon and night. The front
pushes off the coast on Wednesday...as high pressure begins to
build in from the northwest.
Near term /through tonight/...
anomalously deep upper low over southern Canada looks to push a strong
shortwave southeast through the Great Lakes/upper Midwest today. This
allows low level flow from the SW to increase across the local
area...for another very warm to hot afternoon. Highs again 90-95...except
cooler 80s at the beaches. Forcing for ascent will remain rather
minimal across the local area much of today...before increasing
somewhat by late afternoon/evening into the overnight hours. In
addition...strong SW flow in the boundary layer often dries the akq
County Warning Area out (especially southeast Virginia/NE nc). Therefore...will maintain chance
probability of precipitation (30-40%) across far north-northwest portions of the County Warning Area until
evening...tapering to only 15-20% probability of precipitation in southeast Virginia/NE NC. Better
forcing does arrive tonight...especially northwest-west parts of the County Warning Area.
However...this will largely be offset by poor diurnal timing. Storm Prediction Center
has backed off on their slight risk area for the local area
today...basically keeping it across our northwest/northern most counties...which
is in line with the aforementioned reasoning. Shower/thunderstorm coverage
should actually increase across the County Warning Area tonight given height falls and
approach of a surface cold front (pops 30-50%). Warm tonight with lows
Short term /Tuesday through Wednesday/...
by Tuesday...models in decent agreement west/ timing...the surface cold
front moves into the region and upper level support including rrq
forcing from the upper jet arrives later in the day. Still
somewhat unclear as to precipitation coverage in the morning hours due to
varying model solutions and presence of old boundaries from tonight.
Will carry high chance probability of precipitation most areas in the am hours with likely probability of precipitation
by afternoon all zones...some severe potential exists (mainly straight
line wind threat) as deep layer shear values increase to > 30 knots
(not bad for time of yr). Severe threat will tend to transition to
mainly a heavy rain threat by Tuesday night as the cold front slowly
moves east. Best chance of severe thunderstorms on Tuesday (slight risk by
spc) will be across eastern portions of the County Warning Area where the best
buoyancy/instability will be located along and ahead of the cold
front. Localized flooding may also be an issue...and may persist
overnight Tuesday into Wednesday am given slow movement of the
front...strong forcing for ascent...and precipitable waters in excess of 2
inches. Will continue to highlight these threats in the severe weather potential statement. If
tempered by clouds/precipitation highs Tuesday would generally remain in the
middle/upper 80s...but could reach into the lower 90s if some sun
develops for a few hours through midday. Have blended these 2
scenarios for forecast highs...generally going upper 80s northwest to around 90 f
southeast. Lows Tuesday night middle 60s northwest to around 70 f southeast.
On Wednesday...models now also into decent consensus regarding the surface
front position...just pushing off the southeast Virginia/NE NC coast as of
12z/Wed. Low level flow shifts to the north-NE most areas behind the
front with a cooler/drier airmass eventually overspreading the
region from the W/NW. Likely probability of precipitation will still prevail through the
morning along the coast (chc probability of precipitation elsewhere)...but skies should
become partly sunny along/west of I-95 in the afternoon as any
leftover precipitation is confined to the coast. Cooler west/ highs in the
upper 70s to Lower-Middle 80s.
Long term /Wednesday night through Sunday/...
long term period will feature slightly below normal temperatures and frequent
chances for precipitation. For Thursday...surface hi pressure will be centered over the
Ohio Valley with a broad area of weak low pressure over the southeast states...and
middle-level energy approaching from the Central Plains/Midwest. With low
pressure near the Carolinas...could see some rain showers/thunderstorms over southeast areas of
the forecast area...but nothing widespread expected. Hi temperatures average in the middle
80s. The aforementioned surface hi moves off the NE CST Friday...with
approaching middle-level energy leading to a continued chance for
rain showers/thunderstorms (30-40% pops). The pattern continues into Sat and sun
with chance probability of precipitation. Exact timing of the precipitation is difficult to predict
with this being several days out. Hi temperatures Friday through sun in the middle
80s...with low temperatures in the middle to upper 60s.
Aviation /15z Monday through Friday/...
surface high pressure has settled off the southeast coast...with
low pressure well north of the region and a frontal boundary aligned
from northern New England back through the Ohio Valley. A south-southwest wind
will increase to 10-12kt this morning...with gusts up to 20kt
possible this afternoon. Isolated-scattered afternoon/evening rain showers/thunderstorms and rain are
expected as the aforementioned frontal boundary nudges southward.
A stronger cold front arrives from the west Tuesday and Tuesday
night and will maintain the potential for shra/tsra. The front
slowly moves offshore Wednesday...with drier air prevailing
through Friday as high pressure builds north of the region.
a southerly wind will continue to average 10-15kt (15-20kt north of cape
charles) today and tonight as high pressure remains anchored off the
southeast coast...and secondary low pressure develops over the Great
Lakes. This area of low pressure lifts north of the Great Lakes Tuesday
and Tuesday night...with the trailing cold front approaching from
the northwest Tuesday...and slowly crossing the area Tuesday night. 14/00z
wavewatch builds seas to 5ft out near 20nm tonight north of Parramore
Island. However...the nwps wave model based on forecast wind grids
keeps seas at 4ft...which is further supported by our local wave
algorithm. Given this...no Small Craft Advisory will be issued at this time.
Showers/thunderstorms are likely Tuesday afternoon and evening as the front
crosses the area. A wind shift to north is expected behind the front. A
modest sub-Small Craft Advisory 10-15kt northerly surge is possible over the Bay
early Wednesday as cooler air filters in from the northwest. High pressure
then builds north of the region through the end of the week as weak low
pressure lingers over the southeast. This will maintain light
onshore flow at or below 10kt.