Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Wakefield Virginia
722 am EDT Fri Sep 30 2016

Synopsis...
an upper level low lingers over the Ohio Valley today. Meanwhile,
high pressure builds well north of the region and steers a
moisture rich airmass into the region through today. Slowly
improving conditions are expected into the weekend as the upper
low lifts back to the north.

&&

Near term /through tonight/...
latest GOES water vapor imagery depicts the stubborn and
anomalous upper low over central Kentucky. Plume of deep moisture
has located along the coast, with blended total precipitable
waters upwards of 150 to 200 percent. Showers, some heavy at
times, persist over the Maryland Eastern Shore as an upper level
disturbance lifts over the Delmarva. They heavy rain threat
continues through the morning thanks to anomalous moisture and
diffluent flow aloft. Elsewhere, showers associated with another
spoke of energy lifting around the upper low has spread into the
Piedmont. Stable low levels has resulted in fog and stratus
between the areas of showers. The Flood Watch for the Maryland
Eastern Shore has been extended up noon to account for potential
of locally heavy showers.

Another piece of energy expected to lift around the southern
periphery of the upper low today as surface low pressure slowly
lifts along the southeast coast. The stalled frontal boundary
remains over the Piedmont. The boundary will provide enhanced low-
level convergence this afternoon as the upper level disturbance
lifts into the region. Mid level dry air also begins to punch into
the region from the southwest. Drying mid levels and dewpoints in
the upper 60's progged to result in marginal instability this
afternoon. Instability could be enhanced by breaks in the clouds.
Deep layer shear will also be increased thanks to deep southerly
flow upstream of the upper low. The result will be a line of
showers and thunderstorms lifting across the region this afternoon
into this evening. Hi-res guidance disagreeing on the exact
evolution of the showers/thunderstorms, but based on the air mass
and associated upper level forcing, expect the line to be fairly
organized. Storm Prediction Center has the area in a marginal risk for severe weather.
The main limitation being cape and clouds. Gusty winds and small
hail are possible, but locally heavy rainfall remains the main
threat. Best coverage will be north and west of Richmond. Highs
generally in the upper 70's to low 80's.

Area of showers lifts northeastward this evening toward the
northeast zones as the front begins to lift. Deepest moisture flux
and convergence pushes offshore, which will limit overall rainfall
amounts. However, additional localized flooding is possible in the
areas sensitive from the previous days rain. Drying inland this
evening through the overnight with some breaks in the clouds
possible over the southern Piedmont. Mild again with lows in the
mid to upper 60s.

&&

Short term /Saturday/...
dry air continues to entrain into the system Saturday as the
upper low fills and lifts northward. The result will be gradually
improving conditions. Addition energy lifts over the region in
southwest flow aloft, so can't rule out isolated to scattered
showers east of Interstate 95. Sky conditions also improve with a
partly cloudy sky inland, but remaining moistly cloudy near the
coast. Highs Saturday range from the upper 70's to low 80's, but
less humid as dewpoints drop into the upper 50's to low 60's
inland.

&&

Long term /Saturday night through Thursday/...
anomalous upper low over the Ohio Valley during the short term will
make its way slowly north and northeast early next week...allowing
for high pressure to build into the mid Atlantic states. A chance
for showers remains Sunday over the Chesapeake Bay and portions of
Hampton Roads and east and end all areas by Monday morning. A strong
surface high will remain over southeast Canada which will increase
its influence across the eastern Seaboard early next week with its
associated easterly flow. A chance for showers returns to the
forecast Tuesday and Wednesday. Tropical cyclone Matthew may have an
influence late in the week...especially in the marine area.
Uncertainty remains in terms of the timing and track. Refer to
guidance from the National Hurricane Center and extended forecasts
from the weather prediction center for details.

High temperatures from 75 to 80 Sunday and Monday lower to around 70
in the northern Piedmont to the upper 70s northeast North Carolina
by Thursday. Lows will range through the 60s.

&&

Aviation /11z Friday through Tuesday/...
onshore flow and an anomalously moist air mass has resulted in
widespread IFR conditions across the region early this morning.
Conditions have been bouncing between MVFR and IFR at
korf/kphf/kecg...but expect overall IFR conditions to persist
through 12-14z. Ceilings improve to MVFR mid morning. Showers
have diminished inland, but persist over the Maryland Eastern
Shore. Heavy rain remains a threat at ksby. Onshore surface winds
are generally at or below 10 knots.

Another round of showers and thunderstorms expected across the
region this afternoon. Showers may be heavy at times. MVFR
ceilings expected to persist through the afternoon from kric to
ksby while improving southeast. Winds become east to southeast at
or below 10 knots.

Outlook: unsettled conditions persist through the overnight with
another period of IFR conditions possible. Flight conditions
finally begin to improve Saturday as the front pushes offshore.
High pressure builds in from the southwest through early next
week as low pressure remains over the northeast.

&&

Marine...
strong/anomalous sfc high pressure (1035 mb+) still centered over
eastern Canada with a weak trough of low pressure along the Virginia
coast. The stronger pressure gradient is shifting north and winds have
diminished significantly except across the northern coastal zones
where 20-25 knots winds persist for a few more hrs. Sca's for the
mouth of the Bay have been extended through 1 PM (for 4 ft waves)
elsewhere, sca's will remain in effect through today/tonight for
southern coastal waters (and into Sat farther north as seas are slow
to subside with residual 9-10 sec period swell).

Calmer marine conditions expected Sat ngt thru Mon.

&&

Tides/coastal flooding...
the synoptic pattern with strong high pressure centered over
eastern Canada with a slow moving boundary/sfc low pressure inland
over the Carolinas/mid-Atlantic will continue to bring persistent
east-northeast flow to the area this evening/Fri. As of 11z, departures avg
1.5 to 2.0 feet for the most part.

Have updated cfw to expand the coastal Flood Warning to include
all of the Virginia Northern Neck zones through the upcoming high tide
cycle that occurs late this morning into the aftn and the Maryland
Eastern Shore counties along the Bay (both for moderate flooding
expected). Elsewhere, have continued coastal flood advisories
(and expanded to include Virginia beach) to include both the upcoming
morning/early aftn high tide cycle and the following late
evening/early Sat am cycle. Looking at latest currents data in the
Lower Bay suggests outgoing tides are slowly strengthening but
water will remain piled up in the Bay for at least 2 more cycles.

In addition, high rip risk for all beaches as seas are remaining
elevated at 5-7 ft with 9-10 second dominant periods.

&&

Akq watches/warnings/advisories...
Maryland...coastal Flood Advisory until 1 PM EDT this afternoon for
mdz024-025.
Flash Flood Watch until noon EDT today for mdz021>025.
Coastal Flood Warning until 9 PM EDT this evening for
mdz021>023.
NC...none.
Virginia...coastal Flood Advisory until 4 am EDT Saturday for vaz089-090-
093.
Coastal Flood Advisory until 2 am EDT Saturday for vaz084>086-
095>097-523>525.
Coastal Flood Advisory until noon EDT today for vaz098.
Coastal Flood Advisory until 1 PM EDT this afternoon for
vaz099-100.
Coastal Flood Warning until 5 PM EDT this afternoon for
vaz075>078.
Marine...Small Craft Advisory until 10 PM EDT Saturday for anz650-652-
654.
Small Craft Advisory until midnight EDT tonight for anz656-658.
Small Craft Advisory until 1 PM EDT this afternoon for anz634.

&&

$$
Synopsis...ajz/Sam
near term...ajz/Sam
short term...ajz/Sam
long term...lsa
aviation...ajb/Sam
marine...lkb
tides/coastal flooding...akq

National Weather Service Glossary of Abbreviations