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fxus61 kakq 271017 
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Area forecast discussion
National Weather Service Wakefield Virginia
617 am EDT Thu Apr 27 2017

Synopsis...
a cold front approaches the mid Atlantic region today, stalling
near the mountains tonight. High pressure prevails off the
southeast coast the rest of Friday through the weekend. The next
cold front pushes across the region early next week.

&&

Near term /until 6 PM this evening/...
latest GOES water vapor imagery depicts a broad/anomalous upper
trough encompassing much of the western/central conus, with an
upper level ridge over the east. At the surface, weak area of
low pressure is located offshore the northeast coast with high
pressure well offshore extending westward over the southeast. A
cold front associated with the upper trough is located along the
Mississippi River valley. A dense fog advisory remains in
effect for the lower Maryland Eastern Shore, with an area of
dense fog visible in the obs and on satellite. Otherwise, only
some patchy fog inland as light southerly flow and relatively
dry low levels have kept widespread fog at Bay.

Fog expected to erode/lift shortly after daybreak in response to
quickly warming temperatures. The upper level ridge axis slides
offshore late morning as the central US trough de-amplifies and
lifts over the Ohio Valley and into the Great Lakes region. An
associated cold front will reach the central Appalachians late
today. Increasing return flow ahead of the front (southwest
gusts of 20-25 mph) and 850mb temperatures around +14 to +16c
(+1 Standard deviation) results in a warm day, with temperatures
generally 10+ degrees warmer than yesterday. Highs generally in
the mid 80's. Cooler along the coast. Increasing mid to upper
level clouds late today may keep some of the far western
Piedmont in the low to mid 80's. Otherwise, outside of some high
clouds spreading over the region today from a decaying line of
showers, a mostly sunny sky is expected.

&&

Short term /6 PM this evening through Saturday/...
showers and thunderstorms progged to develop along the cold
front this afternoon from the Ohio Valley to the southeast. Hi-
res guidance pushes a weakened version of the convective line
into the Piedmont early this evening as the upper level forcing
becomes displaced from the deepest Gulf moisture. Short term
guidance indicating better moisture return compared to 24 hours
ago thanks to a developing 30-40 kt low level jet. Good moisture
flux advects anomalous precipitable water values into the
region ahead of the line/pre-frontal surface trough. Thermal
soundings indicate elevated instability as height falls and cold
air advection aloft steepen mid level lapse rates. Showalters
range from -1 to -2. Deep layer shear progged around 30-40 knots
due to increasing winds aloft. However, given the lack of
overall forcing and the convective line outracing the front,
have kept pops in the chance category tonight. Main threat from
thunderstorms will be locally heavy rainfall. Mild tonight, with
lows generally in the mid to upper 60's.

Weak surface trough/convergence boundary stalls near the coast
Friday morning as the deepest moisture pushes offshore. Even
though the best moisture pushes offshore, enough moisture and
instability near the coast will keep mention of isolated to
scattered showers and thunderstorms in the forecast through
early-mid afternoon. Meanwhile, the subtropical ridge amplifies
off the southeast coast Friday. Early morning clouds and
convection will temper temperatures from reaching their full
potential Friday afternoon. Highs similar to today, generally in
the mid (possibly upper) 80's. Cooler near the coast.

Heights continue to build into Sunday as 850mb temps warm to +16
to +18c (+2 Standard deviations). The result will be the warmest
day of the season with widespread readings in the low 90's.
Dewpoints in the 60's will push heat index values into the mid
90's inland. A backdoor front progged to drop into the northern
mid-Atlantic region late Saturday, but models indicate large
spatial and timing differences. While the models indicate a
great deal of instability, soundings indicate a cap just above
850mb. Moisture is also limited with precipitable water values
at or below 1.25 inches. Will maintain slight chance pops across
the north near the dropping front, but believe sea-breeze
boundaries will struggle to overcome the lack of moisture and
warm temperatures aloft.

&&

Long term /Saturday night through Wednesday/...
temperatures are expected to remain well above normal through sun,
as an upper level ridge remains anchored just off the East Coast.
A backdoor cold front could affect nrn portions of the area Sat
night thru Sun morning with a slgt chc of showers, then a slowly
approaching cold front FM the west could produce isolated or
widely sctd showers or tstms sun aftn into sun evening, esply
wrn half of the region. Lows Sat night in the mid 60s to near
70. Highs on sun in the upper 70s to mid 80s.

That cold front will push thru the mtns by late Mon, then cross
the area and move off the coast Mon night into Tue morning. Have
high chc to likely pops for showers/tstms during this period.
Highs on Mon in the upper 70s to mid 80s. Lows Mon night mainly
in the upper 50s to mid 60s. Weak high pressure will provide dry
wx for later Tue morning thru at least most of Wed, as it slides
FM the Gulf Coast states to off the southeast coast. Highs on Tue in
the 70s, and mainly in the mid to upper 70s on Wed.

&&

Aviation /10z Thursday through Monday/...
outside of IFR conditions due to fog across the Maryland Eastern
Shore, widespread VFR conditions observed early this morning.
Light southerly winds and relatively dry low levels indicated in
soundings will limit overall fog development, but some early
morning patchy fog possible north and east of Richmond. IFR
conditions prevail thru early morning for ksby. Otherwise, sky clear.

Cold front approaches from the west today with increasing
southwest flow late morning through the afternoon. Expect gusts
of 20-25 knots. Scattered afternoon cu expected inland, with
decks at 4-6k feet above ground level. Weakening line of convection expected to
push across the region this evening through late tonight. Lower
ceilings/visibilities will be tied to convection.

Outlook...next frontal boundary will provide a focus for more
shower/tstm development late Sat. Cigs/vsbys lower in any
convective activity.

&&

Marine...
a cold front approaches the waters today resulting in an increase of
south and southwest winds through tonight. Deep low pressure over
the upper Great Lakes will move north into Canada which will relax
the pressure gradient by Friday.

Southeast to south winds were generally 10 knots or less early this
morning. Seas subsided overnight but remain 4 to 5 ft north of
Parramore Island. While there may be lull in 5 foot seas late this
morning...they are expected to build once again late today and into
tonight as winds increase.

Replaced Small Craft Advisory for hazardous seas with a Small Craft Advisory. This is to avoid
confusion with winds increasing today. The Small Craft Advisory was also expanded
to anz654 (parramore island to cape charles) where Small Craft Advisory
conditions are expected to develop by this afternoon. There is
indication the Small Craft Advisory may be needed for the rest of the coastal
zones for a short period this evening but will let the day shift
assess the need. Elsewhere conditions are expected to stay
below Small Craft Advisory. Although winds over land are expected to gust over 20
knots today...the cool water will inhibit mixing over the
marine area.

The cold front that approaches the waters today will dissipate over
the area Friday morning. A disorganized pressure pattern will
produce light winds over the waters Friday. Seas are forecast to
subside to below 5 feet by midday Friday. Benign conditions are
indicated for the marine area through the weekend. Another deep low
pressure system will move through the upper Midwest early next week.
This along with an approaching cold front will increase the
pressure gradient locally and another Small Craft Advisory may be needed starting
Monday.

&&

Tides/coastal flooding...
there is gradual improvement in water levels that have been
elevated by a new moon and long period swells. Some locations
will continue to have high tides get within a few tenths of a
foot of minor flood. At this time...the high tide cycle early
Friday morning at Bishops Head Maryland touches minor flood.

&&

Climate...
it appears likely that Richmond and Norfolk will end the month
with the warmest April on record. Warm temperatures during most
of the month combined with an unseasonably warm period to end
April are expected to push the average temperature above that
which occurred in 1994. At Richmond...the previous record was
63.2 and at Norfolk it was 64.7. Both were set in 1994. This
month's temperatures could be around a degree above those
values.

&&

Akq watches/warnings/advisories...
Maryland...none.
NC...none.
Virginia...none.
Marine...Small Craft Advisory until 1 PM EDT Friday for anz650-652-654.

&&

$$
Synopsis...alb/bmd
near term...Sam
short term...Sam
long term...tmg

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