Scientific Forecaster Discussion
fxus61 kakq 230843
Area forecast discussion
National Weather Service Wakefield Virginia
443 am EDT Tue may 23 2017
a frontal boundary draped across northeast North Carolina early
this morning will lift back north into southeast Virginia this
afternoon, as a potent low pressure system tracks along the
boundary through this evening. Unsettled conditions continue
Wednesday and Thursday as an upper level trough approaches from
Near term /until 6 PM this evening/...
as of 4 am, a frontal boundary was just south and east of the
local area with high pressure situated over the Ohio Valley.
While clouds are plentiful this morning, pcpn has been slow to
advance northward given The Wedge setup over the local area.
Just now starting to see some steadier rain moving into
Mecklenburg/Lunenburg County. The frontal boundary to our south
will gradually creep back northward into southeast Virginia this afternoon
and will be the focusing mechanism for our well-advertised rain
event through tonight. A series of low pressure systems will
ride NE along this boundary today allowing for multiple bouts of
rain, some of which may be heavy at times. The most potent of
these sfc lows is expected to move across southeast portions of the forecast area
late this aftn and evening, and should provide our best chance
of locally heavy rain. With deep layer moisture returning,
categorical pops quickly ramp up from SW to NE and overspread
the entire area by mid to late morning into the afternoon.
23/00z suite of models (nam/GFS/gefs/ecmwf) still all over the
place with timing and placement of heaviest quantitative precipitation forecast today and exact
track of the strongest low late today into tonight. As mentioned
above, the general consensus is for this low to track across
southeast portions of the Virginia late today into tonight and so that
is when/where we'll show our highest quantitative precipitation forecast amounts. The threat
for heavy rain and possible minor flooding will continue to be
mentioned in the hwo, but have opted against a Flood Watch at
this time as 6hr ffg is generally 4-6" across much of the area,
with some values of 3-4" across the Piedmont and Maryland ern shore.
Quantitative precipitation forecast through 06z Wednesday averages 0.5-1" north to 1-3" south,
and higher amounts are possible. Highs today will range from
65-70 Piedmont to the low/mid 70s along the Albemarle Sound.
Short term /6 PM this evening through Thursday/...
the potent shortwave/surface low pushes offshore Tuesday
evening with a secondary wave moving offshore around/after 06z.
Will carry likely/categorical pops (55-85%) in the evening, then
tapering off overnight into Wed morning. Lows tues night in the
mid 50s west to mid 60s southeast coast.
Yet another wave approaches from the SW Wednesday aftn as an
upper low approaches from the west. This wave tracks across the
region Wednesday evening through the early overnight hours
bringing another round of likely pops along with a chc of
embedded thunderstorms. Current 00z guidance suggests the best
instability remains southeast. However, the potential for some
strong to severe storms will need to be monitored with 500mb
height falls and strengthening/veering flow at the 500mb level.
Storm Prediction Center currently has our southeast counties in a marginal risk. Unsettled
conditions continue into Thursday with chc to likely pops
continuing along with a chc of thunder. Mostly cloudy to
overcast Tuesday night through Thursday. Highs Wednesday/Thursday
ranging through the 70s most places. Lows Wed night in the 60s.
Long term /Thursday night through Monday/...
trough axis tracks across the region Thursday night as the
surface low tracks just north of the region. Will keep mention
of chance pops across the northeast portion of the local area
Thursday night. Dry conditions and a clearing sky is forecast
Friday as the trough axis and deepest moisture push offshore and
westerly flow aloft commences. Temperatures Friday generally
around average in the mid to upper 70's. Upper level flow
becomes northwest Friday night and Saturday ahead of an upper
level ridge building over the Ohio Valley. A warm front lifts
into the region Saturday, providing a focus for showers and
thunderstorms, but overall moisture is expected to be limited.
Will keep only slight chance pops for the Piedmont Saturday at
this time. Warmer, with highs in the upper 70's to low 80's.
Better chances for showers and thunderstorms are expected
Saturday night as upstream convection develops and tracks along
the frontal boundary and into the region. However, spatial and
timing differences exist so have capped pops in the low end
chance range. Thereafter, unsettled conditions persist Sunday
through Monday as an upper level trough tracks across the
Midwest into the eastern Continental U.S.. a great deal of uncertainty
exists in the medium range guidance, but it appears moisture
return will be limited. Will keep mention of low end chance pops
in the forecast. Highs both days generally in the low to mid
Aviation /09z Tuesday through Saturday/...
MVFR to IFR ceilings are prevalent early this morning with LIFR ceilings
at kphf. Widespread precipitation develops later this morning
and continues most of the day. The rain may be heavy at times,
especially this aftn/eve, reducing visibility. IFR ceilings will
be widespread into tonight.
Outlook...other low pressure systems will impact the area but not to
the extent as the one today. Nevertheless...aviation conditions
will be reduced at times through Thursday. High pressure builds
over the area Thursday night and Friday with drying. Moisture
returns with a chance for precipitation developing during the
rather challenging forecast with respect to confidence and timing of
any Small Craft Advisory level winds due to a wide range of model solutions even in
the short term. Low pressure progged to lift NE along a frontal
boundary late today / tonight. The actual strength of the low as it
tracks across the lwr ches Bay and off the Delmarva will determine
just how strong the north-northeast winds will be. Believe there is just enough
agreement for a 6-10 hour period of Small Craft Advisory winds across the ches Bay
from 22z through 08z tonite to Post marginal Small Craft Advisory headlines. Not
enough confidence hoist any headlines along the coastal waters so
held off there. This includes seas as they are running about a foot
below current forecast. Seas may eventually reach 5 feet out near 20
nm, but expect this would be more swell driven from the low moving
offshore rather than wind driven.
The next front pushes offshore Thursday night, with increasing
southwest winds Thursday ahead of the front. Minimal Small Craft Advisory conditions
higher astronomical tides results in above normal water levels
this week. Rather wide spread in model guidance as to where the
low actual tracks makes for a difficult forecast. Expect some
northern sites to reach action stage during the afternoon high
tide cycle today.
Marine...Small Craft Advisory from 4 PM this afternoon to 4 am EDT
Wednesday for anz632-634.
Small Craft Advisory from 7 PM this evening to 1 am EDT
Wednesday for anz630-631.