Scientific Forecaster Discussion
fxus61 kakq 182039
Area forecast discussion
National Weather Service Wakefield Virginia
339 PM EST Sat Nov 18 2017
a strong cold front moves across the area late tonight then pushes
off the coast Sunday morning. High pressure builds into the area
Sunday afternoon through Tuesday. The next cold front crosses the
area early Wednesday.
Near term /until 6 am Sunday morning/...
latest msas has a warm front located ivof the Mason-Dixon line. The
main low lifts across the gt lakes and into southern Canada late
tonight with the trailing cold front not progged into the area until
after midnight. Latest data supports a dry evening across the fa
with pcpn not moving east of mts until around 04z. Expect rising
dewpoint temps as the low level S-SW flow quickly increases pw's
into the 1"-1.25" range. Thus, temps not falling much this evening
with readings between 55-60.
Latest data continues to support a quick-moving band of showers
along and ahead of the cold front just after midnight out in the
Piedmont, reaching the coast by Sunday morning. The increasing pw,
along with a narrow axis of low-level convergence/forcing, will lead
to a broken line of showers through the overnight period. Thus have
maintained likely to categorical pops, highest across the north. No
cape to speak of, so kept thunder out of the grids.
Breezy to windy conditions continue through the night. H92-850 winds
increase to 40-50 kt as gradient tightens just ahead of the front.
Expect strongest winds to be within a few hours of frontal passage
as subsidence behind the departing boundary mixes down some of that
wind. Mild most of the night east cooling off late across the west.
Lows upr 40s west to mid-upr 50s along the coast.
Short term /6 am Sunday morning through Tuesday/...
cold front and any lingering shwr activity along the coast arnd 12z
quickly moves offshore by 15z. Tsctns show rather quick drying of
the column so expect skies to become mstly sunny. Blustery with
gusty west-northwest winds and only a slow rise in temps despite the sun.
Winds diminish towards sunset. Highs in the mid 50s-lwr 60s.
Sfc high settles over the sern states Sun night and Mon then drifts
off the coast tues. Passage of an upr level system will usher in one
last surge of cold air advection Sun night. Otw, dry with a slow warming trend.
Lows Sun night in the upr 20s northwest to mid 30s southeast. Highs Mon in the upr
40s-lwr 50s. Lows Mon night in the 30s to near 40 se. Highs Tue in
the upr 50s to lwr 60s.
Long term /Tuesday night through Saturday/...
model differences make for a challenging mid week and Holiday fcst.
The next cold front progged to cross the area tues nite. Challenge
comes from just how much moisture gets entrained ahead of the front
from a trof off the Carolina coast and weak low progged to move NE
along it? GFS much more aggressive with the moisture than the European model (ecmwf).
For now, elected to keep measurable rainfall east of i95 Tue nite
and Wed with slght chc pops across the east thurs. Lows Tue nite in
the 40s to near 50 se. Highs Wed 55-60. Lows Wed nite in the 30s to
lwr 40s se. Cool thurs with highs mid 40s-lwr 50s.
Dry and cool Fri and Sat as high pressure builds into the area.
Highs Fri 50-55. Lows mid 30s-lwr 40s. Highs Sat 55-60.
Aviation /20z Saturday through Thursday/...
VFR conditions to start the forecast period with only high/mid
level clouds overspreading the region through 04z. South winds
become gusty btwn 15-25 kts. Main concern this forecast will be
one of wind shear tonight with models showing 35-50kt at 2k ft
above ground level. Added ws to all taf sites ahead of the cold front tonight.
The cold front crosses the area btwn 08z-13z sun with a band of
showers. Tsctns show some short-lived MVFR ceilings with the
showers along and just ahead of the fropa. Winds quickly swing
around to the west-northwest Post-frontal and will be highest within a few
hours of frontal passage, but will remain gusty through Sunday.
West winds avg 15-25 kt with gusts 30-35 kts.
Outlook: high pressure builds over the area later Sunday through
Monday then tracks off the sern coast Tuesday. VFR conditons
expected during this time frame.
late this aftn, sfc high pressure was cntrd off the mid Atlc
coast, while sfc low pressure was cntrd over extrm wrn Ohio. A
cold front extended SW FM the low thru srn in and down into the
lower MS valley. South-southwest winds were 10-20 kt with gusts into the
upper 20s (kt) late this aftn over the waters. The pressure
gradient between the high offshore and the approaching cold
front will tighten this evening into early Sun morning,
resulting in SW winds increasing to 20-30 kt with gusts ranging
from 25-40 kt. The cold front will cross the waters generally
between 11z-14z Sun morning, with winds then shifting to the northwest
behind the front. On the late this aftn fcst, have decided to go
ahead and hoist the Gale Warning (one headline) for the entire
coastal waters, due to gale conditions (gusts) expected within
the next 12 hrs. Also, for now, have kept sca's in effect for
all the other waters, even though there could be isolated gusts
to 35 kt at the mouth of the ches Bay or the Currituck snd.
Decent cold air advection, a persistent tight pressure gradient,
and rapid pressure rises (5-9mb) behind the front will all
contribute to a continuation of strong northwest winds 20-30 kt with
gusts of 25-40 kt through sun. Breezy to windy conditions will
prevail over much of the area on sun, and generally uniform
with slightly stronger winds occurring over the warmer waters.
Winds should remain generally unchanged Sun night with northwest winds
averaging 15-25 kt with gusts averaging 30 kt. Will still have
to monitor for possible gale gusts at the mouth of the ches Bay
or the Currituck snd during sun. A secondary surge in northwest winds
may be possible Sun night, as the coldest part of the airmass
swings across the area. However, relaxing pressure gradient with
high pressure building over the Gulf Coast states into the Tennessee
Valley will likely prevent a very strong surge from happening.
High pressure continues to build over the southeast states into
the srn mid Atlc region Mon/Mon night, then sliding out to sea
on Tue. Calmer sub-Small Craft Advisory conditions anticipated Mon aftn into Wed.
Marine...Small Craft Advisory until 7 am EST Monday for anz633-635>638.
Small Craft Advisory until 10 am EST Monday for anz630>632-634.
Gale Warning from 7 PM this evening to 4 am EST Monday for
Gale Warning from 7 PM this evening to 3 PM EST Sunday for