Scientific Forecaster Discussion
fxus61 kakq 070005
Area forecast discussion
National Weather Service Wakefield Virginia
705 PM EST Fri Dec 6 2019
a cold front crosses the area tonight with high pressure returning
for the weekend. Low pressure tracks across the Great Lakes region
early next week, dragging a strong cold front across the area Tuesday
night. Canadian high pressure builds in on Thursday before
moving offshore by late Friday.
Near term /through Saturday/...
as of 345 PM EST Friday...
Late afternoon upper air analysis shows troughing across the
ern conus, W/ two distinct shortwaves tracking ewd:
one across the eastern Great Lakes and another near al/GA. At
the surface, ~1012 mb low pressure is over south-central New York
while ~1030 mb high pressure is centered from Kansas to Minnesota. A
trailing cold front extended S-SW from central PA to
Mississippi. Broken-overcast mid level clouds prevail across the area in
advance of the cold front. Radar mosaic is showing a few light
echoes across the area, but any rain that is trying to fall is
not close to reaching the ground, given a pronounced dry layer
from around 700 mb to the sfc. Return SW flow has allowed it to
warm up quite a bit today (despite the cloud cover), with
temperatures mainly in the 50s across the area. There are a few
readings near 60f in southeast Virginia/NE NC.
The cold front will cross the area tonight. Some very weak mid-
level ascent is moving through the area, and will continue to
move through as the upper trough axis crosses the region.
Despite this, the low levels will still remain quite dry (w/
some moistening right with the fropa). Cannot rule out a stray
shower from 00-06z tonight (mainly across srn VA, NE NC, and
the lower ern shore...where pops are mainly in the slight chc
range). Elsewhere, expect a dry frontal passage with decreasing clouds
from north to S behind the front (mainly after midnight). Winds
become north tonight allowing for some cold air advection to set in. Lows by
12z Sat mainly in the 30s except for low 40s in southeast Virginia/NE NC.
Short term /Saturday night through Monday/...
as of 345 PM EST Friday...
Sunny but cool Sat as high pressure builds into the northeast
Continental U.S. And the sfc flow turns to the north-northeast. Not particularly cold
for early December (850 mb temps of -1 to -3c) with highs
ranging from the mid 40s north to the upper 40s S. Clear W/ light
winds Sat night as the high becomes centered over srn New
England, with sfc ridging extending south-southwest into our area. Given the
clear skies/light winds, went a bit cooler than model consensus
Sat night. Forecast lows are mainly in the mid 20s inland, with
low 30s across coastal southeast Virginia/NE NC. The high pushes offshore of
the New England coast on sun. This allows the sfc flow to
become SSE, veering to the west-southwest in the mid-levels. This will
allow warm air advection to commence on sun. Deep-layer moisture starts to
increase during the latter half of the day on sun as a series of
disturbances in west-southwest-SW flow aloft approach the local area (as a
trough aloft starts to amplify in The Rockies/high plains). In
addition, a trough of low pressure develops at the sfc along the
Carolina coast by sun evening. Milder sun with highs ranging
from the upper 40s northwest to the upper 50s southeast.
Rain quickly develops/moves into the area Sun night from S to north
as a warm mid-level airmass overruns relatively cooler air near
the surface. This happens as the weak trough of low pressure
approaches from the S. Pops of 30-50% during the evening
increase to 60-70% in most areas after 06z Mon. Qpfs through 12z
Mon are mainly in the 0.1-0.25" range. Lows Monday morning
range from around 40f north to around 50f southeast. Periods of showers
continue throughout the day on Mon as the first upper level
disturbance/area of sfc low pressure crosses the region. Models
are hinting at a (relative) lull in the pcpn across sern zones
during the latter half of the day on Mon, while numerous showers
move across northern/western portions of the County Warning Area (w/ somewhat
of an in-situ wedge lingering across the piedmont). Adjusted
pops to reflect this thinking (chc pops across southeast Virginia/NE NC with
likely pops north/west from 18z Mon-00z tue). Highs Mon range
from the low-mid 50s northwest to the mid-upper 60s southeast.
Long term /Monday night through Friday/...
as of 345 PM EST Friday...
The aforementioned trough aloft quickly amplifies across the
Midwest Mon night-Tue as strong sfc low pressure deepens as it
tracks from the upper Midwest to southeast Canada. A series of upper
disturbances (in SW flow aloft) will continue to track
toward/across the region through Tue as the associated cold
front slowly approaches from the W/NW. Strong warm air advection will continue
through Tue (850 mb temps rising to 8-11c by 12z tue) under
deep-layered SW flow. With the area likely remaining in the warm
sector from Mon night-Tue, expect at least a chc of
(occasional) showers to continue from Mon night through the
first part of the day on Tue. Have pops in the 30-60% range for
the most part from 00-18z Tue, as most of the rain will remain
to our west through midday Tue (latest 12z/06 models are
slowing the eastward progression of the upper trough axis). Mild
Monday night with lows mainly in the 50s.
It is still looking like the frontal passage holds off until
sometime during the latter half of the day on Tue. As a result,
look for highs well into the 60s on Tuesday...with the potential
for some low 70s in Hampton Roads/NE NC. Pops increase to 60-70%
by Tue aftn in all areas except for far southeast Virginia/NE NC as the upper
trough axis continues to slowly move toward the region. The cold
front is progged to move S of the County Warning Area by late Tue night, but
a long-duration light to moderate rain is expected to continue
before ending from northwest to southeast Wed am (as the upper trough axis
finally approaches/crosses the region). As cooler air filters
into the region behind the front Tue night, the rain is expected
to change over to snow in areas to our northwest (while a cold rain
continues across our cwa). Cannot rule out a brief changeover to
snow (or a rain/snow mix) closer to 12z Wed across our far northwest
zones, but not expecting any impacts from snow that does fall
(temps remain above freezing). Additionally, 12z/06 eps
probabilities of at least 1" of snow are only 10-20% across
Louisa/Fluvanna counties from Tue night-Wed am. Lows Tue night
range from the mid 30s north/west to the low-mid 40s in southeast
It will be dry but colder from Wed aftn-Thu as strong high
pressure builds into the Great Lakes by midweek before quickly
migrating eastward. The high becomes centered near/over the
local area by Thursday evening. This will result in a short-
lived period of below average temperatures from Wed night-Thu
night, due to cold Canadian air sweeping across the region
behind the departing front. Forecast highs are mainly in the
mid-upper 40s on Wed (some readings around 50 across the se),
colder on Thu with highs ranging from the upper 30s-low 40s.
Lows Wed night/Thu night mainly in the 20s (although some teens
are possible across northwest zones). Model consensus is forecasting
the high to move offshore of the New England coast on Fri as low
pressure develops near the Gulf Coast. This low will likely
track across our region next weekend. However, it is looking
like any threat for impacts due to wintry precipitation will
likely remain north of the region (12z eps probs for 1" of snow are
~0% across our County Warning Area next weekend).
Aviation /00z Saturday through Wednesday/...
as of 705 PM EST Friday...
VFR conditions will prevail through the 00z taf period. Mid/high
level clouds (cigs 7-12k feet) will affect the taf sites this
evening into early Sat morning, as a cold front drops across
the area. There is a slight (15-20%) chc of shras at sby/ecg
from 00-06z Sat, but did not include any mention of pcpn in the
tafs (even if shras do occur, conditions will remain vfr). The
other terminals should remain dry through the taf period. The
sky will clear out from north to S Sat morning. Sky clear conditions then
prevail through the day on Sat. SW winds 5-15 kt this evening
will turn to the west tonight before eventually becoming north-north-northeast Sat
morning. North-northeast winds could gust to 20 kt at orf/ecg on Sat, with
a few gusts to 15 kt possible elsewhere.
Outlook...high pressure builds into the area Sat into Sat night
before moving offshore on sun. VFR conditions are expected to
continue through the weekend. Periods of showers are then
expected from late Sun night through Tue night, as low pressure
tracks well to our northwest (which will drag a strong cold front
through the region). Degraded flight conditions are likely
during this time period (due to both cigs/vsbys).
as of 300 PM EST Friday...
SW winds are currently running 10-15 kt, except 15-25 kt with gusts
up to 30 kt off the lower Eastern Shore. These winds will continue
through the evening hours ahead of a cold front. Waves 1-2 ft; seas
2-4 ft (highest north). Scas remain in effect north of Parramore
Winds become north/northwest late tonight into early Saturday after the front
crosses the area waters. Winds increase to 15-20 kts in the Bay with
gusts to 25 kts, and 20-25 kts with gusts to around 30 kts in the
coastal waters. Waves in the Bay build to 2-4 ft and seas build to 3-
5 ft in the middle and northern coastal waters and 4-6 ft in the
southern coastal waters. Small Craft Advisory will be in effect for the Bay, rivers,
coastal waters, and Currituck Sound from early Saturday morning
through early Saturday afternoon, lingering into Saturday evening
for the southern coastal waters and Currituck Sound.
Winds along with waves/seas will subside by late Saturday night as
the pressure gradient relaxes and high pressure builds into the area
for the remainder of the weekend.
Marine...Small Craft Advisory from 1 am to 1 PM EST Saturday for
Small Craft Advisory from 11 PM this evening to 1 PM EST
Saturday for anz630>632-634.
Small Craft Advisory from 1 am to 7 PM EST Saturday for anz633-
Small Craft Advisory until 1 PM EST Saturday for anz650-652.