Scientific Forecaster Discussion
fxus61 kakq 302000
Area forecast discussion
National Weather Service Wakefield Virginia
400 PM EDT sun Apr 30 2017
Bermuda high pressure prevails off the southeast coast tonight
into midday Monday. A cold front approaches from the west Monday
afternoon, and pushes across the region Monday night, with high
pressure returning Tuesday and Wednesday.
Near term /until 6 am Monday morning/...
the ridge aloft over the sub-tropical wrn Atlantic will
continue to prevail tonight as a cold front over the Mississippi
Valley pushes ewd tonight. Surface high pressure will remain
anchored off the southeast coast, with a quasi-stationary
boundary over the Delmarva lifting north as a warm front.
Temperatures this afternoon are generally in the low/mid 80s
across the region. These values will slowly fall into the 70s
this evening, with overnight lows in the mid/upper 60s. Mostly
clear this evening, with some patchy stratus developing late
Short term /6 am Monday morning through Wednesday/...
the cold front approaches from the west Monday aftn as the Central
Plains trough lifts into the Great Lakes. The front is expected
to slow as it pushes across the Appalachians with strong
surface heating to the Lee of the mountains. Therefore, pops
should be slow to increase through the aftn, and mainly over the
Piedmont initially. The ridge will hold strong along the coast
with the ern half of the area remaining dry through much of the
day Monday. 500mb flow ahead of the trough reaches 70-80kt,
which yields 0-6km bulk shear ~50kt. However, mid-level lapse
rates (850-600mb) are rather poor, but much steeper around
500mb, and the net result is 0-1km MLCAPE values of 500-1000
j/kg once the strongest synoptic forcing arrives locally (mainly
21-03z). The Storm Prediction Center day 2 marginal risk has been expanded ewd to
the interior coastal plain, with a slight risk introduced for
the Piedmont. Precipitable water values ~1.5in combined with strong forcing
could result is some locally moderate to heavy rain. The cold
front crosses the region Monday night and pushes offshore by 12z
Tuesday. Pops taper off from northwest-southeast from 06-12z as drier air
arrives from the northwest. Highs Monday will generally be 80-85f W,
with mid/upper 80s farther east (upper 70s for the Atlantic coast
of the ern shore. Lows Monday night range from the upper 50s west
to the low/mid 60s along the coast.
A south to southwest wind will become breezy by mid morning as
the sfc pressure gradient responds to the approaching strong
cold front. Gusts around 25-30 mph should be common by late
morning...increasing to sustained winds of 20-25 mph with gusts
averaging 30-35 mph. Model cross sections of lapse rates (and
essentially the mixing layer) are supportive of these speeds,
which are higher than model guidance.
A trough aloft builds over the ern conus Tuesday and dampens to
a more zonal flow pattern by Wednesday. Surface high pressure
builds across the southeast states Tuesday, then dissipates
Wednesday as a dry cold front approaches from the north.
Temperatures will be lower Tuesday, but still on the warm-side
of normal with highs ranging from the mid 70s to near 80 under a
mostly sunny sky. Mostly clear Tuesday night with lows ranging
through the 50s. Mostly sunny Wednesday with highs in the
mid/upper 70s, and locally upper 60s/low 70s for the Atlantic
coast of the ern shore.
Remaining breezy Monday night into Tuesday due to cold air
advection and a continued tightened sfc pressure gradient behind
the cold frontal passage. The wind becomes westerly with speeds
averaging 15 mph with gusts around 25 mph inland and 20 mph
with gusts around 30 mph...mainly after midnight Monday night.
For Tuesday, a west-southwest wind will average 20 mph with gusts of 25-30
Long term /Wednesday night through Sunday/...
sfc high pressure north of the area slides closer to the
New Jersey shore Wednesday night and east of the New England coast
on Thursday as a warm front lifts north into the region.
Meanwhile, sfc low pressure develops over the Tennessee/Ohio valleys
into Friday. Southeast/onshore winds become breezy at the coast
Thursday into Thursday night...becoming more S on Friday
after the warm front lifts well north of the area. Decent
amount of uncertainty of how/where the sfc low will develop
and where it will track Friday through Saturday night
(including when its associated cold front will cross the
region). Kept the forecast fairly general/broad-brushed
during this time. Weak cold air advection behind the low
may be reinforced by another colder shot of Canadian, but
again, there is a lot of uncertainty at this point. Overall,
a brief warming trend can be anticipated for Thu night/Fri
with a gradual cool down with highs below normal and lows
Aviation /20z Sunday through Friday/...
high pressure is anchored off the southeast coast as of 18z,
with a quasi-stationary boundary immediately north of sby. A SW wind
is averaging 8-12kt this aftn, with gusts up to 20kt possible at
ric, and sct aftn cu with bases of 3.5-5kft. The aforementioned
boundary will move north as a warm front tonight as a cold front
pushes through the Ohio Valley. The sky will be mainly clear
through around 08z aside from some cirrus. The wind will
generally be S aob 10kt through roughly 06z, before becoming SW
and gradually increasing thereafter as the pressure gradient
tightens. MVFR stratus is possible primarily between 08-14z, but
vsby restrictions are not expected given a persistent wind
overnight. Stratus should scatter and lift after 14z with a SW
wind increasing to ~15kt with gusts to ~25kt.
The cold front approaches from the west late in the day and passes
across the region overnight. This will bring the potential for
showers/tstms from late aftn/early evening for ric and then
shifting to the coast during the evening through the early
overnight hours. Any showers/tstms have the potential to
produce sub-VFR conditions along with locally strong wind gusts.
High pressure returns Tuesday and Wednesday and slides offshore
Thursday as low pressure approaches from the west. This low
pressure system potentially impacts the region Thursday night
winds generally SW 10-15kt through tonight...increasing
initially with typically diurnal push around sunrise and
continuing to increase through Monday as a strong cold
front approaches the region. Low-end Small Craft Advisory conditions to
begin for the Bay around sunrise Monday morning with the
normal diurnal push. Currituck Sound and ern Virginia rivers
to experience low-end Small Craft Advisory winds by mid morning...then
winds/seas/waves increase all waters in the afternoon as
the sfc pressure gradient really tightens up in response
to the front as it nears the mountains. S-SW winds will
average 15-25kt with gusts of 25-30kt primarily Mon aftn
into Mon evening before the frontal passage. A brief period
of gale force gusts around 35 kt will be possible (especially
over the coastal waters) during the frontal passage late Mon
evening into the overnight hours. Cancelled gale watch since
any gale gusts will be related to convection/front (rather
than synoptically-driven) and can be handled with special
marine warnings as needed. Small Craft Advisory flags hoisted for all waters
with beginning and end times adjusted. See wbcakqmww for
more details. Seas build to 4-6ft Mon aftn and increase to
5-8ft north/4-6ft south Mon night. Waves on ches Bay build
to 4ft by late Mon morning/early aftn with up to 5ft possible
in the middle of ches Bay Mon evening.
Winds become west-southwest behind the front after midnight Mon night
and then turn more SW on Tue. Wind speeds slowly diminish
within this timeframe...averaging 15-20kt by mid morning Tue.
Waves on ches Bay anticipated to be 2-3ft by sunrise Tue.
Seas will be slower to subside below 5ft until mid morning
Tue for srn coastal waters and not until Tue evening for nrn
coastal waters. Small Craft Advisory flags incrementally drop off from south
to north as Tue progresses. Again, please see wbcakqmww for
Fairly benign conditions anticipated for Wed/Wed night with
high pressure over the area. Variable aob 10kt Wed/N-NE
aob 15kt Wed night. A warm front is expected to lift north
across the waters Thursday as low pressure develops over the
Tennessee/Ohio valleys into Friday. Southeast/onshore winds become breezy with
speeds averaging 15-20kt Thu aftn at least through Fri aftn.
Seas anticipated to build to 4-6ft and persist into Sat
morning before subsiding. Small Craft Advisory conditions should be expected
during this time.
flood advisory continues in Mecklenburg County, with vdot continuing
to report numerous roads closed in the Kerr dam area, creating ongoing
all 4 climate sites broke record high minimum temps for 4/28...4/29
and for the month of April. See pnsakq for details.
Record high temps for today 4/30:
ric...93 in 1974
orf...93 in 1888
sby...86 in 1974
ecg...90 in 1974
Record high minimums for today 4/30:
ric...63 in 2014
orf...67 in 1994
sby...63 in 1983
ecg...65 in 2014
Richmond and Norfolk will end of the month as the warmest April
on record. Below are the average temperatures through the 29th
and the previous records. The new records will likely be more
than one degree of the previous records.
avg temp record
location to date avg temp year
-------- ---- ---- ----
Richmond 63.7 63.1 1994
Norfolk 66.0 65.3 1994
Marine...Small Craft Advisory from 10 am Monday to 10 am EDT Tuesday
Small Craft Advisory from 10 am Monday to 8 am EDT Tuesday for
Small Craft Advisory from 4 am Monday to 6 PM EDT Tuesday for
Small Craft Advisory from 2 PM Monday to 4 PM EDT Tuesday for
Small Craft Advisory from 2 PM Monday to 10 am EDT Tuesday for
Small Craft Advisory from 2 PM Monday to 11 PM EDT Tuesday for