Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kakq 292004 

Area forecast discussion
National Weather Service Wakefield Virginia
404 PM EDT Sat Apr 29 2017

Bermuda high pressure prevails off the southeast coast through the
Monday. A backdoor cold front will drop south across the northern
Delmarva Peninsula tonight, then lifts back north as a warm front
Sunday. A cold front pushes across the region Monday night with high
pressure returning Tuesday.


Near term /until 6 am Sunday morning/...
current WV imagery depicts a strong mid/upper ridge
centered over the sub-tropical wrn Atlantic, with an active stream
of convection on the nrn periphery of the ridge from the Central
Plains through the Ohio Valley. At the surface, high pressure is co-
located with the ridge aloft offshore, with a stationary front from
the Midwest to the northeast. Stratus from this morning along with a
warm nose ~850mb has resulted in a rather strong cap this aftn,
which has hampered cu development despite a very unstable airmass.
Temperatures as of 19z average from the mid 80s to around 90, with
unusually high dewpoints (that are in record territory for april)
generally in the low 70s across the area.

A shortwave trough is expected to track across PA/New Jersey late this aftn
through the evening. This is expected to trigger iso/sct
showers/tstms as depicted in the hrrr over NE Maryland and the nrn
Delmarva mainly after 22z. Effective shear is progged to be 35-40kt
in this region, which could result in some locally strong tstms in
vicinity of an MLCAPE gradient over the Delmarva. Mlcinh remains
rather high in this area, so any development of tstms over the lower
Maryland ern shore will likely be conditional dependent on outflow from
the north. The shortwave trough will drag the stationary boundary swd as
a backdoor cold front late tonight. Mid-level instability persists
overnight with the potential for showers/tstms in vicinity of the
backdoor boundary. Pops remain low ranging from 20-30%. Very mild
for late April with lows in the upper 60s to low 70s.


Short term /6 am Sunday morning through Tuesday/...
the front lifts back to the north as a warm front Sunday as
the upper ridge builds ahead of a trough digging across the Central
Plains. 850mb temperatures actually peak tonight and then drop back
to 14-16c by Sunday. Therefore, highs will be a few degrees lower
mid/upper 80s, but still well above normal. One exception will be
the lower Maryland ern shore in vicinity of the boundary where highs should
be 5-10f lower than today. There is a lack of a trigger for
convection, so forecast pops area below 15%. Continued mild Sunday
night with lows in the mid/upper 60s.

A cold front approaches from the west Monday 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 are rather poor, which is limiting 0-
1km MLCAPE values of 500-600 j/kg once the strongest synoptic
forcing arrives locally (mainly 00-06z). The Storm Prediction Center day 3 marginal risk
remains immediately west of the local area given some question as to how
unstable the thermodynamic profile will become. 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 with lows Monday night ranging from the upper 50s west to the
low/mid 60s along the coast. Breezy Monday with a SW wind ~15 mph
with gusts up to 25 mph.

A trough aloft builds over the ern conus Tuesday as surface high
pressure builds across the southeast states. Temperatures will be
lower, but still on the warm-side of normal with highs ranging from
the mid 70s to near 80 under a mostly sunny sky. A WSW wind of 10-15
mph is expected with gusts up to 20-25 mph possible.


Long term /Tuesday night through Saturday/...
a secondary frontal boundary is expected to cross the
area Tuesday night and should bring cooler air to the
region. Isolated showers could occur north of the
Delmarva, however westerly winds aloft should provide
enough of a downsloping effect to keep the forecast dry
into Wednesday. Lows Tuesday night in the 50s (lower 60s
coastal southeast Virginia/NE nc). Highs Wednesday in the mid-upper 70s
(upper 60s to lower 70s beaches) under mostly sunny skies
and sfc high pressure with light SW-west winds. Sfc high
slides offshore Wednesday night with lows in the
mid-upper 50s northwest to lower 60s southeast.

A warm front is expected to lift north across the area on
Thursday as low pressure develops along it Thursday night
into Friday. Increased clouds and precipitation chances
anticipated during this timeframe. Southeast winds become breezy
at the coast on Thu and become more S Thu night into Fri.
Overall, temperatures will be cooling with highs Thu/Fri
in the upper 60s northwest to low-mid 70s southeast. Lows Thu night in
the mid-upper 50s northwest to lower 60s southeast.


Aviation /20z Saturday through Thursday/...
a stationary front will stay north of the area through the
forecast period. This should allow for VFR conditions through
tonight. One exception to this may be at sby this evening as a
weak disturbance moves along the front which may help bring
scattered showers and storms to the Eastern Shore, allowing
conditions to briefly drop to sub VFR conditions. In addition,
the guidance suggests some marine air will move into the Eastern
Shore overnight into Sunday morning as the front briefly moves
south of sby, potentially allowing for MVFR conditions.

Outlook...mainly dry weather expected through the remainder of
the weekend, although some convection is possible across Delaware
tonight along a backdoor cold front. Next frontal boundary late
Monday into Tuesday with possibility of showers and thunderstorms.


generally S-SW winds aob 15kt through Sunday night. Seas
average 2-4ft tonight; 2-3ft sun/Sun night. Waves average

Low-end Small Craft Advisory conditions should begin for the Bay around
sunrise Monday morning when normal diurnal winds increase,
however speeds will continue to increase into the aftn as
the pressure gradient tightens substantially ahead of a
strong cold front which is approaching the region. All
waters should be within low-end Small Craft Advisory conditions by mid to
late Monday morning (s-SW 15-20kt/seas 3-5ft/waves 3-4ft)...
then solid Small Craft Advisory conditions by Monday aftn (15-25kt with
gusts to around 30kt Bay, sound, ocean/seas average 5-7ft/
waves 4ft). Strong Small Craft Advisory winds persist ahead of/along the cold
frontal passage and then taper off rather quickly behind it
as winds become more westerly 15-20kt (gusts around 25kt
ocean). Seas may peak at 8ft in nrn coastal waters out near
20nm Monday night. Small Craft Advisory winds should end either by sunrise or
by mid morning on Tuesday. Wind speeds become more SW again
on Tue and remain breezy 10-15kt due to weaker cold air
advection occurring. Seas will be slower to subside, therefore
Small Craft Advisory flags should persist for the coastal waters through early
Tue aftn srn waters and as late as midnight Tuesday night nrn

Fairly benign conditions anticipated for Wed/Wed night with
high pressure over the area. Variable aob 10kt Wed/southeast aob 15kt
Wed night. A warm front is expected to lift north across the
waters Thursday as low pressure develops along it Thursday
night into Friday. Southeast winds persist on Thu and become more S
Thu night into Fri. Wind speeds could increase to low-end Small Craft Advisory
(15-20kt) and seas could build to 5ft due to a tightening
pressure gradient. Will need to monitor the evolution of this
potential system.


keeping flood advisory in Mecklenburg County going today, with
vdot continuing to report numerous roads closed in the Kerr dam
area, creating ongoing navigation concerns.


it still appears likely that Richmond and Norfolk will each end
the month with the warmest April on record. Very warm temperatures
expected today and an unseasonably warm April to date should combine
to push the April 2017 average temperature above that which occurred
in 1994. As noted below, both of the previous records on the books
were established in 1994. This month's temperatures look to end up
around one degree above those values.

Average temperatures / record average temperature
through 4/28/17:

Apr 2017
avg temp record
location to date avg temp year
-------- -------- ------ ----
Richmond 63.1 63.2 1994
Norfolk 65.3 64.7 1994


Record high temps for today 4/29:
ric...93 in 1974
orf...92 in 1974
sby...89 in 1974
ecg...90 in 1974

Record high min temps for today 4/29:
ric...67 in 1956
orf...66 in 1981
sby...65 in 1974
ecg...67 in 1981


Akq watches/warnings/advisories...


near term...ajz
short term...ajz/mpr
long term...bmd

National Weather Service Glossary of Abbreviations