Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 121132

Area Forecast Discussion
National Weather Service Wakefield VA
732 AM EDT Mon Mar 12 2018

Low pressure will deepen as it moves off the Carolina coast
this morning and off the Delmarva tonight. High pressure
returns on Tuesday.


The latest surface analysis continues to show 1030+ mb sfc high
pressure centered over the northern Plains, ridging E-NE
through the Great Lakes and on into the Delmarva. To the
southwest, an inverted sfc trough is developing from the eastern
Tn Valley up toward the Mason-Dixon line. Aloft, potent, rather
compact trough was noted on IR/WV composite sliding across the E
TN Valley toward the southern Appalachians. Meanwhile, a
strengthening northern stream shortwave was analyzed dropping
out of central Ontario toward the western Great Lakes this

Overall, the 00z models remain resolute with tracking potent
southern stream shortwave E-SE today, eventually sliding
offshore this afternoon into tonight. Expect rapid cyclogenesis
to occur offshore of the Carolina coast this afternoon and
adjecting NE tonight into Tuesday. Main change with 00z cycle
was to push shortwave a bit farther to the south. Best lift and
QPF remain along and just NNE of the vorticity maxima. However,
this likely means that the majority of QPF remains to our south.
Therefore, have nudged QPF down slightly. Given marginal
temperatures this morning into the afternoon, expect a messy
mixed pcpn scenario inland. Lighter QPF/less favorable dynamics
likely portend to lighter pcpn intensity and a persistent light
rain with snow and sleet mixing in at times.

Temperatures in most locations will stabilize as precipitation
moves through. As for snowfall accumulations, plumes and WPC
guidance have each nudged down with this cycle...with a slushy
accumulation ~1" in the going Winter Weather Advisory area.

Next issue was with deformation band modeled to drop across the
area late this aftn into this evening as transfer of energy to
the coastal low occurs. This band has been modeled by the 00z
NAM and a majority of the high res models to drop across western
VA into north central NC, before sliding offshore tonight. This
will result in a narrow corridor of very impressive
OPRH/strong lift will be impressive as it does so. The limiting
factors will be two-fold. One, this banding will be encountering
a warmer antecedent airmass, where model consensus is for
1000-850mb thicknesses of ~1310m (would take a lot too cool
/wet-bulb that to snow/sleet). Second, the OPRH/QG forcing is
maximized across central and eastern NC between 22 and 03z this
afternoon/evening. Long story short, confidence has increased
but remains low that NE NC and South central VA (mainly 58
south) could sneak out a quick 1-2" of snow. Will be adding a
stronger worded HWO entry in this area, but after collaborating
with WPC and neighboring offices, will not be adding an advisory
at this time for SE CWA. Elsewhere across central VA including
most of metro Richmond, see the potential for a slushy snowfall
accumulation under ~1" (i.e. up to a coating of wet snow/sleet,
mainly grassy/elevated areas).

Slightly quicker timing results in a higher confidence that
Wintry wx threat will be quicker to abate for much of the area
Monday night, and lowered POP/Snow totals account for these
lowered totals, but again still some uncertainty during this
period and will need to watch this closely. Pcpn moves out
before midnight out west, and after midnight along the coast.
Lows upr 20s- lwr 30s.


No major change in forecast rationale for the midweek period.
Becoming partly/mostly sunny Tue behind the departing system.
Gusty NW flow will keep highs well below normal, mainly in the
mid- upper 40s (around 50 F far S). Cold/mostly clear to partly
cloudy and dry Tue night with lows in the mid 20s to lower 30s.

Upper low progged to be slowly shifting ENE into New england on
Wed, with a significant shortwave trough rotating around the
base of this feature and traversing through the mid Atlc and
Carolinas. At this time, it still appears downslope flow at
lower/mid levels will inhibit measurable precip across the AKQ
CWA. However, cannot rule out a few isolated/scattered rain/snow
showers during the late morning through the aftn (mainly north).


Overall pattern becoming more progressive during the extended
period. Wed night/Thu time frame still begins with cold upper
N/NE of the region but this will be moving offshore of New
England, allowing thu to trend a little warmer than Wed (though
still remaining below normal). Upper flow further deamplifies
Thursday night through Saturday, allowing for temperatures to
return to or above normal by Saturday. Expect generally dry
weather Thursday through Friday night, but models suggest the
potential for showers Saturday/Saturday night, as shortwave
energy moves out of the Midwest toward the region.

High temperatures Thursday are expected to be mainly in the
upper 40s to mid 50s, mid 50s to lower 60s on Friday (coolest
on the Lwr MD/VD Eastern Shore). Warmer still on Saturday with
high temps in the upper 50s east to the mid 60s south/southwest.
Lows Wednesday night in the mid 20s western and northern
portions to low 30s southeast, then mainly in the 30s next
Thursday night, and upper 30s west to mid 40s SE next Friday


High pressure is centered N of the region this morning and is
ridging to the SW along the Piedmont with a general light NE
wind. Light overrunning moisture from low pressure located SW
of the area is resulting in a band of -RA across srn VA/NE NC.
This general pattern should continue early this morning with
occasional light rain at ECG/ORF/PHF. Nevertheless, VFR
conditions this morning with cigs lowering to ~5kft. Conditions
deteriorate later this morning through this afternoon, as low
pressure develops off the Outer Banks. Cigs gradually lower to
MVFR and then eventually IFR during the aftn. Mainly areas of
-RA during the morning, becoming heavier during the aftn with
 pcpn mixing with PL at times, some brief SN possible after 20z
 mainly S of RIC- ORF. A strong N to NE wind is expected to
 develop during the aftn and evening gusting to 20-25kt and
 potentially ~30kt at ORF/ECG.

Outlook: Improving conditions are expected later tonight and
Tuesday as high pressure returns. An upper trough rotating
through the area Wednesday and Thursday could bring brief
periods of MVFR cigs, especially at KSBY. High pressure returns


Parent lo pres tracking into the srn mtns attm...w/ a coastal lo
beginning to take shape off the GA-SC coast. Transfer of energy
from the parent lo to the coastal lo will take place today...w/
the coastal lo becoming the primary storm by this eve. NE winds
increasing through today (to 15-30 kt). By this eve...a period
of gales (30-35 kt...gusts to 40-45 kt on the ocean waters) is
expected as coastal storm intensifies E of NC. Wind probs do
suggest a lo prob (10-15%) of gusts aoa 50 kt - primarily over
the NC ocean waters (this eve)...something to watch today. Winds
become N tonight...then NW Tue as the lo tracks ENE away from
the coast. SCAs will linger into/through a good part of Tue due
to CAA. NW or W winds 15-25 kt for Tue night thru Thu night.


Increasing NE winds today will result in a slow rise in tidal
anomalies. Period of tide anomalies avgg close to 1 ft above
normal expected this eve/tonight (potential to 1.5 ft above
normal invof mouth of the Ches Bay and srn ocean waters). Kept
forecasts below minor flooding thresholds for now.


VA...Winter Weather Advisory until 6 PM EDT this evening for VAZ048-
MARINE...Small Craft Advisory until 7 AM EDT Tuesday for ANZ635>637.
     Gale Warning until 7 AM EDT Tuesday for ANZ634-650-652-654-656-
     Small Craft Advisory until 2 PM EDT Tuesday for ANZ630>633-638.


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