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Area forecast discussion 
National Weather Service Wakefield Virginia 
857 PM EST Sat Mar 13 2010 


Synopsis... 
a slow moving low pressure system will track slowly across the middle 
Atlantic region tonight...then gradually push off the coast Sunday. 
High pressure builds back across the area early next week. 


&& 


Near term /through Sunday/... 
anthr quick update to zone forecast product/grids to account for rapidly changing cndtns. 
Mini "wrm sctr" along the coast between surface low and upper level nrgy has 
resulted in a bit more instability allowing tstrms to develop across 
the Bay and Eastern Shore areas. In addtn...areas of dense fog being rptd 
along the Eastern Shore so update was mainly for those areas next few hours. 
Showers with lclly heavy rainfall moving north from southern Virginia into central Virginia. Have 
issued now's / sps's with these cells. 


Marine wise...nearshore seas have jumped back up to between 8-9 feet at 
oxb...so issued anthr high surf advisory through the rest of the night 
from paramore isl on north. Will let middle shift evaluate the need to 
extend it if necessary. 


Prvs dscn: 
Erly evening update to account for current trends. Surface low currently moving 
into the northern half of ches Bay while upper level nrgy rotating east-northeast around 
surface low. Radar loop shwng precipitation echoes xpanding across southern inland 
counties and this trend is forecasted to continue through the evening hours in both the 
RUC/WRF models. Thunder becoming more isolated in nature due to lack 
of dytm htng. Decided to increases probability of precipitation into likely Cat for rest of 
evening hours across southern counties as this is the area where best lift is 
prognosticated with upper level nrgy. Kept isolated thunder wording for next few 
hours as airmass remains marginally unstable. Also added fog to Eastern 
Shore areas based on current surface observation there. Lows in the 40s. 


Upper low persists sun with unsettled conditions continuing. Have 
not gone with likely probability of precipitation suggested by NAM...although would not be 
surprised to see an area of widespread precipitation to the north 
of the upper low. Temperatures cooler than today...with highs most areas in 
the 50s to near 60 southern portions. 


&& 


Short term /Sunday night through Tuesday/... 
surface low intensifies off the Delaware-Maryland-Virginia coast Sunday 
night/Monday..causing unsettled conditions to persist. Think best 
chance for precipitation Sunday night through Monday will be across our 
Delaware-Maryland-Virginia counties...and areas adjacent to the Bay/coast...although 
cannot rule out isolated showers anywhere in our County Warning Area. Fair amount 
cloudiness across region...combined with some cold advection 
behind low...will keep temperatures in the 50s most areas. Could get near 
or just above 60 degrees SW portions of County Warning Area...where sunshine is most 
likely. 


Upper low finally moves away from the coast on Tuesday...with precipitation 
threat ending. However...flow off ocean and lingering low level cold 
air will keep temperatures a few degrees below normal. 


&& 


Long term /Tuesday night through Saturday/... 
split flow prevails over the eastern United States by the middle of 
next week in the wake this weekends storm system. An upper low 
center is situated over the lower Mississippi Valley Wednesday. This 
upper low center slowly drifts across the deep south through the end 
of the week. Models have generally indicated more cloud over south 
and less north. However...the 12z GFS has suggested the possibility 
of light rain in the Elizabeth City area and northern Outer Banks 
Thursday night. A dry forecast will continue at this point and see 
if the slightly wetter trend continues. The upper low drifts off the 
coast by Saturday with a strong storm system digging into the 
Mississippi Valley. Slight chance probability of precipitation were introduced for Saturday 
night at the end of the forecast period. However...at this time the 
slower European model (ecmwf) solution is preferred...which suggests a Sunday/Sunday 
night event as opposed to the faster GFS. Temperatures through the 
end of the week should average near to slightly above normal. 
However...by Saturday warm air should surge northward ahead of the 
approaching system. Temperatures well into the 70s are possible 
along and west of the Interstate 95 corridor...but at this time a 
more conservative around 70 was introduced for Saturday. 


&& 


Aviation /02z Sunday through Thursday/... 
as of 0030z...showers and isolated thunderstorms were developing 
across southern Virginia as well as the Eastern Shore. Cold air 
aloft associated with the upper level low was producing unstable 
air and lift was being enhanced as a short wave approaches from 
the southwest. 


Areas of fog were developing on the Eastern Shore which may impact 
ksby. IFR or LIFR should predominate during most of tonight and Sun 
morning under the influence of moist easterly flow. Generally left 
the rest of the taf sites with VFR/MVFR but this may briefly lower 
in precipitation and for a few hours near dawn due to the moist ground. 


Conditions generally improve during the day sun as winds turn to 
westerly and drier air begins to work into the area. A few showers 
will still be possible on sun. Mainly VFR is expected Monday conditions 
but with low pressure still just offshore...a few showers will 
again be possible. Mainly VFR and dry conditions will prevail the rest 
of the week. The only thing to watch for will be patchy fog near 
sunrise. 


&& 


Marine... 
added 3 foot waves to the mouth of the Chesapeake Bay. Buoy 99 
reporting 8 foot seas. Most of this is from a southeast swell. A call 
at 5 PM to the Chesapeake Bay bridge Tunnel authorities provided 
a visual of fairly calm seas with a southeast swell...estimated to be 
under 4 feet. 


Winds will temporarily increase to 10 to 15 knots over most of 
the coastal waters overnight as a short wave moves through. 
Otherwise...wind speeds will be light over the coastal Atlantic... 
Chesapeake Bay...and Currituck Sound as a broad surface low is 
situated over the area. Surf will remain high in the coastal 
Atlantic nevertheless and the Small Craft Advisory is extended 
through Monday for now. The upper low remains over the Tennessee 
Valley today...and it will slowly move east toward the middle 
Atlantic by Sunday night. As the upper low drifts off the middle 
Atlantic coast it triggers surface cyclogenesis over the ocean. A 
northerly wind is expected to strengthen during this time with 
gales possible over the Atlantic Monday afternoon and Monday 
night. The Bay and sound are likely to reach small craft 
criteria...but will delay any small craft issuance at this point 
for the Bay and sound since it is not until Monday afternoon and 
models have struggled with this system. High pressure eventually 
returns by the middle of next week with the wind relaxing and seas 
subsiding. 


&& 


Hydrology... 
runoff from rainfall last 36 hours is affecting area main Stem 
rivers this afternoon...and will continue to do so through Monday. 
Appomattox river and Chowan basin tributaries prognosticated to go to at 
least 3/4 bankfull. Best chance for flooding will be on the James 
River at Richmond Westham. Current forecast is about a foot above 
flood stage...but still have 24 hours to monitor...as most upstream 
gages forecast to remain below flood stage. 


&& 


Tides/coastal flooding... 
the latest model extratropical water level guidance is indicating that 
anomalously high tides could produce minor coastal flooding during 
high tide cycles Sunday and Sunday night for the lower Maryland 
Eastern Shore of the Chesapeake...for the Lewisetta area...and for 
the Ocean City area. Tides are generally expected to average around 
2 feet above normal. Coastal flood advisories will be issued for the 
Chesapeake Bay areas in question. Model guidance over-forecast Ocean 
City for the past cycle...so will wait on further guidance before 
issuing an advisory for Ocean City. 


Low pressure re-intensifies off the coast Sunday night and 
lingers through Monday night producing a period of northerly along 
shore wind. Latest model extratropical water level guidance is 
suggesting a round of minor to perhaps moderate coastal flooding 
with high tide cycles from Monday into Tuesday. 


&& 


Akq watches/warnings/advisories... 
Maryland...high surf advisory until 6 am EDT Sunday for mdz025. 
Coastal Flood Advisory until 8 am EDT Monday for mdz021>023. 
NC...none. 
Virginia...high surf advisory until 6 am EDT Sunday for vaz099. 
Coastal Flood Advisory until 8 am EDT Monday for vaz077-078. 
Marine...Small Craft Advisory until 7 PM EDT Monday for anz650-652-654- 
656-658. 


&& 


$$ 
Synopsis...mpr 
near term...mpr/wrs 
short term...worse 
long term...ajz 
aviation...lsa 
marine...ajz/lsa 
hydrology... 
tides/coastal flooding... 

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