292 
fxus61 kakq 220616 
afdakq 


Area forecast discussion 
National Weather Service Wakefield Virginia 
216 am EDT Monday Mar 22 2010 


Synopsis... 
low pressure over Tennessee will track northeast through the Ohio 
Valley overnight and Monday. The low will eventually move off the 
coast of New England by Tuesday afternoon. High pressure will 
build across the area Wednesday and Thursday...with a cold front 
approaching from the west on Friday. 


&& 


Near term /until 6 am this morning/... 
latest weather analysis showing strong negative tilt upper low centered over 
MS...with surface low tracking into eastern Tennessee. Still expect some 
precipitation to move in from the west-southwest after midnight...and bringing 
likely probability of precipitation into western zones towards Erly morning (but will keep quantitative precipitation forecast amts 
low/gnly less than .10-.20"). Temperatures remain mild overnight west/ southerly 
flow and clouds...ranging through the 50s. Have added a schc thunderstorms to 
far southern zones after 3am...as h850 warm air advection slowly tracks in from the 
SW. 


&& 


Short term /6 am this morning through Wednesday/... 
main batch of steady precipitation should be moving into the County Warning Area from the 
SW by daybreak. With warm air advection and low level SW jet both NAM and GFS 
depict negative showalter indices (instability aloft) over much of 
Virginia/NC during the morning hours. This suggests a decent chance for elevated 
thunderstorms during the morning hours and have added this to the forecast. Will 
carry 80% probability of precipitation on Monday...but am concerned about a split precipitation 
pattern...with fairly minimal quantitative precipitation forecast values over much of central Virginia. 
Based on latest data not looking for any severe threat given time of 
day...but some gusty winds are possible given the prognosticated instability and 
shear. 


Best lift & instability (along with the frontal bndry) lifts NE into Northern 
Neck & Eastern Shore areas drng Monday afternoon. Data suggests dry punch of 
air from the SW dmnshs precipitation chances aftr 18-20z or so across southwestern counties. 
Will keep skies M cloudy for now...but would not be surprised to see 
some prtl sunshine mainly S of i64 late Monday afternoon. Highs in the 
M-u60s...near 70 southwestern counties given any sun. Only carrying 20% probability of precipitation 
Monday night/mainly north as County Warning Area becomes entrenched betwn the surface low 
well to our north and the upper low still off to the west. Lows mainly in 
the 40s. 


Tuesday/Tuesday night...consensus forecast has the upper low centered across S central 
Virginia at 12z Tuesday...tracking east-northeast off the Delaware-Maryland-Virginia between 18z Tuesday and 00z 
Wednesday. With cold air aloft and instability west/ daytime heating...have 
retained at least 20% probability of precipitation on Tuesday...despite a dry low level flow. Highs 
Tuesday tricky depending on amount of cloud cover...gnly going middle/upper 
50s NE to the lower l60s west of ches Bay where more sun is expected by 
later afternoon. Becmg mclr Tuesday night...lows mainly 40-45. 


Wednesday...next fast moving northern stream shortwave moves well to our 
north on Wednesday...in low levels a downsloping westerly flow will 
prevail allowing mostly sunny skies... deep mixing and warmer 
temperatures. 12z mex guidance highs in the upper 60s north to lower 70s 
central and S look reasonable and have stayed close. 


&& 


Long term /Wednesday night through Sunday/... 
latest GFS/European model (ecmwf) continue to show backdoor surface front dropping S of 
the forecast region Wednesday night. Strengthening west-east upper level deformation 
zone will allow for a quick increase in some middle/upper level cloudiness 
over the middle Atlantic region on Thursday...still well out ahead of the upper 
trough/surface low pressure system. For now feel there would be 
sufficient breaks/transparency for at least a partly sunny forecast. As 
for temperatures...cooler along the coasts with the ensuing onshore flow 
following the backdoor front (highs upper 50s/lower 60s)...65 to 70 
farther inland. 


Thursday night/Fri...medium-range models continue to show best rain 
chances during this portion of the extended forecast...as another cold front 
drops S of the forecast area...then stalls somewhere along the Carolinas 
while serving as an anafront as low pressure tracks across the Tennessee Valley 
and southern middle Atlantic region. Given the time frame (still 4-5 days out)... 
for now have kept probability of precipitation capped at or below 50%. 


Temperatures cooler Friday-sun as the next system tracks through and with the 
low level cold air advection behind it for the weekend (esp on sat). Sat looks to be the 
coolest day...as low level thicknesses support highs in the 50s 
area-wide. Lows over the weekend are currently prognosticated in the 
middle/upper 30s over most inland locales. 


&& 


Aviation /06z Monday through Friday/... 
with low pressure over the Ohio Valley and a cold front swinging 
northeast across the Carolinas...expect to see some showers after 
12z through the early afternoon hours. Out ahead of the 
front...ceilings are generally VFR and should remain that was as 
the low levels are still dry. But as the front arrives...expect to 
see a band of showers form. The line of showers could have a split with 
one area lifting NE through central Virginia from northwest of ric toward sby...while 
more showers develop along the coast where the moisture is deeper. 
There could be enough instability for some lightning...but for now 
have just gone with showers based upon the morning timing. With in 
the showers expect MVFR conditions...although visibility could reach IFR levels. 


The cold front should clear between 18z and 21z with a healthy dry 
slot behind it. This should allow for gradual clearing. The upper 
low will swing into the region after 6z and slowly March across 
the area through Tuesday afternoon before exiting to the east. 
With the cold air associated with the upper low...the instability 
should produce some showers. 


Once the upper low exits...high pressure builds in with rising 
heights aloft for Wednesday into Thursday with VFR conditions expected. 






&& 


Marine... 
raised flags (sca's) for Monday over the Bay/coastal waters as S/southeast 
flow increases ahead of an approaching low pressure system. Look 
for building seas over the coastal waters on Monday...before seas 
relax a bit over the southern waters Monday night. Winds/waves are 
expected to increase again (to at or above Small Craft Advisory criteria) on Tuesday over the 
coastal waters as well as Currituck Sound and the lower ches Bay...as 
the low moves along the New England coast...deepens...and gives 
way to increasing gradient (wrly) flow and low level cold air advection. Therefore 
despite the lull that is anticipated Monday night...decided to keep 
the Small Craft Advisory headlines going through the day on Tuesday across all waters. 


&& 


Akq watches/warnings/advisories... 
Maryland...none. 
NC...none. 
Virginia...none. 
Marine...Small Craft Advisory from 7 am this morning to 7 PM EDT 
Tuesday for anz630>633-654-656-658. 
Small Craft Advisory from 10 am this morning to 7 PM EDT 
Tuesday for anz650-652. 


&& 


$$ 
Synopsis...lkb 
near term...lkb/tmg 
short term...lkb 
long term...bkh 
aviation...ess 
marine...bkh/jef 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)