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Area forecast discussion 
National Weather Service Wakefield Virginia 
148 am EDT sun Mar 21 2010 


Synopsis... 
high pressure becomes centered off the middle Atlantic coast through 
Sunday. Low pressure tracks across the northern Middle Atlantic States 
Sunday night and Monday. The trailing cold front crosses the area 
Monday afternoon. Another front moves through late Tuesday. 


&& 


Near term /until 6 am this morning/... 
upper ridge/surface hi pressure will slide farther out to sea overnight...but 
will maintain dry weather across the region. Just some incrsng cirrus from 
the west-southwest expected overnight. Othrwise...clear or mostly clear sky with low 
temperatures ranging through the 40s to around 50. Meanwhile...the next storm 
system is strengthening over the lower MS vlly. 


&& 


Short term /6 am this morning through Tuesday/... 
the upper low will continue to amble eastward over the deep south 
Sunday and Sunday night. High clouds will overspread the forecast 
area during the day. In addition cumulus development is likely ahead 
of the upper system as evidenced by an expansive cumulus field over 
the Tennessee and Ohio valleys Saturday afternoon. Sunday will be 
another mild day despite increasing cloud cover with forecast values 
in the low and middle 70s. 


The cold front aloft associated with the cyclone approaches from the 
southwest late Sunday night and lifts northeast across the area 
Monday and Monday evening. A period of steady rain is expected with 
the frontal passage. There is some weak instability aloft concurrent 
with the frontal zone...so thunder is possible with the primary rain 
band. A compact thermal gradient develops in the middle-level Theta-E 
field off the coast late Sunday night/early Monday 
morning...basically taking the form of a middle-level warm front. Again 
there is some weak instability aloft with this feature. If this is 
the case...some rain showers could precede the primary rain band 
over the lower Delaware-Maryland-Virginia. Low temperatures will be mild...upper 40s 
to middle 50s Sunday night...so maximum temperatures Monday will remain 
mild despite the rain. 


The upper low drifts across the region Monday night before lifting 
off the New Jersey coast by Tuesday. Cyclogenesis is possible off 
the Carolina coast late Monday night and Tuesday morning...which 
could bring a few more rain showers. High temperatures Tuesday will 
be challenging. Upper 50s and low 60s are expected with plenty of 
cloud cover. However...it is possible that temperatures could be 
higher in the western zones with any clearing as thickness values 
begin to rise during the afternoon. 


&& 


Long term /Tuesday night through Saturday/... 
vertically-stacked low pressure moving off the Atlantic coast Tuesday night 
will give way dry and seasonably mild conditions on Wednesday as flat upper 
ridging builds into the middle Atlantic region. The GFS is a little faster 
with the northwest-southeast progression of the northern stream jet axis/shortwave 
trough well north of the forecast area. It is this feature aloft which will 
eventually drop a surface backdoor front southward through the region 
(wed night per both the ECMWF/gfs)...before that happens expect 
temperatures to rebound well into the 60s (some lower 70s) over interior 
portions of the region on Wednesday...with cooler temperatures near the coast. A 
little cooler on Tuesday behind initial (weak) backdoor front...albeit 
mainly eastern portions toward the coasts as the temperatures aloft remain very 
similar. 


Conditioned with the mention of rain beginning on Friday...as both the 
GFS/European model (ecmwf) show another backdoor front pushing into the region...with 
this feature serving as an anafront late Friday/early Sat as a southern 
stream wave moves across the Lower Middle Atlantic region. Cooler temperatures 
Friday/Sat as a result of the likelihood of increased clouds/rain chances. 


&& 


Aviation /06z Sunday through Thursday/... 
VFR conditions will persist for another taf cycle before 
restrictions develop twrds daybreak Monday. 


A large band of rain showers/thunderstorms and rain showers will works its way SW/NE through the 
region Monday morning into early afternoon. Dry slot at middle levels will shut 
chances of precipitation off over SW County Warning Area...with lingering chances of rain showers over 
the Northern Neck into the Eastern Shore late day. However...MVFR/IFR ceilings 
look to remain low along the coastal third...but could see enough 
dry air to allow for VFR conditions over central VA/NC. 


Another issue Monday am will be wind direction and potential for maximum 
Crosswinds over southeast Virginia/NE NC Monday am. Guidance showing winds at the 
surface to be out of the southeast (140-160 degrees) 10-20z Monday and 
eventually out of the south late afternoon/early evening. Low level jet moves 
over the region at that time with winds of 35-45 kts at 1-2k feet. 


Upper level low moves over the region Tuesday with MVFR ceilings developing...with 
chances for late am/PM rain showers activity (esp north central Virginia/Maryland eastern 
shore). Winds shift to the northwest Tuesday night into Wednesday which could make 
for crosswind issues once again for phf/orf. 


&& 


Marine... 
winds have backed more southeast toward the coast this afternoon (as was 
anticipated)...however over the past hour the sea/Bay breeze 
component was able to turn the wind completely around at Norfolk 
(where surface winds are currently NE 5-10 kts). Expect the current 
regime to hold serve for a few more hours...with the southeast/south-southeast flow 
near the coast by sunrise gradually veering more S/south-southwest overnight. 
Wind speeds and waves however will remain below Small Craft Advisory 
(sca) criteria. 


Next chance for sca's will be on Monday as S/southeast flow increases ahead of 
the next low pressure system. This low will move over the middle Atlantic 
region into Tuesday and eventually pushing offshore Tuesday night and on 
Wednesday. Could see a brief period of low-end gales Tuesday night and early 
Wednesday before high pressure (weakening gradient flow) builds into the 
region from the west. 


&& 


Akq watches/warnings/advisories... 
Maryland...none. 
NC...none. 
Virginia...none. 
Marine...none. 


&& 


$$ 
Synopsis...ajz 
near term...tmg 
short term...ajz 
long term...bkh 
aviation...ccw 
marine...bkh