431 
fxus61 kakq 202005 
afdakq 


Area forecast discussion 
National Weather Service Wakefield Virginia 
405 PM EDT Sat Mar 20 2010 


Synopsis... 
high pressure over the middle Atlantic region this weekend will give 
way to low pressure will from the southwest late Sunday night. The 
associated cold front crosses the area Monday. 


&& 


Near term /until 6 am Sunday morning/... 
satellite channels reveal that the upper ridge of the past few days 
continues to continues to control the weather over the local 
area...and that will continue through the night. Cirrus clouds will 
increase through the overnight...but the prevailing sky condition 
will remain mostly clear. Low temperatures will be slightly warmer 
than the past few mornings with the presence of a light 
southwesterly wind. Readings will generally be in the low and middle 
40s. Meanwhile...the next storm system is strengthening over the 
Southern Plains. 


&& 


Short term /6 am Sunday 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 /20z Saturday through Thursday/... 
clear skies covered the taf sites at 17z. Scattered clouds above 12k feet will 
begin to show up Sun morning. Most of the cloud development will occur 
beyond 18z. Winds are expected to back toward southeast by late Sat afternoon 
as a sea breeze develops. 


Conds deteriorate Sun night as the next weather system approaches. Periods 
of MVFR/IFR and wdspr precipitation can be expcted Monday. There will also be a 
chance for embedded thunderstorms Monday. Some improvement but a continued chance of 
showers can be expected Monday night and Tuesday. This will be followed by 
VFR/dry conds Wednesday and Thursday. 


&& 


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...ajz 
short term...ajz 
long term...bkh 
aviation...lsa 
marine...bkh