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Area forecast discussion 
National Weather Service Wakefield Virginia 
1250 am EDT Sat Mar 20 2010 


Synopsis... 
high pressure will prevail over the middle Atlantic through Sunday 
bringing mild and dry conditions. Low pressure will arrive from the 
southwest Sunday night with the associated cold front crossing the 
area Monday. 


&& 


Near term /until 6 am this morning/... 
an upper ridge/surface hi pressure will provide another clear and cool night to 
the region. Tweaked a few min temperatures...based on current observation. Low temperatures 
will range from the middle 30s to lower 40s. 


&& 


Short term /6 am this morning through Monday/... 
the upper ridge will remain firmly entrenched over the region 
Saturday. The airmass will warm a few more degrees with maximum 
temperatures reaching the middle and upper 70s...aside from slightly 
cooler readings near the coast. Dewpoints...and hence minimum 
relative humidity values will remain low. There is not much 
indication that minimum relative humidity values will be any higher 
Saturday afternoon than Friday afternoon...which presently range 
from 15 to 20 percent away from the immediate coast. The wind will 
be light as the surface gradient remains rather nebulous. 


By Saturday night and Sunday an upper low moves over the lower 
Mississippi Valley. The wind begins to shift more southerly and high 
clouds will begin to increase. Relative humidity values start to 
climb slightly...but will remain on the lower side as temperatures 
remain mild with maximums Sunday again in the 70s. 


The upper low trundles toward the southern Appalachians Sunday night 
and Monday. A cold front aloft ahead of the approaching cyclone 
should bring a period of rain showers to the forecast area Monday 
morning...possibly into the afternoon for the Eastern Shore. Drier 
and cooler air aloft moves in behind the front...and surface 
temperatures are expected to remain mild...so a few showers or 
thundershowers are possible in the wake of the front. Models have 
been trending slower and farther south with the track of the upper 
system...so there is still some uncertainty as to how the system 
evolves for the local area. 


&& 


Long term /Monday night through Friday/... 
rain chances linger Monday night and on Tuesday as low pressure slowly 
traverses the middle Atlantic region from west to east. System at this point is 
nearly vertically stacked...though both the GFS/European model (ecmwf) are similar in 
showing the middle level low passing across the Carolinas to near the 
Virginia/NC border. Over the forecast area...any dry-slotting we see on Monday 
will be filled in a bit Monday night and Tuesday...as given the southern 
track of the upper low...our chances for wrap-around showers are 
improved somewhat than if the upper vorticity were to scoot by north of the 
region. The upshot is maintaining at least minimal probability of precipitation in all areas 
Monday night and Tuesday...highest over the northern areas (where the activity 
is expected to be more scattered vs. Isolated). 


Otherwise...cooler on Tuesday with the wrap-around moisture and 
predominately northerly flow in place. Highs in the low-middle 50s over 
the lower Eastern Shore and far eastern Virginia to the upper 50s/lower 60s elsewhere. 


Wednesday and Thursday still look tranquil weather-wise with deep-layer ridging 
moving across the middle and southeast Atlantic Seaboard. The late March sun along 
with the downslope flow and gradually developing warm air advection in the llvls 
will help temperatures warm into the lower 60s over the lower Eastern Shore to 
65-70 elsewhere. Thursday looks to be the warmest day as 850 mb temperatures are 
projected to climb to near +8c per the latest European model (ecmwf) (with +10c temperatures 
knocking on the door to our sw). This should help boost surface temperatures 
well into the 70s over the interior portions of central and S-central Virginia 
(i.E. At least middle 70s). 


12z GFS indicated a rather large departure for the Friday-Sat period 
compared to it's 06z predecessor. However...12z European model (ecmwf) has trended 
much the same way as the GFS...sticking with the more consistent 
European model (ecmwf)...though a bit slower than the GFS with the initial cold frontal passage 
Thursday night/early Friday. It's looking more like a cooler/wetter pattern 
taking shape Friday-Friday night as a secondary low forms along the front 
over the southeast region...then gradually pushes off the Carolina coast. 
For now...given the time frame (7 days out)...for now have decided 
to add a chance of rain to the forecast with temperatures slightly cooler 
than guidance. 


&& 


Aviation /06z Saturday through Wednesday/... 
VFR conditions continue once again for the taf cycle. Generally 
clear skies will persist through the taf period. Look for mainly a 
southerly flow today with sust winds at or below 10 kts. Some scattered high 
clouds will start to try and work its way into central sections 
of the region twrds sun am (esp around and west of ric). 


Next chance of flight restrictions/precipitation comes Monday into Tuesday as 
a low moves across the area. This could produce some MVFR/IFR 
conditions. Potential will exists for the chances of convection on 
Monday am/Erly PM and threat of southeast wind maximum Crosswinds issues for 
orf/phf...wind direction 140-150 degrees (30-45 kts 1k-2k ft). 


&& 


Marine... 
conditions through the weekend will be marked by sub-Small Craft Advisory conditions 
across all waters as high pressure dominates...with winds generally 
10-15 kts or less and wave heights < 4ft. Next chance for sca's will 
be on Monday associated with the next low pressure system that will 
move through the middle Atlantic region. 


&& 


Fire weather... 
an upper level ridge will continue to prevail over the middle Atlantic 
region through Sunday. A very dry airmass is situated underneath the 
ridge and afternoon minimum relative humidity values Saturday will 
again plummet to the 15 to 20 percent range inland...with higher 
values along the immediate coast. A light northwest wind will shift 
to southwest by Saturday afternoon. An upper level low pressure system 
approaching from the southwest will bring a moistening trend by 
Sunday with rain showers expected by Monday. 


&& 


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/jef 
fire weather... 

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