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Area forecast discussion 
National Weather Service Wakefield Virginia 
835 PM EST Sat Nov 21 2009 


Synopsis... 
high pressure will build east into northern New England and 
strengthen overnight into Monday morning. Meanwhile...low 
pressure along the Gulf Coast...will track northeast to a position 
off the southeast coast. The low will continue northeast up the 
East Coast Monday through Tuesday. 


&& 


Near term /until 6 am Sunday morning/... 
latest weather analysis depicts surface hi pressure over the eastern Great 
Lakes/western New York. To the south...developing surface low pressure noted 
this evening along the central Gulf Coast region. Aloft...upper 
ridging over the northern/Central Plains has nosed east into the 
upper MS valley. Meanwhile...a strong southern stream upper low was 
noted across the arklatex region. 


Overnight... 
no major changes needed to the going forecast...with only some 
tweaks to sky/T grids at this time. Surface high to the northwest will slide east 
towards northern New England into Sun morning. Dry and chilly tonight with 
a good deal of hi clouds persisting...maintaining mainly partly cloudy 
conds. Min temperatures mainly in the upper 30s to middle 40s...but again will 
likely see some cooler lows northwest of ric and over interior sections of the 
lower Eastern Shore. 


&& 


Short term /6 am Sunday morning through Tuesday/... 
12z NAM/GFS/ECMWF now in general agreement for the short term with 
the onset of coastal low precipitation now delayed until Sun night into Monday morng. 
Have adjusted sky cover and probability of precipitation accordingly. So...will likely 
see at least some opaque sunshine all areas during Sunday 
morning...W/clds increasing and thickening from S to north for the 
remainder of Sun afternoon into Sun night. Maximum temperatures on sun in the middle 
50s to lower 60s. Rain will become likely from S to north later Sun night into 
Monday morng...as low pressure moves to just off the southeast CST. 


Rain then likely all areas during Monday...as the low tracks to just 
east-southeast of hat. Highs on Monday ranging through the 50s to lower 60s. Diminishing 
rain chances from SW to NE Monday night into Tuesday morng...as the low tracks 
farther away to the east-northeast. Do not expect significant rainfall amts 
from this system...with quantitative precipitation forecast around .25 inch most areas...possibly 
around .50 inch closer to the CST. 


Cloudy or mostly cloudy Tuesday morng...then becmg prtly sny over at least 
southeast Virginia and NE NC Tuesday afternoon. Maximum temperatures in the upper 50s to lower 60s. 


&& 


Long term /Tuesday night through Saturday/... 
by Tuesday night/Wed...GFS/ECMWF show ridging in the middle levels off the 
East Coast...with a fairly weak surface pressure pattern across the middle 
Atlantic. Not much of a trigger for any precipitation...but low level 
cloudiness may be difficult to scour out. Overall will keep the 
forecast dry Tuesday ngt/Wed...bringing in 20% chance for -ra from west to east 
later Wednesday/Wednesday night....as weak overrunning scenario sets up. Still a 
lot of uncertainty west/ the evolution of the system after 
that...GFS/ECMWF appear to be trending towards each 
other...developing a low pressure system off the southeast coast 
Thanksgiving day...and tracking it off the Virginia convective available potential energy/middle Atlantic coast 
Thursday ngt/Fri. Meanwhile...the main upper low energy remains well off 
to our north. Have bumped forecast up to 30% chances for rain over southeast 
Virginia/NE NC (although bulk of precipitation stays offshore or to the south 
for now). For central Virginia...keeping probability of precipitation capped in 20% range per more 
of a split flow. 


Flow turns westerly on both models by later Thursday ngt/Fri...and 
should see drier and cooler weather for Fri/Sat. Some model 
discrepancies in the position of the upper low...but will keep it 
dry for now as the consensus is for main energy to stay over the 
NE Continental U.S.. high temperatures gnly in the upper 50s/lower 60s 
Wed/Thu...cooling to the middle/upper 50s Friday...and Lower/Middle 50s Sat. 
Lows mainly in the 40s to lower 50s Wed/Thu...then 30s to lower 40s 
Fri/Sat. 


&& 


Aviation /01z Sunday through Thursday/... 
high clouds were across the area this afternoon. A band of stratocu with 
ceilings of 050 northwest of ric was spreading southeast but appears on satellite to be 
dissipating. Will carry scattered clouds at ric and sby. 


It appears that temperatures will not drop low enough overnight for fog but 
will need to watch sby looking at NAM bufr sounding. Left out of taf 
for now. 


Clouds begin to thicken on sun with the approach of the next system. 
Ceilings lower to MVFR with areas of IFR Sun night and Monday. High 
pressure builds in with VFR conds for Tuesday and Wednesday. The next weather 
system may bring a return of lower ceilings and a chance for precipitation on Thursday. 


&& 


Marine... 
cndtns continue below Small Craft Advisory levels tonight and Erly Sunday (mainly 
10-15 knots although a tad stronger over the south). Conditions 
deteriorate on Sunday...as the surface high moves well off to the 
NE...and low prs along the southern states moves slowly NE late sun 
into Erly next week. With the prs gradient prognosticated to increases aftr 18z 
Sunday will continue with headlines for Small Craft Advisory from the mouth of the 
ches Bay on S and for the coastal waters (as seas build to 5+ ft). 


NAM/GFS now in better agreement west/ the eventual track of this 
systm (gfs has trended slower)...and confidence is higher that a 
period of at least 25 knots winds should develop for the coastal waters 
and southern Bay. Concerned with the strength of the surface high into New 
England (both NAM/GFS depict 1035 mb+). Even though the surface low off 
the carolin as is only prognosticated to be around 1015 mb...this synoptic 
pattern tends to yield stronger winds than those predicted by the 
models. For now have bumped winds to a solid 25 knots with gusts to 
30 knots on the coast...and gone a bit higher than wave watch for seas 
(up to 9 feet offshore). May even see a 3-6 hour period of gales on 
Monday (but will stay west/ Small Craft Advisory for now). Will end the Small Craft Advisory headlines 
Monday afternoon (at the end of the 4th prod)...although lt St wave watch has 
seas aa 5 feet through midweek west/ residual swell. 


&& 


Akq watches/warnings/advisories... 
Maryland...none. 
NC...none. 
Virginia...none. 
Marine...Small Craft Advisory from 1 PM Sunday to 6 PM EST Monday for 
anz632-633-650-652-654-656-658. 
Small Craft Advisory from 6 PM Sunday to 6 PM EST Monday for 
anz630-631. 


&& 


$$ 
Synopsis...tmg/mam 
near term...tmg/mam 
short term...tmg 
long term...lkb 
aviation...lsa 
marine...lkb 

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