Weather

492 
fxus61 kakq 060344 
afdakq 


Area forecast discussion 
National Weather Service Wakefield Virginia 
1044 PM EST Monday Jan 5 2009 


Synopsis... 
a slow moving cold front will slowly push southward overnight. Low 
pressure will form along this boundary and moves east across the 
middle Atlantic region Tuesday. Another cold front crosses the region 
on Wednesday. High pressure builds back over the region for 
Thursday. 


&& 


Near term /until 6 am Tuesday morning/... 
early evening analysis depicts slow moving surface boundary draped across 
southern tier of County Warning Area (va/NC border)...with broad 1020mb surface high 
pressure nosing into northern middle atl region. A surface trough was 
noted now bisecting the northern tier of the County Warning Area...with dewpoint 
temperatures taking a quick dive behind the trough (dewpoint in the 
low 30s far north...with dewpoints in the l50s south of the front 
over interior nc). 


Overrunning/isentropic lift (295-305k sfc) will continue to increase 
overnight...with precipitation is expected to resume over the next few 
hours over the southwestern County Warning Area. Model timing of front has slowed 
a bit...so have accordingly held off higher probability of precipitation until after 
midnight elsewhere. Precipitation will increase in areal cvg and intensity 
from SW to NE overnight...with little/if any precipitation over Northern 
Neck/Eastern Shore until daybreak. Interestingly enough...there was 
was enough instability south of the boundary for some scattered convection 
over the Piedmont of NC. This should diminish overnight as front 
slowly slips farther southward. Still...could easily have a rumble 
of thunder or two over the next few hours across Southside Virginia. 


Biggest forecast challenge for the night is the possibility of 
frozen precipitation over northern County Warning Area. Model soundings...continue to keep 
appreciable ice pellets/freezing rain north and west of the County Warning Area (ie cho and north). 
For our area...rn should be dominant p-type. That said...bufr 
soundings/plumes (especially gfs) point towards enough cold air 
present just above bl for sleet to mix in with rain...especially 
over traditionally cooler western sections of Louisa/Fluvanna 
counties. Held off on any advisories for now with little in the way 
of ice accretion expected. Night crew will be able to re-evaluate 
as trends evolve and issue an advisory if necessary. Farther 
east...there is the possibility that some sleet could mix in at 
times with the rain as far east as the Northern Neck and lower 
Eastern Shore...with precipitation onset looking to be around/just after 
sunrise this morning. So...along with the likely/categorical rain 
chances for Tuesday...have held onto a chance for light sleet beginning Tuesday 
morning and lasting through the early half of the afternoon (before 
changing to all rain) for our northern tier of counties roughly along 
a lku/xsa/sby line. Overnight lows to just above freezing over the 
north...to u40s across the southeastern County Warning Area. 


Tuesday can basically be summed up as rainy and cool...with rain 
falling heavy at times...especially south of metropolitan ric into south 
central Virginia and the Tidewater region. Have continued categorical probability of precipitation 
during this time for the entire County Warning Area. Wedge gradually breaks down 
by late in the day...but not before keeping temperatures generally stable 
for much of the daylight hours tomorrow. Went with maxima in the 
middle 30s far northwest and over interior Maryland...with temperatures in the M/u50s 
over Tidewater and NC coastal plain. 


By event's end on late Wednesday/early Thursday morning...1 to 2 inches of 
quantitative precipitation forecast can be expected for many locations across the County Warning Area. Though we 
are looking at a very rainy period the next two days, do not think 
quantitative precipitation forecast is enough to warrant any flood watches at this time. 


&& 


Short term /Tuesday night through Thursday/... 
temperatures warm on Wednesday after warm front lifts north over the area. 
Bbndry finally begins to mv offshore Wednesday night...and thus finally 
ending precipitation chances. High pressure builds back over the region for 
Thursday...and we can expect a return to more climatology normal temperatures in the 
middle-upper 40s. 


&& 


Long term /Thursday night through Monday/... 
high pressure builds in from the west Thursday night. The ridge axis will be 
overhead of our forecast area on Friday...then will shift offshore Friday night as a 
cold front approaches from the northwest. The front will move through Sat and 
have increased probability of precipitation to 30-40% during frontal passage. The front slows down and 
stalls out across NC on sun and will keep 20-30% probability of precipitation over S/southeast 
sections...closest to the front. High pressure then returns from the west 
late sun through early next week. 


High temperatures in the extended will start out cold under northwest flow with 
850 mb temperatures falling to -12 to -13c behind the cold front. Highs Friday in 
the upper 30s to middle 40s...lows near 20 to near 30. Temperatures warm up on 
Sat and sun as SW flow becomes established ahead of the next cold 
front...with highs in the upper 40s to middle 50s...and lows in the lower 
30s to middle 40s. Colder next Monday behind the front...highs in the upper 
30s to middle 40s and lows near 20 to near 30. 


&& 


Aviation /03z Tuesday through Saturday/... 
a cold front near the Virginia/NC border south of the taf sites as of 01z 
and will remain nearly stationary during the next 24 hours. Mainly 
MVFR ceilings north of the front will lower to IFR/LIFR within a few 
hours after the first precipitation. The NAM is doing well with the 
placement of precipitation in Kentucky/Tennessee and used it to forecast rain 
initiation between 05 and 09z. There may be some ice pellets 
(surface temperatures above freezing) at sby at first. As a primary 
low moves toward the central Appalachians...the front is expected to 
move north of ecg Tuesday afternoon possibly with a secondary low on it between 
ecg and orf by late in the day. 


The primary low will continue moving north and eventually turn winds 
to the south at the taf sites. Widespread IFR conditions can be 
expected overnight Tuesday night improving to VFR/MVFR on Wednesday. There 
will be some showers in the area Wednesday especially in the afternoon. 
Winds turn to the west Wednesday night as a cold front moves through and 
VFR conditions will return Wednesday night and continue into Friday as 
high pressure builds in. Another cold front approaches Saturday 
along with a brief period of possible showers and lower aviation 
conditions. 


&& 


Marine... 
winds have become NE behind a back door frontal boundary which has 
pushed just S/SW of the waters. Cold air advection behind this feature still looks 
minimal...and winds are expected to remain below Small Craft Advisory levels (10-15kt) 
tonight. Winds will then increase and seas will build on Tuesday due to 
a tightening pressure gradient...with high pressure nosing down from the 
north/NE and deepening low pressure advancing towards the waters from the 
interior southeast US states. Small Craft Advisory in effect for all coastal waters by early 
Tuesday afternoon. Expect some 4 feet seas/waves to sneak into the mouth of the 
ches Bay under NE fetch and Small Craft Advisory will commence late Tuesday afternoon for the 
southern most Bay zone. 


The frontal boundary will lift back to the NE by late Tuesday...with 
increasing southerly flow setting up across all waters by midnight 
Tuesday night. Small Craft Advisory flags have also been raised for the Currituck sand and 
for ches Bay from New Point Comfort Virginia north beginning Tuesday night. 
Extended all Small Craft Advisory headlines through the end of the 3rd forecast period... 
although they will likely need to remain in effect through Friday until 
high pressure finally returns to the region by late Friday into Sat. 


&& 


Akq watches/warnings/advisories... 
Maryland...none. 
NC...none. 
Virginia...none. 
Marine...Small Craft Advisory from 4 PM Tuesday to 6 PM EST Wednesday 
for anz632. 
Small Craft Advisory from 10 PM Tuesday to 6 PM EST Wednesday 
for anz633. 
Small Craft Advisory from 4 am to 6 PM EST Wednesday for 
anz630-631. 
Small Craft Advisory from 1 PM Tuesday to 6 PM EST Wednesday 
for anz650-652-654-656-658. 


&& 


$$ 
Synopsis...mam 
near term...mam/smf 
short term...mam/smf 
long term...jrl 
aviation...lsa 
marine...jrl 

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