374 
fxus62 krah 121951 
afdrah 


Area forecast discussion 
National Weather Service Raleigh NC 
251 PM EST Friday Mar 12 2010 


Synopsis... 
unsettled weather with occasional showers is expected through Sunday 
in association with several upper level disturbances. 


&& 


Near term /through Saturday/... 
as of 120 PM Friday... 


Little change from earlier thinking. Still expect bulk of precipitation to 
occur tonight...shifting northeastward Saturday morning. 


At 18z...999mb surface low positioned southeast of Cape Fear. This slowly 
deepening system has enhanced low level Ely across the central and 
northern coastal plain...advecting Atlantic moisture into the 
region. As afternoon wears on...expect showers to become numerous 
over the northern half of the forecast area. 


Late this afternoon through this evening expect rainfall intensity 
to pick-up in the far west-northwest as upper divergence will be increasing as 
a result of strong 300mb jet crossing the northern Gulf into the 
central Florida Peninsula. Fairly deep (below 8000ft) east-southeast flow as a 
result of surface low in vicinity of the southern-central NC coast 
and a distinct 850mb trough approaching from the SW will create 
decent upslope flow parameters. This should result in periods of 
moderate to locally heavy rainfall immediately west-north of central 
NC. The greatest threat for any prolong moderate rain in our region 
will be over The Triad then NE along the Virginia border counties. 
Projected rainfall amounts between a half to one inch are well below 
flash flood guidance so do not anticipate a watch. However could 
hear rumbles of thunder late this evening and overnight as 850-500mb 
lapse rates increase to between 6-6.5 degree c/km. Wind profile while 
support of some updrafts the magnitude of the winds are weak to 
marginal so not expecting any severe storms. 


On Saturday...850mb trough lifts NE away from the region. In its 
wake...westerly flow will advect drier air into the region. Approach of 
mud/upper level cyclone though will result in 850-500mb lapse rates 
approaching 7 degree c/km. Any residual moisture coupled with this 
instability aloft would support isolated thunderstorms...especially 
east of Highway 1. Wind profile unidirectional but only 25-30kts 
through the column. Thus could see some wind gusts 30-35kts with the 
storms. May see some hail though with any storms with sustained 
updrafts due to freezing levels between 6000-8000ft. 


Temperatures Saturday dependent upon whether any breaks occur. Due to the 
downslope component of the low level and subsidence behind the 
exiting middle level trough...may see enough breaks to allow for for 
some partial sun. Due to relative mild conditions overnight...could 
see temperatures rebound 15-18 degrees from morning low temperatures. Thus have 
raised maximum temperatures about 3 degrees from previous forecast. 


&& 


Short term /Saturday night through Monday night/... 
as of 245 PM Friday... 


Saturday night: 
cold advection in the low levels on Saturday evening 
will help to increase stability in the low levels of the 
atmosphere... as the surface trough/cold front moves through the 
area. However... the potent middle/upper low is expected to move across 
the area on Saturday night/Sunday evening. Thus... even with the 
decreasing instability in the low level expect we could still see 
some showers continue/develop into the overnight hours... with the 
NAM more excited about chances for showers and the GFS. For now will 
go with a chance of showers County Warning Area wide. With mostly cloudy skies 
expected... temperatures should bottom out in the lower to middle 40s. 


Sunday through Monday night: 
middle/upper level low begins to lift off to the northeast durning this 
period. However... short wave energy and moisture wrapping around the low 
will keep at least isolated chances for showers across the area 
during the day on Sunday. Otherwise... skies are expected to remain 
party to mostly cloudy through the period. High temperatures Sunday and 
Monday look to generally range from the upper 50s to lower 60s... 
with overnight lows in the upper 30s to lower 40s. 


&& 


Long term /Tuesday through Thursday/.. 
as of 125 PM friday: 


Broad cyclonic flow aloft is expected to continue across the region 
through a good portion of the extended... with surface high pressure 
drifting/building into the area from the northwest. Another short wave is 
expected to track through the l/west pattern during next week... and 
close off over the Gulf Coast states on Wednesday night into 
Thursday. As the middle/upper level low moves slowly eastward across 
the Gulf states a surface low is expected to develop of the 
southeastern U.S. Coast on Thursday. However... the best lift and 
moisture associated with this system are expected to remain to the 
south and east of the area. Thus... will continue a dry forecast 
during this time. Temperatures look to be near to slight below normal 
during this time frame... as low level flow remains north to 
northeasterly. Expect high temperatures in the upper 50s to lower 60s... 
through Thursday. Lows during the extended look to remain near 
normal... upper 30s to lower 40s. 


Expect dry conditions to continue into Friday... however... 
questions remain with regard to how amplified the upper level flow 
pattern will be across the North America late next week. The GFS 
continues to be quite progressive... allowing low level flow to 
become southerly on Friday... while the ec considerable slower. 
However... low level thickness values do increase on the ec as broad 
troughiness begins to move east of the area... giving way to 
increasing heights. HPC still prefers the ec late next week... 
despite the feeling that it may be a bit too slow and amplified. 
Thus... will the uncertainty will trend high towards climatology... with 
highs in the lower to middle 60s. 




&& 


Aviation /18z Friday through Wednesday/... 
as of 100 PM Friday... 


A prolong period of IFR/MVFR ceilings expected through Saturday 
morning as moist low level east-southeast flow coupled with the approach of an 
upper level disturbance from the west-SW will cause extensive 
cloudiness along with scattered to numerous showers...especially 
across the western and northern Piedmont into the northern coastal 
plain. The approach of the upper level system late tonight will 
increase the middle level lapse rates...slightly enhancing the 
potential for isolated thunder. This threat appears to be greatest 
between Charlotte and Fayetteville. 


The threat for isolated thunder will continue Saturday into early 
Saturday evening as another upper level system approaches from the 
west. Not too overly concern with strong wind gusts but the stronger 
storms may be accompanied by small hail. Otherwise expect MVFR or 
low end VFR ceilings Saturday through early Sunday. 


May see isolated to scattered showers Sunday afternoon as upper 
level low will reside aloft. This system drifts east Sunday night. 
In its wake...low and middle level flow will back northerly...advecting drier 
more stable air into the region. This will lead to a period of VFR 
conditions Monday through Wednesday. 


&& 


Rah watches/warnings/advisories... 
none. 


&& 


$$ 


Synopsis...wss/Vincent 
near term...wss 
short term...bsd 
long term...bsd 
aviation...wss 

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