307 
fxus62 krah 071817 
afdrah 


Area forecast discussion 
National Weather Service Raleigh NC 
115 PM EST Wednesday Jan 7 2009 


Synopsis... 
a strong cold front will sweep across the area...bringing very windy 
conditions this afternoon into this evening. Behind the front... 
there will be drier and chilly conditions through Friday. 


&& 


Near term /through tonight/... 
as of 1055 am Wednesday... 


Shallow convective line swept across central North Carolina during 
the morning. Transfer of strong convective winds to the ground was 
supported mainly in the coastal plain...where earlier msas images 
showed surface-based instability to near 0c...aided by surface 
temperatures from 65 to near 70 degrees. Convective line has moved 
to the east...which will be followed by the front as the day wears 
on. 


Amdar sounding from krdu showed winds near or above 50kt not far off 
the surface...and NAM and GFS bufr soundings for the afternoon show 
50kt within the first 2k feet across central North Carolina in 
cold-air advection and steepening lapse rates during the afternoon. 
12z upper-air analysis showed very good cold-air advection aloft... 
with temperature falls of 10-15c at 850mb and 700mb from kgso to 
kbna. Will certainly maintain the Wind Advisory and considered a 
High Wind Warning due to the mixing potential...but both the latest 
NAM and RUC are consistent with a lull in the gradient as the 
surface low moves off to the northeast...followed by the strongest 
thickness packing ushering in the truly colder air around and mainly 
after 21z...after peak diurnal heating. Temperatures that fell 
slightly behind the convective line are starting to rise again... 
though in some places in the south and the coastal plain 
temperatures will likely not recover all the way back to near 70 
degrees due to clouds and mostly scattered precipitation. 


Tonight...passage of initial 850-700mb trough this evening may 
cause a few showers early across the north. Otherwise windy 
westerly flow will advect cooler drier air. Expect winds to 
subside below advisory criteria by midnight. Mixing near surface 
will prevent air mass from realizing full cooling potential. Went 
with min temperatures near or on the warm side of guidance (mid/upper 30s 
north to lower 40s se). 


&& 


Short term /Thursday through Friday night/... 
as of 315 am Wednesday... 


Models have come in wetter between 2000-10000ft over the region Thursday 
with the passage of another distinct middle level trough. Appears to 
be enough lift through the column to generate a few instability 
showers. Due to the cold temperatures aloft...may see a few snow showers 
across the north in spite of surface temperatures near 40 degrees. For 
now....will have probability of precipitation no higher than 20%. Winds will be blustery 
but not as strong as those expected later today. 


Thursday night through Friday night....high pressure will build 
into the region from the west. This will lead to a tranquil 
weather pattern. With surface high in vicinity by Friday 
morning...winds should subside to near calm. If skies remain 
clear...temperatures should fall into the middle and upper 20s. As high 
drifts east Friday and Friday night...air mass will begin to 
modify. High temperatures Friday be close to normal while min temperatures Friday 
night should be a few degrees warmer than Thursday night...especially 
in the west. 


&& 


Long term /Saturday through Tuesday/... 
as of 236 am Wednesday... 


The medium range models continue to advertise a mostly dry cold 
frontal passage on Saturday. Just as in the previous runs... the 
main upper level dynamics are forecast to pass well north of our 
region... with very little low level moisture transport in the lower 
levels ahead of the front. However... the 00z/European model (ecmwf) continues to 
indicate a slightly better chance of showers with the front... with 
little support from the 00z/GFS. For now... we will maintain a 
slight chance of showers on Saturday at 20 percent. Saturday should 
also be warmer as the SW winds increase ahead of the front. If 
there is enough sunshine... the temperatures could reach into the 60s even 
in the northwest Piedmont. With the expected increase in middle and high level 
moisture.... we will maintain the current 58-65 northwest to southeast. 


A colder dry north flow will follow the front Saturday night into 
Sunday. The air mass will be of modified polar origin. The coldest 
air will remain west of the Appalachians until Sunday night and 
Monday. Sunday temperatures should be a few degrees above normal. Lows 
35-40 and highs Sunday 50-55 or so. For Monday... lows will dip into 
the 20s with highs in the middle 40s to near 50 (very close to the 30 
year average). 


Monday night and tuesday: model spread continues to be of concern 
and results in a low confidence forecast. An increasingly +pna 
pattern is supported which should build a western U.S. Upper ridge 
and downstream eastern U.S. Trough. Before this occurs... there 
could still be some interaction of an old stalled baroclinic zone 
along the Gulf Coast and possible ejection/interaction of the SW US 
trough with northern stream energy. We continue to favor any 
cyclogenesis/frontal waves remaining far enough south and east of 
central NC to keep our weather dry... but the lack of run to run and 
model to model continuity makes this a low confidence forecast. 


&& 


Aviation /18z Wednesday through Monday/... 
as of 115 PM Wednesday... 


Drier air will continue to move into central North Carolina with 
wind gusts the primary aviation factor through tonight. With 925mb 
winds of 40-50kt this afternoon and only gradually diminishing to 
25-35kt overnight...there will be some wind gusts at the surface at 
or a few knots above 35kt at times this afternoon through early 
evening before subsiding. There should be enough cold-air advection 
allowing some wind gusts into the teens kts overnight based on the 
model sounding profiles from both the NAM and the GFS. Most ceilings 
will be VFR or high MVFR with scattered clouds...if any...tonight. 


Middle-level wave moves into central North Carolina early Thursday 
combined with a surface trough that moves through the state. With 
modest divergence aloft along with low-level convergence...enough 
lift will be generated to at least provide for the development of 
low VFR or high MVFR ceilings by 18z. In addition to the clouds... 
lift should be sufficient to generate scattered areas of rain. This 
rain may be mixed with a little snow based on above freezing layers 
on the NAM and GFS bufr soundings of only near 1500ft before 18z. 
Surface temperatures will be warm...above freezing expected. 925mb 
winds of 20-30kt will allow for the continuation of a few gusts... 
though not as gusty certainly as this afternoon. 


Beyond the 18z valid taf period...high pressure brings VFR 
conditions Thursday night through Friday. Clouds will increase and 
lower into Saturday with the approach and passage of a cold front. 
Expect moderate surface wind gusts ahead of the front from the 
southwest Saturday...and behind the front from the west and 
northwest late Saturday into Sunday. Conditions should be VFR Sunday 
and Monday under high pressure. 


&& 


Rah watches/warnings/advisories... 
Wind Advisory until midnight EST tonight for ncz007>011- 
021>028-038>043-073>078-083>086-088-089. 


&& 


$$ 
Synopsis...Badgett/djf 
near term...wss/djf 
short term...wss 
long term...Badgett 
aviation...djf 

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