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Area forecast discussion 
National Weather Service Buffalo New York 
1226 PM EST Sat Nov 21 2009 


Synopsis... 
high pressure will build over the region this weekend before 
shifting off the New England coast by early next week. While high 
pressure will be in place today...residual cloud cover will remain 
before giving way to sunshine for Sunday and Monday. A storm system 
will approach from the Midwest on Wednesday and bring the next 
chance of rain with unsettled conditions lasting through the end of 
the week. Temperatures will continue to remain above average through 
the first half of next week before a cooling trend by the 
Thanksgiving Holiday. 


&& 


Near term /through tonight/... 
1230 PM update...region covered under a low stratus deck at 
midday...with some earlier sunny breaks having filled in as 
expected. Just too much low level moisture around. Satellite loop 
show a weak middle level trough moving across northwest PA and this should 
continue to push east and allow for some subsidence in its 
wake...as evident by clearing over lower Michigan...but probably 
too late to allow for any of this clearing to push into our area 
today...with sunset before 5 PM. And...any clearing tonight would 
lead to some fog toward daybreak. Temperatures steady in mid to upper 40s at this time and 
will be going nowhere this afternoon under the dense low deck. A 
very novemberlike look to the day. Tweaked temperature and sky grids 
accordingly. No other changes at this time. Previous disc follows... 


Models continuing to insist that improving conditions will take 
place tonight. Middle level ridging advancing into the region 
tonight behind the upper wave will help push out the middle level 
moisture and some shallow warm air advection could weaken the 
subsidence inversion and allow for some partial clearing. Any 
clearing will result in the development of fog late tonight. 
Temperatures overnight will depend greatly on amount of clearing 
which can take place. With little change in air mass expected will 
lean overnight temperatures toward bias correction numbers 
suggesting upper 20s to lower 30s along the southern tier and east 
of Lake Ontario to the middle and upper 30s along the lake plain. 


&& 


Short term /Sunday through Tuesday/... 
at the start of the period an expansive area of high pressure will 
stretch from Quebec southward across the lower lakes and down the 
Appalachians. Some stratus may still linger in the morning across 
the higher terrain of the southern tier...but expect continued 
subsidence and drying to finally erode this and leave plenty of 
sunshine everywhere during the afternoon. 850mb temperatures of around +4c 
will continue to support above average temperatures with highs in the lower 
50s in most locations...with upper 40s across the north country. The 
surface high will slowly drift into the Canadian Maritimes by 
Monday. Southeast return flow may allow some increase in moisture 
during the day across the southern tier...but otherwise expect a 
fair amount of sunshine. Similar 850mb temperatures will support highs in 
the lower 50s again across the lower elevations...a few degrees 
cooler across higher terrain. 


Monday night and Tuesday significant model differences become 
apparent with the handling of a weak coastal system. Moisture 
channel imagery shows a weak southern stream cutoff low moving 
through southeast Texas early this morning. The GFS continues to 
take a piece of this system and plume of associated moisture up to 
the west of the Appalachians...with another piece of energy spawning 
a weak coastal low off the Carolinas. This allows a notable period 
of rain to lift north across the County Warning Area Monday night and Tuesday in the 
GFS solution. The NAM and Canadian Gem emphasize the coastal system 
only...keeping all of the precipitation along the coastal plain Monday 
night into Tuesday. The difference in sensible weather is huge... 
with a rainy GFS solution versus a dry and even partly sunny NAM 
solution. 


The new 00z European model (ecmwf) just coming in also supports the NAM solution with 
most if not all of the precipitation focusing along the coast. Will choose 
to follow the model consensus and throw out the GFS solution. This 
allows US to stay close to forecast continuity with a dry forecast 
for most of the County Warning Area Monday night and Tuesday. Will keep some low 
chance probability of precipitation east of Lake Ontario to handle the potential for coastal 
moisture making it back that far west. 


&& 


Long term /Tuesday night through Saturday/... 
the now well advertised pattern change still appears on track to 
arrive for the Thanksgiving Holiday. The current pattern across the 
noam sector is more or less zonal...with transient relatively low 
amplitude troughs moving through the westerlies along and just north 
of the US/Canadian border. The gefs ensemble mean continues to 
forecast the nao index to become weakly negative by the end of the 
month...with the pna index trending positive. In the mean...this 
should yield a colder pattern for the Great Lakes and northeast for 
the last week of November into early December with a trough favored 
over the eastern Continental U.S. In such a pattern. The indices are not 
forecast to be particularly strong however...so no dramatic pattern 
change is expected...rather a trend towards cooler and more 
seasonable temperatures. 


Looking at the details...there are still the typical differences in 
the handling of shortwave features and associated surface systems 
for the second half of the week. The GFS continues to eject a lead 
shortwave and associated surface low into the Great Lakes region on 
Wednesday with another system for Thursday and Friday as the main 
middle level trough crosses the region. The European model (ecmwf) does not support this 
first low on Wednesday...but does come into agreement with the 
system for Thursday/Friday. The Canadian Gem is in good agreement 
with the GFS solution showing both systems. 


For now...given the model uncertainty will simply stick with 
forecast continuity and keep chance probability of precipitation from Wednesday right 
through Friday. Temperatures become cold enough by Thursday and 
Friday to bring precipitation type issues into the forecast. On 
Thanksgiving...the GFS forecasts 850mb temperatures of around -4c while the 
European model (ecmwf)...with its slower single low evolution has 850mb temperatures above 
freezing still. Have leaned towards the GFS/Gem idea... but even 
this would still support mainly rain across the lower elevations 
with a rain/snow mix across higher terrain. Colder air filters into 
the region Thursday night and Friday with a chance of rain/snow 
everywhere. At this time...pattern does not look at all favorable 
for any meaningful snow...with just weak wrap around precipitation and an 
unfavorable northwest flow preventing any significant lake effect. 


&& 


Aviation /18z Saturday through Wednesday/... 
dense stratus deck will continue across most of the region 
through the evening...perhaps breaking up a bit later 
tonight...allowing for some fog to form. Will therefore expect 
MVFR ceilings...with perhaps a period of LIFR conditions in fog near 
daybreak...just about anywhere. Conditions should improve to VFR 
by midday Sunday as the low cloudiness finally Burns off as high 
pressure provides for some good subsidence...but confidence in 
timing of this improvement is fairly low. 


Outlook... 
Sunday night through Tuesday...mainly VFR. 
Wednesday...VFR with chance showers. 


&& 


Marine... 
high pressure builds over the region tonight and Sunday with 
light winds. As the high departs...east winds will increase some 
on Monday and Tuesday with choppy conditions developing on the 
west half of Lake Ontario...but conditions are expected to remain 
below Small Craft Advisory criteria. 


&& 


Buf watches/warnings/advisories... 
New York...none. 
Marine...none. 


&& 


$$ 


Synopsis...Hitchcock 
near term...sfm/tma 
short term...Hitchcock 
long term...Hitchcock 
aviation...sfm 
marine...Hitchcock 

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