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Area forecast discussion 
National Weather Service Buffalo New York 
646 am EST Monday Nov 23 2009 


Synopsis... 
a large area of high pressure extending from northern New England 
into the Great Lakes will retreat to the Canadian Maritimes today. A 
weak middle level disturbance will bring an increase in cloud cover and 
perhaps a few light showers to the region tonight and Tuesday. A 
weak ridge of high pressure will bring a return to mainly dry 
weather Tuesday night before an area of low pressure moves into the 
Great Lakes later Wednesday bringing the next chance of showers. 
Above average temperatures will continue through much of this week 
before a significant cool down and possibly a change towards more 
wintry weather by next weekend. 


&& 


Near term /through tonight/... 
for the most part skies are clear across western and central New 
York early this morning. 11-3 micron imagery showing area of 
increasing stratus working northwest into the southern tier of New 
York state in weak low level southeasterly flow. This trend will 
likely continue through the rest of the early morning hours with 
low stratus pushing across most of southern New York state. Areas 
which remain clear will likely experience some patchy fog through 
sunrise. 


Once any stratus Burns off this morning...most of the remainder 
of the day today looks to be in fine shape as strong 1035+ mb high 
centered over northern New England slides eastward. Cloudiness 
will gradually increase from south to north this afternoon as 
complex low pressure system lifts north out of the southeastern 
states. Temperatures today should be similar to Sunday with little 
change in air mass...sref/MOS bias corrected numbers suggesting 
highs in the lower to middle 50s. 


The low lifting through the southeast looks to get sheared to the 
northeast and east tonight forming a coastal low. This should 
take most of the deeper moisture with it. There is still a 
question on how far north and west the precipitation shield will 
get across our area with the coastal low pushing to near Cape Cod 
by Tuesday morning. At this point...will remain close to 
continuity and suggest a low chance for showers across south and 
eastern areas with a slight chance extending across northwest 
sections. 


&& 


Short term /Tuesday through Wednesday night/... 
at the start of the period a weak middle level trough will be lifting 
northeast across the area. Model guidance has had a difficult time 
with this feature in respect to timing and precipitation potential. Latest 
00z/23 guidance is backing off on quantitative precipitation forecast/probability of precipitation and once again focusing 
most of the stronger forcing and moisture transport along the 
coastal plain near a developing low offshore. To the west of the 
Appalachians...this will just leave a weak surge of moisture lifting 
north across the area...with only weak middle level lift from a 
Delaware-amplifying middle level trough. Will back off on probability of precipitation and go low 
chance for Tuesday from the southern tier through The Finger lakes 
into the Tug Hill region. Have kept the Niagara Frontier and Saint 
Lawrence valley dry with less northern extent on latest model 
guidance. Any precipitation that does fall will be light...with quantitative precipitation forecast less 
than a tenth of an inch. This system will bring an increase in cloud 
cover to the entire region with low level moisture becoming trapped 
under a subsidence inversion once again...a common occurrence at 
this time of year. Any precipitation will end by Tuesday night with a weak 
ridge of high pressure building over the lower lakes...but clouds 
will remain for most of the region. 


On Wednesday an area of low pressure will lift from the middle 
Mississippi Valley into the Central Lakes. The warm advection Wing 
ahead of this system will lift across the lower lakes through the 
course of the day. Latest model guidance is slowing the timing of 
this feature...and also shifting the track more to the northwest. 
The net result will be a more optimistic forecast for Wednesday... 
and will need to back off on probability of precipitation as a result. In fact...the 00z NAM 
holds most of the precipitation off until Wednesday night. Will go with 
chance probability of precipitation for now...increasing from west to east through the day. 
925mb temperatures rise to +6c...and southerly downslope winds should boost 
temperatures into the upper 50s in the lower elevations. A few places in 
the Genesee Valley and central New York may eclipse 60. Low to middle 50s 
will do it for the higher terrain of the southern tier and north 
country without the benefit of compressional downslope warming. 


Wednesday night the surface low will remain nearly in place over the 
upper Great Lakes as a complex middle level evolution takes place... 
with another shortwave dropping into the western periphery of the 
developing middle level trough. Again the next result was to slow the 
forward progress of this system from previous runs...and should keep 
the bulk of organized precipitation north and west of the area. Will keep 
chance probability of precipitation going for now...but much of this period may end up being 
rain free. 


&& 


Long term /Thursday through Sunday/... 
a relatively weak surface low will remain over the upper lakes on 
Thanksgiving. Given the position of the surface and middle level 
features...expect the Holiday to be mainly rain free. Was tempted to 
remove probability of precipitation altogether...but for now will back off to low chance to 
account for the potential of future model changes. If the current 
trend continues...probability of precipitation may be removed for Thanksgiving. It now 
appears colder air will hold off until Friday...so the above average 
temperatures will continue through the Holiday. 


Things get much more interesting by days 5-7. A potent middle level 
vortex is forecast to drop into the Ohio Valley Thursday night... 
then move towards the eastern Seaboard Friday and Friday night. At 
the same time...a southern stream system will round the base of the 
developing trough...with the two features coming in close proximity 
along the northern middle Atlantic coast. Strong middle level forcing 
moving atop a tight baroclinic zone along the coast may result in 
strong coastal cyclogenesis...with the resulting surface low lifting 
north across New England late Friday through Saturday. Utilizing a 
potential vorticity analysis...it can be seen that the system 
responsible for this potential is still over the North Pacific... 
apparent in moisture channel imagery offshore of British Columbia. 
Until this system moves into the North American radiosonde 
network...model forecasts should be viewed with caution. 


Looking at the latest 00z/23 models...the GFS continues to bring a 
strong coastal low well inland across New England. The European model (ecmwf) is 
weaker and farther east...while the Canadian Gem continues to show a 
very different evolution with little coastal cyclogenesis...bringing 
in colder temperatures and wrap around precipitation almost 24 hours faster than 
other model guidance. The 00z/23 Navy NOGAPS is similar to the 
European model (ecmwf). At this time range...little detail will be offered in the 
grids with just chance probability of precipitation for the entire period. Expect precipitation to 
be mainly rain through Friday...before colder air aloft wraps into 
the area and brings increasing chances of snow Friday night into 
Saturday. For now will go with rain/snow mix across the lower 
elevations and more snow across the higher terrain. Will introduce 
mention of this system into the severe weather potential statement. At this early juncture...the 
marginal boundary layer temperatures suggest the better chance for 
accumulating snow will be over the higher terrain. 


&& 


Aviation /12z Monday through Friday/... 
stratus pushing slowly northwest across the region early this 
morning. IFR ceilings had developed at kjhw for much of the night 
but the stratus has eroded there. The western edge of the stratus 
deck should eroded before reaching and taf sites. Light fog... 
generally 4-5 miles will burn off by 13z. The remainder of the 
day will see increasing middle and upper level cloudiness working 
northward ahead of the southeastern states low. Middle level ceilings 
will likely develop by 00z tonight. VFR conditions are expected 
through the end of the taf period...although ceilings will continue 
to lower with the chance for the western edge of the precipitation 
shield associated with the low pushing up the eastern Seaboard 
reaching eastern and southern airfields by 06z. 


Outlook... 
Tuesday...mainly VFR. 
Wednesday and Thursday...VFR/MVFR with a chance of rain showers. 
Friday...MVFR with a chance of rain/snow showers. 


&& 


Marine... 
winds will remain out of the east through midweek on both lakes Erie 
and Ontario. The easterlies will increase later today and this 
evening and create choppy conditions on Lake Ontario. The forecast 
east-southeast wind direction should keep the largest wave action 
well offshore and along the Canadian shoreline...so no small craft 
advisories will be issued at this time. Winds will diminish later 
tonight. 


&& 


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


&& 


$$ 


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

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