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Area forecast discussion 
National Weather Service Buffalo New York 
326 PM EDT Friday Aug 8 2008 


Synopsis... 
low pressure over the Saint Lawrence valley will keep unsettled 
conditions across the area through this evening...along with 
below normal temperatures. 


High pressure over the Ohio Valley will then briefly build northeast 
into the lower lakes and provide our area with a dry Saturday... 
before another low and cold front drops southeast from the Central 
Lakes along with more cool and unsettled weather for Saturday night 
and Sunday. This will be followed by a gradual return to drier 
conditions on Monday and Tuesday as the low lifts northeast away 
from our area. 


&& 


Near term /through Saturday/... 
a large upper level low can be found over Quebec at 3pm with a 
deeper low near James Bay. The latter will be the focus for 
Saturday night. Water vapor imagery shows the edge of the upper low 
influence moving toward western New York. Expect scattered shower 
activity over western New York to diminish quickly this evening as the 
above mentioned back edge works its into western New York while at the 
same time we lose our daytime heating. 


Further to the east...convection will continue from about kroc east 
through the evening hours as a more consolidated area of showers and 
thunderstorms noted in the radar imagery works its way southeastward 
across Lake Ontario and central New York. The western edge...approaching 
kroc...has lost some of its energy over the past hour or two...but 
there is still active weather moving toward the Eastern Lake Ontario 
region. Therefore will continue to emphasis showers and 
thunderstorms lasting into the evening hours over this region of 
New York. 


As the night wears on...drier air will work its way eastward and 
shut down any remaining shower activity. However...the next concern 
will be for the development of fog. For now will address this with 
patchy fog...but more widespread fog is indeed possible as a surface 
ridge builds into the area with light winds...abundant low level 
moisture...and a relatively cool airmass in place. 


For Saturday...expect a generally cool and clear start to the 
morning but with some foggy areas...then a quiet period into the 
afternoon hours. The question then is whether there will be enough 
instability to create a renewed shower threat in the afternoon as 
the James Bay low approaches. Will lean toward the dry side with 
our local WRF run ensemble...as well as the operational WRF and GFS 
keeping the region dry through the afternoon. About 40 percent of 
the sref members bring in precipitation by the end of the day. 


&& 


Short term /Saturday night through Sunday night/... 
in the short term period...a strong shortwave/associated closed 
upper low will drop southeast through the large-scale eastern North 
American trough...moving from the upper Great Lakes late Saturday 
afternoon to a position over Lake Ontario on Sunday...then east to 
the Adirondacks Sunday night. This feature will bring another round 
of cool and unsettled weather to our region for most of this time 
frame...with Saturday night and Sunday looking to be the most active 
periods for convection. 


By late Saturday afternoon...a cold frontal boundary out in advance 
of the digging low is expected to be pushing into an increasingly 
unstable airmass across southern Ontario. Strong low level 
convergence and lift associated with this feature will combine with 
an increasingly diffluent flow aloft to generate a deep layer of 
ascent in the increasingly unstable airmass...leading to the 
development of a band of strong convection to our north and west 
during the middle to late afternoon hours. 


As we get into early Saturday evening...this area of convection will 
begin to sag into western New York state as the frontal boundary and 
supporting upper level features approach...and as the protecting 
influence of the Lake Erie breeze weakens with the loss of daytime 
heating. With strong synoptic-scale forcing continuing...and the 
convection also likely to get an added boost from the Warm Lake Erie 
waters given lake surface-850 mb Delta-T values of 13c and a fairly 
well-aligned SW flow off the lake...feel that categorical probability of precipitation are 
in order for the western part of the state tomorrow evening. 
Therefore...have raised these values from existing continuity. Would 
not be at all surprised to see a brief period of heavier 
lake-enhanced convection downwind of Lake Erie during this time 
frame...but for now will just use generic shower/thunderstorm 
wording in the forecast. 


As Saturday night progresses...the frontal boundary and associated 
band of convection will slowly traverse the area from west to 
east...reaching The Finger lakes by midnight...and the Eastern Lake 
Ontario region during the overnight hours. Have maintained high probability of precipitation 
for rain showers/thunderstorms and rain as this feature pushes across the region...though 
have used slightly lower values /high likelies/ across our eastern 
zones as the activity will have lost the support of Lake Erie by the 
time it gets that far east. Behind the front...have tapered precipitation 
chances back to the chance range...leaving scattered showers/storms 
in the forecast as the upper low begins working into the area along 
with its associated cold pool aloft. 


Sunday looks to be rather similar to yesterday and today...a cool 
and unsettled day as the core of the upper low and coldest air aloft 
move right across our region. While 850 mb temperatures of +7 to +9c will 
only support afternoon highs in the 65-70 range...this will be 
plenty warm enough to generate sufficient instability for the 
development of widespread afternoon convection as 500 mb readings 
drop to as low as -20c...which is a good 3 to 4 degrees colder than 
what we have seen yesterday and today. Will therefore indicate 
likely probability of precipitation for this period...with hail once again likely to be a 
concern given the unseasonably cold temperatures aloft. 


The convection should gradually weaken and become more scattered 
from southwest to northeast during the course of Sunday night as we 
lose diurnal heating/instability...and as the center of the upper 
low pushes on into the Adirondacks. Have thus dropped probability of precipitation back to 
the high chance range after sunset...then have gradually lowered 
them further from SW to NE during the course of the night. 


&& 


Long term /Monday through Friday/... 
in general...the extended portion of the forecast will continue to 
feature large-scale upper ridging across the western part of North 
America...with a downstream trough remaining in place across the 
east. As a result...we should continue to see temperatures averaging 
a bit below normal during this period...along with periodic chances 
for convection. 


In terms of precipitation chances...expect that the threat of 
convection will briefly be on the wane Monday and Tuesday as this 
weekend's closed low lifts out across New England...and heights 
aloft rebound a little in response. This will then be followed by a 
renewed threat of more showers and storms Wednesday through the end 
of the week as yet another upper level closed low digs south across 
the Great Lakes and northeast. Have indicated this general idea in 
the forecast by tapering off from southwest to northeast Monday 
through Tuesday...then re-inserting them for the Wednesday to Friday 
period. 


&& 


Aviation /20z Friday through Wednesday/... 
areas from kroc west should see primarily VFR conditions for the 
next 24 hours as the main effects of an upper level low over 
Quebec head east. There may be some brief MVFR conditions with 
scattered showers for the afternoon and early evening hours. 


For areas east of kroc...expect continued shower activity today with 
some MVFR conditions for the afternoon and evening hours. This 
will trend toward VFR everywhere later tonight. 


All areas should experience excellent flying conditions during 
Saturday morning with the exception of some possible valley fog 
typical valley locations. 




Outlook... 
Saturday...VFR but widespread MVFR or IFR Sat night with showers. 
Sunday...VFR...possibly MVFR Sunday morning with showers. 
Monday through Tuesday...generally VFR. 


&& 


Marine... 
a brisk northwesterly flow of cool air will continue across the 
lower Great Lakes into this evening...before weakening during the 
course of the night as weak ridging builds into western New York 
state. This will help to maintain 3 to 5 foot waves on Lake Ontario 
through early evening...before seas gradually subside during the 
late evening and overnight hours. Small craft advisories will thus 
remain in effect for Lake Ontario tonight...ending across the 
western part of the lake at 00z...and 08z further east. 


On Saturday...our flow will turn more southwesterly and freshen a 
bit as an upper low digs across the Central Lakes...though 
conditions should remain a little below Small Craft Advisory 
criteria. A cold front associated with the low is then expected to 
cross the lower lakes Saturday night with an organized band of 
showers and thunderstorms preceding its passage...and a weaker more 
westerly flow following in its wake. 


As the cold pool associated with the upper low overspreads the area 
later Saturday night and Sunday...waterspouts will once again become 
a big concern for marine interests...and will likely remain so at 
least through Sunday night. As such...have added a mention to the 
forecast. 


&& 


Buf watches/warnings/advisories... 
New York...none. 
Marine...Small Craft Advisory until 4 am EDT Saturday for loz043-044. 
Small Craft Advisory until 8 PM EDT this evening for 
loz042. 
Small Craft Advisory from 8 PM this evening to 4 am EDT 
Saturday for loz045. 


&& 


$$ 


Synopsis...jjr 
near term...zaff 
short term...jjr 
long term...jjr 
aviation...zaff 
marine...jjr 

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