309 
fxus61 kcle 210819 
afdcle 


Area forecast discussion 
National Weather Service Cleveland Ohio 
319 am EST Friday Nov 21 2008 


Synopsis... 
high pressure over the Central Plains will move up the Ohio Valley 
Saturday and off the Carolina coast Monday. Another clipper low 
will drop southeast through the Great Lakes Monday dragging a 
trailing cold front across our area. 


&& 


Near term /until 6 PM Friday evening/... 
latest models runs show little change. Coldest part of the airmass 
will be over the area today with Lake Erie to 850 mb and 700 mb temperature 
differential impressive. Middle level moisture should be sufficient for 
seeding process to keep Good Lake effect shsn occurring so no plans 
to changes current warnings and advisories. As flow starts to back 
some during the day if no decent bands have developed through 
Cuyahoga into Summit and Portage day shift may have to take a good 
look at whether warnings will still be needed. With temperatures now below 
freezing throughout the area and winds possibly gusting to 30 miles per hour 
will probably see some blowing and drifting so will add in mention 
of this for snowbelt. 


&& 


Short term /6 PM Friday evening through Sunday night/... 
shifting of bands of lake effect remain on track to shift east into 
mainly the eastern half of snowbelt by late tonight where they will 
probably hang up into early Sat afternoon before tapering off during 
the rest of the afternoon and evening...thus lake effect warning 
ending time of 4 PM Sat still seems reasonable. Somewhat concerned 
for Erie County where backing flow could allow for long fetch across 
Lake Erie and keep a significant snow band over part of the County. 
However...drier air and subsidence with axis of high pressure moving 
in may be enough of a negative factor to offset the longer fetch. 


High pressure and flow shifting to south-southwest expected to provide dry 
weather Sunday before next round of precipitation to arrive later Sun night 
as another clipper and cold front approach. Airmass prognosticated to warm 
enough so that precipitation type should be rain. Will adjust grids more 
to show threat for rain over mainly northwest half of County Warning Area which won't 
conflict with lows in far eastern part of area that drop below 
freezing. Can't imagine this situation producing freezing type 
precipitation as moderate south-southwest low level flow generally not conducive around 
here for any frozen precipitation. Think that if cloud cover thickens 
enough for precipitation to occur temperatures will remain or rise above freezing 
point anyway. 


&& 


Long term /Monday through Thursday/... 
models are in decent agreement with the next storm system that will 
move across the Great Lakes into the New England states next week. 
European model (ecmwf) is slightly slower with the eastward progression of the upper 
level features which could keep rain over Northern Ohio and 
northwestern PA into Monday evening. Uncertainty at this time will 
be how much warming can occur over the snowpack across northeast 
Ohio and northwest PA for Monday as a strong southwesterly flow develops. 
For now will leave a rain/snow mix for much of the region with snow 
over the higher terrain east of cle. Believe at some point Monday 
evening we should see all snow as the colder air spills across Lake 
Erie with some lake effect snows once again developing and 
persisting into Wednesday night. Warnings/advisories will likely be 
needed for this middle week event. 


There then becomes much uncertainty for late Wednesday into Thursday 
as the models struggle with the movement of energy in the trough 
that will remain over the Great Lakes. 


Temperatures will be warmest on Monday with highs approaching 40 
degrees...assuming cloud cover is not to thick from the approaching 
storm system. 


&& 


Aviation /06z Friday through Tuesday/... 
northwest flow with plenty of moisture and increasing instability. 
The models are consistent in bringing in drier air into Northwest 
Ohio overnight...so improved conditions. Elsewhere tried to time 
the snow showers. Otherwise MVFR to IFR conditions. An upper trough 
will be moving across the area around daybreak and into Friday 
morning. This will cause plenty of IFR conditions for northeast 
Ohio and northwest PA. After the trough moves through improving 
conditions and more snow showers for the afternoon. Use the nam12 
1000-700 mb relative humidity as a guide. It seems to have a good 
handle on things. The lake and 500 mb temperature difference on 
Friday will be well over 40c...thunder will occur especially near 
the Lakeshore from cle east. 


For cle not much snow showers expected until after 5am as upper 
trough moves in. Snow fall around daybreak will be 1 to 2 inches. 


Outlook... 
Lake effect continues into early Saturday. Most of the lake 
effect would affect traditional snowbelt which would include Erie 
with snow showers reaching cak/yng. VFR conditions may return by 
Saturday night. The VFR conditions should continue through Sunday 
as high pressure moves east across the forecast area. Another cold 
front is anticipated for Monday as deepening low pressure moves 
east across the region. Conditions may begin to improve over 
western Ohio Tuesday with lake effect snow showers continuing over 
the eastern portion of the forecast area. 


&& 


Marine... 
northwesterly winds will remain in the 15 to 25 knot range today 
into early Saturday. As high pressure builds in on Saturday the 
gradient will begin to relax with winds decreasing. Current Small 
Craft Advisory time frame still looks reasonable. Next storms system 
will cause an increasing southwesterly flow for Sunday and Monday. 
May need to keep an eye on water levels in the western basin on 
Monday when the strongest southwesterly flow is anticipated. A cold 
front then dives through the Great Lakes on Monday with strong 
northwesterly winds expected. A Small Craft Advisory will likely be 
needed by Monday night. 


Otherwise lake effect snows will persist through Saturday for the 
eastern half of the lake. Cant rule out a bit of thunder east of cle 
through this evening. May see a return of some rain for Monday into 
Monday night before switching back over to Snow. Lake effect snows 
will then persist on Tuesday into Wednesday. 


&& 


Cle watches/warnings/advisories... 
Ohio...Lake effect snow warning until 4 am EST Saturday for 
ohz011>013-021>023. 
Lake effect snow warning until 4 PM EST Saturday for ohz014- 
089. 
Lake effect Snow Advisory until 4 am EST Saturday for ohz033. 
PA...lake effect snow warning until 4 PM EST Saturday for 
paz001>003. 
Marine...Small Craft Advisory until 3 PM EST Saturday for lez142>149. 


&& 


$$ 
Synopsis...Adams 
near term...Adams 
short term...Adams 
long term...Mullen 
aviation...kieltyka 
marine...Mullen 

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