220 
fxus63 kdlh 042118 
afddlh 


Area forecast discussion 
National Weather Service Duluth Minnesota 
318 PM CST Thursday Dec 4 2008 


Discussion...main forecast challenges are ending les event and 
clipper system for Friday night. Afternoon water vapor loop shows 
deep cold core trough continuing to sink southeast over the upper 
Midwest/western Great Lakes. Surface winds have backed 
westerly...and will continue to do so this evening as the upper 
trough pushes eastward. As a result...lake effect snow bands 
should continue to migrate eastward...out of the forecast area...despite 
continued cold airmass in place over Western Lake Superior /h85 
temperatures around -20c attm/. Let warning expire as scheduled 
accordingly. Otherwise...convective cloud streets along with scattered 
flurries/shsn will diminish this evening and overnight...setting 
up a cold night for the Northland. Winds of 5 to 10 miles per hour along with 
surface lows reaching the single digits above and below zero will 
result in wind chills in the 10 to 20 below zero range for late 
tonight and Friday morning. Should see a fairly good recovery of 
temperatures Friday ahead of next approaching Alberta clipper system. 


Forecast attention then turns positively tilted trough diving 
southeast Friday evening through the overnight across the dlh forecast area. 
This system looks to bring generally 1 to 3 inches to the 
Northland...with the highest amounts into northwest Wisconsin where 
strongest 2-d fgen occurs late Friday night per NAM. Gusty winds 
along with this event being the first widespread accumulating snow 
will make for some travel problems into Saturday morning. A les 
event looks likely once again for the South Shore with a gusty 
northwest winds...and 850 mb temperatures dropping to near -20c Saturday 
through Saturday night. 


Extended...Sunday through Thursday 
extended period will begin with brief ridging on Sunday...with lake 
effect snows diminishing over northwest Wisconsin...and dry weather 
elsewhere. Warm air advection and isentropic lift will bring increasing clouds and 
snow chances by Sunday night into Monday...generally from west to 
east. While deep moisture will be limited...some light to moderate 
snow accumulations certainly appear possible. Weak high pressure 
will then return late Monday into early Tuesday...except for some 
lingering light snow over our eastern zones. Another clipper system 
will bring a round of light snow to much of the region on 
Wednesday...before a more potent system approaches from the 
southwest late Wednesday into Thursday. Models are in a bit of 
disagreement...but generally prefer the GFS and GFS 
ensembles...which do not support significant phasing of the northern 
and southern branches of the jet over the plains. This would 
effectively keep the low weaker and a tad further south. 
Otherwise...cold and below normal temperatures will prevail through 
the period with a deep 500 mb trough centered near Hudson Bay. The 
coldest temperatures are likely Wednesday into Thursday...with 850 mb 
temperatures of -20c to -24c. However....the GFS suggests temperatures will 
begin to warm slightly by late Thursday and beyond as the the trough 
slowly pushes off to the north and east. We believe this may be a 
bit fast...especially when considering other model guidance...and 
only warmed temperatures slightly. 


&& 


Aviation...low VFR and MVFR ceilings will prevail through 18z 
Friday. Scattered snow showers will also persist through 00z this 
evening...and may also bring visibilities as low as 2sm. The ruc13 and 
nam12 suggest a temporary rise in ceiling heights and mainly 
scattered clouds for southern areas including kbrd during the 
evening hours...from 00z to 06z...before MVFR again becomes more 
prevalent after 06z. Warm air advection will spread middle level clouds 
into the region on Friday morning...ahead of an approaching 
shortwave...but ceilings will remain mostly low VFR through 
18z...before deteriorating to MVFR from northwest to southeast in 
low clouds and light snow Friday afternoon. 




&& 


Point temps/pops... 
dlh 0 18 11 16 / 20 20 80 30 
inl -4 15 1 8 / 20 40 80 20 
brd 0 21 14 17 / 10 20 80 20 
hyr -2 19 13 20 / 20 10 80 40 
asx 5 18 11 19 / 50 20 80 50 


&& 


Dlh watches/warnings/advisories... 


Minnesota...none. 
WI...none. 
Ls...Small Craft Advisory until 4 PM CST Friday for lsz121-lsz146- 
lsz147-lsz148. 




$$ 


Liles/bettwy