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fxus63 kgrb 172006 
afdgrb 


Area forecast discussion 
National Weather Service Green Bay WI 
306 PM CDT Wednesday Mar 17 2010 


Short term...tonight and Thursday. 


Latest RUC analysis and visible/IR/WV imagery show high pressure 
stretching across the Great Plains into the western Great Lakes this 
afternoon...and low pressure moving over southern Saskatchewan and 
Manitoba. With full sunshine...temperatures have warmed into the 
upper 50s to middle 60s. Dewpoints havent quite worked out as 
planned...as many of the Sandy soil areas have stayed in the lower 
30s. Still seeing pockets of below 25 percent relative humidity/S from Sturgeon Bay to 
Merrill though. With high clouds poised to move into the area 
tonight ahead of the low...clouds/temps/dewpoints are the main 
forecast concerns over the next 24 hours. 


Tonight...high pressure will slide to the south across the Great 
Plains while low pressure will move into SW Ontario ahead of a 
shortwave traversing over the central Canadian prairie. As the 
middle-level ridge passes overhead...will start to see some of the 
cirrus over southern Canada spill into northern Wisconsin. The 
combination of this cirrus and a tightening pressure gradient will 
lead to warmer lows than the past couple nights. Will go with a 
blend of the mosg and the previous forecast. 


Thursday...the surface low will continue to move across southern 
Ontario and Northern Lake Superior. It will drag a surface trough 
across the forecast area late morning through middle-afternoon that 
will shift our wind direction from southwest to the west-northwest. 
The wind shift will do little to cool off the seasonably warm 
temperatures...as the cooler air will still reside over the northern 
plains. Gustier winds will produce good mixing...that should help 
bring down the drier air from aloft better than today. 925mb temperatures 
suggest temperatures ranging from around 60f north to upper 60s in the 
downsloping areas. Will have a little more moisture and cloud cover 
in the air than today...so will knock off a degree. 


Long term...Thursday night through next Wednesday. A return to below normal temperatures 
still in the forecast starting this weekend as the two branches of the 
jet phase over the eastern Continental U.S. And the mean flow aloft turns northwest over 
WI. Since this phasing is taking place to our east...NE WI will be 
on the northern edge of a system this weekend with minor snow 
accumulations possible. Mean flow to flatten early next week before a 
new shortwave trough digs into The Rockies which should spin up another 
system by mid-week. 


Weak frontal boundary to slide through the northern half of WI Thursday night bringing 
with it an increase in clouds...but little in the way of precipitation as 
deep moisture and lift are lacking. Cooler air behind the fnt will allow 
temperatures in the north to drop to around the freezing mark...while 
areas still ahead of the fnt (e-cntrl) may stay above 40 degrees. An 
increasing frontogenetical forced area of precipitation is prognosticated to develop 
from the Central Plains northeastward through the Midwest into SW sections of 
WI. Qstn remains as to how far into WI this precipitation can get Friday 
afternoon. GFS and Canadian are more aggressive than the NAM/UKMET/ 
European model (ecmwf) and our previous forecast was basically a split of the model guidance. Have 
kept the gist of the previous forecast by bringing chance probability of precipitation to central WI and 
slight chc's to parts of north-central and east-central WI. Temperatures will be tempered 
by the clouds and may need to tweak values down a couple of degrees. 


A surface wave is then expected to rise NE along the now stalled frontal 
boundary into central sections of Illinois Friday night. Expect to see a large area 
of precipitation move along the strengthening baroclinic zone from OK to southern 
WI and will need to carry relatively hi probability of precipitation for southern/eastern sections of 
the forecast area. As temperatures drop overnight...snow will begin to mix with the 
rain and completely turn over to all snow on the northern edge of the precipitation 
shield. Warm ground initially should allow the snow to melt at 
first...but do expect to see some minor accumulations (an inch or 
two psbl) by daybreak. Subtle differences have developed among the 
models (esp the European model (ecmwf) and ukmet) now showing greater separation in 
the branches of the upper jet which would allow the stalled frontal 
boundary to sag farther southeast on Sat. This minor shift would be enough 
such that north-central WI may not see any snow now...while the heavier 
quantitative precipitation forecast axis would reside over southern WI. Light snow is still expected over 
most of the forecast area...but addl accumulations would be held in 
check (less than an inch) and mainly focused over east-central WI. Temperatures 
will be held down by a good amount of clouds with most locations only 
getting into the upper 30s. 


NE WI to reside between the southeast moving northern branch (ovr western ontario) 
and the eastward moving southern branch (ovr the ozarks) Sunday night. East-central 
WI remains close enough to the stalled boundary such that one cannot 
completely rule out a chance of light snow. As the northern branch digs southeast 
into the Great Lakes on Sunday...it will drive a cold front through WI and 
turn the winds north-northwest sending 800 mb temperatures down to around -14c over Western Lake 
Superior by 00z Monday. Not expecting much precipitation from the cold front itself 
since all the Gulf moisture is tied up by the southern stream system. Have 
kept a small chance pop for east-central WI and across Vilas County as lake 
effect snow potential increases. 


Phasing of the two streams Sunday night into Monday will translate to 
another big storm for the East Coast with coastal rain and inland 
snow. For NE WI...we will be under a dry northwest flow aloft with hi pressure 
building into the region. Vilas County may still have a Few Lake effect 
snow showers Sunday night...but influx of drier air should limit the 
potential. Even with the return of some sunshine on Monday...temperatures 
are forecast to struggle to approach 40 degrees. 


The hi pressure drifts across WI Monday night and is already well to our 
east by Tuesday. Return flow to develop over the western Great Lakes as winds 
turn southerly just above the surface on Tuesday and a warm front starts to lift 
north over the plains. Even though isen lift will be on the increase... 
do not knwo if enough moisture will be in place for precipitation. Prefer to 
downplay probability of precipitation for Tuesday and only mention a slight chance pop for the northwest 
half of the forecast area in the afternoon. Progressive flow across 
the Continental U.S. Will bring a shortwave trough quickly into the Central Plains by 
next Wednesday. As Gulf moisture begins to get tapped...anticipate an 
increasing chance of precipitation along with warmer temperatures. 
&& 


Aviation...VFR conditions expected through period with only high 
clouds expected from time to time. 
&& 


Grb watches/warnings/advisories... 
none. 
&& 


$$ 
Mpc/kallas 

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