597 
fxus63 kfgf 042032 
afdfgf 


Area forecast discussion 
National Weather Service Grand Forks ND 
230 PM CST Thursday Dec 4 2008 


Discussion... 
forecast challenge concerns temperatures and snow chances. 


Models close through period and will continue with most consistent 
GFS for details. 


Main challenge tonight will be cloud trends and resulting 
temperatures. Cloud shield dropping southward in wake of shear axis 
passage around 25kts. Some breaks noted and areas becoming more 
cellular but unless clouds dissipate at sunset they will hold till 
atleast midnight. In addition as surface high shifts southward 
surface flow becomes west-SW along with modest mixing and respectable 
warm advection. All of these factors should limit temperature drop 
overnight. With some potential for clearing will keep temperatures 
below numerical guidance which is calling for steady temperatures 
overnight. 


Warm advection/mixing continues Friday in advance of next 
shortwave/clipper system. Depending on what clouds do overnight 
could be some early solar to help lift temperatures. Moisture/clouds 
increase from northwest-southeast during afternoon. GFS 285k surface showing 
lowering condensation pressure deficits across north half of forecast area with 
pretty decent isentropic lift. With this will increase probability of precipitation to 
likely along with minor accumulations. 


Lift shifts into northwest/west central Minnesota during evening and will increase 
probability of precipitation this area. Lift shuts down by 06z along with drying column. 
With progressive nature of clipper do not expect significant 
accumulations. As low shifts towards the Great Lakes cold advection 
returns and looks to be sufficient surface gradient on back side of 
low to make for blustery conditions and depending on snow amounts 
may see some blowing and drifting possibly requiring an advisory. 


High builds in on Saturday for diminishing wind and cloud cover. 
With good possibility of snow cover and cold pool shifting over forecast area 
temperatures may struggle to recover and will trend temperatures 
towards colder mav guidance. 


With surface high overhead...light mixing and likely sky clear and some 
fresh snow could see the first widespread sub-zero night and will 
lower temperatures accordingly. 


High shifts east Sunday along with increasing mixing/warm advection. 
GFS showing fair amount of isentropic lift and lowering condensation 
pressure deficits in warm advection zone. Trends also look quicker 
so will spread probability of precipitation farther east as well as increasing to chance 
category. 


Long term [mon-thu]... 
lot of uncertainty remains in the long term forecast...which becomes 
most evident by Wed/Thu. At 12z Wednesday...the latest GFS run shows surface 
high pressure over the northern plains and the 00z European model (ecmwf) run has a 
compact surface low right over central ND. The Canadian model does not 
shed much light on the matter...with a solution quite different too. 
Will therefore stick pretty close to the HPC numbers today...which 
place a bit higher confidence in the GFS ensemble...especially by 
Wed/Thu. If anything...the trend today is colder temperatures...with values 
dropping some 10 to 15f from inherited temperatures. 


&& 
Aviation... 
pretty solid deck of clouds has yet to rotate south through the 
area...accompanied by some light snow or flurries. Metar sites are 
reporting wide variations in ceilings in this area...but it looks 
predominantly about where it is at now or a bit lower. As surface winds 
switch west later tonight...models are trying to indicate rising 
ceilings. This would only be temporary though...as next upstream 
clipper brings more lower clouds toward 18z Friday. 




&& 


Fgf watches/warnings/advisories... 
ND...none. 
Minnesota...none. 
&& 


$$ 
Voelker/vgodon