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Area forecast discussion 
National Weather Service Bismarck ND 
901 PM CST Thursday Nov 20 2008 


Update... 
currently...surface high is situated over eastern North Dakota. 
With clear skies over all but the far southwest...temperatures 
have dropped off quickly. Day shift indicated this may be a 
problem and had already lowered minimum temperatures over the 
eastern County Warning Area. It appears we will have to drop them a bit 
more...with current temperatures only a few degrees from overnight 
forecast lows. Went around 5 below from eastern Bottineau and 
northern Pierce...north and east through Rolette County. We will 
need to cut temperatures farther west (central nd) also...as there 
is little cloud cover this evening. Southerly return flow is 
picking up in the far west...so do not expect temperatures to fall 
off too much there. 


Looking at the latest RUC...and 18z GFS/NAM/ECMWF...it looks like 
models are having a hard time bringing precipitation into the far 
west before 12z. Latest satellite and radar loops are indicating 
mostly clear skies over much of eastern Montana with little in the 
way of cloud cover until you get west of Havre and Billings. 18z 
NAM bufr soundings are showing very dry lower atmosphere over the 
west through 12z. Therefore...think we can get rid of the slight 
chance probability of precipitation in the far west overnight. 


&& 


Previous discussion... /issued 255 PM CST Thursday Nov 20 2008/ 


Short term...tonight through Sunday night 
short term models in decent agreement and not a lot of changes to 
ongoing grid package. Bumped some probability of precipitation down on Sunday as moisture 
and lift are somewhat limited and downgraded to flurries in my east. 
Stayed slight chance probability of precipitation in coordination with western neighbors. 


Energy from Bay of Alaska low now over western Washington and Oregon 
forecast to reach the Western Plains by Friday morning. All models 
in agreement with band of heaviest snow over southwest and south 
central North Dakota but HPC quantitative precipitation forecast and winter weather desks have 
backed off a bit with accumulations with only 1 plus over that 
region. Have pulled back a bit in agreement but snowfall totals will 
still round to 2 inches in places and that seems possible. 


Weak pressure falls ahead of next system will swing winds to the 
southeast...however main energy and lift remain north of 
border especially on NAM model solution. Dropped slight chance 
portions northeast to flurries but to remain in coordination with 
western neighbors left slight chance there...this may be revisited 
with next model run. 


Long term...Monday through Thursday night 
GFS and European again looking similar in the beginning of the 
extended period. Monday will see the building of an upper level 
ridge over North Dakota as a low exits the region to the Great Lakes 
and eastern North America. A more zonal west-to-east flow over North 
Dakota on Tuesday as a shortwave moves across central Canada. 


The models begin to diverge on Wednesday/Thursday. This morning's 
European model develops a weak shortwave in the flow of the 
westerlies that moves east quickly across southern/central Canada. 
The GFS however digs a stronger shortwave and develops it farther 
south - across southern Saskatchewan and the Dakotas/Minnesota. The 
hydromet prediction center favors a blend of the GFS and 
European...and mentioned a more northerly track of this system is 
preferred. Will keep the forecast dry for now...with such 
uncertainty in placement of a storm system for days 6/7. If future 
model runs are consistent with the feature and develop it farther 
south...then later forecasts will likely show a chance of snow for 
Wednesday night/Thursday. 


Otherwise...highs in the 30s and 40s. Lows in the teens and 20s. 


Aviation... 
cool surface high from south central Canada will continue to move 
south/southeast into the Dakotas and Minnesota. MVFR broken clouds 
over central/eastern North Dakota associated with an exiting upper 
level shortwave are expected to decrease gradually from west to 
east. Some snow showers with 3-5 miles visibilities will be scattered 
across central North Dakota through late afternoon and across 
eastern North Dakota through early evening. Then clearing skies all 
areas until after 09-12z when the next low pressure system develops 
over Wyoming tonight and brings MVFR and IFR ceilings and visibilities with 
snow to southwestern North Dakota Friday morning spreading to 
central ND Friday afternoon. 


&& 


Bis watches/warnings/advisories... 
none. 
&& 


$$ 
Twh