225 
fxus63 kbis 210949 
afdbis 


Area forecast discussion 
National Weather Service Bismarck ND 
349 am CST Friday Nov 21 2008 


Short term...today through Sunday night... 
forecast concern today into tonight revolves around snowfall 
accumulations over our southwest County Warning Area. A Winter Weather Advisory 
for snow will be issued for southwest North Dakota today through 
early Friday night. Please refer to biswswbis for further details. 


A progressive pattern continues through the short term as evident 
on the latest water vapor imagery and radar images. Our next 
shortwave trough aloft...negatively tilted...was located over western 
Montana with a an upper low seen forming over northwest Montana. 
This low and attending trough will move southeast today. A northwest/southeast 
orientated 100kt 300 mb jet over Idaho was punching through the aforementioned 
upper trough producing an area of upward motion/light snow from 
northwest Wyoming into central Montana. Major concern is advisory 
amounts today into early tonight over the southwest. HPC westward 
paints 2 to 4 inches which is supported by the NAM mostly...but 
not as much per GFS and sref. After collaborating with HPC and 
surrounding offices...decided to issue a Winter Weather Advisory 
for snow of 2 to 4 inches over our four southwest counties. The 
GFS and NAM agree with a very sharp boundary of where the maximum snowfall 
quickly decreases to just about nothing. This northwest/southeast line runs from 
around Watford City...to Bismarck...to Ashley. Areas west and 
south of this line will see the best snowfall...while along and 
east of this line will get little to none. Our northern and 
northeast zones will remain dry today. The upper trough outruns 
the surface front this afternoon hence the strongest vertical motion 
remains over the southwest before waning early this evening. A 
transitory ridge moves through Saturday keeping the region dry. 
Another surface cold front slides through Saturday night with the 
attending upper trough moving through on Sunday. A colder 
northwest flow develops Sunday with precipitation remaining rather 
sparse at this time. 


Long term...Monday through Thanksgiving... 
progressive pattern continues in the extended period bringing a 
chance for above normal temperatures leading into the Thanksgiving 
Holiday. 500 mb ridging will bring modified Pacific air into the 
northern plains Monday...Tuesday and Wednesday. Highs should rise 
into the lower 40s across with dry weather. On Thanksgiving models 
bring a disorganized/fractured upper trough into the northern 
plains. I left Thursday dry with a bit cooler temperatures in the 30s. 




&& 


Aviation...a warm front across central Montana at 10z will move to 
central North Dakota by 06z. Snow will develop across southwest 
North Dakota with dik deteriorating to IFR ceilings and visibilities in snow 
from 18z and 06z. MVFR ceilings expected between 20z and 06z at 
isn...Mot...bis and jms. Edge of snow region expected south and west 
of a line from isn to bis to jms. 




&& 


Bis watches/warnings/advisories... 
Winter Weather Advisory from 8 am this morning to 11 PM MST this 
evening for ndz040-041-043-044. 


&& 


$$ 


Kansas/warm air advection