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fxus63 kbis 082201 
afdbis 


Area forecast discussion 
National Weather Service Bismarck ND 
401 PM CST Thursday Jan 8 2009 


Synopsis... 


The ongoing winter storm Marks the onset of a positive Pacific North 
American pattern...since models/ensembles agree on a deep eastern 
North American trough. With such a well established snow pack...it 
will be difficult to warm up the region...so expect most of North 
Dakota to remain in an active weather pattern with a steady influx 
of Arctic air by the beginning of next week. 


&& 


Short term...Thursday through Sunday night... 


Ongoing winter storm presents the most challenge for today. The 
first band of precipitation to form across North Dakota has resulted 
in assorted precipitation type reports from snow in Williston and 
Grassy Butte to freezing rain...ice pellets...and snow in 
Dickinson. Imagine that as vertical velocities 
increase...collocated with heavier radar returns...periods of 
localized dynamic cooling will cause any areas of freezing rain to 
change over to snow. That is likely to change as warm air 
advection aloft increases in advance of the 700 mb low center. In 
fact...the sheriffs offices in Grant and Hettinger counties have 
already issued no travel advisories. 


Right now...expect that the 700 mb low will pass through Williston on 
a path toward McIntosh/Mobridge. The heaviest amounts of snow are 
expected to the northeast of the 700 mb low. The 280k isentropic 
surface viewed using the 12 UTC GFS output indicates a very well- 
defined trowal structure that passes right over Bismarck. Using 
latest NCEP/HPC quantitative precipitation forecast amounts and a 12 to 1 snow to liquid ratio for 
the first part of the storm and a 16 to 1 ratio after 6 PM north 
and east of the Missouri River...have increased snowfall 
accumulations to 5 to 8 inches for the event. 


As far as ice accumulations are concerned...the southwestern part of 
the state has already seen ice accumulations near the Painted 
Canyon...and areas throughout the southwest should expect a 
continued wintry mix through the day. That said...it is likely that 
temperatures will rise above freezing in the far southwest...but 
soil temperatures are still below freezing. So...there is enough 
of a chance that ground surfaces will remain ice covered to leave 
rain out of the forecast grids and keep everything frozen in the 
grids. 


Additionally...based on mesoscale discussion from NCEP/Storm Prediction Center and 12 
UTC NAM soundings...have shifted freezing rain area just a bit 
east and have upgraded four counties to a Winter Storm Warning to 
account for the possibility of exceeding 0.25 inches of ice 
accumulation there. 


Thereafter...gusty winds are forecast to spread from west to east 
across the state beginning around noon on Friday. This will cause 
tremendous blowing snow and drifting problems. Based on visibilities 
observed two days ago with the passage of a cold front and gusts to 
26 knots at Bismarck...anticipate widespread reduced visibilities 
below one quarter mile with corridors of near zero visibilities 
possible in open country. 12 UTC NAM/GFS both indicate 6 hour 
pressure rises of 20 mb over the western part of the state. If 
this verifies...winds could reach high wind criteria as well. As 
always...will monitor situation closely. 


A series of weak middle level impulses then moves through the 
Dakotas in advance of the next storm system as outlined below. 


Long term...Monday through Thursday... 


Latest European model (ecmwf) and GFS consistent with another Arctic surge in the 
extended with the GFS most aggressive in terms of areal coverage. 
The GFS encompasses our western zones with the frigid air while the 
European model (ecmwf) mainly keeps it in our central/eastern zones. 850 mb temperatures around 
-23c and with a surface high pressure between a 1045mb per European model (ecmwf) and 
1059mb GFS. With our deep snow cover...went much lower than guidance 
and feel confident that lows will range between -20f and -30f over 
our central and eastern zones for Wednesday/Thursday mornings. The Arctic air 
will be preceded by a strong clipper Monday night into Tuesday with 
more snow. Based on the GFS and European model (ecmwf) quantitative precipitation forecast totals...the track of the 
heaviest snow looks to align from northwest to southeast...from 
Williston to Bismarck/to Linton and Ellendale. Could see advisory 
snow amounts...around 3 inches in this area with lesser amounts 
surrounding this area...but will need to watch since this is still 
far out in the forecast period. Arctic air remains over the area 
through Thursday then shifts east. 


&& 


Aviation... 


LIFR to vlifr ceilings will dominate tonight. Freezing 
rain will be just one of The Hazards this evening and tonight over 
kdik...with kisn and kbis seeing mainly snow. Kmot and kjms look to 
remain cold enough for all snow. Appears freezing rain will impact 
Dickinson through 08z before changing over to snow. Williston may 
see a brief mix of freezing rain/snow/ice pellets this evening 
before changing to snow by around 02z. Snow will be the 
precipitation type over kmot/kbis/kjms through 18z Friday. Strong 
northwest winds of 20kt to 35 knots will commence around 12z Friday 
causing blowing and drifting of snow. This will provide for MVFR 
visibilities from 12z Friday through 18z Friday. 


&& 


Bis watches/warnings/advisories... 
Winter Storm Warning until 6 PM CST /5 PM MST/ Friday for ndz001- 
009-017>020-032>035-041-042-047. 


Winter Weather Advisory until 6 PM CST /5 PM MST/ Friday for 
ndz031-040-043>046-050. 


Winter Storm Warning until 6 PM CST Friday for ndz002>005- 
010>013-021>023-025-036-037-048-051. 


&& 


$$ 


Scheck/Kansas