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fxus63 kbis 070119 
afdbis 


Area forecast discussion 
National Weather Service Bismarck ND 
819 PM CDT Monday Oct 6 2008 


Update... 


Earlier forecast looks on track...so only made minor changes to 
sky grids. The western edge of the warm conveyor belt is the 
demarcation line separating mostly clear skies from overcast. 
There are a few patches of scattered middle level clouds in the 
mostly clear side of the state...so did not clear things out 
entirely. 


For this weekend...the 18 UTC GFS has trended toward the 12 UTC 
European model (ecmwf) solution...which has been rather consistent over its past 
several runs. Both models now deliver snow to western and/or 
central North Dakota this weekend...though there is still 
considerable uncertainty with such a forecast this far out. Will 
continue to keep an eye on this storm as models/ensembles converge 
on a solution. 


&& 


Previous discussion... /issued 228 PM CDT Monday Oct 6 2008/ 


Short term...tonight through Thursday night... 
there are multiple forecast concerns during the short term period. 
Precipitation chances tonight and Tuesday night/Wednesday...fog and 
frost tonight across the west...and forecast low temperatures late 
in the short term forecast period. 


The occluded front that moved through western and central North 
Dakota yesterday is now in eastern North Dakota near the Minnesota 
border. The upper level low can be seen spinning through eastern 
Montana using water vapor. Northeastern Montana radars show a line 
of showers rotating around the upper level low and moving toward the 
east southeast. Will leave a chance of isolated showers in the 
forecast out west as upper level low progresses eastward this 
evening. 


12z soundings for Glasgow and Bismarck show the atmosphere beginning 
to dry in the lowest levels. As a fast moving surface high builds 
into North Dakota in the wake of the low...expect further drying 
through the atmosphere tonight. Despite the moisture 
that fell yesterday will leave fog out of the forecast for now as 
model soundings show further significant drying of the atmosphere. 
Clear skies tonight will allow temperatures to drop into the lower 
30s across the west. Isolated frost may occur in some outlying areas. 


A fast moving shortwave ridge will move across the northern plains 
tomorrow with the next weather maker quickly on its heals. 
Temperatures will rebound quickly tomorrow and some moisture will 
return under southerly flow. 


A fast moving shortwave will effect the mainly northern tier 
counties late Tuesday into early Wednesday. The short wave will 
quickly push a cold front across the state overnight. Models show 
that most of the weak vorticity with this system will be along to 
north of the Canadian border. However the northern tier will be 
under the left exit region during this period adding some additional 
lift. Expect mainly scattered showers during the over night hours. 
Breezy conditions develop on Wednesday as another surface high 
builds in and daytime heating allows for some mixing of strong winds 
to the surface during the daytime hours. Temperatures will begin 
dropping on Wednesday into Thursday with a very cold night on 
Wednesday night. 


Long term...Friday through Monday... 
considerable uncertainty continues during the long term period. The 
models have been struggling with how to handle the upper level 
energy across the Gulf of alaskan region early in the period. With 
that said...the latest guidance from the 12z GFS and Canadian are 
hinting at a solution similar to what the European has been 
advertising for the last couple of runs. In addition...an increasing 
number of the GFS ensemble members also support a southwest upper 
low...rather then a more progressive open wave solution. 


The end result is looking as though there will be an increasing 
chance of precipitation towards the end of the work week as we get 
into a warm air advection/isentropic lift region ahead of the 
developing storm. Additionally...as is the case with closed upper 
lows...dynamic cooling can be rather robust and become an efficient 
column cooler. Depending on the exact track of the upper low this 
could result in an atmosphere cold enough to support snowfall 
across western North Dakota. 


Aviation... 
the main batch of energy and precipitation associated with a surface 
front will reside across the eastern portion of the North Dakota 
late this afternoon and into tonight. However...with that being 
said...the upper level short wave will swing across the state this 
afternoon and evening. This will bring some lower clouds at or above 
4k feet...along with a few isolated showers this afternoon. Have 
added vcsh to cover this. Winds will generally remain out of the 
west and skies will slowly clear from west to east as a surface 
ridge of high pressure builds in across the western Dakotas 
tonight. 


Fire weather... 
marginal fire weather conditions out across the southwest this 
afternoon. Saving Grace is that temperatures are only reaching the 
lower 60s helping to keep min relative humidity values at Bay and above critical 
levels. Tuesday looks to be quieter as far as fire weather hazards 
go as lighter winds are expected. 


Wednesday is a completely different story. Strong northwest winds 
behind a surface cold front will coincide with afternoon percent relative humidity 
values falling into the lower 20s and upper teens. This will of 
course elevate the fire danger over western ND...and may necessitate 
fire weather headlines. Users are urged to stay tuned for future 
updates. 


&& 


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


$$ 


District of Columbia/NH/kb/scheck