703 
fxus65 kbyz 072055 
afdbyz 


Area forecast discussion 
National Weather Service Billings Montana 
255 PM MDT Tuesday Oct 7 2008 


Short term...valid for Wednesday and Thursday... 


A 150 knots jet was prognosticated by both models to move across the area 
tonight through Wednesday. Cold front pushing through western Montana this 
afternoon will slide southeast across the area tonight. Frontogenesis band 
will accompany the cold front...however downslope flow will cut down 
precipitation chances somewhat over western and central areas. In 
addition...associated shortwave will pass by to the north of the 
forecast area. Thus low probability of precipitation were in good shape. Only change was to 
go with chance probability of precipitation NE near best moisture and lift this evening. 
Will continue to leave out mention of thunder as instability was 
limited...and only an isolated lightning strike was observed over Montana 
this afternoon. Low temperatures were in good shape. Wednesday looked 
mostly dry under a fast west-northwest flow aloft. Left low probability of precipitation in NE big 
horns in the morning...otherwise dried out probability of precipitation. It will be windy on 
Wednesday with 25 to 30 knots winds mixing down to the surface. Mixing down 
from 700 mb supported temperatures a few degrees lower than 
forecast...but with abundant sunshine and downslope flow...should be 
able to reach forecast values. Minimum relative humidities will be 
in the 20s so will just highlight the gusty northwest winds in the fire 
weather forecast. 


Upper jet will exit the area Wednesday night and some jet divergence will 
move across the region as an upper wave begins to dig into the 
Pacific northwest. Moisture ahead of the wave was quite limited so have cut 
back on probability of precipitation and limited them to just the mountains. Have also 
lowered sky cover and as a result nudged temperatures down toward 
the bias corrected met guidance. 


GFS was showing good run-to-run continuity in handling the evolution 
and track of developing upper low Thursday and Thursday night...and was in 
line with the European model (ecmwf). The upper low will continue to dig S while 
strengthening Thursday and Thursday night. The center of the low was forecast 
to be over S Idaho by 12z Friday. Moisture will slowly move north into the 
area on Thursday so have lowered morning probability of precipitation. Kept probability of precipitation similar to 
previous forecast Thursday afternoon. Warmed the east a bit on Thursday based 
on mixing profiles and later moisture arrival NE. Raised probability of precipitation to 
likely across much of the west and south Thursday night. Upper 
difluence...shortwave energy moving around upper low...jet 
divergence...deep east flow to between 600 and 700 mb and some 
frontogenesis will bring the likelihood of precipitation to these 
areas. 850 mb temperatures will fall below zero Thursday night...so 
expect precipitation type to be all snow late at night. Lowered min 
temperatures a little Thursday night due to cold 850 airmass. Arthur 


Long term...valid for Friday...Sat...sun...Mon...Tue... 


Major early winter storm taking shape across the region into this 
weekend with significant changes and a potential for accumulating 
snows even into the lower elevations. Quite a bit of changes made to 
going forecast as medium range guidance has become consistent with 
its solution of a strong and unseasonably cold system. 


Strong upper low expected to dig south through Idaho into northern 
Utah Friday into Friday night before making a turn to the 
northeast. Lee side low forms around southeast Wyoming allowing 
low level cold air and deep upslope flow to push south into the 
region. In the upper levels...good diffluent flow continues with 
exit region of jet lifting into southeast Montana. If current 
solutions verify...a cold and wet period is in store for the area 
through at least Saturday night. Have raised precipitation chances 
considerably for Friday through Saturday night when best upper 
support shifts over the area. It does appear to be cold enough for 
mostly all snow. With widespread precipiation looking more 
certain...temperatures have been lowered several degrees as well. 
Amounts remain uncertain this far out with this system given 
temperatures close to or even above freezing. A minor change in 
positioning of system could keep temperatures warmer with more 
rain in the lowest elevations. Given warmer ground for this time 
of year...snowfall rates and time of day will play a role in 
accumulations as well. All of these concerns will continue to be 
highlighted in the hazardous weather outlook until we get closer 
and amounts become more certain. 


Sunday and beyond...went more with the most consistent European model (ecmwf) model 
which tends to clear things out a bit quicker with just some 
lingering light wrap around moisture for Sunday...then dry and 
warmer temperatures into early next week. GFS will have to be 
watched as it brings another wave wrapping around system with 
precipitation lingering into Monday. 


Frieders 




&& 


Aviation... 


VFR conditions will prevail across the region into Wednesday morning. A 
cold front will progress through the area this evening resulting 
in some gusty southwest winds ahead of the front...shifting to the 
northwest. A few showers or an isolated storm could accompany the 
front. Frieders 




&& 


Preliminary point temp/pops... 


Wednesday Thursday Friday Sat sun Monday Tuesday 
----------------------------------------------------------- 
bil 043/060 031/047 030/038 026/037 026/042 027/052 032/058 
20/u 02/r 66/o 66/S 43/west 11/b 10/b 
lvm 032/060 022/047 024/037 019/038 020/044 026/055 031/057 
20/u 04/o 66/S 66/S 33/west 21/north 11/b 
hdn 041/063 030/051 030/039 026/037 025/044 026/055 031/060 
20/u 03/r 66/o 66/o 43/west 11/b 10/b 
mls 041/061 027/052 030/042 028/040 027/045 028/057 033/060 
20/north 02/r 33/o 45/o 43/west 21/b 11/b 
4bq 041/059 029/051 028/042 027/038 027/043 027/057 032/060 
20/north 03/r 66/o 66/o 43/west 21/b 10/u 
bhk 039/057 024/051 024/042 024/039 025/046 026/054 028/058 
30/north 02/r 45/o 55/o 43/west 21/b 11/b 
shr 039/061 030/048 028/040 025/035 025/041 026/056 031/058 
20/b 14/o 66/o 66/S 43/west 21/b 10/u 


&& 


Byz watches/warnings/advisories... 
Montana...none. 
Wyoming...none. 


&& 


$$ 
Weather.Gov/Billings