405 
fxus65 kbyz 212109 
afdbyz 


Area forecast discussion 
National Weather Service Billings Montana 
309 PM MDT Thursday Aug 21 2008 


Short term...valid for Friday and Sat... 


Difficult forecast developing for evening. Strong upper low with 
impressive dynamics and strong 300mb jet moving across North 
Pacific states and into northern rockies. Main middle level cold 
front still west of our forecast area and seems to have little 
push at this time. Weak convection ahead of front in warm sector 
across our area has little punch to it. Just south and southwest 
atmosphere has mixed out and shows very dry air with dewpoints in 
the upper 20s from Dillon in southwest Montana to Buffalo in 
northeast Wyoming. 


Forecasts are still showing good forcing moving over our area late 
this afternoon through middle evening. However...concern is the 
result of slower frontal passage and upper low dynamics may 
result in main deeper convection occurring to our north and 
northeast this evening...making our inherited probability of precipitation a bit overdone 
for the south sections. Will count on enough q vector forcing still 
over forecast area this evening to provide deeper convection over 
mainly northern zones before heading into northeast Montana. Will 
reduce probability of precipitation somewhat for south zones this evening and keep higher 
probability of precipitation from Musselshell eastward. Will keep mention of damaging 
winds in many areas due to large dewpoint depressions and very 
strong middle level flow. 


Very strong subsidence develops behind jet maximum by 06z this evening 
from Billings west which should effectively shut off any 
precipitation in that area...with just lingering scattered showers 
in the northeast. Brisk northwest flow and downward forcing will 
make for windy conditions across the region overnight. This will 
continue into Friday...with strongest winds in Baker area. 
Otherwise...dry and cooler temperatures still look good for 
Friday. Flat ridging for the start of the weekend with gradual 
warming back to around seasonal norms. Bt 




Long term...valid for sun...Mon...Tue...Wed...Thu... 


Upper level ridge will be anchored over the area on Sunday 
bringing a return to hot summertime temperatures. While ridge is 
not as strong as previous ridge it does have more of a downslope 
low level flow which will help maximize temperatures. Ridge is 
expected to break down on Monday with strong Lee side troughing for 
a very dry and hot day with downslope winds. Strong cold front to 
move through the area Monday night and could see some convective 
activity into Tuesday with much cooler temperatures. Precipitation 
amounts should be pretty light as the bulk of energy with the 
system stays to the north. Tuesday and Wednesday should see below 
normal temperatures with most of the moisture having pulled east 
of the area by Wednesday. Models indicate a broader ridge trying 
to influence the area for the end of next week with continued 
stronger flow aloft supporting some Lee side troffing. Borsum 


&& 


Aviation... 


Showers and thunderstorms over the western half of the area will 
move into Wyoming and southeast Montana this evening. A front will 
move across the area with strong westerly winds spreading from 
west to East. Mountain obscurations will be possible over the 
western mountains during the evening with clearing expected 
overnight. Friday will be mostly clear with less wind. Borsum 


&& 


Preliminary point temp/pops... 


Friday Sat sun Monday Tuesday Wednesday Thursday 
----------------------------------------------------------- 
bil 051/074 048/085 056/094 061/098 060/087 056/081 055/081 
50/u 00/u 00/u 00/u 02/T 22/T 22/T 
lvm 045/070 039/084 049/093 053/095 052/085 047/076 047/079 
40/u 00/u 00/u 00/u 22/T 22/T 22/T 
hdn 052/075 046/087 053/097 059/100 059/089 054/084 054/082 
50/u 00/u 00/u 00/u 02/T 21/b 12/T 
mls 055/073 049/084 058/097 064/101 064/090 059/085 059/084 
60/north 00/u 00/u 00/g 02/T 22/T 12/T 
4bq 054/073 046/083 056/094 060/099 060/089 058/083 055/084 
40/north 00/u 00/u 00/u 01/u 21/b 12/T 
bhk 052/072 046/081 053/093 059/097 058/088 056/083 056/082 
60/north 00/u 00/u 00/u 12/T 22/T 12/T 
shr 050/071 044/084 052/094 055/096 054/087 051/080 050/081 
30/u 00/u 00/u 00/u 01/b 21/b 21/u 


&& 


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


&& 


$$ 
Weather.Gov/Billings