Weather

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Area forecast discussion 
National Weather Service Glasgow Montana 
936 PM MDT Sat Sep 6 2008 


Short term...for northeast Montana...tonight through Monday... 
update...going forecast is in excellent shape. Have just updated 
to remove probability of precipitation across the north as shower activity quickly 
diminished with the loss of solar heating. Did keep probability of precipitation in across 
the far southern zones however as they are in vicinity of a 100kt 
jet and the associated dynamic lift. Dewpoints are all over the 
place as a result of shower activity this afternoon. As per the 
00z ggw sounding the lower levels of the atmosphere are rather dry 
and observed dewpoints are lowering across the northern zones. 
Thus feel frost is a possibility late tonight and early Sunday 
morning as temperatures dip into the lower to middle 30s. Gilchrist 


Previous discussion...the weather system currently making its way 
across the area will slide off to the southeast tonight with 
surface high pressure working its way in from the northwest. 
Northwest flow remains aloft and another disturbance in this flow 
is expected to slide south southeast mostly to our west across 
western into central Montana tonight and Sunday. Still some 
differences of opinion as to how far east this feature will spread 
showers. Latest satellite imagery placement of this feature 
indicates better to keep the current chance/slight chance probability of precipitation in 
the southwest portion of the County Warning Area for tonight and Sunday. The 
surface high...dwindling moisture and lack of anything substantial 
as far as energy is concerned across the rest of the County Warning Area will mean 
dry through tonight and Sunday. Upper trough then begins to drift east 
Sunday night with perhaps some semblance of a short-wave upper 
ridge for Monday with weak high pressure still hanging on at the 
surface though drifting east as well. Cool temperatures tonight although 
it appears dewpoints to remain up enough to preclude anything really 
cold as sky clears across the north. Remaining cool Sunday behind 
the weak cold front of today with readings mainly upper 50s to 
lower 60s. Warmer Monday with more sun and warmer air coming in 
with the short-wave ridge. Temperatures still below normal though for 
early September. 


Long term...Monday night through Saturday... 
model consensus appears to bring the short wave trough through 
Wednesday afternoon. Proper onset of cloud cover...and shower activity 
is still represented in the long term forecast...so no changes 
made. A possible warm up is depicted in the models late in the 
forecast period...as a short wave ridge builds in from the 
southwest on Friday. Model solutions diverge on intensity so will 
keep an eye on later runs for perturbations in the pattern. 
Shallenberger 


Previous long term discussion...a shortwave upper ridge Tuesday with 
thicknesses climbing well into the 560s dm. This brings sunny 
skies and temperatures back to normal...after what will end up as more 
than a week of cooler than normal weather. Then another moderately 
strong shortwave from the northwest arrives Wednesday. Some model runs have 
been indicating some split of energy possible. NOGAPS has a 
significant cut-off upper low develop from the main upper trough 
and move well to the SW of Montana. An earlier European model (ecmwf) run had a similar 
solution on the split...that ended up moving back into NE Wyoming Sat. 
Other models have the main upper system possibly closing off as it 
moves across NE Montana. 


In any case...Wednesday looks threatening for scattered showers...and 
unstable enough for isolated thunderstorms as well. Models also show 850 
mb winds up to 35 knots behind the cold front...with moderate cold 
advection. So a windy...showery...and cooler day expected Wednesday. 
Have lowered highs. 


Model consensus then has a change in the upper pattern with the 
upper ridge moving into the inland west...then weakening by late 
in the period. This will bring a dry and warmer weather for Thursday 
and Friday with mean relative humidity falling below 30 percent Friday. Models have shown a 
dry cold front near parallel to the jetstream dragging S across 
the area late Friday night or Sat morning as the upper ridge weakens. 
Latest GFS is moister and much cooler with this than previous 
runs or other models...so will go more conservatively with the 
cooling. MOS though is on the warm side throughout the forecast 
period and barely notices any cold fronts at all. Simonsen 




&& 


Aviation... 
scattered to isolated showers will continue to move across the 
region this afternoon. Brief mfvr ceilings are possible with the 
heavier showers. Skies are expected to clear late tonight along 
with diminishing north winds as high pressure moves into the 
state. Rae 




&& 


Glasgow watches/warnings/advisories...none. 


&& 


$$ 


Weather.Gov/Glasgow