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Area forecast discussion 
National Weather Service Glasgow Montana 
925 am MST Monday Nov 23 2009 


Short term...for northeast Montana...today through Wednesday... 
latest MOS is slightly cooler for this afternoon...other than that 
current forecast is in good shape. 


Previous discussion... 
the upper low will drop into the Central Plains today with drier 
air aloft moving over the forecast area as upper ridging builds in 
from the Pacific northwest. The sky should clear from west to east 
during the afternoon with a clear sky over the entire area by 
tonight. Afternoon maximum temperatures will remain above seasonal 
averages. Warm advection will commence Monday night creating 
rather large minimum temperature differences between the higher 
elevations and the typical cold air drainage locations where 
temperatures should be close to normal. 


Tuesday...a vigorous shortwave trough will dig southeast over the 
Canadian prairies driving a strong dry cold front through 
northeast Montana. Gusty northwest wind will develop along and 
behind the cold front. 850mb wind speeds reach upwards of 30-35kt 
and cold air advection and a strong pressure gradient should kick 
up a rather brisk surface wind. Sustained winds could approach and 
reach 15-20 miles per hour with gusts to 40 miles per hour...so a lwa might be required 
for Fort Peck Lake. The cold boundary moves past the County Warning Area borders 
by sunset where it finds a bit of moisture. Any resulting showers 
should remain beyond our borders through Tuesday night. 


Wednesday...an upper level ridge amplifies over western Continental U.S. As 
it slides east. The cold boundary retreats east through the County Warning Area by 
late afternoon. The strong surface high and approaching upper ridge 
will begin to ramp up 1000mb-500mb thickness heights to as high as 
550dm over the SW corner to introduce warm air advection from the west. Scattered 




Long term...Wednesday night through Monday... 
upper ridge will bring a warm and dry Thanksgiving to the forecast 
area. That ridge will move to the east on Friday while the warm 
and dry weather continues. While 850 mb temperatures are 
forecasted to be +5 to +8c both days...light winds and limited 
daylight will limit mixing. Also...the nighttime cold air drainage 
both Wednesday night and Thursday night will provide a seasonably 
cold start to valley locations in the morning which may limit 
warming potential even further. 


Cold front will move through the area Friday night followed by an 
upper trough on Saturday. Both the GFS and European model (ecmwf) want to split the 
moisture with this system around northeast Montana. Will maintain 
a slight chance of rain and snow at this point as models have been 
changing the moisture placement from run to run with this system. 
Gusty northwest winds and cooler temperatures on Saturday appears 
to be the main impact at this point. 


Beyond Saturday...models start to differ in timing. It looks like 
both models keep the colder air over the area on Sunday although 
European model (ecmwf) is faster than the GFS in moving the trough to the east. 
Likewise...the European model (ecmwf) brings the next upper ridge in faster than 
the GFS early next week. Either way...a warming trend for Monday 
looks reasonable at this time. Forrester 


&& 


Aviation... 
VFR conditions will continue today and tonight. Middle level clouds 
near 10kft above ground level will clear by afternoon. Light and variable winds 
will become west to northwest 10 to 15 knots by late morning. The 
winds will become light and variable again this evening. 




&& 


Climate... 
there has been no precipitation at the Glasgow Airport since a 
trace was received on October 28th. That is a total of 25 days as 
of November 22nd. That ties the second longest number of days 
without any precipitation at the Glasgow Airport. The record is 28 
days from October 20th through November 16th 1987. There is 
currently no rain or snow forecast until Friday night. If this 
holds true...this current dry streak will become the longest on 
record at the Glasgow Airport. There are longer dry periods prior 
to 1948 when observations were taken downtown in Glasgow. The 
longest span not corrupted by missing data was a remarkable 46 
days from September 16th trough October 31st 1906. Ajz 


&& 


Glasgow watches/warnings/advisories...none. 


&& 


$$ 


Weather.Gov/Glasgow