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Area forecast discussion 
National Weather Service Glasgow Montana 
247 am MST Sat Nov 21 2009 


Short term...for northeast Montana...today through Monday... 
an energetic short wave trough and cold front sweep over the zones 
today. The main effect will be strong winds westerly winds behind 
the front. A strong surface trough anchored by a low centered in 
southern Saskatchewan will maintain a strong pressure gradient 
across the surface. These winds will be reinforced by 850mb winds 
of 35-40kts resulting in surface wind gusts of equal strength. The 
lwa seems like a slam-dunk so will renew the npw during this 
package. Moisture is rather anemic with this system so expect 
mostly cloud cover with little precipitation. A vorticity maximum around 
the base of the upper level trough could produce some moisture in 
southern Alberta/Saskatchewan that might spread a bit across the 
international border. So will maintain probability of precipitation just below text 
mention for now. The other previously mentioned concern was the 
expected low relative humidity values for today which could produce near critical 
fire weather conditions. See fire weather separate discussion below. 


Tonight/Sunday...upper flow veers to the northwest late tonight as 
the upper trough base moves east. A short wave upper ridge follows 
but is quickly followed by the next short wave trough. This next 
wave sends a weak cold front into the County Warning Area by afternoon which could 
produce light precipitation over the western zones. 850mb 
temperatures remain near 0*c or just below so mixed precipitation 
is a possibility. With the atmosphere decoupling at sunset...the 
relaxing gradient will allow winds to drop below lwa criteria. 


Sunday night/Monday...the base of the trough drops south into 
northern Colorado...taking most of the energy to our south. 
However the inverted surface extends north into northeastern 
Montana which will keep conditions a bit unsettled. While 
NAM...UKMET and ec stay dry...based on GFS...Gem and sref...slight 
chance probability of precipitation seem appropriate for snow overnight. Conditions do 
not change much for Monday so will keep slight chance probability of precipitation going. 
Surface highs will drop down much closer to normal while 850mb 
temperatures hover around -4*c. So expect any precipitation to 
fall as snow and possibly rain showers. Quantitative precipitation forecast amounts will not 
produce accumulations. Scattered 




Long term...Monday night through Saturday... 
shortwave trough drops southeast out of Saskatchewan during the 
day Tuesday and may bring a slight chance of rain or snow. This 
fast moving system will have limited moisture with it. 


An upper ridge builds into the area on Wednesday and will bring 
warm and dry weather through Thanksgiving day for sure. 


Models have some differences on track of a shortwave that moves 
inland from the Pacific on Friday. European model (ecmwf) takes the system south of 
the area while the GFS brings it across Montana. Either way...a 
cold front will affect the forecast area on Friday with cooler 
temperatures expected next weekend. Will keep the forecast dry for 
the most part for now. Forrester 




&& 


Aviation... 
VFR conditions. A mix of middle and high level clouds will move 
through the area today with skies clearing tonight. Southeast 
winds early this morning will become west around 15z and increase 
to 20 to 25 knots by 18z. The winds will diminish to 10 to 15 
knots this evening. 




&& 


Fire weather... 
a strong west wind will develop today behind a cold front. Wind 
speeds are expected to reach 20 to 30 miles per hour...with gusts to 40 miles per hour 
during the late morning and afternoon hours. Afternoon minimum 
relative humidity values are expected to briefly drop into the 20 
to 30 percent range before beginning a steady recovery near 
sunset. Therefore...a brief period of critical fire weather 
conditions are possible this afternoon...but highlights are not 
expected at this time due to the short duration of low relative 
humidity due to shortening sunlight hours. The most susceptible 
areas will be the Little Rocky Mountains and the Missouri breaks 
region of zones 119 and 121...which will experience a rather poor 
relative humidity recovery last night. Ajz/scattered 




&& 


Glasgow watches/warnings/advisories... 
lake Wind Advisory from 10 am this morning to 5 PM MST this 
afternoon for Fort Peck Lake. 


&& 


$$ 


Weather.Gov/Glasgow