Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Glasgow Montana
219 PM MDT Monday Sep 1 2014
Short term...for northeast Montana...tonight through Wednesday...
Synoptic set up... a large area of hot high pressure exists over
the Desert Southwest with a ridge spur creeping up the coast of
California. A broad trough lies over the northern and central US
plains and Canadian plains. Behind this flow is fairly zonal
across the Pacific northwest and British Columbia. Meanwhile a
large cold core trough is exiting the the Gulf of Alaska and
running southeast into the British Columbia coastline.
This afternoon through tonight... peak heating and cold air aloft
from the broad exiting trough will generate some afternoon showers
and thunderstorms that should quickly drop off over night. As
skies clear... a slight chance exists for fog along river
bottoms... especially along the Yellowstone River Valley where
light rain fell earlier in the day.
Tuesday through Tuesday evening... deserts southwest high pressure
will push north. This will slightly warm the middle levels and
stabilize out the atmosphere for a brief time. Expect clear to
partly cloudy skies and dry conditions. Meanwhile... trough from
the Gulf of Alaska will slam into the developing ridge over the
intermountain west and form a tight gradient over the Pacific
Wednesday... momentum from the the incoming trough will quickly
overpower the weak ridge across northeast Montana and drag in a
shortwave with Pacific moisture. During the morning hours the
shortwave should pass over the Lee Side Mountain trough and mix
out the atmosphere and surface layer quickly morphing the trough
into a cold front. The cold front should move through the whole
County Warning Area by the afternoon hours bringing cold air advection in the form of
increasingly strong northwest winds and light rain showers. Most
of the vorticity maximum energy generating the lift for thunderstorms should
be to the north of the County Warning Area with northern sections having the
highest chances for their own thunder.
Long term...Wednesday night through Monday...
Going forecast in overall good shape depicting lingering showers
and cool temperatures behind the exiting upper low on Wednesday
night into Thursday. Upper ridging then rebounds back into the
northern High Plains in a westerly flow aloft...making for dry
conditions and warming temperatures through early next week. Only
tweak was to trend temperatures and sky toward the latest model
Previous long term discussion...
elongated positive tilted trough extends from Hudson Bay to
California midweek with a strong shortwave along the Canadian
border. As this shortwave zips east...the southern portion of the
trough cuts off and lingers near the California coast into the
weekend. Well developed low develops below the shortwave but for
now the models keep the heaviest precipitation generally north of
the border as the storm system tracks east on Thursday.
Behind the shortwave...with the split flow around the California
low...models deflect most of the moisture across the southern
states or well north in Canada. This will result in mostly dry
conditions for Montana with west to northwesterly flow...and
warming temperatures into next weekend. Ebert
flight category: VFR outside of isolated showers and
thunderstorms this evening.
Synopsis: embedded disturbances in a northwest flow aloft will
keep isolated showers and thunderstorms in the forecast this
evening...although confidence is not high enough at this time to
specifically address in the terminal forecasts. Otherwise
conditions will be mainly dry with overall good flying weather.
Visibility: unrestricted...possibly MVFR in stronger showers or
thunderstorms through this evening.
Cigs: scattered-broken middle level clouds...possibly MVFR in stronger showers
or thunderstorms through this evening.
Winds: southwest at 5-15kts...going westerly Tuesday morning.