Area Forecast Discussion
Issued by NWS Great Falls, MT
FXUS65 KTFX 210955
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
355 AM MDT Tue Oct 21 2014
Today through Thursday...Models remain in decent agreement
bringing a negatively tilted upper trof across the area this
afternoon. Southwest flow aloft will increase ahead of the
approaching trof and clouds will increase through the morning. An
associated surface cold front will push across the area this
afternoon with showers developing along and behind the front as it
pushes east. Enough instability within the airmass for an isolated
thunderstorm to develop. Isolated lightning strikes have occurred
in Idaho as the front passed through. Cooler air following in the
wake of the cold frontal passage will allow snow levels to fall to
5500 to 6000 feet. Light accumulating snow can be expected at this
elevation with 1 to 3 inches of snow possible above 7000 feet.
Most of the snow will fall over the mountains of southwest
Montana. Mountain passes may see a rain/snow mix by evening. The
upper trof moves quickly to northeast Montana by Wednesday morning
bringing an end to the precipitation. Temperatures will remain
cool Wednesday even as upper ridging takes place during the
afternoon. Southwest flow aloft increases again Wednesday night
and continues Thursday as another upper trof approaches the Pacific
Northwest coast. A few showers will be possible over the Rocky
Mountains with the plains remaining dry. Temperatures will remain
near to slightly above seasonal averages through the period.
Thursday Night through Tuesday...Overall, seasonably mild weather
expected as a progressive pattern steers a series of Pacific low
pressure troughs through the area during the period. High pressure
ridge centered over the Rocky Mountain states at start of period
quickly gives way to Pacific low pressure trough during the weekend.
Models are in relatively close agreement with timing and strength of
system as it moves through with both ECMWF and GFS calling for
temperatures 10 to 15 degrees cooler and areas of rain or snow
showers, mainly over the west and southwest mountains. Downslope
winds will limit precipitation chances over the plains and valleys.
This low pressure trough starts working off to the east on Monday
with high pressure again rebuilding briefly before the next trough
begins pushing in Tuesday.
High pressure will keep dry and stable conditions for the next 6
hours. Winds will begin to pick up out of the southwest through the
night. Mid level ceilings, and the chance for showers, will increase
from the southwest after 12Z, spreading over the plains by 18Z. Most
locations will remain VFR with intermittent periods of MVFR and
isolated IFR in showers. Conditions look to improve from the
southwest after 00Z Wednesday.
.PRELIMINARY POINT TEMPS/POPS...
GTF 60 38 62 44 / 60 40 0 10
CTB 58 37 62 42 / 60 20 0 10
HLN 60 36 61 40 / 70 40 10 10
BZN 63 31 57 32 / 40 50 10 10
WEY 50 24 46 24 / 60 50 10 10
DLN 58 31 56 37 / 60 50 0 10
HVR 65 39 63 39 / 30 30 10 0
LWT 69 37 61 40 / 30 50 10 10