Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 181802

Area Forecast Discussion
National Weather Service Great Falls MT
1140 AM MDT Sat Aug 18 2018

Aviation Section Updated.


Upper level shortwave trough is positioned over Southwest MT
and moving quickly to the east. Radar indicates a few showers
broadly along a line from Helena to Havre, but surface
observations suggest that little, if any rain is reaching the
ground under these showers. All recent lightning activity is
occurring well away to our east. At the surface, a cold front is
advancing quickly north to south through North-central Montana.
The shift to gusty north winds and slightly cooler temperatures
will occur through Great Falls around 11am, progressing further
south from there into early afternoon. Satellite imagery and
surface observations indicate that visibility may actually lower
behind the front due to higher smoke concentrations arriving from
British Columbia wildfires. Short term models are consistent in
generating light rain showers over Lewis and Clark county this
afternoon. These showers appear to be shallow convection with
little lighting potential. The forecast was updated to refine
precipitation potential based on this short term model guidance.
Furthermore, winds were updated to better match observed trends.
Skies have cleared over southwest Montana, but showers and
isolated thunderstorms will remain possible through this



Upper level disturbance continues to move eastward through the
northern Rocky Mountain region, producing scattered showers and
thunderstorms. Cooler temperatures are expected through the
weekend and into Monday, with a good chance for showers Sunday
night. Warmer and drier conditions return to the region by the
middle of next week.


Updated 1740Z.

Scattered showers continue this afternoon over central Montana,
causing temporary MVFR conditions at KLWT. Winds have shifted to
northerly with a frontal passage that has transported higher smoke
concentration over North-Central MT. Visibility is reduced with MVFR
or temporary IFR conditions in smoke at KCTB. Expect smoke to
produce MVFR conditions at KGTF/KHVR through this afternoon. Rain
showers gradually clear overnight, with lower smoke concentration
anticipated on Sunday.



Cooler temperatures are expected through the weekend and into
Monday, along with scattered showers/thunderstorms. Warmer and
drier conditions likely to return to much of the region by next
Tuesday, with the potential for breezy conditions next Wednesday.


/ISSUED 523 AM MDT Sat Aug 18 2018/

Today through Monday...An upper level disturbance currently over
southwest Montana will continue to move slowly eastward today.
Scattered showers and thunderstorms are expected, mainly over
southern portions of the forecast area, and temperatures will be
cooler as a Canadian cool front pushes southward into Montana. It
is worth noting that model consistency is very poor after today
with the ECMWF keeping cooler and unsettled conditions as a
secondary upper level disturbance moves inland across the Pacific
Northwest while the GFS keeps this feature along the West Coasts.
Have gone with the more consistent ECMWF solution and kept the
unsettled and cooler conditions in place with another chance for
precipitation expected Sunday night into the day on Monday. mpj

Monday night through Saturday...Model differences become even more
pronounced by mid-week as the GFS retrogrades the disturbance out
over the Pacific Ocean and builds a strong ridge aloft over
Montana. Meanwhile the ECMWF keeps this feature over the Pacific
Northwest before moving it eastward through the state on Thursday.
Even though confidence is rather low, have opted to continue with
a mostly dry and warmer forecast for mid-week and beyond rather
than make any significant change to the going long term period.


GTF  81  53  80  53 /  20   0  10  30
CTB  80  50  77  49 /  10   0  10  40
HLN  81  54  82  54 /  40  10  10  40
BZN  77  49  80  50 /  30  20  10  40
WEY  70  38  74  37 /  40  20  10  10
DLN  76  46  79  48 /  30  10  10  20
HVR  85  52  78  52 /  50   0  10  30
LWT  76  50  74  50 /  60  30  10  20



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