Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 292102

Area Forecast Discussion
National Weather Service Missoula MT
302 PM MDT Tue Jul 29 2014

.DISCUSSION...Scattered showers and isolated thunderstorms will
continue through this evening across parts of the Northern
Rockies. This is especially so for Lemhi County, southwest Montana
(Butte area) and along the Continental Divide. The key threat will
be heavy rain from storms with extremely slow storm motion that
may produce urban, small stream or even flash flooding. These
storms should show signs of diminishing shortly after sunset.

Another round of afternoon/evening showers and thunderstorms will
develop on Wednesday as an upper level disturbance (presently
tracking through Nevada and northern California) makes its way
across Idaho and Montana. Again the chief threat will be for heavy
rain from slow moving thunderstorms which could result in similar
flooding threats to perhaps a more widespread area. Those living
near recent wildfire burn scars, narrow canyons, urban areas with
poor drainage or other typically flood prone locations should be
on the lookout for approaching storms and have a plan in place to
avoid the dangers of flooding.

Yet another weather feature is forecast to move around the ridge
of high pressure and approach the Northern Rockies on Friday. This
impulse appears to originate from the remnants of what was once
Tropical Storm Hernan (now an extra-tropical cyclone) over the
eastern Pacific. The global models (GFS & ECMWF) are having
trouble showing consistency with this feature, largely due to the
complexities associated with the transition from tropical to
extra-tropical and thus we approach the forecast for Friday and
Friday night with some caution. Either way, a modest push of
monsoonal moisture is likely to occur Friday into Saturday and
could result in heavier precipitation. But how widespread and
strong will largely depend upon where this feature tracks,
something we hope to hone in on with upcoming model runs.

A hot weekend with afternoon thunderstorms appears at hand as
monsoonal moisture and waves of instability stream into the
Northern Rockies. This trend seems likely to continue even into
next week.


.AVIATION...The afternoon and evening thunderstorm threat will be
mostly at KSMN and KBTM. Breezy north winds are possible at KMSO
and KGPI late this afternoon as well. Conditions will clear out
after sunset with winds diminishing area-wide.


ID...FIRE WEATHER WATCH from Wednesday afternoon through Wednesday
     evening Eastern Lemhi County...Southern Clearwater
     Mountains...Western Lemhi County.



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