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000
FXUS65 KMSO 230958
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
358 AM MDT Thu May 23 2013

.DISCUSSION...The area of heaviest precipitation that produced
heavy snow this morning and resulted in power outages across
parts of southwest Montana overnight has since moved north and is
presently over the Bob Marshall/Scapegoat Wilderness areas. It
seems likely that Seeley Lake is experiencing their heaviest
snowfall, but do not anticipate more than 1 to 2 inches of snow
through daybreak resulting in little if any impact. However this
may not be the case over southwest Montana where snow continues to
fall in Butte, Anaconda and up towards Georgetown Lake. Given the
continued snow, already known impacts and in anticipation of a
challenging morning commute have issued a Winter Weather Advisory
that is in effect till 10am. Main impacts will be the weight of
any additional snowfall on area vegetation, power lines and
continued slushy roadways. Things should start to improve shortly
after sunrise.

The focused area of precipitation will gradually work its way
north throughout the day and eventually into Canada this
afternoon. Dramatic cooling and drying has been observed behind
the precipitation and a clearing trend this morning is likely
across southwest and west central Montana. However another
disturbance, clearly visible on satellite data off the Oregon
coast, will rotate through the Great Basin and up into southwest
Montana later this afternoon. This wave and its attendant upper
level jet streak will interact with an already moist atmosphere
that will be slowly growing more unstable due to daytime heating
to produce another round of showers and thunderstorms. Models have
gradually be trending west with this convective precipitation,
spreading it from Lemhi County, Idaho northeast basically along
the Divide through this evening. Key threats and potential impacts
will be very heavy rainfall and perhaps some pea sized hail. There
will be a brief break in the train of waves pushing off the larger
Pacific Northwest low pressure system late Thursday night into
early Friday. However by Friday afternoon/Saturday early morning
models are suggesting that a portion of the main low may break
away and move quickly through northwest Montana. This will shift
colder air once again into Montana along with another round of
precipitation. However precipitation and snowfall amounts should
be significantly less than those experienced over the past twenty-
four hours with snow likely limited to locations above 5000ft.

The northwestern United States will remain under an upper level
low that will keep rotating moisture and instability into western
Montana and north central Idaho. This will keep a chance of
showers in the forecast for Saturday and through the rest of the
forecast period. Temperatures will remain slightly below normal.

&&

.AVIATION...A low pressure system will keep a chance of showers
over the region. This system will have the greatest impact on KGPI
and KBTM. In addition, snow showers will obscure the mountains and
passes along the Continental divide.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY until 10 AM MDT this morning
     Butte/Blackfoot Region.

ID...None.
&&

$$

Dickerson/Kolata

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