Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 301013

Area Forecast Discussion
National Weather Service Missoula MT
413 AM MDT Thu Mar 30 2017

.DISCUSSION...An upper level low pressure system moving on shore
over central Oregon early this morning will dig south into Nevada
by this afternoon. At the same time a mid-level circulation will
develop north of the main upper low, bringing with it an area of
heavier precipitation. And here in lies the main forecast
challenge over the next 24 hours.

Forecast models have been consistently inconsistent, so to speak,
for several days now with each model presenting varying realistic
solutions for where this mid-level circulation will develop. The
GFS and ECMWF are farther north and spread the heaviest
precipitation over all of Lemhi County, but as far north as the
Anaconda/Butte/Southern Bitterroot areas of SW/SC Montana. Yet
the NAM and Canadian solutions maintain their insistence that this
precipitation will barely influence Lemhi County and SW/SC
Montana, instead falling across southern Idaho (Boise/Pocatello
areas). Based on the latest satellite, radar and surface pressure
trends in central Oregon (where the mid level circulation is
beginning to take shape) we`re inclined to believe a more
northerly track. This maintains the previous forecast which has
the heaviest rain/snow falling throughout Lemhi County and extending
north up to the far southern Bitterroot Valley & SW Montana
(including Butte and Anaconda). This falls in line most with the
ECMWF analysis and continues to support the previously issued
Winter Weather Advisory above 6500 feet, in effect until early
Friday morning.

Tonight cooler air will be brought into the Northern Rockies via
persistent easterly flow aloft. And steady drying throughout the
atmosphere will gradually end showers by Friday morning and the
sky start to clear in response to developing high pressure.
Seasonably cool, Friday and at least Saturday morning will be
quite nice throughout the Northern Rockies. But this will be short
lived as yet another weather system begins to spread clouds and
eventually precipitation into the region late Saturday and
Saturday night.

Next week a cold front will move through the region Sunday night
and Monday. Showers, some snow shower in the mountains, and gusty
winds are the only expected impacts from this system. There may be
some minor travel inconveniences due to rapidly changing
conditions. The worst conditions will likely be in southern Lemhi
county, Idaho as the main energy with this system is forecast to
move through the Snake River basin and into central Wyoming. This
will cause wrap around moisture and cooler temperatures in Lemhi

Tuesday and Wednesday a ridge builds over the region, causing some
very nice March weather. However the ridge will be shortlived and
when it breaks down will leave central Idaho with moist, upslope
flow and rain showers.


.AVIATION...Showers are likely to bring temporary visibility
reductions and occasionally lowered ceilings at KMSO and KGPI.
However heavier, more persistent rain and even snow will impact
air field operations and weather conditions at KBTM and KSMN.
Gusty northerly winds (at least 20 knots) are anticipate this
evening as the precipitation comes to an end at these airfields
and though the region.


ID...Winter Weather Advisory until 9 AM MDT Friday ABOVE 6500 FEET
     for the Eastern Lemhi County...Western Lemhi County.


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