000
FXUS65 KMSO 171000
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
400 AM MDT Fri May 17 2013

.DISCUSSION...The first in a series of mid level weather
disturbances is approaching central Idaho and western Montana
this morning. This wave is helping to initiate an area of showers
across central Idaho than will gradually work its way north into
western and southwest Montana this morning. The precipitation
returns over central Idaho have been light, but steady producing a
few hundredths of an inch per hour. All model data suggest that
precipitation will become more widespread as it moves north in
response to the wave becoming more defined and thus stronger. A
second, more intense wave presently moving on shore over central
California with be responsible for additional showers late this
afternoon across west central Montana and into northwest Montana
tonight. Although there will likely be pockets of heavier
precipitation and/or isolated thunderstorms producing bursts of
stronger precipitation, by and large rainfall will remain
persistently light throughout the day.

The main portion of a broad upper level trough will move over the
Northern Rockies on Saturday. The atmosphere under these types of
scenarios is often littered with showers, especially during the
afternoon, with a focus for the heaviest and/or more persistent
precipitation drawn near subtlety embedded mid level weather
disturbances. Though great variation remains in place amongst the
models, believe the focus for heavier or more persistent
precipitation will shift towards northwest Montana. However those
with plans to be outdoors on Saturday should plan to encounter at
least a few rain showers and continued cool, breezy conditions;
especially during the afternoon. Similar conditions (cool, breezy
and showery) are likely on Sunday. At this time the focus for the
heaviest precipitation appears to be along the Divide.

Monday...Next week will start a warming trend as a weak ridge
builds in between the two systems. Despite the ridge, there will
be enough residual atmospheric moisture and instability for a
chance of afternoon showers and even a thunderstorm or two across
much of the region.

Tuesday through Thursday...Confidence is high for a cutoff low to
affect the northern Rockies next week, and this will be a wet
system. However, considerable uncertainty remains in how this
system will be positioned, which will have dramatic impacts on
exactly which areas will have the most precipitation. If the low
system remains west of the area (over the Pacific Northwest), as
currently advertised by the forecast models, then thunderstorms
will be a key element for the Tuesday/Wednesday forecast. Another
possible scenario is for heavy rains across northwest Montana,
where river levels are high and runoff is in its peak season. This
remains a concern that will be monitored closely for potential
flooding impacts.

&&

.AVIATION...Showers will be developing this morning across Lemhi
County and southwest Montana, while conditions remain favorable in
northwest Montana. Moisture will be spreading north this morning
and the atmosphere will become increasingly more unstable during
the day. Expect scattered showers and Isolated thunderstorms this
afternoon and into the evening hours across north-central Idaho
and western Montana, which will temporarily lower ceilings and
reduce visibilities. On the other hand, southwest Montana and
Lemhi County will likely see steady rain develop during the day
with low ceilings and more frequently reductions to visibilities.
Mountain obscurement is also likely. KBTM and KSMN airfields will
be most impacted by rain, lower ceilings, reductions to
visibilities and terrain obscurations.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

$$

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