Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 282031

Area Forecast Discussion
National Weather Service Missoula MT
231 PM MDT Tue Mar 28 2017

.DISCUSSION...Numerous clouds and a few showers in far nw Montana
will persist through the evening hours. Temps struggled to reach
the mid 40s to near 50 today.

By Wednesday morning a weather disturbance will move into the
northern Rockies (NR) and bring widespread showers to the region
through the day. Valleys of west central and southwest Montana
look to be somewhat shadowed out and spared from any long duration
precip. More likely some scattered showers are expected there.

Late Wednesday through Thursday morning a more vigorous and wet
weather system will impact mainly central Idaho, Lemhi county and
the Bitterroot Mountains. A nice westerly flow will help enhance
precip in these areas. Precip totals of .50" to 1.25" are
expected. Snow levels will remain fairly high. Mud slides which
could block roads are possible.

Late Thursday morning the overall weather pattern will change as
all models are showing a cut off low pressure system developing.
across much of the Great Basin and quite possibly as far north as
the NR. The big issue is WHERE WILL IT DEVELOP? The favored area
most models project is south central Idaho down to the Great Basin
and 4 corners region. If this happens the NR expect an unstable
atmosphere favorable for scattered rain and snow showers with low
to maybe moderate impacts. HOWEVER one solution has the mid level
low feature further north which would impact Lemhi county and sw
Montana. If this solution is correct then some decent spring snow
could impact Lost Trail/Homestake Passes.

As with all closed lows there is usually a lot of uncertainty for
details until we see the whites of its eyes, or when it actually
develops. So be prepared for updates as we will have a little
better idea later tomorrow.

A couple of really fine spring days will hover over the NR Friday
afternoon and Saturday. A ridge noses its way into the region.
This more stable air will bring dry conditions with a lot of sun
through Saturday. Sun will help temperatures rise into the mid and
maybe upper 50s each day.

Sunday into Tuesday another trough over the area will bring a
return for cooler temps and showery conditions.


.AVIATION...Westerly flow will continue to bring clouds and a few
mountain showers across northwest Montana through 29/1200z. Winds
have been tricky to forecast for KGPI today: When the clouds thin
enough to allow sunshine the atmosphere becomes unstable enough
to mix down the westerly winds. When the clouds thicken, the
southeasterlies take over. Winds at the remaining terminals will
be northwest to northerly around 10 knots. An upper level warm
front will move over the region by 29/1500z providing increasing
chances for steady rainfall at KGPI and across the Clearwater
Mountains in Idaho. Westerly downslope winds will limit rain
chances and bring with it light to moderate mountain wave activity
over west-central and southwest Montana from 29/1500z to 30/0000z.



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