Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 052043

Area Forecast Discussion
National Weather Service Missoula MT
243 PM MDT THU MAY 5 2016

...A few strong thunderstorms late this afternoon and evening...

.DISCUSSION...Cirrus clouds are inhibiting heating and cumulus
development this early afternoon. Some clearing of this cirrus
shield is expected over the next few hours, which will aid in the
development of cumulus, showers, and thunderstorms. Right now it
appears the best potential for the strongest convection will be
over central Idaho and the southern Bitterroot, then move north-
northeast through Missoula between 4-6 pm and into the
Flathead/Mission, Seeley/Swan valleys, and along the Continental
Divide during the early to mid evening hours. The main impacts
from storms, aside from heavy rain and lightning, will be the
potential for gusty winds of 40-45 mph.

A second surge of showers/thunderstorms in central Idaho up
through northwest Montana is expected late this evening through
the overnight hours.

The next significant weather impact over the region will quickly
set up during the overnight hours. A strong surface high pressure
will dive south from Alberta and increase an easterly pressure
gradient across the Continental Divide. Northeast to east winds
will become pretty gusty across the Divide into the Flathead
valley overnight, then spreading southward through the day
Friday. Expect gusts over 30 mph in Kalispell for several hours
FRIDAY WILL BE TO FLATHEAD LAKE. The windy conditions, especially
along the east and south side of the lake, will increase waves
and choppy conditions. Winds will diminish by Saturday morning.

Saturday through Sunday morning will be the nicest part of the
weekend, with plenty of sun and warm temperatures into the mid
and upper 70s under a ridge.

These conditions won`t last long as a trough of low pressure
entering from British Columbia will make its presence known
Sunday afternoon and evening. Moisture and instability will
increase ahead of the approaching front, helping to kick off
showers and thunderstorms across the region, with the best
potential for some strong storms in southwest Montana and Lemhi
county in Idaho.


Expect temperatures to cool off 20 degrees from Sunday`s highs,
translating to cooler than normal conditions with highs only in
the 50s. A closed low actually develops within this trough and
will sit over the region through at least Tuesday. Unseasonably
cold temps can occur under such lows. While some much-welcomed
precip amounts are expected, snow levels are expected to lower to
4000-5000 feet. This is a big change, given all the warm temps we
have received over the last month. So...given the increasing
confidence for a change to cold and wet conditions, in addition
to possible mountain snow, folks with outdoor plans should monitor
the latest forecasts for any specifics with regards to potential
snowfall in higher elevations.


.AVIATION...Isolated strong thunderstorms will impact the region
from roughly 05/2300Z through 06/0300Z, with KMSO and KGPI being
the two terminals most likely to be affected by thunderstorms. For
KMSO: gusty erratic outflow winds, heavy downpours (albeit
brief), and lightning has the best chance of impacting aviation
operations from 05/2300Z-06/0200Z. For KGPI: similar impacts
should be expected, however the best timeframe for impacts to
GPI`s terminal will range between 06/0000Z-06/0400Z. KBTM and KSMN
may see brief bouts of thundershower activity, however the
strongest will definitely be further north and west of these
locations. Once the cold front passes later tonight, expect a
strong easterly gradient to develop, bringing gusty east winds to
all terminals through the day Friday. Gusts up to 25-30 KTS will
be common.



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