Area Forecast Discussion
Issued by NWS Missoula, MT

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370
FXUS65 KMSO 200950
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
350 AM MDT Sun May 20 2018

.DISCUSSION...

Relatively dry conditions will be present across much of the
Northern Rockies through this morning. Shower and thunderstorm
activity will increase this afternoon, spreading from the south
over time. Most of the shower/thunderstorm activity will exist
along and south of the I-90 corridor. Any thunderstorm that forms
will have the potential of brief, heavy rainfall. Rain today may
cause seasonal small streams to react, however the effect on
mainstem rivers (e.g., Clark Fork River) will be negligible. Aside
from the small streams, area rivers will remain fairly high, yet
stable.

The signal of diurnal showers and thunderstorms will continue for
both Monday and Tuesday across the Northern Rockies. Afternoon
temperatures will be warmer than recently, providing the
instability necessary for the afternoon/evening showers and
thunderstorms. Similar to this afternoon, any thunderstorm that
develops will have a potential of brief, heavy rainfall. Unlike
this afternoon, showers and thunderstorms will also exist across
much of the region. Rivers will have a slow response to the
seasonally warm temperatures that will accelerate high elevation
snowmelt by a bit.

On Wednesday, the low pressure system that has been hanging around
the Great Basin will finally move northward toward the Northern
Rockies. This will lead to more thunderstorms Wednesday afternoon
especially along and south of the I-90 corridor. As the low
pressure moves off to our east on Thursday, showers are expected
to linger around the area mountains.

Starting Friday, a ridge of high pressure will build over the
region and will lead to the warmest temperatures of the week.
Highs are expected to be in the upper 70s to low 80s for most
valleys across central Idaho and western Montana Friday and
Saturday.

&&

.AVIATION...High level cloudiness will be present over the
Northern Rockies through 20/1800Z. Winds at area terminals will be
mostly light and variable during this time. After 20/1800Z,
shower and thunderstorm activity will increase and spread from the
south. A brief thunderstorm is possible near KSMN and KBTM
20/2000Z through 21/0100Z. The main effect of thunderstorms on
these terminals will be brief lowered ceilings and visibility
restrictions. Most of the shower and thunderstorm activity will
exist south of KMSO, obscuring terrain at times. North of KMSO,
including near KGPI, variable high cloudiness will continue for
the rest of the 24-hour period.

&&

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

$$



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