Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 230237
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
837 PM MDT Fri Sep 22 2017

.UPDATE...

Satellite imagery this evening shows an elongated upper level low
extending from Western MT SW into Northern NV. A weakening lobe
of shortwave energy is lifting north toward southern AB while
another piece of energy is lifting north from NW WY into S-central
MT. Overall precipitation coverage and intensity has decreased
across the region and will continue to do so through the remainder
of this evening behind the shortwave exiting N to AB, however
areas of drizzle and low cloud-cover will likely persist into
Saturday morning across much of the area. Incoming energy from WY
may clip eastern portions of the forecast area late tonight with
another round of light rain/snow. Additional snow accumulation in
the advisory areas should be very light with perhaps an additional
inch or so possible in eastern portions of the Little Belts and
Snowies later tonight as the second wave passes through. Hoenisch


&&

.SYNOPSIS...
A slow moving upper level low pressure system will move through the
region tonight. As a result, areas of rain and snow will gradually
diminish late tonight and during the morning hours on Saturday. For
Saturday afternoon it will remain cool, with highs only around 50
degrees. A northwesterly flow aloft will then reside over the
region from Sunday through next Wednesday. As a result, expect a
slow warming trend for next week, and just a small chance for a
passing light shower.

&&

.AVIATION...
Updated 2342z.
Areas of rain/snow/fog continue to drift north into the Cut
Bank/Havre areas while locations to the south continue to see low
clouds and a few showers. IFR/MVFR conditions will likely
predominate overnight before low clouds lift and begin to break up
on Saturday morning. Mountains/passes remain obscured through much
of the forecast period. mpj

&&

.PREV DISCUSSION...
/ISSUED 542 PM MDT Fri Sep 22 2017/
Tonight through Sunday...Main concern this evening is rain/snow over
the region. One area of rain/snow has pushed eastward into
northeastern MT along the front...while another area of
precipitation continues to rotate around the upper level low. Thus
high pops continue this evening in the Great Falls/Helena areas, but
QPF amounts will be low. Impacts have been low on higher elevation
highways this afternoon as the snow has been melting, but near
sunset, expect higher elevation roadways to gradually develop
snow/ice as they cool this evening. Thus the winter weather
advisory will continue for now. The precipitation continues into
Saturday morning over Central MT before diminishing in most areas.
For Saturday night/Sunday...the upper level low redevelops
southeast of the region, allowing for a small chance for precip in
my far eastern sections of the CWA. Otherwise cool temperatures on
Saturday will warm a touch for Sunday. Brusda

Sunday night through Thursday night...main forecast concerns in the
long term are moderating temperatures (especially towards the middle
of the upcoming work week) and precipitation chances (mainly Tuesday
and Tuesday night).

The Northern Rockies and Northern High Plains will remain beneath
broad H500 troughing to begin the long term, with a H500 closed low
over the Central Rockies beginning Sunday night. The aforementioned
H500 closed low will slowly lift from the Central Rockies and into
North Dakota through the day on Tuesday, all the while as H500
ridging begins to build into the Pacific Northwest and Intermountain
West. The Northern Rockies will be caught in-between these two upper
level features, which will generally lead to northwest flow from
late Monday through Wednesday morning. During this period of
northwest flow, a quick moving disturbance is expected to dive
southeast from the British Columbia/Alberta region and into the
Intermountain West/Northern Rockies/Northern High Plains. At this
time, there are significant spatial differences between varying
model solutions with the evolution of this quick moving disturbance,
thus the very vague regional descriptions. None-the-less, there
exist a chance for light precipitation Tuesday morning and into the
early morning hours on Wednesday across portions of North Central
and Southwest Montana (better chances exist within the GFS solution
which has the upper level disturbance moving from British Columbia
and into the Intermountain West, placing North Central and Southwest
Montana beneath the best upper level support). Following the quick
hitting disturbance Tuesday/Tuesday night, H500 ridging finally
begins to move into the Northern Rockies during the day on
Wednesday, persisting over the region for the remainder of the long
term period. High temperatures beneath this upper level ridge will
moderate, with most locations climbing to near normal to slightly
above normal values on Wednesday and Thursday. - Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  33  51  32  55 / 100  10  10  10
CTB  30  53  29  58 /  50  10  10   0
HLN  32  52  32  55 /  40  30  10  10
BZN  32  49  31  50 /  30  10  20  20
WEY  28  46  25  44 /  40  20  20  20
DLN  30  46  26  47 /  40  10  10  10
HVR  36  54  34  59 /  20  10  10  10
LWT  33  48  32  51 /  30  20  20  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until midnight MDT tonight above 5500
feet for Beaverhead...Gallatin...Madison...Meagher.

Winter Weather Advisory until midnight MDT tonight above 4500
feet for Broadwater...Cascade...Central and Southern Lewis and
Clark...Fergus...Jefferson...Judith Basin.

&&

$$

weather.gov/greatfalls



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