Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 211440
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
840 AM MDT Mon Sep 21 2020

.UPDATE...
Forecast remains on track for this week, with warmer and drier
conditions expected through mid-week, then a brief cool down
overnight Tuesday into Wednesday morning. Little to no updates
were made to the forecast this morning, other than bumping up
current temperatures over parts of northcentral Montana this
morning.

&&

.SYNOPSIS...
Dry, warm, and breezy conditions prevail across the region on
Monday. On Tuesday, a disturbance aloft brings a weak cold front
into north central Montana with a few showers expected over the
Glacier Park region. Another weather system affects the region
Wednesday and Thursday for increasingly strong and gusty winds
across north central Montana. Numerous showers can be expected
along the Continental Divide and the Rocky Mountain Front with
this stronger system.

&&

.AVIATION...
545 AM MDT Mon Sep 21 2020 (21/12Z TAF Period)

West to southwest flow aloft prevails today through Tuesday morning
with scattered to broken high clouds moving over the forecast area.
Breezy and occasionally gusty surface winds will develop across the
region by 18Z and continue through 02Z Tuesday. Widespread VFR
conditions will prevail through the forecast period. mpj

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.

NOTE: Amendments not scheduled for Ennis (KEKS) due to ongoing
runway closure.

&&

.FIRE WEATHER...

High pressure aloft will then help warm temperatures back above
normal through mid-week, which will cause afternoon humidity to
fall into the 20 to 25 percent range in some areas. Winds will be
fairly light during this period, but there is a potential for
strong westerly winds to return Wednesday night into Thursday
ahead of the next possible precipitating system, so there is a
chance for near-critical fire weather conditions during that time
period. There is some uncertainty as to just how strong those
winds could be, so will continue to monitor the situation for now.

&&

.PREV DISCUSSION...
/ISSUED 545 AM MDT Mon Sep 21 2020/

The upper level trough that brought areas of precipitation and
gusty winds to the forecast area over the weekend moves eastward
today. Dry, warm, and breezy conditions prevail this afternoon
with variable high clouds moving through the region expected to
produce a Chinook Arch along the Rocky Mountain Front. A weak
disturbance aloft brings a surface cold front through northern
portions of the Great Falls forecast area on Tuesday with winds
becoming north-northwesterly across much of north central Montana.
This system will be generally dry except for some scattered
showers over the mountains of Glacier Park and possibly the
adjacent plains of western Glacier and Pondera Counties. Generally
quiet conditions can then be expected Tuesday night before a
stronger system approaches the region on Wednesday. This system
appears to be what would normally be considered "seasonal" for
early Autumn with increasingly gusty southerly surface winds
ahead of a surface cold front bringing warm temperatures for
Wednesday afternoon. Winds aloft veer to the west Wednesday night
with abundant Pacific moisture bringing widespread precipitation
to western Montana and over the Continental Divide due to
orographic lift. Locations east of the Divide will see strong
downslope winds develop that will limit precipitation over the
plains to the western half of the CWA. At this time the big
question will be whether or not highlights will be needed for High
Winds and/or Fire Weather concerns. If the proper conditions
materialize, it appears that the most likely time frame will be
Wednesday afternoon through Thursday afternoon. RH will be lower
on Wednesday, but winds could be stronger on Thursday. For now we
will be watching forecast trends as new model runs zero in on the
situation.

Friday and Saturday will see the upper level trough gradually
move eastward through the region with winds aloft becoming more
northwesterly. This will allow scattered showers to spread
across much of the forecast area with temperatures expected to be
near or below seasonal averages. Model ensembles and the NBM then
appear to favor northwesterly flow aloft for Sunday and Monday
with temperatures rebounding back into the mid to upper 70s for
highs. At this time these models also favor mostly dry conditions
for much of the forecast area. However, isolated showers over the
western mountains should not be ruled out. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  75  44  72  45 /   0   0  10   0
CTB  70  45  68  43 /   0   0  10   0
HLN  75  43  75  45 /   0   0  10   0
BZN  76  42  79  42 /   0   0  10  10
WYS  69  30  73  30 /   0   0  10  10
DLN  73  41  75  43 /   0   0   0   0
HVR  74  45  75  44 /   0   0   0   0
LWT  74  45  77  44 /   0   0  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

http://www.weather.gov/greatfalls



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