Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 231815
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1215 PM MDT Sat Mar 23 2024

...Aviation Section Updated...


.SYNOPSIS...

An impactful winter system remains on track to develop across the
region this afternoon, lasting into Sunday. Much colder than average
temperatures will linger into early next week before a warming trend
commences mid-week.

&&

.UPDATE...

The morning update has been published. Weak isentropic ascent
will continue to maintain patchy fog and some very light snow over
Central/North-central through early this afternoon. There are
also some snow showers creeping into Southwest Montana, though
slightly warmer temperatures and less ominous antecedent
conditions look to reduce the roadway impacts here. Later this
afternoon and evening bands of rain, snow, and even some
thunderstorms will move into the southwest. These areas will be
monitored for gusty winds and the potentiaL for brief, but intense
bursts of snow given mid -level lapse rate above 7.5C/km. Farther
north, snow will be more widespread and may become heavy at times
for northern areas this evening into tonight as an H700 vort max
slides southeastward through the plains. The northerly upslope
areas along the highway 200 corridor look to be most at risk for
heavier snow banding. No changes were made to the current winter
weather products, but will take another look for the afternoon
package. Otherwise, pops were raised for most areas through early
this afternoon and patchy fog was added for central/North-central
locations. Temperatures in the southwest are a tricky endeavor
today with warmer air progged, by most guidance, to briefly move
in before colder air wins out again this evening. Cloud cover and
northward moving precipitation will play a role on thinning out
the shallow cold layer in places like Dillon. I opted to lower
highs to the 40s for some of these areas, but overall confidence
is fairly low. - RCG


&&

.AVIATION...
1215 PM MDT Sat Mar 23 2024 (23/18Z TAF Period)

The main concern for this TAF period is precipitation affecting all
terminals during most of this TAF period. At the KEKS and KBZN
terminals this precipiation will begin as rain before transitioning
to snow Saturday evening. For all other temrinals the precipitation
will be all snow. Saturday night through early Sunday morning the
snow will heavy at times, reducing visbility down to LIFR levels.
There is fog reducing visbility to MVFR levels at the KGTF terminal.
This fog will dissipate in the next couple of hours. This afternoon
there is a slight chance (10%) of thunder in Southwestern Montana.
However there wasn`t enough support and confidence from models to
include thunder in the KEKS or KBZN TAFs. There will be mountain
obscuration through the duration of this TAF period. -IG

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

&&

.PREV DISCUSSION...
/ISSUED 333 AM MDT Sat Mar 23 2024/

This weekend...There is a lot to unpack across the region for this
weekend, the first being a band of snow shifting northeastward
across North-central Montana this morning. After a brief lull for
most this morning, another round of precipitation, mainly snow,
develops this afternoon and evening. Most areas will see entirely
snow, but across Southwest Montana valleys, rain may mix in at times
today before a cold front progresses southward, with perhaps a few
rumbles of thunder along and south of I-90. Widespread snow
slowly winds down Sunday before ending Sunday night. More details
below:

First, weak isentropic ascent and frontogenesis well ahead of an
approaching Pacific NW trough is allowing for mainly light snow
across the plains of North-central Montana early this morning.
Isentropic ascent will slowly weaken through the rest of the
night, allowing the band of snow to weaken. A Winter Weather
Advisory remains in effect until 6 AM this morning where an
additional inch of snow will be possible. Some lingering light
snow looks likely across the Hi-Line after 6 AM, but does not
look to be impactful enough at this time to warrant extending the
advisory a few more hours.

Next, the most impactful weather of the weekend will begin to
develop this afternoon and evening as the aforementioned Pacific NW
trough encroaches upon the region. Before the main period of snow
begins for most areas mid-afternoon today, another area of
isentropic ascent looks to kick off across the western portions
of the plains late this morning and early afternoon. Overall, snow
amounts here do not look to be much higher than across other
areas, the main impact is simply that snow will start earlier.
Winter Weather Advisories here begin a few hours before the rest
of the advisories and warnings kick in across the region. Ascent
associated with the approaching trough will result in snow
developing across the region this afternoon for most areas. The
caveat will be for across portions of Southwest Montana, where
warmer near-surface air ahead of a southward advancing cold front
will result in rain for a few hours in the afternoon. Cooling
aloft will also result in sufficient lapse rates for a few rumbles
of thunder across Southwest Montana this afternoon and evening.
As this more convective type of precipitation intersects colder
temperatures near the surface, intense bursts of snow will be
possible late this afternoon and evening across primarily
Southwest Montana, but into Central Montana as well.

Given easterly low level flow, areas east of terrain across the
plains look to be most favored for the heaviest snow over an
extended period, with timing for the heaviest rates looking to be
this evening and overnight into Sunday morning. Elsewhere the
duration of greater snow rates appears to be more narrow, lasting
for a few hours or so. Given the lower confidence in a more
prolonged period of greater impacts, most areas will remain in the
Winter Weather Advisory, with Winter Storm Warnings in place
across eastern portions of the plains. Most snow looks to end
Sunday afternoon and evening, but a lagging upper level wave will
allow for lingering light snow Sunday night.

Next week... Broad troughing looks to remain in place across much of
the Central CONUS, putting the region under an unsettled
northwesterly flow aloft Monday and Tuesday. Chances for light
precipitation will be around, mostly in the mountains.

Ensembles favor a brief period of upper level ridging mid-week
before another Pacific NW trough approaches the Northern Rockies
Thursday and Friday. Temperatures look to trend to near or
perhaps a touch above average Wednesday and Thursday, with
Wednesday looking like the best day to stay dry. More precipitation
looks to move in late week as broad troughing returns to the western
CONUS. Precipitation type at lower elevations looks to be tied to
timing, i.e either daytime rain or nighttime snow. Hence confidence
with respect to precipitation type/amounts remains low at this time.
-AM

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  30  15  23  10 /  80 100  80  40
CTB  24  13  21   6 /  90  90  70  20
HLN  39  19  27  15 /  70  90  60  30
BZN  45  19  30   8 /  90  90  70  20
WYS  44  21  31   2 /  80  90  70  10
DLN  48  23  32  17 /  80  80  60  20
HVR  25  12  22   7 /  80 100  80  30
LWT  31  11  19   5 /  60 100  90  60

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM MDT Sunday for East Glacier
Park Region-Eastern Glacier, Western Toole, and Central Pondera-
Eastern Pondera and Eastern Teton-Eastern Toole and Liberty-Hill
County-Northern High Plains-Southern High Plains-Southern Rocky
Mountain Front.

Winter Storm Warning from 3 PM this afternoon to midnight MDT
Sunday night for Bears Paw Mountains and Southern Blaine-Fergus
County below 4500ft-Northern Blaine County-Snowy and Judith
Mountains.

Winter Weather Advisory from 3 PM this afternoon to 6 PM MDT
Sunday for Beaverhead and Western Madison below 6000ft-Big Belt,
Bridger and Castle Mountains-Canyon Ferry Area-Cascade County
below 5000ft-Elkhorn and Boulder Mountains-Gallatin Valley-
Gallatin and Madison County Mountains and Centennial Mountains-
Gates of the Mountains-Helena Valley-Judith Basin County and
Judith Gap-Little Belt and Highwood Mountains-Madison River
Valley-Meagher County Valleys-Missouri Headwaters-Northwest
Beaverhead County-Ruby Mountains and Southern Beaverhead
Mountains-Upper Blackfoot and MacDonald Pass-Western and Central
Chouteau County.

&&

$$

http://www.weather.gov/greatfalls


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