Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 250603
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1202 AM MDT Mon May 25 2020

...AVIATION SECTION UPDATED...

.SYNOPSIS...

Isolated light showers over Central and North-central areas are
expected to diminish this evening. After some patchy fog Monday
morning, it should be near to slightly above normal and mostly dry
across the state for the Memorial Day holiday, though a few
showers could sneak into northwest Montana in the later afternoon
hours. A few mainly mountain showers may persist into Tuesday,
with dry and increasingly warm conditions through the rest of the
week.

&&

.UPDATE...

The evening update has been published. The isolated light showers
east and southeast of Great Falls are expected to diminish and
end by 6Z. With clearing skies, there could be some patchy fog
development over the eastern portion of Central/North-central
Montana and portions of Gallatin County, particularly the West
Yellowstone area. The next system is due in by tomorrow evening
and will initially bring breezy conditions and increasing clouds
for the Memorial Day Holiday but any precipitation should hold
off until the evening and overnight hours. Not expecting much QPF
with this system but there are some model uncertainties in terms
of coverage that the midnight shift will look at tonight. RCG

&&

.AVIATION...
Updated 1200 AM MDT Mon May 25 2020 (25/06Z TAF Period)

VFR conditions are noted across the area, though some scattered low
to mid-level clouds linger across parts of SW and central MT early
tonight. However, mainly clear skies are expected across the area
overnight into tomorrow morning. Mid and high cloud shield will
build back in from the west Mon afternoon, with a low-VFR overcast
between 3000 and 6000 feet expected across the area Mon evening and
overnight. Showers are possible across central and SW MT between 00z
and 06z Mon night, but any precip was kept to PROB30 groups as
coverage may be limited, and mainly in the mountains. -Kredensor

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

&&

.PREV DISCUSSION...
/ISSUED 156 PM MDT Sun May 24 2020/

Rest of This Afternoon and Tonight...

An upper level low currently centered along the Wyoming/Montana
border southeast of Billings will continue to slowly shift east and
northeast through tonight across SE MT over the next 24 hours. As it
does so, isolated to widely scattered showers and a few weak
thunderstorms will impact much of eastern parts of north-central and
central Montana, but an isolated shower can not be totally ruled out
over nearly all of the forecast area. As the core of the upper low
shifts far enough to the east this evening, precip chances should
quickly drop off this evening, and clear completely overnight. Clear
skies are also expected overnight as a shortwave ridge builds across
the CWA. As of now, using MAV/MET guidance for RH values I felt
comfortable and upper ridging overhead I put some patchy to areas of
fog in the grids over fog-prone parts of the area, particularly
Meagher County in the upper Smith River Valley.

Memorial Day through Tuesday...

It should remain dry through the afternoon hours for the Memorial
Day holiday, with highs at lower elevations mainly from the mid-60s
to the mid-70s. Brilliant sunshine in the morning will yield to
increasing high clouds in the afternoon as a shortwave trough works
in from the west and flattens the ridge, bringing some moisture to
the area. A few showers can`t be ruled out Monday afternoon in the
higher terrain along the Divide north of Lincoln.
The deeper moisture bringing lowering clouds and and some more
widespread drizzle or shower chances should hold off until around
sunset for most of north-central and SW MT. Even so, the bulk of
precip should remain in the mountains, and perhaps some of the high
valleys of SW MT. A second, weaker shortwave may pass through during
the day Tue, which could keep mainly mountain shower chances going
through Tue afternoon. Highs Tuesday should push into the 70s for
most locations, especially across north-central MT where daytime
cloud cover is forecast to be lesser. -Kredensor

Tuesday night through next Sunday... Zonal flow will persist Tue
night into Wed morning. While general clearing and drying are
expected, some models are hinting at some precip across SW MT during
the day Wed. However, models broadly agree that ridging will start
to build into SW MT Wed afternoon and evening, which may allow for
the valleys of SW MT from Helena southward to get into the lower
80s, while north-central MT stays in the 70s. Ridging is expected to
strengthen across the northern Rockies later this week into the
weekend, allowing for mainly dry conditions, though a few stray
mountain showers can`t be ruled out Thu or Fri. Highs are forecast
to be in the upper 70s to mid-80s on Thu, and in the 80s to near 90
Fri and Sat. There are some hints of a disturbance moving northeast
through the NW side of the ridge later Sat into Sun, possibly
bringing precip to the CWA, but confidence is pretty low on that at
this time, so POPs were kept on the lower side for now. -Kredensor

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  41  71  49  73 /  10   0  20   0
CTB  42  68  46  70 /   0  10  10  10
HLN  41  72  50  75 /   0  10  30  20
BZN  37  71  48  73 /  10   0  30  20
WYS  29  61  37  64 /  20   0  20  30
DLN  37  69  48  71 /   0   0  20  20
HVR  45  74  50  76 /   0   0  10  10
LWT  40  68  47  70 /  10   0  20  10

&&

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

$$

http://www.weather.gov/greatfalls



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