Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 250545
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1145 PM MDT Thu May 24 2018

...UPDATED AVIATION...

.UPDATE...
Updated forecast is out. Only adjustment this evening was to add a
few thunderstorms in the Havre/Harlem areas until about Midnight.
Scattered showers/thunderstorms will gradually diminish over
Southwest MT after Midnight as well. Patchy fog is possible in the
West Yellowstone area towards morning. The rest of the forecast is
on track. Brusda

&&

.SYNOPSIS...
A weak weather disturbance and lingering moisture will result in
scattered showers and a few thunderstorms over southwest Montana
this evening. However, warmer and drier conditions are expected on
Friday. Showers and thunderstorms will increase across western
portions of Montana late Friday with more widespread and potentially
severe thunderstorms expected Saturday.

&&

.AVIATION...
Updated 0600Z.

Mainly clear skies and VFR conditions are expected for the rest of
tonight into Friday morning. Partly cloudy skies will then return
for Friday afternoon and evening...with mainly VFR conditions
still expected. Some isolated thunderstorms are possible across
western and southwestern portions after 00z_Saturday. Still mainly
expecting mountain thunderstorms...although KHLN to KBZN to KEKS
could see a brief thunderstorm with gusty winds. Only KHLN had enough
confidence to include in the forecast at this time. Anglin

&&

.HYDROLOGY...
Adjustments today...additional showers and thunderstorm activity
should be light through Friday so the immediate threat for rapid
minor flooding has lessened. However, snowmelt continues to fuel
rises on many of the mainstem rivers. Flood Watches have been
upgraded to warnings for the Missouri River at Toston and the
Gallatin River near Logan. Flood watch for the Sun River near
Simms begins this weekend.

Current Highlights:

Flood Watch from Saturday evening through Tuesday afternoon for the
Sun River in Cascade County.

Small stream flood advisory for Meagher County until 615 PM Friday.

Flood Warning in effect until 300 PM MDT Sunday for the Big Hole
River near Melrose in Beaverhead and Madison Counties.

Flood Warning in effect until 145 AM MDT Monday for the Jefferson
River near Three Forks.

Flood Warning in effect until 1000 PM MDT Saturday for the Missouri
River near Toston in Broadwater County.

Flood Warning in effect until 1015 PM MDT Saturday for the Gallatin
River near Logan.

&&

.PREV DISCUSSION...
/ISSUED 600 PM MDT Thu May 24 2018/
Tonight and Friday...Upper level ridge continues to build over the
Pacific NW tonight, then shifts eastward across the Northern Rockies
and Montana on Friday. Only isolated showers or possibly a
thunderstorm can be expected over north-central and Central Montana
late this afternoon through this evening, but scattered to numerous
showers and a few thunderstorms can be expected in far southwest
Montana. Friday still looks to be the warmest and driest of the next
several days with most lower elevation sites seeing afternoon
temperatures approach or exceed 80 degrees. Hoenisch/mpj

Friday night through Saturday night...Pacific shortwave energy
undercutting the upper ridge into CA Friday night carves out
another closed low over the great Basin this weekend, which is
slow to lift out to the NE through early next week. The first
piece of energy lifts north out of the Great Basin across the
Northern Rockies Friday night, bringing a chance of evening and
overnight convection, primarily to western portions of the
forecast area. Saturday still looks to have the greatest potential
for more widespread and potentially severe thunderstorm activity
as a surface trough shifts eastward across the region under moist
and unstable southerly flow aloft. Timing and location of the
surface trough will be critical to the location of any severe
thunderstorms activity with latest models continuing to suggest
eastern portions of the forecast area will have the best
potential from mid afternoon through the evening.

Sunday through Thursday...The Great Basin upper level low slowly
trudges east-northeast Sunday and Monday for continued mostly
diurnal showers and thunderstorms. Latest models suggest deepest
moisture and greatest coverage of precipitation will be focused
over southern and eastern portions of MT with some potential for
drier air to move into northern portions of the forecast area
which would help limit the coverage of precipitation there. Models
spread increases with the eventual exit of the upper level low
through the middle of next week and arrival of the next upstream
trough. Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  52  82  54  81 /   0   0  30  50
CTB  51  81  52  76 /   0   0  20  50
HLN  51  80  53  79 /   0  20  40  60
BZN  47  78  48  78 /  20  20  20  50
WEY  37  71  38  69 /  50  10  10  30
DLN  44  75  45  73 /  30  40  30  50
HVR  55  84  55  85 /  20   0  10  40
LWT  50  77  52  79 /  10  10  10  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

Flood Watch from Saturday evening through Tuesday afternoon for the
Sun River in Cascade County.

Small stream flood advisory for Meagher County until 615 PM Friday.

Flood Warning in effect until 300 PM MDT Sunday for the Big Hole
River near Melrose in Beaverhead and Madison Counties.

Flood Warning in effect until 145 AM MDT Monday for the Jefferson
River near Three Forks.

Flood Warning in effect until 1000 PM MDT Saturday for the Missouri
River near Toston in Broadwater County.

Flood Warning in effect until 1015 PM MDT Saturday for the Gallatin
River near Logan.

&&

$$

http://www.weather.gov/greatfalls


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