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793
FXUS65 KTFX 232030
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
230 PM MDT Wed May 23 2018

.SYNOPSIS...

Showers and thunderstorms over the region will gradually diminish
overnight as low pressure aloft moves eastward. Afternoon high
temperatures will be well above seasonal averages Thursday and
Friday. Scattered to numerous afternooon and evening showers and
thunderstorms can be expected in southwest portions of the state
but only isolated thunderstorms are expected in north-central
Montana.

&&

.DISCUSSION...

Tonight though Friday...Low pressure aloft will continue to move
eastward over Montana tonight. Showers and thunderstorms currently
over the forecast area will gradually diminish during the evening
hours as drier air begins to move in from the north. Upper level
ridge building west of the region will bring warming Thursday but
lingering moisture/instability as well as weak energy moving
around the upper level low in AB/SK will keep a threat for
afternoon/evening showers and thunderstorms, primarily over SW MT.
The upper level ridge shifts across the region Friday providing
the driest and warmest day of the period before conditions turn
more active again for the upcoming holiday weekend. Hoenisch/mpj

Friday night through Wednesday...Another upper level low will slowly
progress from the Great Basin area to the northeast in similar
fashion to the current situation. The first piece of energy to
eject out of the Great Basin low is forecast to track north
through Western MT Friday night, with the potential for showers
and thunderstorms primarily over western portions of the forecast
area, followed by more widespread chances for showers and
thunderstorms Saturday and Sunday across a larger portion of the
forecast area as flow aloft again turns the southeast and east.
Timing of the individual disturbances to impact the region this
weekend into early next week becomes increasingly difficult with
spread increasing among various models, but in any case,
precipitation will most likely be convective in nature and more
numerous during the afternoon and evening periods. At this point
Saturday holds the best potential for stronger thunderstorm
activity with models suggesting some pockets of moderate
instability and possible support from a weak upper jet and mid
level divergent flow. Various model solutions differ with how long
the upper low will linger over the western US into early/middle
portions of next week with details likely to improve in the coming
days. Hoenisch

&&

.AVIATION...
Updated 1821Z.

Low pressure aloft will continue moving eastward, spreading clouds,
showers, and isolated/scattered thunderstorms over the forecast
area. Precipitation, low clouds and areas of fog will produce
periods of IFR/MVFR conditions along with mountain obscurations
through 06Z Thursday. Thereafter, shower activity should decrease
from the west. Coulston/mpj

&&

.HYDROLOGY...

Overall pattern of warm temperatures (causing high mountain
snowmelt) with a chance of thunderstorms (some with heavy rain) will
continue a general rise in river and creek levels, especially across
central and southwest Montana. The following highlights are in
effect, but additional ones may be needed through Thursday:

Flood Warning for Big Hole River near Melrose - Above Minor flood
stage. Forecast maintains rise to just shy of Moderate flood stage
by Memorial Day (5/28).

Flood Warning for Jefferson River near Three Forks - At Minor flood
stage (as of 4 am Wednesday). Forecast maintains rise in level,
possibly reaching Moderate flood stage by this weekend, and
continuing to just shy of Major flood stage through Memorial Day
weekend.

Flood Watch for much of central and southwest Montana - Especially
for potential for Missouri River at Toston and Sun River near both
Simms and Vaughn to reach flood stage.
Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  52  78  53  82 /  30  20  10  10
CTB  50  77  51  82 /  10  10   0  10
HLN  49  77  52  81 /  30  20  20  30
BZN  47  74  47  79 /  50  30  40  20
WEY  40  63  36  70 /  50  30  50  10
DLN  46  71  44  76 /  50  50  40  30
HVR  53  81  54  85 /  50  20  10   0
LWT  49  74  50  79 /  80  30  10  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Thursday evening Beaverhead...Broadwater...
Cascade...Central and Southern Lewis and Clark...Eastern Teton...
Fergus...Gallatin...Jefferson...Judith Basin...Madison...
Meagher...Southern Rocky Mountain Front.

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

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

&&

$$

http://www.weather.gov/greatfalls