Area Forecast Discussion
Issued by NWS Great Falls, MT

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS65 KTFX 212315
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
515 PM MDT Mon May 21 2018

.UPDATE...

Made minor tweaks to PoPs/QPF and thunderstorm coverage through
the overnight, with no other significant changes.

&&

.SYNOPSIS...

A large low pressure system will bring widespread shower and
thunderstorms today through tonight. Brief heavy rain and
lightning will be the main concern for today. This low pressure
system then lingers across the area for Tuesday and again
Wednesday...continuing widespread chances for showers and
thunderstorms. Locally heavy precipitation will again be the main
threat with any thunderstorm. Temperatures will also be near to
slightly above normal...with highs in the 60s and 70s and lows in
the 40s and 50s.

&&

.AVIATION...
Updated 2315Z.

Thunderstorm activity diminishes this evening. However, shower
activity and perhaps an isolated thunderstorm or two may linger
through the night with plenty of moisture, lift, and instability.
MVFR to brief IFR conditions are possible with these lingering
showers. A brief break in activity is then possible for Tuesday
morning...returning VFR conditions. More showers and thunderstorms
are then expected by late Tuesday morning into Tuesday afternoon.

&&

.HYDROLOGY...

Flood Warning for Big Hole River (NW Madison/NW Beaverhead Counties)
through 3 pm MDT Monday (today): The river gauge reading near
Melrose has fallen somewhat Sunday night, but it remains just above
flood stage. The current forecast has it staying above flood stage
on Monday and rising to Moderate flood stage Thursday evening, where
it could remain into next week. Will therefore change the warning
wording to be Until Further Notice.

Flood Watch for the Jefferson River at Three Forks (along the
borders of Jefferson, Madison, Gallatin, and Broadwater Counties):
The river level has remained steady just below flood stage, but it
is forecast to exceed flood stage Monday evening, likely due to
snowmelt and shower/thunderstorm runoff, possibly reaching Major
flood stage on Thursday.

Additional locations may approach or exceed flood stage Tuesday or
Wednesday and may require further flood highlights if Monday
morning`s forecasts are consistent with those from Sunday night. We
are monitoring the Missouri headwaters area (including the Missouri
River near Toston and the Gallatin River near Logan) and the Sun
River (near Simms). Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  51  72  50  72 /  50  30  20  50
CTB  47  76  47  74 /  20  20  10  40
HLN  49  72  50  71 /  50  50  30  70
BZN  47  70  48  66 /  50  50  40  80
WEY  33  65  38  57 /  30  40  50  80
DLN  43  69  45  65 /  50  30  40  70
HVR  53  78  52  77 /  20  30  10  40
LWT  49  69  48  65 /  60  70  40  80

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

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

Flood Watch from Tuesday morning through Friday afternoon
Broadwater...Gallatin...Jefferson...Madison.

&&

$$

http://www.weather.gov/greatfalls



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.