Area Forecast Discussion
Issued by NWS Great Falls, MT

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360
FXUS65 KTFX 180409
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1009 PM MDT Tue Apr 17 2018

.UPDATE...

No update to current forecast, as it is trending well. Have only
updated hourly data to reflect current trends.
Brusda/Coulston

&&

.SYNOPSIS...

Upper level high pressure ridge builds over Montana tonight
through Thursday for slightly warmer temperatures and generally
dry conditions. However, an isolated shower or two can not be
ruled out over the mountains tonight and Wednesday. A better
chance for showers, or possibly a thunderstorm, can be expected
in southwest Montana Thursday while central and northern portions
of the state should remain dry.


&&

.AVIATION...
Updated 2325Z.

VFR conditions are expected across Central and southwest Montana.
West winds will gust over 30 kts at times before diminishing into
the evening. Some isolated showers are possible over Southwest
Montana into the early evening causing local MVFR
conditions...before skies clear overnight. Wednesday looks to have
VFR conditions. db

&&

.HYDROLOGY...
Updated 315 AM Tuesday (4/17).

Flood advisories for lowland snowmelt flooding continue for much of
north-central Montana. The greatest area of concern continues to be
along the Hi-Line east of Liberty County, where snow analyses
indicate 2 to 4 inches of snow-water equivalent remains. Gradually
warming temperatures with plenty of strong spring sun this week will
continue to melt the snow, likely continuing or possibly increasing
flooding coverage.

This snowmelt runoff will also persist in moving into primary
drainages, continuing or possibly expanding areas of river flooding
along the Hi-Line. Flood Warnings will continue at least through the
next few days for Big Sandy Creek near Havre (Moderate flooding)
and the Milk River near Harlem (currently approaching Moderate
flooding). The level of Battle Creek near Chinook fell from
Moderate flood stage Monday morning to Minor flood stage by Monday
evening, and it is holding steady there currently. Will keep the
Flood warning going there until the River Forecast Center comes
out with an updated forecast. Also of note, Fresno Reservoir has
almost filled up and water releases have increased. This will
likely cause the Milk River to rise further downstream of the dam
over the next week or so. The main concern from this will be the
river gauge point near Havre, which is already approaching Action
stage.

River/creek levels will continue to be closely monitored in case any
additional river flood warnings are required.

&&

.PREV DISCUSSION...
/ISSUED 525 PM MDT Tue Apr 17 2018/

Tonight through Thursday...Isolated to scattered showers are
possible this evening from residual moisture left over from
Monday`s precipitation. However, a building shortwave ridge over
the region is expected to bring warming temperatures and mostly
dry conditions to much of Montana on Wednesday but can not rule
out an isolated shower over the mountains. The ridge will be
nudged eastward Wednesday night into Thursday as a strong upper
level low drops southward along the West Coast then moves inland
to the Four Corners Region of the southwest USA. This system is
expected to bring some moisture into southwest Montana for a
chance of rain/snow and possibly a thunderstorm or two Thursday
afternoon. Surface winds through the short term period or expected
to be generally light to breezy with isolated stronger gusts
possible during the afternoon hours each day.

Thursday Night through Tuesday...The model forecasts have been in
good agreement among each other and from run to run, adding to the
confidence in the solution for this time period. A low pressure
system will move east across the southwestern United States Thursday
night through Friday night, while high pressure aloft to the north
of this system keeps the TFX forecast area dry with above normal
temperatures. A shortwave trough will then move a Pacific cold front
through the area Saturday into Saturday night. This will bring a
good chance of light snow showers to the mountains, but there will
be only a slight chance of rain showers associated with the frontal
passage at lower elevations. Gusty west winds will spread east over
the area in the wake of the front Saturday afternoon and evening,
which will cool temperatures closer to normal by Sunday and continue
the chance of mountain snow showers. Although this will be a fairly
quick period of stronger winds, it will need to be monitored for
possible high wind highlights. A disturbance on the back side of the
shortwave trough will bring another chance of rain and snow showers
to the area Sunday night through Monday night. Models begin to
differ somewhat in their solutions Monday night into Tuesday. The
ECMWF/Canadian models move weak high pressure in the area, but the
GFS quickly brings an increasingly moist southwest flow in the wake
of the disturbance. Until the details get sorted out, will go with a
broad-brushed chance of showers with near normal temperatures,
similar to what the consensus model blend depicts.
Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  30  51  30  55 /  10   0   0  10
CTB  29  47  28  50 /  10  10  10  10
HLN  30  50  30  56 /  10   0  10  10
BZN  23  49  28  53 /  10  10  10  20
WEY  15  40  21  46 /  10   0   0  30
DLN  23  46  28  51 /  10  10  10  20
HVR  29  48  29  50 /  10  10  10  10
LWT  27  48  30  53 /  20  10  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

Flood Warning in effect until further notice
for Big Sandy Creek near Havre.

Flood Warning in effect until further notice
for Milk River near Havre.

Flood Warning in effect until further notice
for Lodge Creek near Havre.

Flood Warning in effect until further notice
for Battle Creek near Chinook.

Flood Warning in effect until further notice
for Milk River near Harlem.

Areal Flood Warning in effect until 815 PM MDT Sunday
for Hill...Blaine Counties.

Areal Flood Advisory in effect until 345 PM MDT Wednesday
for Glacier County.

Areal Flood Advisory in effect until 815 AM MDT Thursday
for Teton County.

Areal Flood Advisory in effect until 830 PM MDT Thursday
for Liberty County.

Areal Flood Advisory in effect until 715 AM MDT Friday
for Fergus County.

Areal Flood Advisory in effect until Noon MDT Friday
for Eastern Pondera...Southern Toole Counties.


&&

$$

http://www.weather.gov/greatfalls



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