Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 220546

Area Forecast Discussion
National Weather Service Great Falls MT
1145 PM MDT Thu Mar 21 2019

Aviation and Hydrology sections updated

Mild conditions continue through Friday, however, mid to upper level
clouds will begin to drift north on Friday. Scattered rain and
mountain snow showers begin to develop over the Southwest Friday
night into Saturday. A cooling trend with more widespread
precipitation is expected this weekend.


Mainly focused on updating Max and Min temperatures for this evening
and overnight into tomorrow morning, as well as fog development
across the region. Focused on the Helena valley for fog, having the
highest confidence given the persistence of fog over the past few
nights/mornings. Also brought patchy fog chances to Havre, Cut Bank,
and Bozeman again for tonight into tomorrow morning, even though
there is lower confidence for fog development in those areas. A
Flood Advisory was issued this evening after receiving reports from
local law enforcement of roads being impacted by minor flooding in
judith Basin and Fergus Counties. -TP


Updated 1140 PM MDT Thur Mar 21 2019 Main concern tonight is fog
redeveloping around sunrise Friday. Helena is the most likely
location to have dense fog for a few hours after 12z, with
increasing clouds over Bozeman it is looking less likely to be
dense. Some fog possible in Cut Bank/Havre, but winds are limiting
the confidence for dense fog in those areas. Otherwise, expect
increasing clouds over the region on Friday afternoon/evening with
scattered showers developing south of Bozeman by Friday evening.


Flood watch issued for Clear Creek south of Chinook. Latest forecast
brings the river near flood stage on Friday. This should be a short
event, as cooler temperatures expected over the weekend and the snow
pack continues to melt.

A Flood Advisory has been issued for Judith Basin and Fergus
Counties given reports of minor flooding over some roadways in the
area. As overnight temperatures drop below freezing and the water
begins to freeze, slippery roads may lead to difficult and dangerous
travel conditions. Expect runoff to increase though again during the
daylight hours for both Fri/Sat in this area.

Watching the storm system for the weekend, with the potential up to
0.50 inches qpf over Southwest MT. Flood highlights might be needed
for portions of Southwest MT.


/ISSUED 538 PM MDT Thu Mar 21 2019/

Rest of this afternoon through Friday night...upper level low was
over Southern California as of this afternoon and continues to
undercut the ridge that extends northwest from the Texas Gulf
Coast to the Yukon/Northwest Territories in Canada. Moisture from
the Gulf of Mexico will continue to stream northwest within the
southeast flow aloft, which will lead to increasing cloud cover
(especially in the mid- to upper levels) from south to north
across the region through the day on Friday. Mild temperatures
will continue on Friday across the region, with possibly some
patchy fog being possible in valleys/river valleys Friday morning.

Saturday and Sunday...Temperatures trend cooler through the weekend
with periods of rain and snow developing as a series of shortwaves
move across the Pacific northwest. Sunday appears to be the more
impactful day in terms of rain and accumulating mountain snow. An
upper level shortwave lifting northeastward will interact with a
surface cold front moving south beginning early Sunday morning and
continuing through the day. There are some details that still need
to be worked out in terms of where the heaviest precipitation will
fall but at this time the focus appears to be along the Continental
Divide, parts of the southwest, and along the Hi-Line where liquid
precipitation totals are currently forecast to roughly fall in the
1 to .35 inch range with locally higher amounts possible. Any rain
that does fall on remaining snow cover over the plains and valleys
could enhance runoff issues associated with ponding water. Snow may
mix with the rain or become all snow at times in the valleys and
plains especially at night but snow accumulations over these areas
should be minimal with most locations receiving less than an inch.
Mountain areas may see accumulations up to 6 inches.

Monday through Thursday...Drier conditions briefly return on Monday
as a transient ridge crosses the region. Model solutions diverge
into next week, but in general support seasonally average
temperatures with periods of rain and snow as a series of Pacific
systems move through.


GTF  26  46  30  49 /   0   0  10  10
CTB  25  49  30  51 /   0   0   0  10
HLN  18  46  24  46 /   0   0  10  10
BZN  16  45  21  45 /   0  10  10  20
WEY  17  46  22  45 /   0  30  40  50
DLN  20  44  24  42 /   0  10  50  30
HVR  23  48  26  50 /  10  10  10   0
LWT  26  52  30  51 /   0   0   0  10



Flood Advisory - Judith Basin and Fergus Counties.

Flood Watch - Chinook Creek


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