Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 200422
AFDGGW

Area Forecast Discussion
National Weather Service GLASGOW MT
922 PM MST Sun Feb 19 2017

.SHORT TERM...for northeast Montana...tonight through Tue...
Update...

The forecast remains on track tonight with dense fog and ice jam
flooding the primary threats. A few minor tweaks to winds and
minimum temperatures were made to the overnight period, but
otherwise will let things ride for now. Maliawco

Previous Discussion...

A westerly to southwesterly flow aloft will prevail through
Tuesday. A weak shortwave trough is expected to move across the
area tonight, bringing a slight chance of precipitation from the
west and south. The latest GFS model output keeps this mainly
along the North Dakota border, where other models keep this more
over our western and southern areas...so decided to leave a
slight chance in for both regions. Either way...as this spreads
north and east overnight, temperatures in the far northeast corner
of the state will likely get cold enough to see a wintry mix of
precipitation. With light winds expected across the area overnight,
areas of fog are also a potential concern, especially near river
valleys over the eastern part of the CWA.

Monday and Tuesday...Temperatures will again be above normal as a
ridge moves across northeast Montana. A stronger embedded shortwave
is anticipated to move across the region Tuesday, bringing
another chance of precipitation to the area. This may start out as
wintry precipitation in the morning along and north of Highway 2,
but should transition to rain area-wide throughout the day.
Accumulations are currently expected to be less than a tenth of an
inch.

Hickford



.LONG TERM...Tue night through Sun...

Main forecast challenges in the extended period now revolve
around the increased chances for precipitation amid colder
temperatures after the middle of the week.

Models have now begun to line up showing some banded
precipitation, especially across our northern zones late Tuesday
night, then through our central and southern zones Wednesday
afternoon through Thursday.

Daily fluctuations between day warm and night cold will bring
changeovers between rain and snow each day. Some accumulation is
possible. At this time, expecting 2-4 inches of snow near the
Little Rockies / Zortman area.

Beginning Thursday, temperatures will struggle to reach above
freezing as the cold air mass from the Canadian Rockies sweeps
down through our region.

BMickelson
Previous long term discussion: A shortwave trough moves through
Eastern Montana Tuesday Night and drops a cold front south through
the area. Models have differences in track of the surface low
with GFS and NAM along the Canadian border while the ECMWF well to
the south in SE Montana and into South Dakota. Either way, it
looks like there will a good chance of either rain early and snow
late north of the Missouri River.

The cold front becomes quasi-stationary south of the forecast area
during the day and Wednesday and both the GFS and ECMWF want to
develop an area of overrunning precipitation but in different
locations of the forecast area. Temperatures will be borderline
for rain vs snow. Will mention a chance of rain and snow over
most of the region with the best chance in the north.

Upper trough moves inland from the Pacific on Wednesday and into
the Central and Northern Rockies on Thursday. The surface low
tracks well to the south across Colorado and Kansas which will
keep most of the precipitation to the south of the forecast area
with this system. However, flow aloft becomes split with this
system on Thursday and models are hinting at a northern stream
wave that could bring a chance of snow into Northeast Montana.

Friday is expected to be mainly dry and colder with temperatures
closer to normal with the forecast area between systems.

A shortwave trough in NW flow aloft moves through the area on
Saturday. There could be enough moisture for a slight chance of
snow. Another wave late Sunday could bring a slight chance of
snow.

Forrester



&&

.AVIATION...

Flight Category: LIFR for KGGW and KOLF. VFR for KGDV and KSDY
with isolated IFR through 15Z.

Synopsis: Lingering low clouds and fog seem likely to persist
through the overnight hours, especially across the lower elevation
area in our NE portion of our CWA. KGGW and KOLF will likely be
impacted more than KSDY and KGDV.

Winds: Light and variable winds tonight will set up from the west
at 5 to 10.

BMickelson/Proton


&&

.HYDROLOGY...

Ice Jam was detected just south of Glendive on the Yellowstone
river this afternoon. River levels measured at Glendive show a
steady, however slow uptick in river levels as the 5 mile long ice
jam moves downstream into Glendive. River is still 5 feet below
flood stage at 8pm.

A ice jam has formed at the highway 24 bridge over the Milk River
downstream of Glasgow earlier today and remains in place. The Milk
River continues to very slowly rise, and remains 5 feet below
flood stage as of 5pm this afternoon.

The big muddy river in Sheridan county near Antelope continues to
rise with a 4 foot increase in river levels noted so far today and
remains 4 feet below flood stage.

Warmer than normal weather will continue for another 48 hours for
the region that will continue to add more water into the river
systems and add to any flooding issues.

A flood watch is in effect for Prairie, Dawson, and Richland
counties along the Yellowstone River for ice jam flooding through
Tuesday afternoon.

A flood watch is in effect for Sheridan county for the big muddy
river through Tuesday afternoon.

A flood watch is in effect for Valley county for areas along the
Milk River downstream from Hinsdale to the confluence of the
Missouri River through Tuesday afternoon.

Proton


&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 8 AM MST Monday for Central and
Southern Valley...Daniels...Eastern Roosevelt...Northern
Valley...Sheridan...Western Roosevelt.

Flood Watch through Tuesday afternoon for Central and Southern
Valley...Dawson...Prairie...Richland...Sheridan.

&&

$$

weather.gov/glasgow



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