Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 240214

Area Forecast Discussion
National Weather Service Great Falls MT
814 PM MDT Mon Apr 23 2018


Most of the forecast through tomorrow morning was left unchanged.
One adjustment was to scale-back POPs to have fair weather for
our entire CWA by tomorrow morning. This is based on the
expectation of any lingering rain and/or snow showers dissipating
this evening as the atmosphere stabilizes in response to nocturnal
cooling and a building high pressure ridge. The only other change
was to add patchy fog to the grids across southwest and central
MT. See the previous discussion for more details on the fog
potential. Any fog that does develop will likely dissipate by late
morning on Tuesday.



Rain and snow that impacted areas from Helena to Lewistown and
points south will push east this afternoon, leaving clearing skies
and cooler temperatures in its wake overnight. Some fog is likely
tonight as well. Beyond today, generally mild and dry conditions
are expected.


Updated 2302Z.

Mainly VFR expected next 24-hours. However, widespread VFR to MVFR
CIGS, associated mountain obscuration, and isolated rain and/or snow
showers over SW MT will likely exit the region to the southeast
between 00Z/Tue and 09Z/Tue as the latest storm system exits MT to
the southeast. However, clearing skies, light surface winds, and
residual moisture behind this system may allow fog to develop
between 04Z/Tue and 15Z/Tue in the valleys of SW MT and along some
of the central MT plains. This includes KBZN/KEKS/KLWT.


/ISSUED 304 PM MDT Mon Apr 23 2018/

A compact, but well-defined, spring storm system continues to push
east through Montana at this time. The band of rain and snow that
impacted areas from Helena to Lewistown and points south continues
to push east, with improving conditions noted on area webcams. As
this system pulls away, clouds will clear out tonight allowing for
widespread sub-freezing temperatures. Clearing skies plus the recent
moisture from precipitation and, in some cases, flooded grounds will
allow areas of fog to develop tonight. This will be monitored in
case any dense fog products are necessary.

After tonight, the threat of high-impact weather will decrease for
several days as upper level ridging builds in. Of note, though, a
shortwave will dive SE out of Canada mid-week looks to have enough
moisture/instability to produce some diurnally-driven showers.
Towards the end of the week, ridging re-builds, likely allowing the
first widespread 70s to near 80 temperatures locally.

By the weekend, a moist, SW flow aloft may develop as another large
upper level low shifts inland off the Pacific. This setup appears
favorable for at least some increase in the risk of showers/storms,
some of which could be strong. As this upper low moves inland, a
more unsettled, and potentially cooler, pattern may develop.



Updated 300 PM April 23

River flooding continues along the Milk River Valley. Flooding
concerns may increase across SW MT and areas adjacent to the Rocky
Mountain Front through the week.

Rivers in our forecast area are cresting now, or have crested,
along the Milk River Valley. This trend continues this week. It
must be stressed, though, that fields, yards, pastures, etc will
remain water logged for some time, even after the rivers/creeks
fall. In some cases, the water could remain around for a couple of

With increasing temperatures this week, attention will then turn
towards increasing snowmelt coming out of the Rockies and how that
will impact not only mainstem rivers, but also creeks/streams
coming out of the mountains (as has already been an issue in parts
of Madison County). Please continue to monitor river forecasts in
this area as well as any ongoing or future flood products through
the week.


GTF  30  63  38  64 /  10   0   0  10
CTB  29  65  35  58 /   0   0   0  20
HLN  28  58  33  67 /  20   0   0  10
BZN  23  52  28  65 /  40   0   0  10
WEY  19  47  21  54 /  30   0   0   0
DLN  26  53  29  65 /  30   0   0   0
HVR  30  64  36  64 /   0   0   0  10
LWT  27  55  33  65 /  30   0   0  10



Flood highlights continue for portions of North-Central and
Southwest MT.


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