Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 230527 CCA

Area Forecast Discussion...corrected to add fog mention in update
National Weather Service Great Falls MT
1128 PM MDT Sat Sep 22 2018

Updated Aviation Discussion


Made some adjustments to the going forecast, mainly as a result
of the cool Canadian airmass over north central Montana. First,
temperatures appear to be cooling faster than expected, so have
lowered lows about 4 to 7 degrees. The larger drop in forecast
lows is along the Hi-Line (Sweetgrass Hills area, primarily),
where temperatures are already in the upper 30s. The northeast
winds from this airmass has also allowed some radar echoes to
develop already along the Rocky Mountain Front west and northwest
of Great Falls, so have moved up the rain development over the
plains (Great Falls to Havre) about 3 hours to begin around
midnight. The short range models continue to be aggressive with
the band of precipitation that develops, so have generally
increased the PoPs as well over the plains and in the central
valleys well into the likely range late tonight into Sunday
morning. Am also thinking that there may be enough lifting of
clouds along the northern Rocky Mountain Front area (including
Cut Bank) that patchy fog may form again tonight. There is also
a chance that low clouds from southern Alberta may advect south
into that same area after midnight.  Coulston



Generally dry conditions with increasing cloud cover can be
expected through the rest of today. A cold front will move across
the region late tonight through Sunday. This front will bring with
it chances for showers and cooler temperatures through Sunday.
Cool temperatures and scattered showers will then linger to start
the work week on Monday.


Updated 0000Z.

Precipitation development is likely to occur along an axis from
KHLN-KGTF-KHVR overnight with MVFR ceilings and Mtn obscuration also
increasing in these areas. Precipitation will sink south to affect
SW MT terminals Sunday morning through early afternoon with
improving conditions to the north. With upper trough axis over the
region Sunday afternoon scattered showers are possible and an
isolated thunderstorm cannot be ruled out. Light and variable winds
tonight will become west to northerly on Sunday. Hoenisch


/ISSUED 600 PM MDT Sat Sep 22 2018/

Tonight through Monday...A flattening ridge will allow for
southwest flow through tonight bringing increased moisture to the
area and increased cloud cover. This flow has made for some near
to slightly above average temperatures for today...with some
breezy winds at times. A cold front, currently across the Pacific
NW, will push across the region late tonight through the day on
Sunday. Overall chances for precipitation remain across much of
the same areas as previous forecasts, although the better chances
may have shifted slightly south southeast, with the best chances
now from Helena to Great Falls to near Havre and southeast of this
line including much of southwest MT. Snow levels should remain
above 7000 feet during the day, leaving mainly rain and perhaps an
isolated thunderstorm as the expected results. This front will
continue to progress out of the area Sunday night, diminishing
shower activity from northwest to southeast. Snow levels may lower
to around 6500 feet by Monday, causing some mountain snow
possible across the Rocky Mountain Front and the mountains in the
southwest. Monday then sees the typical northwest flow pattern
behind the front. Below average temperatures and scattered showers
are expected. High temperatures are expected to be in the 60s on
Sunday and 50s on Monday. Low temperatures will remain in the 30s
and 40s throughout the short term period.

Monday night through Saturday...Drier conditions and weak ridging
move across the area Tuesday and Wednesday. Temperatures will be
slightly below seasonal averages during this time period. Models
continue to suggest strong amplification of the upper ridge from
the eastern Pacific northward late next week, supporting a cross-
polar flow and transport of a significantly colder airmass south
by next weekend. Confidence in the overall trend to much colder
temperatures is growing along with potential for wintry
precipitation, even at lower elevations, however at this time
range additional fluctuations in model solutions are likely over
the next several days before any specific details can be
highlighted. Hoenisch


GTF  44  63  40  56 /  60  70   0  30
CTB  35  62  39  56 /  10  10  10  30
HLN  46  62  40  58 /  60  80   0  20
BZN  39  61  36  58 /  20  60  30  20
WEY  32  60  27  55 /  10  40  40  10
DLN  40  63  31  58 /  20  50  20  10
HVR  41  64  42  57 /  40  40  20  30
LWT  43  59  38  53 /  30  80  20  40



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