Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 270610
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1210 AM MDT Tue Jul 27 2021

...AVIATION SECTION UPDATED...

.SYNOPSIS...

Hot temperatures are expected on Tuesday beneath a potent upper
level ridge, with high temperatures climbing into the 90s to near
100 degrees. Isolated to scattered showers and thunderstorms are
then possible Tuesday afternoon and evening across the region,
especially for areas south of the Montana Highway 200 corridor.

&&

.UPDATE...

No update is required this evening. Initial push of monsoon
moisture continues to advect into the region, resulting in an
increase in mid- to high level clouds. A few elevated showers
crossing the Divide may move over the north-central plains later
this evening into the overnight hours with little expected impact.
Despite the increased cloud cover, there will be poor overnight
humidity recovery over the mountains. Another weak front will
slide through North-central MT on Tuesday morning before likely
staling out along or just north of the I90 corridor during the
afternoon and may create some containment difficulties for area
wildfires. A few more elevated showers/thunder can be expected
Tuesday afternoon/evening, mostly over the southwest. -RCG


&&

.AVIATION...
1210 AM MDT Tue Jul 27 2021 (27/06Z TAF period)

Overall, expect VFR conditions to be prevailing through the period.
There will be periods of MVFR visibility in haze and smoke, but
confidence in any time period isn`t there for any terminals. We can
expect isolated showers and thunderstorms across the area Tuesday
afternoon and evening, but the lack of coverage keeps confidence too
low to put it into a prevailing or even a PROB30 group for most
terminals. Any showers or thunderstorms tomorrow could produce
gusty surface winds and LLWS, in addition to turbulence. -Kredensor

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.

&&

.FIRE WEATHER...

While a few isolated showers and thunderstorms are possible late
this afternoon and evening with the first wave of monsoonal
moisture returning over the Northern Rockies, little to no
precipitation is expected. Gusty/erratic winds and isolated dry
lightning strikes will be the primary concern with any area of
precipitation through this evening, but given the antecedent dry
conditions this first wave of monsoonal moisture may just
materialize as increasing mid- and upper level clouds. Moisture
recovery tonight and through the morning hours on Tuesday will be
poor to say the least, with the worst recovery occurring in
thermal belt locations. A weak frontal boundary is then expected
to move south from Canada late tonight and through the day on
Tuesday, bringing a wind shift to the northwest or north. This
wind shift is expected to interact with the Central Montana
mountains between 8am and 2pm before moving across the remainder
of Central and into northern portions of Southwest Montana. While
a brief 1 to 2 hour window of sustained winds of 10-20 mph and
gusts approaching 30 mph are possible with this wind shift, do not
currently anticipate winds to remain high enough for an extended
period of time to warrant a Red Flag Warning. None-the-less,
elevated fire weather conditions will be found across most of the
Northern Rockies on Tuesday. Precipitation chances and coverage
are then expected to increase from Tuesday onward through the end
of the work week, especially for areas south of the Montana
Highway 200 corridor. - Moldan

&&

.PREV DISCUSSION...
/ISSUED 152 PM MDT Mon Jul 26 2021/

The upper level ridge strengthens over the region into Tuesday,
leading to even warmer temperatures nearing daily record highs for
some areas. The Excessive Heat Watch for Fergus county has been
upgraded to a Heat Advisory, with the addition of Liberty, Hill,
Blaine, Chouteau, Cascade, Judith Basin, Central and Southern
Lewis and Clark, Meagher, Jefferson, and Broadwater counties also
to the Heat Advisory. This Heat Advisory will be in effect from
12z Tuesday through 06z Wednesday to cover the hottest period, in
addition the slow cooling process Tuesday night (an extension
through all of Tuesday night may be needed as some areas will
likely not cool below 65 to 70 degrees). There are better chances
for thunderstorms over Southwest Montana Tuesday afternoon with
increasing moisture and a weak disturbance embedded in the
southwest flow aloft. However, much of the moisture will likely
remain somewhat elevated, so the concern for dry t-storms will
continue on Tuesday. A weak frontal boundary is expected to drop
south/southeast across the region from early Tuesday morning and
through the remainder of the day, bringing a wind shift to the
northwest/north and brief period of sustained winds of 10-20 mph
and gusts approaching 30 mph. - Moldan/Kredensor

Wednesday through next Monday...
Deterministic and ensemble models seem to be in generally good
agreement on the pattern for the second half of this week. Thus
reasonably good confidence is placed in the National Blend of
Models solution and no major edits were made away from it. As the
upper-level ridge remains centered over the central and southern
Rockies, Montana will remain under the northwest edge of the
ridge. Thus we are likely to remain near to a bit above normal,
but no excessive heat is expected at this time. On that upper-
level flow, and with an upper low off of California directing
moisture up the west side of the ridge, each day is expected to
feature at least some chance of showers and thunderstorms.
Available guidance continues to indicate that the best chance for
precipitation will be across the southern half of our CWA, but we
can expect occasional isolated showers and thunderstorms to make
it out onto the north-central plains. Models increasingly diverge
on the strength of the ridge and disturbances that may or may not
pass through it early next week, so the potential placement and
degree of precipitation chances may change significantly going
forward. -Kredensor

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  64  97  65  90 /  10  10  20  10
CTB  60  92  61  84 /  10  20  20  20
HLN  65  98  66  94 /  20  30  20  20
BZN  56  98  59  93 /   0  20  20  40
WYS  43  88  50  83 /   0  20  20  60
DLN  57  94  58  89 /  10  20  20  50
HVR  62  98  65  90 /  10  10  20  10
LWT  62  97  64  90 /  10  10  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 6 AM Tuesday to midnight MDT Tuesday night
Blaine...Broadwater...Cascade...Central and Southern Lewis and
Clark...Chouteau...Fergus...Hill...Jefferson...Judith Basin...
Liberty...Meagher.

&&

$$

http://www.weather.gov/greatfalls


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