Wildfire in Montana, July 17 to 31, 2021

Area Forecast Discussion
National Weather Service Great Falls MT
1215 PM MDT Sat Jul 17 2021

...AVIATION SECTION UPDATED...

.SYNOPSIS...

A hot and dry weekend is expected across the Northern Rockies,
with high temperatures by Sunday ranging from 95 to 105 degrees.
Monday will be as equally as hot as Sunday; however, isolated
to scattered showers and thunderstorms are expected during the
afternoon and evening hours as monsoonal moisture begins to lift
northeast from the Great Basin and Desert Southwest.

&&

.UPDATE...

No major changes were made with this morning's update. Biggest
story today will be the continuation of hazy and smoky skies.
While some of the smoke/haze has thinned out a bit this morning,
westerly winds will likely bring thicker smoke back into the area
for the afternoon.
Ludwig

&&

.AVIATION...
1215 PM MDT Sat Jul 17 2021 (17/18Z TAF period)

Overall, VFR conditions are forecast to prevail through the period,
though there may be temporary MVFR conditions due to smoke.
Otherwise, the main concern over the next few days, and especially
Sunday into Monday, will be density altitude issues due to the
increasingly hot conditions. -Kredensor

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

&&

.PREV DISCUSSION...
/ISSUED 500 AM MDT Sat Jul 17 2021/

Today through Wednesday...primary concern over the period will be
temperatures and precipitation chances. First with respect to
temperatures, the H500 ridge is already firmly in place over the
Northern Rockies early this morning, and will only amplify further
through the morning hours on Monday before shifting slightly to
the east on Tuesday and Wednesday as embedded shortwaves lift
northeast within the upstream side of the ridge axis. 1000-500mb
thicknesses are expected to peak at ~5800 to 5850m by Sunday and
Monday, which will equate to afternoon temperatures in the mid-90s
to near 105 degrees for these days. High temperatures today,
Tuesday, and Wednesday of 90 to near 100 degrees are expected
beneath slightly lower 1000-500mb thicknesses. All of the
Excessive Heat Warnings and Heat Advisories remain in place from
prior forecast issuance's as model guidance continues to indicate
a prolonged period of hot afternoon temperatures over several
days, combined with limited relief during the overnight hours.
This will be especially true over eastern portions of Central and
North Central Montana (i.e. Fergus, Chouteau, Hill, and Blaine
Counties) as overnight low temperatures are only expected to fall
into the mid-60s to mid-70s, which is some 10 to 25 degrees above
normal.

With respect to precipitation chances, monsoonal moisture will begin
to lift northeast from the Great Basin and Desert Southwest Sunday
night, moving over portions of the Continental Divide and Southwest
Montana Monday afternoon and evening. This will lead to isolated to
scattered shower and thunderstorm development over these areas.
Strong downburst winds will be a concern beneath any area of
precipitation given inverted-v soundings over this timeframe. A
stronger push of monsoonal moisture is then expected to lift
northeast late Monday night through Tuesday night across the entire
CWA, which is expected to result in isolated to scattered showers
and thunderstorms across the entire CWA. PWATs of ~1", which is 2-3
standard deviations above normal, combined with increasing moisture
in the low to mid-levels is expected to lead to better chances for
wetting rains at all locations. Additional chances for showers and
thunderstorms are then expected on Wednesday as another shortwave
lifts northeast within the southwest flow over the Northern Rockies,
with the best chance for precipitation existing over Southwest and
eastern portions of Central and North Central Montana. - Moldan

Thursday through next Saturday...the upper level ridge will begin to
be broken down as a shortwave over the Pacific Northwest and
Southern BC slides east over the International Border. This is
expected to result in increasing southwest to westerly surface winds
and temperatures moderating closer to normal values for mid-July. In
addition, daily chances for isolated to scattered showers and
thunderstorms will exist, especially over the higher terrain of
Southwest and Central Montana. - Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  95  59  98  60 /   0   0   0   0
CTB  91  55  94  58 /   0   0   0   0
HLN  96  63 100  64 /   0   0  10   0
BZN  95  55  99  57 /   0   0  10   0
WYS  86  42  89  44 /   0   0   0   0
DLN  92  55  94  56 /   0   0  10   0
HVR  98  63 101  66 /  10   0  10   0
LWT  93  62  96  63 /  10   0  10   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon Sunday to 9 PM MDT Monday Eastern
Pondera...Eastern Teton...Gallatin...Jefferson...Madison...
Meagher.

Heat Advisory from noon Sunday to 9 PM MDT Tuesday Broadwater...
Cascade...Central and Southern Lewis and Clark...Judith Basin...
Liberty...Toole.

Excessive Heat Warning from noon today to 9 PM MDT Tuesday
Blaine...Chouteau...Fergus...Hill.

&&

http://www.weather.gov/greatfalls