NWS Great Falls, MT wrote its last area forecast discussion before the first event at Oct 4, 10:35 AM MST, 1 hour 10 minutes earlier.
Area forecast discussion, Oct 4, 10:35 AM MST, 1 hour 10 minutes before
Area Forecast Discussion
National Weather Service Great Falls MT
1135 AM MDT Mon Oct 4 2021
Aviation Section Updated.
.UPDATE...
A Red Flag Warning has been issued for Tuesday afternoon. For
today, clear skies and warm temperatures are expected. Tomorrow
will be another warm, dry day. Temperatures and winds will be
higher tomorrow than they will be today, which is why the Red Flag
Warning has been issued. - AM
&&
.SYNOPSIS...
A southwesterly flow aloft will help warm temperatures to near
daily record highs today and Tuesday, but it will also cause
afternoon humidity to become low. Winds will also mix down to the
surface during the afternoon hours, causing gusts to between 20
and 30 mph at times, and increasing overall fire weather
concerns. However, a Pacific weather system will bring cooler
than normal temperatures with an increasing chance for rain later
this week, possibly even bringing some measurable snow to the
mountains.
&&
.AVIATION...
1135 AM MDT Mon Oct 4 2021 (04/18Z TAF period)
VFR conditions will continue over the area through at least the
next 24 hours. Areas of mainly high cloudiness will pass overhead
as the flow aloft shifts from westerly to southwesterly through
the period. However, smoke from a fire in Jefferson County may cause
some minor reduction in visibility at KHLN between 18Z and 03Z as
that flow aloft shifts. Otherwise, light winds will become southerly
and somewhat gusty (mostly up to 25 kt at times) after 16Z and
through 01Z or so.
-Coulston
Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.
&&
.FIRE WEATHER...
The flow aloft will shift from westerly to more southwesterly
today into Tuesday, but it will remain quite warm and dry, which
will continue elevated fire weather conditions. Temperatures will
warm to between 10 and 20 degrees above normal during the day
through Tuesday, and afternoon humidity will mostly fall into the
5 to 15 percent range at lower elevations with poor overnight
recovery in general for much of North Central and Southwest
Montana. These breezy southwest winds will also translate down to
the surface during the afternoons, including through north-south
oriented valleys, gusting at times to between 20 and 30 mph.
Overall, though, winds will not become excessively strong, so Fire
Weather Watches/Warnings are not anticipated at this time.
A Pacific low pressure trough will then move more moisture, along
with a Pacific cold front, into the area beginning on Wednesday,
which will bring wetter conditions with cooler than normal
temperatures for the latter portion of the week. Right now, the
coolest and wettest period will likely be Friday. However, the
best chances for wetting rain will likely be more so over fire
weather zones 116, 117, and 118, and possibly into Fergus County
as well. At least light measurable snow will also be possible in
the mountains.
&&
.PREV DISCUSSION...
/ISSUED 449 AM MDT Mon Oct 4 2021/
Today through Tuesday... This should remain a dry and much warmer
than normal period with breezy southwest winds during the
afternoons for North Central and Southwest Montana. The westerly
flow aloft will shift more southwesterly, but it will be bringing
air up from the dry areas of the Desert Southwest and Great Basin.
This will continue the very low relative humidity with poor
overnight recovery. Temperatures will also warm to between 10 and
20 degrees above normal for early October (mostly 80s at lower
elevations), which will cause some locations to approach record
highs for the date. This warm air will also help mix the breezy
southwest winds aloft down to the surface during the afternoon,
possibly causing gusts at times in the 20 to 30 mph range for much
of the area, which will cause increased fire weather concerns
(please see FIRE WEATHER section for more details). A disturbance
is forecast to move over the area tonight, but it should only
bring areas of mid and high clouds. Because the airmass is so dry,
overnight temperatures should fall back mostly into the 40s,
except for some mid 20s and 30s in the higher mountain valleys.
The more southwesterly flow aloft will also help move smoke from
fires in Southwest Montana, as well as from over much of the
western United States, more so over the plains; however, any
reductions in air quality should remain minor.
Wednesday through next Monday... Wednesday will begin a
transition to a period of cooler and wetter weather for the
forecast area. A low pressure trough off the Pacific coast is
responsible for shifting the flow aloft more southwesterly over
the area, and this trough will start to move onshore Wednesday
into Thursday. This will cause the southwest flow aloft to tap
into the Pacific moisture and become more unstable, bringing an
increase in clouds, showers, and thunderstorms. Scattered showers
and thunderstorms should first move into Southwest Montana on
Wednesday, then into North Central Montana Wednesday night, but
the best chance for thunderstorms will remain over the southwest.
The low pressure trough should continue moving across the
Northern Rockies and Great Basin area Thursday into Friday,
continuing the chance for precipitation with southwest
thunderstorms, as temperatures cool to up to 10 degrees below
normal by Friday. This will help lower the snow level as well,
which should bring measurable snowfall to the mountains, mainly
above mountain passes. Forecast models have been a bit uncertain
as to just how low the snow levels will get, so there is low
confidence in the need for winter weather highlights at this
time, but it is a situation that will bear watching. Overall,
though, the trend is to keep the best precipitation accumulation
during this period over the area along and south of a Great Falls
to Lewistown line. A weak high pressure ridge is then forecast to
move into the area for Saturday and Sunday, which should help dry
out the area, but temperatures will likely only warm back to
normal. A second low pressure trough from the Pacific will bring
the potential for another round of cool and wet weather beginning
next Monday.
-Coulston
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 83 47 84 51 / 0 0 0 0
CTB 80 45 82 45 / 0 0 0 0
HLN 83 43 85 49 / 0 0 0 10
BZN 81 38 83 43 / 0 0 0 10
WYS 70 24 72 35 / 0 0 0 20
DLN 77 39 79 46 / 0 0 0 20
HVR 85 45 87 50 / 0 0 0 0
LWT 83 48 83 49 / 0 0 0 0
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 6 PM MDT Tuesday Eastern
Glacier/Toole/Central/Eastern Pondera/Liberty...Lewis and Clark
National Forest Rocky Mountain District-Rocky Mountain Front.
&&
http://www.weather.gov/greatfalls