671
FXUS65 KTFX 031740
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1140 AM MDT Wed Jul 3 2024

.Aviation Section Updated...

.SYNOPSIS...
Unsettled weather continues today and tomorrow as upper level
troughing helps promote the development of afternoon showers and
thunderstorms. Temperatures begin to warm over the weekend and next
week, setting the stage for the start of a heat wave next week.

&&

.Update...

Only minor updates this morning, mainly to nudge PoPs up through
the morning hours to better match radar trends. Otherwise the
remainder of the forecast remains on track an no other updates
were needed. - Moldan

&&

.AVIATION...
03/18Z TAF Period

Unsettled weather is expected to continue through around 04/02Z
before tapering off. During this time, expect intermittent showers
and thunderstorms, periods of mountain obscuration, and periods of
low-VFR to MVFR conditions. By later in the afternoon clouds are
expected to break for KEKS, KWYS, KHLN, and KCTB while lingering mid
to high level clouds will persist for all other sites through the
rest of the period.

-thor

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

&&

.PREV DISCUSSION...
/ISSUED 540 AM MDT Wed Jul 3 2024/

Key Points:

-Afternoon showers and a few thunderstorms continue today and
Independence Day

-Near to below average temperatures expected to continue through
Independence Day

-Temperatures begin to warm over the weekend and next week, with
a heat wave likely beginning next week

Short term (through Independence Day)... Broad upper level
troughing remains through Independence Day across the Northern
Rockies, which will result in a continuation of the recent cool
and unsettled weather that we have seen the past few days. Early
morning radar imagery shows widely scattered rain showers in an
area bounded to the north by US 2 and to the south by a Lewistown
to Great Falls to Lincoln line, and these showers are slowly
moving east. These showers will continue through the day today,
with the focus of the showers gradually shifting to the south over
the higher terrain. With these showers around, temperatures will
struggle to get out of the mid 60s, with just a few locations
along the Missouri River managing to see 70 this afternoon.

While the upper level trough will shift a bit for Independence
Day, north westerly flow aloft will help to keep the atmosphere
primed for a few instability showers in the afternoon, especially
across Central Montana. With the axis of todays trough shifted a
bit to the east, temperatures will manage to warm a bit, with most
locations seeing highs in the 70s with a few isolated areas
reaching 80 degrees.

Extended (Friday through next Wednesday)... Temperatures begin to
trend warmer to end this week as an impressively strong upper
level ridge begins to develop over California/Nevada, with a ridge
axis extending up the West Coast. Highs on Friday and Saturday
will reach the upper 70s and low 80s for most of the lower
elevations as the ridge builds with a few ring of fire
thunderstorms developing on the fringes of this upper level ridge
(the edges of upper level ridges like these tend to be favorable
to some thunderstorm development, hence the nickname ring of
fire). Depending on the timing of any showers or thunderstorms,
some relief from the heat will be possible where the storms move
through, especially if they manage to produce some cool outflow
breezes.

As we head into early next week, the ridge will continue to
strengthen and shift eastward, putting us into what looks like the
beginning of the first heat wave of the summer, with many
locations seeing multiple days of temperatures exceeding at least
90 degrees as early as Monday (and even Sunday for the Helena
valley). With the ridge overhead, any shower or thunderstorm
activity will be incredibly isolated/nonexistent, which while not
allowing for any atmospheric relief from the heat, will also
reduce the risk for natural fire starts. Ensemble data for next
week shows a high likelihood of this heat wave extending through
at least all of next week, with some indications that it could
last all the way through the following week as well (meaning at
least 10 days), with some areas possibly seeing multiple
consecutive days of temperatures over 100. Great Falls, for
example, has multiple consecutive days with at least 50% of the
ensemble members forecasting at least 100, with some of those
exceeding the all time record high of 107 (July 25, 1933). While
this degree of heat is not guaranteed yet, it is time to start
preparing for the possibility of heat well outside the
climatological norm. Ludwig

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  67  47  74  47 /  70  30  20  10
CTB  67  46  72  45 /  70  20  20  10
HLN  74  50  79  50 /  70  40  10   0
BZN  69  42  73  45 /  50  30  10  10
WYS  64  33  67  33 /  40  10  10   0
DLN  68  39  73  42 /  30  10   0   0
HVR  70  50  74  50 /  70  30  30  10
LWT  64  44  68  45 /  80  30  50  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

http://www.weather.gov/greatfalls