526
FXUS65 KTFX 280218
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
818 PM MDT Mon May 27 2024


.SYNOPSIS...

Tuesday will be warmer with highs 10 to 15 degrees above normal
across north central, central, and southwestern Montana. By
Tuesday evening, a cold front will make its way into western
Montana and bring a chance of showers and thunderstorms to the
region. Some storms may produce gusty winds and small hail as well
as locally heavy rain which may lead to minor flood concerns for
areas that have recently received rain and snow. Behind the front,
the rest of the week will remain closer to normal with drier
conditions persisting through the weekend.

&&

.UPDATE...

Transient ridging will remain in place through Tuesday morning
before shortwave energy within an increasing southwesterly flow
aloft brings a round of scattered late afternoon and evening
showers and thunderstorms. The previous forecast package is
handling current trends well, so no updating will be necessary
this evening. - RCG

&&

.AVIATION...

28/00Z TAF Period

Upper level ridge of high pressure shifts east across the Northern
Rockies through Tuesday morning, maintaining a dry west to northwest
flow aloft. VFR conditions are expected at all terminals for much if
not all of the TAF period; however, higher level clouds will
increase tonight into Tuesday morning and scattered shower and
thunderstorm activity associated with an approaching Pacific trough
will develop and cross the Continental Divide around 29/00Z and
beyond. Winds become light this evening and turn more southerly by
Tuesday morning. - RCG

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

&&

.HYDROLOGY...

A Pacific weather system will bring a threat of heavy downpours
with associated showers and thunderstorms, first to the
Continental Divide and adjacent areas Tuesday afternoon and
evening, then to the remainder of North Central, Central, and
Southwest Montana Tuesday night through Wednesday. The concern is
that this precipitation will fall on warming high mountain
snowpack, which could increase the amount and speed of runoff out
of the mountains. While most rivers should be able to handle this
runoff with a low risk of minor flooding, smaller creeks and
streams may run out of their banks. This situation will continue
to be monitored for possible flood highlights.

&&

.PREV DISCUSSION...
/ISSUED 218 PM MDT Mon May 27 2024/

Today through Thursday... A calm day remains for Memorial Day with
generally partly cloudy skies and winds that will slowly calm down
heading into the evening/overnight hours before the front arrives on
Tuesday.

Things heat up for Tuesday afternoon with widespread chances of 80
degrees or higher along the northern plains and lower elevations
across central and southwestern Montana. Along with the heat and the
arriving front comes the risk for afternoon showers and
thunderstorms across the region. The severe weather threat across
western and central Montana remains under a Marginal Risk (<15%
chance) for Tuesday evening. The latest model guidance has storms
first moving into the areas immediately east of the divide between 4
and 6 PM. After that, scattered thunderstorms will continue pushing
eastward through portions of central and southwestern Montana. The
biggest threat with these thunderstorms will be the wind potential
with small hail remaining a secondary threat. A small wild card with
the severe threat will be how far east it extends. Currently SPC
cuts off the Marginal Risk at a line between Inverness and Bozeman.
Some convective allowing models are proposing around a 20% chance
that some stronger showers/ thunderstorms may last a little further
east, possibly impacting Havre and Lewistown. More than likely these
areas will see less on the side of strong convection and rather the
remnants of whatever is propagating from the west but
precipitation chances were increased to reflect the probability of
some heavier showers and gusty winds further east. -thor

As the cold front moves east across the area Tuesday night into
Wednesday, so will the focus for additional showers and
thunderstorms, as gusty winds shift more westerly behind the front.
The increased moisture and cooler temperatures will be firmly in
place by Wednesday, continuing the main threat for heavy downpours
with the storms. This could cause increased runoff out of the
mountains of Southwest and Central Montana, so the Weather
Prediction Center (WPC) has that area under a Marginal Risk (5 to
15% chance) for flash flooding (for more details on this potential,
please see the HYDROLOGY section).

As the cold front exits the area Wednesday night into Thursday, the
main portion of the shortwave trough will move into the area.
This will further cool temperatures below normal, but keep a chance
of showers and isolated thunderstorms over the area.

Friday through next Monday... Model ensemble clusters seem to agree
with keeping a broad upper level trough over the area on Friday,
likely continuing the near to slightly below normal temperatures
with a chance of showers and thunderstorms. Slightly more than half
of the clusters (56%) then start to bring weak high pressure ridging
in for Saturday, while the other 44% want to keep the weak trough in
place. There is then better agreement in building in the weak ridge
for Sunday into Monday, but 25% of the clusters forecast the ridge
to start shifting east with the approach of another trough. The
National Blend of Models (NBM) seems to resolve this uncertainty
well by warming temperatures through the weekend into early next
week, but bring in a slight chance of showers and thunderstorms
Sunday into Monday. -Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  45  82  53  66 /   0  10  40  50
CTB  42  78  49  61 /   0  20  50  20
HLN  48  84  53  65 /   0  20  50  60
BZN  41  81  47  64 /   0  10  40  90
WYS  34  71  41  62 /   0   0  40  90
DLN  42  78  46  65 /   0  20  50  80
HVR  44  83  54  70 /   0   0  30  50
LWT  41  76  51  65 /   0   0  20  90

&&

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

$$

http://www.weather.gov/greatfalls