Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 292304
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
505 PM MDT Mon May 29 2017

Updated Aviation Discussion

.UPDATE...

Based on latest mesoscale model guidance and existing satellite
and radar trends, we have expanded shower/storm chances east to
the Interstate 15 corridor from Vaughn north to the Canadian
border for the remainder of this afternoon into early evening.
Will update and expand the areal coverage of the Special Weather
Statement to cover these areas. Cassell


&&

.SYNOPSIS...

Weak instability will bring a few thunderstorms through this
evening...however...storms should be mainly confined to the
mountains. Elsewhere will see dry conditions with continued warm
conditions. Similar conditions look to return for Tuesday and
again on Wednesday...with warming temperatures and chances for
mountain thunderstorms. Tuesday and Wednesday could see high
temperatures return into the 80s for some lower elevation areas.

&&

.AVIATION...
Updated 2305Z.

Mainly VFR and quiescent conditions expected next 24-hours as high
pressure continues building in from the west. In the immediate short-
term, scattered showers and isolated thunderstorms will continue to
develop along and west of Interstate 15 and over higher terrain
through early evening before diminishing through the remainder of
the evening. The main threats will be gusty winds, brief
downpours, small hail, and frequent lightning.  Cassell

&&

.PREV DISCUSSION...
/ISSUED 241 PM MDT Mon May 29 2017/

Tonight through Wednesday...Ridge of high pressure will continue
to build in across the region through the short term period,
bringing warming temperatures and chances for mainly mountain
thunderstorms. Current weak instability and moisture is enough to
develop thunderstorms across the higher elevations of the CWA.
These cells will be isolated to widely scattered and generally
remained confined to the mountains...although cannot rule out an
isolated storm across the adjacent lower elevations this
evening...especially in Glacier County. The remainder of the CWA
will see mainly dry conditions tonight. As the sunsets tonight the
thunderstorm threat should also diminish. A very similar pattern
sets up for Tuesday as the mentioned ridge continues to move
across the region. Perhaps a slight amount more of instability
will be present...however...thunderstorms should mainly remain to
the mountains and adjacent lower elevations. Wednesday the ridge
moves east of us and we switch to unstable but dry southwest flow.
Once again thunderstorms will be possible...and mainly only in the
mountains. Warming trend will continue through Wednesday with each
day being slightly warmer than the previous. High temperatures in
the 80s will be found Tuesday and especially Wednesday. Winds will
be generally tame...although some increased afternoon breezes are
possible. Anglin

Wednesday Night through Monday...The upper level ridge in place at
the start of the period is unlikely to stick around long as a broad
upper level trough begins to be carved out from the Pacific Ocean
into the Western US. Given the pattern, it is likely that a more
active and unsettled period will ensue across the area beginning mid-
week and potentially continuing beyond Day 7.

Within this pattern, it is likely that several Pacific cold fronts
will traverse the region, each bringing a chance of showers and
thunderstorms. Right now, it appears the greatest coverage of
showers/storms will be Thursday and again later Sunday into Monday,
although the timing is likely to change somewhat, especially with
the front over the weekend. With both fronts, shear looks to be more
than adequate for organized convection. However, instability remains
the bigger question mark which leads to lower confidence regarding
the potential of strong/severe storms. That said, the pattern
certainly looks favorable for a few strong to severe storms if
enough instability can be realized. Of note, CIPS Analog guidance
shows a decent signal for a few strong/severe storms, especially on
Thursday. Otherwise, the only other impact of note is the potential
for stronger wind gusts Friday and again on Monday. Friday looks
like the best setup for stronger, but below high wind criteria,
winds. Late in the period, the models are hinting at a brief shot of
below/well below normal temps, but too early to get specific on
that. Martin

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  49  79  50  85 /   0  10   0  10
CTB  47  79  47  83 /  20   0   0  10
HLN  51  82  51  86 /  20  10  10  10
BZN  44  79  45  84 /   0  10  10  10
WEY  38  70  35  75 /  10  20  10  10
DLN  47  78  47  82 /   0  10  20  10
HVR  45  81  47  88 /   0   0   0   0
LWT  44  74  47  82 /   0   0   0  10

&&

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

$$

weather.gov/greatfalls



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