Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 252343
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
543 PM MDT Tue Jul 25 2017

...Update to Aviation...

.SYNOPSIS...

A few showers and thunderstorms will be possible this evening
across southwestern Montana. The remainder of the area will remain
dry...with a few clouds...and near normal temperatures. Better
chances of rain and storms return on Wednesday and again Thursday
where a few storms may become strong to possibly severe. The heat
will return by late week and into the weekend with mid to upper
90`s possible areawide.

&&

.DISCUSSION...

Tonight through Thursday...Weak waves will ride over a building
ridge each day in the short term bringing chances for showers and
thunderstorms. Tonight we will see those chances remain south of a
line from Butte to Miles City across southern Montana.
Thunderstorm threat not looking as high as earlier given the
abundant cloud cover throughout today. Still cannot rule out an
isolated thunderstorm with lightning and gusty winds being the
main threats. Only isolated showers are then possible tonight in
the southwest. Similar pattern sets up for Wednesday...with a bit
more instability...that will be able to push slightly further
north. Isolated to widely scattered thunderstorms will be possible
during the afternoon and evening hours...possibly as far north as
Great Falls to Lewistown. Gusty winds and lightning being the main
threats. Liquid water totals will be low...with only the far
southwest having chances of more than an tenth of an inch. A
slightly stronger wave then pushes through Thursday. With ample
daytime heating...widespread instability will be found. With just
enough shear...scattered thunderstorms will be possible on
Thursday...with perhaps some isolated areas of wetting rain. A few
stronger storms are also possible on Thursday...with gusty winds
being the main threat. Temperatures will steadily warn during the
short term...with highs back in the 90s by Wednesday and Thursday.
Anglin

Thursday night through Tuesday...Ongoing convective activity in
response to an approaching weak shortwave trough across the Pacific
Northwest will continue into the evening hours on Thursday across a
large majority of the CWA. Taking a closer look at dynamic and
thermodynamic support during this time frame, it appears that given
very marginal bulk shear, modest mixed-layer instability and a
steep well-mixed boundary layer that orographically enhanced, pulse-
type cell clusters will persist, mainly across central and
southwestern areas well into after sunset. Threats will include the
potential for damaging wind gusts and dangerous lightning. This will
lead to the threat for new fire starts given persistent drought
conditions across the area. It is important to note that while this
is not expected to be a widespread severe weather event for the
area, recent drought conditions and the potential for damaging
downburst winds and dangerous lightning will still be just as
impactful. All people with outdoor interests should be weather aware
in the case of hazardous, fast changing weather conditions through
the evening and overnight hours on Thursday.

Rain and storm chances will push off to the east on Friday with
drying conditions returning into the weekend. Latest long-range
guidance still suggests largely positive H5 height anomalies in
response to the return of a very strong ridging pattern across the
entire western U.S. For our area, temperatures are expected to soar
once again into the mid to upper 90`s areawide during the weekend,
and even lasting into next week. There is a chance of some dry
thunderstorm activity late in the evenings of Saturday, Sunday and
Monday across southwestern areas. However, with little precipitation
likely under any one storm, lightning will support the continued
threat for new fire starts as drought conditions persist through the
rest of the period. KLG

&&

.AVIATION...
Updated 2343Z.

Upper level ridging will build over Montana tonight through late
Wednesday afternoon. Scattered showers and a few thunderstorms are
possible south of a KHLN to KLWT line this evening through about 04z
and Wednesday afternoon after 18Z. Monsoon moisture being pulled
into the region will bring scattered to broken mid-level clouds to
southwest Montana while mostly clear to partly cloudy skies prevail
over north central Montana. Widespread VFR conditions will prevail
but can not rule out local and short-lived MVFR conditions and/or
mountain obscurations in the vicinity of precipitation. mpj

&&

.FIRE WEATHER...

Showers and thunderstorms will gradually move further northward
each day over the next several days. The storms today will affect
areas mainly south of Butte...then push northward to around Great
Falls on Wednesday...and then move to near the Canadian border by
Thursday. Some storms will be strong...with frequent lightning
and produce strong wind gusts. Afternoon temperatures will
gradually warm over the next few days...with hot/mostly dry
conditions expected by this weekend. Wetting rains will be hard to
come by...except in the far southwest through Wednesday. Thursday
could see a few storms produce a wetting rain...although coverage
will be widely scattered. Anglin/Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  55  91  60  93 /  10  10  10  20
CTB  50  88  54  91 /   0   0   0  10
HLN  58  89  61  90 /  10  20  30  40
BZN  54  86  55  86 /  20  30  40  30
WEY  48  75  44  76 /  50  50  40  40
DLN  53  83  54  82 /  30  40  30  30
HVR  56  93  61  96 /   0   0  10  10
LWT  57  87  59  88 /  10  10  30  20

&&

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

$$

weather.gov/greatfalls



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