Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 251730
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1130 AM MDT Tue Jul 25 2017

...Updated Aviation Section...

.UPDATE...

Little updates needed this morning. A weak disturbance will ride
over the ridge later this afternoon through the evening hours
bringing a thunderstorm threat to mainly SW MT...mainly south of a
line from Butte to Miles City. Gusty winds and lightning will be
the main threats. Little precipitation is expected from these
storms...although a slight bump in precipitable water may be just
enough to prevent a true dry thunderstorm. However...a tenth of
an inch or less is generally expected. With increased cloud
cover...high temperatures may be slightly lower and closer to
normal for today. Anglin

&&

.SYNOPSIS...

Expect another dry and warm day areawide today with warm afternoon
temperatures once again. A few thunderstorms will develop late
afternoon and evening across southwestern areas. Better chances of
rain and storms return on Wednesday and into 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...


&&

.AVIATION...
Updated 1730Z.

VFR conditions are expected throughout the duration of the 2518/2618
TAF period, however, terminals like KEKS and KBZN may approach MVFR
with any passing shower/thunderstorm. Scattered showers were moving
across Southwest Montana this morning, are are expected to
transition to scattered thunderstorms by this afternoon. Some storms
this afternoon and early this evening could produce gusty winds.
With east to east southeast winds in the low levels, some mountain
obscuration is possible over Central and into North Central Montana
due to smoke from large fires burning in Eastern Montana. - Moldan

&&

.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 Helena...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. Brusda

&&

.PREV DISCUSSION...
/ISSUED 553 AM MDT Tue Jul 25 2017/

Today through Thursday...Overall expect showers/thunderstorm
activity to increase in coverage and gradually move further
northward each day. The storms today will affect areas mainly
south of a Boulder to Townsend line...then shift a bit further
north on Wed to about a Great Falls to Lewistown line. By
Thursday, storms will be possible across much of the region. The
main threat from any storms will be lightning and strong wind
gusts. For now, I held off on the mention of any dry
thunderstorms...but most storms will likely produce less than a
tenth of an inch today and Wednesday...with the storms on
Thursday slightly more wetter. The marginal risk of severe storms
also starts to affect portions of Southwest MT on Wed and much of
the region on Thursday. Afternoon temperatures will be near normal
today...then generally go on a slow warming trend for Wed/Thu.
Brusda

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  83  55  91  60 /  10  10   0  10
CTB  80  52  88  55 /   0   0   0   0
HLN  86  59  90  61 /  10  10  20  30
BZN  85  55  86  55 /  20  20  20  30
WEY  75  46  75  44 /  50  40  40  30
DLN  82  54  82  53 /  20  30  30  30
HVR  83  55  92  60 /   0   0   0  10
LWT  81  57  87  59 /  10  10  10  20

&&

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

$$

weather.gov/greatfalls



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