Area Forecast Discussion
Issued by NWS Great Falls, MT

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848
FXUS65 KTFX 231726 CCA
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1126 AM MDT Sun Jul 23 2017

Aviation Section Updated

.UPDATE...

Raised temperatures a couple of degrees for this afternoon, but
the more significant change was to add a slight conditional threat
for dry thunderstorms this evening across much of the region. The
threat is conditional on there being just enough sufficient
moisture, as well as the timing of any lifting mechanism in the
form of a shortwave disturbance. As of mid-morning hours, these
issues have still not been resolved. The main threat if a few
isolated dry showers/thunderstorms do develop will be the
potential for new fire starts as well as gusty winds. Cassell


&&

.SYNOPSIS...
Expect another dry and warm day across the area today. Winds will be
gusty at times which will lead to an increased fire danger.
Thunderstorm chances return to start the week with the better chance
by midweek. Temperatures will remain slightly above-normal before
more hot weather returns by late week.

&&

.AVIATION...
Updated 1726Z

Likelihood of VFR conditions through Monday is high for
KGTF/KLWT/KHLN/KEKS/KBZN, but moderate for KCTB/KHVR. A very low
threat of a TSRA exists across the area this afternoon and evening
and across SW MT Monday afternoon. For now, I introduced a SCT layer
to cover the potential, but confidence isn`t high enough to add
TSRA/VCTS at any terminal for now. Tonight, a cold front will bring
a noticeable wind shift and gusty winds to KCTB, KHVR, and possibly
as far south as KGTF/KLWT. The wind shift may be accompanied by a
brief period of lower CIGS, possibly as low as MVFR for a very short
time. The potential for lower CIGS is highest at KCTB/KHVR, but
confidence is low regarding how low the CIGS will be. MARTIN

&&

.PREV DISCUSSION...
/ISSUED 455 AM MDT Sun Jul 23 2017/
Today through Tuesday...An upper level ridge will begin to shift
eastward today...but hot afternoon temperatures are still
expected. A wind shift will move southward through the region
overnight, shifting winds to the north. On Monday, a brisk
westerly flow aloft develops resulting in very warm temperatures
by late afternoon. Temperatures remain near seasonal normals on
Tuesday as an upper level ridge begins to redevelop over the
Pacific Northwest. There will be a small chance for a passing
wet/dry thunderstorm mostly on Monday and Tuesday over the eastern
and southern sections of the region. However, confidence is quite
low in any thunderstorm activity at this time. The main threat
from any storms will be the lack of rainfall and potential for
gusty winds. Brusda

Tuesday night through Sunday...Latest model guidance continues to
illustrate a notable drying trend through the long range. Beginning
with Tuesday night and early Wednesday, A closed upper low rotating
off the northern Coast of California will begin to get pulled slowly
northwards in response to weak ridging breaking down in SW Canada.
This shortwave will help feed increasing tropospheric moisture into
the area overnight with small, perhaps terrain enhanced nocturnal
clusters of showers and storms making its way as far north as SW
parts of the CWA through daybreak Wednesday. It is looking like by
the daytime hours on Wednesday that most areas will remain dry as
the aforementioned weak ridge holds tight over the majority of the
area. However, by later in the afternoon and evening, increasing
spotty convection area wide will become a good bet, with a few
storms being strong given modest instability across central and
southern areas. Another important note will be lightning activity as
recent drought conditions may enhance the possibility of new fire
starts. Also, breezy conditions are looking possible Thursday
afternoon and evening with the passage of the shortwave trough that
may exacerbate fire weather conditions.

We begin to see a pattern shift beginning on Friday and lasting into
next weekend with the return of the dominant four-corners ridge in
the desert southwest. With good agreement on most long range model
guidance, I`ve started to bump temperatures up enough to reflect
this with highs easily reaching the lower to mid 90s area wide, with
perhaps upper 90`s for some through next weekend. Of course this
will continue to be fine-tuned as we get closer in the week. KLG

&&

.FIRE WEATHER...
Red Flag Warning continues for today as gusty winds and low
humidity is expected this afternoon. A cold front will move
southward through the region during the overnight hours tonight.
Expect a wind shift to the north. The winds will be strong/gusty
at times overnight...especially over North Central MT. On Monday
expect breezy west winds to develop by the afternoon hours along
with low humidity. Thus a fire weather watch has been issued for
this time frame. Additionally there is a small chance for a
passing dry thunderstorm. Some storms could produce strong gusty
erratic wind gusts. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  94  57  87  51 /  10  20   0   0
CTB  91  51  79  46 /   0  20   0   0
HLN  94  63  92  56 /  20  20   0  10
BZN  93  58  90  52 /  20  10  10  10
WEY  82  49  82  46 /  20  10  10  10
DLN  88  58  88  53 /  10  10  10  10
HVR  96  58  84  51 /  10  20   0   0
LWT  92  63  85  52 /  20  20   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 9 PM MDT this evening Central and Eastern
Lewis and Clark National Forest Areas...Chouteau and Fergus
Counties...Eastern Glacier/Toole/Central/Eastern
Pondera/Liberty...Helena and Townsend Ranger Districts of the
Helena National Forest...Hill and Blaine Counties...Lewis and
Clark National Forest Rocky Mountain District-Rocky Mountain
Front...Lincoln Ranger District of the Helena National Forest.

Fire Weather Watch from Monday afternoon through Monday evening
Central and Eastern Lewis and Clark National Forest Areas...
Chouteau and Fergus Counties...Eastern
Glacier/Toole/Central/Eastern Pondera/Liberty...Helena and
Townsend Ranger Districts of the Helena National Forest...Hill
and Blaine Counties...Lewis and Clark National Forest Rocky
Mountain District-Rocky Mountain Front...Lincoln Ranger District
of the Helena National Forest.

&&

$$

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