Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 131131
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
531 AM MDT Sun Aug 13 2017

...UPDATED AVIATION SECTION...

.SYNOPSIS...

An approaching storm system will introduce the chance of
widespread rain and thunderstorms across most of Montana today.
Rain totals across the area will range from one tenth of an inch
to a quarter inch, with any stronger storm dropping locally
heavier rainfall at times. In addition, any stronger storm may
contain gusty winds through this evening before the bulk of the
precipitation departs our area by early Monday morning. Ongoing
spotty shower and storm chances will persist through the day on
Monday but will remain limited in coverage, temperatures will
continue near-seasonal and quite comfortable through the upcoming
week with mostly dry conditions expected through the end of the
week.

&&

.DISCUSSION...

Today through Tuesday...Latest infrared satellite imagery depicts
the well-advertised storm system finally impacting the Pacific
Northwest with increased rain shower activity across the region.
Downstream of this approaching system, a small disturbance out
ahead of the increasing west-southwesterly flow aloft has
introduced a few morning showers for central and southern areas.
This precipitation will remain on the light side this morning with
increasing clouds through the early to mid afternoon hours today.
As the main dynamics associated with the approaching storm system
pulls closer, we will begin to see an increase in widespread
shower and storm activity later this afternoon and lasting through
the evening hours. There is the potential for storm development
out ahead of the main rain mass pressing eastward this afternoon.
However, how much sunshine we receive before the thicker cloud
cover arrives remains in question. More sunshine this afternoon
may help build instability and enhance the development of a few
stronger storms for central and southern areas before the arrival
of the main rain mass. Either way, many will still see at least
one tenth to a quarter inch of rain, with the potential for
heavier totals for those under any stronger storm.

We begin to see an end to the widespread rain coverage early
Monday morning, with our area remaining in a persistent
southwesterly flow aloft, I cannot rule out an isolated shower or
storm Monday afternoon, but will mainly be for southwestern areas.
Tuesday will feature continue drying conditions with continued
near-seasonal temperatures. KLG

Tuesday night through Sunday...We stay in a quasi-zonal upper-
level flow aloft as we get into the middle part of the week. A
passing weak disturbance may ignite some isolated showers or
storms Thursday afternoon, however coverage will remain limited,
and mostly confined to central and southwestern areas. We return
to a weak ridging pattern aloft by late week and into the weekend
with the potential for dry weather and moderating temperatures
back to slightly above-normal. Fortunately, there continues to be
no sign of any extreme heat returning in the foreseeable future.
KLG


&&

.AVIATION...
Updated 1131Z.

Ongoing light rain showers in response to an approaching weak upper-
level disturbance will persist for HVR and EKS early this morning.
Expect light rain showers to expand northward to HLN and GTF
terminals by mid to late morning with increasing cloudiness. Cloud
cover will increase for all terminals through the afternoon hours as
the next batch of rain and storms approach from the west by early to
mid afternoon and lasting well into the early part of the night. At
any point, limited visibility within any heavier thunderstorm may
bring down conditions to MVFR, and perhaps lower at times.
Regardless, it is safe to say all terminals across the area will see
rainfall later this afternoon and evening with periods of lower
visibility caused by heavy rain and low ceilings, as well as gusty
winds. We will see most of this activity depart the area before
midnight tonight with only isolated showers possible areawide
through Monday morning. KLG

&&

.FIRE WEATHER...

The main concern over the next 12 to 24 hours is increased
thunderstorm activity followed by a cold front with gusty winds.
Expect the chance of widespread showers and thunderstorms across all
TFX fire weather zones this afternoon and into the early evening
as a front pushes through. While RH doesn`t look critically low
later today, the increased lightning activity followed by gusty
winds with the front is certainly concerning. And, some
thunderstorms will likely be dry. For these reasons, we have
decided to issue a Red Flag Warning for all TFX fire zones
(112-118) to highlight the potential of elevated to critical fire
weather conditions with the passage of the front. Beyond this
weekend, drier conditions are expected along with near normal
temperatures. MARTIN/KLG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  85  53  78  47 /  30  30  10  10
CTB  81  49  75  44 /  40  20  10  10
HLN  81  53  78  49 /  40  30  10  20
BZN  83  51  75  48 /  40  50  50  30
WEY  74  42  67  38 /  30  50  60  60
DLN  80  49  75  46 /  40  40  50  20
HVR  89  57  81  51 /  10  50  10  10
LWT  83  54  75  49 /  30  60  30  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon today to 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.

Red Flag Warning until 9 PM MDT this evening Deerlodge/Western
Beaverhead National Forest...Eastern Beaverhead National Forest.

&&

$$

weather.gov/greatfalls



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