Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 281716
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1115 AM MDT Wed Sep 28 2016

AVIATION SECTION UPDATED

.DISCUSSION...

Last night`s cold front has remained north of the southwest zones.
Temperatures will be quite a bit cooler across the central and
northern zones while temperatures will be well above seasonal
normals to the south. Current forecast on track...update not
planned. Zelzer

&&

.AVIATION...Updated 1715Z.

High pressure aloft will keep Central and Southwest Montana dry with
VFR conditions through the next 24 hours. An upper level disturbance
will move through the southwest flow aloft Thursday and approach the
Montana/Idaho border Thursday afternoon. The air mass will become
slightly unstable with a chance of showers or thunderstorms over
Southwest Montana, including KBZN.

&&

.PREV DISCUSSION...
/ISSUED 544 AM MDT Wed Sep 28 2016/

Today through Friday...Cold front that came blasting out of Canada
yesterday evening has stalled across central MT...and is
currently bringing some cool morning lows along the high plains
near the Rocky Mountain Front. This stalled frontal boundary will
bring cooler temperatures today in the 60s and 70s. Mainly dry
conditions are also expected today given the limited low level
moisture to work with. Mid level flow becomes southwest
today...setting up mid level warm front near the MT and CAN
border. With some limited moisture caught in this flow...some
partly cloudy skies will be found across the northern half of the
CWA today...with mainly clear skies across the south. Dry
conditions and mainly clear skies are then expected for tonight.
Southwest flow continues for Thursday...pulling up some limited
monsoonal type moisture from AZ and NM. Some weak to modest
instability will be found across the CWA by Thursday afternoon.
Areas that can tap into the monsoonal moisture will have chances
for showers and a few non severe thunderstorms...with the best
chances coming across the south and west. Other areas will be too
capped for any thunderstorm development...seeing only increasing
clouds and slightly warmer temperatures in the 70s. More and more
of this weak monsoonal moisture gets pulled into the region for
Thursday night into Friday. Stronger heating for Friday...with
highs in the mid to upper 70s...will bring modest instability
across the region. Much of the air will initially be capped for
Friday. As a disturbance of the Pac NW moves closer to
land...temps will slightly cool aloft. This may be just enough to
break down the cap for some areas across portions of the CWA.
Isolated to scattered thunderstorms will be possible. A
strengthening jet could provide enough shear for a few isolated
stronger thunderstorms...however...severe weather is still not
expected at this time. Western and southern portions will again
have the best chances for thunderstorms...however...a few isolated
storms will be possible across the high plains of central MT by
late Friday afternoon...provided the cap can diminish.

Other note in the short term are the possibilities for Northern
Lights Wednesday night and perhaps again Thursday night. The Space
Weather Prediction Center (SWPC) is predicting a G1-G2 (Minor-
Moderate) geomagnetic storm during this time period. Predicted Kp
(Planetary K-Index) values of 5 to 6 are possible. The importance
of these numbers are it takes about a 5 for northern and central
MT...with higher numbers of 6 or 7 needed across the south.
Weather wise the best chances to see any northern light activity
will be Wednesday night into Thursday morning from shortly after
sunset until shortly before sunrise...as clouds increase for
Thursday night into Friday. For more details...and the latest
Aurora Forecast...check out the Space Weather Enthusiasts
Dashboard at SWPC`s site. Anglin

Friday night through Wednesday...Dominant feature for the medium
range continues to be an upper level closed low that will start the
period along the British Columbia/Pacific Northwest coast. Models
agree that this system will move inland and transform into an open
trough over the western USA but continue to disagree on location,
strength and timing of the system as it affect Montana and the
Northern Rocky Mountain region. The models also continue to push
back timing of a surface cold front expected to move into the
forecast area over the weekend. As a result, forecast high
temperatures for Saturday and Sunday have climbed steadily higher
over the last few days. Period is expected to start off with
isolated/scattered showers and thunderstorms Friday evening through
Saturday evening with the best chance for precipitation expected
over the western and southwest mountains. As the upper system moves
inland the coverage of showers and stratiform rain/mountain snow
will expand across the entire forecast area for Sunday and Monday.
Tuesday and Wednesday will see a continuation of unsettled
conditions but have gone with only slight chance/chance PoPs due to
uncertainty of the upper low`s position. Temperatures for early to
mid-week will be much cooler with highs expected to be only in the
50s. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  68  47  73  49 /   0   0   0  10
CTB  63  41  68  45 /  10   0  10  10
HLN  74  46  77  48 /   0   0  10  10
BZN  77  49  77  49 /   0  10  10  10
WEY  72  39  67  39 /   0  10  20  20
DLN  77  44  73  46 /   0  10  20  20
HVR  69  47  73  49 /   0   0   0   0
LWT  70  49  76  51 /   0   0  10  20

&&

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

$$

weather.gov/greatfalls


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