Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 200315
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
915 PM MDT Mon Jun 19 2017

.SYNOPSIS...

Unseasonably warm temperatures in the 80s to low 90s will be
experienced across the region for the day on Tuesday. In addition
the warm weather, breezy westerly winds of 15 to 30 mph with gusts
approaching 40 mph will be experienced during the afternoon and
evening hours. Showers and thunderstorms will be possible across
Southwest Montana and the Central Montana Mountains on Tuesday, with
some storms possibly becoming strong and producing gusty winds and
hail. High temperatures will cool slightly into the mid 60s and 70s
for Wednesday and Thursday, with the coolest day of the work week
being Friday following a cold front. On Friday, highs look to only
reach into the 50s and 60s, which would be well below normal for the
end of June.

&&

.UPDATE...The mid- and upper level ridge currently over the region
is a bit weaker than model guidance envisioned. As such, clouds
and showers moving through southern Alberta/Saskatchewan are
sagging farther south than anticipated. Have updated the forecast
this evening to increase clouds and PoPs along the Canadian border
to account for this. Remainder of the forecast is still in pretty
good shape. Overnight low temperature and wind forecasts have not
been changed and the region is still on track for very warm
temperatures on Tuesday. mpj

&&

.AVIATION...
Updated 2315Z.

VFR conditions will continue at least through the day on Tuesday. A
broad high pressure ridge will keep a brisk westerly flow aloft with
scattered mid level clouds over most of the area, with more
cloudiness along the Hi-Line. After 18Z, a weak disturbance in the
flow will bring increasing westerly winds to the area, along with a
chance of isolated showers and thunderstorms south of Interstate 90
(including KEKS).
Coulston

&&

.FIRE WEATHER...

Fire weather concerns will be elevated Tuesday afternoon as
temperatures warm to the mid 80s to near 90 at lower elevations with
relative humidity falling to around 20 to 30 percent.
Strengthening westerly flow aloft and deep afternoon mixing will
promote gusty west winds during the afternoon period on Tuesday,
continuing into the evening period along the Rocky Mtn front and
adjacent plains. Cooler temperatures are expected Wednesday,
although dry and breezy conditions will continue. Fire weather
highlights are not anticipated at this time due to fuel conditions
near peak greenness across much of the area, though the warm/dry
and windy conditions will likely accelerate the drying & curing
process, particularly across far-eastern portions of north-central
MT, where recent precipitation has not been as abundant.
Hoenisch

&&

.PREV DISCUSSION...
/ISSUED 515 PM MDT Mon Jun 19 2017/

Tonight through Wednesday...Upper-level ridging over our area will
be broken-down by multiple shortwave troughs advancing eastward over
Canada on Tuesday. A very weak Pacific cold front accompanying the
leading shortwave will sweep eastward over the CWA Tuesday morning
and early afternoon. Tuesday night through Wednesday, zonal flow
aloft is expected over our region as the aforementioned shortwaves
begin to carve-out a broad upper-level trough over much of western
and central Canada. At the surface, a secondary cold front may
move southward from Canada on Wednesday and reach the Hi-Line by
early evening.

Elevated fire weather concerns continue for Tuesday afternoon. See
the fire weather discussion for further details. In addition,
isolated showers and thunderstorms should develop over the higher
terrain of central and southwest Montana Tuesday afternoon and early
evening, and then move eastward from there. Moderate instability and
vertical wind shear may allow a few of these storms to become
severe, with gusts up to 60 mph and hail up to quarter-size
possible. Drier weather is then expected later Tuesday evening into
Wednesday, but a few showers may affect the Hi-Line Wednesday
afternoon/early evening in association with the aforementioned
secondary cold front. Above-normal temperatures through Tuesday will
cool to near-normal by Wednesday.
Jaszka

Wednesday Night through Monday...A fast zonal flow aloft
punctuated by a 120kt upper level jet will likely be moving over
the region at the start of the period. By Thursday, though, the
models generally agree on a pattern change as several upper level
shortwaves dropping south out of Canada begin to carve out a
larger trough across the NRN Rockies/NRN High Plains. The main
differences amongst the models is how amplified the upper trough
will get (meaning the difference between below/well below normal
temps or climo temps). For now, leaned a bit more towards the more
amplified solution as it has more support among most of the model
data.

As for weather at the SFC, the pattern does not appear to favor any
high-impact weather at this time. The period starts breezy with the
strong jet moving through. A cold front should then drop south out
of Canada late Thursday, ushering in a brief period of below to
potentially well below normal temps for Friday/Friday night. Of
note, with high pressure overhead and light winds, some
plains/valley locations could drop into the 30s Friday night and I
did lower min temps a bit for then. The front may also be
accompanied by a few showers/storms Thursday through Friday. The
threat of severe weather looks very low at this time, though. An
upper level ridge builds over the CWA this weekend and Monday of
next week, with moderating/drying conditions expected.
Martin

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  77  58  87  53 /   0   0  10   0
CTB  73  56  83  49 /   0   0  10   0
HLN  83  58  89  56 /   0   0  10   0
BZN  82  55  89  53 /   0   0  20  10
WEY  75  47  80  44 /   0   0  30  20
DLN  80  55  87  53 /   0   0  20  10
HVR  79  57  90  54 /   0  10  10  10
LWT  73  55  86  53 /   0   0  10  10

&&

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

$$

weather.gov/greatfalls



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