Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 261803
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1200 PM MDT Mon Jun 26 2017

Aviation Section Updated

.SYNOPSIS...

Upper level high pressure ridge over the region will bring hot
conditions to Montana today. An upper level disturbance may kick off
a few thunderstorms this afternoon. Any storm that develops will be
capable of strong, gusty winds. Later tonight, a surface cold front
will sweep across the state with a better coverage of showers and
thunderstorms. The front will bring cooler temperatures with it on
Tuesday.

&&

.UPDATE...

The main change for the update was to adjust POPs some for this
afternoon. Water vapor shows what appears to be a convectively-
induced s/w moving through eastern OR/northern ID at this time.
Right now, very warm mid level temps are keeping the atmosphere
capped. By this afternoon, though, highs should warm well into
the 80s/low 90s which may help to erode the cap. Plus, the above
mentioned s/w may provide a little extra lift to allow isolated
storms to form mid to late afternoon (a bit earlier than was
previously forecast). Given the dry low levels, coverage looks to
be isolated, but went ahead and added low-end pops across part of
the area a little earlier this afternoon. Still looks like the
greatest coverage comes later this evening through tonight as a
cold front pushes through. As for the strength of storms this
afternoon, very dry low levels will lead to very steep lapse
rates. Shear isn`t overly impressive, but adequate for organized
storms. The thinking is that storms will be a bit more pulse-like
in nature this afternoon, with predominantly a gusty/damaging
wind threat. The main wild card for this afternoon may be whether
the lead s/w can actually initiate any storms or whether they hold
off until the front (which comes through late evening/overnight).
Lastly, I upped cloudcover along the Hiline where a Chinook Arch
has developed with more clouds there than previously forecast. Of
note, too, this may tend to limit heating some there and I lowered
max temps a degree or two for today. MARTIN

&&

.AVIATION...
Updated 1800Z.

An upper level disturbance will bring isolated TSRA to part of the
forecast area this afternoon, especially along/east of I-15. These
storms will be capable of strong, gusty, and erratic wind gusts,
potentially in excess of 50kt. A cold front will then move through
overnight with a greater coverage of SHRA/TSRA. At this time, VFR
conditions are expected to prevail, but CIGS/VIS may briefly lower
with any SHRA/TSRA, especially overnight. MARTIN

&&

.FIRE WEATHER...
A Red Flag Warning remains in effect for zone 113 with modest
confidence that there will be critical fire weather conditions
this afternoon into evening, primarily Blaine County. Gusty
southeast winds ahead of a surface low pressure system will
combine with minimum RH values in the teens and increasingly dry
fuels in eastern portions of Fire Weather Zone 113. CC/MPJ/Martin

&&

.PREV DISCUSSION...
/ISSUED 542 AM MDT Mon Jun 26 2017/

Today through Wednesday...Upper level ridge moves over the region
for very warm to hot conditions today. A surface low pressure
system will develop along the east slopes of the Rockies in
southern Alberta for increasing southeast flow at the surface.
Models are in agreement that this low will progress eastward
overnight with a surface cold front sweeping through Montana early
Tuesday. This timing is about 12 to 18 hours slower than models
were indicating over the last few days. As a result, I have
lowered PoPs somewhat for today and tonight and increased them a
bit for Tuesday. Behind the cold front, breezy west to
northwesterly winds will develop across North Central Montana
for Tuesday night and Wednesday. Despite impressive CAPE values
expected across the forecast area today and Tuesday, it appears
that the risk for widespread severe weather is relatively low.
However, I still can not rule out one or two short lived storms
that could produce locally strong outflow winds and marginally
large hail, especially this evening. mpj

Wednesday Night through Sunday...An unsettled, northerly flow aloft
develops Wednesday night and Thursday associated with a closed upper
level low drifting through AB/SK. A cold front trailing behind this
system will lower temperatures into the low- to mid-70s on Thursday.
This pattern brings chances for scattered showers and thunderstorms,
although model guidance continues to differ on the timing and
spatial extent of this activity.  The latest forecast guidance has
slowed the departure of the upper low, with chances for isolated
light rain showers continuing Thursday night into Friday. Model
consensus suggests weak ridging through the weekend, providing
generally fair weather with temperatures near 80F and isolated

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  91  61  77  50 /  20  40  50  20
CTB  88  57  76  48 /  10  30  40  10
HLN  92  61  78  52 /  20  50  60  10
BZN  90  53  76  47 /  20  40  60  30
WEY  81  44  68  38 /  10  50  60  30
DLN  87  54  73  47 /  20  50  50  20
HVR  94  62  81  52 /   0  30  40  20
LWT  88  59  75  48 /  10  40  50  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 8 PM MDT this evening Hill and Blaine
Counties.

&&

$$

weather.gov/greatfalls



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