Area Forecast Discussion
Issued by NWS Great Falls, MT

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS65 KTFX 221002
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
402 AM MDT FRI JUL 22 2016

.DISCUSSION...

Today through Sunday...Water vapor imagery reveals upper level moisture
spreading into the region ahead of a shortwave trough presently
crossing the WA/OR coast. Temperatures remain around 10 degrees
above average today. Surface pressure falls and deep layer mixing
will produce strong gusty winds this afternoon while lowering
afternoon relative humidity below 15 percent for much of central
and southwest MT. Red Flag fire weather warnings are in effect for
this afternoon as discussed below. Forecast soundings reveal
increasing instability and shear today, but with CAPE limited by
high LCLs due to the dry boundary layer. Nonetheless, short term
models consistently support showers and thunderstorms over
northern portions of the Continental Divide - including Glacier NP
- and extending east through our northern counties as the
shortwave trough and associated cold front cross the region. These
forecasts are consistent with observations indicating higher
dewpoint temperatures. Winds turn westerly and strengthen behind
the frontal passage late this afternoon and evening. Winds will
taper on Saturday as temperatures return near to just below
seasonal averages. Fair and pleasant weather prevails on Sunday
with a weak northwest flow aloft over the region. PN

Sunday Night through Friday...High pressure ridging centered
near/slightly west of the Four Corners area will remain in place
through this period. That will keep our region under west-southwest
flow aloft, leading to very warm temperatures and mostly dry
conditions.  Weak disturbances moving through the flow will combine
with a mix of Pacific and monsoonal moisture to produce isolated
thunderstorms each afternoon, mainly over the central and Hiline
counties.  Given the spotty coverage pattern of the moisture and dry
near-surface conditions (aftn humidities in the teens and low 20s),
convective activity on Mon-Wed will likely be a mix of wet and dry
(<0.1 inch rainfall) storms.  Gusty outflow winds and possible fire
starts from lightning are the primary threats from these storms in
the first half of next week. Storm type will trend wetter for
Thurs/Fri as slightly higher moisture is expected after a cool front
passes across the region Wed night. High temperatures will run 5-8
degrees (upper 80s to low 90s) above normal before the cool front
arrives and then drop back close to seasonal values (mid 80s) on
Thurs/Fri.
Waranauskas

&&

.AVIATION...
Updated 0545z.
VFR conditions prevail through mid-day Friday. A weak disturbance
aloft is moving mid-level clouds through central MT tonight. A cold
front will cross through the region late Friday afternoon. Winds
will shift to westerly and become gusty behind the front. Scattered
thunderstorms are probable at KCTB/KHVR/KLWT, producing temporary
MVFR and perhaps even brief IFR conditions if TS move directly over
the terminals. PN

&&

.FIRE WEATHER...
Deep layer mixing and increasing southwest winds this afternoon
will cause minimum relative humidity to fall below 15 percent over
the southern districts. A Red Flag Warning is in effect for MTZ118
this afternoon where fire danger ratings have reached high to very
high due to drying of fine fuels, especially grasses. A cold front
expected to move through the region late this afternoon will bring
cooler temperatures and higher humidity, but gusty west winds will
continue through early Saturday. Isolated dry lightning may be
possible over the higher terrain of southwest Montana where
moisture is increasing aloft while remaining dry at the surface.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  92  55  80  50 /  10  10   0   0
CTB  85  53  77  49 /  30  20  10  10
HLN  93  59  82  54 /  10  10   0   0
BZN  92  49  81  47 /  10  10   0   0
WEY  81  40  72  39 /  10   0   0   0
DLN  89  48  79  47 /   0   0   0   0
HVR  92  58  81  53 /  20  20  20  10
LWT  91  55  78  52 /  20  20  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 1 PM this afternoon to 9 PM MDT this
evening for MTZ118.

&&

$$

weather.gov/greatfalls


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.