Area Forecast Discussion
Issued by NWS Glasgow, MT

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000
FXUS65 KGGW 231818 AAB
AFDGGW

Area Forecast Discussion...UPDATED
National Weather Service Glasgow MT
1218 PM MDT Sun Jul 23 2017

.SHORT TERM...for northeast Montana...tonight through Tue...
Satellite imagery shows smoke from Garfield County fires traveling
north due to the southerly winds, then veering northeast as the
smoke rises higher. This follows the model data.

The shallow ridge over Northeast Montana will get knocked down
tonight as a trough/storm system moves east from British Columbia
into the prairie provinces. In addition, a short-wave embedded
disturbance in the upper flow will move across Southeast Montana
this evening. This disturbance can be seen on visual GOES imagery.
This disturbance could generate thunderstorms, some of which may
move into our area this evening. As a surface trough slides across
the local region, a low level jet could interact with these storms
producing strong and erratic winds, a fire wx concern. With
little moisture available, any thunderstorm generated could be
dry. Therefore went ahead and extended the RFW through tonight
into Monday, which has already been advertised as fire wx
enhanced.

Behind the cold front Monday, wind will shift around to the
northwest and increase to around 15-20kt. This inflow of dry
cooler air will begin to lower temperatures a bit, but RHs will
remain dry. The frontal boundary may also generate a few more
thunderstorms Monday evening.

Tuesday, the Canada storm will continue its journey through the
prairie provinces, putting a lid on our temperatures, which may
actually fall slightly below normal. However, continued northerly
wind will also be dry. There may be just enough wind and low RH to
continue the need for fire wx headlines.

Overall, models under-estimate the wind and over-estimate low RHs.
So tweaked guidance for those parameters.

Templer


.LONG TERM...Tue night through Sun...
The extended forecast starts Monday night and Tuesday with zonal
flow residing across the state of Montana with a closed upper low
pushing further downstream into Manitoba. This pattern will
feature seasonable temperatures, though continued dry conditions.

The concerns arising from the dry airmass will only amplify as an
upper ridge builds and strengthens across the western U.S. and
extends into Montana and adjacent portions of southern and
central Canada into the middle of next week. Expect increasing
temperature trends, with highs returning to the 90s for most
places by Wednesday or Thursday. The large scale subsidence will
drive afternoon minimum relative humidity values down into the 10
to 25 percent range each day.

Precipitation chances appear minimal throughout the long range,
though 00z deterministic models suggest a weak embedded shortwave
could eject into eastern Montana on Thursday on southwest flow
aloft as the ridge axis shifts just downstream of the CWA. In any
case, rainfall amounts would be light, if anything at all were to
materialize. The forecast was trended toward consensus blends
which produced isolated pops for this time.

The bottom line: overall, the continuation of dry weather
conditions and occasional hot temperatures look to continue for
the foreseeable future. Maliawco

&&

.AVIATION...
FLIGHT CAT: VFR.

SYNOPSIS: A ridge will be in place today and exit overnight. A
frontal passage is expected early Monday morning.

HIGH DENSITY ALTITUDE: With temperatures approaching the upper
90s to near 100, takeoff may take longer than expected Today.

WIND: Veering to the south this morning around 10 kts or less,
backing to the southeast and increasing to 10 to 15 kts this
afternoon and evening, Switching to the northwest behind a front
early Monday morning.

GAH



&&

.FIRE WEATHER...

...A Red Flag Warning remains in effect today until 9pm for Fire
Weather Zones 122, 134, 135, 136, and 137...

...A Fire Weather Watch is in effect for all Fire Weather Zones
on Monday from 6am through 9pm...

Southerly winds of 10-15 mph continue the rest of the afternoon.
Temperature peak for a very hot afternoon due to effects from
compressional warming with high temperatures nearing 100 degrees.
The combination of hot temperatures, persistent south winds, and
minimum relative humidity values as low as 10 percent have
continued the critical fire weather conditions.

Tonight: A low pressure storm system moves east across the Canada
prairie provinces, sending a cold front south into Northeast
Montana. Additionally an embedded disturbance in the southwest
upper flow is expected to swing across eastern Montana around
midnight. This could initiate rain showers, thunderstorms, some
dry, and increase southeasterly wind significantly due to a low
level jet that could be mixed down this wind. So there is a
potential for explosive fire growth from those possible erratic
nocturnal winds.

Monday: After the cold front from the north passes through the
area, wind will shift around to the northwest and increase to
around 15-25kt, with higher gusts. Scattered light rain showers
and thunderstorms may also be generated during the evening, which
could cause erratic wind. Otherwise, most surface winds will
diminish during the evening as it veers more to the northeast.

Tuesday: The area will remain under the influence of the Canada
storm system. This will include 10-15kt northwest wind and not as
warm temperatures - near normal in the mid 80s. But because of a
large surface high, the NW wind will be dry, relative humidity
percentage will remain low - in the teens to lower 20s.


&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 9 PM MDT this evening for MTZ122-134>137.

Fire Weather Watch from Monday morning through Monday evening
for MTZ120-122-134>137.

Dense Smoke Advisory until 9 PM MDT this evening for Garfield.

&&

$$

weather.gov/glasgow



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