Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 162359
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
559 PM MDT Wed Aug 16 2017

.SHORT TERM...for northeast Montana...today through Fri...
Latest Update:

Radar returns show that isolated showers have developed and are
tracking across the eastern half of the CWA late this afternoon
and this trend will continue into the evening hours. As such, pops
were adjusted to better reflect these observations and near term
expectations. Maliawco

Previous Discussion...

Northeast Montana will be under a zonal flow aloft tonight. There
will be a split trough arrangement with the northern wave
extending east through the prairie provinces. The southern wave
extends south through California. Then for Thursday the two
troughs join over the local region to bring a short-wave trough
through the forecast zones.

Tonight, a surface low will be positioned over central Montana and
our local western counties, establishing light southeast wind.
With drier conditions, RHs will not be nearly as high. So no fog
is expected.

Thursday, the day begins with continuing zonal flow aloft. But a
short-wave trough begins to work its way through the CWA by mid-
morning. In response to an associated cold front, the surface low
will shift east. Wind will shift around to the northwest. Models
routinely under-estimate nw winds for our area. In addition, while
convective instability will not be strong, lapse rates will be
high. This will allow effective mixing of stronger winds aloft to
the surface. The end result should be 15-20kt gusts with the cold
front in the afternoon and early evening. Daytime relative
humidity is another forecast element that is overdone by models.
So with dry conditions, expect RHs to lower to near critical
values. Therefore, with the wind and low RHs, will upgrade the
fire watch to a Red Flag Warning.

As said above, convective parameters will not be strong. Plus the
lack of moisture should preclude any but only isolated convection
developing. Will keep pops below 15% text mention. Finally, while
wind with low RHs will be sufficient for critical fire wx
conditions, wind strength might not be strong enough for an NPW
for FP Lake, so will let the next shifts re-evaluate the need for
a wind advsry.

Templer


.LONG TERM...Fri night through Wed...

AFTERNOON UPDATE:
Changes to the long term were minor. Main noticable change was a
cool down Saturday afternoon following the front`s passage.
Temperatures dropped about 3 more degrees with the latest update.
Passage still appears to be dry with maybe an isolated shower
cropping up later Sunday afternoon and evening. GAH

PREVIOUS LONG TERM DISCUSSION:
Friday night through Monday afternoon, a hot, western states ridge
of high pressure will give way locally to a dry cold front and a
large-scale upper-level low pressure trough and more zonal flow.
Fire weather concerns might be heightened with the passage of
those gusty frontal winds on Saturday. Only chances for precip are
isolated at best Sunday morning through Monday morning due to
embedded disturbances within this zonal flow.

Beginning Monday evening, the western states ridge of high
pressure builds back in through our region, giving us warmer and
drier conditions through at least Wednesday morning.

BMickelson


&&

.AVIATION...

VFR expected tonight through Thursday.

A dry westerly flow aloft tonight will be followed by an upper-
level short-wave trough with an associated dry cold front. This
will shift easterly wind around to the northwest by Thursday
afternoon. With the efficient mixing of 850-700mb winds to the
surface, expect afternoon wind to become gusty.

Winds: Light easterly wind tonight. Expect a wind shift initially
to begin late in the morning to the northwest. Afternoon wind
strength will then increase to 15kt with gust up to 25kt.

Templer



&&

.FIRE WEATHER...

Dry cold fronts are expected on Thursday and Saturday. Both of
them will bring gusty northwest winds in the afternoon and
evening. On Thursday, highs will be in the 80s with min RH 13 to
27 percent. NW winds around 15 mph with higher gusts behind the
cold front on Thursday will create critical fire weather
conditions over parts of Northeast Montana. Given the recent
tendency for models to under forecast winds, especially behind
cold fronts, and the extremely dry conditions, upgraded the Fire
Weather Watch to a Red Flag Warning for Thursday afternoon and
evening based on critical fire weather conditions.

On Saturday, highs will be near 90 in most areas with min RH 15 to
25 percent. NW winds behind the cold front will be around 15 mph
which could create critical fire weather conditions again.


&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon to 9 PM MDT Thursday for
MTZ120-122-134>137.

&&

$$

weather.gov/glasgow



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