Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 231603
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1003 AM MDT Sat Aug 23 2014

...Widespread rain, heavy at times, through  this afternoon...


.UPDATE...

Satellite imagery this morning shows a deep upper low (for late
August) centered over SE ID, wrapping moisture up and into central and
n-central MT. This low will track slowly east into WY by late this
afternoon. Main axis of precipitation...currently stretching from
around Helena Northeast to the bears paw Mtns. Will slowly pivot
counter-clockwise as the low moves by to our south today. Already
seeing some fairy impressive rainfall totals over north- central
MT this morning with additional precipitation expected in these
same areas throughout the day. So far, snow levels have remained a
bit higher than anticipated, however a fire lookout at around 8800
ft NW of Augusta recently reported a changeover to snow with minor
accumulations. With this information, snow levels were raised by
about 1000 ft. Still expect snow levels to lower down to around
7000 feet later today and have updated to adjust snow levels, QPF
and and snow amounts. Winter weather advisory will continue, but
should be able to expire at 8z as main axis if rainfall pivots
slowly away from the Rocky mtn font. Hoenisch

&&

.AVIATION...
UPDATED 1124Z.
An upper level low pressure trof will continue to keep Central
Montana moist with widespread IFR CIGS and VSBYS. Portions of the
region will see some improvement to MVFR/VFR conditions during the
late morning and afternoon but these improved conditions will be
temporary.

&&

.HYDROLOGY...
A Flood Watch is in effect through Sunday morning for the Rocky
Mountain Front and through Sunday evening for eastern portions of
north-central Montana. Recent rainfall has saturated soils in some
parts of north-central Montana with additional widespread and
prolonged rainfall expected today through Sunday. The highest
rainfall amounts are expected today. Rainfall will be locally
enhanced along the Rocky Mountain Front due to upslope effects with
increasing runoff from mountain streams and creeks. Mudslides are
also possible in areas of steep terrain. There is also an increased
threat for flooding of small streams and creeks as well as low-lying
and poor drainage areas in eastern portions of north-central
Montana. Although rivers are expected to rise through the weekend,
they are generally expected to remain within their banks.
Coulston/MLV

&&

.PREV DISCUSSION...
/ISSUED 525 AM MDT Sat Aug 23 2014/

..Widespread rainfall, heavy at times expected today and tonight...

Today through Monday...

Widespread and at times moderate to heavy rainfall will affect
north-central Montana today as a broad, potent trough of low
pressure with deep moisture and energy continues to move over the
Northern Rockies. Periods of rain and isolated thunderstorm will
also affect southwest Montana though total precip amounts will be
slightly less. Total rainfall amounts today through Sunday evening
will generally range from 1 to 2 inches over north-central Montana
with 0.25 to 0.75 inches across southwest Montana. Isolated higher
amounts near 3 inches are possible over Blaine and Fergus counties
where frontogenetic forcing will be focused this afternoon, thus
leading to heavy and possibly intense rainfall.

In addition to precipitation, the deepening trough will bring an
unseasonably cool, Canadian airmass into the Treasure State. This
cooling will allow snow levels to fall to around 7000 feet along the
Rocky Mountain Front including Glacier National Park. Accumulating
snow is possible in the higher elevations of Glacier National Park
and Bob Marshall Wilderness with 1 to 3 inches above 7000 feet and
up to 1 inch of snow and slush at Logan Pass. Snow will initially
melt on the surface along Going-to-the-Sun Road, however visibility
may be poor in rain, snow and low clouds, thus impacting travelers
and outdoor recreationalists. Unseasonably cold and wet conditions
can also lead to hypothermia. Due to the combination of snow, rain
and unseasonably cold temperatures, a Winter Weather Advisory for
elevations above 6500 feet is in effect until Noon today. High
temperatures this afternoon will range from the 50s across north-
central Montana to around 60 in southwest Montana. In higher
elevations, temperatures will remain in the 40s to near 50. While
overnight lows in the mountains will be in the low to mid 30s,
overnight low temperatures across the plains and southwest valleys
will remain in the 40s due to cloud cover and precipitation.

With the potential for heavy rain in a short duration,
small streams and creeks as well as urban and low-lying, poor
drainage areas may have an increased risk for minor flooding. Will
continue a Flood Watch for eastern portions of the forecast area and
the Rocky Mountain Front thru Sunday evening.

Precipitation will taper from west to east on Sunday as the
upper-level moves into Saskatchewan, however another weak shortwave
will move over southwest Montana Sunday night/Monday so have kept
chance pops. Across north-central Montana, drier conditions are
expected Sunday night and Monday. Temperatures will rise on Monday,
but still remain 15 degrees below seasonal averages. MLV

Monday night through Saturday...An upper level low pressure trof
will continue to affect Central Montana Monday night and Tuesday.
The stronger dynamics will be across the southern portions of the
CWA while, to the north, surface high pressure and drier air will
generally keep the area dry. The trof will be moving east of Central
Montana Tuesday and heights aloft will be rising and the air mass
drying from the north. A high pressure ridge will be over the
Rockies early Wednesday morning and this will begin a period of warm
and dry conditions. The ridge will move east of the zones late
Thursday and heights aloft will begin to fall. The air mass will
remain quite dry, however, and afternoon convection should be
isolated at best through Friday. An upper level low pressure trof
will be over the West late Saturday and move over the Pacific
Northwest Saturday night. Any precipitation ahead of this will
generally be restricted to the Rockies. Zelzer

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  55  45  60  43 / 100  90  60  20
CTB  53  43  60  45 / 100  70  30  10
HLN  59  46  65  45 / 100  90  30  20
BZN  61  42  64  45 /  80  60  30  20
WEY  58  36  59  42 /  80  50  40  20
DLN  60  40  64  43 /  90  60  30  30
HVR  58  47  60  44 / 100  90  80  20
LWT  55  43  57  41 / 100  80  60  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
FLOOD WATCH through late tonight Northern Rocky Mountain Front...
Southern Rocky Mountain Front.

WINTER WEATHER ADVISORY until Noon MDT today FOR ELEVATIONS
ABOVE 6500 FEET FOR Northern Rocky Mountain Front...Southern
Rocky Mountain Front.

FLOOD WATCH through Sunday afternoon Blaine...Chouteau...
Fergus...Hill...Judith Basin...Liberty.

&&

$$

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