Flash Flood Watch 3, NWS Missoula, MT

402 
WGUS65 KMSO 180247
FFAMSO

FLOOD WATCH
NATIONAL WEATHER SERVICE MISSOULA MT
847 PM MDT TUE JUL 17 2012

MTC029-053-180400-
/O.CAN.KMSO.FF.A.0003.000000T0000Z-120718T0600Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
FLATHEAD-LINCOLN-
847 PM MDT TUE JUL 17 2012

...FLASH FLOOD WATCH IS CANCELLED...

THE FLASH FLOOD WATCH FOR FLATHEAD AND LINCOLN COUNTIES IN NORTHWEST
MONTANA HAS BEEN CANCELLED. WIDESPREAD THUNDERSTORMS HAVE COME TO
AN END...ENDING THE FLASH FLOODING THREAT.

$$

Area Forecast Discussion
National Weather Service Missoula MT
331 AM MDT Tue Jul 17 2012

...Wet thunderstorms to impact Northwest Montana again today....

.DISCUSSION...Today's weather will be driven by the interaction
between a cutoff low off the Oregon/Northern California coast and
a plume of monsoon moisture from the Southwest. Today the moisture
plume will move north over Northwest Montana where thunderstorms
are expected. Thunderstorms and showers will be very wet, but are
expected to move at about 15 mph. Flash flooding is a risk if
storms move slower, but considering the storm motion, terrain, and
vegetation will not issue a flash flood watch. However, ponding of
water on roadways can cause hazardous driving conditions, and
heavy rain on saturated soils increases the risk of rock/mud
slides in prone areas.

South of I-90, storms are expected to be more isolated and not as
wet later in the day as drier air starts move into the region from
the south. However, storm motion may be slower, so the storms can
still drop a lot of rain on one location and may be a hazard.
Bottom line, if you see thunderstorms today, be prepared to deal
with a lot of water.

Wednesday the cutoff low slowly progresses west allowing a weak
ridge to build over the area. Expect warming temperatures, fewer
clouds, and only isolated thunderstorms. By Wednesday the
available moisture will have decreased significantly, and while
storms will still be wet, heavy rain is not expected.

Extended model guidance produces very little confidence in the
forecast. The biggest problem is what the cutoff low off the Pacific
northwest coast does. When does it move to the east and where does
it go. With the uncertainty have made very few and minor changes to
the previous forecast. From Saturday on the guidance is showing a
slightly drier and warmer pattern.

&&

.AVIATION....Another day of thunderstorms across the region with
moderate rain. A cutoff low off the Oregon/Northern California
coast continues to interact with a plume of monsoon moisture from
the Southwest. Showers and thunderstorms will increase this
afternoon and cause lowered ceilings, moderate rain, and partial
mountain obscurations. The heaviest rain will impact Northwest
Montana and KGPI, but all terminals across the area have a chance
of thunderstorms today. Drier air will reach Southwest Montana and
Central Idaho around 03Z where conditions will improve at KBTM and
KSMN.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

Leach/Kolata

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
1254 PM MDT TUE JUL 17 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1246 PM     HEAVY RAIN       5 W SOMERS              48.07N 114.32W
07/17/2012  M1.88 INCH       FLATHEAD           MT   TRAINED SPOTTER

            FELL IN 45 MINUTES FROM 12 PM MDT TO 1245 PM MDT.
            MEASURED BY WIRELESS PRECIP GAUGE.

&&

NOBLE