Flash Flood Watch 5, NWS Missoula, MT

617 
WGUS65 KMSO 150231
FFAMSO

FLOOD WATCH
NATIONAL WEATHER SERVICE MISSOULA MT
831 PM MDT THU AUG 14 2014

MTC039-063-150345-
/O.EXP.KMSO.FF.A.0005.000000T0000Z-140815T0300Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
GRANITE-MISSOULA-
831 PM MDT THU AUG 14 2014

...FLASH FLOOD WATCH WILL EXPIRE AT 9 PM MDT THIS EVENING...

THE FLASH FLOOD WATCH FOR A PORTION OF WEST CENTRAL MONTANA WILL
EXPIRE AT 9 PM MDT THIS EVENING. 

$$

Area Forecast Discussion
National Weather Service Missoula MT
1029 AM MDT Thu Aug 14 2014

.UPDATE...There is an increased threat of mid afternoon and
evening isolated severe thunderstorms...mainly Bitterroots to
Missoula to Seeley Lake to Continental Divide and southward to
Butte Anaconda today. Large hail...very heavy rain...strong gusty
winds and frequent lightning are the main threat with severe
storms.

&&

.DISCUSSION...A very unstable atmosphere and possible favorable
lower atmosphere environment for isolated severe thunderstorms is
expected to develop mid to late afternoon over west central and
southwest Montana. Partial clearing is already working
northeastward over this area and will allow significant heating and
instability to develop. The lower atmosphere wind field is
expected to become more favorable for possible rotating updrafts
within individual storms by late afternoon. The main threat area
should be from the Bitterroots to Missoula to Seeley Lake and then
south and east to the Continental Divide. This also includes
Philipsburg, Anaconda, Hamilton, and Butte. However, the area that
could see isolated severe storms may be a bit further north and
west as well...including The eastern Clearwaters of Idaho and
areas north of Missoula (such as Plains and Saint Ignatius).
Widespread showers and thunderstorms are still expected across
north central Idaho and western Montana through the afternoon. The
above is just a higher concern area for possible isolated severe
storms. Confidence is still only moderate...but enough that we are
sharing the potential at this time.

&&

.PREV DISCUSSION... /ISSUED 417 AM MDT Thu Aug 14 2014/

..Main heavy rain threat shifts north today and continues thru
Friday...

DISCUSSION...Low clouds and fog are possible this morning due to
an abundance moisture near the surface from recent rainfall. Low
visibility may affect travel, especially along and near bodies of
water or recently drenched fields.

The next wave of instability rotating around the parent upper low
pressure system, which is sitting on the Washington/Oregon border,
can be seen on morning water vapor satellite imagery steadily
moving north across west central Idaho (basically north of a line
from Ontario, Oregon to Sun Valley, Idaho). An area of rather
robust convection with frequent lightning and moderate/heavy
rainfall has persisted along this wave and will continue slowly
to the north, reaching Idaho & Clearwater County by mid morning
and eventually crossing into Montana between Missoula and Lookout
Pass between 11am and pm. This area of lift will combine with
morning heating to produce additional showers and thunderstorms
across northwest Montana during the afternoon. Again the main
threats will be frequent lightning, gusty winds and brief heavy
rainfall.

All models agree upon a less organized potential for strong/severe
thunderstorms this afternoon than had previously been indicated
in forecasts. This is mainly due to poor timing between waves of
instability and the presence of persistent cloud cover that will
limit daytime heating. However that being said, the best chances
for strong storms today will be across southwest Montana where
there should be a bit more sunshine this afternoon. But given the
recent rainfall believe that severe wind gusts (basically 60 mph
or greater) even here appear very challenging to achieve. Of
greater concern today may be the continued threat for flash
flooding on recent forest fire burn scars across Idaho and
Montana. But the locations and timing for specific threats will
continued to be monitored due to low confidence.

Showers and thunderstorms will continue across Idaho and Montana
through much of tonight as additional waves of instability are
projected to rotate around the upper low as it moves slowly to the
northeast. Timing of these features will be key but still is met
with only modest confidence starting tonight. Models are showing
some agreement with regards to an area of enhanced convection
developing early Friday morning along the Idaho/Washington/Oregon
border that will slowly spread north into the Idaho Panhandle and
northwest Montana throughout the day on Friday. This area of
thunderstorms is forecast to be slow moving due to its positioning
near the center of the eastward traveling upper low and may result
in a persistence of moderate to heavy rainfall across this region
lasting till late Friday night or early Saturday morning. There
could be a threat for urban and/or small stream flooding if the
storm motion is as limited as some models suggest and this will be
closely watched over the next 24 hours. Though there will be some
showers around Saturday afternoon, overall conditions will
be much improved.

Sunday/Monday...Northwest flow develops while temperatures will warm
back to above normal readings. With residual moisture in place on
Sunday there should be showers and possibly a few thunderstorms that
develop across northwest Montana.

Tuesday/Wednesday...The upper level westerly jet strengthens and as
a result breezy conditions will develop across the area. Those
recreating on area lakes may be affected by gusty winds.

Late next week...The ECMWF, GFS and GFS ensemble weather models
are showing a pattern change in the upper level jet stream. They
are amplifying or building a large upper level ridge over the
northeastern Pacific Ocean, a scenario which would place us under
northwest flow and could turn out to be either a dry or wet pattern.
Right now the GFS and ECMWF models are showing a wetter system
possibly bringing widespread precipitation with near normal or
even below normal temperatures to the region by next weekend.

AVIATION...Thanks to rainfall at KMSO last evening, low clouds have
been able to develop and hang around at times this morning. Expect
improvement after sunrise, especially by 14/1500z. KBTM also received
rainfall and could see lower ceilings/stratus deck form by sunrise
but confidence is low. As of 14/1000z an upper level wave was
moving eastward across eastern Oregon into central Idaho. This
wave is expected to track northward across Idaho & Clearwater
Counties of Idaho and into the Idaho Panhandle by 14/1800z. It
will probably be able to provide enough lift to support
thunderstorms at KSMN early this morning. KMSO may see the best
chance for thunderstorm activity between 14/1600z and
14/1800z...for KGPI the best chance would be between 14/1800z and
14/2000z. There has been some indication in the high resolution
models that an embedded strong thunderstorm could be possible
associated with the aforementioned wave. Another round of
thunderstorms will develop from central Idaho into southwest
Montana by this afternoon. Some of these storms may be able to
become strong with gusty winds, hail and heavy rainfall the
biggest threats. Showers and possibly more thunderstorms are
expected tonight. Noble

&&

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

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