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Area forecast discussion 
National Weather Service Riverton Wyoming
1151 PM MDT Sat Jul 4 2015

Update...added 06z aviation discussion

Short term...tonight through Sunday (issued at 254 PM mdt)

Showers and thunderstorms are expected across the southern half
of Wyoming this evening. Gusty winds and small hail will be
possible...the north will be generally dry. Overnight lows will be
warmer...before a combination of a Canadian cold front moving
south into central Wyoming...and an upper level low pressure
trough moving northeast from the Great Basin...will combine for
rather widespread rain showers with embedded thunderstorms Sunday
afternoon. The cloud cover...cold front and precipitation will
cool temperatures 15 to 20 degrees Sunday afternoon. The heaviest
rainfall at this time looks to be centered around the Bighorn
Mountains...while most of the mountain areas can expect rainfall
of a half inch to one inch...locally higher amounts are possible.
Most of the lower elevations will receive less rainfall. Areas
along the foothills...such as Buffalo...Casper... Lander...Cody
and DuBois have the best chances of receiving rainfall of a half
inch or more.

Long term...Sunday night through Saturday

Medium-range models in very good agreement with the evolution of the
overall synoptic pattern through the forecast period. Showers and
isolated thunderstorms will taper off overnight into Monday morning
as moisture sags too the southern part of the state and drier air
begins to filter into northwest Wyoming. Best chance for convection
on Monday will be across southwest Wyoming where moisture will
remain more plentiful and instability more favorable. Expect this
area to push farther to the north and east during Monday evening.
Lifted indices and lapse rates indicate that convection will be
limited or non-existent in Johnson and Natrona counties. Convection
looks to be more widespread Tuesday afternoon and evening as middle-
level shortwave moves across the forecast area. Timing of this
feature in the afternoon would intensify convection...especially
across the north-half of the forecast area. A weak cool front will
slide south early Wednesday slowing the warming trend that had begun
the previous day. Overall...Wednesday looks to be a typical Summer
day in Wyoming...albeit cooler than normal...with scattered
convection that begins midday over the higher terrain. One caveat
here would be the potential for more juicy air and favorable shear
profile in Johnson and Natrona counties behind the weak boundary.
Looks like there could be another weak surge of cool air early
Thursday. This will be short-lived as upper flow begins to back to
the west and eventually the southwest with warmer air surging into
the state. This will occur in response to upper low set to reach the
California coast Thursday/Friday. As this low moves inland...
temperatures will return to or be above seasonal normals with warmer
southwest flow enveloping Wyoming. Best chance for convection Friday
and Saturday will be in the northwest mountains. For now...both the
GFS and European model (ecmwf) depict a dry slot across Wyoming Saturday as upper low
approaches. Could be warm...windy...and dry Friday and more so
Saturday...particularly east of the Continental Divide. This could
be something to follow for fire weather concerns if fuels were to
become critical.

&&

Aviation.../06z issuance/

Moisture will increase from the SW this morning as a cold front
pushes into northern Wyoming. The cold front will push south across
the northern border between 12z-15z and to near a vicinity kriw-kcpr line
by 18z. Scattered-numerous showers and isolated thunderstorms will increase
from the SW through the morning along with local MVFR conditions and
higher mountain obscurations. The best moisture and instability will be
across east central Wyoming where the front will meet the moisture
surging in from the SW. A few thunderstorms could be strong across
Natrona (vcnty kcpr) and southern Johnson counties with heavy rain
and marginally severe hail along with brief MVFR/IFR conditions.
More stable conditions and areas of MVFR/local IFR ceilings will follow
the front from north to south...east of The Divide Sunday
aftn/eve...into kcod-kbyg around 20z and vicinity klnd-kriw-kcpr around
2z Monday. These lower ceilings will continue to push into SW Wyoming
overnight.

&&

Fire weather...

Showers and thunderstorms are expected across the southern half
of Wyoming this evening. Gusty winds and small hail will be
possible...the north will be generally dry. Overnight lows will be
warmer...before a combination of a Canadian cold front moving
south into central Wyoming...and an upper level low pressure
trough moving northeast from the Great Basin...will combine for
rather widespread rain showers with embedded thunderstorms Sunday
afternoon. The cloud cover...cold front and precipitation will
cool temperatures 15 to 20 degrees Sunday afternoon. The heaviest
rainfall at this time looks to be centered around the Bighorn
Mountains...while most of the mountain areas can expect rainfall
of a half inch to one inch...locally higher amounts are possible.
Most of the lower elevations will receive less rainfall. Areas
along the foothills...such as Buffalo...Casper... Lander...Cody
and DuBois have the best chances of receiving rainfall of a half
inch or more.

&&

Riw watches/warnings/advisories...
none.
&&

$$

Short term...c.Baker
long term...cnj
aviation...aem
fire weather...c.Baker

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