Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 090849
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
249 AM MDT TUE SEP 9 2014

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT

GENERALLY FLAT RIDGING CONTINUES ACROSS THE WRN CONUS...WITH FLAT
TROFFING E. EX-CLOSED LOW NOW A DEEP TROF OVR WRN COASTLINE...WITH
UPR HIGH OVR SRN TO SWRN CONUS AND ONLY REMNANTS OF EX-HURRICANE
NORBERT STILL TO THE W OFF CNTRL BAJA COAST. YET ANOTHER WEAK SHORTWAVE
MOVING OVR CWA THRU MODEST RIDGE TODAY/TONIGHT TOUCHING OFF
SHRA/TSRA WITH MOSTLY GUSTY RESULTS...AND A LITTLE RAIN HERE AND
THERE. ANOTHER SLIGHTLY STRONGER SHORTWAVE LIES IN WAIT ACROSS
CNTRL NV/W CNTRL UT...AND WILL ARRIVE THIS MORNING AROUND/BEFORE
SUN-UP ACROSS SWRN WY AHEAD OF THE MAIN TROF.

TODAY/TONIGHT...MOISTURE WILL BEGIN TO COMBINE WITH A MODEST
NORTHERLY SOURCE OF MOISTURE THAT WILL FOLLOW WHAT WAS THE KICKER
SHORTWAVE OF THE OLD COL...TO NEAR/N OF THE FA. AT THE SAME
TIME...LEE CYCLOGENESIS/FRONTOGENESIS PROCEEDS IN EARNEST ACROSS
ERN/NRN WY DOWN INTO ERN CO. ALL THIS SHOULD GIVE A RELATIVELY
BROAD AREA OF PRECIP CHANCES ACROSS MUCH OF THE FA THIS
AFTERNOON...WITH MUCH BETTER POPS ACROSS THE SOUTH...EXPANDING
INTO THE CNTRL/NRN AND ERN FA THIS EVENING AS THE MAIN TROF AND
EVENTUALLY ITS AXIS PUSHES THRU THE CWA...FORCING THE FRONT THRU
THE ERN/NRN FA BY THIS EVENING. SNOW SHOWERS WILL BECOME
INCREASINGLY LIKELY OVER THE HIGHER TERRAIN OF THE NRN MOUNTAINS
TONIGHT AS H7 TEMPS DROP TO BETWEEN -1 AND -3 C AND SNOW LEVELS
DROP FROM AROUND 10K FT TO 8.5K FT...WITH 1 TO 2 INCHES
POSSIBLE...ISOLATED 3IN VALUES IN THE BIG HORNS.

WED THRU THU NIGHT...THE FRONT CONTINUES TO PUSH SWD...LOW TEMPS
BEHIND THE FRONT WED MORNING WILL DROP SOME 10 TO 15 DEG OVER THOSE
ON TUE MORNING...A BIT LESS ACROSS THE SRN AND WRN ZONES. NOW
BACKDOOR STATIONARY FRONT WILL REMAIN IN THE AREA...DRAPED DOWN THE
ERN ABSAROKAS AND POSSIBLY AS FAR S AS THE WIND RIVER
MOUNTAINS...WITH GENERALLY COOL/COLD CLOUDY MOIST CONDITIONS NORTH
AND EAST OF THE FRONT...A BIT WARMER AND DRYER WEST AND SOUTH.
ANOTHER REINFORCING UPR LVL WAVE AND AN ASSOCIATED SECONDARY SFC
COLD FRONT WILL MOVE THRU THE NRN AND ERN FA LATE WED NIGHT THROUGH
THU MORNING...WITH PRECIP CHCS INCREASING ONCE AGAIN OVR THE NRN AND
NERN ZONES. AS LIGHT SNOW SHOWERS WILL HAVE CONTINUED ACROSS THE NRN
MOUNTAINS THRU THE DAY WED...THEY WILL BE ENHANCED ONCE AGAIN
OVERNIGHT WED AS H7 TEMPS CONTINUE TO FALL...RANGING FROM -3 TO -6
C...WHILE SNOW LVLS FALL TO 4500 TO 6500 FEET ACROSS THE NRN ZONES...BY
THU MORNING. 3 TO 6 INCHES WILL BE POSSIBLE ACROSS THE BIG HORNS
ONCE AGAIN FROM WEDNESDAY NIGHT THROUGH THE DAY ON THURSDAY...WITH
EVEN 1 TO 3 INCHES OF WET SNOW POSSIBLE ACROSS PORTIONS OF NORTHERN
JOHNSON COUNTY...ESPECIALLY IN/NEAR THE FOOTHILLS...THRU THURSDAY
MORNING...WITH LESSER AMOUNTS FURTHER SOUTH. A LITTLE LESS SNOW OVER
THE NWRN MOUNTAIN GROUP AS TEMPS THRU DEPTH WILL NOT BE QUITE AS
COLD AND AVAILABLE MOISTURE WILL BE LESS. LOOKING FOR 2 TO 4 INCHES
ACROSS THE HIGHEST REACHES OF THE ABSAROKAS...AND PERHAPS A HALF AN
INCH IN PLACES OVER THE BIG HORN BASIN...AND A WET DUSTING IN
PORTIONS OF THE WIND RIVER BASIN BY THURSDAY MORNING. THRU THE DAY
THURSDAY AND THEN OVERNIGHT...THE SECONDARY FRONT REALLY PUSHES SWD
ACROSS MOST OF THE FA E OF THE DIVIDE...WITH H7 TEMPS PLUMMETING TO
BETWEEN -5 AND -10 C IN AREAS WITH PRECIP POTENTIAL...SNOW LEVELS
DROP TO BETWEEN 4 AND 6K FT...NORTH TO SOUTH...EVERYWHERE NORTH OF
THE FRONT. THRU THE DAY THU TO FRIDAY MORNING...ANOTHER 1 TO 3
INCHES POSSIBLE IN THE ABSAROKAS...WITH 2 TO 5 INCHES IN THE BIG
HORN MOUNTAINS. SNOW AMOUNTS OVER THE LOWER ELEVATIONS CNTRL AND E
WILL GENERALLY BE LOW BUT DICTATED BY WHERE THE FRONT SETS UP AND
MOVES AROUND...AND THEN JUST HOW MUCH LIQUID IS AVAILABLE FOR THESE
AREAS. COLDEST NIGHT OF THE SEASON TO DATE BY FRIDAY MORNING...WITH
TEENS/20S IN THE BIG HORNS...UPPER 20S AND LOWER 30S ERN CNTRL AND
NRN BASIN ZONES...WITH LOWER 20S OVER THE WRN/NWRN MOUNTAINS.

.LONG TERM...FRIDAY THROUGH TUESDAY NIGHT

QUIET AND DRY WEATHER WILL TAKE SHAPE BY THE END OF THE WEEK INTO
THE WEEKEND AND NEXT WEEK. BOTH THE GFS AND ECMWF HAVE COME INTO
AGREEMENT...BUILDING A RIDGE OF HIGH PRESSURE OVER NORTHERN
PORTIONS OF THE INTERMOUNTAIN WEST DURING THIS TIME PERIOD. THE
ONLY DIFFERENCE IS THE ECMWF CONTINUES TO RESOLVE A WEAK DRY COLD
FRONT CLIPPING NORTHERN AND EASTERN PORTIONS ON SUNDAY.
HOWEVER...IT APPEARS THE ECMWF IS TRENDING THIS FEATURE A BIT MORE
EASTWARD THAN MONDAYS 00Z RUN. WITH THIS PATTERN...IT LOOKS LIKE
IT WILL BE A TALE BETWEEN TWO DIVIDES. WARMER TEMPERATURES WEST OF
THE CONTINENTAL DIVIDE...AS H7 TEMPERATURES RETURN TO 10 TO 12C BY
SUNDAY. THE NORTHWEST FLOW PATTERN WILL KEEP THESE TEMPS BETWEEN 6
TO 10C EAST OF THE DIVIDE.

&&

.AVIATION.../12Z ISSUANCE/

SHOWERS AND ISOLATED THUNDERSTORMS WILL OCCUR OVER SOUTHERN WY
THROUGH MOST OF THE DAY. LOCAL MVFR CONDITIONS MAY OCCUR IN SOUTHERN
WY IN HEAVIER SHOWERS OR STORMS. ONLY ISOLATED SHOWERS WILL OCCUR
AFTER 01Z ACROSS THE SOUTH.

OVER CENTRAL WY ISOLATED SHOWERS WILL OCCUR THIS MORNING. ISOLATED
SHOWERS AND STORMS WILL OCCUR DURING THE AFTERNOON INTO THE EARLY
EVENING HOURS. ISOLATED SHOWERS WILL OCCUR AFTER 01Z. EXPECT MVFR
CONDITIONS TO DEVELOP AT KCPR AIRPORT BY 02Z WED AS LOW CLOUDS FORM.
LOW CLOUDS WILL FILL IN OVER CENTRAL WY AFTER 06Z EAST OF THE
CONTINENTAL DIVIDE WITH MVFR CONDITIONS PREVAILING.

OVER NORTHERN WY ISOLATED SHOWERS WILL OCCUR THIS MORNING. A COLD
FRONT WILL PUSH SOUTH THROUGH NORTHERN WY BY 16Z. AROUND 18Z AREAS
OF MVFR CONDITIONS WILL OCCUR ALONG WITH ISOLATED SHOWERS. AT 00Z
MVFR CONDITIONS WILL PREVAIL OVER THE NORTH WITH AREAS OF IFR.
EXPECT ISOLATED SHOWERS OR AREAS OF LIGHT RAIN TO OCCUR OVER THE
NORTH FROM 00Z TO 12Z WED.

&&

.FIRE WEATHER...

FIRE DANGER LOW TODAY AS NEW STORM SYSTEM EMERGES FROM THE WEST AND
NORTHWEST...COOLING TEMPERATURES AND INCREASING BOTH MOISTURE ALONG
WITH PRECIPITATION POTENTIAL. THESE LOWER FIRE DANGER CONDITIONS
WILL PREVAIL THROUGH THE END OF THE WEEK. THE SOUTHERN DISPATCH
ZONES WILL SEE THE GREATEST INCREASE IN PRECIPITATION CHANCES
EARLY...FOLLOWED LATER TODAY AND TONIGHT BY THE EASTERN ZONES.
ISOLATED TO WIDELY SCATTERED CHANCES ACROSS THE WEST...CENTRAL AND
NORTH. SNOW LEVELS WILL BEGIN TO LOWER LATER TODAY AND TONIGHT TO
BETWEEN 7000 AND 7500 FEET OVERNIGHT OVER THE NORTHERN
MOUNTAINS...WITH NEW SNOWFALL 0F 1 TO 3 INCHES IN PLACES BY
WEDNESDAY MORNING. WEDNESDAY...MUCH COOLER EVERYWHERE WITH BEST
CHANCES FOR PRECIPITATION SHIFT TO THE NORTH AND EAST...WITH
SIGNIFICANT PRECIPITATION...BOTH LIQUID AT LOWER ELEVATIONS AND
FROZEN IN THE MOUNTAINS...OCCURRING BY LATE AFTERNOON AND THROUGH
THE OVERNIGHT PERIOD. NEW SNOWFALL THROUGH THE DAY AND OVERNIGHT
PERIOD WEDNESDAY THROUGH THURSDAY MORNING WILL RANGE AS HIGH AS 6
INCHES IN THE BIG HORN MOUNTAINS...2 AND 4 INCHES IN THE NORTHERN
ABSAROKAS...AND EVEN A DUSTING ACROSS THE LOWER ELEVATION OF THE
BIG HORN BASIN AND JOHNSON AND NATRONA COUNTIES. ADDITIONAL
LIGHTER AMOUNTS OF SNOW WILL FALL THROUGH THE REST OF THE DAY AND
THURSDAY EVENING.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...BRAUN
LONG TERM...LAVOIE
AVIATION...AR
FIRE WEATHER...BRAUN







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