Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 012013
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
213 PM MDT MON SEP 1 2014

.SHORT TERM...TONIGHT THROUGH TUESDAY

UPPER LOW QUICKLY EXITING EAST INTO NORTHERN PLAINS WILL KEEP A
FEW SHOWERS AND THUNDERSTORMS EARLY THIS EVENING THEN RIDGING
TAKES HOLD. DRY WEST FLOW WILL DOMINATE LATER TONIGHT AND TUESDAY
WITH INCREASING WINDS TUESDAY AS STRONGER WINDS ALOFT MIX TO
SURFACE CENTRAL AND SOUTH AREAS. WARING WILL RESULT.

.LONG TERM...TUESDAY NIGHT THROUGH MONDAY

THRU WED NIGHT...PROBABLY THE SIGNIFICANT WX PARAMETERS OF THIS
FORECAST PERIOD ARE DIRECTLY AS RESULT OF UPR ZONAL FLOW BEGINNING
TO TRANSITION TO STRONG SW FLOW WHILE AT THE SAME TIME...RAPID
DRYING NEAR SFC OCCURS AS DEEPENING LEE SIDE LOW DEVELOPS ACROSS
ERN WY ALONG WITH A TIGHTENING PRESSURE GRAD/FRONTOGENESIS TO THE
WEST/NORTHWEST. THIS IS DIRECTLY RELATED TO THE INFLUENCE OF THE
APPROACH OF YET ANOTHER LARGE NW CONUS UPR LVL TROF. ADDITIONALLY
AND ASSOCIATED WITH THIS DISTURBANCE...UPR LVL WIND SPEEDS WILL
INCREASE DRAMATICALLY THRU THE DAY WED AS JET LVL WINDS RANGE
BETWEEN 80 AND 100 KTS AHEAD OF THIS TROF. THIS SITUATION ALONG
WITH SFC TO H5 LAPSE RATES RANGING BETWEEN 9 AND 11 DEG
C/KM...ALBEIT NEAR DRY ADIABATIC...WITH STILL BE MORE THAN
UNSTABLE ENOUGH TO BRING DOWN SOME OF THE INCREASED UPR LVL FLOW
AND REINFORCE THE P GRAD INDUCED WINDS AT THE SFC. ATTM...WINDS
LOOK TO REMAIN BELOW HIGH WIND WARNING...HOWEVER FIRE DANGER
ELEMENTS LOOK TO EASILY EXCEED MIN CRITERIA FOR RED FLAG
CONDITIONS WED AFTERNOON...WIND GUSTS >= 25 KTS AND RH<= 15
PERCENT...SO LOOKING TO ADD FIRE WX ZONES 279 280 283 AND 289 INTO
WATCH/WARNING. THANKFULLY THESE CONDITIONS LOOK TO BE SHORT-LIVED
AS THE FRONT MENTIONED ABOVE SWEEPS THRU THE FA FROM N TO
S...ELIMINATING RED FLAG CONDITIONS THURSDAY. ALSO...WITH VERY DRY
AIR IN PLACE FOR MOST OF THE CWA AHEAD OF THE FRONT AND ITS UPR
LVL COUSIN...AND NO TIME TO RELOAD MOISTURE...VERY LITTLE PRECIP
WILL HAVE A CHC TO FALL AND WHAT LITTLE DOES WILL HAVE TO TAKE
ADVANTAGE OF ELEVATION GAINS IN THE NORTHERN MOUNTAINS.

THROUGH THE REST/END OF THE FORECAST...INASMUCH AS WED WILL BE THE
WARMEST DAY OF THE EXTENDED...THURSDAY WILL BE POST FRONTAL AND
LIKELY THE COOLEST WITH HIGHS STRUGGLING TO GET OUT OF THE 60S
ACROSS THE LOWER REACHES WHILE THE MOUNTAINS ONLY GET INTO THE UPR
30S TO LOWER 40S.

OTHERWISE...LR MDLS ARE STRUGGLING SOMEWHAT WITH HOW TO TREAT THE
WRN CONUS TROF THRU THE ENTIRE EXTENDED...STARTING ON FRIDAY.
HOWEVER THERE ARE COMMONALITIES THRU THE EXTENDED WHICH HAVE THE MOST
MERIT WITH RESPECT TO THE FORECAST. OVERALL...RELATIVELY DRY
EXTENDED FORECAST AS WE CONTINUE TO LOSE CONTACT WITH MONSOONAL
MOISTURE THROUGH THE END OF THE PERIOD...ESPECIALLY ACROSS THE
CENTRAL AND NORTHERN FA WHEN COMPARED TO THE PAST FEW WEEKS. EVEN
WITH PERIODS OF UPR LVL INSTABILITY AND A BRUSH WITH ANOTHER (BACK
DOOR THIS TIME) FRONT NEAR THE END OF THE WORK WEEK...AND ANOTHER
WEAKER ONE NEXT MONDAY...HIGHER PRECIP PROBS AND QPF WILL LIKELY STAY
NEARER THE SRN OR SERN ZONES...CLOSER TO A LITTLE BETTER MOISTURE
AND FORCING. HAVE TWEAKED FCST TO REFLECT THIS TREND.

&&

.AVIATION.../00Z ISSUANCE/

A LAST IN A SERIES OF UPPER LEVEL DISTURBANCES IN NW FLOW WILL RACE
SE ACROSS NORTHEAST WYOMING THIS AFTERNOON. AREAS OF MVFR/IFR
CIGS WITH SCT -SHRA AND ISOLATED TSRA WITH LOCAL MTN OBSCURATIONS IN
BIG HORN MOUNTAINS ...WILL LINGER OVER BIG HORN MOUNTAINS AND
EASTERN JOHNSON AND NORTHERN NATRONA COUNTIES 00Z-03Z.  W-NW WIND
AT 15-25KT AND MAINLY SKC CONDITIONS WILL PREVAIL ACROSS THE
SOUTHERN THIRD OF THE AREA.

SKC CONDITIONS WITH DIMINISHING WIND...PATCHY FOG IN THE WESTERN
VALLEYS...WILL PREVAIL TONIGHT WITH SKC FOR TUE WITH WEST
SOUTHWEST WINDS 15 TO 25 KTS GUSTING TO 35 KTS SOUTHWEST AND
CENTRAL AREAS.

NOTE...FAA INFORMS NWS THAT OBSERVATION FRO KCOD WILL BE UNAVAILABLE
UNTIL SOMETIME TUESDAY WHEN REPAIRS ARE EXPECTED.  TAF CONTINUED AS
VFR CONDITIONS ARE ANTICIPATED AT KCOD THROUGH THE FORECAST PERIOD.

&&

.FIRE WEATHER...

DRY WEST SOUTHWEST FLOW ALOFT WILL MOVE OVER SOUTHWEST AND
CENTRAL WYOMING TUESDAY AFTERNOON AND REMAIN THROUGH WEDNESDAY
EVENING. VERY LOW RELATIVE HUMIDITY AND STRONG GUSTY WINDS WILL
DEVELOP ACROSS THE SOUTHWEST AND CENTRAL PORTIONS OF WYOMING AFTER
NOON ON TUESDAY CONTINUING UNTIL AROUND 8 PM MDT TUESDAY EVENING.
THE VERY LOW RELATIVE HUMIDITY AND STRONG GUSTY WINDS WILL
REDEVELOP AFTER NOON ON WEDNESDAY CONTINUING UNTIL AROUND 8 PM MDT
WEDNESDAY EVENING. RED FLAG WARNING IN EFFECT FROM NOON TO 8 PM MDT
TUESDAY FOR WIND AND LOW RELATIVE HUMIDITY FOR FIRE WEATHER ZONES
279...280... 283 AND 289. RED FLAG WARNING AGAIN IN EFFECT FROM
NOON TO 8 PM MDT WEDNESDAY FOR WIND AND LOW RELATIVE HUMIDITY FOR
FIRE WEATHER ZONES 279...280...283 AND 289.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING FROM NOON TO 8 PM MDT TUESDAY
WYZ279-280-283-289.

RED FLAG WARNING FROM NOON TO 8 PM MDT WEDNESDAY
WYZ279-280-283-289.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...BRAUN
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER








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