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000
FXUS65 KRIW 130918
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
318 AM MDT MON MAY 13 2013

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT
TODAY AGAIN WILL BE THE WARMEST DAY THUS FAR THIS SEASON WITH H7
TEMPS CLIMBING TO 13C IN CENTRAL WYOMING. THIS WILL RESULT IN HIGH
TEMPERATURES REACHING THE UPPER 80S TO LOW 90S AT THE LOWER
ELEVATIONS EAST OF THE DIVIDE AND WELL UP IN THE 70S WEST. HIGH
TEMPERATURE RECORDS ARE THREATENED. ONLY ISOLATED THUNDERSTORMS
COULD OCCUR IN THE NORTHWEST MTNS WITH LITTLE LOW LEVEL MOISTURE TO
WORK WITH IN SPITE OF FAVORABLE CAPES. THE CIRCULATION OVER 45N/139W WILL
OPEN UP AS A FAST MOVING VIGOROUS SHORTWAVE TRACKING EAST ALONG THE
CANADIAN BORDER. THIS SHORTWAVE WILL EJECT A COUPLE OF DRY COLD
FRONTS SOUTH ACROSS WYOMING. THE FIRST ONE WILL PUSH SOUTH BETWEEN
09Z AND 15Z TUESDAY MORNING WITH A BRISK WIND SHIFT TO THE NORTH
FUELED BY 8MB 3 HOURLY SURFACE PRESSURE RISES...MAINLY IN JOHNSON
COUNTY. A SECONDARY FRONT WILL PUSH SOUTHWEST AS A DRY BACKDOOR
FRONT TUESDAY EVENING WITH 7MB THREE HOURLY SURFACE PRESSURE RISES.
THE GREATEST DROP IN HIGH TEMPERATURES TUESDAY OVER TODAY WILL BE IN
NORTHERN WYOMING WHERE HIGHS WILL BE 15 TO 20 DEGREES COOLER.
CENTRAL WYOMING WILL BE AROUND 10 DEGREES COOLER AND ONLY 3 DEGREES
OR SO IN SOUTHERN WYOMING. TEMPERATURES WILL BE MORE OR LESS THE
SAME WEDNESDAY WITH ONLY ISOLATED THUNDERSTORMS EXPECTED OVER THE
HIGHEST ELEVATIONS DUE TO A WEAK VORT LOBE WHERE PLENTY OF GROUND
MOISTURE EXISTS.

.LONG TERM...THURSDAY THROUGH MONDAY
DEVELOPING TROUGH OVER THE PACNW WHICH WILL MOVE SLOWLY EWD INTO
WYOMING FRIDAY THROUGH SATURDAY WILL BE THE MAIN WEATHER MAKER IN
THE MEDIUM RANGE. MODEL TIMING IS BETTER TONIGHT BUT SIGNIFICANT
DIFFERENCES DO SHOW UP AT THE END OF THE PERIOD AS TO HOW FAST IT WILL
MOVE OUT. THE GFS IS MORE PROGRESSIVE WHILE THE ECMWF SLOWS THE
SYSTEM OVER ND AND GENERATES A LARGE CLOSED LOW WITH WRAPAROUND
PRECIPITATION INTO MUCH OF THE AREA ON MONDAY. HOWEVER...THE GFS
STILL HAS A COOLER NW FLOW WITH A CHANCE OF SHOWERS SO A BLEND OF
THE TWO IS NOT A BAD COMPROMISE FOR NOW. THE FIRST DISTURBANCE AND
COLD FRONT APPROACHES THE NW LATE THURSDAY WITH POTENTIAL JET
SUPPORT...RIGHT ENTRANCE REGION...AND ACTIVE THUNDERSTORMS. IT WILL
REMAIN GENERALLY WARM...DRY AND WINDY IN THE EAST. TROUGH STARTS TO
DIG INTO THE GREAT BASIN ON FRIDAY WITH AN INCREASING THREAT OF
SHOWERS AND THUNDERSTORMS ACROSS THE WEST AND CENTRAL AREAS WITH
EVEN A FEW IN THE ERN AREAS POSSIBLE. BOTH MODELS HAVE THE TROUGH
MOVING EAST ACROSS THE AREA ON SATURDAY WITH COOLER TEMPERATURES AND
SCATTERED SHOWERS AND THUNDERSTORMS. SOMEWHAT COOL NW FLOW ON
SUNDAY SHOULD KEEP AT LEAST SCATTERED MOUNTAIN AND HIGHER TERRAIN
SHOWERS GOING WITH MOST AREAS HAVING AT LEAST A SLIGHT CHANCE OF
SHOWERS AND ISOLATED THUNDERSTORMS. COOL...MOIST NW FLOW ON MONDAY
WILL LIKELY KEEP AT LEAST SCATTERED SHOWERS ACROSS THE AREA WITH
MORE NUMEROUS SHOWERS IN THE MOUNTAINS. THE SW WILL BE THE DRIEST.

&&

.AVIATION.../12Z ISSUANCE/
VFR CONDITIONS WILL PREVAIL ACROSS THE REGION MONDAY AND MONDAY
NIGHT.  AN UPPER LEVEL DISTURBANCE WILL MOVE ACROSS THE
MONTANA/CANADIAN BORDER MONDAY NIGHT.  SFC SW WINDS WILL INCREASE
ACROSS MOST AREAS AHEAD OF THIS SYSTEM THIS AFTERNOON.  WINDS WILL
CONTINUE TO INCREASE ACROSS MOST AREAS MONDAY EVENING WITH THE
PASSAGE OF A PACIFIC COLD FRONT...ALONG WITH AREAS OF LLWS AND
TURBULENT CONDITIONS VCNTY OF THE DIVIDE AND BIG HORN MTS. ONLY
ISOLD -SHRA/HIGHER MTN -SHSN IS EXPECTED WITH THE FRONT.

A CANADIAN COLD FRONT WILL FOLLOW 08Z-12Z TUESDAY WITH SFC WINDS
SHIFTING FROM THE NORTH TO A VCNTY KCOD-KWRL-KDGW LINE BY 12Z
TUESDAY.

&&

.FIRE WEATHER...
TODAY AGAIN WILL BE THE WARMEST DAY THUS FAR THIS SEASON. THIS WILL
RESULT IN HIGH TEMPERATURES REACHING THE UPPER 80S TO LOW 90S AT THE
LOWER ELEVATIONS EAST OF THE DIVIDE AND WELL UP IN THE 70S WEST.
HIGH TEMPERATURE RECORDS ARE THREATENED. ONLY ISOLATED THUNDERSTORMS
COULD OCCUR IN THE NORTHWEST MTNS LATE TODAY. TUESDAY WILL FEATURE A COLD
FRONT THAT WILL KNOCK HIGH TEMPERATURES DOWN 15 TO 20 DEGREES IN
NORTHERN WYOMING...10 DEGREES CENTRAL WYOMING AND 3 TO 5 DEGREES
SOUTHERN WYOMING. MAINLY DRY WEATHER WITH SIMILAR TEMPERATURES
EXPECTED WEDNESDAY. THE MINIMUM RELATIVE HUMIDITY WILL BE 10 TO
15 PERCENT AT THE LOWER ELEVATIONS EXCEPT FOR THE FAR WEST VALLEYS
WHERE IT WILL BE 15 TO 20 PERCENT. ON WEDNESDAY THE MINIMUM
RELATIVE HUMIDITY WILL ONLY BE IN THE LOW TEENS FROM ROCK SPRINGS
TO CASPER AS WELL AS IN THE UPPER GREEN AND WIND RIVER BASINS.

&&

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

$$

SHORT TERM...LIPSON
LONG TERM...SKRBAC
AVIATION...AEM
FIRE WEATHER...LIPSON