Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 290457
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1057 PM MDT TUE APR 28 2015

.SHORT TERM...TONIGHT THROUGH WEDNESDAY

MOSTLY CLEAR SKIES CAN BE EXPECTED THROUGH WEDNESDAY AS A POSITIVELY
TILTED TROUGH BUILDS IN FROM THE WEST. PATCHY FOG FORMED OVER AREAS
THAT RECEIVED SUBSTANTIAL RAIN/SNOWFALL OVER THE WEEKEND LAST NIGHT
AND THIS MORNING BUT THE SOUNDING PROFILES DID NOT APPEAR IDEAL FOR
FOG DEVELOPMENT JUST AS THEY DO NOT FOR TONIGHT. THE FOG PRETTY MUCH
REMAINED WITHIN THE SHALLOW NOCTURNAL INVERSIONS. ENOUGH EVAPORATION
SHOULD OCCUR TODAY SO AM NOT EXPECTING ANY REDEVELOPMENT OF FOG
TONIGHT WORTH MENTIONING IN THE GRIDS. THE MINIMUM RELATIVE HUMIDITY
ON WEDNESDAY SHOULD DIP INTO THE TEENS AT THE LOWER ELEVATIONS EAST
OF THE DIVIDE. SOUTHWEST WINDS WILL BEGIN TO INCREASE FORM RKS TO
CPR WED AS THE RIDGE AXIS SLIDES OFF TO THE EAST OVER THE PLAINS AND
THE NEXT UPSTREAM TROUGH MAKES LANDFALL ONTO THE PACIFIC COAST THUS
INCREASING THE SOUTHWEST PRESSURE GRADIENT WIND.

.LONG TERM...THURSDAY THROUGH TUESDAY

SHORTWAVE(S) NEARING THE PACNW COAST WILL WEAKEN AS THEY MOVE INLAND
BUT REMAIN STRONG ENOUGH TO PUSH A FRONT AND MODEST MID LEVEL
MOISTURE ACROSS THE WEST AND NORTH WEDNESDAY NIGHT INTO THURSDAY. A
FEW SHOWERS WILL SPREAD FROM N TO S IN THE FAR WEST WEDNESDAY NIGHT
AND THEN MOVE INTO THE NRN ZONES. ON THURSDAY...INSTABILITY IS STILL
RATHER LIMITED AT 100-200 J/KG MAX SO ISOLD TSTMS ALONG THE FRONT
AND DIVIDE WITH SHORTWAVE PASSAGE LOOKS GOOD. GFS WANTS TO TRY AND
GENERATE A WEAK MID LEVEL LOW IN FREMONT COUNTY THU AFTN WITH HIGHER
PCPN POTENTIAL BUT LEANING TOWARDS THE DRIER NAM ATTM. AIRMASS DRYS
OUT AND WARMS BACK FRIDAY INTO SATURDAY WITH A DRY AIRMASS AROUND
THE AREA...ESPECIALLY CENTRAL AND SW. RECENT PRECIP MAY HELP THE
CENTRAL ZONES SOME BUT WITH LESS PCPN IN THE SW...RH`S MAY GET QUITE
LOW THERE. NOT MUCH WIND THOUGH SO JUST WARM AND DRY. FRONTAL
BOUNDARY IN THE MID LEVELS STALLS OUT OVER NRN CO FRI BUT WITH W TO
WNW FLOW NOT SURE ANY CONVECTION WILL OCCUR IN SRN WYO. THE NEXT
WAVE ACROSS THE NORTH MAY JUST SKIM THE NRN MTNS BUT IT`S A TAD
FURTHER NORTH THAN YESTERDAY`S MODEL RUNS. ON SATURDAY...FLOW TRIES
TO BACK TO THE SW IN THE FAR SRN ZONES ALLOWING SOME MID LEVEL
MOISTURE TO LIFT NWD AIDING IN ISOLD MAINLY LATE DAY CONVECTION. IN
THE FAR NORTH...A WEAK DISTURBANCE MAY BRUSH THE FAR NORTH WITH
ISOLD SHOWERS/TSTMS. MODELS START DIVERGING MORE AND MORE EARLY NEXT
WEEK BUT GENERALLY GOING WITH SOME INCREASE IN AT LEAST MID LEVEL
MOISTURE FROM THE WEST OR SW SUNDAY WITH POTENTIAL WEAK EWD MOVING
DISTURBANCE AIDING IS ISOLD TO WIDELY SCATTERED SHOWERS AND TSTMS.
ECMWF HAS MORE INFLUENCE FROM THE NRN STREAM MONDAY WHILE THE GFS
HAS MORE MOISTURE SPREADING NWD IN A SW FLOW AHEAD OF A CA UPPER
LOW. GFS WOULD BE MORE CONDUCIVE TO SHOWERS AND TSTMS THAN THE
ECMWF. STILL SOME POTENTIAL ON THE ECMWF BUT MORE MORE ISOLD/WDLY
SCT COVERAGE. GOING FCST HAS SLGT CHANCE LOWER ELEVATIONS AND CHC
MTNS AND THAT STILL LOOKS GOOD. GFS CONTINUES TO STREAM MOISTURE
NEWD AS THE CA UPPER LOW OPENS UP AND MOVES INTO THE 4-CORNERS AREA.
THE EURO KEEPS THAT SYSTEM FURTHER SOUTH AND A DRIER WSW FLOW. DUE
TO THE UNCERTAINTY YET WILL KEEP GENERALLY 20S ACROSS THE LOWER
ELEVATIONS AND CHC IN THE MTNS. NO SIGNIFICANT COOL AIR WITH THESE
SYSTEMS SO OUTSIDE OF SHOWERS/CLOUD COVER STILL LOOKING AT 60S AND
SOME 70S AT TIMES LOWER ELEVATIONS WITH 40S AND 50S IN THE MOUNTAINS.

&&

.AVIATION.../06Z ISSUANCE/

VFR CONDITIONS WILL OCCUR FOR THE REMAINDER OF TONIGHT AND
WEDNESDAY...WITH ONLY FEW-SCT FAIR WEATHER CUMULUS CLOUDS WEDNESDAY
AFTERNOON. A WEAK LEE TROUGH DEVELOPING WILL ALLOW FOR BREEZY
WESTERLY WINDS TO DEVELOP BY MIDDAY WEDNESDAY...MAINLY IMPACTING THE
KRKS TERMINAL. DURING WEDNESDAY NIGHT...A WEAK SYSTEM WILL IMPACT
THE AREA WITH A COLD FRONT PUSHING INTO NORTHERN WYOMING BETWEEN
09Z-12Z THURSDAY. MVFR CEILINGS ARE POSSIBLE IN WAKE OF THE FRONT.
ALSO A FEW SHOWERS WILL BE POSSIBLE ACROSS NORTHWEST WYOMING AFTER
06Z THURSDAY...BUT COVERAGE IS TOO SPARSE TO MENTION AT KJAC OR KCOD
AT THIS TIME.

&&

.FIRE WEATHER...

CLEAR SKIES TONIGHT WITH SEASONABLY COOL TEMPERATURES WITH LITTLE
TO NO WIND. WEDNESDAY WILL BE THE WARMEST DAY OF THE WEEK WITH
RELATIVE HUMIDITIES BOTTOMING OUT IN THE UPPER TEENS IN MOST AREAS
WITH SOME 20 MPH GUSTS ACROSS RAWLINS DISPATCH...OTHERWISE LIGHT
WINDS. A WEAK COLD FRONT COULD MOVE THROUGH THURSDAY WITH COOLER
TEMPERATURES AND ANOTHER...MUCH QUICKER SYSTEM GRAZING THE AREA
WHICH COULD INCREASE WINDS TO ABOVE 25MPH ON THURSDAY BUT WITH
MORE MODERATE HUMIDITIES IF THE CURRENT COLD FRONT TIMING ENDS UP
BEING CORRECT...WITH THE BULK OF THE FRONT THROUGH THE STATE BY
SUNSET ON THURSDAY. THERE COULD BE SOME THUNDER WITH THIS FRONT AS
WELL...THOUGH THERE IS NOT A LOT OF MOISTURE COMING WITH THE FRONT
MOST OF THE STORMS THAT DO FORM WILL BE WET. TEMPERATURES RISE
BACK INTO THE 70S ON FRIDAY WITH POTENTIALLY VERY DRY AIR MOVING
IN FROM THE WEST WITH LIGHT TO MODERATE WINDS.

&&

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

&&

$$

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










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