Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 281710
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1110 AM MDT THU APR 28 2016

.SHORT TERM...THURSDAY THROUGH SATURDAY NIGHT

UNSETTLED AND COOL WEATHER LOOKS TO CONTINUE INTO THE WEEKEND.
CURRENTLY A FEW LIGHT SHOWERS CONTINUE ACROSS THE AREA BUT NOTHING
HEAVY AT THIS TIME. HOWEVER...IN THIS PATTERN THERE IS ALWAYS A
CHANCE ON OF THOSE ANNOYING SNOW BANDS MAY POP UP. AND THIS LOOKS TO
BE THE RULE OF THUMB FOR MOST AREAS TODAY. MAINLY LIGHT SHOWERS
POSSIBLE AT ANY TIME BUT ESPECIALLY DURING THE AFTERNOON AND EVENING
ALONG WITH WELL BELOW NORMAL TEMPERATURES CONTINUING.  ONE AREA THAT
COULD HAVE MORE ORGANIZED PRECIPITATION WOULD BE SOUTHERN SWEETWATER
COUNTY WHERE SOME MOISTURE MAY CREEP NORTHWARD AS AN UPPER LEVEL LOW
PASSES BY TO THE SOUTH. AT THIS TIME...AMOUNTS ARE EXPECTED TO BE
MAINLY LIGHT AND MAINLY A MIX OF RAIN AND SNOW AND WITH THE LATE
APRIL SUN ANY SNOW WOULD HAVE A HARD TIME STICKING...ESPECIALLY ON
PAVED SURFACES.
THIS SHOULD END LATER TONIGHT AS THE LOW MOVES AWAY TO THE EAST.

FRIDAY SHOULD START OUT MAINLY DRY BUT COVERING OF SHOWERS WILL
INCREASE IN THE AFTERNOON AS EASTERLY FLOW DEEPENS AS THE
AFOREMENTIONED UPPER LEVEL LOW SLOWS DOWN AND TRIES TO TURN MORE
NORTH. THE MODELS HAVE DIFFERENCES ON HOW MUCH MOISTURE MAKES IT IN
WITH THE GFS AND EUROPEAN WETTER THAN THE NAM. FOR NOW...WE SPLIT
THE DIFFERENCE LEANING A BIT MORE TOWARD THE WETTER SOLUTION. THE
BEST CHANCE WOULD BE ACROSS EASTERN WYOMING WITH LESSENING CHANCES
THE FURTHER WEST YOU GO. ACROSS THE WEST...A WEAK SURFACE LOW
PASSING THROUGH IDAHO WILL BRING AN INCREASE IN SHOWERS AS WELL AS
MAYBE ENOUGH INSTABILITY FOR A FEW THUNDERSTORMS. TEMPERATURES
SHOULD BE A FEW DEGREES WARMER...BUT STILL WELL BELOW NORMAL.

THE MOST ACTIVE PERIOD MAY FRIDAY NIGHT INTO SATURDAY AS THE
UPPER LEVEL LOW MOVES INTO THE PLAINS AND A PERIOD OF ABOUT 12 TO
18 HOURS OF NORTHEASTERLY UPSLOPE TRIES TO DEVELOP. AGAIN THE
MODELS ARE SPLIT WITH THE NAM DRIER AND SLOWER...THE EUROPEAN THE
WETTEST AND FASTEST AND THE GFS TAKING THE MIDDLE GROUND.
AGAIN...FOR NOW WE COMPROMISED AND SPLIT THE MIDDLE. HOWEVER...ALL
THE MODELS KEEP THE HEAVIEST PRECIPITATION TO THE EAST OF THE
COUNTY WARNING AREA. THIS PRECIPITATION AREA SHOULD TAPER OFF
LATER AT NIGHT AS LOW MOVES AWAY TO THE EAST AND FLOW TURNS MORE
EASTERLY TO SOUTHEASTERLY. THE EXCEPTION WOULD BE A PLACE LIKE
DUBOIS OR THE LEE OF THE ABSAROKAS WHERE SOME UPSLOPE COULD
DEVELOP. 700 MILLIBAR TEMPERATURES ARE BORDERLINE FOR RAIN OR
SNOW...AROUND MINUS 5 TO MINUS 6 SO PRECIPITATION TYPE MAY DEPEND
A LOT ON DYNAMIC COOLING AND RATE OF THE PRECIPITATION.

.LONG TERM...SUNDAY THROUGH THURSDAY

AT 12Z SUNDAY...MODELS ARE IN DECENT AGREEMENT WITH THE MAIN UPPER
LOW OVER CENTRAL/NORTHERN ARIZONA. THERE WILL BE WEAK DISTURBANCES
ROTATING AROUND THIS UPPER LOW THAT WILL CONTINUE TO GIVE MUCH OF
THE AREA A CHANCE OF PRECIPITATION. THIS COULD BE ENHANCED BY SOME
WEAK UPSLOPE EAST/NORTHEAST FLOW FOR AREAS EAST OF THE DIVIDE.
HOWEVER THE MAIN MODEL TRENDS FOR SUNDAY HAS BEEN FOR LIGHTER
PRECIPITATION AND NOT AS WIDESPREAD AS WHAT IT LOOKED LIKE A FEW
DAYS AGO. STILL TEMPERATURES WILL BE WELL BELOW AVERAGE FOR LATE
APRIL.

THE UPPER LOW BEGINS TO FILL AND SHEAR OUT SUNDAY NIGHT AND
MONDAY WITH UPPER RIDGING BUILDING INTO THE AREA TUESDAY AND
WEDNESDAY. CONVECTION CHANCES WILL BE CONFINED MAINLY TO THE
MOUNTAINS OR ACROSS THE SOUTHWEST PART OF THE FORECAST AREA. A
MAJOR WARMING TREND IS EXPECTED MONDAY THROUGH WEDNESDAY WITH
TEMPERATURES RETURNING TO SEASONAL TO EVEN SLIGHTLY ABOVE AVERAGE.

BY LATE THURSDAY...A STRONG UPPER LOW IS EXPECTED TO BEGIN PUSHING INTO
CENTRAL/SOUTHERN CALIFORNIA. THE DIFLUENT FLOW AHEAD OF THIS
SYSTEM COULD RESULT IN SOME THUNDERSTORM ACTIVITY OVER THE
WEST...BUT THE EAST SHOULD REMAIN DRY...BUT BEGIN TO GET BREEZY TO
WINDY. ABOVE AVERAGE TEMPERATURES ARE EXPECTED THURSDAY WITH 70S
TO NEAR 80 EAST...WITH MID 60S TO LOWER 70S WEST IN THE LOWER
ELEVATIONS.

&&

.AVIATION.../18Z ISSUANCE/

WEST OF THE CONTINENTAL DIVIDE...KJAC/KRKS/KPNA/KBPI AIRPORTS

VFR/MVFR CONDITIONS WILL PREVAIL OVER MOST OF THE REGION THROUGH
THIS EVENING. SHOWERS WILL DEVELOP OVER WEST AND SOUTH WY THIS
AFTERNOON AND EVENING. MAINLY MVFR CONDITIONS WILL RETURN ACROSS
SOUTHWEST WY THIS EVENING...CONTINUING THROUGH 15Z FRIDAY. A GUSTY
NORTHEAST WIND WILL CONTINUE AT/NEAR THE KRKS AIRPORT MOST OF THE
REST OF THE DAY AND EVENING. IMPROVING CONDITIONS EXPECTED AFTER 15Z
FRIDAY.

EAST OF THE CONTINENTAL DIVIDE...KCPR/KCOD/KRIW/KWRL/KLND AIRPORTS

MVFR TO OCCASIONAL VFR CIGS OVER MOST OF THE REGION TODAY AND THIS
EVENING...WITH SOME LIGHT RAIN AND/OR SNOW SNOW SHOWERS THROWN IN
FOR GOOD MEASURE. MVFR TO OCCASIONAL IFR CIGS WILL RETURN LATER THIS
EVENING...LASTING THROUGH 15Z FRI. IMPROVING CONDITIONS EXPECTED
AFTER 15Z FRIDAY.

&&

.FIRE WEATHER...

FEW CONCERNS FOR MOST OF THE WEEK WITH UPPER LEVEL LOW PRESSURE
KEEPING THE WEATHER UNSETTLED. TEMPERATURES WILL AVERAGE BELOW
NORMAL WITH RELATIVE HUMIDITY REMAINING ABOVE CRITICAL LEVELS...SOME
AREAS WELL ABOVE CRITICAL LEVELS. THERE WILL BE A DAILY CHANCE FOR
SHOWERS FROM TODAY LIKELY INTO THE WEEKEND FOR MANY AREAS.

&&

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

&&

$$

SHORT TERM...HATTINGS
LONG TERM...WM
AVIATION...BRAUN
FIRE WEATHER...HATTINGS


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