Area Forecast Discussion
Issued by NWS Riverton, WY

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742
FXUS65 KRIW 291717
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1117 AM MDT FRI APR 29 2016

.SHORT TERM...FRIDAY THROUGH SUNDAY NIGHT

IT LOOKS LIKE WE WILL STAY IN THE COOL AND UNSETTLED PATTERN FOR THE
NEXT FEW DAYS. HOWEVER...THERE IS A BIT OF LIGHT AT THE END OF THE
TUNNEL WE CALL THE SHORT TERM PORTION OF THE FORECAST. THE RADAR IS
FAIRLY QUIET RIGHT NOW WITH ONLY A FEW SHOWERS AROUND. THIS SHOULD
HOLD FOR MOST OF THE MORNING WITH ONLY A FEW SHOWERS AROUND.
PRECIPITATION CHANCES WILL BEGIN TO INCREASE IN THE AFTERNOON
HOWEVER AS AN UPPER LEVEL LOW OVER SOUTHERN COLORADO BEGINS TO TURN
NORTHEASTWARD AND SOME LEE CYCLOGENESIS BEGINS TO OCCUR AND WRAPS A
BIT MORE MOISTURE BACK INTO THE AREA. THERE ARE SOME DIFFERENCES IN
QPF BUT IT DOES NOT LOOK ALL THAT HEAVY THROUGH THE DAYLIGHT HOURS.
WEST OF THE DIVIDE...JUST ENOUGH INSTABILITY WILL BE AROUND FORM A
COUPLE OF THUNDERSTORMS. TEMPERATURES WILL BE A COUPLE OF DEGREES
WARMER THAN YESTERDAY BUT STILL WELL BELOW NORMAL FOR LATE APRIL. AS
FOR SKY COVER...WE KEPT THINGS PESSIMISTIC FOR NOW. IF THERE IS MORE
SUN THAN EXPECTED...MOST PEOPLE WILL BE HAPPY.

STEADIER PRECIPITATION SHOULD THEN BEGIN WRAPPING BACK INTO EASTERN
PORTIONS OF THE AREA...MAINLY AFTER MIDNIGHT. AGAIN THE MODELS ARE
DIFFERING IN TIMING WITH THE NAM ABOUT 6 HOURS SLOWER THAN THE GFS.
FOR NOW WE SPLIT THE MIDDLE. HOWEVER...BOTH MODELS ARE SHOWING THE
STEADIEST AND HEAVIEST PRECIPITATION DURING THE DAY ON SATURDAY. THE
NEXT QUESTION IS HOW MUCH AND WHAT TYPE. IT WILL BE THE LAST DAY OF
APRIL...AND CONDITIONS FOR SNOW ARE BORDERLINE. A LOT WILL DEPEND ON
DYNAMIC COOLING AND PRECIPITATION RATE. THIS COULD BE A SITUATION
WHERE IT COULD SNOW IN SOME AREAS MUCH OF THE DAY BUT DUE TO A
COMBINATION OF ABOVE FREEZING TEMPERATURES AND A HIGH SUN ANGLE THE
SNOW WOULD HAVE A HARD TIME ACCUMULATING...ESPECIALLY ON PAVED
SURFACES. THE GRIDS DO HAVE SOME LOW END ADVISORY AMOUNTS IN
SPOTS...BUT STILL THE QUESTION IF ANY HIGHLIGHTS ARE NEEDED DUE TO
MINIMAL IMPACTS. FOR THIS...WE WILL PUNT BACK TO THE DAY SHIFT. THE
HIGHEST AMOUNTS WOULD BE ACROSS NATRONA COUNTY WHERE THE BEST
MOISTURE WOULD BE. HOWEVER...WINDS ARE NOT IDEAL FOR UPSLOPE THERE.
THINGS WILL TAPER OFF GRADUALLY SATURDAY NIGHT BUT COULD LINGER
LONGER WITH EASTERLY FLOW IN PLACES LIKE THE EAST SLOPES OF THE
ABSAROKAS INTO THE NIGHT.

SUNDAY LOOKS TO HAVE GRADUALLY IMPROVING CONDITIONS AS HIGH PRESSURE
AND DRIER AIR SLOWLY BUILDS IN FROM THE NORTH. THE NAM IS
PARTICULARLY AGGRESSIVE IN MOVING DRIER WHILE THE GFS LINGERS MORE
MOISTURE. WE KEPT THINGS DAMP FOR NOW GIVEN THE RECENT PATTERN. DRY
AIR THEN MOVES IN FOR LATER SUNDAY NIGHT. I THINK THAT LATE SUNDAY
NIGHT IS THE FIRST PERIOD THERE HAS BEEN NO QPF IN THE GRIDS FOR OVER
A WEEK.

.LONG TERM...MONDAY THROUGH FRIDAY

THE BROAD UPPER LOW OVER THE WESTERN U.S. IS EXPECTED TO FILL...AND
SHEAR OUT OVER MONDAY AND TUESDAY...WITH UPPER RIDGING TAKING ITS
PLACE BY LATE TUESDAY OR WEDNESDAY. THE ONLY FLY IN THE
OINTMENT...IS THE 00Z ECMWF SHOWS A SHORTWAVE TROUGH DIVING SOUTH
OUT OF SASKATCHEWAN LATE SUNDAY INTO THE NORTHERN PLAINS SUNDAY
NIGHT. THE ECMWF SHOWS THIS SYSTEM CLOSING OFF AND PUSHING
SOUTHWEST INTO THE COWBOY STATE MONDAY...AND LINGERING ACROSS THE
REGION TUESDAY. THE 00Z GEM ALSO SHOWS THIS FEATURE...BUT HAS
CIRCULATION OVER CENTRAL NEBRASKA AT 00Z TUESDAY. ON THE OTHER
HAND THE GFS AND PREVIOUS MODEL RUNS HAD THE FEATURE IMPACTING THE
UPPER MIDWEST AND GREAT LAKES. HAVE GONE WITH THE LATTER SOLUTION
WITH ANY CONVECTION MONDAY/TUESDAY OVER THE WEST/SOUTHWEST.
WEDNESDAY LOOKS DRY REGARDLESS. THURSDAY AND FRIDAY...MODELS SHOW
A STRONG UPPER LOW GRADUALLY PUSHING INTO CALIFORNIA. SOME ENERGY
AHEAD OF THE FEATURE COULD RESULT IN SOME CONVECTION OVER THE
WEST...WITH A BETTER SHOT ON FRIDAY.

WILL SEE A WARMING TREND NEXT WEEK WITH ABOVE AVERAGE
TEMPERATURES EXPECTED BY WEDNESDAY...AND LASTING THROUGH FRIDAY.

FOR THOSE LOOKING AHEAD TO NEXT WEEKEND...THE POTENTIAL EXISTS FOR
A STORMY WEEKEND WITH SIGNIFICANT PRECIPITATION.

&&

.AVIATION.../18Z ISSUANCE/

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

VFR TO MVFR CIGS MOST AREAS THROUGH TONIGHT...WITH ISOLATED RAIN AND
SNOW SHOWERS OCCURRING NEAR KRKS AND KJAC THROUGH MUCH OF THE
FORECAST PERIOD. ADDITIONALLY... ISOLATED SHOWERS WILL DEVELOP AND
CONTINUE THROUGH LATE TONIGHT. HEAVIEST PRECIPITATION EXPECTED THIS
EVENING FOR MOST LOCATIONS. EXPECT LOCAL IFR CONDITIONS IN LOWER
VSBYS AND CIGS WITH PERSISTENT MOUNTAIN OBSCURATION THROUGH THE
PERIOD. A GUSTY WIND TO CONTINUE AT KRKS THROUGH THIS EVENING.

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

VFR TO MVFR CIGS ACROSS THE REGION THROUGH TONIGHT...WITH ISOLATED
TO WIDELY SCATTERED RAIN/SNOW SHOWERS THIS AFTERNOON AND EVENING.
TONIGHT...EXPECT AREAS OF MVFR TO IFR CIGS AND PERSISTENT MOUNTAIN
OBSCURATION. THEN LIGHT TO MODERATE SNOW WILL MOVE INTO CENTRAL AND
NORTHERN WYOMING BETWEEN 09 AND 14Z SATURDAY...WITH IFR CIGS AND
VSBY REDUCTIONS BECOMING MORE COMMON.

&&

.FIRE WEATHER...

FIRE DANGER SHOULD REMAIN LOW INTO THE WEEKEND AS EASTERLY FLOW
KEEPS TEMPERATURES ON THE COOL SIDE AND RELATIVE HUMIDITY ON THE
HIGH SIDE. THERE COULD BE SOME LOCALLY GUSTY WINDS AT TIMES ON
SATURDAY BUT RELATIVE HUMIDITY SHOULD REMAIN WELL ABOVE CRITICAL
LEVELS. PORTIONS OF CENTRAL WYOMING WILL HAVE ANOTHER CHANCE FOR A
WETTING RAIN EVENT ON SATURDAY.

&&

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

$$

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



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