Area Forecast Discussion
Issued by NWS Riverton, WY

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564
FXUS65 KRIW 261055
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
455 AM MDT TUE APR 26 2016

.UPDATE...

UPGRADED WINTER WX ADVISORY TO A WARNING FOR THE LOWER ELEVATIONS
OF NATRONA COUNTY...AS THE RAIN CHANGED TO SNOW A TAD QUICKER THAN
ANTICIPATED. LOOKS LIKE 1-2 INCHES OF SNOW HAS ALREADY
FALLEN...AND ANOTHER 3-6 INCHES IS LIKELY...WITH THE HEAVIEST
THIS MORNING WITH 1"/HR SNOWFALL RATES POSSIBLE.

&&

.PREV DISCUSSION... /ISSUED 312 AM MDT TUE APR 26 2016/

SHORT TERM...TODAY THROUGH THURSDAY NIGHT

WIDESPREAD SHOWER ACTIVITY NOTED EAST OF THE DIVIDE AND ACROSS
SWEETWATER COUNTY THIS MORNING. WEBCAMS DEMONSTRATE SHOWERS HAVE
TURNED TO SNOWFALL ACROSS PORTIONS OF NATRONA COUNTY WITH THE
WALTMAN AREA EXPERIENCING SNOW COVERED ROADWAYS. SWEETWATER COUNTY
HAS ALSO SHOWN A CONVERSION TO SNOWFALL WITH WEBCAMS AROUND THE ROCK
SPRINGS AREA ALSO SHOWING IMPACTED ROADWAYS. BECAUSE OF THESE
OBSERVATIONS AND CURRENT RADAR TRENDS...THE WESTERN HALF OF
SWEETWATER COUNTY HAS BEEN ADDED TO THE WINTER WEATHER ADVISORY.
THIS IMPACTS AREAS AROUND ROCK SPRINGS...GREEN RIVER...AND
ADDITIONAL LOCATIONS WHERE PERIODS OF MODERATE SNOWFALL WILL RESULT
IN DIFFICULT TRAVEL. OTHERWISE...WINTER WEATHER HIGHLIGHTS REMAIN
THE SAME AS THOSE ISSUED MONDAY EVENING.

THE LOW PRESSURE SYSTEM INFLUENCING THIS SNOWFALL IS EXPECTED TO
CONTINUE TO LIFT NORTHEAST THIS MORNING...WITH WRAP AROUND MOISTURE
CONTINUING TO PRODUCE PERIODS OF HEAVY SNOWFALL ACROSS THE AREA. THE
CORE OF THE LOW PRESSURE LOSES ITS STRUCTURE A BIT DURING THE
EVENING HOURS...AND IS ANTICIPATED TO RECENTER ITSELF AROUND CENTRAL
NEBRASKA BY WEDNESDAY MORNING. AS THIS TRANSITION OCCURS...SNOWFALL
ACROSS THE AREA WILL WEAKEN...WITH MUCH OF THE HEAVIEST
PRECIPITATION ENDING BETWEEN LATE THIS AFTERNOON AND EARLY THIS
EVENING. THE ONE AREA THAT WILL HOLD ONTO MOISTURE LONGER THAN THE
OTHERS IS CASPER MOUNTAIN WHERE SNOWFALL MAY CONTINUE THROUGH THE
EARLY MORNING HOURS OF WEDNESDAY.

RESIDUAL MOISTURE OVER THE AREA ON WEDNESDAY WILL KEEP SOME SHOWER
ACTIVITY OVER THE NORTHERN TWO THIRDS OF THE AREA...WITH LINGERING
MOISTURE SHOWERS POSSIBLE. BY THURSDAY MORNING...THIS FIRST AREA OF
LOW PRESSURE WILL WARBLE AGAIN...WITH ITS CORE MOVING FROM EASTERN
SOUTH DAKOTA TO SOUTH CENTRAL MONTANA. THIS WILL HELP TO CONTINUE
SHOWERS OVER THE NORTHERN PORTION OF THE STATE.

MEANWHILE...ANOTHER AREA OF LOW PRESSURE IS ANTICIPATED TO MOVE OVER
THE DESERT SOUTHWEST BY EARLY THURSDAY AFTERNOON. THIS SYSTEM WILL
BE ABLE TO PUSH ADDITIONAL MOISTURE ACROSS SOUTHWESTERN
WYOMING...ALONG WITH ENOUGH INSTABILITY FOR A FEW THUNDERSTORMS
THURSDAY AFTERNOON. THIS AREA OF LOW PRESSURE WILL LIFT SLIGHTLY AS
IT PROGRESSES EASTWARD...LANDING AROUND THE FOUR CORNERS REGION BY
LATE THURSDAY NIGHT. THIS WILL KEEP SOME MENTION OF SHOWER ACTIVITY
OVER THE MOUNTAINS THROUGH THE REMAINDER OF THE FORECAST PERIOD.

MUCH COLDER TEMPERATURES ANTICIPATED TODAY ACROSS THE CENTRAL AND
EASTERN PORTIONS OF THE STATE....WITH A SLIGHT WARMING TREND
ANTICIPATED AS THE INFLUENCES OF THE LOW PRESSURE SYSTEMS CHANGE.
EASTERN WYOMING WILL HOLD ON TO THE COOLER TEMPERATURES THE
LONGEST.

LONG TERM...FRIDAY THROUGH TUESDAY

INCLEMENT WEATHER WITH BELOW AVERAGE TEMPERATURES CONTINUES THROUGH
THE WEEKEND. AT 12Z FRIDAY...GLOBAL MODELS SHOW AN UPPER LOW IN THE
FOUR CORNERS REGION. THIS UPPER LOW IS PROGGED TO PUSH EAST
NORTHEAST INTO EASTERN/SOUTHEASTERN COLORADO FRIDAY. THE BULK OF
PRECIPITATION ASSOCIATED WITH THIS UPPER LOW ON FRIDAY APPEARS TO
REMAIN SOUTH AND EAST OF THE AREA OR JUST CLIP THE FAR
EAST/SOUTHEAST SECTIONS. FARTHER WEST...ENOUGH MOISTURE AND A
LITTLE INSTABILITY WILL KEEP ISOLATED TO LOCALLY SCATTERED
CONVECTION POSSIBLE. THOUGHT ABOUT REMOVING POPS ACROSS CENTRAL
SECTIONS /BIG HORN AND WIND RIVER BASINS/ BUT ELECTED TO KEEP LOW
POPS ONGOING TO ALLOW SOME LEEWAY IF THE UPPER LOW IS A BIT CLOSER
ON FRIDAY THAN MODELS HAVE NOW.

DURING FRIDAY NIGHT...THE UPPER LOW OVER E/SE COLORADO IS NOW
PROGGED TO SLOWLY PUSH NORTHWARD INTO NE COLORADO/PANHANDLE OF
NEBRASKA...AND MEANDER IN THAT AREA SATURDAY/SATURDAY NIGHT...BEFORE
SHIFTING SLOWLY EAST ON SUNDAY. ALSO...A COMPACT UPPER LOW OVER
NORTHERN IDAHO FRIDAY EVENING IS EXPECTED TO DIVE SOUTHEAST ACROSS
THE INTERMOUNTAIN WEST SATURDAY...INTO THE CENTRAL UTAH AREA
SATURDAY NIGHT...BEFORE DROPPING INTO THE FOUR CORNERS REGION OR
FARTHER SOUTH ON SUNDAY. AT THE SURFACE TO 700MB...MODELS ARE
SHOWING A MOIST NORTHERLY FLOW DEVELOPING...WHICH WOULD INCREASE
PRECIP CHANCES...ESPECIALLY ALONG AND EAST OF THE DIVIDE. 700MB
TEMPERATURES AND SOUNDINGS SUGGEST THE LOWER ELEVATIONS WILL BE ON
THE RAIN/SNOW THRESHOLDS ONCE AGAIN SATURDAY AND SUNDAY.

GLOBAL MODELS ARE HINTING THERE IS DRYNESS /LIGHT/ AT THE END OF THE
EXTENDED...AS AN UPPER RIDGE OVER THE WEST COAST TRIES TO FOLD OVER
THE NORTHERN ROCKIES. THERE IS ENOUGH MOISTURE RESIDUAL MOISTURE
MONDAY FOR THE CONTINUED SLIGHT POPS...BUT ENOUGH DRYING LOOKS TO
TAKE PLACE TUESDAY TO HAVE A DRY FORECAST.

TEMPERATURES WILL BE BELOW AVERAGE THROUGH THE WEEKEND...BUT A
RETURN TO SEASONAL TO EVEN SLIGHTLY ABOVE TEMPERATURES ARE EXPECTED
MONDAY INTO TUESDAY.

AVIATION.../12Z ISSUANCE/

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

DOWNSLOPE NE FLOW WILL BRING PRIMARILY VFR CONDITIONS ACROSS THE
JACKSON VALLEY AND NW WYOMING...WITH THE CONTINENTAL DIVIDE OBSCURED
FURTHER EAST IN -SN.

ACROSS SW WYOMING...IFR/MVFR CONDITIONS IN RASN ARE EXPECTED TO
PREVAIL THROUGH 9Z WEDNESDAY ALONG THE INTERSTATE 80 CORRIDOR
INCLUDING KRKS WITH SOME GRADUAL IMPROVEMENT BY 12Z WEDNESDAY.  KPNA
AND KBPI ARE EXPECTED TO BE ON THE EDGE OF THE PRECIPITATION BAND
(IFR/MVFR CONDITIONS) THROUGH TUESDAY MORNING WITH RASN PUSHING
NORTHWARD INTO THE UPPER GREEN RIVER BASIN IN THE AFTERNOON. GRADUAL
IMPROVEMENT IS EXPECTED IN THIS AREA AS WELL AFTER 9Z WEDNESDAY.

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

WIDESPREAD MVFR/IFR CONDITIONS AND MTN OBSCURATIONS IN RASN ARE
EXPECTED VCNTY AND SOUTH OF A KGCC-KWRL-KDUB LINE THROUGH 12Z WITH
LESS PRECIPITATION AND MAINLY AREAS OF MVFR CIGS NORTH OF THIS
LINE. COLDER AIR WILL BRING A CHANGEOVER TO WIDESPREAD IFR SNOW
FROM VCNTY KBYG-KRIW-KDUB AND SOUTH BY 14Z TUESDAY. THIS ACTIVITY
IS EXPECTED TO PUSH NORTH AND WESTWARD ACROSS THE BIGHORN BASIN
THROUGH THE AFTERNOON WITH POSSIBLY SOME IMPROVEMENT INTO MVFR
RANGE ACROSS THE AREA TUESDAY AFTN WITH SNOW BECOMING MIXED WITH
RAIN BELOW 6KFT. PRECIPITATION WILL GRADUALLY TAPER OFF THROUGH
TUESDAY NIGHT...BUT WIDESPREAD MVFR/IFR CIGS WITH MTN OBSCURATIONS
ARE EXPECTED THROUGH 12Z WEDNESDAY.

FIRE WEATHER...

A SERIES OF LOW PRESSURE SYSTEMS WILL CONTINUE TO IMPACT THE STATE
FOR THE NEXT FEW DAYS. WIDESPREAD SNOWFALL IS EXPECTED THROUGH
WEDNESDAY FOR AREAS EAST OF THE DIVIDE...AND ACROSS SOUTHERN WYOMING
WHERE WINTER WEATHER HIGHLIGHTS REMAIN IN EFFECT. COOLER DAYTIME
TEMPERATURES AND INCREASED HUMIDITY ARE EXPECTED THROUGH AT LEAST
THURSDAY AS ANOTHER AREA OF LOW PRESSURE GAINS INFLUENCE WEDNESDAY
AND THURSDAY. THIS NEXT SYSTEM WILL BRING SHOWERS AND THUNDERSTORMS
ACROSS SOUTHWESTERN WYOMING BY THURSDAY AFTERNOON. AS THIS SYSTEM
IMPACTS SOUTHWESTERN WYOMING...THE FIRST AREA OF LOW PRESSURE WILL
MOVE BACK OVER SOUTH CENTRAL MONTANA...ALSO KEEPING SHOWERS OVER
NORTHERN WYOMING AND INCLUDED MOUNTAIN RANGES.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL MIDNIGHT MDT TONIGHT FOR
WYZ008>011-028>030.

WINTER STORM WARNING UNTIL MIDNIGHT MDT TONIGHT FOR WYZ015-019-
020.

WINTER STORM WARNING UNTIL 6 PM MDT THIS EVENING FOR WYZ018.

WINTER WEATHER ADVISORY UNTIL MIDNIGHT MDT TONIGHT FOR WYZ007-
017.

WINTER STORM WARNING UNTIL 6 AM MDT WEDNESDAY FOR WYZ022.

&&

$$

UPDATE...WM
SHORT TERM...BRANHAM
LONG TERM...WM
AVIATION...AEM
FIRE WEATHER...BRANHAM



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