Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 251800
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1200 PM MDT MON MAY 25 2015

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

WV IMAGERY SHOWING EXPANDING LARGE TROF IN CONTROL OF THE WRN 2/3S
OF THE CONUS WITH TWO CLOSED LOWS CIRCULATING WITHIN THE TROF...ONE
OVR THE HIGH PLAINS INCLUDING WY...THE OTHER UPSTREAM AND OVR THE
NWRN CONUS. SFC SHOWS WEAK P GRADS ACROSS THE WEST...WITH LOW P AND
A WEAK COLD WELL FRONT OFF TO THE E AND SE OVR THE CENTRAL
PLAINS...WHILE WEAK HIGH P HAS SPREAD ACROSS MT.

MORNING RAIN AND SNOW SHOWERS IN ADDITION TO SOME PATCHY FOG WILL
CONTINUE OVR MUCH OF THE FA E OF THE DIVIDE. THE UPR LVL SYSTEM
PUSHES EWD INTO THE PLAINS WITH TRANSITIONAL SW RIDGING TAKING PLACE
ACROSS THE WRN FA WHILE THE ERN PORTION OF THE FA WILL BE UNDER THE
EXITING TROF INFLUENCE AND SOME RETURN VORTICITY ROTATING BACK OVR
THE FA FROM OUT OF THE NE. SHOWER AND THUNDER ACTIVITY WILL REEMERGE
BY THE AFTERNOON AS TEMPS WARM AND ATMOSPHERE BECOMES MORE UNSTABLE.
CAPE OF 500 TO 1000 J/KG AND LOW SHEAR CHARACTERIZES THE MID/LATE
AFTERNOON ATMOSPHERE. STORM MOVEMENT WILL BE ON THE SLOW SIDE AT
LESS THAN 15 MPH...MUCH LIKE THE STORMS OF LATE LAST WEEK...ONLY
STORM MOVEMENT WILL BE FROM NW TO SOUTHEAST GENERALLY. WILL CANCEL
THE CURRENT FLASH FLOOD WATCH THIS MORNING AS PRECIPITATION RATES
HAVE BECOME VERY LIGHT ACROSS MOST OF THE FA AND THE FLASHINESS IS
GONE FOR NOW WITH ALL PAST FLASH FLOOD WARNINGS CONVERTED TO EITHER
FLOOD WARNINGS OR ADVISORIES. MODERATE TO MAJOR FLOODING OCCURRING
NEAR SUSSEX WY ON THE POWDER RIVER. ANOTHER CERTAINLY HYDRO
SPECIFIC DAY...BUT ON A MORE SCATTERED BASIS AS CONVECTION BECOMES
LIKELY THIS AFTERNOON...SO A FLASH FLOOD WATCH MAY BE NECESSARY
ONCE AGAIN LATER TODAY AS CONVECTIVE COVERAGE BECOMES MORE
APPARENT. PWS WILL FALL SOME OVR WHAT THEY HAVE BEEN THE PAST
COUPLE OF DAYS...GENERALLY AOB 0.5 WEST OF THE DIVIDE...TO AROUND
0.75 ACROSS PORTIONS E OF THE DIVIDE. OTHER THAN A COUPLE OF
STRONGER CORES ABLE TO PRODUCE SMALL HAIL...SEVERE WX SHOULD BE
LIMITED...WITH SLOW MOVING OR TERRAIN TIED HEAVY RAIN PRODUCERS
THE MAIN THREAT.

SHOWERS MOSTLY END TONIGHT EXCEPT FOR SMALL CHANCES REMAINING
PRIMARILY OVR THE MOUNTAINS AND YELLOWSTONE PARK AREA AS A SMALL UPR
WAVE BRUSHES THE REGION. THRU THE DAY TUESDAY...INFLUENCES FROM THE
UPSTREAM TROF/CLOSED LOW SYSTEM PUSHES THE SW RIDGE EAST...AND UPR
SWRLY FLOW BEGINS TO OVERTAKE THE FA WHILE AN EMBEDDED SW MOVES
ACROSS THE WRN FA IN THE AFTERNOON...HELPING TO INITIATE A NEW BATCH
OF SHOWERS AND THUNDERSTORMS...ESPECIALLY W OF THE DIVIDE. MORE
ISOLATED STORMS E OF THE DIVIDE...HOWEVER...MAY BE SOMEWHAT STRONGER
LATER IN THE DAY...IF/WHEN THEY CAN GO...OFFERING UP HALF INCH OR
GREATER SIZE HAIL. CONVECTION WILL DECREASE ONCE AGAIN
OVERNIGHT...EXCEPT AGAIN OVR THE NW FA WHICH WILL BE POSITIONED BEST
TO TAKE ADVANTAGE OF THE DYNAMICS AND TRAJECTORY OF THE APPROACHING
TROF AND ITS MOISTURE. WED...POSITION OF THE APPROACHING UPR WAVE
ALONG WITH LEE TROFFING/WEAK CYCLOGENESIS WILL DRYSLOT MUCH OF THE
SW TO CNTRL FA...WITH SCATTERED TSRA WITH ADEQUATE CAPE AND SHEAR
BREAKING OUT AROUND THIS AREA. CONVECTIVE INDICES WILL FAVOR SOME
STORM ORGANIZATION WED...WITH STORMS ABLE TO ROTATE AND A FEW
PRODUCING NEAR SEVERE HAIL..ESPECIALLY OVR THE BIGHORN BASIN AND ERN
CWA. STORMS WILL ALSO MOVE AT A FASTER CLIP...25 TO 30 MPH AND
HOPEFULLY WITH SOMEWHAT LESS POTENTIAL OF
FLOODING.

.LONG TERM...THURSDAY THROUGH MONDAY

VERY BUSY NIGHT TONIGHT SO NOT A LOT OF TIME TO DELVE INTO THE
EXTENDED DETAILS. STILL LOOKS LIKE ANOTHER UPPER LOW MOVING SLOWLY
EAST ACROSS THE AREA THURSDAY INTO FRIDAY WITH A GOOD CHANCE OF MORE
SHOWERS AND A FEW THUNDERSTORMS. A TRANSITORY RIDGE IS THEN
EXPECTED OVER THE WEEKEND AND POSSIBLY THROUGH MONDAY WITH WARMER
AND DRIER WEATHER. THERE IS A POTENTIAL SHORTWAVE THOUGHT THAT MOVES
JUST TO OUR NORTH SUNDAY OR MONDAY WITH A BETTER SHOT OF
SHOWERS/TSTMS FOR AT LEAST THE MOUNTAINS. MORE TIME TO LOOK AT ALL
THIS TOMORROW NIGHT HOPEFULLY.

.AVIATION.../18Z ISSUANCE/

AN UPPER LOW PRESSURE SYSTEM WILL CONTINUE TO SLOWLY MOVE EAST FROM
SOUTHEAST WYOMING INTO WESTERN NEBRASKA TONIGHT. WRAPAROUND
PRECIPITATION WILL CONTINUE TO RESULT IN AREAS OF MVFR...LOCAL IFR
CIGS IN -RA VCNTY AND EAST OF THE DIVIDE AND ALONG THE INTERSTATE
80 CORRIDOR THROUGH 21Z. THESE CONDITIONS WILL BE MORE LOCALIZED
WEST OF THE DIVIDE WITH PATCHY FOG PARTIALLY OBSCURING TERRAIN
THROUGH 21Z.

CIGS WILL LIFT INTO PRIMARILY VFR CATEGORIES ACROSS THE AREA AFTER
21Z MONDAY. THE BETTER INSTABILITY AND MOISTURE WILL BE FOUND
VCNTY AND WEST OF THE DIVIDE WHERE SCT -SHRA AND ISOLD -TSRA ARE
EXPECTED FROM 20Z MON-02Z TUE.

SKIES WILL PARTIALLY CLEAR MONDAY NIGHT WITH PATCHY FOG PARTIALLY
OBSCURING TERRAIN ACROSS THE AREA EARLY TUESDAY MORNING.

.FIRE WEATHER...

FIRE DANGER LOW AND WILL REMAIN LOW THROUGH MOST OF
THE WORK WEEK. SEASONALLY COOL TO WARM TEMPERATURES WILL COMBINE
WITH RELATIVELY MOIST ATMOSPHERIC CONDITIONS TO PRODUCE DECENT
CHANCES FOR SHOWERS AND THUNDERSTORMS EACH AFTERNOON AND EVENING.

&&

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

$$

SHORT TERM...BRAUN
LONG TERM...SKRBAC
AVIATION...C.BAKER
FIRE WEATHER...BRAUN





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