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000
FXUS65 KCYS 172251
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
451 PM MDT FRI MAY 17 2013

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)

ISSUED AT 216 PM MDT FRI MAY 17 2013

TONIGHT...STRONG TO SEVERE THUNDERSTORMS HAVE ERUPTED QUICKLY
ACROSS THE NORTHERN HALF OF THE NEBRASKA PANHANDLE AS THE
CONVECTIVE INHIBITION...CIN...WAS ERODED FAIRLY QUICKLY FROM THE
INITIAL SUPERCELL JUST NORTHEAST OF SCOTTSBLUFF. SEVERE
THUNDERSTORM WATCH 167 IN EFFECT UNTIL 10 PM MDT THIS EVENING FOR
NIOBRARA... SIOUX...DAWES AND BOX BUTTE COUNTIES WHERE SHEAR AND
INSTABILITY HAVE BEEN MAXIMIZED ALONG AND EAST OF THE IMPRESSIVE
DRYLINE.

FOR THIS EVENING...SURFACE TROUGH STRENGTHENS ACROSS THE WYOMING
AND NEBRASKA STATE LINE...WITH LOW LEVEL WINDS BACKING ACROSS
WESTERN NEBRASKA...EFFECTIVELY ADVECTING INCREASING LOW LEVEL
MOISTURE NORTHWESTWARD INTO OUR EASTERN COUNTIES.

LOW LEVELS HAVE MIXED OUT AT KIMBALL WITH DEWPOINTS FALLING TO
30 DEGREES AT 3 PM. MODELS INDICATE LOW LEVEL WINDS CONTINUING
TO BACK THIS EVENING ACROSS WESTERN NEBRASKA...AND WITH OUTFLOW
BOUNDARIES FROM ONGOING STORMS NOW OVER THE NORTHERN PANHANDLE...
ADDITIONAL CONVECTIVE INITIATION LOOKS QUITE PLAUSIBLE OVER THE
SOUTHERN PANHANDLE BASED ON LOW AND MID LEVEL THETA-E ORIENTATIONS.
EXPECT THUNDERSTORMS TO BE OVER NEAR OR AROUND MIDNIGHT.

SATURDAY...INITIAL SHORTWAVE MOVES NORTHEAST ACROSS OUR COUNTIES
IN THE AFTERNOON. STORM PREDICTION CENTER SLIGHT RISK ACROSS
OUR WESTERN NEBRASKA COUNTIES IN THE AFTERNOON AND EVENING LOOKS
GOOD...ESPECIALLY WITH A LOW LEVEL CONVERGENCE BOUNDARY STRETCHING
FROM CHADRON TO SIDNEY AND PROGGED SHEAR AND INSTABILITY.
SCATTERED TO NUMEROUS SHOWERS ANTICIPATED WITH ISOLATED EMBEDDED
THUNDERSTORMS OVER SOUTHEAST WYOMING DUE TO LIFT FROM NEGATIVELY
TILTED SHORTWAVE TROUGH ALOFT.

SATURDAY NIGHT...SECONDARY SHORTWAVE TROUGH ALOFT PASSES OVERHEAD
THOUGH LIFT FROM THE SHORTWAVE WILL BE MITIGATED AND MINIMIZED
BY DOWNSLOPE NORTHWEST WINDS IN THE LOW LEVELS EAST OF THE LARAMIE
RANGE...WHERE RAIN SHADOW EFFECT WILL BE PRONOUNCED. STILL
EXPECT ISOLATED TO SCATTERED SHOWERS FURTHER NORTH IN DEEPER
MOISTURE COLUMN.

SUNDAY...SEVERAL SHORTWAVE TROUGH IMPULSES WILL DUMBBELL AROUND
THE PARENT UPPER TROUGH OVER MONTANA AND WYOMING...AND WITH
ADEQUATE LOW AND MID LEVEL MOISTURE AND CYCLONIC CURVATURE ALOFT...
SCATTERED TO NUMEROUS SHOWERS EXPECTED ALONG WITH ISOLATED
EMBEDDED THUNDERSTORMS DUE TO COLD CORE ALOFT.

.LONG TERM...(SUNDAY NIGHT THROUGH FRIDAY)

ISSUED AT 216 PM MDT FRI MAY 17 2013

VERY ACTIVE AND WET PATTERN SETTING UP FOR THE LONG TERM WITH RAIN
CHANCES JUST ABOUT EVERY DAY.

STARTING OFF SUNDAY NIGHT...BOTH THE GFS AND LATEST ECMWF PRETTY
SIMILAR IN SOLUTIONS WITH A SURFACE LOW EJECTING NORTHEAST OUT OF
EASTERN COLORADO. TWO UPPER LEVEL LOWS...ONE OVER CENTRAL NEBRASKA
AND THE OTHER OVER NORTHERN COLORADO WITH CONVERSE...NIOBRARA AND
THE NORTHERN PANHANDLE RECEIVING THE BULK OF THE MOISTURE
INITIALLY. WE COULD BE LOOKING AT SIGNIFICANT RAINFALL UP THAT
WAY...THE GFS SHOWING CLOSE TO A HALF INCH OVER CONVERSE WHILE THE
ECMWF A LITTLE FURTHER EAST INITIALLY WITH THE QPF OVER
SOUTHWESTERN SOUTH DAKOTA. EVENTUALLY...BOTH DROP THE RAIN FURTHER
SOUTH INTO OUR SOUTHERN COUNTIES DURING THE DAY MONDAY AS ENERGY
DROPS SOUTH AROUND THE BACKSIDE OF THE MORE EASTERN LOW.

GOING TO BE MUCH COOLER MONDAY AS 700MB TEMPERATURES FALL FROM +4C
SUNDAY MORNING TO -2C MONDAY MORNING. BELIEVE AFTERNOON HIGHS ARE
GOING TO STRUGGLE TO REACH 60 MONDAY. TEMPERATURES COULD FALL
MONDAY NIGHT TO WHERE WE SEE SOME MOUNTAIN SNOWS...SAY ABOVE 9000
FEET. ELSEWHERE...IT LOOKS LIKE A COLD RAIN AS OVERNIGHT LOWS FALL
INTO THE LOW 40S AND POSSIBLY UPPER 30S ELSEWHERE.

ECMWF MUCH SLOWER MOVING OUT THE UPPER LOW. IT KEEPS RAIN GOING IN
THE PANHANDLE AND OUR NORTHERN COUNTIES THROUGH TUESDAY
MORNING...EVEN INTO TUESDAY AFTERNOON. WENT AHEAD WITH THIS
SOLUTION...KEEPING OUT EASTERN ZONES WET THROUGH THE DAY TUESDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY AFTERNOON)
ISSUED AT 447 PM MDT FRI MAY 17 2013

WEATHER SEEMS TO BE QUIETING DOWN LATE THIS AFTERNOON. EXPECT
WINDS TO EASE OUT WEST AT KRWL AND KLAR AND THE THUNDERSTORM
ACTIVITY TO EASE OUT IN THE PANHANDLE. SOUTHEAST WINDS DO DEVELOP
AND WILL GIVE IFR CONDITIONS AT KAIA AND KCDR OVERNIGHT. THIS WILL
SET THE STAGE FOR ANOTHER...MORE WIDESPREAD THUNDERSTORM OUTBREAK
FOR SATRDAY AFTERNOON ACROSS MUCH OF SOUTHEAST WYOMING AND
NEBRASKA PANHANDLE. FOR NOW...WILL COVER TAFS WITH VCTS UNTIL WE
CAN GET A BETTER HANDLE ON TIMING. MOST AIRPORTS WILL SEE THUNDER
SATURDAY.

&&

.FIRE WEATHER...
ISSUED AT 216 PM MDT FRI MAY 17 2013

WINDY AND DRY WEST OF THE LARAMIE RANGE THE REMAINDER OF THE
AFTERNOON. THIS AHEAD OF A COLD FRONT LAYING FROM ROUGHLY CASPER
TO SALT LAKE CITY EARLY THIS AFTERNOON. THUNDERSTORMS LOOK TO BE
WELL NORTHWEST OF THE FRONT OVER NORTHWESTERN WYOMING. EXPECT
WINDS TO REMAIN STRONG OVER CARBON AND ALBANY COUNTIES THROUGH
SUNSET...WITH WIND GUSTS OF 25 TO 35 MPH FROM THE SOUTHWEST. BY
SATURDAY MORNING...WE ARE LOOKING AT THIS FRONT MOVING INTO
SOUTHEAST WYOMING WITH WINDS BECOMING MORE NORTHWESTERLY BEHIND
THE FRONT. ALL GUIDANCE SHOWING AN INCREASE IN SHOWER AND
THUNDERSTORM COVERAGE SATURDAY AFTERNOON...MAINLY ALONG AND EAST
OF THE LARAMIE RANGE. VERY UNSETTLED WEATHER FOR SUNDAY THROUGH
MONDAY AS A SLOW MOVING LOW PRESSURE SYSTEM MOVES THROUGH THE
AREA...BRINGING WIDESPREAD WETTING RAINS TO MANY AREAS.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&

$$

SHORT TERM...RUBIN
LONG TERM...CLAYCOMB
AVIATION...CLAYCOMB
FIRE WEATHER...CLAYCOMB