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000
FXUS65 KCYS 171920
AFDCYS

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

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 1240 PM MDT FRI MAY 17 2013

QUITE INTERESTING WEATHER SCENARIO SHAPING UP FOR THIS AFTERNOON
AND EVENING. 18Z...NOON...DEWPOINT DISCONTINUITY AND PSEUDO
DRYLINE ALREADY SHOWING UP FROM EAST OF CHEYENNE TO SOUTH OF
DOUGLAS...WITH SURFACE DEWPOINTS ONLY IN THE LOWER TO MID 20S WEST
OF THIS DRYLINE FEATURE...AND UPPER 40S TO LOWER 50S DEWPOINTS
EAST OF THE DRYLINE AT DOUGLAS...TORRINGTON...CHADRON...
SCOTTSBLUFF...ALLIANCE...KIMBALL AND SIDNEY.

FOR THIS AFTERNOON...VISIBLE SATELLITE IMAGERY SHOWING A WELL
PRONOUNCED FULL SUN AREA OVER THE SOUTHEAST HALF OF OUR COUNTIES.
WATER VAPOR IMAGERY SHOWING A WELL PRONOUNCED DRY SLOT WORKING
NORTHEASTWARD ACROSS NORTHERN COLORADO AND SOUTHEAST WYOMING
WITH ASSOCIATED SHORTWAVE TROUGH ALOFT WORKING NORTHEAST.

LATE THIS AFTERNOON...NORTH TO SOUTH ORIENTED SURFACE TROUGH WILL
EXTEND FROM RAPID CITY...ALONG THE WYOMING-NEBRASKA STATE LINE
INTO EASTERN COLORADO. WARM MID LEVEL TEMPERATURES...700 MB
TEMPERATURES NEAR 12 CELSIUS...LIKELY WILL PROVIDE ENOUGH
CONVECTIVE INHIBITION...CIN...TO LIMIT ANY CONVECTIVE POTENTIAL
ALONG AND EAST OF THE DRYLINE FEATURE UNTIL AFTER 3 PM...AS
LOW LEVEL NEGATIVE THETA-E ADVECTION WILL BE NOTED ALONG AND
WEST OF THE DRYLINE WITH NEUTRAL OR SLIGHT NEGATIVE THETA-E
ADVECTION AT MID LEVELS...700 MB. TO ACCOUNT FOR POSSIBLE
CONVECTIVE INITIATION AFTER 3 PM...OUR TEAM ADDED MENTION OF
ISOLATED THUNDERSTORM EAST OF A LUSK TO KIMBALL LINE...IN CASE
CONVECTIVE INHIBITION...CIN...CAN BE ERODED SUFFICIENTLY. WE
CONCUR WITH STORM PREDICTION CENTER DAY 1 OUTLOOK AND THEIR
REASONING.

FOR THIS EVENING...LOW LEVEL WINDS OVER FAR EASTERN WYOMING
AND WESTERN NEBRASKA WILL BACK...ADVECTING LOW LEVEL MOISTURE
NORTHWESTWARD ROUGHLY EAST OF A LUSK TO PINE BLUFFS LINE...
AND SETTING UP A DECENT LOW LEVEL CONVERGENCE AXIS ALONG AND
EAST OF THE WYOMING AND NEBRASKA STATE LINE. BOTH THE NAM AND
GFS GIVE INDICATIONS THAT CONVECTIVE INITIATION WILL TAKE PLACE
MORE ROBUSTLY AFTER 6 PM THIS EVENING ALONG AND EAST OF THE
WYOMING-NEBRASKA STATE LINE...THUS WE HAVE INCLUDED ISOLATED
TO SCATTERED THUNDERSTORMS THROUGH 9 PM ALONG AND EAST OF THE
STATE LINE...WITH A FEW STORMS POSSIBLY SEVERE DUE TO ADEQUATE
SHEAR AND INSTABILITY.

.LONG TERM...(MONDAY THROUGH THURSDAY)
ISSUED AT 345 AM MDT FRI MAY 17 2013

MODELS HAVING SOME DIFFICULTY WITH THE MOVEMENT OF THE UPPER
SYSTEM AFFECTING THE REGION MONDAY...WITH THE GFS MORE PROGRESSIVE
THAN THE ECMWF. REMAINING COOL TO MILD MONDAY AND TUESDAY WITH
DECENT CHANCES FOR SHOWERS AND A FEW STORMS. DRIER AND WARMER WEDS
INTO THURSDAY WITH UPPER FLOW GRADUALLY BACKING TO SW AHEAD OF
NEXT UPPER LOW THAT WILL DROP OVER THE PACIFIC NW WEDS. SHOULD SEE
AN UPTICK IN CONVECTION LATE WEDS AND THURSDAY AS ANY IMPULSES
EJECT NORTHEAST FROM THIS SYSTEM AND ACROSS THE CWA.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY MORNING)
ISSUED AT 1240 PM MDT FRI MAY 17 2013

21Z TO 00Z...ISOLATED THUNDERSTORMS DEVELOPING EAST OF A LUSK
TO KIMBALL LINE. SOUTH TO SOUTHWEST WINDS GUSTING UP TO 38 KNOTS
AT AERODROMES. VFR PREVAILING OUTSIDE OF THUNDERSTORMS WITH
SCATTERED TO BROKEN CLOUDS AT OR ABOVE 8000 FEET AGL.

00Z TO 06Z...ISOLATED TO SCATTERED THUNDERSTORMS DEVELOPING AND
INCREASING IN COVERAGE EAST OF A LUSK TO KIMBALL LINE WITH A
FEW STORMS POSSIBLY SEVERE EARLY IN THE EVENING OVER WESTERN
NEBRASKA AND EASTERN NIOBRARA COUNTY...PRODUCING SEVERE
TURBULENCE...POSSIBLE STRONG WINDS...HAIL AND HEAVY RAIN.
ELSEWHERE...VFR PREVAILS WITH WINDS VEERING TO WEST AND
DECREASING.

AFTER 06Z...VFR WITH DECREASING CLOUDINESS.

&&

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

$$

SHORT TERM...RUBIN
LONG TERM...HAMMER
AVIATION...RUBIN