Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 241813
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1213 PM MDT SUN MAY 24 2015

.UPDATE...
ISSUED AT 1213 PM MDT SUN MAY 24 2015

THE UPPER LOW IS SITUATED IN SOUTH-CENTRAL WYOMING THIS MORNING
WITH A PRONOUNCED MID/UPPER LEVEL DRY SLOT ON THE EASTERN
PERIPHERY OF THE LOW OVER OUR FORECAST AREA. AT THE
SURFACE...WESTERLY DOWNSLOPE WINDS THIS MORNING ACROSS THE WYO
PLAINS ALLOWED FOR SOME DRYING OF THE LLVLS AS WELL...RESULTING IN
MOSTLY CLEAR SKIES ALONG AND JUST EAST OF THE LARAMIE RANGE.
FURTHER NORTH AND EAST INTO CONVERSE/NIOBRARA COUNTIES AND THE
NEB PANHANDLE...VERY MOIST SOUTHEASTERLY FLOW PERSISTED WHILE THE
BAND OF MODERATE RAIN FROM THE OVERNIGHT PERIOD LIFTED NORTH OUT
OF THE AREA.

OVER THE PAST FEW HOURS...A SURFACE LOW HAS DEEPENED OVER SE
WYO/NORTHERN CO ACCORDING TO MSAS IN RESPONSE TO SHORTWAVE ENERGY
MOVING UP FROM THE SOUTH. MUCH OF THE CLEAR SLOT HAS FILLED IN
WITH MODERATE CU AS SFC WINDS HAVE SHIFTED BACK TO A NORTHEAST-
SOUTHEAST FETCH IN RESPONSE TO THE DEVELOPING LOW. SHOWERS AND
STORMS ARE BEGINNING TO DEVELOP OVER THE MOUNTAINS WITH ADDITIONAL
INVIGORATED CU NEAR THE DIFFERENTIAL HEATING BOUNDARY ALONG AND
EAST OF A LUSK-KIMBALL LINE. SBCAPES OVER MUCH OF THE AREA ARE
RANGING FROM 500 TO 1000 J/KG...HOWEVER MLCAPES ARE STILL ON THE
LOW END BUT STEADILY INCREASING WITH SOME SUNSHINE. ALL IN
ALL...CONTINUE TO THINK THAT SHOWERS AND THUNDERSTORMS WILL BECOME
MORE PREVALENT THROUGH THE AFTERNOON WITHIN MODEST
INSTABILITY...SFC LOW CONVERGENCE AND INFLUENCE FROM THE UPPER
LOW. WEAK FLOW OVERALL WILL MAINTAIN MODEST VALUES OF SHEAR...SO
AGAIN DO NOT EXPECT STORMS TO BECOME SEVERE. HOWEVER WITH A FEW
SUBTLE TERRAIN AND DIFFERENTIAL HEATING BOUNDARIES IN PLACE
ACROSS THE PLAINS...CANNOT RULE OUT A FEW STORMS BECOMING STRONG
WITH THE ENHANCED LLVL FORCING AND AMBIENT INSTABILITY IN PLACE.
OF PARTICULAR NOTE WILL BE ALONG AND EAST OF THAT LUSK-ALLIANCE
LINE. LOOKING MAINLY AT SMALL HAIL AND HEAVIER RAIN...BUT SHORT-
LIVED FUNNEL CLOUDS ARE ALSO A POSSIBILITY AS WELL.

WITH REGARDS TO THE FLASH FLOOD WATCH...OPTED TO KEEP IT IN PLACE
FOR NOW AS ANY THUNDERSTORMS THAT DEVELOP OVER THE AREA WILL BE SLOW
MOVING UNDER GENERAL WEAK FLOW AND COULD REGENERATE OVER THE SAME
AREA DUE TO BOUNDARY INTERACTION AND TERRAIN FEATURES. IF IT BECOMES
EVIDENT THAT THUNDERSTORMS WILL REMAIN WEAK DUE TO LOWER OVERALL
INSTABILITY IN THIS AREA...WILL CANCEL THE WATCH EARLY.

&&

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 240 AM MDT SUN MAY 24 2015

TODAY...JUST AS THE MODELS HAVE PREDICTED...SHOWERS AND A FEW
THUNDERSTORMS HAVE MOVED TO OUR NORTHERN COUNTIES. MODELS SHOWING
THE SLOW MOVING UPPER TROUGH MOVING SLOWLY NORTHEAST TO EAST CENTRAL
WYOMING BY LATE THIS AFTERNOON...WITH THE DEEPEST MOISTURE AND BEST
UPWARD VERTICAL MOTION ACROSS OUR NORTHERN AND WESTERN COUNTIES THIS
AFTERNOON...THUS THE INHERITED FLASH FLOOD WATCH LOOKS IN GOOD SHAPE.

WILL SEE SCATTERED TO NUMEROUS SHOWERS TODAY DUE TO THE PROXIMITY OF
THE UPPER TROUGH...PLENTY OF LOW AND MID LEVEL MOISTURE AND DECENT
LOW LEVEL CONVERGENCE NOTED OVER OUR COUNTIES THIS AFTERNOON.

TONIGHT...OUR UPPER TROUGH FINALLY OPENS UP. DESPITE NEARLY SATURATED
ATMOSPHERE COLUMN...NOT MUCH UPWARD VERTICAL MOTION PROGGED...THOUGH
STILL EXPECT SCATTERED SHOWERS EXCEPT OVER FAR SOUTHEAST WYOMING
WHERE RAIN SHADOWING EFFECT WILL BE MOST PRONOUNCED.

MONDAY...ALTHOUGH THE UPPER TROUGH AXIS MOVES EAST OF OUR COUNTIES...
THERE WILL STILL BE ENOUGH RESIDUAL LOW AND MID LEVEL MOISTURE...
ALONG WITH DIFFERENTIAL HEATING AND INSTABILITY TO PRODUCE
SCATTERED TO NUMEROUS SHOWERS AND ISOLATED LATE DAY THUNDERSTORMS.

MONDAY NIGHT...WITH RIDGING ALOFT...DESPITE THE ABUNDANCE OF LOW AND
LEVEL MOISTURE...WILL SEE IS0LATED TO SCATTERED AFTERNOON AND
EVENING SHOWERS...AND ISOLATED THUNDERSTORMS CLOSER TO CHEYENNE.

TUESDAY...NEXT SHORTWAVE TROUGH ALOFT MOVES INTO WESTERN WYOMING IN
THE AFTERNOON...WITH A LOW LEVEL CONVERGENCE AXIS SETTING UP OVER
OUR WESTERN COUNTIES...AND THUS WITH ADEQUATE MOISTURE...HAVE KEPT
OUR SCATTERED TO NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS WEST OF
A DOUGLAS TO CHEYENNE LINE.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 345 AM MDT SUN MAY 24 2015

NO APPRECIABLE INCONSISTENCIES NOTED WITH THE 00Z MEDIUM RANGE MODEL
SOLUTIONS DURING THE PAST 24 HOURS. THE PROGRESSIVE AMPLIFIED LARGE
SCALE FLOW WILL CONTINUE WITH ONE UPPER TROUGH TRACKING EAST ACROSS
THE MIDWEST/GREAT LAKES AND THE OTHER OVER THE INTERMOUNTAIN WEST.
UPPER RIDGE BETWEEN THE TROUGHS OVER THE HIGH PLAINS WILL LIKEWISE
TRANSLATE EAST ACROSS THE GREAT PLAINS AND MS VALLEY. THE SURFACE
PATTERN WILL BE RELATIVELY WEAK WITH MAINLY LIGHT/VARIABLE WINDS.
THERE WILL BE THE PRESENCE OF A LEE SURFACE TROUGH OVER THE HIGH
PLAINS EARLY IN THE PERIOD WHICH WILL GRADUALLY SLIDE EAST INTO
THE CENTRAL GREAT PLAINS LATE IN THE WEEK. FORCING MECHANISMS FOR
CONVECTION WILL BE THE SURFACE TROUGH AS WELL AS LOW LEVEL UPSLOPE
FLOW AND LIFT FROM THE PASSAGE OF THE UPPER TROUGH. THE UPSHOT IS
CONTINUED CHANCES FOR SHOWERS AND ISOLATED AFTERNOON/EVENING TSTORMS
THROUGH THE WEEK. THE MODELS HINT AT SOME DRYING NEXT WEEKEND...WITH
ISOLATED SHOWERS CONFINED TO THE MOUNTAINS. TEMPERATURES WILL FINALLY
MODERATE TO MORE SEASONAL LEVELS WEDNESDAY AND THURSDAY WITH HIGHS
IN THE 60S AND LOWER 70S. TEMPERATURES COOL SLIGHTLY FRIDAY AND
SATURDAY FROM THE INFLUENCE OF THE UPPER TROUGH...THEN REBOUND SUNDAY
WITH THE RETURN OF AN UPPER RIDGE PATTERN.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1213 PM MDT SUN MAY 24 2015

SCT-TO-BKN COVERAGE OF LOW-LEVEL CUMULUS CAN BE EXPECTED THIS AFTN
ALONG WITH INCREASING SHOWERS AND THUNDERSTORMS. VFR TO MVFR CIGS
SHOULD PREVAIL TODAY...WITH THE WORST CONDITIONS OCCURRING BENEATH
ANY HEAVIER STORMS. SHOWERS MAY CONTINUE THROUGH THE NIGHT ACROSS
MUCH OF THE AREA. IFR/LIFR CONDITIONS ARE POSSIBLE AT KRWL AND MUCH
OF THE WESTERN PANHANDLE AFTER 06Z...CONTINUING THROUGH MID AM
MON.

&&

.FIRE WEATHER...
ISSUED AT 240 AM MDT SUN MAY 24 2015

NO CONCERNS DUE TO RECENT RAINS AND WET GROUND...ALONG WITH
RELATIVELY LIGHT WINDS.

&&

.HYDROLOGY...
ISSUED AT 330 AM MDT SUN MAY 24 2015

CURRENT AND FORECAST RAINFALL FROM SHOWERS DURING THE NEXT 24
HOURS WILL AVERAGE BETWEEN 0.25 AND 0.50 INCHES...WITH LOCALLY
HEAVIER AMOUNTS POSSIBLE WITH THUNDERSTORMS. RUNOFF FROM THIS
RAINFALL WILL MAINTAIN HIGH WATER LEVELS ALONG THE LARAMIE RIVER
AT LARAMIE AND NEAR FORT LARAMIE THROUGH EARLY NEXT WEEK. REFER
TO THE LATEST RIVER AND FLOOD STATEMENTS FOR SPECIFIC INFORMATION.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...FLASH FLOOD WATCH UNTIL 6 PM MDT THIS EVENING FOR WYZ101-103>105-
     109.

NE...NONE.
&&

$$

UPDATE...RJM
SHORT TERM...RUBIN
LONG TERM...JAMSKI
AVIATION...CLH
FIRE WEATHER...RUBIN
HYDROLOGY...JAMSKI



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