FXUS65 KCYS 010103

AFDCYS



AREA FORECAST DISCUSSION...UPDATED

NATIONAL WEATHER SERVICE CHEYENNE WY

700 PM MDT SAT JUL 31 2010



.UPDATE...

CAPPING APPEARS TO HAVE PREVENTED CONVECTION INTO EARLY THIS EVENING 

AND WHAT ECHOES ARE ON RADAR HAVE SHOWN A GENERAL WEAKENING TREND.  

WILL LOWER POPS FOR TONIGHT EXCEPT OVER FAR NORTHERN AND WESTERN 

SECTIONS WHERE A FEW SHOWERS AND WEAK STORMS STILL EXIST.  WILL ALSO 

DECREASE CLOUD COVER OVER THE PLAINS WHERE MOSTLY CLEAR SKIES 

PREVAIL ALREADY.  OTHERWISE NO BIG CHANGES.  



&&



.PREV DISCUSSION... /ISSUED 241 PM MDT SAT JUL 31 2010/ 



.SHORT TERM...TONIGHT THROUGH MONDAY.



TONIGHT...AT MID AFTERNOON...ISOLATED THUNDERSTORMS CONTINUE TO 

DEVELOP ACROSS OUR WESTERN COUNTIES WHILE ISOLATED STRONGER 

THUNDERSTORMS MOVE NORTHWARD TOWARDS OUR COUNTIES FROM NORTHEAST 

COLORADO...SPECIFICALLY WASHINGTON...YUMA AND SOUTHERN LOGAN 

COUNTIES.



FOR THIS EVENING...EXPECT ISOLATED TO SCATTERED THUNDERSTORMS ACROSS 

ALL BUT OUR FAR EASTERN COUNTIES OF NEBRASKA. WITH THE STORMS MOVING 

NORTH NORTHEAST AT 10 TO 15 MPH...IMPRESSIVE LOW AND MID LEVEL 

THETA-E RIDGE AXISES IN PLACE ALONG INTERSTATE 25 AND INCREASING 

AMOUNTS OF LOW/MID LEVEL MOISTURE AND INCREASING PRECIPITABLE WATER 

VALUES...EXPECT A FEW STORMS ALONG AND NEAR THE INSTABILITY AXIS AND 

NORTH-SOUTH ORIENTED THETA-E RIDGE AXISES TO PRODUCE LOCALLY HEAVY 

RAIN...WIND GUSTS TO 50 MPH AND SMALL HAIL. THUNDERSTORMS THIS 

EVENING WILL BE FOCUSED ALONG A LOW LEVEL CONVERGENCE AXIS ACROSS 

OUR FAR WESTERN COUNTIES AND IN THE LOW LEVEL SPEED CONVERGENCE 

NOTED ACROSS OUR SOUTHERN AND SOUTHEAST COUNTIES. A PASSING 

SHORTWAVE TROUGH ALOFT NOTED AT 700 MB WILL HELP TO AID LIFT THIS 

EVENING AND OVERNIGHT. 



LATE TONIGHT...THUNDERSTORMS WILL DECREASE IN AREAL COVERAGE DUE TO 

LOSS OF DAYTIME HEATING AND INSOLATION.



SUNDAY/SUNDAY NIGHT...ZONAL FLOW ALOFT PREVAILS. LOW LEVEL 

CONVERGENCE BOUNDARY WILL SET UP NORTH TO SOUTH ALONG THE WYOMING 

AND NEBRASKA STATE LINE ALONG A SURFACE TROUGH. WITH INCREASED 

MONSOONAL MOISTURE PRESENT...ALONG WITH A FOCUSING BOUNDARY ALONG 

THE COLORADO AND NEBRASKA STATE LINE...EXPECT ISOLATED TO SCATTERED 

AFTERNOON AND EVENING THUNDERSTORMS ONCE AGAIN...MOST NUMEROUS SOUTH 

OF A RAWLINS TO TORRINGTON LINE. INCREASING MONSOONAL MOISTURE 

SUNDAY NIGHT WILL AID A SLIGHT INCREASE IN AREAL THUNDERSTORM 

COVERAGE...AS BETTER DEPICTED BY THE GFS QPF PROGNOSIS OVER THE 

DRIER NAM PROGS.



MONDAY...MONSOONAL MOISTURE FEED STRETCHES FROM THE FOUR CORNERS 

THROUGH NORTHEAST COLORADO INTO CENTRAL NEBRASKA...WITH THE WESTERN 

EDGE OF THE MONSOONAL MOISTURE ACROSS FAR SOUTHEAST WYOMING AND THE 

SOUTHERN NEBRASKA PANHANDLE. WITH LOW LEVEL SOUTHEAST UPSLOPE IN 

PLACE...MECHANICAL LIFT...AND THE PROXIMITY OF THE MONSOONAL 

MOISTURE TAP...WILL SEE AN INCREASE IN AFTERNOON THUNDERSTORM 

COVERAGE WITH SCATTERED THUNDERSTORMS FOCUSED SOUTH OF A RAWLINS TO 

SCOTTSBLUFF LINE. SOME STORMS...AN INCREASE IN COVERAGE FROM 

SUNDAY...WILL LIKELY PRODUCE HEAVY RAIN DUE TO WEAK STEERING WINDS 

ALOFT AND INCREASED AMOUNTS OF AVAILABLE PRECIPITABLE WATER.



.LONG TERM...MONDAY NIGHT THROUGH SATURDAY...

IN GENERAL THE MONSOONAL PATTERN WILL CONTINUE THROUGH THE WEEK AS 

THE UPPER RIDGE AXIS WILL SHIFT EAST OF THE FORECAST AREA ALLOWING 

FOR MOISTURE IN SOUTHWEST FLOW ALOFT TO CONTINUE STREAMING OVER THE 

AREA. THE SOUTHWEST FLOW IS EXPECTED TO BE ENHANCED AS JET STREAKS 

EJECT FROM THE BASE OF THE UPPER TROUGH OVER THE PACIFIC 

NORTHWEST...WITH THE MOST ACTIVE PERIODS EXPECTED TO BE TUESDAY AND 

THURSDAY. WITH THE DISTURBANCES MOVING THROUGH ALOFT...THE MID-LEVEL 

THERMAL RIDGE WILL BE PUSHED WEST OF THE AREA THROUGH THURSDAY AND 

TEMPERATURES WILL DROP TO NEAR NORMAL FOR THIS PERIOD. THE UPPER 

RIDGE IS EXPECTED TO REBUILD TOWARD THE END OF THE WEEK WITH THE 

TEMPERATURE GUIDANCE FROM THE GFS INDICATING A RETURN OF THE THERMAL 

RIDGE ALOFT AND TEMPERATURES WARMING TO 5 TO 8 DEGREES ABOVE NORMAL 

FOR LATE IN THE WEEK.



&&



.AVIATION...FOR 00Z TAF ISSUANCE...

VFR EXPECTED TO PREVAIL OVERNIGHT AND SUNDAY...EXCEPT FOR LOCALIZED 

AREAS OF MVFR WITH ANY SHOWERS OR STORMS.  WINDS WILL SHIFT TO THE 

WEST-NORTHWEST LATER TONIGHT AS A SURFACE TROUGH MOVES THROUGH THE 

AREA. 



&&



.FIRE WEATHER...AFTERNOON AND EVENING THUNDERSTORM COVERAGE WILL 

CONTINUE TO INCREASE EACH DAY THROUGH MONDAY. MINIMUM AFTERNOON 

RELATIVE HUMIDITIES AND MAXIMUM EARLY MORNING RELATIVE HUMIDITIES 

WILL CONTINUE TO INCREASE EACH DAY THROUGH MONDAY AS LOW AND MID 

LEVEL MOISTURE INCREASES AND TEMPERATURES DECREASE GRADUALLY.



&&



.HYDROLOGY...ALTHOUGH THE PROBABILITY IS LOW AT THIS TIME...THERE 

WILL BE A GRADUALLY INCREASING RISK OF LOCALIZED FLASH FLOODING 

ACROSS MOST OF SOUTHEAST WYOMING AND WESTERN NEBRASKA INTO MONDAY.  

WITH WEAK STEERING FLOW ALOFT...ESPECIALLY NEAR THE COLORADO 

BORDER...COMBINED WITH HIGH AND INCREASING PRECIPITABLE WATER VALUES 

AND SEVERAL UPPER LEVEL DISTURBANCES PUSHING ACROSS THE AREA...THE 

POTENTIAL EXISTS FOR THE DEVELOPMENT OF ISOLATED TO SCATTERED SLOW 

MOVING AFTERNOON AND EVENING HEAVY RAIN PRODUCING THUNDERSTORMS... 

STARTING THIS EVENING AND CONTINUING THROUGH MONDAY AFTERNOON.



&&



.CYS WATCHES/WARNINGS/ADVISORIES...

WY...NONE.

NE...NONE.



&&



$$



SHORT TERM/FIRE WEATHER/HYDROLOGY...RUBIN

LONG TERM/AVIATION...CARPENTER