Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 221809 AAB
AFDCYS

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHEYENNE WY
1209 PM MDT WED APR 22 2015

.UPDATE...FOR NOON AVIATION FORECAST PACKAGE.

UPDATE ISSUED AT 1007 AM MDT WED APR 22 2015...

ONLY SOME MINOR MODIFICATIONS NEEDED TO OUR AFTERNOON GRIDDED
FORECASTS...AS THEY ARE IN NICE SHAPE FROM OUR MIDNIGHT SHIFT
SHORT TERM FORECASTER. BASED ON THE 12Z NAM AND GFS...MAIN CHANGE
TO OUR AFTERNOON GRIDDED FORECASTS WAS TO BOOST POPS AND OUR
AREAL COVERAGE OF SHOWERS AND ISOLATED THUNDERSTORMS BASED
ON THE 12Z NAM SHOWING A WELL PRONOUNCED 850/700 MB THETA-E RIDGE
AXIS NORTH TO SOUTH ALONG AND JUST WEST OF THE LARAMIE RANGE AND
INTERSTATE 25...WITH DECENT UPWARD VERTICAL MOTION AND MECHANICAL
LIFT PROGGED WITH A WEAK SHORTWAVE TROUGH ALOFT PASSAGE NEAR
PEAK HEATING AND DECENT POSITIVE THETA-E ADVECTION TO THE SPINE
OF THE LARAMIE RANGE...THUS EXPECT...AS BOTH THE 12Z NAM AND 12Z
GFS INDICATE THE BULK OF THE SHOWER COVERAGE LATE THIS AFTERNOON
AND THIS EVENING OVER AND NEAR THE SOUTHERN LARAMIE RANGE BETWEEN
LARAMIE AND CHEYENNE...WITH LOW LEVEL MOISTURE...FUEL...FOR THE
SHOWERS AND THUNDERSTORMS AIDED BY THE MELTING SNOWPACK FROM OUR
RECENT PRECIPITATION EVENT A FEW DAYS AGO.

&&

.SHORT TERM...(TODAY THROUGH FRIDAY)
ISSUED AT 326 AM MDT WED APR 22 2015

MILD TEMPERATURES WILL HOLD OVER THE CWA THIS PERIOD WITH
GENERALLY INCREASING COVERAGES OF SHOWERS AND A FEW TSTRMS. IR
SATELLITE LOOP DEPICTING MOISTURE FIELD OVER THE SOUTHWEST PART OF
THE U.S. WHICH WILL BE LIFTING NORTHWARD SLOWLY OVER THE NEXT
COUPLE DAYS AHEAD OF AN UPPER LOW OVER SRN CALIFORNIA WHICH WILL
MOVE LITTLE THROUGH THURSDAY. UPPER RIDGE AXIS WILL BE OVER THE
REGION BUT IMPULSES WILL MOVE THROUGH THE RIDGE AND ACROSS THE CWA
HELPING TO SET OFF PCPN MAINLY IN THE AFTERNOONS AND EVENINGS. THE
SW UPPER LOW SHOULD OPEN THURSDAY NIGHT AND MOVE EAST AS A SECOND
UPPER LOW NEARS THE PACIFIC NW WHICH SHOULD INCREASE PCPN EVEN
MORE OVER THE CWA FRIDAY. MODEST AFTERNOON AND EVENING INSTABILITIES
SHOULD ALLOW FOR A FEW TSTRMS THROUGH THE PERIOD.

.LONG TERM...(FRIDAY NIGHT THROUGH TUESDAY)
ISSUED AT 326 AM MDT WED APR 22 2015

WEATHER PATTERN TO BECOME MORE ACTIVE THIS WEEKEND. MODELS
CONTINUE TO EVOLVE WITH CHANGES IN TIMING AND PLACEMENT OF UPPER
LEVEL ENERGY OVER THE EXTENDED PERIOD BUT THERE IS RELATIVELY
CLOSE AGREEMENT WITH A BROAD TROUGH IN PLACE OVER THE ROCKIES
SUNDAY AND MONDAY WITH A CLOSED UPPER LOW OVER THE SOUTHERN
PORTIONS OF THE ROCKIES. THIS PORTENDS SOGGY COOL CONDITIONS THIS
WEEKEND ACROSS THE FORECAST AREA...ESPECIALLY SUNDAY.

FRIDAY NIGHT SHOULD BE ON THE DRY SIDE AS A SHORTWAVE RIDGE
QUICKLY SLIDES OVER THE FORECAST AREA AND SATURDAY WILL LIKELY
START OFF ON THE DRY SIDE AS THE RIDGE PUSHES EAST INTO THE
PLAINS. DIFFLUENT/DIVERGENT FLOW ALOFT WILL DEVELOP SATURDAY
AFTERNOON AND EVENING WHILE INSTABILITY WILL INCREASE...SETTING
THE STAGE FOR SHOWER DEVELOPMENT. CONFIDENT THAT SHOWERS WILL
DEVELOP LATE SATURDAY OR SATURDAY NIGHT AND CONTINUE THROUGH
SUNDAY. THE MAIN QUESTION IS HOW MUCH PRECIPITATION WILL FALL AND
IN WHAT PHASE WILL IT REACH THE GROUND. THIS SYSTEM LOOKS VERY
SIMILAR TO LAST WEEKS WITH RAIN MOSTLY LIKELY INTO THE PLAINS WITH
SNOW ACROSS THE HIGHER ELEVATIONS OF SOUTHEAST WYOMING BUT ONCE
AGAIN PRECIPITATION TYPE WILL BE SOMEWHAT DEPENDENT ON
PRECIPITATION RATE. TEMPERATURES WILL REMAIN ON THE COOL SIDE INTO
EARLY NEXT WEEK SHOULD THE 00Z GFS AND ECMWF SOLUTIONS BE CLOSE TO
CORRECT.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1209 PM MDT WED APR 22 2015

SATELLITE IMAGERY SHOWING SOME CONVECTIVE BUILDUPS FORMING OVER
THE SNOWY AND SOUTHERN LARAMIE RANGES AT MID-DAY. WE CONTINUED
PREVIOUS FORECASTS OF HAVING THUNDERSTORMS IN THE VICINITY OF
RAWLINS...LARAMIE AND CHEYENNE HERE THIS AFTERNOON...DIMINISHING
IN THE EARLY EVENING HOURS. STRONGER WINDS EXPECTED TODAY IN THE
EASTERN ZONES AFFECTING ALLIANCE AND SIDNEY...WITH GUSTS TO 25 KTS
FROM THE SOUTH. OTHERWISE...VFR CATEGORY IN THE FOERCAST THROUGH
TOMORROW MORNING AT ALL SITES.

&&

.FIRE WEATHER...
ISSUED AT 326 AM MDT WED APR 22 2015

NO SIGNIFICANT CONCERNS SEEN FOR THE REST OF THE WEEK WITH
TEMPERATURES MILD AND OTHER WEATHER FACTORS EXPECTED TO REMAIN
NON-CRITICAL. NEARLY DAILY CHANCES FOR SHOWERS AND A FEW TSTRMS
FOR THE REST OF THE WEEK.

&&

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

$$

UPDATE...RUBIN
SHORT TERM...RE
LONG TERM...SML
AVIATION...JG
FIRE WEATHER...RE


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