National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS65 KCYS 151903
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
103 PM MDT WED MAY 15 2013

.UPDATE...
ISSUED AT 1249 PM MDT WED MAY 15 2013

WEATHER SCENARIO EVOLVING MUCH AS THE MIDNIGHT SHORT TERM FORECASTER
EXPECTED. WSR-88D REFLECTIVITY LOOPS SHOWING SCATTERED SHOWERS AND
THUNDERSTORMS DEVELOPING AND INCREASING IN AREAL COVERAGE OVER
THE SIERRA MADRE AND SNOWY RANGES OF SOUTHERN CARBON AND SOUTHERN
ALBANY COUNTIES.

NEUTRALLY TILTED SHORTWAVE TROUGH ALOFT MOVES EASTWARD INTO
CENTRAL UTAH THIS AFTERNOON. IN RESPONSE SURFACE TROUGH DEVELOPS
OVER EASTERN WYOMING AND EASTERN COLORADO WITH A LOW LEVEL
CONVERGENCE AXIS DEVELOPING FROM CASPER TO CHEYENNE.

EXPECT SCATTERED TO NUMEROUS SHOWERS AND SCATTERED THUNDERSTORMS
TO CONTINUE TO DEVELOP THIS AFTERNOON...PRIMARILY WEST OF
INTERSTATE 25...AS THE LOW AND MID LEVEL THETA-E RIDGE AXIS
DEVELOPS NORTH TO SOUTH ALONG INTERSTATE 25...AND LIFT IS PROVIDED
BY MECHANICAL UPSLOPE EAST AND SOUTHEAST WINDS...AS WELL AS
DIFFERENTIAL AND OROGRAPHIC EFFECTS OVER THE MOUNTAINS AND
HIGHER TERRAIN.

STEERING WINDS ARE RELATIVELY WEAK AND EXPECT THUNDERSTORM
MOVEMENT TO BE TO THE NORTHEAST AT ONLY 10 MPH THIS AFTERNOON.
PRECIPITABLE WATER VALUES ARE RUNNING SOME 110 TO 140 PERCENT
OF NORMAL...AND WILL CONTINUE TO INCREASE WITH MOISTURE LADEN
EAST AND SOUTHEAST WINDS ADVECTING LOW LEVEL MOISTURE NORTHWESTWARD
INTO OUR COUNTIES.

BASED ON EXPECTED SPEED SHEAR WITH HEIGHT AND INSTABILITY...ALONG
WITH PRECIPITABLE WATER VALUES AS WELL AS 700-500 LAPSE RATES
FROM 8 TO 9 CELSIUS PER KILOMETER...A FEW STRONG STORMS EXPECTED
ALONG AND WEST OF I-25...PRODUCING RAINFALL AMOUNTS UP TO ONE INCH
PER HOUR... WIND GUSTS TO 55 MPH AND HAIL UP TO THREE QUARTERS OF
AN INCH IN DIAMETER.

AS THE SHORTWAVE TROUGH MOVES ACROSS OUR COUNTIES TONIGHT...
SCATTERED THUNDERSTORMS WILL OCCUR EAST OF I-25 THIS EVENING...
AND CONTINUE OVER WESTERN NEBRASKA LATE INTO THE OVERNIGHT HOURS...
THOUGH DECREASING IN AREAL COVERAGE DUE TO LOSS OF INSOLATION.

ADJUSTED GRIDDED FORECASTS FOR THIS AFTERNOON TO ACCOUNT FOR
TRENDS AND TO INCORPORATE THE 12Z NAM AND GFS MODEL PROJECTIONS.

&&

.SHORT TERM...(TODAY THROUGH THURSDAY NIGHT)
ISSUED AT 324 AM MDT WED MAY 15 2013

A COLD FRONT HAS BACKED INTO SOUTHEAST WYOMING AND AT 08Z WAS
LOCATED FROM PINE BLUFFS TO GLENDO AND THEN TO THE NORTHWEST.
THAT BOUNDARY WILL CONTINUE TO MOVE WEST AND INTO THE LARAMIE
VALLEY THIS MORNING. BEHIND THE FRONT...THE SURFACE WINDS TURN TO
THE EAST OR SOUTHEAST AND THE BOUNDARY LAYER MOISTURE INCREASES.
SURFACE DEW POINTS WILL BE BETWEEN 45F AND 50F AT ELEVATIONS BELOW
5000 FEET MSL IN THE AFTERNOON. A SHORTWAVE TROUGH ALSO APPROACHES
FROM THE WEST THIS AFTERNOON AND WILL MOVE ACROSS THE CWA TONIGHT.
THE RESULT WILL BE AT LEAST A SCATTERED COVERAGE OF THUNDERSTORMS
IN THE AFTERNOON AND EARLY EVENING HOURS.

SOME OF THE STORMS LOOK TO BECOME STRONG NEAR THE EASTERN WYOMING
BORDER THIS AFTERNOON. THE LOW LEVEL THETA RIDGE AXIS WILL BE OVER
THAT AREA ALONG WITH STEEPER LAPSE RATES. CAPE VALUES ALSO APPROACH
1000 K/KG OVER THAT PART OF THE CWA. THE BEST 0-6KM SHEAR WILL OCCUR
OVER THE NORTH PART OF THE CWA. HAIL...GENERALLY SMALL...WIND GUSTS
TO 50 MPH AND A PERIOD OF MODERATE RAINFALL CAN BE EXPECTED WITH THE
ACTIVITY NEAR THE EASTERN WYOMING BORDER. AREAS FURTHER TO THE EAST
MAY BE CAPPED FOR MUCH OF THE AFTERNOON PER FORECAST RAOBS.

AS THE SHORTWAVE TROUGH MOVES EAST TONIGHT...SOME SHOWERS AND
EVENING THUNDERSTORMS WILL PERSIST AHEAD OF THE FEATURE. DRIER AIR
WILL MOVE BACK OVER THE CWA FROM WEST TO EAST WITH TROUGH PASSAGE
AND WILL ALSO PUSH THE LOW LEVEL THETA RIDGE AXIS TO ALONG THE
EASTERN CWA BORDER THURSDAY AFTERNOON. MOST OF THE THUNDERSTORMS
WILL OCCUR OVER THE PANHANDLE THURSDAY AFTERNOON WITH SOME POSSIBLY
STRONG FROM KCDR TO KSNY. IN AREAS ALONG AND WEST OF THE LARAMIE
RANGE...GUSTY WESTERLY WINDS WILL OCCUR ON THURSDAY. DRIER
CONDITIONS WILL BE OVER THE CWA AFTER THURSDAY EVENING.

TEMPERATURES WILL BE COOLER TODAY OVER THE CWA BEHIND THE FRONT AND
THEN WARM SOME FOR THURSDAY.

.LONG TERM...(FRIDAY THROUGH TUESDAY)
ISSUED AT 324 AM MDT WED MAY 15 2013

WARM AND MAINLY DRY WEATHER EXPECTED FRIDAY AS THE CWA LOOKS TO
SEE SOME DRY AIR ADVECTION IN SW FLOW AHEAD OF NEXT UPPER TROF
THAT WILL BE OVER THE WESTERN PART OF THE COUNTRY. THIS UPPER TROF
WILL MOVE SLOWLY EAST OVER THE WEEKEND BRINGING INCREASING CHANCES
FOR SHOWERS AND A FEW STORMS ALONG WITH A COOL DOWN. BEST CHANCES
FOR STORMS WILL BE SATURDAY...MAINLY OVER THE PANHANDLE WHERE
BETTER INSTABILITY SHOULD RESIDE. SUNDAY AND MONDAY LOOKING RATHER
COOL WITH AT LEAST SCATTERED SHOWERS AS UPPER TROF BROADENS SOME
AND CONTINUES A SLOW DRIFT EASTWARD. TROF AXIS SHOULD MOVE EAST OF
THE CWA BY TUESDAY WITH DRIER AND WARMER CONDITIONS BEGINNING TO
RETURN AT THAT TIME.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY MORNING)
ISSUED AT 1143 AM MDT WED MAY 15 2013

THROUGH 00Z...SCATTERED TO NUMEROUS THUNDERSTORMS WILL DEVELOP...
PRIMARILY ALONG AND WEST OF INTERSTATE 25...WITH THE STRONGEST
STORMS PRODUCING LOCALLY HEAVY RAIN...ERRATIC WIND GUSTS TO 55
MPH AND HAIL. THUNDERSTORMS PRODUCING MVFR AND LOCALIZED IFR...
OTHERWISE VFR. ISOLATED THUNDERSTORMS EAST OF INTERSTATE 25.

00Z TO 12Z...SCATTERED TO NUMEROUS THUNDERSTORMS...PRIMARILY ALONG
AND EAST OF INTERSTATE 25 IN THE EVENING...AND ACROSS WESTERN
NEBRASKA AFTER 06Z. STRONGEST STORMS...PRIMARILY IN THE EVENING...
PRODUCING LOCALLY HEAVY RAIN...ERRATIC WIND GUSTS TO 55 MPH AND
HAIL. THUNDERSTORMS WILL PRODUCE MVFR AND LOCALIZED IFR...
OTHERWISE VFR.

AFTER 12Z...DECREASING CLOUDINESS FROM WEST TO EAST WITH VFR
PREVAILING.


&&

.FIRE WEATHER...
ISSUED AT 324 AM MDT WED MAY 15 2013

COOLER AND MORE HUMID AIR WILL BE OVER THE CWA TODAY BEHIND THE
PASSAGE OF A COLD FRONT. AT LEAST A SCATTERED COVERAGE OF
AFTERNOON AND EVENING THUNDERSTORMS WILL ALSO OCCUR OVER THE CWA.
SOME OF THOSE STORMS WILL PRODUCE MODERATE RAINFALL AS WELL AS
BRIEF WIND GUSTS TO 50 MPH.

DRIER AIR WILL MOVE OVER THE REGION ON THURSDAY WITH THE BULK OF
THE SHOWER AND STORM ACTIVITY OVER THE PANHANDLE. IN AREAS ALONG
AND WEST OF THE LARAMIE RANGE...WESTERLY SURFACE WINDS WILL GUST
AS HIGH AS 35 MPH ON THURSDAY. MINIMUM RELATIVE HUMIDITY VALUES
WILL BE BETWEEN 15 AND 25 PERCENT OVER THE LOWER ELEVATIONS ON
THURSDAY...WITHE THE LOWER ELEVATIONS OVER CARBON COUNTY. FRIDAY
WILL BE AN EVEN WARMER...DRIER AND WINDIER DAY WITH CRITICAL FIRE
WEATHER CONDITIONS POSSIBLE OVER THE LOWER ELEVATIONS. COOLER
TEMPERATURES WILL RETURN TO THE REGION STARTING ON SUNDAY AND
LASTING THROUGH EARLY NEXT WEEK.

&&

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

$$

UPDATE...RUBIN
SHORT TERM...WEILAND
LONG TERM...RE
AVIATION...RUBIN
FIRE WEATHER...WEILAND