Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 251849
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1249 PM MDT SAT APR 25 2015

.UPDATE...
ISSUED AT 1249 PM MDT SAT APR 25 2015

FRONTAL BOUNDARY THIS AFTERNOON EXTENDS ROUGHLY FROM CENTRAL
NIOBRARA COUNTY SOUTHWARD THROUGH CENTRAL GOSHEN COUNTY...AND
THEN SOUTHEASTWARD INTO KIMBALL COUNTY IN NEBRASKA. CONVECTION IS
FIRING ALONG THIS BOUNDARY IN ADDITION TO ALONG THE PINE RIDGE IN
THE NORTHERN NEBRASKA PANHANDLE. 18Z MESOANALYSIS SHOWS SBCAPES
OF 500 J/KG ACROSS THIS AREA...WITH THE 1000 J/KG CONTOUR
SITUATED JUST EAST OF OUR COUNTIES. DEEP LAYER SHEAR VALUES ARE
MINIMAL AT 18Z...ALTHOUGH GUIDANCE DOES SHOW AN INCREASE TO 20-30
KTS BY 00Z THIS EVENING. CONTINUE TO ANTICIPATE VIGOROUS
CONVECTION THROUGH THE AFTERNOON WITH MINIMAL ORGANIZATION...WITH
SMALL HAIL AND GUSTY WINDS BEING THE MAIN THREAT. COULD PERHAPS
SEE A STRONGER STORM OR TWO OVER THE PANHANDLE THIS EVENING WITHIN
BETTER ORGANIZED STORMS AS SHEAR INCREASES...BUT WEAK LLVL FLOW
AND OVERALL SHEAR CONTINUING TO BE RELATIVELY MARGINAL LENDS TO
LOW CONFIDENCE IN ANY WIDESPREAD STRONG ACTIVITY.

&&

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 410 AM MDT SAT APR 25 2015

MAIN FORECAST CONCERN FOR THE WEEKEND WILL BE THE PACIFIC STORM
SYSTEM FORECAST TO BECOME A CLOSED LOW NEAR THE FOUR CORNERS
REGION ON SUNDAY. CONFIDENCE IS HIGH REGARDING THE OVERALL
PATTERN...BUT THERE IS LIMITED CONFIDENCE ON SNOW LEVEL...LIQUID
PRECIPITATION AMOUNTS...AND THUS SNOW AMOUNTS OVER THE HIGHER
TERRAIN OF SOUTHEAST WYOMING.

CURRENT WATERVAPOR SATELLITE LOOP SHOWS THE PACIFIC TROUGH DIGGING
SOUTHWARD INTO CALIFORNIA AND NEVADA EARLY THIS MORNING. MODELS
ALL SHOW THE LOCATION OF THIS TROUGH AXIS OVER THE GREAT BASIN BY
THIS AFTERNOON...WITH A DEVELOPING SURFACE LOW PRESSURE CENTER
OVER UTAH. THIS WILL RESULT IN UPSLOPE EASTERLY WINDS THIS
AFTERNOON AS A COOL FRONT SLOWLY DEVELOPS ACROSS THE FORECAST
AREA AND MOVES INTO COLORADO...BECOMING A STATIONARY FRONT. LLVL
INSTABILITY WILL RESULT IN RAIN SHOWER ACTIVITY BECOMING MORE
WIDESPREAD THROUGH THE AFTERNOON...WITH TSTORMS EVENTUALLY
DEVELOPING BY THIS EVENING. THERE IS A LOW RISK OF SEVERE TSTORMS
ACROSS THE HIGH PLAINS THIS AFTERNOON AND THIS EVENING...BUT
CONDITIONS WILL BE MARGINAL AT BEST. ADDED HAIL AND GUSTY WIND
WORDING TO THE FORECAST ACROSS WESTERN NEBRASKA FOR NOW. CURRENT
MODELS SHOW THE POTENTIAL OF A WEAK SQUALL LINE FORMING NEAR THE
WYOMING/NEBRASKA BORDER LATE THIS AFTERNOON WITH INDIVIDUAL CELLS
MOVING NORTHEAST INTO THIS EVENING. THIS ACTIVITY WILL TRANSITION
TO MODERATE TO HEAVY RAINFALL ACROSS THE HIGH PLAINS TONIGHT AS
THE UPPER LEVEL LOW BEGINS TO CLOSE OFF FROM THE MEAN FLOW ALOFT.
MODELS ALL INDICATE A PERIOD OF STRONG UPPER LEVEL DIVERGENCE
TONIGHT DUE TO A LEFT EXIT/RIGHT ENTRANCE JET COUPLET ALOFT. ALL
MODELS PLACE THIS OVER THE EASTERN WYOMING PLAINS AND INTO WESTERN
NEBRASKA SOMETIME BETWEEN 06Z TONIGHT TO 18Z SUNDAY MORNING. THERE
IS SOME CONCERN OF A WIDESPREAD AREA OF HEAVY RAINFALL AND AN
NOCTURNAL THUNDERSTORMS DEVELOPING OVER THE HIGH PLAINS AND MOVING
NORTHWARD SLOWLY THROUGH THE NIGHT. KEPT HIGH POP NEAR 100 PERCENT
TONIGHT AND INTO SUNDAY MORNING. THANKFULLY...SNOW LEVELS WILL BE
HIGH AND ABOVE 8500 FEET. HOWEVER...SOME MODEL RUNS INCLUDING THE
SREF ARE SHOWING RESPECTABLE QPF AMOUNTS OVER THE EASTERN PLAINS.
AREA OF PRECIPITATION SHOULD SHIFT WESTWARD OVER WYOMING ON
SUNDAY.

FOR SUNDAY NIGHT...MODELS SHOW A DEFORMATION BAND SHIFTING EAST A
BIT AS THE MAIN UPPER LEVEL LOW NUDGES EASTWARD OVER NEW MEXICO
AND WESTERN TEXAS. CONFIDENCE IS INCREASING THAT THIS SYSTEM
SHOULD REMAIN WELL SOUTH OF THE FORECAST AREA INSTEAD OF GIVING US
A MORE PROLONGED PRECIP EVENT. BUT WILL HAVE TO CLOSELY MONITOR
THIS SINCE THESE SYSTEMS HISTORICALLY GIVE LAST MINUTE SURPRISES.
SNOWLEVELS LOWER TO NEAR 6500 FEET SUNDAY NIGHT AND EARLY MONDAY
MORNING. THANKFULLY...PRECIP RATES DO NOT APPEAR VERY HIGH WITH
THE DEFORMATION BAND AS THE MAIN UPPER LEVEL LOW IS TOO FAR SOUTH.
REGARDLESS...WILL HAVE TO WATCH SNOWFALL AMOUNTS FOR THE I80
CORRIDOR FROM CHEYENNE WESTWARD TO RAWLINS...AND ESPECIALLY THE
I80 SUMMIT. EVEN THOUGH TEMPERATURE PROFILES INDICATE RAIN AS HIGH
AS LARAMIE...AM NOT CONVINCED GIVEN THE RESULTS OF THE LAST STORM
TO IMPACT THE REGION. LOWERED THE RAIN/SNOW LINE DOWN TO AROUND
6000 FEET FOR LATE SUNDAY NIGHT....WITH 3 TO 5 INCHES OF SNOW
ACROSS THE I80 SUMMIT. WINTER WEATHER ADVISORIES MAY BE NEEDED FOR
PORTIONS OF THE I80 CORRIDOR FOR LATE SEASON IMPACTS.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 333 AM MDT SAT APR 25 2015

A PERIOD OF WARM DRY WEATHER IS ON THE HORIZON THROUGH THE LONG
TERM FORECAST. A FEW SHOWERS MAY LINGER MONDAY NIGHT INTO TUESDAY
WITH RELATIVELY COOL AIR IN PLACE BUT WESTERLY FLOW ALOFT WILL
KICK IN WEDNESDAY AS AN UPPER LEVEL RIDGE EXPANDS ACROSS THE
WESTERN CONUS. DAYTIME TEMPERATURES WILL WARM INTO THE 60S AND
70S ACROSS THE AREA BY THE MIDDLE OF NEXT WEEK AND IT IS LOOKING
LIKE 80S ARE A REASONABLE BET INTO THE NEBRASKA PANHANDLE FOR
LATER PORTIONS OF THE WEEK. OTHER THAN A FEW INSTABILITY SHOWERS
POSSIBLE OVER THE MOUNTAINS THE NEXT CHANCE FOR MORE SIGNIFICANT
PRECIPITATION WILL HOLD OFF UNTIL AT LEAST FRIDAY IF NOT UNTIL
NEXT WEEKEND.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1109 AM MDT SAT APR 25 2015

CONDITIONS ARE SETTING UP FOR A PROLONGED IFR/LIFR EVENT TONIGHT
INTO SUNDAY. FIRST OFF...FRONTAL BOUNDARY CONTINUES TO SAG SOUTH
THIS MORNING INTO EASTERN WYOMING. SHOULD BE LAYING ALONG THE
LARAMIE RANGE BY EARLY THIS EVENING...WHERE IT WILL STAY THROUGH
MONDAY. SHOULD BEGIN TO SEE INCREASING CHANCES FOR SHOWERS AND
THUNDERSTORMS EAST OF THE LARAMIE RANGE LATER THIS AFTERNOON.
EASTERLY TO SOUTHEASTERLY UPSLOPING WINDS WILL BRING A FAVORABLE
SITUATION FOR IFR/LIFR CONDITIONS THIS EVENING AND SUNDAY.
CONDITIONS COULD PERSIST INTO MONDAY EVENING BEFORE WINDS ONCE
AGAIN SHIFT WESTERLY AND THE BOUNDARY MOVES EAST.


&&

.FIRE WEATHER...
ISSUED AT 321 AM MDT SAT APR 25 2015

NO FIRE WEATHER CONCERNS THROUGH EARLY NEXT WEEK AS A PERIOD OF
UNSETTLED WEATHER WILL RETURN TO SOUTHEAST WYOMING AND WESTERN
NEBRASKA THIS WEEKEND. PERIODS OF RAIN SHOWERS AND HIGH ELEVATION
SNOW ARE EXPECTED INTO MONDAY WITH ISOLATED THUNDERSTORMS POSSIBLE
SATURDAY AND SUNDAY. HUMIDITIES WILL TREND MUCH HIGHER THIS
WEEKEND WITH RECOVERIES NEAR 90 PERCENT...AND DAYTIME HUMIDITIES
BETWEEN 60 TO 80 PERCENT.

&&

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

$$

UPDATE...RJM
SHORT TERM...TJT
LONG TERM...SML
AVIATION...GCC
FIRE WEATHER...TJT


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