Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 312118
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
318 PM MDT FRI JUL 31 2015

.SHORT TERM...(TODAY THRU SUNDAY NIGHT)

VIGOROUS SHOWERS AND THUNDERSTORMS DEVELOPED EARLY THIS AFTERNOON
ALONG THE SOUTHERN LARAMIE RANGE...PINE RIDGE...AND W-E ALONG A
CONVERGENCE BOUNDARY THAT FORMED JUST NORTH OF THE CHEYENNE RIDGE IN
NORTHERN LARAMIE COUNTY. MOIST SOUTHEASTERLY FLOW FED THIS
THUNDERSTORM ACTIVITY WITH SBCAPES INITIALLY IN THE 1000-2000 J/KG
RANGE ACROSS LARAMIE COUNTY AND ALONG THE PINE RIDGE. A FEW STRONGER
PULSE STORMS REMAIN ALONG THE PINE RIDGE AT THIS HOUR...WITH THE
WYOMING ACTIVITY DIMINISHING QUITE A BIT AFTER DROPPING A STRONG
COLD POOL AND PUSHING OUT A WELL DEFINED OUTFLOW BOUNDARY. CAN SEE
THE WESTERN EXTENT OF THIS BOUNDARY EXTENDING N-S ACROSS ALBANY
COUNTY WHICH MAY ALLOW FOR A FEW STORMS TO DEVELOP OUT IN THIS AREA
THROUGH THE LATE AFTERNOON AS WELL. WITH RELATIVELY MOIST LOW AND
MIDLEVELS IN PLACE...COULD SEE MODERATE RAIN AND SMALL HAIL WITH ANY
STRONGER STORMS THAT DEVELOP AS SBCAPES OUTSIDE OF THE COLD POOL ARE
STILL ROUGHLY 1000-2000 J/KG ACCORDING TO SPC MESOANALYSIS. FOR
TONIGHT...MOIST SOUTH-SOUTHEASTERLY SFC FLOW WILL CONTINUE AND THE
NOSE OF THE LLVL JET WILL PUSH UP INTO OUR FAR NORTHERN COUNTIES AND
INTO SOUTH DAKOTA. CANNOT RULE OUT A FEW SHOWERS/STORMS OVERNIGHT IN
THESE AREAS.

A WEAK SFC TROUGH STILL LOOKS TO SLIDE SOUTH ACROSS THE CWA TOMORROW
MORNING THRU THE EARLY AFTERNOON WITH AN ISOLATED STORM OR TWO
POSSIBLE ALONG THE FRONT AS IT ROLLS THROUGH. OTHERWISE...WINDS WILL
SHIFT TO THE NORTH AND WILL FILTER IN DRIER AIR FOR SATURDAY NIGHT
AND EARLY SUNDAY. A STRONGER UPPER LEVEL SYSTEM WILL APPROACH FROM
THE SOUTHWEST ON SUNDAY AFTERNOON AND EVENING...INDUCING PRESSURE
FALLS IN THE HIGH COUNTRY AND REINSTATING MOIST EAST-SOUTHEASTERLY
UPSLOPE FLOW TO THE PLAINS BY THE AFTERNOON. WITH INCREASING LIFT
AND MOISTURE ALOFT AND LLVL  MOIST ADVECTION ACROSS THE
PLAINS...EXPECT ANOTHER ROUND OF SHOWERS AND T-STORMS IN THE
AFTERNOON AND EVENING. THE FOCUS FOR CONVECTION LOOKS TO BE OVER THE
HIGHER PEAKS AND ALONG THE LARAMIE RANGE AND NEARBY EASTERN PLAINS.

.LONG TERM...(MONDAY THROUGH FRIDAY)
ISSUED AT 229 PM MDT FRI JUL 31 2015

LONG RANGE MODELS REMAIN IN POOR AGREEMENT FOR MOST OF NEXT
WEEK...ALTHOUGH OVERALL THERE IS MORE CONFIDENCE IN MONDAYS
FORECAST COMPARED TO 24 HOURS AGO. THE GFS IS IN DECENT AGREEMENT
WITH THE ECMWF AND GEM ON MONDAY...ALL SHOWING THE UPPER LEVEL
RIDGE AXIS BREAKING DOWN AND ALLOWING A VIGOROUS UPPER LEVEL
TROUGH TO PUSH FROM SOUTHWEST TO NORTHEAST ACROSS THE FORECAST
AREA MONDAY AFTERNOON. ALTHOUGH LLVL INSTABILITY APPEARS MARGINAL
AT THIS TIME...THE DISTURBANCE WILL PROVIDE JUST ENOUGH MID TO
UPPER LEVEL DYNAMICS TO TRIGGER AFTERNOON SHOWERS AND
THUNDERSTORMS OVER SOUTHEAST WYOMING AND EVENTUALLY THE HIGH
PLAINS OF WESTERN NEBRASKA THAT EVENING. INCREASED POP BETWEEN 25
TO 45 PERCENT ALONG AND WEST OF I25 WITH SLIGHTLY LOWER VALUES
FURTHER EAST.

THERE IS STILL QUITE A BIT OF UNCERTAINTY WITH NEXT WEEKS
FORECAST PAST MONDAY. NUMEROUS MODEL DIFFERENCES WITH THE TIMING
AND TRACK OF SHORTWAVE DISTURBANCES ALOFT ALONG WITH THE
CONSIDERABLE DIFFERENCES IN THE OVERALL PATTERN LATER IN THE WEEK
(THURSDAY AND FRIDAY) IS THE OVERALL FORECAST ISSUE IN THE LONG
TERM. THE TIMING OF THESE DISTURBANCES ARE KEY IN FORECASTING THE
COVERAGE OF POTENTIAL TSTORMS THIS TIME OF THE YEAR...SO THERE
REMAIN LOW CONFIDENCE IN THE LONG TERM. THE ECMWF IS NOW SHOWING
THE STRONG UPPER LEVEL RIDGE EXTENDING NORTHWARD INTO WYOMING FOR
THE MIDDLE TO LATE PART OF NEXT WEEK...AND NOW THE GFS SHOWS A
BACK DOOR COOL FRONT DIVING SOUTHWARD LATE WEDNESDAY AND INTO
THURSDAY. KEPT FORECAST SLIGHTLY ABOVE CLIMO FOR NOW...WITH 15 TO
20 PERCENT POP EACH DAY ACROSS THE HIGH PLAINS...AND HIGHS IN 80S
TO LOW 90S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH SATURDAY MORNING)

CURRENT RADAR LOOP SHOWS CONVECTION DEVELOPING NEAR KCYS LATE THIS
MORNING...MAINLY ALONG THE SOUTHERN LARAMIE RANGE. THIS ACTIVITY
WILL GRADUALLY MOVE AND DEVELOP FURTHER EAST ALONG THE CHEYENNE
RIDGE TOWARDS KSNY THIS AFTERNOON. CONTINUED WITH VCTS FROM KLAR TO
KSNY INTO THIS EVENING...WHERE BRIEF MVFR VIS ARE POSSIBLE IN THE
HEAVIER SHOWERS. OTHERWISE...VFR CONDITIONS ARE EXPECTED THROUGH
TONIGHT.

&&

.FIRE WEATHER...
ISSUED AT 229 PM MDT FRI JUL 31 2015

ISOLATED TO WIDELY SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE
THROUGH THIS EVENING FOR LOCATIONS WITHIN AND EAST OF FWZ ZONES 307-
308. MUCH OF THIS ACTIVITY IS PRODUCING WETTING RAINFALL. DRY
CONDITIONS WILL RETURN TONIGHT...WITH MORE OF AN ISOLATED COVERAGE
OF SHOWERS AND STORMS POSSIBLE TOMORROW ALONG AND EAST OF THE
LARAMIE RANGE. VERY DRY HUMIDITIES WILL PERSIST THROUGH THE WEEKEND
FOR MUCH OF CARBON COUNTY...BUT WINDS STILL LOOK TO BE RELATIVELY
LIGHT.

&&

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

$$

SHORT TERM...RJM
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...RJM



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