Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 171709
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1109 AM MDT SUN AUG 17 2014

.UPDATE...
ISSUED AT 1050 AM MDT SUN AUG 17 2014

LATE MORNING WATER VAPOR LOOP SHOWED A CLOSED UPPER LOW DRIFTING
EAST ACROSS SOUTHERN SASKATCHEWAN PROVINCE WITH A TROUGH EXTENDING
INTO MT/NORTHERN WY. UPPER HIGH WAS SITUATED OVER THE DESERT SOUTHWEST
WITH ZONAL FLOW ALOFT OVER SOUTHEAST WY/WESTERN NE. 12Z RIW/DEN
SOUNDINGS INDICATED A VERY DRY LOW/MID LAYER WITH PRECIP WATER
VALUES OF .42/.52 INCH RESPECTIVELY. THE RIW SOUNDING DEPICTED 35
TO 45 KT WESTERLY WINDS JUST ABOVE 600MB. AS TEMPERATURES RISE TO
AROUND 90 THIS AFTERNOON...EFFICIENT MIXING OF MID LEVEL WINDS TO
THE SURFACE WILL RESULT IN GUSTS TO AROUND 30 KT FOR MUCH OF
SOUTHEAST WY. HUMIDITIES WILL DROP TO 10 TO 15 PERCENT BELOW 8000
FT. CURRENT RED FLAG WARNING FOR ALL WY ZONES EXCEPT THE SIERRA
MADRE AND SNOWY RANGES ON TRACK. WILL NEED TO CLOSELY MONITOR THE
WESTERN NE PANHANDLE FOR POTENTIAL CRITICAL FIRE WEATHER CONDITIONS
WITH WIND GUSTS OF 15 TO 20 MPH AND HUMIDITIES DROPPING TO AROUND
15 PERCENT...ESPECIALLY THOSE COUNTIES BORDERING WY.

LATEST HRRR MODEL KEEPS THE CWA DRY THIS AFTERNOON AND EARLY EVENING
AS SHOWER/TSTORM ACTIVITY WILL BE CONFINED TO CENTRAL/EASTERN CO
AND BLACK HILLS TO NORTHERN NE EASTWARD. THEREFORE...REMOVED SMALL
POPS FOR THE MOUNTAINS. RAISED MAX TEMPERATURES A FEW DEGREES FOR
THE PLAINS.

&&

.SHORT TERM...(TODAY THROUGH MONDAY NIGHT)
ISSUED AT 500 AM MDT SUN AUG 17 2014

MAIN CONCERN FOR TODAY WILL ONCE AGAIN BE FIRE WEATHER AS CRITICAL
CONDITIONS ARE ANTICIPATED FOR MUCH OF SOUTHEAST WYOMING. AN
UPPER LEVEL SHORTWAVE CURRENTLY OVER IDAHO PER WATER VAPOR IMAGERY
WILL MOVE ACROSS NORTHERN WYOMING TODAY AND WILL SYNC UP WITH A
STRONGER UPPER TROUGH MOVING ALONG THE US/CANADIAN BORDER. THE
COMBINATION OF FEATURES WILL DEEPEN THE LEE SIDE SFC PRESSURE
TROUGH THROUGH THE DAY WITH BREEZY NORTHWEST WINDS DEVELOPING
ACROSS SOUTHEAST WYOMING AS THE SFC PRESSURE GRADIENT STRENGTHENS.
GUSTS OF 25 TO 35 MPH LOOK COMMON OVER THIS AREA THRU THE
AFTERNOON AS FORECAST SOUNDINGS SUGGEST THE TOP OF THE MIXING
LEVEL WILL BE UP BETWEEN 500 AND 600 MB WHERE WINDS WILL BE 30 TO
35 KT. THE ALREADY DRY BOUNDARY LAYER AIRMASS COMBINED WITH DRY
AND WARM DOWNSLOPE WINDS WILL TANK HUMIDITIES FAIRLY QUICKLY LATE
THIS MORNING OVER SOUTHEAST WYOMING...WITH HUMIDITIES EXPECTED TO
REMAIN IN THE LOW TEENS FOR MUCH OF THE AFTERNOON. THE COMBINATION
OF LOW RHS AND GUSTY WINDS WILL CREATE CRITICAL FIRE WEATHER
CONDITIONS OVER MUCH OF SOUTHEAST WYOMING WITH THE FOCUS ON AREAS
BELOW 8000 FEET. STARTED THE RFW SLIGHTLY EARLIER THAN PREVIOUS
ISSUANCE AS WINDS SHOULD INCREASE QUICKLY THROUGH THE LATE
MORNING...AND ADDED IN FWZ 302 TO ACCOUNT FOR THE LOWER ELEVATIONS
OF THIS ZONE WHICH SAW MARGINAL CRITICAL CONDITIONS YESTERDAY AND
WILL LIKELY BREACH CRITICAL THRESHOLDS AGAIN TODAY. REGARDING
STORM CHANCES ACROSS THE CWA...CONVECTION ASSOCIATED WITH THE
SHORTWAVE FEATURED APPEARED TO BE SOMEWHAT LIMITED OVER OREGON AND
IDAHO YESTERDAY WITHIN THE DRY AIRMASS. EXPECT A SIMILAR TREND FOR
OUR AREA TODAY WITH MINIMAL DEEP CONVECTION OVER THE CWA. LOOKING
INSTEAD AT SOME TOWERING CU AND PERHAPS A SHOWER OR TWO OVER THE
MOUNTAINS WHERE OROGRAPHIC EFFECTS WILL AIDE IN SOME CONVECTIVE
DEVELOPMENT. LACK OF DEEP LAYER MOISTURE SHOULD KEEP TSTORM
CHANCES MINIMAL THO.

A SURFACE FRONT WILL DROP SOUTH ACROSS THE PLAINS EARLY THIS
EVENING AND OVERNIGHT WITH AN INCREASE IN LLVL MOISTURE AND A
SFC WIND SHIFT TO THE NORTH THEN NORTHEAST WITH FROPA. MODELS
SUGGEST THAT MID LEVEL MOISTURE WILL INCREASE OVER THE ROCKIES
THROUGH THE DAY MONDAY WITH STRENGTHENING FLOW ALOFT. NORTHEAST
UPSLOPE FLOW IN PLACE ACROSS THE PLAINS COMBINED WITH INCREASING
MOISTURE WILL EASE FIRE WEATHER CONCERNS OVER THE FORECAST
AREA...WITH CHANCES FOR SHOWERS AND TSTORMS RETURNING TO THE
MOUNTAINS OF SOUTHEAST WYOMING AND NEARBY LOWER ELEVATIONS IN THE
AFTERNOON. MODELS HINT AT A WAA PATTERN DEVELOPING MONDAY NIGHT
AHEAD OF A SHORTWAVE MOVING UP FROM THE SOUTHWEST WITH
SOUTHWESTERLY H7 WINDS INCREASING TO 15 TO 20 KT OVERNIGHT. COULD
SEE CONVECTION CONTINUE THRU EARLY TUESDAY MORNING AS A
RESULT...WITH THE MAIN FOCUS ACROSS THE PANHANDLE WHERE WAA AND
DEEPEST MOISTURE WILL BE COLLOCATED WITH OROGRAPHIC LIFT OFF THE
PINE RIDGE.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 500 AM MDT SUN AUG 17 2014

MODELS VERY SIMILAR TUESDAY BRINGING A SHORTWAVE THROUGH THE RIDGE
OVER SOUTHERN WYOMING AND DEVELOPING SOME QPF OVER THE WESTERN
MOUNTAINS TUESDAY AFTERNOON. BOTH THE GFS AND ECMWF SPREAD THIS
MOISTURE OUT INTO THE PANHANDLE TUESDAY AFTERNOON...SO KEPT SLIGHT
CHANCE POPS GOING FOR MOST AREAS INTO TUESDAY EVENING. BEST CHANCES
FOR SHOWERS LOOKS TO BE WEST OF THE LARAMIE RANGE THOUGH AND THIS IS
WHERE HIGHEST POPS WERE PLACED.

DRIER AIR FOR WEDNESDAY...BUT STILL SOME CHANCES FOR THE SNOWY AND
SIERRA MADRE RANGES DURING THE AFTERNOON. MOST AREAS SHOULD STAY DRY
WITH WEST TO NORTHWEST DOWNSLOPING WINDS OFF THE LARAMIE RANGE.

A DIFFERENT STORY FOR FRIDAY AND MODELS BEGIN TO DIVERGE. THE GFS
SHOWING A POTENT SHORTWAVE MOVING INTO THE SOUTHEASTERN CWFA FRIDAY
MORNING WITH WIDESPREAD SHOWERS ACTIVITY ACROSS THE SOUTHERN
PANHANDLE BACK INTO EXTREME SOUTHEAST WYOMING. ECMWF MUCH WEAKER
WITH THIS SHORTWAVE AND KEEPS POPS MUCH LOWER THAN THE GFS. ECMWF
DOES EVENTUALLY BRING SOME QPF INTO THE AREA...MAINLY ACROSS OUR
NORTHERN AND EASTERN ZONES...SO DID KEEP SOME SLIGHT CHANCE TO LOW
CHANCE POPS GOING IN THE FORECAST FOR FRIDAY.

ENTERING SATURDAY...GFS SHOWING A 90KT UPPER LEVEL JET MOVING INTO
CENTRAL WYOMING SATURDAY MORNING. 700MB WINDS ON THE INCREASE AS
WELL...WITH 30KT DEVELOPING FRIDAY MORNING OUT WEST. ORIENTATION ON
ECMWF A LITTLE DIFFERENT WITH THE TROUGH MORE PRONOUNCED AND COLDER.
ECMWF 700MB TEMPERATURES SATURDAY AFTERNOON ACROSS NORTHERN WYOMING
DOWN TO 0 TO -2C. COULD BE A SIGNIFICANT COOL DOWN SHOULD THE ECMWF
FORECAST COME TRUE. FOR NOW...DID NOT COOL TEMPERATURES AS MUCH AS
WHAT THE ECMWF MIGHT GO FOR...BUT DID GO LOWER ON TEMPERATURES.
LARGE POSSIBILITIES FOR A TEMPERATURE BUST AS THERE IS A 10C
DIFFERENCE IN 700MB TEMPERATURES BETWEEN THE TWO MEDIUM RANGE MODELS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 500 AM MDT SUN AUG 17 2014

VFR CONDITIONS NEXT 24 HOURS FOR ALL SOUTHEAST WYOMING AND
NEBRASKA PANHANDLE AIRPORTS. MAIN CONCERN TODAY WILL BE GUSTY WEST
WINDS ACROSS SOUTHEAST WYOMING. COULD SEE GUSTS APPROACHING 30KT
AT KRWL AND KLAR THAT COULD PRODUCE SOME LOW LEVEL TURBULENCE ON
TAKEOFFS AND LANDINGS. SHOULD SEE MOSTLY CLEAR SKIES TODAY.


&&

.FIRE WEATHER...
ISSUED AT 500 AM MDT SUN AUG 17 2014

RED FLAG WARNING REMAINS IN EFFECT FOR MUCH OF SOUTHEAST WYOMING
THIS AFTERNOON FOR NORTHWEST WIND GUSTS OF 25 TO 35 MPH COMBINING
WITH HUMIDITIES DROPPING TO THE LOW TEENS. THE HIGHEST THREAT FOR
CRITICAL CONDITIONS WILL BE IN AREAS BELOW 8000 FEET. INCREASING
MOISTURE AT THE SFC AND ALOFT WILL COMBINE WITH GENERALLY WEAKER
WINDS TO DIMINISH FIRE WEATHER CONCERNS FOR MONDAY AND TUESDAY.
CHANCES FOR SHOWERS AND THUNDERSTORMS WILL INCREASE EARLY NEXT
WEEK AS WELL.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...RED FLAG WARNING UNTIL 7 PM MDT THIS EVENING FOR WYZ301>304-306-
     308>310.

NE...NONE.
&&

$$

UPDATE...JAMSKI
SHORT TERM...RJM
LONG TERM...CLAYCOMB
AVIATION...CLAYCOMB
FIRE WEATHER...RJM








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