000
FXUS65 KCYS 140509
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1109 PM MDT MON MAY 13 2013

.SHORT TERM...(TONIGHT THROUGH WEDNESDAY)
ISSUED AT 340 PM MDT MON MAY 13 2013

WITH THE UPPER RIDGE AXIS OVERHEAD THIS AFTERNOON...INSTABILITY IS
REALLY LIMITED AND SCATTERED FLAT CUMULUS ARE THE RESULT.
TEMPERATURES HAVE BEEN 15-20 DEGREES ABOVE NORMAL TODAY WITH 700MB
TEMPS AT A VERY WARM 12C. FOR TONIGHT...SHOULD SEE A REPEAT OF
LAST NIGHT WITH MOST LOCATIONS TO THE EAST OF THE LARAMIE RANGE
STRUGGLING TO GET BELOW 50 DEGREES. SHORTWAVE MOVES ACROSS THE
CANADIAN BORDER TO THE NORTH OF MONTANA-NORTH DAKOTA ON TUESDAY.
HIGHS WILL BE VERY SIMILAR TO THIS AFTERNOON AND WESTERLY WINDS
WILL BE ENHANCED THROUGH THE EARLY AFTERNOON AS THE GFS SHOWS
700MB WINDS AROUND 20 KTS. THERE ARE TIMING DIFFERENCES AS A WEAK
FRONT MOVES ACROSS THE PLAINS SOMETIME IN THE AFTERNOON...WHICH
IMPACTS THE RED FLAG POTENTIAL IN THE WESTERN NEBRASKA PANHANDLE.
THE NAM PUSHES THE SFC TROUGH ACROSS THE PANHANDLE BY 21Z WITH
WEAK NORTHERLY WINDS AND HIGHER DEWPOINTS BEHIND IT. EVEN THE
SLOWER GFS...WHICH SHOWS THE BOUNDARY LAYER FLOW REMAINING
WESTERLY ACROSS MOST OF THE PANHANDLE THROUGH THE LATE
AFTERNOON...DOES NOT INDICATE PARTICULARLY STRONG WINDS (GENERALLY
10-15 KTS IN THE MIXED LAYER). THIS IS DIFFERENT FROM YESTERDAYS MODEL
RUNS THAT SHOWED STRONGER BOUNDARY LAYER WINDS. CERTAINTY IS NOT
HIGH ENOUGH TO WARRANT UPGRADING THE FIRE WEATHER WATCH AT THIS
TIME. WILL LET THE EVENING AND NIGHT SHIFT DECIDE ON WHETHER TO
CANCEL OR UPGRADE THE WATCH.

THERE ARE ALSO DIFFERENCES IN THE CONVECTIVE POTENTIAL ON TUESDAY
AFTERNOON AND EVENING. THE NAM POOLS LLVL MOISTURE BEHIND THE
FRONT WITH LIFTED INDICES DROPPING TO -3C TO -5C...AND THE MODEL
DEVELOPS SCATTERED STORMS OVER THE PLAINS. THE GFS ON THE OTHER
HAND ONLY SHOWS WEAK INSTABILITY AND DOES NOT GENERATE ANY STORMS
IN THE WARM MIDLEVEL AIRMASS. TENDED TO SIDE WITH THE GFS SINCE
THE NAM HAS TENDED TO OVERDO INSTABILITY IN THE PAST FEW WEEKS AND
THE ECMWF SHOWS VIRTUALLY NO QPF ALSO. WINDS BEHIND THE FRONT
BECOME SOUTHEASTERLY OVER THE PLAINS BY WEDNESDAY
MORNING...TRANSPORTING LLVL MOISTURE ALONG AND JUST EAST OF THE
LARAMIE RANGE BY THE AFTN. WITH THE GFS AND NAM BOTH SHOWING MID
40S DEWPOINTS JUST EAST OF THE LARAMIE RANGE BY THE AFTN...ADDED
AN AREA OF WIDESPREAD SLIGHT CHANCE POPS OVER MOST OF THE
SOUTHEAST WY PLAINS. TEMPS WILL BE A GOOD 10-15 DEGREES COOLER ON
WEDNESDAY IN THE POST FRONTAL AIRMASS.

.LONG TERM...(WEDNESDAY NIGHT THROUGH MONDAY)
ISSUED AT 340 PM MDT MON MAY 13 2013

ANY CONVECTION THAT DOES DEVELOP WEDNESDAY AFTERNOON SHOULD
GENERALLY MOVE EAST...AND POSSIBLY AFFECT PARTS OF PANHANDLE ON
WEDNESDAY EVENING. MOST OF THE CONVECTION SHOULD BE DOWNSTREAM OF
THE HIGHER ELEVATIONS OF LARAMIE RANGE...BUT SHOULD QUICKLY
DISSIPATE AFTER SUNSET...DUE TO LIMITED INSTABILITY.

THURSDAY-FRIDAY:
THE CONSENSUS MODELS ARE SHOWING THE UPPER LEVEL TROF DIGGING ACROSS
THE PACIFIC NORTHWEST WHICH WILL ALLOW FOR STRONG SOUTHWEST FLOW TO
DEVELOP OVER AREAS WEST OF LARAMIE RANGE. WIND SPEEDS COULD BECOME
QUITE GUSTY OVER THIS REGION BOTH DAYS ESPECIALLY DURING THE
AFTERNOON INTO THE EARLY EVENING. THIS WILL ALSO CAUSE RELATIVE
HUMIDITY VALUES TO BE ON THE LOW SIDE WHICH MAY AFFECT SOME AREAS
THAT ARE NOT IN GREEN UP. CONVECTION SHOULD BE SOMEWHAT LIMITED.
HOWEVER...WE CANNOT RULE OUT AN ISOLATED SHOWER OR TWO OVER THE
MOUNTAINS.

SATURDAY-MONDAY:
THE MAIN QUESTION DURING THIS TIME FRAME WILL BE HOW MUCH
TEMPERATURES WILL COOL OFF THIS WEEKEND AND THE CHANCES OF SHOWERS
AND THUNDERSTORMS.

THE MODELS ARE SHOWING SOME TIMING AND STRENGTH DIFFERENCES OF THE
UPPER LEVEL TROF THIS WEEKEND. THE GFS IS A SHOWING A LITTLE QUICKER
MOVEMENT OF THE MAIN TROF WITH A MORE OPEN WAVE WHILE THE ECMWF IS A
LITTLE SLOWER AND CLOSES THIS SYSTEM OFF OVER THE NORTHERN PLAINS.
NOT REAL CONFIDENT IN EITHER SOLUTION AT THIS POINT...BUT THE GFS IS
SHOWING SOME TRENDS OF THE UPPER LEVEL TROF DIGGING OVER THE
NORTHERN PLAINS ON SUNDAY. STILL QUITE A BIT OF UNCERTAINTY THIS
FAR OUT...BUT IT STILL LOOKS LIKE THINGS SHOULD COOL OFF THIS
WEEKEND. AT THIS POINT...IT APPEARS LIKE THE FRONTAL BOUNDARY SHOULD
PASS THROUGH MUCH OF SOUTHEAST WYOMING DURING THE MORNING AND THE
NEBRASKA PANHANDLE DURING THE AFTERNOON. HOWEVER...GOOD DOWNSLOPE
FLOW SHOULD PREVAIL BEHIND THE BOUNDARY WHICH SHOULD KEEP US FAIRLY
MILD ON SATURDAY. PRECIPITATION CHANCES SHOULD BE MOSTLY CONFINED TO
THE MOUNTAINS...BUT CANNOT RULE A FEW SHOWERS AND THUNDERSTORMS
DEVELOPING IN THE PLAINS ALONG THE FRONTAL BOUNDARY.
OTHERWISE...DOWNSLOPED REGIONS MAY NOT SEE MUCH IN THE WAY OF
PRECIPITATION.

THE ECMWF IS SHOWING MORE JET ENERGY DIGGING ON THE BACK SIDE OF THE
TROF ON SUNDAY INTO MONDAY. THIS MAY BRING REINFORCING SHOTS OF
COOLER AIR ALONG WITH A CHANCE OF SHOWERS AND ISOLATED
THUNDERSTORMS. THEREFORE...IF THE MODELS COME INTO BETTER AGREEMENT
IN SHOWING THE UPPER LEVEL TROF DIGGING IN THE NORTHERN PLAINS...WE
MAY HAVE EXTENDED PERIOD OF COOLER TEMPERATURES ALONG WITH CHANCE OF
SHOWERS AND ISOLATED THUNDERSTORMS. RIGHT NOW...IT APPEARS LIKE
HIGHS SHOULD GENERALLY BE IN THE 70S IN THE EASTERN PLAINS ON
SATURDAY...WITH MAINLY 60S WEST OF THE LARAMIE RANGE. HOWEVER...WE
MAY COOL OFF TO THE 50S AND 60S ON SUNDAY AND MONDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY EVENING)
ISSUED AT 1104 PM MDT MON MAY 13 2013

VFR ACROSS THE AREA TONIGHT AND TUESDAY. A FEW THUNDERSTORMS
POSSIBLE TUESDAY AFTERNOON OFF OF THE MOUNTAINS AND ALONG THE
INTERSTATE 80 CORRIDOR. STRONG WIND GUST POSSIBLE IN THE VICINITY
OF SHOWERS AND THUNDERSTORMS TUESDAY AFTERNOON...OTHERWISE WIND
WILL BE RELATIVELY LIGHT ACROSS THE FORECAST AREA. SOME GUSTS
AROUND 25 MPH OVER SOUTHEAST WYOMING TUESDAY WITH GUSTS 15 TO 20
MPH IN THE NEBRASKA PANHANDLE. A COLD FRONT WILL MOVE INTO
NORTHERN PORTIONS OF THE FORECAST AREA TUESDAY AFTERNOON WITH
WINDS SHIFTING FRONT HE WEST TO THE NORTH.

&&

.FIRE WEATHER...
ISSUED AT 340 PM MDT MON MAY 13 2013

ANOTHER WARM DAY IS IN STORE FOR THE REGION ON TUESDAY. THE WARM
TEMPERATURES WILL CAUSE MINIMUM AFTERNOON HUMIDITIES TO DROP TO
AROUND 15 PERCENT ACROSS LOWER ELEVATIONS. WESTERLY WINDS AHEAD OF
A COLD FRONT COULD BE GUSTY AT TIMES THROUGH THE AFTERNOON...WITH
OCCASIONAL GUSTS TO 20-25 MPH. THE COMBINATION OF VERY DRY
CONDITIONS AND BREEZY WINDS COULD RESULT IN RAPID FIRE SPREAD OVER
THE NEBRASKA PANHANDLE...WHERE FUELS ARE CURRENTLY CRITICAL. IT
WILL NOT BE QUITE AS DRY ON WEDNESDAY AFTERNOON AS TEMPERATURES
WILL BE AROUND 10 DEGREES COOLER.

&&

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

$$

SHORT TERM...FINCH
LONG TERM...REC
AVIATION...LIEBL
FIRE WEATHER...FINCH