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000
FXUS65 KCYS 191000
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
400 AM MDT SUN MAY 19 2013

.SHORT TERM...(TODAY AND MONDAY NIGHT)
ISSUED AT 224 AM MDT SUN MAY 19 2013

SEVERE THUNDERSTORMS FROM SATURDAY EVENING HAVE SINCE DISSIPATED
AND PUSHED WELL TO THE NORTHEAST OF WESTERN NEBRASKA. THE FRONTAL
BOUNDARY RESPONSIBLE FOR THIS ACTIVITY HAS NOW SHIFTED EASTWARD
INTO CENTRAL NEBRASKA...AND WILL CONTINUE TO SLOWLY PUSH EASTWARD
TODAY. THEREFORE...EXPECT STRONG OR SEVERE THUNDERSTORMS TO BE
WELL EAST OF THE FORECAST AREA TODAY WITH A COOLER AIRMASS OVER
SOUTHEAST WYOMING AND WESTERN NEBRASKA. HIGH TEMPERATURES TODAY
WILL LIKELY NOT REACH 65 DEGREES ACROSS MOST OF THE AREA.

IR SATELLITE AND WATER VAPOR LOOPS SHOW THE MAIN NEGATIVELY TILTED
TROUGH AXIS PUSHING EAST INTO THE HIGH PLAINS OF WYOMING AND
COLORADO. MODELS INDICATE THE VIGOROUS SHORT WAVE...WHICH
TRIGGERED THE SEVERE WEATHER YESTERDAY...WILL AID A DEVELOPING
STORM SYSTEM OVER THE DAKOTAS AND FAR EASTERN WYOMING STARTING
TODAY. BELIEVE THIS HAS ALREADY STARTED TO TAKE PLACE AS CURRENT
SURFACE OBS ACROSS SOUTH DAKOTA AND NEBRASKA SHOW RAPIDLY FALLING
PRESSURE FALLS...AND LOCATIONS FROM CASPER EASTWARD TO DOUGLAS
AND LUSK ARE NOW REPORTING LIGHT TO MODERATE RAIN AND NORTHERLY
WINDS ALONG WITH LOWERING CEILINGS. THIS IS THE WRAP AROUND RAIN
BAND BEGINNING TO DEVELOP ON THE WESTERN HALF OF THE STORM SYSTEM.
WITH LOW TO MID LEVEL MOISTURE ADVECTION WRAPPING COUNTER CLOCKWISE
AROUND THE STORM SYSTEM INTO SOUTHEAST WYOMING...BELIEVE SHOWER
ACTIVITY WILL BECOME WIDESPREAD BY LATE TODAY AS A SECONDARY
BOUNDARY PUSHES SOUTH ACROSS THE AREA. SOME LLVL INSTABILITY WILL
COMBINE WITH THE COOLER AIR ALOFT TO PRODUCE ISOLATED
THUNDERSTORMS...MAINLY FURTHER SOUTH NEAR THE COLORADO BORDER BY
LATE TODAY. BY TONIGHT...UPSLOPE FLOW COMBINED WITH CONVERGENCE
AND MOISTURE ADVECTION WILL RESULT IN WIDESPREAD RAIN SHOWERS
MOVING FURTHER SOUTH INTO SOUTHERN WYOMING.

FOCUS WILL THEN SHIFT TO WINDY CONDITIONS ACROSS THE MAJORITY OF
THE FORECAST AREA AND THE POTENTIAL FOR HEAVY SNOW ACCUMULATIONS
OVER THE HIGHER MOUNTAINS OF SOUTHEAST WYOMING BY MONDAY. MODELS
IN GOOD AGREEMENT...SHOWING 700MB TEMPERATURES AS LOW AS -2C
ACROSS WYOMING BY MONDAY MORNING. THIS TRANSLATES TO A SNOW LEVEL
AROUND 8000 FEET OR SLIGHTLY BELOW. ALL MODELS INDICATE MODERATE
TO HEAVY QPF (AROUND 1 INCH OR GREATER) FROM THE SNOWY/SIERRA
MADRE RANGES...NORTHEAST TO THE NORTHERN LARAMIE RANGE AND THEN
EAST INTO CONVERSE AND NIOBRARA COUNTIES THROUGH MONDAY AFTERNOON.
WITH LOW SNOW LEVELS...THERE IS SOME CONCERN OF HEAVY SNOW
ACCUMULATIONS IN THE SNOWY...SIERRA MADRE...AND NORTHERN LARAMIE
RANGE THROUGH MONDAY. INCREASED POP AND SNOW ACCUMULATIONS WITH
CURRENTLY 5 TO 10 INCHES IN THE FORECAST. MAY NEED A LATE SEASON
WINTER WEATHER ADVISORY OR WINTER STORM WARNING FOR THESE
LOCATIONS. AS THE SURFACE LOW CONTINUES TO INTENSIFY AND EVEN
RETROGRADE WESTWARD A BIT...SURFACE WINDS WILL BEGIN TO INCREASE
BY MONDAY MORNING WITH GUSTS UP TO 45 MPH POSSIBLE OVER THE HIGH
PLAINS. MONDAY MAY VERY WELL BE A MISERABLE DAY WITH WIND DRIVEN
RAINFALL AND COOL TEMPERATURES IN THE 40S OR LOW 50S FOR DAYTIME
HIGHS. MATTER OF FACT...CAN NOT RULE OUT A FEW SNOWFLAKES IN THE
HIGHER VALLEYS WEST OF THE LARAMIE RANGE INCLUDING THE LARAMIE
VALLEY. STEADY RAINFALL WILL THEN PUSH SOUTHWARD TOWARDS THE I80
CORRIDOR BY NOON MONDAY. ALTHOUGH MODELS ALL SHOW LESS QPF (0.25
TO 0.50 TOTAL) FROM LARAMIE EASTWARD TO SIDNEY NEBRASKA...THERE
WILL BE MORE INSTABILITY IN THESE LOCATIONS WHICH MAY PRODUCE
LOCALLY HEAVY RAIN AMOUNTS DUE TO CONVECTION AND EMBEDDED THUNDER.
INCREASED POP BETWEEN 60 TO 80 PERCENT ACROSS THE WHOLE FORECAST
AREA ON MONDAY. INCREASED WINDS AS WELL...WITH GUSTS UP TO 50 MPH
NOT OUT OF THE QUESTION ACROSS THE HIGH PLAINS OF WYOMING.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 224 AM MDT SUN MAY 19 2013

MAIN CONCERN WITH THIS FORECAST PACKAGE IS THE TIMING OF WHEN THE
RAIN WILL EXIT THE REGION ON TUESDAY AND CHANCES OF CONVECTION
THROUGH THE WEEK.

TUESDAY-TUESDAY NIGHT:
LATEST MODEL TRENDS ARE SHOWING THE POSITION OF THE CUTOFF LOW A BIT
FURTHER WEST THAN PREVIOUS RUNS. ENSEMBLES ARE EVEN SHOWING VERY
SIMILAR TRENDS. AS A RESULT...THIS WILL FAVOR MUCH OF OUR REGION
STAYING IN THE COOL CONVEYOR BELT OF PRECIPITATION THROUGH THE FIRST
HALF OF THE DAY TUESDAY. WE DID BUMP UP PRECIPITATION CHANCES ACROSS
THE EASTERN HALF OF THE FORECAST AREA ON TUESDAY MORNING TO REFLECT
THIS POTENTIAL. WE ALSO KEPT SNOW CHANCES GOING IN THE MOUNTAINS
DURING THE EARLY MORNING HOURS WITH EVEN A CHANCE OF RAIN/MIXED WITH
SNOW IN VEDAUWOO AND LARAMIE. THE MODELS ARE SHOWING SOME SIGNS OF
SUBSIDENCE BUILDING INTO THE WESTERN HALF OF THE FORECAST AREA
DURING THE AFTERNOON WHICH SHOULD SHIFT THE BETTER CHANCES OF RAIN
FURTHER EAST. THIS SHOULD ALLOW TEMPERATURES TO WARM UP A BIT FROM
MONDAY`S HIGHS...MAINLY IN THE UPPER 50S TO AROUND 60. THE BULK OF
THE PRECIPITATION SHOULD COME TO AN END ON TUESDAY NIGHT AS THE
CLOSED LOW MOVES EAST AND BEGINS TO FILL IN ACROSS THE NORTHERN
PLAINS. TEMPERATURES ALSO SHOULD BE ABLE TO RADIATE OUT ON TUESDAY
NIGHT AS THE SURFACE RIDGE BUILDS OVER THE AREA.

WEDNESDAY-WEDNESDAY NIGHT:
THIS SHOULD BE ONE OF THE BETTER DAYS OF THE WEEK AS THE UPPER LEVEL
RIDGE BUILDS OVER THE AREA AND ALLOWS FOR DRYING CONDITIONS.
HOWEVER...WE MAY SEE A FEW SHOWERS AND ISOLATED THUNDERSTORMS
DEVELOP OVER THE LARAMIE RANGE. HOWEVER...ANYTHING THAT DOES DEVELOP
OVER THE LARAMIE RANGE WILL BE SLOW MOVING DUE TO WEAK FLOW ALOFT.
THE BULK OF THIS CONVECTION SHOULD DISSIPATE AFTER SUNSET DUE TO THE
LIMITED SHEAR AND INSTABILITY.

THURSDAY-SATURDAY:
THE MODELS ARE IN GOOD AGREEMENT IN SHOWING A POTENT UPPER LEVEL
TROF MOVING INTO THE PACIFIC NORTHWEST. AHEAD OF THIS FEATURE...WE
SHOULD BEGIN TO SEE GOOD RETURN FLOW BUILDING INTO THE AREA WITH 50
DEGREE DEWPOINTS MOVING BACK INTO THE AREA BY THURSDAY EVENING. THIS
SHOULD SET THE STAGE FOR AFTERNOON THUNDERSTORMS ALONG AND EAST OF
THE LARAMIE RANGE. CAPE VALUES UP TO 1500 J/KG AND SHEAR VALUES
BETWEEN 30 AND 50KTS MAY PROVIDE A CHANCE OF STRONG TO SEVERE STORMS
THROUGH SATURDAY. TEMPERATURES SHOULD BE QUITE MILD WITH HIGHS
MAINLY IN THE 70S AND 80S THROUGH THE LATTER HALF OF THE WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY EVENING)
ISSUED AT 1043 PM MDT SAT MAY 18 2013

ACTIVE WEATHER THE NEXT 24 HOURS AS A SLOW MOVING LOW PRESSURE
SYSTEM MOVES ACROSS THE AREA. LOOKING AT LOWERING CIGS SUNDAY MORNING
IN THE PANHANDLE...ESPECIALLY KCDR...KAIA AND KSNY. KCDR AND KAIA
HAVE THE NEST CHANCES OF GOING DOWN AS FORECAST BY THE LATEST HRRR
MODEL. THE OTHER AERODROME THAT COULD GO DOWN IS KRWL EARLY THIS
MORNING. HAVE INTRODUCED IFR AT THESE THREE AIRPORTS...KRWL...KCDR
AND KAIA WITHIN THE NEXT 6 HOURS. WIDESPREAD SHOWER AND
THUNDERSTORM ACTIVITY SUNDAY AS THE LOW TURNS WINDS NORTHERLY THEN
NORTHEASTERLY. THESE WINDS COULD BE QUITE STRONG IN THE PANHANDLE
SUNDAY AFTERNOON AND EVENING.


&&

.FIRE WEATHER...
ISSUED AT 224 AM MDT SUN MAY 19 2013

NO FIRE WEATHER CONCERNS THROUGH THE MIDDLE OF THE WEEK AS
UNSETTLED WEATHER...INCLUDING MOUNTAIN SNOWFALL AND WIDESPREAD
RAINS ACROSS THE LOWER ELEVATIONS...WILL KEEP FUELS GREEN AND
RELATIVE HUMIDITIES WELL ABOVE CRITICAL VALUES. TEMPERATURES WILL
BE COOLER AND CHANCES OF PRECIPITATION WILL CONTINUE THROUGH
MONDAY NIGHT.

&&

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

$$

SHORT TERM...TJT
LONG TERM...REC
AVIATION...CLAYCOMB
FIRE WEATHER...TJT