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000
FXUS65 KCYS 071825
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1125 AM MST FRI MAR 7 2014

.UPDATE...
ISSUED AT 1101 AM MST FRI MAR 7 2014

ANOTHER INTELLECTUALLY FASCINATING AND CHALLENGING WEATHER SCENARIO
FOR THIS AFTERNOON WITH THIS PROGRESSIVE SHORTWAVE TROUGH ALOFT
PASSAGE.

PROGRESSIVE POSITIVELY TILTED SHORTWAVE TROUGH MOVES SLOWLY SOUTHEAST
INTO NORTHERN COLORADO BY EARLY EVENING...WITH A FEW HOURS OF
LIGHT TO MODERATE...AND OCCASIONAL HEAVY SNOW...EXPECTED ALONG AND
SOUTH OF A RAWLINS TO SCOTTSBLUFF LINE...AND ESPECIALLY NEAR AND
ALONG THE WYOMING AND COLORADO STATE LINE THIS AFTERNOON...AS
NEARLY SATURATED LOW AND MID LEVELS OF THE ATMOSPHERE ARE LIFTED
DYNAMICALLY AND OROGRAPHICALLY. RELATIVELY IMPRESSIVE 500-300 MB
AND 700-500 MB QUASIGEOSTROPHIC LIFT NOTED AND THE NAM AND GFS
QUITE SIMILAR IN THEIR DEPICTION OF QPF.

IN FACT...CHEYENNE WSR-88D NOW SHOWING INCREASING REFLECTIVITY
DEVELOPING ALONG A SNOW BAND ORIENTED EAST WEST ALONG THE CHEYENNE
RIDGE MOVING NORTH TOWARDS INTERSTATE 80 OVER LARAMIE COUNTY...
SO SNOW INTENSITY AND COVERAGE EXPECTED TO INCREASE ALONG I-80
OVER LARAMIE COUNTY THROUGH THE EARLY AFTERNOON...INCLUDING
CHEYENNE.

INHERITED GRIDDED FORECASTS WERE ON TRACK FROM OUR MIDNIGHT SHIFT
TEAM. BASED ON TRENDS...IN RECENT MODELS...SATELLITE...RADAR...
SURFACE OBSERVATIONS AND NUMERICAL GUIDANCE...HAVE ADJUSTED
GRIDDED FORECASTS FOR THIS AFTERNOON TO REFLECT CURRENT TRENDS.

HEAVIEST SNOW EXPECTED TO FALL COINCIDENT TO THE BEST UPWARD
VERTICAL MOTION COUPLET AND DEEPEST SATURATED ATMOSPHERIC MOISTURE
COLUMN FROM LARAMIE TO CHEYENNE TO PINE BLUFFS. LOOKS LIKE A
WET SNOW WITH SNOW TO LIQUID RATIOS OF 10 TO 1.

&&

.SHORT TERM...(TODAY THROUGH SATURDAY NIGHT)
ISSUED AT 551 AM MST FRI MAR 7 2014

RADAR RETURNS CONTINUE TO EXPAND IN COVERAGE OVER THE CWA EARLY THIS
MORNING...WITH A FEW SITES REPORTING MAINLY RAIN OFF AND ON THROUGH
THE NIGHT. THE MAIN SURGE OF COLD AIR IS STILL UP IN NORTHERN
WYOMING BUT IS STEADILY MOVING SOUTH. THE SFC PRESSURE PATTERN
INDICATES AN INVERTED TROUGH FEATURE DEVELOPING OVER THE ROCKIES AS
AN UPPER LEVEL LOW APPROACHES WESTERN COLORADO...AND AS THE SFC COLD
FRONT THAT MOVED ACROSS THE HIGH PLAINS OVERNIGHT HAS SLOWED ITS
PROGRESS ALONG THE LARAMIE RANGE. MODELS SHOW THIS FEATURE
PERSISTING THROUGH THE AFTERNOON...AND WILL INDUCE NORTH-
NORTHEASTERLY UPSLOPE FLOW ACROSS THE EASTERN HALF OF THE FORECAST
AREA. WINDS DO NOT LOOK TO BECOME THAT STRONG THOUGH AS THE FRONT
WILL EVENTUALLY MOVE THROUGH THE REMAINDER OF WYOMING AND WEAKEN
THE INVERTED TROUGH. STILL...SHOULD SEE A PERIOD OF UPSLOPE
FORCING AIDED BY MODERATE CAA THROUGH EARLY AFTERNOON. THIS SFC
FORCING WILL COMBINE WITH WEAK MIDLEVEL ENERGY AND THE DIFFLUENT
RIGHT ENTRANCE REGION OF THE UPPER JET TO BRING A GOOD CHANCE FOR
RAIN/SNOW TO THE FORECAST AREA TODAY. WITH MANY AREAS STILL IN THE
MID 30S TO 40S...RAIN WILL LIKELY BEGIN THE EVENT BUT PRECIP WILL
EVENTUALLY CHANGE OVER TO SNOW AS THE MORNING PROGRESSES AND
COLDER AIR FILTERS IN FROM THE NORTH. LI VALUES OVER THE
MOUNTAINS ARE PROGGED TO BE SLIGHTLY NEGATIVE THIS AFTERNOON AS
WELL...SO WILL LIKELY SEE SOME ENHANCEMENT TO THE SNOW OUT IN THIS
AREA. LACK OF SIGNIFICANT FRONTOGENESIS ANALYZED WILL KEEP LOCAL
ENHANCEMENTS DUE TO BANDING AT A MINIMUM FOR THIS EVENT. ALL IN
ALL...STILL EXPECTING 1 TO 3 INCHES OF ACCUMULATION ACROSS THE
EASTERN PLAINS AND HIGH VALLEYS OUT WEST...WITH 5 TO 9 INCHES IN
THE SNOWY AND SIERRA MADRES AND 3 TO 6 IN THE LARAMIE RANGE BY
MIDNIGHT TONIGHT. THE UPPER TROUGH AXIS WILL MOVE OVERHEAD TONIGHT
WITH DRIER AIR AND SUBSIDENCE MOVING IN FROM THE NORTHWEST SO
SHOULD END THE SNOW CHANCES FROM NORTH TO SOUTH THIS EVENING.
THEREFORE...CUT THE SNOW ADVISORY ABOUT 6HRS SHORT AS SNOW SHOULD
BE ENDING EARLIER THAN PREVIOUSLY THOUGHT.

AFTER A COOLER DAY TODAY IN THE POST-FRONTAL ENVIRONMENT...SATURDAY
WILL MODERATE BACK INTO THE 40S AND 50S AS AN UPPER LEVEL RIDGE
BUILDS OVERHEAD FROM THE WEST. IN ADDITION...A STRONG WAVE MOVING
INTO THE PAC NW WILL BEGIN TO DEEPEN THE LEESIDE PRESSURE TROUGH
LATE IN THE DAY...SO WESTERLY WINDS SHOULD BE ON THE INCREASE LATE
SATURDAY AND SATURDAY NIGHT.

.LONG TERM...(SUNDAY THROUGH THURSDAY)
ISSUED AT 312 AM MST FRI MAR 7 2014

UPPER LEVEL RIDGE AXIS WILL SHIFT OVER SOUTHEAST WYOMING SUNDAY
WHILE AT THE SOME TIME BEGINS TO FLATTEN. SHOULD SEE LOTS OF
SUNSHINE TO START SUNDAY WITH SOME HIGH CLOUDS SPILLING INTO THE
AREA DURING THE AFTERNOON. SOME OF THE WARMEST TEMPERATURES THUS
FAR THIS YEAR WILL OCCUR SUNDAY AFTERNOON WITH WIDESPREAD 50S WEST
AND 60S EAST AND COULD SEE A FEW 70S INTO THE NEBRASKA PANHANDLE.

MODELS HAVE SLOWED UP THE PROGRESSION OF A WEST COAST TROUGH ON
MONDAY. MODELS NOW SHOWING THE UPPER LEVEL TROUGH AXIS OVER THE
INTERMOUNTAIN WEST MONDAY AFTERNOON WITH SHORTWAVE RIDGING OVER
SOUTHEAST WYOMING. THIS WILL LEAD TO ONE MORE WARM DAY BEFORE A
COLD FRONT MOVES THROUGH MONDAY NIGHT. TEMPERATURES MONDAY SHOULD
BE AS WARM AS SUNDAY IF NOT A BIT WARMER. TEMPERATURES ALOFT WILL
WILL BE WARMER BUT INCREASING MID AND HIGH CLOUDS MAY INHIBIT FULL
MIXING.

COOL AND WET TUESDAY AS THE UPPER TROUGH AXIS MOVES INTO THE
ROCKIES AND A COLD FRONT MOVES ACROSS THE FORECAST AREA. LOOKS
LIKE ANOTHER ROUND OF SNOW FOR MOST OF THE AREA TUESDAY INTO
TUESDAY NIGHT. AT THIS TIME NOT EXPECTING ANYTHING SIGNIFICANT FOR
SNOW AMOUNTS BUT THERE IS POTENTIAL DEPENDING ON THE SPEED AND EXACT
TRACK OF THE UPPER LOW.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 550 AM MST FRI MAR 7 2014

A STORM SYSTEM MOVING ACROSS THE ROCKIES TODAY WILL BRING POOR
AVIATION CONDITIONS TO THE FORECAST AREA. EXPECTING RAIN TO CHANGE
TO SNOW THROUGH THE MORNING WITH IFR/LIFR CONDITIONS ANTICIPATED
THROUGH EARLY AFTERNOON. NORTH-NORTHEAST SFC WINDS WILL SHIFT TO
THE WEST-NORTHWEST TONIGHT WHICH SHOULD HELP TO END THE SNOW AND
LIFT CIGS/VSBYS. BUT A MOIST BOUNDARY LAYER WITH FRESH SNOWPACK
COULD KEEP MVFR/IFR THROUGH TONIGHT FOR MOST AREAS.


&&

.FIRE WEATHER...
ISSUED AT 312 AM MST FRI MAR 7 2014

NO FIRE WEATHER ISSUES THROUGH NEXT WEEK. A SHOT OF RAIN AND SNOW
TODAY THEN DRY THROUGH THE WEEKEND WITH MILD TEMPERATURES AND
WINDY CONDITIONS. ONE MORE WARM DAY MONDAY THEN ANOTHER CHANCE FOR
RAIN AND SNOW TUESDAY.

&&

.HYDROLOGY...
ISSUED AT 1101 AM MST FRI MAR 7 2014

MELTING SNOW CAUSING SOME FLOODING PROBLEMS OVER PORTIONS OF THE
FORECAST AREA. SEVERAL STREETS CURRENTLY UNDER WATER IN LUSK
WYOMING AS THE NIOBRARA RIVER OVERFLOWS ITS BANKS. SHERIFFS OFFICE
THERE REPORTED FLOODING WAS SLIGHTLY WORSE THIS MORNING...COMPARED
TO LAST NIGHT.

INTO KIMBALL COUNTY NEBRASKA...MANY ROADS UNDERWATER DUE LARGELY
TO OVERLAND FLOODING. THE FLOODING IS OCCURRING EVEN THOUGH THERE
IS NOT ALL THAT MUCH SNOW TO MELT. THE BIGGEST FACTOR IS LIKELY
THE FROZEN GROUND. VERY COLD TEMPERATURES OVER THE LAST FEW MONTHS
HAVE FROZE THE GROUND AND IS LIKELY NOT LETTING SNOW MELT SOAK
INTO THE GROUND. ALSO LAST FALL WAS VERY WET WHICH PROBABLY IS NOT
HELPING ANY. THE FROST DEPTH A FEW DAYS AGO WAS 4 INCHES IN
CHEYENNE BUT WITH MILD TEMPERATURES...IS NOW COMPLETELY THAWED.
THESE FLOODING AREAS SHOULD NOT BE FAR BEHIND IN LOSING THEIR
FROZEN GROUND LAYER. SHOULD START TO SEE RELIEF OVER THE NEXT DAY
OR TWO AS RUNOFF PUSHES OUT OF THE AREA AND WATER STARTS TO SOAK
INTO THE GROUND.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER WEATHER ADVISORY UNTIL MIDNIGHT MST TONIGHT FOR WYZ112-
     114.

NE...NONE.
&&

$$

UPDATE...RUBIN
SHORT TERM...RJM
LONG TERM...SML
AVIATION...RJM
FIRE WEATHER...SML
HYDROLOGY...RUBIN/SML