Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 041729
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1129 AM MDT MON MAY 4 2015

.UPDATE...
ISSUED AT 1000 AM MDT MON MAY 4 2015

A CHECK OF THE I-80 WEBCAMS INDICATED THAT THE DENSE FOG WAS
LIFTING BETWEEN CHEYENNE AND LARAMIE...ESPECIALLY AT THE SUMMIT.
THE DENSE FOG ADVISORY WAS ALLOWED TO EXPIRE AT 10 AM...WITH
AREAS OF FOG LINGERING THRU THE LATE MORNING.

UPDATE ISSUED AT 459 AM MDT MON MAY 4 2015

WEBCAMS ALONG INTERSTATE 80 HAVE SHOWN VIS REALLY COMING DOWN FROM
THE SUMMIT TO JUST EAST OF BUFORD. MOIST SOUTHEAST WINDS WILL
CONTINUE THROUGH THE MORNING AND HRRR SHOWS LIFR CONDITIONS
CONTINUING IN THE SOUTHERN LARAMIE RANGE AND TO THE EAST OF THE
ALBANY-LARAMIE COUNTY LINE THROUGH 16Z. THUS...WITH THE
EXPECTATION THAT THE FOG WILL BE QUITE PERSISTENT THROUGH MID
MORNING...DECIDED TO ISSUE A DENSE FOG ADVISORY FOR THE SOUTHERN
LARAMIE RANGE AND ADJACENT FOOTHILLS THRU 16Z.

&&

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 230 AM MDT MON MAY 4 2015

THE GFS AND NAM BOTH PROG A WEAK MID LEVEL VORT MAX MOVING INTO
NORTHEAST COLORADO AND THE SOUTHERN NEBRASKA PANHANDLE THROUGH MID
MORNING. RADAR IMAGERY SHOWS SOME WEAK ECHOES ACROSS PORTIONS OF
NORTHERN COLORADO (GENERALLY MOVING NORTHWARD)...BUT NO LIGHTNING
OR STRONGER CONVECTIVE CELLS. WHILE THESE SHOWERS COULD MOVE INTO
AREAS ALONG INTERSTATE 80 THROUGH MID MORNING...ANY ACCUMULATIONS
WILL BE LIGHT. WITH SFC HIGH PRESSURE ACROSS THE DAKOTAS...LOW LEVEL
WINDS OVER THE PLAINS ARE TURNING TO THE EAST AND SOUTHEAST. THE
HRRR HAS LIFR CONDITIONS DEVELOPING AFTER 10-11Z ALONG THE CHEYENNE
RIDGE FROM THE INTERSTATE 80 SUMMIT TO CHEYENNE. WITH GOOD LOW LEVEL
UPSLOPE...THESE LOWER CIGS AND VIS PERSIST THROUGH 18Z. THUS...KEPT
THE MENTION OF FOG GOING THROUGH THE ENTIRE MORNING. TEMPS WILL BE
AROUND 15 DEGREES COOLER TODAY FOR AREAS ALONG AND EAST OF THE
LARAMIE RANGE IN THE POST FRONTAL AIR MASS. THE AIR MASS IS RATHER
STABLE WITH LI VALUES GENERALLY ABOVE 0C...THUS AFTN CONVECTION WILL
BE QUITE LIMITED. A BETTER CHANCE OF TSTMS WILL EXIST TO THE WEST OF
THE LARAMIE RANGE. WHILE AN ISOLATED HIGHER RAINFALL AMOUNT IS
POSSIBLE THROUGH MIDDAY TUESDAY...THE MODELS REALLY DO NOT SHOW MUCH
QPF WITH THE INCREASED STABILITY.

ON TUESDAY LOW CLOUDS WILL BE MUCH MORE WIDESPREAD AND PERSISTENT
ACROSS THE PLAINS THROUGH THE MORNING OR EVEN EARLY AFTN WITH THE
POTENTIAL FOR FOG ONCE AGAIN MAINLY ALONG THE CHEYENNE RIDGE.
SUBTROPICAL MID LEVEL LOW OVER ARIZONA TODAY WILL PROGRESS
NORTHEASTWARD INTO COLORADO ON TUESDAY. COOLING ALOFT AHEAD OF
THIS FEATURE ALONG WITH INCREASING PW VALUES (UP TO 1.0 INCHES
ACROSS THE PANHANDLE BY TUESDAY AFTN)...WILL PROMOTE A MORE
WIDESPREAD COVERAGE OF SHOWERS AND TSTMS. HAVE THE HIGHEST POPS ON
TUESDAY AFTN AND EVENING OVER THE PANHANDLE WHERE THE MODELS HAVE
BEEN CONSISTENTLY SHOWING THE BEST FORCING. SPC DOES HAVE THE
SOUTHERN PANHANDLE IN A MARGINAL RISK FOR SEVERE STORMS ON
TUESDAY...HOWEVER WITH RATHER WEAK INSTABILITY AND SHEAR...ONLY
SMALL HAIL WOULD BE A CONCERN. THE UPPER LEVEL WAVE WILL MOVE INTO
WESTERN SOUTH DAKOTA BY WED WITH SFC WINDS BECOMING NORTH TO
NORTHWEST OVER MUCH OF THE CWA BY THE AFTN. KEPT THE 40-50 PERCENT
POPS GOING DURING THE AFTN AS RATHER HIGH PW VALUES (0.75-1.0
INCHES) ARE SHOWN ACROSS THE PLAINS ALONG WITH WEAK INSTABILITY.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 230 AM MDT MON MAY 4 2015

ACTIVE WEATHER IN THE LONG TERM CONTINUES WITH DAILY RAIN/THUNDER
CHANCES ALSO THE POSSIBILITY OF A WINTER WEATHER EVENT FOR NEXT
WEEKEND.

FOR WEDNESDAY NIGHT...FIRST LOW LOOKS TO TRACK OFF TO THE
NORTHEAST INTO CENTRAL SOUTH DAKOTA AND WE SHOULD BE SEEING
SHOWERS AND THUNDERSTORMS COMING TO AN END BY LATE EVENING.

ANOTHER COLD FRONT LOOKS TO MOVE INTO THE AREA THURSDAY MORNING
WITH ANOTHER ROUND OF RAIN SHOWERS DEVELOPING ACROSS THE AREA
THURSDAY AFTERNOON...PERSISTING INTO FRIDAY.

REMARKABLY STRONG AGREEMENT BETWEEN THE GFS AND ECMWF ON THE
MOVEMENT OF THE SECOND LOW THROUGH THE ROCKIES THROUGH THE
WEEKEND. BOTH BRING THE LOW THROUGH SOUTHERN NEVADA FRIDAY...WITH
IT EJECTING NORTHEAST INTO NORTHERN COLORADO SATURDAY NIGHT. BOTH
SHOW -4 TO POSSIBLY -6C TEMPERATURES AT 700MB SATURDAY NIGHT INTO
SUNDAY...WHICH WOULD TURN RAIN OVER TO SNOW FOR MANY LOCATIONS
ABOVE 6000 FEET. NEED TO BE WATCHING FOR WINTER HEADLINES FOR
POSSIBLE HEAVY SNOW THIS WEEKEND. WE WILL CERTAINLY BE MONITORING
THIS LOW AS IT DRAWS CLOSER.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 1129 AM MDT MON MAY 4 2015

MVFR CIGS LIKELY TO CONTINUE TO AFFECT KCYS THIS AFTERNOON THEN
LOWERING TO IFR/LIFR TONIGHT INTO TUESDAY MORNING.  ELSEWHERE MAINLY
VFR WITH SCTD SHOWERS INTO THIS EVENING...THEN LOWERING TO MORE
WIDESPREAD MVFR/IFR CIGS WITH LOWERED VSBYS IN AREAS OF FOG.

&&

.FIRE WEATHER...
ISSUED AT 230 AM MDT MON MAY 4 2015

A COOL AND WET WEATHER PATTERN WILL MEAN MINIMAL FIRE WEATHER
CONCERNS THROUGH THE WEEK. AFTERNOON AND EVENING SHOWERS AND
THUNDERSTORMS CAN BE EXPECTED EACH DAY...WITH GOOD CHANCES FOR
MEASURABLE PRECIPITATION AND WETTING RAINS. MINIMUM RELATIVE
HUMIDITY VALUES SHOULD BE WELL ABOVE CRITICAL THRESHOLDS.

&&

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

$$

UPDATE...MJ
SHORT TERM...ZF
LONG TERM...GCC
AVIATION...RE
FIRE WEATHER...ZF


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