A potent upper level disturbance produced a brief period of moderate snow over the southern Laramie Range.
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The episode as NWS CYS wrote it up.
A potent upper level disturbance produced a brief period of moderate snow over the southern Laramie Range.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Cheyenne, WY wrote its last area forecast discussion before the first event at May 19, 3:13 AM MST, 47 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHEYENNE WY 413 AM MDT TUE MAY 19 2015 .SHORT TERM...(TODAY AND THURSDAY) ISSUED AT 402 AM MDT TUE MAY 19 2015 VERY TRICKY FORECAST TODAY ACROSS THE AREA...AND ESPECIALLY THE HIGH PLAINS. THE MAIN FORECAST CONCERN WILL BE WHEN RAIN CHANGES TO SNOW ACROSS THE AREA AND HOW MUCH...IF ANY...ACCUMULATES. CURRENT KCYS AND KFTG RADAR LOOPS SHOW A VAST INCREASE IN PRECIPITATION COVERAGE OVER COLORADO AS A LARGE SHIELD OF PRECIPITATION DEVELOPS ACROSS THE ROCKY MOUNTAINS AND COLORADO PLAINS AT THIS HOUR. THIS PRECIPITATION IS QUICKLY EXPANDING NORTH...BUT ALSO EXTENDS SOUTHWARD INTO SOUTHERN COLORADO DUE STRONG UPPER LEVEL DIFLUENCE AHEAD OF A PACIFIC JET. MOST OF SOUTHEAST WYOMING AND WESTERN NEBRASKA WILL BE IN THIS AREA OF UPPER LEVEL DIFLUENCE THROUGH THE DAY IN ADDITION TO JET DYNAMICS FROM THE APPROACHING PACIFIC JET. IN ADDITION...A STRONG SURFACE HIGH OVER THE NORTHERN PLAINS WILL REMAIN IN PLACE AND ACTUALLY INTENSIFY AND SHIFT WESTWARD TODAY AND TONIGHT...WITH ADDITIONAL FRONTOGENESIS ALONG SOUTHERN WYOMING AND CENTRAL COLORADO AS COOLER AIR MOVES INTO THE REGION. WIDESPREAD PRECIP AMOUNTS BETWEEN 0.50 TO 1.00 LIQUID CAN BE EXPECTED FROM THE LARAMIE RANGE EASTWARD...WITH LESSER AMOUNTS WEST OF THE LARAMIE RANGE. WOULD NOT BE SURPRISED TO SEE SOME LOCATIONS RECEIVE 1.50 LIQUID BY TONIGHT ACROSS THE HIGH PLAINS. AS THE SURFACE HIGH STRENGTHENS AND THE UPPER LEVEL DISTURBANCE MOVES NORTHEAST...MODELS SHOW 700MB TEMPERATURES LOWERING BETWEEN -3C TO -5C EAST OF THE FRONTAL BOUNDARY...WHICH SHOULD BE JUST WEST OF THE LARAMIE RANGE. MODEL SOUNDINGS SHOW NEARLY ISOTHERMAL TEMPERATURES FROM 700MB DOWN TO THE SURFACE. THIS SUGGESTS THE POTENTIAL FOR HEAVY SNOW ACROSS MOST OF THE HIGH PLAINS EVEN THOUGH CURRENT TEMPERATURES ARE IN THE 40S TO LOW 50S. EVEN THE I80 SUMMIT IS HOVERING AROUND 35 DEGREES. MODELS SHOW THESE TEMPERATURES FALLING STEADILY TODAY WITH RAIN CHANGING TO SNOW. DO NOT EXPECT MUCH SNOW WEST OF THE LARAMIE RANGE DUE TO THE SHALLOW DEPTH OF THE COLD AIR. IN TERMS OF IMPACT...SHOULD BE MINOR TO MODERATE ACROSS THE AREA DUE TO THE TIME OF YEAR AND THE SNOWFALL MAINLY OCCURRING DURING THE DAY. HOWEVER...THESE IS SOME UNCERTAINTY WITH SOME ENSEMBLE MEMBERS SUGGESTING HIGH SNOWFALL RATES AND ACCUMULATING SNOW DOWN TO 4500 FEET. WILL HAVE TO KEEP AN EYE ON PERSISTENT MODERATE/HEAVY SNOWFALL RATES AS THE RAIN CHANGES TO SNOW ACROSS THE AREA. IF THESE HEAVY SNOWFALL RATES PERSIST AND BECOME THE NORM...MAY BE LOOKING AT LOCALLY SIGNIFICANT SNOW ACCUMULATIONS WITH HEAVY SNOW BANDS MOVING ACROSS THE AREA FROM SOUTH TO NORTH. NOT CONFIDENT ENOUGH IN THIS SCENARIO TO EXPAND THE WINTER WEATHER ADVISORY THOUGH...SO ONLY KEPT THE ADVISORY GOING FOR THE I80 SUMMIT WHICH AS THE BEST POTENTIAL IN SEEING HEAVY SNOWFALL AND ACCUMULATING SNOWFALL ON THE ROADWAYS. FURTHER EAST...1 TO 4 INCHES MAY ACCUMULATE ON GRASSY SURFACES BEFORE MELTING IN BETWEEN BANDS...WITH VERY LITTLE ACCUMULATION ON THE ROADWAYS. WILL WATCH THESE TRENDS THROUGH THE MORNING AND ADJUST ACCORDINGLY. WILL HAVE TO ALSO MONITOR RIVER LEVELS AND POTENTIAL FLASH FLOODING IF SNOW LEVELS DO NOT LOWER...AS THE LARAMIE RIVER AND AREA CREEKS AND STREAMS REMAIN HIGH. BY TONIGHT...THE UPPER LEVEL DISTURBANCE LIFTS NORTH AND EAST INTO THE DAKOTAS AND WEAKENS. HEAVY PRECIP RATES SHOULD COME TO AN END BY MIDNIGHT WITH SNOWFALL BECOMING LIGHTER AND MORE SHOWERY IN NATURE. DECENT AMOUNT OF COLD AIR ACROSS THE HIGH PLAINS...SO CAN NOT RULE OUT ADDITIONAL LIGHT SNOW ACCUMULATIONS. DRIZZLE AND FOG MAY BECOME A PROBLEM ALONG THE SOUTH FACING RIDGES SUCH AS THE CHEYENNE RIDGE FROM CHEYENNE TO SIDNEY TONIGHT AND INTO EARLY WEDNESDAY. HIGH TEMPERATURES TODAY AND WEDNESDAY WILL BE 20 TO 30 DEGREES BELOW NORMAL. ALTHOUGH PRECIPITATION WILL GENERALLY COME TO AN END BY WEDNESDAY...UPSLOPE FLOW AND THE REMNANT STATIONARY FRONT ALONG THE LARAMIE RANGE WILL RESULT IN SCATTERED SHOWERS AND ISOLATED THUNDER OVER WYOMING. WARMER TEMPERATURES ARE EXPECTED ON THURSDAY AS A SHORT WAVE RIDGES MOVES ACROSS THE AREA. TEMPERATURES WILL STILL BE BELOW NORMAL THOUGH AND GENERALLY IN THE MID 50S TO MID 60S. BREAK IN THE PRECIPITATION WILL BE SHORT LIVED...AS ALL MODELS INDICATE ANOTHER PACIFIC STORM SYSTEM MOVING TOWARDS THE AREA. INITIALLY...EXPECT A ROUND OF SCATTERED SHOWERS AND TSTORMS LATE ON THURSDAY WITH THE POTENTIAL FOR STRONG TSTORMS AS FORECAST CAPE VALUES CLIMB NEAR 1000 J/KG ALONG WITH PLENTY OF UPPER LEVEL DIFLUENCE AHEAD OF THE NEXT PACIFIC STORM. INCREASED POP BETWEEN 40 TO 60 PERCENT ACROSS SOUTHEAST WYOMING THURSDAY AFTERNOON. .LONG TERM...(THURSDAY NIGHT THROUGH MONDAY) ISSUED AT 302 AM MDT TUE MAY 19 2015 IF YOU ARE LOOKING FOR A BREAK IN THE COOL AND WET WEATHER PATTERN...YOU MAY BE WAITING FOR A WHILE. EXTENDED MODELS SHOW NO SIGN OF CURRENT WEATHER PATTERN CHANGING ANYTIME SOON. THE HEMISPHERIC LONGWAVE PATTERN WILL REMAIN LOCKED IN PLACE WITH MANY BLOCKING FEATURES ACROSS THE NORTHERN HEMISPHERE. NOT THE LEAST BEING THE HIGH OVER LOW BLOCK ACROSS WESTERN CANADA AND WESTERN CONUS RESPECTFULLY. A CONTINUOUS STREAM OF PACIFIC SYSTEMS WILL SLIDE UNDER THE UPPER LEVEL HIGH OVER WESTERN CANADA DURING THE FORECAST PERIOD AND BEYOND. THIS MEANS CHANCES FOR SHOWERS NEARLY EVERYDAY...ALONG WITH THUNDERSTORMS AND EVEN THE POTENTIAL FOR SNOW ON OCCASION. THE NEXT CHANCE FOR SNOW OUTSIDE OF THE MOUNTAIN MAY COME AGAIN AS EARLY AS FRIDAY. AT THIS TIME KEPT THE MENTION OF SNOW OUT OF THE GRIDS BUT WILL HAVE TO KEEP A CLOSE EYE ON THE TRACK AND STRENGTH OF THE SHORTWAVE TROUGH WHICH IS PROGGED TO MOVE OVER THE AREA FRIDAY. THE NUMERICAL MODELS ARE WARM ENOUGH TO KEEP PRECIPITATION AS RAIN BUT THE MODELS HAVE HAD A WARM BIAS WITH THE LAST FEW SYSTEMS. THIS VERY WELL MAY AGAIN BE THE CASE FRIDAY. FORTUNATELY...BASED ON THE CURRENT MODEL TIMING THE HEAVIEST PRECIPITATION WOULD BE DURING THE DAYTIME HOURS...MAKING ACCUMULATIONS OF SNOW UNLIKELY...ESPECIALLY OVER ROADWAYS. ECMWF AND GFS SHOWING DISTINCT DIFFERENCES IN THE PLACEMENT OF YET ANOTHER DISTURBANCE SATURDAY. THE GFS IS SLIGHTLY SLOWER AND MUCH FARTHER WEST WITH SHORTWAVE ENERGY. NOT CONFIDENT IN ANY ONE SOLUTION AT THIS TIME...BUT THE DIFFERENCE HAVE SIGNIFICANT FORECAST IMPLICATIONS. THE ECMWF SOLUTION SUGGESTS COOLER TEMPERATURES WITH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS...AND VERY LITTLE CHANCE FOR SEVERE THUNDERSTORMS. THE WARMER GFS WOULD SUGGEST A CHANCE FOR SOME SEVERE STORMS INTO THE PLAINS LATE SATURDAY. BY SUNDAY THE BOTH MODELS PUSH THE MAIN DYNAMICS INTO THE PLAINS...OF COURSE ANOTHER SYSTEM WILL BE HOT ON ITS HEALS DROPPING SOUTH ACROSS THE INTERMOUNTAIN WEST. && .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT) ISSUED AT 1149 PM MDT MON MAY 18 2015 AN UPPER LEVEL LOW PRESSURE SYSTEM WILL MOVE ACROSS THE FORECAST AREA TUESDAY. SHOWERS WILL DEVELOP ACROSS THE AREA TONIGHT WITH WIDESPREAD PRECIPITATION THROUGH THE DAY TUESDAY. RAIN WILL CHANGE TO SNOW OVER THE MOUNTAINS OF SOUTHEAST WYOMING TONIGHT WITH SNOW SPREADING INTO THE PLAINS AFTER SUNRISE TUESDAY. WIDESPREAD MVFR TO IFR ACROSS THE AREA. LIFR POSSIBLE ALONG AND EAST OF THE LARAMIE RANGE AS SNOW DEVELOPS WITH SNOW BEING HEAVY AT TIMES MAINLY ABOVE 3500 FEET MSL. AS PRECIPITATION WINDS DOWN TUESDAY EVENING...WIDESPREAD STRATUS...FOG...AND DRIZZLE WILL OCCUR OVER THE AREA. && .FIRE WEATHER... ISSUED AT 302 AM MDT TUE MAY 19 2015 NO FIRE WEATHER CONCERNS THIS WEEK DUE TO UNSEASONABLY COOL TEMPERATURES AND HIGH CHANCES OF PRECIPITATION. EVEN SOME SNOW IS EXPECTED OVER THE MOUNTAINS AND PORTIONS OF THE HIGH PLAINS EARLY THIS WEEK. DAYTIME RELATIVE HUMIDITIES WILL LIKELY NOT LOWER BELOW 50 PERCENT UNTIL LATE THIS WEEKEND OR EARLY NEXT WEEK. && .HYDROLOGY... ISSUED AT 302 AM MDT TUE MAY 19 2015 LARAMIE RIVER WILL CONTINUE TO RUN AT RELATIVELY HIGH LEVELS THROUGH THIS WEEK BUT AT THIS TIME IS EXPECTED TO REMAIN WITHIN ITS BANKS. HOWEVER...THE FIRST OF A SERIES OF PACIFIC STORMS WILL IMPACT THE REGION TODAY AND INTO TONIGHT. WILL HAVE TO CLOSELY MONITOR HOW MUCH PRECIPITATION WILL FALL AS A STRONG AREA OF LOW PRESSURE MOVES ACROSS THE AREA...WITH ANOTHER POSSIBLE BY THE END OF THE WEEK. HIGHEST PRECIPITATION AMOUNTS ARE LIKELY ACROSS THE PLAINS WHICH COULD BE ENOUGH TO PUSH THE LARAMIE RIVER AT FORT LARAMIE INTO MINOR FLOODING. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING FOR WYZ116. NE...NONE. && SHORT TERM...TJT LONG TERM...SML AVIATION...SML FIRE WEATHER...TJT HYDROLOGY...TJT
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE CHEYENNE WY 859 PM MDT MON MAY 18 2015 WYZ103>105-109>117-191045- NORTH LARAMIE RANGE-FERRIS/SEMINOE/SHIRLEY MOUNTAINS- SHIRLEY BASIN-CENTRAL CARBON COUNTY-NORTH SNOWY RANGE FOOTHILLS- SOUTHWEST CARBON COUNTY-SIERRA MADRE RANGE- UPPER NORTH PLATTE RIVER BASIN-SNOWY RANGE-LARAMIE VALLEY- SOUTH LARAMIE RANGE-SOUTH LARAMIE RANGE FOOTHILLS- 859 PM MDT MON MAY 18 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EAST CENTRAL WYOMING...SOUTH CENTRAL WYOMING AND SOUTHEAST WYOMING. .DAY ONE...TONIGHT AREAS OF RAIN WITH PATCHY FOG ARE EXPECTED ACROSS THE AREA OVERNIGHT. THE RAIN SHOULD CHANGE TO SNOW AT ELEVATIONS ABOVE ABOUT 7500 FEET. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY SNOW IS POSSIBLE THROUGH LATE TUESDAY WITH SNOW LEVELS LOWERING TO AROUND 5000 FEET. ACCUMULATING SNOW IS POSSIBLE ABOVE 6000 FEET. THUNDERSTORMS WILL RETURN TO SOUTHEAST WYOMING LATE THIS WEEK. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED. NEZ002-003-019>021-054-055-095-096-WYZ101-102-106>108-118-119- 191045- DAWES-BOX BUTTE-SCOTTS BLUFF-BANNER-MORRILL-KIMBALL-CHEYENNE- NORTH SIOUX-SOUTH SIOUX-CONVERSE COUNTY LOWER ELEVATIONS- NIOBRARA COUNTY-CENTRAL LARAMIE RANGE AND SOUTHWEST PLATTE COUNTY- EAST PLATTE COUNTY-GOSHEN COUNTY-CENTRAL LARAMIE COUNTY- EAST LARAMIE COUNTY- 859 PM MDT MON MAY 18 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF WESTERN NEBRASKA...EAST CENTRAL WYOMING AND SOUTHEAST WYOMING. .DAY ONE...TONIGHT NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY SNOW IS POSSIBLE THROUGH LATE TUESDAY WITH SNOW LEVELS LOWERING TO AROUND 5000 FEET. ACCUMULATING SNOW APPEARS UNLIKELY AT THIS TIME WITH THE BEST CHANCES NEAR THE WYOMING BORDER AND ALONG THE PINE RIDGE. THUNDERSTORMS WILL RETURN TO THE AREA LATE THIS WEEK. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED.
The national radar mosaic for the moment the first event began.
1 winter weather. Local standard time, as filed.
The Crow Creek SNOTEL site (elevation 8330 ft) estimated four inches of snow.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2015Every state in 2015This day in weather historyWarnings in Wyoming, May 2015
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 572043.