Flash Flooding and Flooding in Colorado, May 8 to 15, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
405 PM MDT FRI MAY 8 2015

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 225 PM MDT FRI MAY 8 2015

STRONG UPPER LEVEL LOW IS CURRENTLY OVER LAS VEGAS MOVING SLOWLY
EASTWARD. AHEAD OF THIS SYSTEM THERE HAVE BEEN A COUPLE OF
DISTINCT WAVES THAT ORGANIZED THE PRECIPITATION TODAY. ONE MOVED
BY EARLIER AND THE SECOND IS MOVING NORTHWARD ACROSS THE FORECAST
AREA RIGHT NOW. THERE IS SOME CLEARING BEHIND THE SECOND WAVE BUT
ALL MODELS HAVE ANOTHER WAVE OF UPPER LEVEL FORCING WILL BE
MOVING NORTH FROM SOUTHEAST COLORADO OVERNIGHT. THIS FEATURE WAS
SEEN NICELY IN THE CIRA SYNTHETIC IMAGERY FROM THE NAM NEST
OVERLAID WITH SOME FORCING FIELDS ON AWIPS. WITH THIS EXPECT
INCREASE IN SHOWER ACTIVITY ACROSS THE PLAINS OVERNIGHT AS SEEN IN
THE HRRR RUNS OF LATE AND INCREASED POPS FROM SOUTH TO NORTH TO
LIKELY BEFORE DECREASING THEM AGAIN LATER TONIGHT FROM SOUTH TO
NORTH. RAINFALL AMOUNTS COULD BE AS HIGH AS AN INCH OR SO IN SOME
AREAS BUT NO REAL FOCUS INDICATED AT THIS TIME TO WARRANT ANY
HYDROLOGY HIGHLIGHTS BEYOND WHAT HAS BEEN PUT OUT AT THIS TIME.

A VERY ACTIVE DAY IN STORE FOR SATURDAY WITH ALL KINDS OF WEATHER
ACROSS THE AREA. MODELS ARE IN GENERAL AGREEMENT IN MOVING THE
UPPER LEVEL LOW NORTHEASTWARD ACROSS THE 4 CORNERS REGION AND INTO
EASTERN COLORADO BY THE END OF THE DAY. THIS WILL BRING OF COURSE
A LARGE AMOUNT OF UPPER LEVEL FORCING WITH IT...FIRST ACROSS THE
MOUNTAINS AND THEN INTO EASTERN COLORADO BY THE AFTERNOON. THE 700
MB LOW INITIALLY STARTS OUT RATHER ELONGATED BUT THEN WITH RAPID
CYCLOGENESIS EAST OF THE MOUNTAINS IT CONSOLIDATES NEAR LIMON
AFTER 00Z/SUNDAY. OROGRAPHIC FLOW WILL NOT BE FAVORABLE IN THE
MOUNTAINS WEST OF THE DIVIDE UNTIL THE UPPER LOW PASSES BY SAT
NIGHT BUT WITH THE STRONG DYNAMICS SHOULD SEE SNOW INCREASE WITH
EMBEDDED THUNDERSTORMS AS THE DAY GOES ON. FOR NOW KEPT THE WATCH
AS IS BUT WOULD LIKELY BE ENOUGH TO HOIST A WARNING ALTHOUGH
LOWERED OVERALL AMOUNTS TO 8 TO 16 INCHES TOTAL. SOME ADDITIONAL
SNOW TONIGHT BUT MORE SCATTERED IN COVERAGE WITH SNOW LEVEL DOWN
TO AROUND 9000 FEET. ON THE PLAINS SHOULD BE A LULL IN THE
PRECIPITATION IN THE MORNING WITH SOME PARTIAL CLEARING THAT COULD
SET THE STAGE FOR SEVERE WEATHER AS THE SYSTEM REDEVELOPS EAST OF
THE MOUNTAINS. BEST CHANCES FOR SEVERE WOULD LIKELY BE MORE TO THE
EASTERN PART OF THE PLAINS BUT COULD GET ALL THE WAY BACK TO THE
URBAN CORRIDOR. THEN UPSLOPE SHOULD INCREASE LATE WITH MORE
WIDESPREAD PRECIPITATION DEVELOPING FROM NORTH TO SOUTH LATER IN
THE AFTERNOON. SNOW CHANCES AT LOWER ELEVATIONS COME LATER IN THE
PERIOD AS COLDER AIR COMES IN ON THE BACKSIDE OF THE SYSTEM.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 225 PM MDT FRI MAY 8 2015

STRONG UPPER LOW WILL MOVE FROM SOUTH CENTRAL COLORADO 00Z SUNDAY TO
SOUTHWEST NEBRASKA 12Z SUNDAY. THE SURFACE LOW WILL TRACK TO THE
NORTHEAST OF THE UPPER LEVEL LOW. STRONG TO SEVERE STORMS MAY LINGER
INTO THE EARLY EVENING HOURS OVER THE PLAINS. AFTER THIS...A
DEFORMATION ZONE WILL DEVELOP ON THE BACKSIDE OF THE LOW.
PRECIPITATION WILL START OFF AS RAIN...BUT QUICKLY TURN TO SNOW
SATURDAY EVENING ACROSS THE PLAINS. UNCERTAIN WHERE THIS ZONE WILL
FORM...BASED ON SLIGHTLY DIFFERENT STORM TRACKS. EXPECT MOST AREAS
TO SEE PERIOD OF SNOW...WITH A SMALL BAND OF 3 TO 6 INCHES OF
SNOWFALL EAST OF I-25 BY SUNDAY MORNING.

RAIN AND SNOW WILL END SUNDAY MORNING AS THE LOW LIFTS NORTHEAST OF
THE REGION. IT WILL BE CLOUDY A COOL BEHIND THE SYSTEM WITH HIGHS
MAINLY IN THE 40S. IT WILL BE SLIGHTLY UNSTABLE IN THE MOUNTAINS
WITH ISOLATED/SCATTERED SNOW SHOWERS. FOR SUNDAY NIGHT...FROST WILL
BE LIKELY MOST LOCATIONS AS SKIES PARTIALLY CLEAR. EXPECT LOW ACROSS
THE AREA TO BE IN THE 20S TO LOWER 30S.

FOR EARLY NEXT WEEK...UPPER LEVEL RIDGE WILL MOVE ACROSS THE REGION
MONDAY AND MONDAY NIGHT. THIS WILL BRINGING DRIER CONDITIONS TO THE
AREA. STILL A SLIGHT CHANCE FOR SHOWERS OVER THE MOUNTAINS...
OTHERWISE DRY CONDITIONS WILL PREVAIL. IT WILL BE COOL MONDAY BEHIND
THE EXITING LOW WITH HIGHS IN THE 50S TO LOWER 60S ACROSS NORTHEAST
COLORADO.

ON TUESDAY...FLOW ALOFT WILL BECOME SOUTHWESTERLY AS AN UPPER LEVEL
LOW DIGS SOUTH ALONG THE CALIFORNIA COAST. TEMPERATURES WILL WARM
INTO THE 60S TUESDAY UNDER THE SOUTHWESTERLY. MAY BE ENOUGH MOISTURE
FOR ISOLATED THUNDERSTORMS ACROSS THE AREA.

THE LOW WILL WEAKEN AND LIFT NORTHEAST ACROSS THE INTERMOUNTAIN WEST
ON WEDNESDAY. AS THE TROUGH AXIS MOVES ACROSS THE REGION...EXPECT IT
TO PRODUCE SCATTERED TO ISOLATED SHOWERS AND THUNDERSTORMS. WILL
BUMP POPS UP INTO THE SCATTERED RANGE FOR THIS. TEMPERATURES WILL
ALSO WARM AS A SOUTH TO SOUTHWEST FLOW PREVAILS.

FOR THURSDAY AND FRIDAY...ANOTHER UPPER LEVEL LOW MOVES OVER
CALIFORNIA. THIS WILL KEEP A SOUTHWEST FLOW ALOFT ACROSS THE CENTRAL
ROCKIES. THERE IS A SHORT WAVE RIDGE FOLLOWING WEDNESDAY'S SYSTEM.
WILL BE TRICKY TO TIME THIS...BUT THERE SHOULD BE A WINDOW WHERE IT
WILL BE DRY ACROSS THE AREA. ONCE THIS RIDGE SHIFTS EAST OF THE
AREA. EXPECTED SCATTERED/ISOLATED SHOWERS AND THUNDERSTORMS TO
RETURN TO THE REGION. WILL GO WITH ISOLATED TO SCATTERED POPS FOR
THURSDAY AND FRIDAY...WITH THE LOWER POPS ON THURSDAY WHEN THIS
RIDGE MAY MOVE ACROSS THE AREA. TEMPERATURES WILL REMAIN COOL WITH
HIGHS IN THE 60S...SLIGHTLY BELOW NORMAL FOR THIS TIME OF YEAR.

&&

.AVIATION...(FOR THE TAFS THROUGH 00Z SATURDAY LATE AFTERNOON)
ISSUED AT 225 PM MDT FRI MAY 8 2015

A LINE OF THUNDERSTORMS MOVING THROUGH THE METRO AREA WILL SHIFT
TO THE NORTH BY 22Z...SO SHOULD SEE CIGS/VSBYS IMPROVE
SIGNIFICANTLY AT THAT TIME. WL KEEP IFR/MVFR CIGS WITH THE TSTMS.
THE SE-ELY WINDS STILL PROGGED THIS EVENING AND OVERNIGHT.
ADDITIONAL LIGHT SHOWERS MAY RETURN LATER THIS EVENING. CIGS WL
LOWER AT THAT TIME...WITH IFR/MVFR CONDITIONS REDEVELOPING AFTER
06Z. ENELY WINDS MAY INCREASE SATURDAY MORNING WITH THE SURFACE
LOW INTENSIFYING OVER SERN CO. STORM THAT DEVELOP LATE SATURDAY
MORNING/AFTN COULD BE STRONG...WITH SEVERE POTENTIAL TO THE SOUTH
AND EAST OF DENVER.

&&

.HYDROLOGY...
ISSUED AT 225 PM MDT FRI MAY 8 2015

THUNDERSTORMS PRODUCING VERY HEAVY RAINFALL IN THE DENVER AREA
SHOULD WEAKEN AS THEY SHIFT NORTHWARD. A FLOOD ADVISORY IS IN
EFFECT FROM THE FRONT RANGE FOOTHILLS EASTWARD DOWN THE SOUTH
PLATTE RIVER THROUGH 11 PM SUNDAY NIGHT TO ACCOUNT FOR ALL THE
CURRENT AND FUTURE RUNOFF OVER THE WEEKEND.  STORMS/SHOWERS MAY
REDEVELOP OVERNIGHT WITH GENERALLY LIGHT RAINFALL EXPECTED. ON
SATURDAY AFTERNOON AND EVENING...ADDITIONAL SHOWERS/TSTMS AS A
STRONGER TROUGH MOVES ACROSS COLORADO. STREAMS WILL CONTINUE TO
RUN HIGH WITH MODERATE TO HEAVY RAIN SHOWERS DEVELOPING IN THE IN
THE FOOTHILLS AND THE NORTHEAST PLAINS SATURDAY AFTERNOON AND
SATURDAY NIGHT.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM SATURDAY AFTERNOON THROUGH LATE SATURDAY
NIGHT FOR COZ033-034.

FLOOD ADVISORY IN EFFECT THROUGH 11 PM MDT SUNDAY NIGHT FOR
MORGAN...CENTRAL LOGAN...JEFFERSON...SEDGWICK...WASHINGTON...
BROOMFIELD...EASTERN GILPIN...EASTERN LARIMER...ELBERT...DOUGLAS
..SOUTHEAST CLEAR CREEK...ADAMS...BOULDER...DENVER...ARAPAHOE AND
WELD COUNTIES.

SHORT TERM...SZOKE
LONG TERM...MEIER
AVIATION...COOPER
HYDROLOGY...COOPER

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
1114 AM MDT FRI MAY 8 2015

COZ030>051-091715-
JACKSON COUNTY BELOW 9000 FEET-
WEST JACKSON AND WEST GRAND COUNTIES ABOVE 9000 FEET-
GRAND AND SUMMIT COUNTIES BELOW 9000 FEET-
SOUTH AND EAST JACKSON/LARIMER/NORTH AND NORTHEAST GRAND/
NORTHWEST BOULDER COUNTIES ABOVE 9000 FEET-
SOUTH AND SOUTHEAST GRAND/WEST CENTRAL AND SOUTHWEST BOULDER/
GILPIN/CLEAR CREEK/SUMMIT/NORTH AND WEST PARK COUNTIES ABOVE
9000 FEET-LARIMER AND BOULDER COUNTIES BETWEEN 6000 AND 9000 FEET-
JEFFERSON AND WEST DOUGLAS COUNTIES ABOVE 6000 FEET/GILPIN/CLEAR
CREEK/NORTHEAST PARK COUNTIES BELOW 9000 FEET-
CENTRAL AND SOUTHEAST PARK COUNTY-
LARIMER COUNTY BELOW 6000 FEET/NORTHWEST WELD COUNTY-
BOULDER AND JEFFERSON COUNTIES BELOW 6000 FEET/WEST BROOMFIELD
COUNTY-
NORTH DOUGLAS COUNTY BELOW 6000 FEET/DENVER/WEST ADAMS AND
ARAPAHOE COUNTIES/EAST BROOMFIELD COUNTY-
ELBERT/CENTRAL AND EAST DOUGLAS COUNTIES ABOVE 6000 FEET-
NORTHEAST WELD COUNTY-CENTRAL AND SOUTH WELD COUNTY-MORGAN COUNTY-
CENTRAL AND EAST ADAMS AND ARAPAHOE COUNTIES-
NORTH AND NORTHEAST ELBERT COUNTY BELOW 6000 FEET/NORTH LINCOLN
COUNTY-
SOUTHEAST ELBERT COUNTY BELOW 6000 FEET/SOUTH LINCOLN COUNTY-
LOGAN COUNTY-WASHINGTON COUNTY-SEDGWICK COUNTY-PHILLIPS COUNTY-
1114 AM MDT FRI MAY 8 2015

...WINTER STORM WATCH SATURDAY AFTERNOON THROUGH SATURDAY NIGHT IN
THE MOUNTAINS...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTHEAST AND NORTH CENTRAL
COLORADO.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THE WET AND COOL WEATHER PATTERN ACROSS COLORADO WILL CONTINUE
TODAY AND TONIGHT AS UPSLOPE WINDS AT LOW LEVELS COMBINE WITH
SOUTHWEST FLOW ALOFT TO PRODUCE PERIODS OF LIGHT TO MODERATE RAIN.
SOME THUNDERSTORMS MAY BE EMBEDDED WITHIN THE MORE WIDESPREAD RAIN
SHIELD...PRODUCING LOCALLY HEAVY RAINFALL AT TIMES. THERE IS ALSO
A SLIGHT RISK OF SEVERE THUNDERSTORMS ON THE EASTERN PORTIONS OF
THE PALMER DIVIDE. LARGE HAIL...DAMAGING WINDS AND POSSIBLY A BRIEF
FUNNEL CLOUD OR SHORT-LIVED TORNADO WILL BE THE PRIMARY THREATS.
RIVERS AND STREAMS WILL BE RUNNING HIGH FROM THE RECENT DAYS OF
WET WEATHER AND WILL CONTINUE TO BE MONITORED CLOSELY.

THE SNOW LEVEL IN THE MOUNTAINS WILL BE AROUND 9000 FEET TODAY
LOWERING TO ABOUT 8500 FEET TONIGHT. AREAS ABOUT 9000 FEET COULD
SEEN 1 TO 3 INCHES OF SNOW WHILE UP TO 5 INCHES WILL BE POSSIBLE
IN AREAS ABOVE 10500 FEETE.  THE MOUNTAIN PASSES WILL MAINLY BE
WET BUT COULD HAVE BECOME SNOW AND SLUSH COVERED AT TIMES
ESPECIALLY DURING HEAVIER SHOWERS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

A STORM SYSTEM WILL MOVE FROM THE FOUR CORNERS SATURDAY INTO
SOUTHEAST COLORADO SATURDAY NIGHT AND THEN INTO NORTHWEST KANSAS
BY SUNDAY MORNING. THIS SYSTEM TRIGGER MORE SHOWERS AND
THUNDERSTORMS SATURDAY WITH HEAVY SNOW POSSIBLE IN THE MOUNTAINS
BY AFTERNOON. A FEW SEVERE STORMS WILL BE POSSIBLE ACROSS THE
PLAINS SATURDAY AFTERNOON THROUGH EARLY SATURDAY EVENING.
HEAVY RAIN...LARGE HAIL AND ISOLATED TORNADOES ARE THE MAIN
THREATS WITH THE SEVERE STORMS.

BY SATURDAY NIGHT...COLDER TEMPERATURES WILL MOVE INTO NORTHEAST
COLORADO WHICH WILL ALLOW THE RAIN TO CHANGE TO SNOW. THERE IS A
CHANCE FOR A BAND OF HEAVY WET SNOW SOMEHWERE ALONG THE FRONT
RANGE AND ACROSS THE PLAINS INTO EARLY SUNDAY. TRAVEL IN THE
MOUNTAINS MAY BECOME DIFFICULT AT TIMES DUE TO SNOW COVERED
ROADS...ESPECIALLY SATURDAY AFTERNOON THROUGH SATURDAY NIGHT.

A DRYING TREND IS EXPECTED BY EARLY NEXT WEEK AS A FLAT UPPER
LEVEL RIDGE BUILDS OVER THE AREA. TEMPERATURES WILL ALSO
GRADUALLY RETURN TO SEASONAL NORMALS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.