Tornadoes and Hail in Colorado, June 10, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
330 PM MDT THU JUN 10 2010

.SHORT TERM...ANOTHER CHALLENGING CONVECTIVE DAY WITH A SUBSTANTIAL
CAP THAT IS IN PLACE OVER NORTHEASTERN COLORADO.  LBF 18Z SOUNDING
AND A 19Z VORTEX2 SOUNDING FROM STERLING BOTH SHOW THE STRONG CAP
THAT IS NOT LIKELY TO BE OVERCOME BY WARMING ALONE.  BUT WE DO HAVE
AN APPROACHING SHORTWAVE AND UPPER LEVEL FORCING THAT LOOKS LIKE IT
IS TIED TO THE SOUTHERN END OF A JET STREAK.  MODELS BRING THIS
RAPIDLY ACROSS THE AREA IN THE NEXT FEW HOURS.  THIS IS LIKELY WHY
WE HAVE SEEN THE INCREASE IN FORCED CLOUDINESS OVER THE MOUNTAINS
DURING THE LAST FEW HOURS.  LIGHTNING ALSO CLOSER TO THE WY BORDER
AND NOW IN A CELL WEST OF BOULDER.  ALSO...MAYBE A SLIGHT COOLING
TREND ALOFT IN THE LATEST ACARS SOUNDINGS.

THERE IS NO OBVIOUS BOUNDARY AT THIS TIME ON THE PLAINS AND IT SEEMS
THAT THE MOST LIKELY WAY THAT STORMS WILL END UP ON THE PLAINS WILL
BE AS THE CONVECTION NOW OVER THE FOOTHILLS MOVES EAST.  THE LATEST
NAM...RUC13 AND TREND ON THE HRRR HOURLY RUNS INDICATES THAT THIS IS
THE MOST LIKELY SCENARIO.  THERE IS GOOD DEEP VERTICAL WIND SHEAR
BUT THE LOW LEVEL FLOW ON THE PLAINS REMAINS RELATIVELY WEAK.
DEWPOINTS ARE CERTAINLY HIGH ON THE EASTERN PLAINS ALTHOUGH STILL
QUITE COOL AT AKO AND NEARBY AREAS THAT HAD ALL THE CLOUDS THIS
MORNING.  SO LIKELY WHAT WE WILL SE IS A BROKEN LINE OF CELLS COMING
OFF THE FOOTHILLS AND PUSHING EAST OVER THE NEXT COUPLE OF HOURS
NEAR THE FRONT RANGE AND THEN LINGERING INTO THE EVENING FARTHER
EAST.  WIND AND HAIL WOULD SEEM TO BE THE MAIN SEVERE THREATS AT
THIS TIME.

BIG UPPER LEVEL TROUGH WILL CONTINUE TO DEEPEN IN THE WEST AND CLOSE
OFF NEAR LAS VEGAS ON FRIDAY.  AT LOW LEVELS HIGH PRESSURE STILL IS
FORECAST TO BUILD SOUTHWARD FRIDAY WITH THE UPSLOPE GRADUALLY
DEEPENING.  PROBABLY WILL REMAIN TOO COOL FARTHER EAST ON THE PLAINS
FOR MUCH UNTIL LATE...BUT STILL LOOKS GOOD FOR WIDESPREAD STORMS
DEVELOPING ALONG THE FOOTHILLS FRIDAY AFTERNOON.  RIGHT NOW THE
CONCERN FOR HEAVY RAINS IS MOST PROMINENT  ESPECIALLY GIVEN THE
STAGE OF CREEKS AND RIVERS AT THIS TIME BUT CERTAINLY CANNOT RULE
OUT SEVERE FOR FRIDAY AFTERNOON ALONG THE FRONT RANGE.

.LONG TERM...CAN NOT STATE IT ANY CLEARER...A COMPLEX WEATHER
FORECAST NEXT FEW DAYS TO SAY THE LEAST. ALL STARTS WITH DEEPENING
MOIST...UNSEASONABLY COOL UPSLOPE FLOW FRONT RANGE EASTWARD FRIDAY
AFTERNOON INTO FRIDAY NIGHT. WHILE WEST OF THE CONTINENTAL DIVIDE A
MUCH DRIER AND WARMER ENVIRONMENT WILL PREVAIL WITH PERSISTENT
DOWNSLOPE AND/OR GUSTY SWLY FLOW. MODELS INDICATE MODERATELY STRONG
QUASI-GEOSTROPHIC LARGE SCALE ASCENT MOVING OVER THE FCST REGION
FRIDAY NIGHT IN ADVANCE OF THE DEEP UPPER LEVEL CYCLONE APPROACHING
THE 4-CORNERS AREA. CAPE VALUES FRIDAY EVENING APPROACH 2000 J/KG
ALONG EAST SLOPE OF THE FRONT RANGE AND MID-LEVEL LAPSE RATES
STEEPEN WITH COOLING ALOFT. EVENING MEAN PRECIPITABLE WATER VALUES
ON THE PLAINS CREEP UP INTO 1.0-1.4 INCH RANGE AND WITH 10-20KTS OF
LOW-LEVEL EASTERLY UPSLOPE FLOW...COULD SEE A NUMBER OF HOURS OF
DEEP CONVECTION CAPABLE OF MODERATE TO HEAVY RAINFALL AND POSSIBLY
SMALL HAIL. QPF VALUES DIFFER FROM ONE MODEL TO THE NEXT BUT ALL
INDICATE 6-HR AND 12-HR QPF VALUES IN THE 0.5 TO 1.5 INCH
RANGE...WITH A BULLS EYE OVER AND NEAR THE NRN FRONT RANGE FTHLS
AROUND 06Z/SAT. PERSISTENT UPSLOPE FLOW SHOULD CONCENTRATE THE
HEAVIER CONVECTIVE PRECIPITATION OVER AND NEAR THE FRONT RANGE
FOOTHILLS FRIDAY NIGHT. HEAVIER RAINFALL MAY EXACERBATE THE FLOODING
NOW OCCURRING ON SMALL STREAMS AND CREEKS IN AND ALONG THE FRONT
RANGE. SHOULD ONE OF THESE HEAVY RAIN MAKERS SIT OVER A DRAINAGE
BASIN FOR 30 MINUTES TO AN HOUR...COULD SEE SERIOUS HIGH WATER RISES
ON CREEKS IN THE AREA.

SATURDAY...MODELS SHOW A SECOND REINFORCING SURGE OF UNSEASONABLY
COOL AND MOIST AIR MOVING SOUTHWARD ACROSS NERN COLORADO DURING THE
MORNING HRS. EXTENSIVE LOW-LEVEL CLOUD COVER AND CHILLY BNDRY LAYER
TEMPERATURES SHOULD PRETTY MUCH SQUELCH THUNDERSTORM FORMATION ON
THE PLAINS SATURDAY. WHEREAS HIGH COUNTRY AREAS ABOVE THIS FRONTAL
AIRMASS SHOULD MANAGE TO HEAT UP AND DESTABILIZE ENOUGH FOR
SCATTERED T-STORMS. ALTHOUGH ITS PROBABLY NOT UNTIL THE AFTERNOON
WHEN MOST OF THIS CONVECTION SHOULD DEVELOP. DRASTIC COOL DOWN
PROBABLY THE MOST NOTABLE CHANGE IN OUR WEATHER THIS WEEKEND.
TEMPERATURE MOS GUIDANCE INDICATE MAX TEMPS IN THE MID 50S TO LOWER
60S ON THE PLAINS BOTH DAYS. THAT/S AT LEAST 20 DEGS F BELOW NORMAL.

SATURDAY INTO SUNDAY...DEEP UPPER TROUGH AND CYCLONE TO OUR WEST/
SOUTHWEST SLOWLY MIGRATES NORTHEASTWARD ACROSS THE REGION DURING THE
PD. BEST LARGE SCALE FORCING AND STEEPEST MID-LEVEL LAPSE RATES OVER
THE AREA SUNDAY MORNING. TEMPERATURES ALOFT STEADILY COOL SAT NIGHT
WITH 700 MB TEMPS IN THE -2 TO -3C RANGE OVER AND JUST EAST OF THE
FRONT RANGE SUNDAY MORNING. MODEL SNOW FIELDS INDICATE SEVERAL
INCHES OF SNOW ACCUMULATION OVER THE LARAMIE AND FRONT RANGES
ROUGHLY ABOVE 9500 FT MSL...WITH A MIX OF RAIN AND SNOW BELOW THAT
DOWN TO AROUND 8000 FT MST. NAM INDICATES UPWARD OF A HALF FOOT OF
SNOW OVER THE HIGHEST ELEVATIONS IN LARIMER AND BOULDER COUNTIES BY
MIDDAY SUNDAY. REALLY CAN/T ARGUE WITH THIS.

DURING THE DAY SUNDAY...MOST MODELS SHOW THE UPPER TROUGH AND MOST
OF ITS ENERGY AND PRECIPITATION MOVING OUT OF THE AREA. ALTHOUGH IT
STILL REMAINS QUITE COOL ESPLY EAST OF THE MTNS.

NEXT WEEK...SHOULD SEE A TREND TOWARDS DRIER AND WARMER CONDITIONS
WITH A RETURN TO NEAR ZONAL FLOW AND WEAK SUBSIDENCE ALOFT.

&&

.AVIATION...LINE OF SCATTERED TSTMS EXPECTED TO MOVE OFF THE
FOOTHILLS OVER THE NEXT FEW HOURS WITH STRONG WINDS AND HAIL THE
MAIN THREAT.  MOST OF THIS SHOULD BE EAST OF THE AIRPORTS BY 02 TO
03Z.  SOME PATCHY FOG POSSIBLE AT DIA AFTER 08Z ALONG WITH BROKEN
LOW CLOUDS WITH POSSIBLE CIGS NEAR 3000 FT.  CLOUDS SHOULD BREAK UP
ON FRIDAY SLOWLY THEN A THREAT OF STORMS AFTER 21Z.

&&

.HYDROLOGY...OVERBANK STREAMFLOW WILL CONTINUE ON STREAMS IN
LARIMER...BOULDER...AND WELD COUNTIES. WARMER TEMPERATURES IN THE
HIGH COUNTRY MAY BRING A SLIGHT INCREASE IN RUNOFF TONIGHT.
WIDESPREAD RAIN WILL DEVELOP OVER THE REGION FRIDAY...WITH HEAVIEST
RAINFALL AMOUNTS EXPECTED ON FRIDAY NIGHT AND SATURDAY. LOOK FOR 1
TO 2 INCHES AND ISOLATED HIGHER AMOUNTS FRIDAY AFTERNOON THROUGH
SUNDAY. THIS MAY CAUSE STREAMS TO RISE BACK TO LEVELS SEEN EARLIER
THIS WEEK.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...FLOOD ADVISORIES FOR RIVERS AND
STREAMS IN PORTIONS OF LARIMER...BOULDER...AND...WELD COUNTIES.

...FLOOD WATCH 6PM MDT FRIDAY THROUGH 6AM MDT SUNDAY FOR THE
NORTHERN FOOTHILLS AND NORTHERN PARTS OF THE URBAN CORRIDOR...ZONES
35..38..39..42..43...

SZOKE/BAKER

HAZARDOUS WEATHER OUTLOOK...CORRECTED
NATIONAL WEATHER SERVICE DENVER CO
1144 AM MDT THU JUN 10 2010

COZ030>051-111200-
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-
1144 AM MDT THU JUN 10 2010

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

.DAY ONE...TODAY AND TONIGHT

A SURGE OF NORTHERLY WINDS MOVED THROUGH THE AREA THIS MORNING AND
ALONG WITH SOME CLOUDINESS THIS HAS TEMPORARILY STABILIZED THE LOWER
ATMOSPHERE.  HOWEVER CONDITIONS SHOULD BECOME MORE UNSTABLE DURING
THIS AFTERNOON WITH INCREASING SUNSHINE AND WINDS BECOMING MORE
EASTERLY AS A LOW PRESSURE STRENGTHENS NEAR THE PALMER DIVIDE.  IN
ADDITION AN APPROACHING WEAK UPPER LEVEL DISTURBANCE WILL HELP TO
COOL CONDITIONS ALOFT LATER TODAY.  SO THE INGREDIENTS WILL BE IN
PLACE FOR POTENTIAL SEVERE STORMS LATER THIS AFTERNOON AND THIS
EVENING.  THE STORMS SHOULD DEVELOP IF THE MID LEVEL CAPPING
INVERSION CAN BE OVERCOME.  THE GREATEST THREAT IS EXPECTED TO BE
MORE IN THE NORTHEAST CORNER OF THE AREA WHERE SUPERCELL STORMS ARE
POSSIBLE BY LATE TODAY WITH ISOLATED TORNADOES.  OTHERWISE THE MAIN
THREAT SHOULD BE HAIL UP TO GOLF BALL SIZE AND DAMAGING WINDS UP TO
70 MPH MAINLY NORTH OF INTERSTATE 70.

HIGH WATER WILL CONTINUE ON RIVERS IN LARIMER...BOULDER...AND WELD
COUNTIES. WARMER TEMPERATURES IN THE HIGH COUNTRY MAY BRING A SLIGHT
INCREASE IN RUNOFF TONIGHT.  SEE THE LATEST FLOOD STATEMENTS AND
ADVISORIES.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

TEMPERATURES TURN STEADILY COOLER ON FRIDAY AND EVEN COLDER THIS
WEEKEND AS MOIST UPSLOPE FLOW BEHIND A COUPLE OF STRONG COLD FRONTS
COMBINE WITH THE LIFT AND INSTABILITY PRODUCED BY AN UNUSUALLY COOL
AND MOIST UPPER LEVEL STORM SYSTEM WHICH PASSES OVER THE REGION THIS
WEEKEND. SCATTERED THUNDERSTORMS DEVELOPING FRIDAY AFTERNOON
FOLLOWING PASSAGE OF THE FIRST OF TWO COLD FRONTS MAY PRODUCE
PERIODS OF MODERATE TO HEAVY RAINFALL AND SMALL HAIL ON THE
PLAINS...PARTICULARLY ALONG THE FRONT RANGE. A SECOND REINFORCING
SURGE OF UNSEASONABLY COOL AND MOIST AIR ARRIVING SATURDAY MORNING
IS EXPECTED TO PRODUCE EXTENSIVE LOW CLOUDINESS AND PERIODS OF LIGHT
TO MODERATE RAINFALL FROM THE FRONT RANGE EASTWARD THROUGH SATURDAY
NIGHT. TEMPERATURES ON THE PLAINS SATURDAY AND SUNDAY WILL BE
UNSEASONABLY COOL FOR JUNE WITH DAYTIME READINGS STRUGGLING TO REACH
THE 60 DEGREE BOTH DAYS. HIGH COUNTRY AREAS GENERALLY WEST OF THE
CONTINENTAL DIVIDE SHOULD SEE LITTLE TEMPERATURE CHANGE UNTIL THIS
WEEKEND. SATURDAY NIGHT INTO SUNDAY HIGH COUNTRY AREAS GENERALLY
ABOVE 8000 FEET COULD SEE A MIXTURE OF RAIN AND SNOW...WITH SEVERAL
INCHES OF SNOW ACCUMULATION POSSIBLE OVER EAST SLOPES OF THE FRONT
RANGE ROUGHLY ABOVE 9500 FEET BY SUNDAY AFTERNOON. SCATTERED RAIN
SHOWERS AND THUNDERSTORMS WILL AGAIN DEVELOP AT LOWER ELEVATIONS ON
SUNDAY WITH PASSAGE OF THE MAIN STORM SYSTEM TO OUR WEST. DRIER AND
WARMER CONDITIONS SHOULD RETURN TO THE OUTLOOK AREA FOR NEXT
WEEK.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED FOR LATER THIS AFTERNOON
AND THIS EVENING.

SZOKE/BAKER