Tornado and Damaging Winds in Colorado, June 26, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
400 AM MDT FRI JUN 26 2009

.SHORT TERM...SHORTWAVE TROUGH AND ASSOCIATED COLD FRONT WILL MOVE
ACROSS THE AREA FROM WEST TO EAST TODAY. STRONGEST DEEP QG FORCING
ASSOCIATED WITH THIS FEATURE IS ALREADY OVER EASTERN COLORADO MOVING
EAST...THOUGH THERE SHOULD BE SOME LOW LEVEL CONVERGENCE ALONG THE
WIND SHIFT. LARGE AREA OF MOISTURE AND LIGHT SHOWERS CONTINUES
BEHIND THE TROUGH AXIS...AIDED BY A LITTLE COOLING ALOFT. WE WILL
REMAIN IN A WEAKLY CAPPED ENVIRONMENT AHEAD OF THE FRONT...WHICH
SHOULD MOVE THROUGH DENVER AROUND NOON. THE FRONT SHOULD TRIGGER
THUNDERSTORM ACTIVITY WHICH SHOULD DEVELOP EASTWARD ACROSS THE
PLAINS INTO THE BETTER MOISTURE/INSTABILITY THIS AFTERNOON. CAPES
WILL RANGE FROM 1000 J/KG OR SO AROUND DENVER TO AROUND 2500 J/KG IN
THE NORTHEAST CORNER. A BIT MORE SHEAR TODAY...SO BETTER HAIL/WIND
POTENTIAL THOUGH HAIL THREAT STILL LIMITED BY THE HIGH FREEZING
LEVEL. HEAVY RAIN STILL EXPECTED AS WELL THOUGH WITH STORMS EXPECTED
TO MOVE FASTER...FLASH FLOOD RISK LOOKS TO BE LOW. SOME QUESTION
ABOUT HOW MUCH/STRONG CONVECTION THERE WILL BE BEHIND THE FRONT.
WEST WINDS ALOFT SO DOWNSLOPING...THOUGH LOW LEVELS MAY BE NORTH OR
A LONGMONT ANTICYCLONE MAY DEVELOP LATER IN THE DAY GIVING A SHOT OF
CONVERGENCE ALONG THE FOOTHILLS. OFTEN THE WEAK CONVECTION WE EXPECT
OVER THE MOUNTAINS WILL NOT SURVIVE IN WESTERLY FLOW...BUT EVEN WITH
SLIGHTLY COOLER/DRIER AIR COMING IN THERE STILL LOOKS TO BE A LITTLE
CAPE. I WILL STICK WITH SCATTERED POPS EXPECTING SOME WEAK
CONVECTION. THE WHOLE THING MAY WIND UP SKIPPING OVER DENVER SINCE
THE TIMING IS SO EARLY. EXPECT OVERNIGHT CLEARING TO BE SLOW AS
WINDS ARE LIGHT...SUBSIDENCE NOT THAT STRONG...AND SLIGHT COOLING
MAY HELP THE CLOUD DECK TO PERSIST. ONLY MINOR CHANGES TO PREVIOUS
FORECAST...MAINLY SLIGHT COOLING TODAY AND SLIGHTLY LOWER POPS ALONG
THE FRONT RANGE.

.LONG TERM...MODELS HAVE THE BOTTOM OF AN UPPER TROUGH MOVING ACROSS
THE FORECAST AREA SATURDAY AFTERNOON AND EVENING.  THE FLOW ALOFT
BECOMES WESTERLY BY SATURDAY AFTERNOON AND CONTINUES THROUGH SUNDAY
NIGHT.  JET LEVEL SPEEDS ARE PRETTY WEAK.  THE QG VERTICAL VELOCITY
FIELDS HAVE DOWNWARD MOTION PROGGED ON SATURDAY AND MUCH OF SATURDAY
NIGHT.  WEAK UPWARD MOTION IS PROGGED ON SUNDAY AND SUNDAY EVENING.
THE LOW LEVEL PRESSURE AND WIND FIELDS SHOW HIGH PRESSURE MOVING IN
FROM THE NORTHWEST AND NORTH ON SATURDAY WITH WEAK UPSLOPE FLOW IN
THE BOUNDARY LAYER INTO SATURDAY EVENING.  ON SUNDAY AND SUNDAY
NIGHT...A WEAK GRADIENT POINTS TO NORMAL DIURNAL WIND CONDITIONS.
FOR MOISTURE...MODELS HAVE SOME MID LEVEL MOISTURE ON SATURDAY AND
SATURDAY NIGHT.  MOISTURE INCREASES A BIT ON SUNDAY.  FORECAST
SOUNDINGS HAVE PRECIPITABLE WATER VALUES IN THE 0.65 TO 0.95 INCH
RANGE FROM SATURDAY THROUGH SUNDAY NIGHT.  THE HIGHER NUMBERS ARE
PROGGED FOR SUNDAY.  BOUNDARY LAYER DEW POINT VALUES ARE IN THE MID
40S TO LOWER 50S F ON SATURDAY...WITH 50S F ON SUNDAY.  THERE IS NO
THETA-E AXIS FOR THE FORECAST AREA ON SATURDAY.  BY SUNDAY...A
DECENT ONE COVERS MUCH OF THE FORECAST AREA.  ON LATE DAY SATURDAY
...THERE IS MINIMAL CAPE OVER THE DIVIDE EASTWARD INTO THE FOOTHILLS
AND PARK COUNTY...THATS IT.  THE CAPE IS CONSIDERABLY HIGHER FOR
LATE DAY SUNDAY...WITH VALUES IN THE 500 TO 1500 J/KG RANGE.  THE
LAPSE RATE FIELDS HAVE A PRETTY DECENT MID LEVEL CAP IN PLACE
SATURDAY.  BY SUNDAY...THIS CAP IS WEAKER AND OVER THE EASTERN HALF
OF THE FORECAST AREA ONLY.  THE SHEAR PROFILE IS CONDUCIVE TO SUPER
CELL DEVELOP OVER THE EASTERN PLAINS ON SUNDAY.  THE QPF FIELDS SHOW
A TAD OF MEASURABLE PRECIPITATION OVER THE SOUTHWESTERN FORECAST
AREA ONLY ON SATURDAY.  ON SUNDAY...THERE IS SOME OVER MUCH OF THE
FORECAST AREA.  FOR POPS...MINIMAL FOR THE PLAINS ON SATURDAY...
20%-30%S FOR THE MOUNTAINS AND FOOTHILLS.  ON SUNDAY WILL UP THEM
INTO THE 20%-40% RANGE.   FOR TEMPERATURES...SATURDAYS HIGHS ARE
1-3 C COOLER THAN TODAYS.  SUNDAYS ARE 2-4 C WARMER.  FOR THE
LATER DAYS...MONDAY THROUGH THURSDAY...MODELS HAVE THE CENTER OF THE
UPPER RIDGE TO OUR IMMEDIATE SOUTH AND SOUTHWEST THROUGH THE
PERIODS.  WILL CHANGE NOTHING THIS UPDATE.

&&

.AVIATION...SCATTERED THUNDERSTORMS ARE EXPECTED THIS AFTERNOON AND
EVENING. A COLD FRONT WILL MOVE THROUGH DENVER AROUND 18Z WITH THE
WIND SHIFTING TO THE NORTH TO NORTHWEST. THERE IS POTENTIAL FOR MVFR
CEILINGS AND VISIBILITIES WITH THUNDERSTORMS...BUT THE ENVIRONMENT
WILL BE A BIT DRIER THAN YESTERDAY SO THE RISK IS LOWER.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...NONE.

GIMMESTAD/RJK

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE DENVER CO
115 PM MDT FRI JUN 26 2009

COZ030>051-271200-
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-
115 PM MDT FRI JUN 26 2009

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

...HEAVY RAIN POSSIBLE AGAIN WITH THUNDERSTORMS THIS AFTERNOON AND
EVENING...

.DAY ONE...TODAY AND TONIGHT

A WIDE SWATH OF SHOWERS AND THUNDERSTORMS CROSSING THE COLORADO HIGH
COUNTRY...SOME OF WHICH WERE PRODUCING HEAVY RAIN AND SMALL HAIL...
WILL MOVE EAST ACROSS THE EASTERN PLAINS OF COLORADO DURING THE
AFTERNOON AND EVENING HOURS. ATMOSPHERIC MOISTURE REMAINS QUITE
ABUNDANT AS EVIDENT BY DEWPOINT TEMPERATURES IN THE 50S IN THE HIGH
COUNTRY AND UPPER 50S TO MID 60S ON THE PLAINS.

WINDS ALOFT WERE SOMEWHAT STRONGER TODAY IN ADVANCE OF THE LOW
PRESSURE TROUGH MOVING ACROSS COLORADO TODAY...WHICH WILL HELP TO
MOVE STORMS FASTER TODAY. HOWEVER HIGH COUNTRY STORMS WILL BE
CAPABLE OF LOCALLY HEAVY RAINFALL AND SMALL HAIL...WITH MINOR
FLOODING A POSSIBILITY ON CREEKS AND SMALL STREAMS. AS THIS LINE OF
STORMS MOVES OUT ONTO THE PLAINS SOME STRENGTHENING IS LIKELY.
STORMS MOVING OFF THE FOOTHILLS AND ACROSS THE I-25 URBAN CORRIDOR
AROUND MID-AFTERNOON WILL BE CAPABLE OF HEAVY RAIN...SMALL HAIL AND
GUSTY WINDS. FARTHER OUT ACROSS THE PLAINS WHERE GREATER MOISTURE...
INSTABILITY AND SHEAR EXIST...IN ADDITION TO PRODUCING HEAVY
RAINFALL...A FEW STORMS MAY PRODUCE LARGE DAMAGING HAIL AND POSSIBLY
A BRIEF TORNADO.

THUNDERSTORM RAINFALL RATES OF 3/4 TO 1 1/2 INCHES PER HOUR ARE
PROBABLE...WITH RATES LOCALLY UP TO 2 1/2 INCHES PER HOUR POSSIBLE
WITH THE HEAVIER STORMS ON THE PLAINS. THEREFORE MINOR FLOODING OF
STREETS...CREEKS AND LOW LYING AREAS WILL BE POSSIBLE...PARTICULARLY
IN THOSE URBAN AREAS THAT EXPERIENCED HEAVY RAINFALL AND MINOR
FLOODING YESTERDAY.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THERE WILL ONLY BE A SLIGHT CHANCE OF AFTERNOON AND EVENING
THUNDERSTORMS SATURDAY THROUGH TUESDAY AS HIGH PRESSURE BUILDS OVER
THE AREA. THERE WILL BE AN INCREASE IN STORM COVERAGE ALONG WITH
SLIGHTLY COOLER TEMPERATURES FOR WEDNESDAY AND THURSDAY AS THE RIDGE
WEAKENS AND MOISTURE INCREASES.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED TODAY OR TONIGHT. ALTHOUGH
SPOTTERS ARE URGED TO RELAY REPORTS OF HEAVY RAIN AND ANY FLOODING
TO THE NATIONAL WEATHER SERVICE IN BOULDER.

BAKER/ENTREKIN