Tornadoes and Hail in Colorado, May 29, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
315 AM MDT TUE MAY 29 2007

.SHORT TERM...SURFACE LOW PRESSURE ACROSS SERN CO WITH INITIAL
PRE-FRONTAL SURGE PUSHING SOUTHWARD ALLOWING A WEAK N-NE LOW LVL
FLOW TO DEVELOP. STRONGER SURGE ACROSS NW CO WITH MAPS ANAYLSIS
SHOWING 3 MB PRESS RISE MOVING EASTWARD AND BAND OF SHOWERS WILL
MOVE INTO THE NRN MTNS/FOOTHILLS BEFORE DAYBREAK. THIS STRONGER
SURGE WILL ENHANCE NERLY LOW LVL FLOW ACROSS NERN CO THIS AM WITH
GRADUAL MOISTENING OF THE AIRMASS AS JET STREAK PROVIDES FAVORABLE
ASCENT ACROSS MUCH OF NERN CO BY THIS AFTN. FCST SOUNDINGS SHOW
AIRMASS TO BECOME MOIST ADIABATIC BY LATER THIS AFTN WITH GOOD
UPSLOPE FLOW TO AROUND 10000 FT AND INCREASING MID LVL FLOW TO
50-60KT BY 00Z. EXPECT SOME HEAVY RAINERS AND EMBEDDED TS BUT WITH
COOLER LOW LVLS...SVR THREAT APPEARS LOWER OVER THE FRONT RANGE/ADJ
PLAINS. AS FREEZING LVLS LOWER THERE COULD BE A LOT OF SMALL HAIL
WITH SFC BASED CAPES AROUND 500-1000J/KG. FURTHER SOUTHEAST OVER THE
PALMER DIVIDE...THERE COULD BE A SEVERE STORM AS BETTER SFC HEATING
WILL ALLOW CAPES OF 1000-2000J/KG ACROSS LINCOLN COUNTY AND ELEVATED
TERRAIN OF ELBERT COUNTY WITH POTENTIAL FOR LARGE HAIL. EXPECT A
DECREASE IN PRECIP FROM NORTH TO SOUTH LATER TNT OVER THE EASTERN
PLAINS AS SRN PTN OF THE STRONG UPPER TROF SHIFTS EAST ACROSS NRN
CO. OVERALL WILL BOOST POPS TO LIKELY ACROSS ALL OF ERN CO FOR THIS
AFTN/EVENING. FOR TODAY...SNOW LEVEL WILL REMAIN RELATIVELY HIGH
AROUND 10000 FEET THEN LOWERING TO AROUND 9000 FEET OVERNIGHT.
AIRMASS DRYS OUT OVERNIGHT AS TEMPS COOL SO DONT EXPECT ANY
SIGNIFICANT SNOWFALL OVER THE FOOTHILLS.

.LONG TERM...A SERIOUSLY BLOCKED UP UPR AIR PATTERN OVER THE CONUS
AS FORETOLD BY MANY OF THE OPERATIONAL MODELS WILL PREVENT THE
CLOSED UPR LOW/TROUGH OVR THE NRN GREAT PLAINS FROM MOVING MUCH
THROUGH 12Z/FRIDAY. THIS WOULD THEREBY RESULT IN AN EXTENDED PD
OF BELOW AVERAGE TEMPERATURES...PARTLY/MOSTLY CLOUDY SKIES AND A
CONTINUED CHANCE OF PRECIPITATION FOR THE FCST AREA. WRF AND GFS
DROP THE H5 LOW OH SO SLOWLY SEWRD FM OVER NERN MONTANA AT 12Z/WED
TO OVER WRN SOUTH DAKOTA BY 12Z/FRI. MODELS FOR THE PAST COUPLE DAYS
HAVE SHOWN A SIMILAR PROGRESSION...SO SEE LITTLE REASON TO GO
AGAINST THEM. AS THE UPR LOW TRACKS SOUTHEASTWARD...SO DOES A POOL
OF UNSEASONABLY COOL AIR ALOFT WHICH MIGRATES OVER SERN WYOMING AND
NRN COLORADO BY WEDNESDAY MORNING. 700-500MB LAYER TEMPS COLDER ON
THE WRF COMPARED TO THE GFS BY AS MUCH AS 3C...AND THEREFORE THE
WARMER MOS TEMP GUIDANCE VALUES OFFERED BY THE GFS ON WEDNESDAY.
HOWEVER THE MODELS BEGIN TO SHOW WARMING AT ALL LEVELS BY THURSDAY.
AS OF 00Z/FRI 700MB TEMPERATURE OVER DENVER FCST TO BE SOME 8C
WARMER ACCORDING TO THE GFS. HOWEVER...WRF NOT AS AMBITIOUS AS IT
INDICATES A 700MB TEMP AT THE SAME TIME ABOUT 4C COOLER. NOT KNOWING
FOR SURE WHICH SOLUTION WILL WIN OUT...SO WILL GO WITH SOME SORT OF
COMPROMISE.

AS FOR PRECIPITATION CHANCES DURING THE PERIOD 12Z/WED THROUGH
00Z/FRI...SEE ISOLATED SHOWERS/TSTORMS ON THE PLAINS AND SCATTERED
SHOWER/T-STORM COVERAGE IN THE MTNS AND PALMER DIVIDE ON WEDNESDAY.
ON THURSDAY WITH WARMER TEMPERATURES...MODEL SOUNDINGS INDICATE
STEEP LAPSE RATES AND CAPE VALUES IN THE 500-1100 J/KG RANGE ON THE
PLAINS BY AFTERNOON. ALL THIS IN ADVANCE OF ANOTHER COOL AIR SURGE
WHICH THE WRF SHOWS SLIDING THROUGH NERN COLORADO LATE IN THE DAY.
EVEN THOUGH SOUNDINGS INDICATE LOWER PW VALUES...INCREASING DEEP
LAYER SHEAR MAY BE ADEQUATE TO SUPPORT A BATCH OF SEVERE STORMS EAST
OF THE I-25 URBAN CORRIDOR. EXPECT TEMPERATURES ON THURSDAY TO
RETURN TO NEAR AVERAGE ASSUMING THE GFS VERIFIES. NOT SO ACCORDING
TO THE WRF AS IT STILL HAS A POOL OF CHILLY AIR OVERHEAD WITH THE
CLOSED UPR LOW STILL SPINNING TO OUR NORTH. THAT SAID LEANING MORE
TOWARDS THE WARMER GFS FOR NOW.

BY FRIDAY...MEDIUM RANGE MODELS FINALLY SHOW THE UPR LOW LIFTING OUT
AND HEIGHTS RISING ACROSS THE STATE AS AN UPPER RIDGE BUILDS OVER
THE GREAT BASIN. SEE A DRIER AND WARMER DAY WITH PW VALUES LOWERING
BELOW 0.40 INCH. HOWEVER...THIS TIME OF YEAR CAN/T RULE OUT A FEW
AFTERNOON/EVENING T-STORMS OVER THE HIGHER ELEVATIONS. SHOULD ALSO
SEE AFTERNOON TEMPERATURES RISING ABOVE 80F ON THE PLAINS.

SATURDAY AND BEYOND...MADE NO CHANGES TO THIS PORTION OF THE FCST.

&&

.AVIATION...SFC WINDS WILL CONTINUE TO SHIFT AND INCREASE FROM THE
N-NE AT FRONT RANGE AIRPORTS THRU TODAY. SHOWERS AND SCT T WILL
DEVELOP BY AFTN WITH BEST CHANCE FOR STORMS BTWN 21-03Z AND MVFR
CONDITIONS POSSIBLE. CONDITIONS IMPROVING AFT 06Z WITH CIGS/VSBYS
BECOMING VFR.

&&

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

&&

ENTREKIN/BAKER

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DENVER CO
1046 AM MDT TUE MAY 29 2007

COZ030>051-301200-
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-
1046 AM MDT TUE MAY 29 2007

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

.DAY ONE...TODAY AND TONIGHT

SHOWERS AND THUNDERSTORMS WILL BECOME MORE NUMEROUS THROUGH THIS
AFTERNOON AND EVENING WITH HEAVY RAIN AND SMALL HAIL EXPECTED ACROSS
MUCH OF THE AREA.  THERE IS A SLIGHT CHANCE OF SEVERE STORMS...
MAINLY ACROSS SOUTHERN ELBERT AND LINCOLN COUNTIES WHERE STRONGER
SURFACE HEATING AND WARMER TEMPERATURES WILL PRODUCE STRONGER
INSTABILITY.  HAIL UP TO ONE INCH IN DIAMETER IS POSSIBLE WITH THE
STRONGER STORMS OVER THE PALMER DIVIDE.

A MUCH COOLER AIRMASS HAS MOVED ACROSS EASTERN COLORADO TODAY WITH
TEMPERATURES ONLY IN THE 60S ON THE PLAINS THIS AFTERNOON.  THE
COOLER AND SHOWERY WEATHER IS DUE TO A STRONG UPPER LEVEL
DISTURBANCE MOVING ACROSS THE NORTHERN ROCKY MOUNTAIN STATES.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

THERE WILL BE A CHANCE OF LATE DAY SHOWERS AND THUNDERSTORMS FOR
MUCH OF THE FORECAST AREA THROUGH FRIDAY.  SOME DRYING AND WARMING
IS EXPECTED FOR THE WEEKEND INTO EARLY NEXT WEEK.  HOWEVER A SLIGHT
CHANCE OF LATE DAY SHOWERS AND STORMS WILL CONTINUE IN THE HIGH
COUNTRY THROUGH THE PERIOD.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED ACROSS ELBERT AND LINCOLN COUNTIES
THIS AFTERNOON AND EVENING.  ELSEWHERE...RAINFALL REPORTS WOULD BE
APPRECIATED.

DANKERS/KOOPMEINERS