Severe Thunderstorm Warning 78, NWS Denver/Boulder, CO

NORTHEAST AND NORTH CENTRAL COLORADO AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER COLORADO
150 PM MDT FRI JUL 21 2000

...2ND AMENDMENT TO ADD ZONES 46 AND 47 TO TORNADO WATCH...

IN FOR ANOTHER ROUGH RIDE ACROSS NORTHEASTERN CO LATER THIS AFTN AND
ERLY THIS EVE.  SPC HAS NERN CO UNDER MODERATE RISK THIS AFTN AND
EVE WITH SLIGHT RISK ALG THE FNT RANGE.  SEE EITHER A TORNADO OR SVR
TSTORM WATCH COMING OUT ANY TIME NOW.  CONVECTIVE INITIATION IN SERN
WY AS OF 19Z OCCURRING UNDER FRONT LEFT QUAD OF A 60-70KT SPEED
MAX.  SEWRD TRACKING SPEED MAX CAN BE SEEN ON WATER VAPOR IMAGERY
OVR THE CO/WY BORDER NORTH OF STEAMBOAT.  SYNOPTIC LIFT PROVIDED BY
SPEED MAX...STG SFC HEATING AND COOLING ALOFT AND SFC DEWPTS IN THE
UPR 50S/LOWER 60S WILL PROVIDE THE INGREDIENTS FOR ISOLD TO WDLY SCT
SVR TSTMS.  SFC PLOTS AND LOW LVL WINDS OFF 88D SHOWING FORMATION OF
DEN CYCLONE WITH PREVALENCE OF SELY WINDS E OF A FNL-DEN-LIC LINE.
RUC AND ETA SBCAPES AS OF 19Z ALREADY IN THE 3000-3500 J/KG RANGE
OVR MORGAN...SWRN WASHINGTON AND NRN LINCOLN CTYS.  A 2ND CAPE
MAXIMA ALSO SHOWING UP OVR LOGAN CTY.  ETA AND NGM SHOWS 7H SHRTWV
AND MID-LVL SPEED MAX SWEEPING ACRS NERN PLNS OF CO BTWEEN 20Z-00Z
WITH INDICATIONS OF WHAT LOOKS LIKE A SQUALL LINE IN THE WIND...
BNDRY LYR VORTICITY...SFC-7H OMEGA..RH LAPSE RATE FIELDS.  STORMS
EXPECTED TO COME OFF THE MEDICINE BOW MTNS IN SERN WY AND RACE SEWRD
ACRS NERN PLAINS AT 25-35KT.  MID TO LATE AFTN TEMP PROFILE BECOMES
QUITE FAVORABLE FOR LARGE HAIL PRODUCTION WITH PASSAGE OF MID-LVL
THERMAL TROF. SHEAR PROFILE TODAY DOES NOT LOOK AS FAVORABLE AS
YESTERDAY...HWVR SHOULD HV ENOUGH TURNING WITH HEIGHT FOR ISOLD
TORNADOES/LANDSPOUTS ALG ADVANCING STORM FRONT.  BUT MAIN SVR WX
LOOKS TO BE LARGE HAIL (2-3 INCH DIAMETER RNG) AND VERY STG STRAIGHT
LINE T-STORM WINDS (IN EXCESS OF 60 KTS).  MDLS SHOW STORM FRONT
RACING SEWRD OUT OF THE CWA BY 03Z WITH VRY STG DOWNWARD FORCING...
STABLIZATION AND DRYING IN ITS WAKE.  COULD ALSO SEE A ONE OR TWO
SVR STORMS FIRING ALG THE FRONT RANGE/CNTRL AND SRN URBAN CORRIDOR
BTWN 22Z-02Z WITH PASSAGE OF VIGOROUS OUTFLOW BOUNDARIES.  OVRNGT...
DO NOT SEE A LOT OF LOW LVL MSTR HANGING AROUND FOR LOW CLOUD/FOG
FORMATION.  SO CLR/MO CLR SKIES WILL BE THE RULE.

ON SATURDAY...FLOW ALOFT REMAINS NWLY WITH UPR RIDGE AMPLIFYING OVR
UT AND WRN CO.  STILL SEE ENOUGH MSTR AND INSTABILITY AROUND FOR
WDLY/SCT TSTORMS IN THE MTNS AND ON THE PLAINS.  AS DAY GOES
ON...MDLS SHOW LOW LVL MOISTURE DECREASING ACRS THE PLAINS WITH
DRIER NWLY FLOW ALOFT MIXING DOWN THRU THE AFTN.  SKIES WILL
GENERALLY BY MO SUNNY/PARTLY CLDY ON SAT WITH MAX TEMPS SIMILAR TO
THOSE OBSERVED TODAY.

LOOKING AHEAD TO SUN THRU WED...SEE SLOW WARMUP SUN AND MON WITH
RISING HEIGHTS AS GREAT RIDGE SHIFTS EWRD.  ENUF MID-LVL MSTR AROUND
FOR A FEW LATE DAY...MOSTLY HIGH BASED STORMS BOTH DAYS.  BY
TUE...FLOW ALOFT BECOMES ZONAL AS PER MRF...UKMO AND ECMWF AS WRN
CONUS RIDGE FLATS AND RETREATS TO THE DESERT SW.  MOISTURE LVLS
INCREASE WITH WHAT APS TO BE A WK FRONTAL PASSAGE ON TUE.  SO
SLIGHTLY COOLER ON TUE WITH A CHANCE FOR AFTN/EVE SHWRS AND TSTORMS.
WILL ALSO MENTION CHC OF TSTMS AS WELL ON WED.               BAKER

.DEN...TORNADO WATCH THIS EVE UNTIL 9 PM MDT FOR PORTIONS OF NERN CO
         ZNS 42..44..48..49 AND 50.
       TORNADO WATCH THIS EVE UNTIL 10 PM MDT FOR ERN ELBERT AND
         LINCOLN CTYS ZNS 46 AND 47.

COZ030-032>050-212200-

SIGNIFICANT WEATHER OUTLOOK FOR NORTHEAST AND NORTH CENTRAL COLORADO
NATIONAL WEATHER SERVICE DENVER CO
140 PM MDT FRI JUL 21 2000

THIS OUTLOOK PERTAINS TO THE FOLLOWING COLORADO COUNTIES

ADAMS     ARAPAHOE     BOULDER   CLEAR CREEK   DENVER       DOUGLAS
ELBERT    GILPIN       GRAND     JACKSON       JEFFERSON    LARIMER
LINCOLN   LOGAN        MORGAN    PARK          PHILLIPS     SEDGWICK
SUMMIT    WASHINGTON   WELD

SYNOPSIS...SURFACE HIGH PRESSURE OVER THE GREAT PLAINS ALONG WITH
CONTINUED WEAK LOW LEVEL UPSLOPE FLOW WILL KEEP THE AIR MASS OVER
NORTHEASTERN COLORADO VERY MOIST NEAR THE SURFACE AS DEWPOINTS
INCREASE INTO THE LOWER 60S.  STEEP LAPSE RATES AND AN UPPER LEVEL
DISTURBANCE WILL CONTRIBUTE TO THE OVERALL INSTABILITY OF THE
ATMOSPHERE.  WITH HEATING...SCATTERED SHOWERS AND THUNDERSTORMS ARE
FORMING OVER THE EASTERN FOOTHILLS AND THE HIGHER TERRAIN OF BOTH
THE CHEYENNE RIDGE AND PALMER DIVIDE EARLY THIS AFTERNOON.  THESE
STORMS WILL SPREAD TO THE SOUTHEAST OVER THE PLAINS DURING THE
MID AND LATE AFTERNOON AND EVENING.  THE GREATEST INSTABILITY WILL
GENERALLY BE EAST OF A CONVERGENCE LINE FROM EAST OF CHEYENNE
WYOMING TO JUST EAST OF LIMON...WHERE AMPLE SHEAR WILL BE PRESENT TO
PRODUCE A FEW SEVERE THUNDERSTORMS WITH LARGE HAIL...DAMAGING WINDS
AND POSSIBLE TORNADOES.

IN SPITE OF MODERATE STORM MOVEMENT...SOME OF THE THUNDERSTORMS WILL
PRODUCE LOCALLY HEAVY RAIN OVER THE FOOTHILLS WHICH COULD POSE A
FLASH FLOOD THREAT IN THE HI MEADOWS AND BOBCAT FIRE BURN AREAS.

THE AIR MASS OVER THE MOUNTAINS AND MOUNTAIN VALLEYS WILL REMAIN
RELATIVELY DRY AND STABLE WITH LITTLE CONVECTIVE DEVELOPMENT
ANTICIPATED EXCEPT ALONG AND EAST OF THE FRONT RANGE.

SPOTTER ACTIVATION WILL BE NEEDED THIS AFTERNOON AND EVENING
OVER THE FRONT RANGE URBAN CORRIDOR AND THE NORTHEASTERN PLAINS.

GARD...WFO BOULDER