Severe Thunderstorm Warning 16, NWS Denver/Boulder, CO

NORTHEAST AND NORTH CENTRAL COLORADO AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER COLORADO
255 PM MDT SAT APR 29 2000

SHORT TERM DISCUSSION:  WITH UPR LOW NEARING THE 4-CORNERS AND A
VORT MAX ROTATING OUT OF THE BASE OF THE TROUGH...DYNAMIC LIFT
COINCIDING WITH THE TIME OF MAX HEATING WILL PRODUCE AN EVENING OF
ACTIVE WX ACRS THE FCST AREA.  SEVERE THUNDERSTORM WATCH BOX WL BE
IN EFFECT FOR MOST OF OUR PLAINS COUNTIES EARLY THIS EVENING.  SFC
FRONT FM WY HAS STALLED ACRS ERN LARIMER AND NWRN WELD COUNTY WHILE
RADAR SHOWS A DRY LINE BOUNDARY DRAPED ACRS THE NRN DEN AREA.  IN
BETWEEN THESE TWO AREAS WL BE WHERE MOST OF THE THUNDERSTORM
ACTIVITY TAKES PLACE.  SATELLITE PICTURES SHOW SCT CONVECTION ALSO
DEVELOPING AND MOVG OVR CENTRAL MTNS.  THIS PCPN HAS A CHANCE OF
CONTINUING WELL INTO THIS EVENING AS CO WL BE UNDER DIVERGENT FLOW
ALOFT ON THE NE SIDE OF THE UPR LOW.  WL MENTION LOCALLY HEAVY
SNOWFALL IN THE MTNS...BUT NOT GO WITH ANY HI-LITES.

LATER TONIGHT...AFTER THE COLD FRONT DROPS SWD TO THE PALMER
DIVIDE...STRONG UPSLP FLOW WL DEVELOP WITH MODELS SHOWING ABUNDANT
MSTR ACRS NE CO (6 G/KG SPECIFIC HUMIDITY AT 700 MB).  WITH THE
DIVERGENCE ALOFT REMAINING IN PLACE...THIS SHOULD LEAD TO A WDSPRD
STRATIFORM PCPN EVENT ON THE PLAINS.  TEMPS ALOFT WL GRADUALLY COOL
ENOUGH THAT SOME SNOW MAY MIX IN ARND SUNRISE ...BUT THE MAIN
MESSAGE IS THAT MOST AREAS SHOULD SEE AT LEAST A LITTLE PCPN BY
MRNG.  THESE THREE WX SITNS OUGHT TO BE ENOUGH TO KEEP US BUSY FOR A
WHILE.                KDRBY

LONG TERM DISCUSSION:  UPR LVL LOW WL MOVE ACRS NRN NM ON SUN AND
THEN BECOME NEARLY STATIONARY OVR NERN NM SUN NGT INTO MON AND BEGIN
TO WEAKEN.  MAIN QUESTION FOR SUN IS HOW MUCH SNOW WL FALL IN THE
MTNS AND FOOTHILLS.  GRIDDED FIELDS GIVING VARYING SOLUTIONS WITH
700 MB FLOW RANGING FM NLY TO NELY.  NGM SHOWS THE BEST UPSLOPE FLOW
WHILE AVN AND MESO-ETA SHOW MORE OF A NLY COMPONENT.  BASE ON HOW
LOUSY ALL THE MODELS WERE WITH LAST WEEKENDS EVENT IN THE MTNS NOT
SURE WHAT TO BELIEVE.  THERE WL BE FAVORABLE QUASI-GEOSTROPHIC
ASCENT THRU SUN AFTN WITH FAVORABLE POTENTIAL VORTICITY ALONG WITH
GEOFRONTOGENESIS IN THE 850-850 MB LYR.  HOWEVER LAPSE RATES ARE FCST
TO DROP TO 4-5 C/KM ON SUN.  THUS THERE ARE SEVERAL CONFLICTING
SIGNALS.  SNOW MODEL DOES GIVE NR WARNING CRITERIA FOR 12 HR PERIOD
BEGINNING 06Z TONIGHT THRU 18Z SUN.  OVR THE LOWER ELEVATIONS ONCE
AGAIN WL BE FACED WITH WHAT TYPE OF LOW LVL FLOW WL BE IN PLACE.  IF
FLOW IS MORE NELY LIKE NGM SHOWS THEN WOULD SEE WDSPRD RN ACRS NERN
CO MUCH OF THE DAY WHILE MORE NLY COMPONENT MAY LIMIT PCPN ALONG AND
NR THE FOOTHILLS.  NO MATTER WHAT HAPPENS TEMPS ON SUN WL BE MUCH
COOLER WITH READINGS HOLDING IN THE 40S ACRS NERN CO DUE TO CONSIDERABLE
COOLING AT 700 MB AND CLD CVR.

BY SUN NGT GRIDDED DATA STILL SHOWS SOME UPSLOPE COMPONENT HOWEVER
QUASI-GEOSTROPHIC ASCENT WL BE WEAKENING ALONG WITH LOW LVL
GEOFRONTOGENESIS.  STILL COULD SEE SOME PCPN IN SRN AREAS OF CWA AND
IN THE MTNS AND FOOTHILLS WITH LESSOR CHCS OVR NRN PTNS OF CWA.
SNOW LEVELS COULD DROP TO AROUND 6000 FT SUNDAY NIGHT.  ON MON UPR
LVL LOW IS FCST TO WKN QUITE A BIT HOWEVER WK UPSLOPE FLOW IS FCST
OVR RGN AND WITH CONSIDERABLE MSTR STILL COULD SEE SCT SHOWERS OVR
AREA.

IN EXTENDED PD UPR LVL SYS SHOULD MOVE EAST OF RGN BY TUE SO SHOULD
SEE A RETUWRN TO A WARMER AND DRIER PTRN FOR MID-WK.   KLEYLA

.DEN...???

COZ030-032>050-291900-

SIGNIFICANT WEATHER OUTLOOK FOR NORTHEAST AND NORTH CENTRAL COLORADO
NATIONAL WEATHER SERVICE DENVER CO
1135 AM MDT SAT APR 29 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:  A STRONG UPPER LEVEL WEATHER DISTURBANCE WILL MOVE OVER
COLORADO FROM THE SOUTHWEST THIS AFTERNOON AND EVENING WHILE A COLD
FRONT MOVES SOUTHWARD OUT OF EASTERN WYOMING.  THE AIRMASS OVER
NORTHEAST COLORADO WILL BECOME WARM AND UNSTABLE THIS AFTERNOON
AHEAD OF THE APPROACHING UPPER LEVEL SYSTEM.  INCREASING SOUTHEAST
WINDS ACROSS THE EASTERN PLAINS THIS AFTERNOON WILL ALSO BRING
INCREASING LOW LEVEL MOISTURE INTO THE REGION.  THE COMBINATION OF
THE UNSTABLE AIRMASS AND THE PASSING UPPER LEVEL DISTURBANCE WILL
PRODUCE A ROUND OF STRONG THUNDERSTORMS ON THE PLAINS THIS AFTERNOON
AND EVENING.

AT 11 AM...THE COLD FRONT WAS MOVING INTO NORTHWESTERN WELD COUNTY.
THE FRONT IS EXPECTED TO CONTINUE MOVING SOUTHWARD ALONG THE
INTERSTATE 25 CORRIDOR THROUGH THE AFTERNOON...REACHING THE DENVER
AREA AFTER 3 PM.  BEHIND THE COLD FRONT...THUNDERSTORM ACTIVITY WILL
BE LIMITED.

AREAS EAST OF A LINE FROM GREELEY TO DENVER INTERNATIONAL AIRPORT TO
ELIZABETH WILL HAVE THE HIGHEST CHANCE OF STRONG AND POSSIBLY SEVERE
THUNDERSTORMS DEVELOPING.  SCATTERED SHOWERS AND THUNDERSTORMS WILL
DEVELOP OVER THE FOOTHILLS AND I-25 CORRIDOR BY 2 PM AND THEN PUSH
EASTWARD THROUGH THE LATE AFTERNOON AND EVENING.  THE MAIN THREAT
FROM THE STRONG THUNDERSTORMS WILL BE FROM LARGE HAIL.  SOME
THUNDERSTORMS IN WELD COUNTY AND THE DENVER METRO AREA MAY PRODUCE
LOCALLY HEAVY RAINSHOWERS AS THEY INTERACT WITH THE COLD FRONT.
A FEW SMALL AND SHORT-LIVED TORNADOES MAY ALSO DEVELOP IN SOUTHERN
WELD AND CENTRAL ADAMS COUNTIES AS THE INITIAL THUNDERSTORMS
DEVELOP.

SPOTTER ACTIVATION MAY BE NEEDED FOR THUNDERSTORMS THAT DEVELOP IN
WELD...MORGAN...EASTERN ADAMS AND EASTERN ARAPAHOE COUNTIES.

DANKERS