SPC MESOSCALE DISCUSSION 1490 FOR PORTIONS OF NERN CO/SERN WY...WRN
NEBRASKA AND NWRN KS CONCERNING...SEVERE THUNDERSTORM POTENTIAL...

VALID 122011Z - 122300Z

THUNDERSTORMS WILL LIKELY INTENSIFY WHILE MOVING EWD OUT OF THE
FRONT RANGE OF NRN CO/FAR SRN WY. ADDITIONAL CONVECTIVE DEVELOPMENT
WAS OCCURING ALONG SURFACE CONVERGENCE ZONE ACROSS PORTIONS OF
WCENTRAL NEBRASKA. ALTHOUGH WIND SHEAR REMAINS MARGINAL...MODERATE
TO HIGH INSTABILITY WILL FAVOR SEVERE CONVECTIVE UPDRAFTS...WITH
HAIL AND DAMAGING WINDS THE PRIMARY THREATS. A WW MAY BE ISSUED FOR
THE AREA IN THE NEXT HOUR OR SO.

LATEST RADAR IMAGERY OUT OF BOULDER AND CHEYENNE INDICATES
CONVECTION WAS DEVELOPING OVER THE FRONT RANGE TO THE W AND NORTH
OF FORT COLLINS WAS BEGINNING TO SLOWLY PROPAGATE INTO THE HIGH
PLAINS. SURFACE MESOANALYSIS INDICATES A WELL DEFINED ENELY WIND
FIELD ACROSS MUCH OF NERN COLORADO AIDING IN MOIST UPSLOPE FLOW.
ALTHOUGH MID LEVEL FLOW REMAINS FAIRLY WEAK...LATEST PROFILER DATA
FROM PLATTEVILLE AND MEDICINE BOW WYOMING INDICATES BETWEEN 20 AND
30 KTS OF 0-6 KM OF SHEAR. THEREFORE...CONVECTIVE ORGANIZATION WILL
BE MORE DEPENDENT ON STORM SCALE/OUTFLOW INTERACTIONS FOR
INTENSIFICATION. CONVECTIVE DEVELOPMENT WAS ALSO OCCURRING ACROSS
PORTIONS OF NERN COLORADO TO THE NORTH OF THE PALMER DIVIDE ALONG
SURFACE CONVERGENCE ZONE FROM NEAR DEN TO NE OF LIMON. AGAIN DEEP
LAYER SHEAR WILL REMAIN FAIRLY MARGINAL...BUT MUCAPES FROM 2000 TO
3000 J/KG WILL SUPPORT ISOLATED SEVERE CONVECTION. 

ADDITIONAL CONVECTIVE DEVELOPMENT WAS OCCURING FARTHER TO THE
NORTHEAST ALONG SURFACE FRONTAL BOUNDARY NEAR NORTH PLATTE
NEBRASKA. VWP OUT OF LBF AND PROFILER FROM MCCOOK INDICATE
SUFFICIENT DEEP LAYER SHEAR VALUES FROM 30 TO 40 KTS SUPPORTIVE OF
ORGANIZED SEVERE CONVECTION. GIVEN VERY UNSTABLE AIRMASS IN PLACE
WITH MUCAPES FROM 3000 TO 4000 J/KG FROM WRN NEBRASKA INTO NWRN
KS...CONVECTION WILL LIKELY INTENSIFY OVER THE NEXT FEW HOURS.
CONVECTION SHOULD SLOWLY PROPAGATE SEWD AROUND 15 KTS. LARGE HAIL
AND DAMAGING WINDS WILL BE THE PRIMARY THREAT.

..CROSBIE.. 07/12/01