Tornado Warning 49, NWS Hastings, NE

SOUTH CENTRAL NEBRASKA/NORTH CENTRAL KANSAS FORECAST DISCUSSION...
NATIONAL WEATHER SERVICE HASTINGS NE
315 PM CDT TUE AUG 17 1999

...THUNDERSTORM FORECAST THE MAIN CHALLENGE...

LATEST RADAR MOSAIC/VISIBLE IMAGERY/LIGHTNING DATA SHOWING AN
INCREASE IN CONVECTIVE TRENDS THIS AFTERNOON.  A STRONG CELL HAS
DEVELOPED OVER NE CO...LINGERING CONVECTION CONTINUES TO DEVELOP
OVER NE KS...AND A MIX OF STRATIFORM/CONVECTION RAINS CONTINUE OVER
WRN/NRN NEBRASKA.  SEE WW 643 FOR DETAILS ON THIS ACTIVITY.

19Z LAPS DATA SHOWING 6700 J/KG OF CAPE OVER SMITH COUNTY KS.  18Z
SURFACE ANALYSIS HAS FRONT FROM SW TO NE KS.  H25 ANALYSIS FROM THIS
MORNING SHOWING 90 KNOT JET CORE OVER ABR.  MODELS AND SATELLITE
DEPICT TWO SHORTWAVES HEADING THIS WAY FROM THE SW.  THESE WAVES ARE
ALREADY HELPING TO FIRE THE CONVECTION OVER THE HIGH PLAINS. AN
ADDITIONAL WEAK WAVE IS PROGGED SLIDE TO OUR NORTH OUT OF MT...WHICH
IN COMBINATION WITH THE SRN WAVES WILL ENHANCE THE UPPER DIVERGENCE
DRAMATICALLY AFTER DARK.  THIS WILL ALSO PLACE THE REGION UNDER THE
RIGHT READ QUAD OF ABOVE MENTIONED JET CORE.  THE VERTICAL MOTION
FROM THE DIVERGENCE...DPVA...AND FRONTAL BOUNDARY WILL RESULT IN
MUCH MORE CONVECTION TONIGHT WITH SOME STORMS POSSIBLY SEVERE GIVEN
THE MAGNITUDE OF INSTABILITY.

EXPECT CONVECTION OVER WRN HIGH PLAINS TO BECOME ORGANIZED INTO A
FAIRLY LARGE MCS/MCC AND MIGRATE ESE NEAR THE SURFACE BOUNDARY.
315K ISENTROPIC SURFACE SLANTS UPWARD FROM KS INTO NEBRASKA AND IF
THE H85 WINDS CAN EXCEED 20 KNOTS THE ISENTROPIC LIFT ALONG THIS
SURFACE SHOULD HELP SUSTAIN THE MCS INTO THE MORNING HOURS.  IN
ADDITION TO ALL OF THIS...THE NORTHERN WAVE SHOULD BRING A WEAK
FRONTAL BOUNDARY INTO THE CWFA SOMETIME DURING THE MORNING
HOURS...WHICH WILL HELP RE-FIRE CONVECTION.  CERTAINLY SOME CONCERN
FOR EXCESSIVELY HEAVY RAINFALL AMOUNTS...BUT FFG VALUES ARE MOSTLY
AROUND OR ABOVE 2.O INCHES.  MOST AREAS HAVE NOT SEEN SIGNIFICANT
RAINS FOR A FEW DAYS.  WILL MENTION HEAVY RAIN IN ZONES AND
MONITOR.

ETA/NGM/RUN/AVN/MM5 ALL GENERATE RAIN OVER THE CWFA TONIGHT...SO
WILL GO WITH 80 POPS FROM I-80 SOUTH TO THE BORDER...WITH 70
ELSEWHERE.  ADAP DATA STILL SHOWING A 3-4 DEGREE C CAP OVER THE
CWFA...SO THIS CAP SHOULD KEEP THE LATE AFTERNOON/EARLY EVENING
HOURS QUIET.

AFTER THE THREAT OF LINGERING MORNING SHOWERS ESPECIALLY IN THE
EAST...MODELS BRING A DECENT SURFACE HIGH INTO REGION WITH
SUBSTANTIALLY DRIER AIR.  THE UPPER RIDGE PATTERN RETROGRADES BACK
TO THE WEST WITH CWFA IN NW FLOW FOR THE REST OF THE WEEK.  THIS
ALWAYS BRINGS SOME CHANCE FOR WEAK WAVES MOVING THROUGH THE NW
FLOW...BUT WE SHOULD REMAIN DRY ENOUGH TO INHIBIT MUCH RAIN INTO
THU.  AVN SHOWS A WAVE ON FRIDAY THAT SHOULD MAINLY AFFECT AREAS TO
OUR EAST...BUT THIS MAY WARRANT A CHANCE IN THE EAST ON FRI.

GUIDANCE TEMPERATURES LOOK REASONABLE EXCEPT THE HIGHS THURSDAY MAY
BE A BIT COOLER THAN FWC/FAN.

.GID...NONE.

NIETFELD