Severe Thunderstorm Warning 84, NWS Topeka, KS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
311 PM CDT FRI JUN 19 1998

...FORECAST CHALLENGES NEXT FEW DAYS ARE TEMPERATURES...FRONTAL
   POSITION AND THUNDERSTORM CHANCES...

18Z SURFACE CHART SHOWS OLD BOUNDARY TO THE SOUTH OF CWA HAS BECOME
MORE OF A MOISTURE GRADIENT AS TEMPERATURES ARE ONLY A FEW DEGREES
WARMER TO THE SOUTH OF THIS FEATURE. BOUNDARY SEEN ON VISIBLE SATL
LOOP AT 20Z FROM NEAR SLN AND EMP TO SGF WITH LINE OF CU PROBABLY
LOCATING LEADING EDGE OF DEEPER MOISTURE AND INSTABILITY. BOUNDARY
WILL CONTINUE TO OVERSPREAD ALL OF CWA TONIGHT IN SLY LO LVL FLOW OF
15 TO 25 KNOTS. SOME CONCERN THAT WDLY SCT CONVECTION COULD DEVELOP
IN INSTABILITY AXIS NEAR MO BORDER...BUT MID LVL FORCING APPEARS WEAK
WITH BETTER LIFT EAST OF CWA. HAVE DRY FCST GOING ATTM AND WILL NOT
CHANGE.

H5 LOW CURRENTLY OVER NRN ROCKIES MOVES SLOWLY EWRD INTO SCENT CANADA
BY 48 HRS. WATER VAPOR LOOP ALSO SHOWS VORT MX NOW MOVING ONSHORE
OVER SRN CA THAT SHOULD ALSO FACTOR INTO HELPING TRIGGER TSTMS LATER
SAT INTO SUN. AVN MODEL LOOKS BEST WITH THIS SRN BRANCH FEATURE AND
MOVES SEVERAL WEAK WAVES THROUGH H5/H7 FLOW OVER KS AND MO BETWEEN 36
AND 72 HRS TO INCREASE VERT MOTION FIELDS NEAR SFC/H85 BOUNDARY THAT
MOVES INTO FA LATE SAT AND BEYOND.

FOCUS THEN SHIFTS TO APPROACHING COLD FRONT THAT IS SHOWN BY ALL 3
MODELS TO MOVE INTO NERN KS BY 00Z SUN. AFTER EXAMINING BOTH ETA AND
AVN MODEL OUTPUT ON AWIPS...WILL HOLD OFF ON ANY MENTION OF PCPN TIL
AFTER THE AFTERNOON HOURS ON SAT. FEEL H7 WARMING IN THE 12C TO 14C
RANGE WILL LIMIT INITIAL CONVECTIVE DEVELOPMENT OVER IOWA AND NW
MO...WITH DEVELOPMENT OVER ERN FA SAT EVENING/NIGHT. VERT MOTION
FIELDS AND SFC/H85 MOISTURE CONVERGENCE APPEAR STRONG ENOUGH NEAR
FRONT TO FIRE CONVECTION. AIRMASS ALSO BECOMES EXTREMELY UNSTABLE BY
36 HOURS WITH ETA SHOWING CAPES AOA 3000 J/KG AND TOTAL/TOTALS AROUND
60C. FEEL CONVECTION WILL DEVELOP THROUGH THE NIGHT IN REGION OF
STRONG H85 CONVERGENCE INTO FRONT AS SHOWN BY BOTH ETA AND AVN...WITH
ACTIVITY THEN MOVING EWRD INTO MO. WILL CARRY HIGHEST POPS OVER SERN
2/3 FA WHERE PROXIMITY TO FRONT WILL GIVE BEST CHANCE FOR MEASURABLE
PCPN. BOTH ETA AND AVN ALSO SHOW GOOD Q-VECTOR FORCING NEAR FRONT
AFTER 30 HRS IN THE 850-700MB LAYER. THE VERT MOTION IN THIS LAYER
SHOULD HELP WEAKEN CAP AND ALLOW FOR SOME RELEASE OF ABOVE MENTIONED
INSTABILITY.

MAX TEMPS TRICKY NEXT FEW DAYS WITH FRONT TO CROSS NCENT KS BY EARLY
-MID AFTN ON SAT. H85 THERMAL AXIS SETS UP MORE INTO SCENT AND ECENT
KS WITH AIRMASS LIKELY TO REACH OR EXCEED 100F THESE AREAS. WILL
STILL GO 95-100F NCENT ZONE AND ECENT ZONE. WILL KEEP ARND 95F GOING
FOR NERN CORNER. ON SUN...AMOUNT OF LEFTOVER CONVECTION AND CLOUD
COVER MAIN CONCERN. BOUNDARY MAY BE S OF ENTIRE CWA IF ENOUGH
OVERNIGHT CONVECTION OCCURS AND OUTFLOW FORCES BOUNDARY SOUTH DURING
THE NIGHT. IN ANY EVENT...MX TEMPS SHOULD BE BETWEEN 5 TO 10F COOLER
SUN...ESPECIALLY NORTHERN 1/2 FA.

COULD SEE MORE NOCTURNAL CONVECTION SUN NIGHT INTO MON GIVEN
FAVORABLE LOCATION OF LOW LVL BOUNDARY...STRONG H85 INFLOW AND
CONVERGENCE...HIGH INSTABILITY AND WEAK H7/H5 WAVES TO EJECT OVER
ABOVE FEATURES.

.TOP...NONE.

BARLOW