Severe Thunderstorm Warning 84, NWS Des Moines, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
220 AM CDT TUE JUN 13 2000

...QUESTION IS HOW MUCH MESOSCALE ACTION THIS MORNING AFFECTS THIS
AFTERNOON'S SEVERE POTENTIAL...

850MB WARM FRONT ACTIVATED AROUND 04Z, WITH NUMEROUS CELLS AND NEAR
SEVERE HAIL, BUT MOSTLY HEAVY RAIN.  THANKFULLY, THE CELLS ARE
MOVING ALONG AND ARE ELEVATED ENOUGH THAT MESOCYCLONES ARE UNLIKELY
TO BE TORNADIC THIS MORNING.  I EXPECT THE BAND OF STORMS TO FILL IN ACROSS
NW IA SOON TO MEET UP WITH THE CONVECTION NEAR FSD.  ELEVATED CAPES
AND LLJ AT THE THETA E RIDGE POSITION CREATED CLASSIC PATTERN FOR
NOCTURNAL DEVELOPMENT OF THESE STORMS.  SYNOPTIC WARM FRONT IS NOW
UP TO TQE-CNC-UIN LINE, FORECASTED TO SURGE N THIS MORNING.
HOWEVER, OUTFLOW FROM MCS MAY INTERACT WITH THE WARM FRONT AND -10
SHOWALTER AIRMASS FOR REDEVELOPMENT.  GREAT WIND PROFILE AT SLATER
WITH STRONG VEERING AND WAA.  THIS WOULD LIKELY KEEP THE BOUNDARY AT
BAY WHERE IT IS FOR A WHILE LONGER, HAVING A BIG IMPACT ON SFC BASED
CONVECTION THIS AFTERNOON IN NORTHERN AND CENTRAL IA.  WILL PLAY
THIS ROUTE AS MESOETA SUGGESTS IT AS WELL.  E-W BOUNDARY IN PLACE
AND AGREE WITH 94E, SO FFA MAY BE NEEDED LATER THIS MORNING IF
CONVECTION FIRES THIS MORNING, WITH ANOTHER ROUND THIS AFTERNOON AND
EVENING.  SEVERE WEATHER COMPOSITE CHART FOR 21-00Z REFLECT A NEAR
CLASSIC SETUP OTHERWISE WITH A PREFRONTAL AREA OF CONVECTION,
FOLLOWED BY A SQUALL LINE THIS EVENING.  BEST PARAMETERS ARE UPPER
DIFFLUENCE AXIS, 500 MB 50 KT JET PUNCHING INTO WESTERN IA, AND
CLASSIC MOIST AND THERMAL RIDGE POSITIONS AT SFC/850 MB.  BUFKIT
POINT DATA ALSO SUGGESTS 2 SEPARATE AFTERNOON AND EVENING ROUNDS OF
CONVECTION.  HELICITY FIELDS ARE BEST ALONG THE WARM FRONT, AND
SINCE IT IS UP IN THE AIR ON THAT ONE AT THIS POINT, I WILL INCLUDE
TORNADO THREAT OVER ALL OF FORECAST AREA IN THE SEVERE WEATHER
OUTLOOK.  SQUALL LINE BOW SEGMENTS LOOK LIKELY THIS EVENING WITH
GOOD CURVED HODOGRAPH WITH STRONG MID LEVEL WINDS.  I STILL BELIEVE
GOOD RECOVERY OF AIR MASS BEHIND MCS.  WILL GO ABOVE GUIDANCE IN THE
SW ZONES AS WARM FRONT ALREADY N OF THAT AREA, SO GOOD WARMING
SHOULD TAKE PLACE.  HOWEVER, FWC VALUES OF 75-80 LOOK GOOD N GIVEN
EXPECTED MORNING CONVECTION AND CLOUD DEBRIS.  WED-THU LOOK
BEAUTIFUL, BUT WILL SIDE WITH THE WARMER FAN WITH W-SW SURFACE FLOW
BEHIND COLD FRONT ON WED.  IN FACT, THAT SW FLOW IS UIN RESPONSE TO A
SECONDARY COLD FRONT, AND LIS STAY BELOW 0.  SO WILL INSERT A CHANCE
OF TSRA N HALF OF CWA WED.

.DSM...NONE.
KULA

IAZ037>039-048>050-060>062-073>075-083>086-094>097-132105-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
333 PM CDT TUE JUN 13 2000

...SEVERE THUNDERSTORM WATCH NUMBER 439 CANCELLED...

THUNDERSTORMS HAVE MOVED TEMPORARILY MOVED EAST...OUT OF THE WATCH
AREA IN THE DES MOINES COUNTY WARNING AREA.

COUNTIES CLEARED FROM THIS WATCH ARE...

APPANOOSE...BLACK HAWK...CLARKE...DAVIS...DECATUR...GRUNDY...
HARDIN...JASPER...LUCAS...MAHASKA...MARION...MARSHALL...MONROE...
POLK...POWESHIEK...STORY...TAMA...WAPELLO...WARREN...AND WAYNE.

SOME OF THE LARGER TOWNS NO LONGER IS THIS WATCH INCLUDE...

DES MOINES...AMES...WATERLOO...OTTUMWA...MARSHALLTOWN...AND LAMONI.

A TORNADO WATCH REMAINS IN EFFECT FOR A LARGE PART OF WESTERN IOWA
UNTIL 8 PM.

STAY TUNED TO YOUR FAVORITE WEATHER INFORMATION SOURCE FOR LATER
UPDATES...AND POSSIBLE WATCHES AND WARNINGS.

SEARCY