Event #3

NSSL Ops: Chris Porter

Start:  4/23/03 19:00 UTC
End:    4/24/03 03:50 UTC

April 23, 2003 2000 UTC outlook from SPC:

STRONG/SEVERE CONVECTIVE DEVELOPMENT IS UNDERWAY NEAR/JUST AHEAD OF
DRY LINE CURVING FROM SOUTHWEST KANSAS THROUGH THE EASTERN TEXAS
PANHANDLE INTO AREAS WEST OF DEL RIO...AND IN CLOSE PROXIMITY TO
SURFACE LOW AND MID-LEVEL CIRCULATION CENTER NOW REDEVELOPING INTO
NORTHEAST COLORADO.  NEUTRAL TO NEGATIVELY TILTED SHORT WAVE TROUGH
AXIS TRAILS SOUTH SOUTHEASTWARD FROM LOW...AND HAS PROVIDED MID/
UPPER FORCING SUPPORTING ACTIVITY.  
   
COLD FRONT WILL CONTINUE TO GRADUALLY MERGE WITH DRY LINE ACROSS
WESTERN OKLAHOMA/WESTERN TEXAS LATE THIS AFTERNOON AND EVENING.  AS
THIS OCCURS...SQUALL LINE WILL CONTINUE TO SOLIDIFY AS IT
PROGRESSES EASTWARD THROUGH MOIST AND WEAK TO MODERATELY UNSTABLE
ENVIRONMENT. 
   
STRONGEST FORCING FOR UPWARD VERTICAL MOTION IS EXPECTED TO BECOME
FOCUSED IN NORTHWEST TEXAS BETWEEN ABILENE/ WICHITA FALLS/FORT
WORTH BETWEEN NOW AND 24/00Z...IN EXIT REGION OF COUPLED
SUBTROPICAL/POLAR JETS...WHERE INTERSECTION OF SURFACE DRY
LINE/WARM AND COLD FRONTS WILL BECOME LOCATED.  INSTABILITY IS
BECOMING MAXIMIZED ACROSS THIS REGION ON NOSE OF LOW-LEVEL THERMAL
RIDGE...WITH SURFACE-BASED CAPE AROUND 2000 J/KG.  MODERATE
SOUTHEASTERLY SURFACE FLOW NEAR BOUNDARY INTERSECTION WILL
CONTRIBUTE TO PRONOUNCED LOW-LEVEL HODOGRAPH CURVATURE BENEATH 30
TO 50 KT SOUTHERLY LOW-LEVEL JET.  COUPLED WITH STRENGTHENING
MID/UPPER FLOW...HODOGRAPHS WILL BECOME INCREASING FAVORABLE FOR
TORNADIC SUPERCELLS ALONG/JUST AHEAD OF SQUALL.  ISOLATED STRONG
TORNADOES ARE POSSIBLE...AND MAY APPROACH THE DALLAS/FORT WORTH
AREA BY THE 24/00-02Z TIME FRAME BEFORE ACTIVITY BEGINS TO DIMINISH
LATER THIS EVENING WITH LOSS OF DAYTIME HEATING.
   
Personal notes:
No problems were encountered in running the 2D wind retrieval algorithm.
From 1900 UTC on the 23rd to 0030 UTC on the 24th, retrievals primarily
focused on one storm that propagated from North Texas across the Red River
into southwestern Oklahoma and spawned one tornado 20 miles west of Walters
Oklahoma in Cotton County at 2217 UTC on the 23rd.  Comparing 2D wind 
retrieval vectors with the radial velocities from KTLX showed a mixture of
good and speculative retrievals.  A sequence of images can be seen at:

http://www.nssl.noaa.gov/~porter/2D_wind_alg/Apr23-24/images.html.

Reasonable wind retrievals are obtained at 2104 UTC and 2129 UTC. At 2104 UTC,
an elongated circulation is retrieved generally in the region of greatest 
azimuthal shear.  However, some surrounding regions such as northwest of the
azimuthal shear region contain retrieved wind vectors in direct disagreement
with radial wind values. At 2129 UTC, largest wind speed retrievals are 
coincident with maximum inbound velocities and a minimum in retrieved wind 
speeds are found in regions of near zero radial velocities.

However, at 2158 UTC, the retrieved wind solution is very questionable with
decreased wind speeds and a wind direction distortion in the area of greatest
azimuthal shear instead of a well-defined circulation.  An image at 2213 UTC
is also shown representing calculated wind vectors just 4 minutes before a
tornado is seen by storm-spotters.  The retrieved solution at 2213 UTC is 
similar to that of 2158 UTC with a very weak circulation produced by the 2D
wind algorithm.

From 0126 UTC to 0350 UTC on the 24th, the genesis and evolution of a bow 
echo was observed.  A sequence of images (generally 15 minutes apart) show
the retrieved wind solutions for this event.  Overall, the retrieval algorithm
appears to perform very well most likely because of a very well defined convergent
region along the leading edge of the bow echo.  


Forecaster comments:
None