SPC AC 181736
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1236 PM CDT TUE AUG 18 2009
VALID 191200Z - 201200Z
...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS SRN PLAINS TO MID MS
VALLEY...
...SYNOPSIS...
MID-UPPER LEVEL HEIGHT FALLS ARE FCST ACROSS MUCH OF CENTRAL CONUS
AND MID MS VALLEY REGION THROUGH PERIOD. SHORTWAVE TROUGH INITIALLY
OVER CO/UT BORDER REGION SHOULD MOVE EWD ACROSS CENTRAL ROCKIES AND
ADJOINING HIGH PLAINS DAY-1...THEN EJECT NEWD FROM ERN KS TO WI/LM
AREA AND WEAKENING BY 20/00Z. FARTHER N...SHORTWAVE TROUGH AND
ACCOMPANYING SPEED MAX -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY
OVER FAR NRN PORTIONS BC/SK -- WILL DIG SEWD ACROSS CANADIAN HIGH
PLAINS DAY-1. BY 20/12Z...THIS FEATURE WILL CONTINUE SEWD ACROSS
NRN PLAINS...EVOLVING INTO HIGH-AMPLITUDE SHORTWAVE TROUGH TRAILING
SSWWD ACROSS OK FROM EMBEDDED MID-UPPER LOW OVER WRN OR NRN MN.
AT SFC...CYCLONE IS FCST TO DEVELOP OVER NRN PORTIONS SK/MB IN
ADVANCE OF AMPLIFYING MID-UPPER PERTURBATION. LOW WILL MOVE SEWD TO
NWRN MN BY ABOUT 20/00Z...WITH SFC COLD FRONT TRAILING SWWD ACROSS
ERN NEB...CENTRAL/W-CENTRAL KS AND SERN CO. OCCLUSION/TRIPLE-POINT
CYCLONE MAY DEVELOP AROUND END OF PERIOD OVER UPPER MI...WHILE COLD
FRONT REACHES ERN IA...NRN MO...NWRN OK AND NERN NM. SEPARATE SFC
BAROCLINIC ZONE -- NOW ANALYZED FROM NERN LOWER MI SWWD ACROSS NRN
MO...SERN KS...WRN OK AND TX SOUTH-PLAINS REGION -- IS PRECEDED BY
AGGREGATE OUTFLOW BOUNDARY ACROSS WRN MO...ERN/SRN OK AND NW TX.
FRONTAL ZONE WILL BE REINFORCED BY ADDITIONAL CONVECTIVE COMPLEXES
BEFORE MIDDAY WEDNESDAY...CAUSING ITS PROGGED NWD RETURN ACROSS
SRN/CENTRAL PLAINS AS WARM FRONT TO BE IMPEDED IN SEGMENTED FASHION.
MEANWHILE...SEPARATE/SYNOPTIC WARM FRONT SHOULD EXTEND FROM MN
CYCLONE SEWD ACROSS SERN IA/NRN IL...OH AND PA AT 20/00Z...MOVING
SLOWLY NWD TO LOWER MI...SRN ONT AND WRN NY BY END OF PERIOD.
...SRN PLAINS TO MID MS VALLEY...
ONE OR TWO COMPLEXES OF TSTMS...WITH AT LEAST MRGL POTENTIAL FOR
STG-SVR GUSTS AND HAIL...SHOULD BE ONGOING AT BEGINNING OF PERIOD
OVER PORTIONS S-CENTRAL HIGH PLAINS INTO KS. CONSENSUS OF SREF AND
OPERATIONAL PROGS...BUT NOT OVERWHELMING MAJORITY...MAINTAIN
TEMPORAL CONTINUITY WITH THIS ACTIVITY AND SHIFT IT NEWD ACROSS
LOWER MO VALLEY REGION DURING DAY...WHILE SOME PROGS GENERATED NEW
CONVECTION CLOSER TO SFC WARM FRONT ACROSS PORTIONS IA. THIS
DISCREPANCY MATTERS BECAUSE OPERATIONAL WRF...ETA-KF..SPECTRAL AND
SEVERAL SREF MEMBERS INDICATE OPTIMAL JUXTAPOSITION OF BUOYANCY AND
SHEAR SHOULD BE ACROSS PORTIONS NRN MO...NERN KS...AND/OR
CENTRAL/SRN IA DURING 19/21Z-120/03Z TIME FRAME...AND MCS VERSUS
RELATIVELY DISCRETE CONVECTIVE MODE WILL EXERT STG INFLUENCE ON
POTENTIAL FOR SUPERCELLS...LARGE HAIL AND TORNADOES. GIVEN
1. STRENGTH OF ONGOING COLD POOL OVER S-CENTRAL PLAINS
2. LIKELIHOOD OF ITS REINFORCEMENT OVERNIGHT DAY-1 INTO EARLY DAY-2
IN SOME MESOSCALE AREAS...AND
3. CONSIDERABLE UNCERTAINTY REGARDING ITS MIXING AWAY DIURNALLY
DAY-2 AND TIMING AND ROBUSTNESS OF WARM SECTOR AIRMASS RETURNING NWD
ACROSS THIS AREA...
CATEGORICAL OUTLOOK WILL BE HELD TO BROAD AREA OF 15-PERCENT SVR
PROBABILITIES WITH UNDERSTANDING THAT POTENTIAL EXISTS FOR
RELATIVELY DENSE/EMBEDDED CONCENTRATION OF SVR AROUND MESOBETA SCALE
BOUNDARIES.
ADDITIONAL OR BACKBUILDING DEVELOPMENT ALSO IS POSSIBLE ALONG/AHEAD
OF SFC COLD FRONT ACROSS PORTIONS KS/OK. BUOYANCY AND LAPSE RATES
ALOFT ARE FCST TO INCREASE WITH SWD EXTENT AHEAD OF FRONT ACROSS
THIS REGION...IN CONJUNCTION WITH STG DIURNAL HEATING.
HOWEVER...DEEP-LAYER SHEAR -- WHILE STILL FAVORABLE...SHOULD
DECREASE SWD.
...UPPER MS VALLEY...
SCATTERED TSTMS MAY DEVELOP INVOF NRN SEGMENT OF SFC COLD FRONT
DURING AFTERNOON...MOVING EWD ACROSS MN WITH DAMAGING GUSTS
POSSIBLE. LARGE SCALE ASCENT AHEAD OF MID-UPPER LEVEL SHORTWAVE
TROUGH WILL CONTRIBUTE FAVORABLE DESTABILIZATION ALOFT...WHILE
DIURNAL SFC HEATING REDUCES SBCINH IN SUPPORT OF CONVECTIVE
DEVELOPMENT. DEEP-LAYER SHEAR WILL BE LIMITED BY NEARLY
UNIDIRECTIONAL PREFRONTAL BOUNDARY LAYER FLOW IN MOST AREAS...BUT
STILL SUFFICIENT TO SUPPORT SOME SVR POTENTIAL WITH THIS ACTIVITY.
..EDWARDS.. 08/18/2009
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
|
