Good evening everyone!
Based on information contained in the Storm Prediction Center (SPC) Day 4 – 8 Severe Weather Outlook, and earlier analysis of F5 DATA Severe Weather Software utilizing the GFS model output (GFS is the only model that goes out far enough in the forecast period in the software), a good probability exists for a more substantial Severe Weather event during day 5. From the day 4/5 outlook:
…DISCUSSION… DAY 4-5/ MODELS APPEAR TO BE CONVERGING TOWARD A SLOWER…MORE AMPLIFIED SOLUTION REGARDING THE UPPER TROUGH FORECAST TO MOVE THROUGH THE CNTRL AND SRN PLAINS AND MID MS VALLEY AREA BY THURSDAY /DAY 5/ WITH ECMWF ALSO TRENDING SLOWER…BUT STILL REMAINS THE FASTER MODEL. PRECEDING THIS FEATURE…RICHER GULF MOISTURE /LOW-MID 60S DEWPOINTS/ WILL ADVECT THROUGH THE WARM SECTOR UNDERNEATH STEEP MID-LEVEL LAPSE RATES RESULTING IN MODERATE-STRONG INSTABILITY OVER THE SRN PLAINS AND A PORTION OF THE LOWER MS VALLEY BY WEDNESDAY /DAY 4/. IT STILL APPEARS A FEW SEVERE STORMS COULD DEVELOP ALONG THE DRYLINE DAY 4 OVER THE SRN PLAINS AND NEAR THE DRYLINE/FRONT INTERSECTION OVER NWRN OK/SWRN KS. HOWEVER…CAPPING WILL BE A CONCERN FOR SEVERE STORM COVERAGE ALONG THE DRYLINE AS WELL AS FARTHER EAST IN WARM SECTOR. CONFIDENCE IN WHERE TO PLACE A 30% OR GREATER SEVERE AREA REMAINS LOW FOR DAY 4…BUT A CATEGORICAL RISK AREA WILL PROBABLY BE NEEDED FOR THE NEXT DAY 3 UPDATE.
GIVEN MODEL TRENDS…IT NOW APPEARS A MORE SUBSTANTIAL SEVERE THREAT MIGHT DEVELOP FROM THE SRN PLAINS INTO THE LOWER-MID MS VALLEY REGION THURSDAY /DAY 5/ AS THE SHORTWAVE TROUGH EJECTS ENEWD RESULTING IN HEIGHT FALLS ACROSS THE WARM SECTOR AND A STRENGTHENING LLJ. STORMS MAY DEVELOP ALONG THE DRYLINE AND DRYLINE/PACIFIC FRONT MERGER OVER THE SRN PLAINS AS WELL AS FARTHER EAST IN THE WARM SECTOR. SEVERE THREAT WILL LIKELY SPREAD EWD INTO THE LOWER MS VALLEY AREA BY LATER THURSDAY AFTERNOON AND EVENING.
The following Severe Weather Indices were indicated by the software GFS output…valid for 4:00 p.m. CDT on Thursday. I have 2 sites posted so you may compare values and understand what they mean:
SBCAPE: 2500 – 3000 j/kg
MLCAPE: 1500 – 2000 j/kg
LIFTED INDEX: -8 to -10
CRAVEN BROOKS: 30,000 – 50, 000
THETA – E: 330 – 345K
SURFACE DEW POINT: 65F
850 MB DEW POINT: 54 – 57F
700 MB – 500 MB LAPSE RATE: 7.5 – 8.0 C/km
TOTALS – TOTALS INDEX: 56 – 60
K INDEX: 30 – 40
The mid level lapse rates are considered steep enough for severe thunderstorms to develop. The concern for CAPPING mentioned in the outlook, is due to the fact that IF the atmosphere destabilizes enough from heating at the surface to overcome capping near the dryline, storms could become quite violent.
Again, this is out in the period by at least 96 hours, and parameters will change. I will be monitoring this for significant changes. The following sites will explain the Severe Indices.
MOKANSCAN SEVERE WEATHER INDICES
THE WEATHER PREDICTION SEVERE INDICES PAGE
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST / SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS
OFFICIAL SKYWARN SPOTTER (ADVANCED)