Last year, for instance, after chasing for 12 years, the significance of the 700mb map finally came home to me. I'm the kind who needs to have concepts connected to practical experiences, and while I may be a slow learner, two busts out in Iowa drilled into my brain that once 700mb temps exceed the 12 degree mark during peak season, you'd either better move to where the cap is breakable or else love watching turkey towers rise and die. My second Iowa bust last year was in southwest IA/northwest MO. While lots of chasers were scoring farther north up toward MN, my buddy Bill and I went for monster 6,000 CAPE moving up from northeast KS. It was my fault. We both knew it was a risk and were a hair away from heading north, but CINH seemed like it could erode, and I reasoned that if the cap did break, then we'd have Armageddon on our hands. It didn't help that the SPC issued an MD for our area. But the cap held. We got a crapload of towering Cu's and one patch of elevated convection, but that was it. Meanwhile, tornado reports were filtering in from 150 miles north of us.
That advise, while it may work most of the time, wouldn't have held true for me on June 3, 2001 in south-central Kansas. I sat under a monster cap all afternoon along an outflow boundary near Medicine Lodge, KS. 700 temps were 12C-14C across Oklahoma and southern Kansas. Fortunately, we had a weak mid-level trough swinging through which would be our only hope to break the monster inversion. Here are the MD's issued for that event:
SPC MESOSCALE DISCUSSION 1015 FOR FAR NRN OK..FAR SRN KS
CONCERNING...SEVERE THUNDERSTORM POTENTIAL...
MONITORING LATEST INSTABILITY ANALYSES NEAR THE OK-KS BORDER FOR
SIGNS CONVECTION MAY BE IMMINENT. ACTIVITY WOULD DEVELOP AND
BECOME SEVERE VERY QUICKLY ONCE CAP IS BROKEN...MEANING A TORNADO
WATCH MAY BE REQUIRED IN THE NEXT HOUR OR TWO.
LATEST INSTABILITY ANALYSES INDICATE EXTREME INSTABILITY HAS
DEVELOPED ALONG AND JUST SOUTH OF OUTFLOW BOUNDARY NOW EVIDENT
WITHIN MESONET DATA FROM JUST NORTH OF TUL TO NEAR PNC TO JUST
NORTH OF END AND GAG. SURFACE-BASED CAPES HAVE INCREASED TO OVER
6000 J/KG OVER N-CENTRAL OK...WHERE LOWER 90F TEMPERATURES ARE
COLLOCATED WITH LOW-MID 70F DEW POINTS. 18Z SOUNDINGS FROM DDC AND
OKC INDICATED SUBSTANTIAL CAP...WITH INVERSION MAXIMUM TEMPERATURE
OF 23C-25C IN THE 5-6 KFT LAYER. HOWEVER...FORECAST SOUNDINGS FROM
THE ETA AND ETAKF FOR 18Z BOTH HANDLED THIS INVERSION LAYER VERY
WELL. IN ADDITION...ETAKF STILL SUGGESTS CONVECTION WILL DEVELOP
NEAR THE BOUNDARY BETWEEN 21-23Z...INVOF REGION OF CURRENT
WEAKENING OF CAP ON CURRENT ANALYSIS IN N-CENTRAL OK.
MASS CONVERGENCE NEAR THE BOUNDARY WITH SLY WIND GUSTS NEAR 25 KT
ACROSS WARM SECTOR...COMBINED WITH FURTHER WARMING AND MOISTENING
OF THE BOUNDARY LAYER ALONG THE KS/OK BORDER...MAY OVERCOME STRONG
CAP LATER THIS AFTERNOON. GIVEN THE DEGREE OF INSTABILITY...LMN
PROFILER SUGGESTS DEEP LAYER WILL REMAIN MORE THAN FAVORABLE FOR
SUPERCELLS WITH 0-6 KM SHEAR AROUND 40 KT.
..EVANS.. 06/03/01
SPC MESOSCALE DISCUSSION 1019 FOR NRN OK AND SRN KS
CONCERNING...TORNADO WATCH 358...
LOW LEVEL BOUNDARY AT 22Z WAS MOVING SLOWLY NWD AND WAS LOCATED E-W
CLOSE TO THE OK/KS BORDER...APPROXIMATELY FROM ABOUT 50 N GAG TO
20 S BVO. TEMPERATURES HAVE WARMED INTO THE UPPER 80S/LOWER 90S
JUST SOUTH OF THE BOUNDARY AND WITH DEWPOINTS IN THE LOWER
70S...MLCAPES ARE NEAR 4500 J/KG. DESPITE THE STRONG
INSTABILITY...THE AIR MASS REMAINS STRONGLY CAPPED. HOWEVER...
LATEST SATELLITE PICTURES SHOW THE CU HAVE BEEN SWELLING ABOUT 50NW
END...CLOSE TO WHERE THE 21Z RUC DEVELOPS CONVECTION BY 00Z. IF
STORMS CAN DEVELOP...THE STORMS ARE LIKELY TO BECOME RAPIDLY SEVERE
GIVEN THE EXTREME INSTABILITY AND DEEP LAYERED SHEAR AROUND 40 KT.
..IMY.. 06/03/01
SPC MESOSCALE DISCUSSION 1022 FOR NRN OK AND SRN KS
CONCERNING...TORNADO WATCH 358...
NO THUNDERSTORMS HAVE DEVELOPED IN WW AS OF YET...AND WW MAY BE
CANCELLED SHORTLY.
THOUGH SOME POSSIBILITY STILL EXISTS FOR STORMS TO DEVELOP ALONG
THE BOUNDARY LOCATED ALONG THE OK/KS BORDER...EVENING SOUNDINGS
SHOW THE AIR MASS ALONG AND SOUTH OF THE BOUNDARY REMAIN STRONGLY
CAP. THE LOW LEVEL JET AT 35 KT CONTINUES TO IMPINGE UPON THE
BOUNDARY...AND A BRIEF WEAK THUNDERSTORM DEVELOP ALONG THE BOUNDARY
AN HOUR AGO. HOWEVER THE STORM WAS NOT ABLE TO DEVELOP AN ORGANIZED
STRONG UPDRAFT. AS THE LOW LEVEL JET INCREASES...CONVECTION IS
EXPECTED TO DEVELOP NORTH OF THE BOUNDARY...BUT MAY NOT BE
SUFFICIENT TO INITIATE STORMS ALONG THE BOUNDARY. THUS...THE
TORNADO WATCH MAY BE CANCELLED SHORTLY.
Needless to say, we had lost all hope for initiation, so we started to head back to Tulsa. As we were dropping south on I-35 back into Oklahoma, a storm finally developed and was giving the cap all it could to survive. We stopped to watch it for a few minutes then decided to give it a chance. Once it finally overcame the inversion it exploded and quickly developed into a sculpted supercell with an incredible bell-shaped meso. We approached the cell just as twilight was setting in. The non-stop lightning was something similar to what I had seen just two months earlier in Hoisington, KS on April 21st.
We managed to get inside the "bear's cage" on the southern flank of the meso as a tornado descended in an open field near Murdock, KS. It was nearly 10pm at this point, however the intense lightning made the tornado quite visible. While we would have rather had a daytime tornado, this was still a nice consolation prize. The storm didn't last more than a couple of hours before it ran too far into the stable air north of the OFB, thus promptly ending its life. Unfortunately at the time I didn't have a video camera which had quality low-light capabilities, so this tornado was nothing more than a first-hand experience for me and the three other chasers riding along that day.
The point of my story is there are no absolutes when it comes to
our rules for weather forecasting and chasing. While 95% of the time, a strong cap (12C+ 700 temps) may not be overcome, the 5% in which that rule is broken are the days you hope to be there. If there is one thing I learned from that chase is that persistence pays off.
Also, didn't Vortex II opt out of chasing on May 22 in South Dakota because of their concerns for the cap not breaking?