Chase Log: April 24, 2002 – Dawn Patrol

http://www.spc.noaa.gov/climo/reports/020424_rpts.html NWS data for April 24
It’s about 1:30 am here in Story County. The SPC has just issued the following discussion:

SPC MESOSCALE DISCUSSION 0490 FOR ERN NEB AND WRN IA CONCERNING…SEVERE THUNDERSTORM POTENTIAL… VALID 240342Z – 240700Z
CONVECTIVE INITIATION IS EXPECTED ACROSS ERN NEB BETWEEN 23/05Z AND 07Z. POTENTIAL EXISTS FOR DAMAGING WINDS AND SEVERE HAIL WITH STORMS IN ERN NEB AND WRN IA OVERNIGHT. WE ARE CURRENTLY MONITORING THE AREA FOR A POSSIBLE SEVERE THUNDERSTORM WATCH.
AT 0330Z…A STRONG SEWD MOVING COLD FRONT WAS LOCATED FROM 25 W MHE TO 35 N LBF. WIND GUSTS IN EXCESS OF 50KT HAVE BEEN OBSERVED WITH GRADIENT WINDS AND A NWLY LOW-LEVEL JET IN POST-FRONTAL REGIME ACROSS CENTRAL SD LATE THIS EVENING. STRONG LOW-LEVEL CONVERGENCE ASSOCIATED WITH THE FRONT WILL INTERACT WITH SURFACE DEWPOINTS IN THE MID 50S TO AROUND 60 ACROSS THE DISCUSSION AREA DURING THE OVERNIGHT PERIOD. A 50KT SLY LOW-LEVEL JET OBSERVED AT OMAHA AT 0330Z SHOULD CONTINUE TO MAINTAIN OR IMPROVE LOW-LEVEL MOISTURE PROFILE OVER ERN NEB AND WRN IA IN ADVANCE OF THE FRONT. STRONG LOW-LEVEL FORCING AND 100MB MLCAPE VALUES BETWEEN 500-1000 J/KG WILL LIKELY RESULT IN A RAPIDLY DEVELOPING…NARROW LINE OF CONVECTION COINCIDENT WITH THE BOUNDARY AS IT MOVES SEWD. STORMS WILL LIKELY FIRST DEVELOP ALONG A LINE FROM OFK TO GRI BETWEEN 05Z AND 07Z. WBZ HEIGHTS AROUND 7 KFT SUGGEST SEVERE HAIL WITH STRONGER CELLS WITHIN THE LINE. INTENSITY OF FRONT ALSO SUGGESTS DAMAGING WIND GUSTS WILL BE LIKELY WITH PASSAGE OF CONVECTIVE LINE LATE TONIGHT AND INTO THE EARLY MORNING HOURS ACROSS ERN NEB AND WRN IA

So I’m up monitoring the situation. Seems I’ll be looking at weather in an hour or two.

7:50 am.

URGENT – IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 144
STORM PREDICTION CENTER NORMAN OK
722 AM CDT WED APR 24 2002

THE STORM PREDICTION CENTER HAS ISSUED A SEVERE THUNDERSTORM WATCH FOR PORTIONS OF
CENTRAL AND SOUTHERN IOWA
NORTHEAST KANSAS
NORTHERN AND WESTERN MISSOURI
SOUTHEAST NEBRASKA

EFFECTIVE THIS WEDNESDAY MORNING AND AFTERNOON FROM 730 AM UNTIL 100 PM CDT.

HAIL TO 2 INCHES IN DIAMETER…THUNDERSTORM WIND GUSTS TO 70 MPH…AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.  THE SEVERE THUNDERSTORM WATCH AREA IS ALONG AND 100 STATUTE MILES EITHER SIDE OF A LINE FROM 25 MILES WEST OF LEAVENWORTH KANSAS TO  45 MILES NORTHEAST OF DES MOINES IOWA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS AND POSSIBLE WARNINGS.  SEVERE THUNDERSTORMS CAN AND OCCASIONALLY DO PRODUCE TORNADOES.

DISCUSSION…POST FRONTAL CONVECTION EXPECTED TO INCREASE IN COVERAGE OVER THE NEXT SEVERAL HOURS AS STRONG COLD FRONT CONTINUES TO UNDERCUT PLUME OF VERY MOIST/UNSTABLE BUT CAPPED INFLOW ORIGINATING OVER THE SRN PLAINS.  WHILE STORMS SHOULD SHOW AN ELY OR ENELY MOTION…OVERALL CLUSTER/BAND OF STRONGEST ACTIVITY EXPECTED TO MOVE MORE ESE OR SE WITH TIME.  PRIMARY THREAT WILL BE LARGE HAIL. MEAN STORM MOTION VECTOR 26035.

I’m going mobile…  7:57am

It’s 8am, I’m in my truck and I have a decision to make. The main line will be here in just under two hours. I could wait for it and maybe get some winds and hail. But as seen on that radar map there was a storm farther west and south that had signatures of Meso rotation. I decided to head for Perry, Iowa

I started driving and was surprised that the NWS hadn’t called NA0R in to operate K0DMX yet. however I was about half way there and NA0R checked into the linked system and advised us that he was on his way to the NWS office (doing the speed limit I’m sure).
I was at Madrid when enough spotters were reporting in that NA0R-mobile decided to formalize the SKYWARN net.

I continued westward and southward and set up shop around HWY 144 / HWY 169. NA0R mobile, now K0DMX, at the NWS office told me that it would be 30-45 minutes before a cell reached my location. but he also mentioned that I might want to “drift” south. so I drifted.

Just as I got to Adel some time later, a cell was passing over me. There were two concentrations of activity. One to my south, and one to my north-ish. It appeared to be one cell that was elongating and dissipating somewhat due to the spreading of it’s updraft energy. K0DMX confirmed this on radar and I told him that due to the apparent intensity of the north cell I would track it. Jim was quick to note that the south cell was the strongest on radar

Often cells appear stronger from a spotter’s perspective as they dissipate because they begin to lose the updraft and drop everything they have whereas the updraft of a stronger cell will keep more of the moisture and hail aloft and appear to be the weak cell when it may be a healthy growing cell. It’s hardest to tell which cell is strongest when you can’t see any of the mid and upper level features of a cell or storm system.
Taking into consideration what Jim said, I turned around and began to track the south branch of the storm. I noted and reported a shelf cloud. The shelf cloud was pretty high and was extending between and in front of the two precipitation shafts one on the north and one on the south. It was one of the weirdest shelf clouds I’ve seen.

I got on HWY 6 just east of Adel and I pulled off into a gravel median. (you know the one’s in the middle of a divided highway that say No U-Turns / Emergency or Authorized vehicles only). I watched the cell for a few minutes, reported very gusty winds upwards of 50mph with heavy rains and several cloud to ground strikes with very litte in cloud lightning.

9:34AM – I was back in Adel headed for Desoto. Jim had told me that there wasn’t anything else, “much”. He said he didn’t want to get me too far out of ‘my area.’ I told him I was up for anything. (hey I started in Ames, what’s another 10 miles?) So he ‘suggested’ that I make my way to Desoto. I made my way..
As I arived in Desoto the cell met me, I encountered 50+ mph winds, and pea to dime sized hail with heavy downpours

10:00AM the cell has just moved out of Desoto and now I have gentle rain with some wind. The NWS issues a Warning for a few counties away but I don’t see any way I could get in front of those storms, catch them? maybe, get in position, doubtful.

I call K0DMX and report the end of the cell and current weather. He notes no other storms in area and suggests I call it a morning. I took him up on the offer.

Going though Des Moines I was tempted to stop at the NWS office and say hey… but got behind a semi and didn’t see the exit till I passed it, I opted not to turn around.

11:04 AM Back at Ames.

—    a generally boring morning. was expecting a bit more out of the storms, oh well. there’s always another one.

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