2010-05-13
East-Central Indiana
2010-05-12 14:00
The SPC has painted a Slight Risk area across Indiana and Ohio for a couple of days. The latest (17Z today) forecast keeps us inside the 30% risk area.
(Paraphrasing the SPC Day 2 discussion) Intensification of showers and thunderstorms along an advancing cold front is expected with afternoon heating/destabilization. With somewhat weak veered boundary layer flow ahead fo the front, only an isolated tornado threat is currently expected. However, the favorably-moist boundary layer and deep-level shear will be more than sufficient to support organized storms and supercells. Large hail is expected, and linear convective organization near and ahead of the advancing front may produce widespread damaging winds. Storms should die down across the region as the cold front pushes through and as sunset nears.
Analyzing the 06Z NAM with BUFKIT, it looks as though intense thunderstorms are likely in Fort Wayne around 14:00 tomorrow; with a better chance of supercells and isolated tornadoes in western Ohio, particularly in the Dayton area, by 17:00. A CAPE of 2615 is expected in the Dayton area at 17:00, with a LI of -5.9, a SWEAT of 441, a BRN of 33.08, and an EHI of 2.21. For BUFKIT screenshots, see 2010-05-13 KDAY Forecast Sounding (contains 2 large images).
The 12Z NAM from twisterdata.com shows a slightly different picture. Compare the 21Z (17:00 EDT) CAPE forecasts over the area (at right). The 06Z NAM showed 3000+ CAPE from just of west of Dayton over to the IN border, then arcing up through Findlay and then back down into south-central OH. The 12Z NAM shows an area of 3000+ CAPE in eastern IN along and north of I-70 (our Target Area), and then another area in central and south-central OH.
The EHI (far left) within the Target Area is greater than 3, and in its northeastern quadrant exceeds 4. The Lifted Index (left) is better than -7 throughout most of the Target Area. Along with a bulk shear of 45-50kts, about a 90° Sfc-500mb crossover, and 25-30kt 500mb storm-relative winds, the Target Area presents the best chase potential close to home so far this season … even better than the conditions last Friday when several chasers, including The TVN Dominator, were in Fort Wayne (and we were in Fort Benning, GA).
2010-05-12 16:30
The 18Z NAM weakens the overall CAPE (right) throughout Indiana and Ohio, moving the best region of CAPE (>2500) over northeastern IN (the new Target Area). Similarly the EHI (middle right) has shifted so that the strongest EHI (>3) is over the new Target Area. The best Lifted Index (far right) is still over the former Target Area (but now is only -6), whereas the LI over the new Target Area is about -5. The bulk shear over the new Target Area is about the same as over the former Target Area, the Sfc-500mb crossover is a little stronger, and the 500mb storm-relative winds are now 20-25kt. The chase potential has dropped, and even though the new Target Area is closer to home, there are more lakes, hills, and trees in the new Target Area. Let's hope the Target Area moves back down to flatter, more open terrain before tomorrow afternoon; and the chase potential rises back up to where it was.
NO-GO
2010-05-13 18:00
It seemed promising for a while earlier this afternoon, as the cool damp morning (temps in the 50s until after noon) quickly became a sultry early afternoon, with a temp of 80° at about 14:00 with a dewpt of nearly 70°. But, the dewpt then began a steady decline, and is now only 60°. This is the case throughout northern IN; chances for any significant weather seem to be steadily eroding.
Earlier in the afternoon, a line of thunderstorms passed from south of Terre Haute, to south of Indy, to mostly south of Dayton. These storms did not become severe.
A bit later in the afternoon, a cell developed just west of Toledo OH and became severe warned as it moved over Lake Erie. However, the cold lake waters quickly killed that cell.
At about the same time, a lone cell developed west-northwest of Kalamazoo MI and tracked eastward north of I-94. It has maintained itself (i.e. but not intensified); it is currently located between Lansing and Jackson and still moving slowly eastward.
Some convection has appeared over northwestern IN and northeastern IL (south of Chicago) over the last hour; but no significant development within that area of convection is evident yet.
My theory was that the high-level cloudiness spewing off the mesoscale system that has traveled out of OK and into southern MO today has put a damper on convective development in our area. The Northern IN WFO offers this explanation:
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NORTHERN INDIANA 458 PM EDT THU MAY 13 2010
.UPDATED… NEGATIVES TO CONVECTIVE INITIATION MENTIONED IN PREVIOUS SHORT TERM DISCUSSION APPEAR TO BE WINNING OUT AS PRE-FRONTAL OUTFLOW BOUNDARIES CONT TO MIX OUT THIS AFTN DIMINISHING FORCING MECHANISMS. THUS HAVE REMOVED REMAINDER OF TORNADO WATCH FROM OUR CWA AND CONTD TREND OF LOWERING POPS FOR LATE THIS AFTN AND TNGT.
&&
.PREV DISCUSSION… /ISSUED 416 PM EDT THU MAY 13 2010/
SHORT TERM…/TONIGHT/
WARM FRONT HAS LIFTED NORTH INTO MI THIS AFTERNOON LEAVING CWA IN UNSTABLE WARM SECTOR OF LOW PRESSURE SYSTEM OVER THE UPR MS VALLEY. TRAILING CDFNT MOVG THROUGH MID MS VALLEY WILL MOVE EAST ACROSS OUR CWA OVERNIGHT. AIRMASS IMMEDIATELY AHEAD OF CDFNT OVER IL IS NOT AS UNSTABLE AS IN OUR AREA DUE TO LINGERING AFFECTS OF MORNING CONVECTION. MODIFIED TAMDAR SOUNDING FROM SBN THIS AFTN ALSO SHOWING WK CAPPING AROUND 6000FT OVER OUR AREA. THIS AND LACK OF A FOCUSING MECHANISM HAS PREVENTED DEEP CONVECTION IN OUR CWA MUCH OF THE DAY. GIVEN THESE NEGATIVES, HAVE LOWERED POPS INTO CHC RANGE FOR THIS AFTN/EVE. ANY STORMS THAT DO DVLP WILL STILL HAVE POTENTIAL TO BECOME SVR WITH VERY UNSTABLE CONDITIONS AND STRONG DEEP LAYER SHEAR AND ALSO WILL LIKELY PRODUCE LOCALLY HEAVY RAINFALL AS PRECIP WATER VALUES POOLING AROUND 1.6 INCHES. HWVR, GIVEN LACK OF WIDESPREAD HEAVY RAIN OVERNIGHT AND QUESTIONABLE COVERAGE OF CONVECTION AHEAD OF TONIGHT`S FRONT, HAVE DECIDED TO DROP AREAL FLOOD WATCH. TRIMMED WRN PORTION OF TORNADO WATCH #167 EARLIER, AND AS APPEARS BEST FORCING MECHANISM ALONG PRE-FRONTAL TROF MOVG INTO SERN INDIANA AND NORTH CENTRAL OH ATTM, WILL PRBLY BE ABLE TO DROP REMAINDER EARLY.
|  IN-AL-99 |
