Indystorm

9 minutes ago, jojo762 said:

Not every day that you see several tornadic supercells at 10am with a 80/50 TOR watch already issued. Going to be interesting to watch this evolve. Not sure what ramifications these current storms will have for the potential in Indiana later quite yet. 

WF tornadoes can be quite active...I remember Utica IL.  Then if you get clearing and heating before the cold front round two can occur.

WF or differential heating boundary in the affected area...PAH is 69/62 and EVV is 57/56.  Helicity high as well.

32 minutes ago, janetjanet998 said:

Sun trying to come out over  SW parts of the outlook area

 

also I'm surprised there isn't a mention over central IL to NW IND for a secondary area

 

 

That area of subsidence you mentioned behind the initial line is where I would anticipate redevelopment later today with the cold front in addition to the emphasis on the enhanced area to the east.

8 minutes ago, HillsdaleMIWeather said:

0Z NAM looks mediocre at first, then supercell city

Yes, the key is to get that early morning convection out of the way to allow for destabilization.  I'm a bit surprised at the amount of cells up near Chi town and nw In as well on NAM 3k 

71 at my place just ne of Indpls today....Felt wonderful.  That warm front and sunshine coming through midday really did the trick.

It seems like we are in rather uncharted territory with a deep 971-972 mb low out in western Kansas. Even if the low fills as it heads east  I'm thinking Thursday will depend on amount of breaks in cloud cover we get and how high the dew point gets in Indiana as key factors for svr potential.

STP is at 3 to 7 across much of central and eastern IN per NAM for Thursday afternoon and evening.

KIND Wed. morning thoughts on Thursday....

.SHORT TERM /Tonight through Friday Night/...
Issued at 354 AM EDT Wed Mar 13 2019

Forecast challenges focus on impacts from gradient winds and severe
storms Thursday as the weakening surface low tracks into the western
Great Lakes by Thursday evening. While some murkiness lingers within
the details which lowers confidence a bit...remain concerned about a
period of high impact weather for central Indiana on Thursday.

The initial axis of prefrontal convection that will expand east from
the High Plains this morning should be located in the vicinity of the
Mississippi River by early evening. While the focus for stronger
convection will remain southwest of the forecast area from mid
evening into the early overnight...expect scattered showers will
overspread the region with some embedded thunderstorms as model
soundings show elevated instability present above an expanding
shallow inversion. Surface flow will be gusty with a strong 850mb
jet nearing 70kts moving through the area late tonight...but the
presence of the strengthening inversion should keep most of the
stronger winds aloft from reaching the near surface layer through
daybreak Thursday.

The bulk of the hi-res guidance shifts most of the prefrontal
convection set to impact the region tonight east of the area
Thursday morning which when coupled with the dynamics present over
the area later in the day...raises the ceiling for potential severe
weather ahead of the occluded boundary during the afternoon. The
initial low level jet will shift east of the area Thursday morning
but a second jet will swing around the base of the upper low over
the Plains and nose back into the region by the afternoon. Further
up in the atmosphere...mid and upper level diffluence will increase
with the presence of stronger jets in both layers over the Ohio
Valley. 100+kts noted at 500mb Thursday afternoon is particular
impressive. BL shear will steadily increase across the area into the
afternoon and while strongest helicities in the 0-1km and 0-3km
layer will be focused east of central Indiana...values remain more
than sufficient to support severe convective development.

With all of the factors present above...confidence is higher in a 2-
4 hour window during the afternoon where storms can develop and may
quickly become severe as they rapidly move east. The key to whether
the severe threat is isolated or more substantial will come down to
available instability and moisture return in the dry slot between
the prefrontal convection and the occluded front. Hi-res guidance
has shifted more ominously in the direction of a potential greater
threat with MLCAPE levels rising to near 1000 j/kg with dewpoints
climbing into the mid and upper 50s within a narrow axis over the
forecast area by 18-19Z. And while lapse rates aloft are a bit lower
than would be desired to support a greater severe threat...there
does appear to be enough of a steepening within the 700-500mb layer
overlaid on the instability axis over the region.

Should this come to fruition...the hi-res solution suggestive of a
broken but potentially potent line of convection developing in the
Wabash Valley around midday and moving east through the afternoon is
becoming a real possibility. All severe threats would be on the
table...damaging winds most prevalent considering the screaming
winds aloft which any stronger cell would be able to tap into.
However...the presence of long curving hodographs courtesy of the
stronger low level helicity levels supports a tornado threat and wet
bulb zero values at 6-7kft also present a hail risk.  As mentioned
above...there is still some detail that model runs later today and
tonight will hopefully clear up...but the threat for severe storms
is higher than it looked to be Tuesday. Stay tuned.

Not to be lost in the growing severe threat is the continued concern
for strong gradient winds outside of any convection due to the
intense flow aloft. Remain reasonably concerned that there could
still be periods Thursday where stronger boundary layer mixing can
occur and support peak gusts rising into advisory criteria at a
minimum. Again...the convective development could scuttle a more
widespread and prolonged high wind threat and with some clarity
still needed...will not introduce any headlines as of yet. Will
however highlight the high wind and severe potential via an SPS.

Yes, I think the April 11, 1965 Palm Sunday tornadoes in IN had a positive tilt trough.  Supposed to get  near 70 here in IN this Thursday. Current CAMS are concerning.

Usual caveats of instability concerns applies this far north this early in season.  I;m waiting for warmer temps and richer dew points.  But ya never know.  Your point on forcing is well taken. o6z NAM 3k says that Thursday afternoon and evening could be rather volatile around parts of central IL and IN.

10 minutes ago, Jackstraw said:

May not be severe but a nice little line moving through central IN.  I'm ready to kick off the chase season 

Portents of things to come.  I shall remember today by having a t storm and 36 degrees early this afternoon.

Met on WTVA doing a detailed play by play on the cell as it heads east to the area just south of Columbus.  Thanks for the link posted above.  Showing power outage reports from the affected area per utility.  Certainly a very low hanging wall cloud if not a TOG.

Looks like a string of several supercells are trying to develop between Winona and Memphis just east of I-55 in Mississippi.

Meso discussion out for possible watch for southern IL along WF with pressure falls and clearing.

 Mesoscale Discussion 0174
   NWS Storm Prediction Center Norman OK
   0317 PM CST Sat Mar 09 2019

   Areas affected...southern Illinois and vicinity

   Concerning...Severe potential...Watch possible 

   Valid 092117Z - 092315Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Isolated strong to severe storms are possible this
   afternoon, with damaging wind or perhaps a tornado.

   DISCUSSION...A warm front continues to move northward across the St.
   Louis area and into southern Illinois, with substantial clearing
   allowing for additional heating as well. Surface analysis shows mid
   50s F dewpoints surging northward, with 2hr pressure falls up to 6
   mb. An axis of near-60 F dewpoints exists over extreme southern
   Illinois southward into Arkansas as of 21Z.

   A small cluster of thunderstorms is currently moving toward the St. 
   Louis area with indications of strong wind gusts. This is very near
   the surface low/upper vort track, and is coincident with strong
   cooling aloft.

   A small window of opportunity might exist for at least isolated
   severe storms ahead of the surface low and near the warm front.
   Forecast soundings indicate instability is weak, but may briefly
   increase enough to support low-topped supercells. Wind shear
   profiles are very strong, and should a supercell form, a tornado
   threat would naturally exist.

   ..Jewell/Thompson.. 03/09/2019

Confirmed tor near Savannah TN by spotters.

Keep an eye on east central MO as well as northern MS.  Clearing has happened behind the initial line of storms and the area is closer to the surface low pressure.

Aside from northern MS area I would watch east central MO from Jeff City east to Illinois where clearing has happened behind the initial line of storms and the area is closer to the surface low itself.

Just joining the discussion after attending a business meeting earlier today.  Thank you Janet for starting this thread in the Tennessee Valley subforum.   SPC was thinking of a possible lull early this afternoon once the first wave of storms moves ne and that differential heating boundary can serve to become a focus.

New Day one has enhanced 10% hatched tor from far southern IL to ne MS.

After initial storms move through the area, 12z WRF-ARW shows an intense supercell developing at 20z from se MO northeastward to Cairo, PAH, EVV and along the Ohio River Valley until it lines out around 00z.  Something to surely be concerned about if this model is correct.  Outside of this sub there is also a significant cell in the Tunica MS region moving ne.

Enhanced shifted northward in the Mississippi Valley to now include PAH and far southern tip of IL with 30% hatched.

Will be interesting to see what SPC thinks.  Yes, the kinematics/dynamics are stronger farther north, but instability is always the fly in the ointment at this time of year.

This evening's NAM 3k shows surface CAPE increasing to over 800 j/kg in sw iN, increasing helicity, and sig tor approaching 2 sw into western KY.   Getting into the warm sector with quite the temp contrast between EVV and IND by OOz.   Will need to bear watching.

Don't know if this is just the NAM being the NAM or if there is any real legitimacy to it.  But I will keep watching the PAH and EVV areas on Sat. for sure.  Depends on if storms can play that WF.  That CAPE and helicity are both increasing though.  We'll see if it holds in future runs.