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Significant Severe Weather Threat Friday 10/4


tornadotony

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6hr projection off the mesoanalysis ***time sensitive*** of the effective sig tor and 0-3km CAPE surface vorticity

 

 

 

 

Pretty strong signals torward Western IA of any supercell having a very good potential of a strong tornado associated with them around 21 to 23z.

 

Yes, low-level shear values forecast by the RAP are quite impressive; >300 m2s-2 0-1 km SRH over eastern Iowa at 23z.

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I think most of SPC's concerns remain focused on convective evolution. For instance, RAP remains hesitant on destabilization in the Missouri River area, more bullish further east. The round of supercells  the HRRR develops this evening around the MIssouri River do not backbuild enough to tap the extreme instability further south. 

 

Of course the parameters are such that the supercells to the east will rotate as well -- but overall I think there's still quite a lot of uncertainty.

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Hanging in west Omaha - ready to move north and west to meet the arc of storms that look like they will form in the next 2 to 3 hours.  looking like just north of Grand Island is where the triple point is setting up expect initiation in 1 to 2 hours to the northeast of that area, then quickly move northeast.  Satellite trends are really holding that boundary further south than any of the models except maybe the RAP have shown.  I think far northeast Nebraska, southern MN, northwest Iowa may be too far north.  The further south that boundary stays the more ominous it becomes for Omaha metro.

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I think most of SPC's concerns remain focused on convective evolution. For instance, RAP remains hesitant on destabilization in the Missouri River area, more bullish further east. The round of supercells  the HRRR develops this evening around the MIssouri River do not backbuild enough to tap the extreme instability further south. 

 

Of course the parameters are such that the supercells to the east will rotate as well -- but overall I think there's still quite a lot of uncertainty.

1kmv.gif?1380910245300

 

Shouldn't be any questions by now...

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My research shows that on Oct.14, 1966 twelve tornadoes hit IA including an F-5 at Belmond. Blizzard warnings were out for CO and WY and 4 inches of snow later fell in the Sioux City area.  IA certainly has a record of powerful storms in October.

Yeah I have been thinking about that event for the past few days. Though the Belmond tornado probably would be rated EF3/EF4 by today's standards. 

 

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I may venture out west of Oklahoma City a bit later this afternoon. The past few runs of the HRRR have been consistent in showing a discrete supercell (tail-end charlie) moving towards the OKC metro from the west/southwest this evening. At least that would prove entertaining for structure shots and maybe some hail.

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MESOSCALE DISCUSSION 1931
NWS STORM PREDICTION CENTER NORMAN OK
0128 PM CDT FRI OCT 04 2013

AREAS AFFECTED...PARTS OF ERN NEB/NERN KS/SWRN AND CENTRAL IA/NWRN
MO

CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY

VALID 041828Z - 042030Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...ONGOING EVOLUTION OF THE ENVIRONMENT INVOF THE MID MO
VALLEY CONTINUES TO SUGGEST SLOWLY INCREASING SEVERE RISK. WW
ISSUANCE WILL LIKELY BE REQUIRED IN THE NEXT 1-2 HOURS AS SEVERE
POTENTIAL -- INCLUDING THE RISK FOR A FEW TORNADOES -- EVOLVES.

DISCUSSION...LATEST VISIBLE SATELLITE IMAGERY SHOWS LITTLE IN THE
WAY OF SURFACE-BASED CU DEVELOPMENT IN PROXIMITY TO THE SURFACE LOW
OVER CENTRAL NEB AND ASSOCIATED/ATTENDANT COLD/WARM FRONTS. AN 18Z
RAOB FROM TOP INDICATES THAT CAPPING REMAINS IN PLACE...THOUGH
HEATING/MIXING WILL CONTINUE TO ERODE THE INVERSION WITH TIME --
AIDED BY ASCENT INVOF THE SURFACE SYSTEM.

ATTM...GREATEST RISK FOR INITIAL DEVELOPMENT APPEARS TO EXIST OVER
SERN NEB AND NERN KS -- I.E. JUST SOUTHEAST OF THE SURFACE LOW --
SOMETIME WITHIN THE NEXT 1-2 HOURS.
AS HEATING OF THE MOIST
BOUNDARY LAYER INTO THE LOW TO MID 80S SUPPORTS MIXED-LAYER CAPE NOW
INTO THE 1000 TO 2000 J/KG RANGE...VIGOROUS UPDRAFTS SHOULD EVOLVE
RATHER QUICKLY AFTER INITIAL ONSET OF DEEP CONVECTIVE DEVELOPMENT.
ORGANIZATION WILL BE AIDED BY A FAVORABLY STRONG DEEP-LAYER WIND
FIELD FEATURING FLOW THAT VEERS MARKEDLY WITH HEIGHT -- PARTICULARLY
NEAR AND TO THE COOL SIDE OF THE WARM FRONT EXTENDING ESEWD ACROSS
FAR SERN NEB AND THE NRN TIER OF NWRN MO COUNTIES.
ALONG WITH AN
EVENTUAL RISK FOR LARGE HAIL AND LOCALLY DAMAGING WINDS...THE RISK
FOR A FEW TORNADOES IS ALSO APPARENT -- PARTICULARLY WITH STORMS
DEVELOPING IN THE ZONE OF STRONGEST LOW-LEVEL SHEAR INVOF THE WARM
FRONT.

 

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