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Tim from Springfield (IL)

May 26-28 Severe Threat

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SPC still has a Day 2 marginal for Friday that includes MO/IL/IN:

http://www.spc.noaa.gov/products/outlook/day2otlk.html

...Missouri east to the Ohio Valley...
   Substantial variability exists with latest guidance regarding
   thunderstorm development along the frontal boundary across Missouri
   Friday afternoon, and potentially just north of the warm front over
   the Ohio Valley Friday night. Convective inhibition will likely hold
   through much of the day, but frontal convergence may result in
   isolated thunderstorm development in the 21z-03z time frame along
   the cold front. Strong surface-based buoyancy and 35-40 kts of
   deep-layer shear would support severe storms with any sustained
   updrafts. Given uncertainty regarding development, will retain the
   Marginal Risk with this outlook.

   Developing warm advection Friday night and lift with a mid-level
   impulse may result in thunderstorm development north of the warm
   front. Guidance remains divergent regarding the location of the
   front and the potential for development, but believe sufficient
   confidence exists to maintain Marginal Risk across portions of the
   Ohio Valley. Moderate elevated buoyancy and 45 kts of westerly
   mid-level flow would be sufficient for a severe hail and wind risk.
 

 

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Saturday will be the day to watch for severe in at least the southern half of this subforum, including MO, C/S IL & IN, and S OH.  S MO and SW IL (including STL) currently in an Enhanced risk:

http://www.spc.noaa.gov/products/outlook/day3otlk.html

...Central/southern Plains east to the middle Mississippi Valley...
   An MCS with some severe potential may be ongoing at 12z Saturday in
   the Kansas/Nebraska border region, and diurnal intensification of
   this complex is possible with a severe threat extending east across
   the lower Missouri Valley.

   Additional potentially explosive thunderstorm development is
   anticipated in the vicinity of the southward sagging cold front from
   central/eastern Oklahoma northeast into the western Ohio Valley
   Saturday afternoon, and along the dryline from central Oklahoma
   southwest into north Texas. More isolated development is possible
   farther southwest towards the Edwards Plateau region. GFS and ECMWF
   forecast soundings reveal an environment characterized by strong to
   extreme surface-based instability and 40-50 kts of deep-layer shear,
   and storms should rapidly become severe with all severe hazards
   possible, including significant severe hail and wind. Tornado
   potential will exist, and likely be influenced by boundary/storm
   interactions. Upscale growth into multiple clusters appears probable
   late Saturday and Saturday night as a 40-kt southwesterly low-level
   jet develops with a continued severe risk. 

   ...Ohio/Tennessee Valley Region east to the mid-Atlantic...
   Moderate/pockets of strong instability will exist Saturday
   afternoon, and scattered severe thunderstorms are expected to
   develop with diurnal heating, potentially aided by ascent with
   convectively enhanced low-amplitude impulses within the westerly
   mid-level flow. Effective shear ranging from 35-45 kts and steep
   mid-level lapse rates will promote a risk for large hail, damaging
   winds, and an isolated tornado.  Storms may merge into clusters with
   time with a continued severe risk Saturday evening.

   ..Bunting.. 05/25/2017
 

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Friday IL/IN could go if atmo can recover from any morning MCS. Heights will be slowly rising, and no clear new short-wave, but a boundary will remain. LLJ that is frustrating Plains chasers should be pointing toward Hosier Alley on Friday.

Saturday is definitely the day. Reading between the lines of the SPC Enhanced Risk, parts of the Mid-South may be upgraded to Moderate Risk by game time. I'd watch that warm front all the way through the Ohio Valley though. Speed shear is not super strong, but more than strong enough. Directional shear is looking great from surface to WSW aloft. Low level shear will be enhanced along the warm front, along outflow boundaries, ahead of meso lows, and of course east of the synoptic low coming out of Missouri into the Mid-South or Illinois.

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8 hours ago, Wmsptwx said:

In town for the 500 Sunday, not looking great at this point.

Welcome to Indpls.  Although there's currently a 70% chance of showers and t storms Sunday we'll try to get a race in for you.  My main concern is how far north Sat. night's MCS comes and how much lingers into Sunday.

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0z GFS is the opposite of the 0z NAM for Saturday...

1 hour ago, HillsdaleMIWeather said:

0Z NAM gets the instability gradient even further north Saturday.

 

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Day 1 and 2 outlooks about the same this morning from SPC, but new D3 for Sunday introduces a slight risk to as far NE as Indy in time for the 500:

http://www.spc.noaa.gov/products/outlook/day3otlk.html

...Mid Mississippi Valley/Ohio Valley...
   An upper-level trough is forecast to move eastward into the mid to
   upper Mississippi Valley on Sunday as a cold front advances
   southeastward into the Ohio and mid Mississippi Valleys. A moist
   airmass is forecast ahead of the front with surface dewpoints in the
   mid to upper 60s F. This should be enough for the development of
   moderate instability by afternoon across prats of western Tennessee,
   Kentucky, southern Indiana and Ohio. Model forecasts along this
   corridor generally develop scattered convection during the late
   afternoon as the upper-level trough approaches. GFS forecast
   soundings at 00Z/Monday from Memphis, Tennessee northeastward to
   Louisville, Kentucky show MLCAPE values of 2000 to 2500 J/kg with
   0-6 km shear values from 40 to 50 kt. If the convection can develop
   into clusters with discrete cells, then the environment would
   support supercells with large hail, wind damage and possibly a
   tornado threat. If convection tends to organize into line segments,
   wind damage could be the primary threat. A tendency to go linear may
   be the more likely outcome due to unidirectional wind profiles and
   the deep-layer shear vectors being somewhat parallel to the
   boundary. The exact corridor with the highest severe threat will
   likely depend upon the position of the cold front by late Sunday
   afternoon.
 

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5% TOR probs added now for today

.IL/IN/OH  
  
MORNING SATELLITE LOOPS SHOW A WELL-DEFINED MCV OVER EASTERN IA.   
STRONG HEATING/DESTABILIZATION IS OCCURRING ALONG THE SOUTHEAST  
FLANK OF THIS SYSTEM, WITH DEWPOINTS CLIMBING INTO THE 60S.  BY MID  
AFTERNOON, MLCAPE VALUES OF 1000-1500 J/KG ARE EXPECTED AS FAR  
NORTHEAST AS FROM NORTH-CENTRAL IL INTO CENTRAL IN AND WESTERN OH.   
THUNDERSTORMS ARE LIKELY TO DEVELOP AHEAD OF THE MCV, WITH 12Z CAM  
SOLUTIONS STRONGLY FAVORING A BOWING MCS MOVING ACROSS CENTRAL IN  
INTO WESTERN OH.  WHILE DAMAGING WINDS ARE LIKELY THE MAIN THREAT,  
INCREASING LOW-LEVEL VERTICAL SHEAR BY LATE AFTERNOON MAY ALSO  
CONTRIBUTE TO SOME RISK OF A FEW TORNADOES.  THE ACTIVITY SHOULD  
WEAKEN AS IT MOVES INTO MORE STABLE AIR OVER CENTRAL OH THIS  
EVENING.  

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REA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
1252 PM CDT FRI MAY 26 2017  
   
MESOSCALE DISCUSSION  
  
1249 PM CDT  
  
WELL DEFINED MCV LIFTING ENE ACROSS THE MISSISSIPPI RIVER EARLY  
THIS AFTERNOON IS HELPING TO SPARK SOME RENEWED CONVECTION ALONG  
ITS SOUTHERN FLANK WITHIN AN INCREASINGLY UNSTABLE WARM SECTOR   
JUST SOUTHWEST OF THE LOT CWA. AREA OBSERVATIONS AND SATELLITE   
IMAGERY INDICATE A WARM FRONT IS DRAPED FROM NEAR MLI SOUTHEAST   
THROUGH BMI TOWARDS CMI AND IS EXPECTED TO GRADUALLY LIFT INTO THE  
SOUTHERN HALF OF THE LOT CWA THROUGH MID TO LATE THIS AFTERNOON.   
WITHIN THE WARM SECTOR, DEW POINTS ARE INCREASING INTO THE LOW TO   
MID 60S WHICH IS CONTRIBUTING TO 1000+ J/KG MLCAPE. THIS IS   
ACCOMPANIED BY 40-50KT 0-6KM SHEAR ALONG WITH A CORRIDOR OF   
ENHANCED EFFECTIVE SRH IN THE VICINITY OF THE WARM FRONT. THIS   
POINTS TO A DEVELOPING SUPERCELL THREAT ACROSS PORTIONS OF CENTRAL  
ILLINOIS THAT MAY POSSIBLY CONTINUE INTO EAST CENTRAL ILLINOIS   
LATER TODAY, WITH A NON-ZERO TORNADO THREAT PARTICULARLY NEAR THE   
WARM FRONT. THE PRIMARY SEVERE THREATS CONTINUE BE LARGE HAIL AND   
DAMAGING WINDS. EXPECTED STORM MOTIONS AND BUNKERS RIGHT MOVING   
SUPERCELL VECTORS ARE FAIRLY NORMAL TO THE ORIENTATION OF THE WARM  
FRONT WHICH WILL HELP LIMIT RESIDENCE TIME FOR ANY INDIVIDUAL   
STORM ON THE BOUNDARY, WITH THE SEVERE THREAT RAPIDLY DIMINISHING   
NORTH OF THE FRONT. STORMS SHOULD EVENTUALLY CONGEAL INTO A LINE   
WITH PROPAGATION ESE ALONG THE INSTABILITY GRADIENT. A QLCS   
TORNADO THREAT WOULD STILL EXIST GIVEN THE FAVORABLE SHEAR. THE   
GREATEST SEVERE THREAT SHOULD START TO EXIT EAST OF THE CWA BY   
EARLY TO MID EVENING.  
  
DEUBELBEISS  

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Mesoscale Discussion 0845
   NWS Storm Prediction Center Norman OK
   0125 PM CDT Fri May 26 2017

   Areas affected...Central and eastern Illinois and far western
   Indiana

   Concerning...Severe potential...Watch possible 

   Valid 261825Z - 262100Z

   Probability of Watch Issuance...60 percent

   SUMMARY...An area of convection over western Illinois will gradually
   intensify while moving eastward into the discussion area.  A WW will
   be considered around/just after 20Z.

   DISCUSSION...Convection over western Illinois is moving eastward
   along and just north of a subjectively analyzed surface boundary
   lifting slowly northward across central/eastern Illinois.  Along and
   south of this boundary, weak to moderate instability has developed
   in response to warming surface temperatures (nearing 80F) and low to
   mid-60s dewpoints.  This warm front will continue to lift northward
   slowly during the day, and the attendant increase of instability and
   lift associated with an approaching remnant mesoscale convective
   vortex over northwestern Illinois will foster scattered
   thunderstorms capable of hail and damaging wind gusts.  A few
   tornadoes will also be possible owing to backed surface flow in
   vicinity of the lifting warm front/surface boundary especially if
   convection can maintain a favorable (cellular) storm mode.

   Convective trends will be monitored for a possible WW issuance
   around or just after 20Z.

   ..Cook/Hart.. 05/26/2017

mcd0845.gif

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ULLETIN - EAS ACTIVATION REQUESTED  
TORNADO WARNING  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL  
435 PM CDT FRI MAY 26 2017  
  
THE NATIONAL WEATHER SERVICE IN CHICAGO HAS ISSUED A  
  
* TORNADO WARNING FOR...  
  SOUTHEASTERN LIVINGSTON COUNTY IN CENTRAL ILLINOIS...  
  FORD COUNTY IN EAST CENTRAL ILLINOIS...  
  SOUTHWESTERN IROQUOIS COUNTY IN EAST CENTRAL ILLINOIS...  
  
* UNTIL 515 PM CDT  
      
* AT 435 PM CDT, A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO  
  WAS LOCATED NEAR GIBSON CITY, MOVING EAST AT 35 MPH.  
  
  
           DAMAGE IS LIKELY.   
  
* THIS DANGEROUS STORM WILL BE NEAR...  
  PAXTON AND BUCKLEY AROUND 500 PM CDT.   

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4 minutes ago, Hoosier said:

No confirmation yet but the latest updated statement mentions funnel clouds.

Circulation is getting better organized too, pretty strong inflow into the storm.

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Just now, Stebo said:

Circulation is getting better organized too, pretty strong inflow into the storm.

Was pretty messy about 10min ago as it went through a rough cycle as it interacted with another cell forming to the south, however appears to be regaining its composure now and organization appears to be increasing again.

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Just now, NWLinnCountyIA said:

Was pretty messy about 10min ago as it went through a rough cycle as it interacted with another cell forming to the south, however appears to be regaining its composure now and organization appears to be increasing again.

Yeah I would be very concerned as it looks like it might produce any moment now.

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5 minutes ago, Stebo said:

Yeah I would be very concerned as it looks like it might produce any moment now.

Agreed. Inflow increasing scan by scan as well as gradually tightening up. Rankin needs to pay attention here as its gonna pass close by.

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10 minutes ago, JasonOH said:

Still no debris signature. Any CC drop is in the BWER, so it means nothing.

Looking at the radar presentation....I think these storms may be slightly elevated above a shallow warm/inversion layer so far...diminishing their full Tornado potential so far

 

but not hail

..A TORNADO WARNING REMAINS IN EFFECT UNTIL 545 PM CDT FOR NORTHERN  
VERMILION AND NORTHEASTERN CHAMPAIGN COUNTIES...  
      
AT 528 PM CDT, A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO  
WAS LOCATED NEAR POTOMAC, OR 11 MILES SOUTH OF CLAYTONVILLE, MOVING  
EAST AT 35 MPH.  
  
HAZARD...TORNADO AND TENNIS BALL SIZE HAIL.   
  
SOURCE...RADAR INDICATED ROTATION. AT 526 PM A TRAINED SPOTTER   
         REPORTED TENNIS BALL SIZE HAIL IN RANKIN.   

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