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sbnwx85

Severe Threat 8/12/19

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I haven't ever started a new thread before so a mod can feel free to change something if needed. This has been discussed in the short/medium range severe thread but it's not everyday we get a 10% hatched TOR threat from SPC in this region...especially in August. There's a chance this becomes an impressive, if not small, regional outbreak so let's get the party started.

Discussion also mentions possible upgrade to moderate risk.

Quote

Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Mon Aug 12 2019 Valid 121630Z - 131200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SOUTHEAST IA TO WEST-CENTRAL IN... ...SUMMARY... A few tornadoes, a couple possibly strong, and significant damaging winds will be likely across southeast Iowa through central Illinois, mainly this evening. ...IA/IL/IN... An upgrade to Moderate Risk for tornado and/or wind may become necessary in later outlooks today. A leading MCV is tracking east into eastern IA with a lingering surface cyclone centered over west-central IA. This latter feature should move east into northern IL through this evening. Diffuse convective outflow from remnant leading MCS over southern IL has been shunted across southeast to northwest MO. Nevertheless, air mass recovery is underway north of the boundary into extreme southern IA and west-central IL. Further erosion of the prior cold pool amid cloud breaks should yield at least weak to moderate surface-based buoyancy by late afternoon in IA to northern IL. More robust destabilization is expected farther south where greater unimpeded insolation occurs while a plume of 77-81 F surface dew points is advected north from the Mid-South. Despite relatively warm mid-level temperatures, the very rich boundary-layer moisture and surface heating should yield a plume of large buoyancy with MLCAPE likely reaching 3000-4000 J/kg across much of MO into central/southern IL. Renewed thunderstorm development is probable towards late afternoon near the surface cyclone in southeast IA and during the early evening to the southeast in central IL within a corridor of strengthening low-level warm advection. The initial storms will likely be supercells capable of producing all hazards, given the enhanced low-level shear/hodograph curvature near the cyclone/warm front. Hodographs aloft should tend to favor relatively quick upscale growth, but even semi-discrete supercells will pose a risk for at least a few tornadoes, a couple of which be may strong. A forward-propagating MCS should eventually evolve along the MLCAPE gradient from central IL into central IN where severe wind gusts will remain a threat before weakening overnight. ...TX Panhandle to southern KS/northern OK... A remnant midlevel trough will drift slowly east-northeastward over the TX Panhandle, as a weak cold front moves slowly southeastward from KS/CO. Surface heating and deep mixing will result in inverted-v profiles along and south of the front, and will support the potential for isolated strong downburst winds. Convection will tend to develop east-northeastward tonight along the front, with strong downdrafts still possible in an environment of lingering large CAPE/DCAPE. ...ME... A midlevel trough over James Bay will pivot east-southeastward to Maine overnight. In advance of this trough, a weak pre-frontal trough at the surface and band of weak ascent will provide a focus for thunderstorm development this afternoon. Though moisture and lapse rates will be modest, increasing deep-layer westerly shear and surface heating on the south edge of the thicker clouds could support storms capable of producing isolated damaging gusts and marginally severe hail. ...Dakotas... Widespread clouds and rain are spreading slowly eastward across the eastern Dakotas in association with a couple of diffuse MCVs from overnight convection. A little clearing of clouds and surface heating will be possible from west to east this afternoon, in advance of a larger-scale trough moving east-southeastward from MT to ND. Isolated thunderstorm development and a low-end severe threat will be possible this afternoon if sufficient near-surface destabilization occurs, given enough vertical shear for organized storms. ..Grams/Dean.. 08/12/2019

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I have to wonder how that 60kt 500mb speed max  currently over eastern IA will play a role...

it is forecast to move into IND and weaken decreasing deep layer shear

in fact 16z RAP only has 35-40 kt flow at 00z over IL..unless it is weakening it too fast

with COD down....can't view the radar VADs

 

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a couple hours old but DVN update..mentionss faster movement of the speed max or MCV

.UPDATE...
Issued at 1145 AM CDT Mon Aug 12 2019

An MCV and upper level shortwave were moving into east central
Iowa at 11 am, spawning a large area of redeveloping showers as
the lift was encountering the destabilizing airmass over southeast
Iowa, northeast MO and west central IL. With MUCAPES of 1000
J/KG, this activity that formed over the last hour has yet to
produce lightning, but could intensify as the large scale lift
from the shortwave spreads east-southeast into an area that has
seen filtered sunshine. Bulk shear values of 30 to 40 kts in the
0-3 km layer in this same area will also favor intensification.

These trends have so far not been handled by high res convective
allowing models, which continue to catch up to the faster
progression of the MCV. Will still need to watch for the track
and timing of the main surface low out over west central IA late
this morning, which will be the main trigger for additional storms
later this afternoon and evening as 12Z global models have this
feature reaching west central IL by 00Z. Trends with cloud cover
and how much surface CAPE develops in the wake of the current
activity will be critical as there may be sufficient low level
shear/helicity along the surface boundary and low center for
supercells and related severe weather hazards including tornadoes.
This is outlined in SPC`s Enhanced Risk area maintained over SE
IA into west central IL.

The forecast has been updated for the trends with less
thunderstorm coverage, but widespread showers late morning into
early in the afternoon. This may also hold high temperatures down
some, especially across the north.

 

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ILX and DVN are doing special soundings now so SPC is likely waiting to see what they reveal before issuing a MCD.

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The forecasts for 0-3 km shear late afternoon/early evening are definitely something to keep an eye on. 

~ 40 knots (westerly vector). As this grows upscale into a line, any N/S bowing segment could be pretty nasty with that background environment.

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First MD of the event is out: https://www.spc.noaa.gov/products/md/md1717.html

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Quote

Mesoscale Discussion 1717 NWS Storm Prediction Center Norman OK 0346 PM CDT Mon Aug 12 2019 Areas affected...Central/southeast IA...Northern IL...Far northeast MO Concerning...Severe potential...Tornado Watch likely Valid 122046Z - 122215Z Probability of Watch Issuance...80 percent SUMMARY...Thunderstorms capable of primarily damaging winds and a few tornadoes are possible late this afternoon into the evening. Tornado watch issuance is likely prior to 23Z. DISCUSSION...An MCV is currently moving through the upper Mississippi Valley, with a weakening area of primarily stratiform rain noted across northeast IA into northern IL. In the wake of the MCV, clearing has been noted across central into southeast IA, with cumulus gradually increasing along an outflow/differential heating boundary from west-central IL into southeast IA. Lapse rates are generally weak across this region, but continued heating of a very moist low-level airmass will result in the development of moderate to locally strong buoyancy (MLCAPE of 1500-3000 J/kg) from southeast IA into northwest/central IL. Forcing for ascent will be somewhat nebulous in the wake of the leading MCV, but scattered thunderstorm development is eventually expected in the vicinity of the surface boundary and a weak surface low across central IA. Area VWPs and the 20Z ILX sounding depict sufficient deep-layer shear for organized convection, and initial development will include the potential for a few discrete supercells. Some increase in low-level flow/shear is expected with time into the evening, and a tornado threat will evolve with any supercell, particularly in the vicinity of the surface boundary which may move slowly northward over the next 2-3 hours. A strong tornado will be possible if any supercell can become sustained in the zone of enhanced low-level helicity near and just north of the boundary. Otherwise, locally severe wind gusts and marginally severe hail will be possible with any discrete convection. Most HREF members depict some sort of upscale growth this evening into portions of central IL, which would pose an increasing risk of more widespread damaging winds and potentially QLCS tornadoes. Tornado watch issuance by 23Z is likely in order to cover these threats, though earlier watch issuance is possible if deep convective initiation appears imminent. ..Dean/Grams.. 08/12/2019

 

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Our flight from Houston to ORD with a 5:51 departure time delayed an hour. They say it is an air traffic control delay due to expected weather. Gotta be a pretty standard preemptive thing. Would be neat to get a view of some boomers from up top.

Sent from my SM-N960U using Tapatalk

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Boundary is pretty evident on satellite, but you can also see a nice wind shift from AWG to MPZ. 

To the east it is lifting a little bit (moving into the GBG vicinity now). Will also have to watch the area between the low level stratus and the aforementioned boundary though. Quickly modifying and has the best combination of low LCLs and high shear.

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4 minutes ago, janetjanet998 said:

So far not much .. I think there is an inversion layer and the cloud cover helped to keep Instability down 

ILX special is probably more representative than DVN. DVN looks pretty rain cooled overall.

ILX though is pretty nice looking if storms can punch that low level inversion (which they should with some cooling lift/saturation).

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29 minutes ago, OceanStWx said:

ILX special is probably more representative than DVN. DVN looks pretty rain cooled overall.

ILX though is pretty nice looking if storms can punch that low level inversion (which they should with some cooling lift/saturation).

I could tell visually around 4 there was an inversion .... and the CU was shallow

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24 minutes ago, janetjanet998 said:

The meso came out 3 hours ago and said watch Likely by 23z if not sooner .. it’s almost 00z.    Another clue of a problem 

Yeah pretty classic "wait and see", but given the convection increasing in coverage they will probably make a decision soon.

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3 minutes ago, OceanStWx said:

Yeah pretty classic "wait and see", but given the convection increasing in coverage they will probably make a decision soon.

The 0100z SPC OTLK also should be out shortly - in the next 30 minutes or so - that should be an interesting read as well

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38 minutes ago, yoda said:

The 0100z SPC OTLK also should be out shortly - in the next 30 minutes or so - that should be an interesting read as well

Which is delayed a few minutes...

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AY 1 CONVECTIVE OUTLOOK    
NWS STORM PREDICTION CENTER NORMAN OK  
0801 PM CDT MON AUG 12 2019  
  
VALID 130100Z - 131200Z  
  
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM IL TO  
SOUTHWEST OH...  
   
..SUMMARY  
  
SCATTERED SEVERE THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS EVENING  
ACROSS ILLINOIS AND INDIANA INTO SOUTHWEST OHIO LATER TONIGHT.  
DAMAGING WINDS ARE THE PRIMARY THREAT.  
   
..01Z UPDATE  
  
ORGANIZED DEEP CONVECTION HAS STRUGGLED TO DEVELOP EARLY THIS  
EVENING ACROSS THE MID MS VALLEY IN THE WAKE OF EARLY-DAY REMNANT  
MCS. 13/00Z SOUNDING FROM DVN SUPPORTS THIS DELAYED DEVELOPMENT WITH  
POOR LAPSE RATES AND SEASONALLY WEAK BUOYANCY. HOWEVER, ILX EXHIBITS  
SUBSTANTIAL MUCAPE WITH AMPLE SHEAR FOR SUSTAINED ROTATING UPDRAFTS.  
OVER THE LAST HALF HOUR OR SO SCATTERED UPDRAFTS HAVE GRADUALLY  
DEEPENED ACROSS CENTRAL IL SUCH THAT LIGHTNING IS NOW OBSERVED ALONG  
A CORRIDOR FROM ADAMS COUNTY TO MACON COUNTY. LATEST THINKING IS  
CONVECTION WILL GRADUALLY GROW UPSCALE, SHIFTING EAST TOWARD CENTRAL  
IN WITHIN BROAD WESTERLY FLOW REGIME. HAVE LOWERED SEVERE PROBS  
ACROSS MUCH OF IA AND NORTHERN IL TO REFLECT A MORE NARROW CORRIDOR  
OF EXPECTED SEVERE. DAMAGING WINDS SHOULD BE THE GREATEST SEVERE  
RISK WITH THIS ACTIVITY.  
  
ELSEWHERE, ISOLATED SUPERCELL HAS DEVELOPED AHEAD OF UPPER TROUGH  
SOUTH OF MOT. THIS STORM HAS EVOLVED ALONG PROGRESSIVE FRONT AND  
SHOULD PROPAGATE SOUTHEAST ALONG A NARROW CORRIDOR OF INSTABILITY  
WITH AN ATTENDANT THREAT FOR PRIMARILY HAIL.  
  

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LOT mentions convection is elevated 


AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
713 PM CDT MON AUG 12 2019  
   
MESOSCALE DISCUSSION  
  
713 PM CDT  
  
THE CONVECTIVE THREAT ACROSS THE AREA HAS DIMINISHED SOMEWHAT  
SINCE EARLIER. WE STILL CONTINUE TO MONITOR FOR SEVERE POTENTIAL,  
MAINLY SOUTH OF A LINE FROM LA SALLE-PERU TO KANKAKEE TO   
RENSSELAER. NORTH OF THERE, FOR ROCKFORD TO CHICAGO, THE POTENTIAL  
FOR WIDESPREAD EVENING THUNDERSTORMS HAS ALSO DIMINISHED SOME.  
LOCALLY HEAVY RAINFALL THOUGH IS A GIVEN WITH ANY DEEPER SHOWERS  
TONIGHT.  
  
DETAILS HAVE BECOME MORE CLEARER WITH THE GENERAL CONVECTIVE   
EVOLUTION FOR TONIGHT, BUT CERTAINLY STILL SOME FUZZINESS. THE   
LATEST SURFACE ANALYSIS HAS A A 1007 MB LOW NEAR THE SOUTHEAST   
IOWA BORDER WITH MISSOURI. AN ATTENDANT SLOW-MOVING WARM FRONT IS   
DRAPED TO THE EAST-SOUTHEAST, TO JUST SOUTH OF BLOOMINGTON-   
NORMAL. TO THE NORTH OF THERE, SOME REINFORCEMENT FROM A   
STATIONARY BOUNDARY THAT MAY BE LAKE-ENHANCED, IS INCHING   
SOUTHWEST. BETWEEN THESE TWO BOUNDARIES IS AN AREA OF VERY LIGHT   
EASTERLY SURFACE FLOW ALTHOUGH WITH MID 70S DEW POINTS AND STRONG   
SHEAR PROFILES ALOFT DUE TO 45-50 KT 700-500 MB FLOW AND VEERING   
PROFILES FROM 1-4 KM. ISOLATED, SHALLOW CONVECTIVE INITIATION   
THAT HAS OCCURRED IN THIS QUASI-WARM FRONTAL ZONE HAS BEEN   
SUPERCELLULAR PER RADAR AND SPOTTER PHOTOS, BUT ALMOST ENTIRELY   
ELEVATED WITH ROTATION ABOVE 1 KM. THIS HAS BEEN NON-SUSTAINING   
AND THAT IS LIKELY DUE TO WEAK LAPSE RATES AND LIMITED EFFECTIVE   
PROFILES. SOME DEEPER, LOWER ROOTED CONVECTION HAD RECENTLY DONE A  
LITTLE BETTER SOUTH OF BLOOMINGTON NEAR THE EFFECTIVE FRONT.  
  
AS A SHORT WAVE ACROSS NORTHERN MISSOURI APPROACHES, WARM ADVECTION   
ALOFT STRENGTH SHOULD CONTINUE TO INCREASE, WITH 25 KT 850 MB FLOW   
ON RECENT ILX VWP DATA. ACROSS WESTERN, CENTRAL, AND PARTS OF   
NORTHERN ILLINOIS (MAINLY SOUTH OF I-88), THIS SHOULD RESULT IN AN   
INCREASE IN SHOWERS AND SOME STORMS THROUGH 9-10 P.M. THAT WILL MOVE   
EASTWARD. THE LIGHTNING HAS BEEN ALMOST NON-EXISTENT IN THE AREA   
THUS FAR OWING TO THE VERY MOIST CONDITIONS (PWATS 1.9-2.1  
INCHES) BUT SHOULD SEE SOME IN THE SOUTHERN CWA AT LEAST IN THE  
NEXT SEVERAL HOURS. THE SIGNAL FOR AN ORGANIZED CONVECTIVE   
COMPLEX THAT WOULD TRACK ACROSS THE SOUTHERN CWA HAS BEEN LESS IN   
OBSERVATIONAL TRENDS AND CONVECTIVE ALLOW MODEL SOLUTIONS, SO   
EXPECTING MORE SCATTERED ACTIVITY, SOME OF WHICH CERTAINLY STILL   
COULD BE SEVERE GIVEN THE DEEP LAYER SHEAR OF OVER 40 KT. THE ZONE  
OF EFFECTIVE LOW-LEVEL SHEAR AND HELICITY LOOKS LIKE IT IS PRETTY  
NARROW ALONG AND NORTH OF THE WARM FRONT, MAYBE BY ABOUT 30 MILES  
OR SO, AND AT LEAST RIGHT NOW LIKELY ONLY INCLUDES PARTS OF   
LIVINGSTON AND FORD COUNTIES FOR WHAT WOULD BE SOME TORNADO   
POTENTIAL IF MATURE CONVECTION CAN DEVELOP AND TRACK OVER THAT   
AREA. THE LIGHTER SURFACE WIND FIELD THOUGH IS A PROBLEM FOR THAT.  
WILL CONTINUE TO WATCH THIS AREA CLOSELY THOUGH AS WE CONTINUE  
THROUGH THE EVENING.  
  
AS FOR HEAVY RAIN, THERE HAS BEEN TROPICAL-LIKE RAINFALL RATES IN  
ACTIVITY THUS FAR, AGAIN APART FROM ANY LIGHTNING. RAINFALL RATES  
TO ONE INCH PER HOUR HAVE BEEN SEEN WITH 35 DBZ ECHOES. IN THE   
CENTRAL CWA, WHERE THERE IS BOTH LOW-LEVEL CONVERGENCE ASSOCIATED  
WITH THE NORTHERN FRONTAL BOUNDARY AND LOW-LEVEL WARM ADVECTION   
PUSHING AGAINST THIS FROM THE SOUTH, IS THE CORRIDOR WHERE THERE   
CAN BE MULTIPLE ROUNDS OF SHOWERS. GIVEN THOUGH A GRADUALLY   
DIMINISHING TIME WINDOW OF THIS, THE FLASH FLOOD THREAT STILL   
LOOKS SLIGHT/LOCALIZED.  
  
MTF  
  

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ULLETIN - EAS ACTIVATION REQUESTED  
TORNADO WARNING  
NATIONAL WEATHER SERVICE LINCOLN IL  
814 PM CDT MON AUG 12 2019  
  
THE NATIONAL WEATHER SERVICE IN LINCOLN HAS ISSUED A  
  
* TORNADO WARNING FOR...  
  SOUTHWESTERN MENARD COUNTY IN CENTRAL ILLINOIS...  
  NORTHWESTERN SANGAMON COUNTY IN CENTRAL ILLINOIS...  
  SOUTHEASTERN CASS COUNTY IN WEST CENTRAL ILLINOIS...  
  NORTHEASTERN MORGAN COUNTY IN WEST CENTRAL ILLINOIS...  
  
* UNTIL 845 PM CDT.  
      
* AT 814 PM CDT, A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO  
  WAS LOCATED NEAR ASHLAND, OR NEAR VIRGINIA, MOVING EAST AT 25 MPH.  
  
  HAZARD...TORNADO AND QUARTER SIZE HAIL.  
  
  SOURCE...RADAR INDICATED ROTATION.  

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Maybe we just needed to break the cap and get enough cooling.  Here we go.   That horizontal line of storms has me worried about flash flood potential as well as ramping up severe aspects.

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URGENT - IMMEDIATE BROADCAST REQUESTED  
TORNADO WATCH NUMBER 575  
NWS STORM PREDICTION CENTER NORMAN OK  
825 PM CDT MON AUG 12 2019  
  
THE NWS STORM PREDICTION CENTER HAS ISSUED A  
  
* TORNADO WATCH FOR PORTIONS OF   
  CENTRAL ILLINOIS  
  WESTERN AND CENTRAL INDIANA  
  EXTREME EASTERN MISSOURI  
  
* EFFECTIVE THIS MONDAY NIGHT AND TUESDAY MORNING FROM 825 PM  
  UNTIL 300 AM CDT.  
  
* PRIMARY THREATS INCLUDE...  
  A COUPLE TORNADOES POSSIBLE  
  SCATTERED DAMAGING WINDS LIKELY WITH ISOLATED SIGNIFICANT GUSTS  
    TO 75 MPH POSSIBLE  
  ISOLATED LARGE HAIL EVENTS TO 1.5 INCHES IN DIAMETER POSSIBLE  
  
SUMMARY...INCREASINGLY FOCUS BAND OF CONVECTION HAS FORMED OVER  
CENTRAL IL, ALONG WITH ISOLATED, POTENTIALLY SEVERE CONVECTION  
NORTHWEST OF STL, ALL MOVING INTO A FAVORABLE ENVIRONMENT FOR  
SUPERCELLS AND BOW ECHOES.  ACTIVITY SHOULD PROGRESS  
EAST-SOUTHEASTWARD OVER THE WATCH AREA, WITH ALL SEVERE TYPES  
POSSIBLE.  
  

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