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(T. F. “Storm” Walsh)

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I will reiterate, my forecasts are based on the available information at the time of analysis, and are only as accurate as the information analyzed and the solutions provided.

Good day everyone!

The Storm Prediction Center (SPC) has issued a MARGINAL risk for severe thunderstorms in the current DAY 2 Outlook: IN MO/AR TO THE OH AND TN VALLEYS…

…SPC SUMMARY…
A low-probability severe thunderstorm threat is forecast from Sunday afternoon into Sunday night from Missouri-Arkansas into the Ohio and Tennessee Valleys.

SPC DAY 2 SEVERE THUNDERSTORM OUTLOOK (LINKED FOR OUTLOOK TEXT)

TORNADO PROBABILITY

Probability of a tornado within 25 miles of a point.
HAIL PROBABILITY

Probability of one inch diameter hail or larger within 25 miles of a point.
DAMAGING THUNDERSTORM WIND PROBABILITY

Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
The following is the current CSU – MLP severe weather forecast map and NSSL ML probability forecast:
CSU – MLP DAY 2 FORECAST (CLICK FOR LARGER IMAGE)

DAY 2 PROBABILITY CONVERSION TABLE

SPC DISCUSSION EXCERPT: Primary forecast challenge is the degree of surface-based destabilization by Sunday afternoon, which will largely influence tornado and severe thunderstorm wind potential. Latest guidance remains split into two paths. This evening’s RRFS/RAP/HRRR/HRW-ARW suggest that a plume of meager buoyancy with MLCAPE up to 500 J/kg should become established ahead of a cold front across the Ozarks to a portion of the Mid-MS Valley near the surface cyclone by afternoon. Meanwhile the NAM and HRW-NSSL indicate little to no surface-based buoyancy in the warm-moist sector along the front. Guidance consensus does suggest at least a low-topped, thin QLCS should become established along the front from IL/IN towards AR by early evening.

The progressive nature of the front along with the paucity of surface-based instability downstream renders large uncertainty in whether lightning-producing convection will be maintained Sunday night along the front. However, kinematic fields will become increasingly impressive, with strong gusts likely accompanying low-topped convection along the front. CAM consensus though is for convection to wane early morning Monday as instability remains negligible. As such, have maintained the prior level 1-MRGL risk for wind, with a subset of low tornado probabilities from MO to IN.

The following maps will not be available until the SPC DAY 1 outlook.  Please visit the page by clicking the provided link.
00Z NADOCAST TORNADO PROBABILITY (CLICK FOR LARGER IMAGE)
http://data.nadocast.com/202512/

NADOCAST SIGTOR PROBABILITY (CLICK FOR LARGER IMAGE)
Based on my analysis of the severe weather indices, the forecast calls for a weak to marginally unstable atmosphere at the moment.  Indices indicate at the moment, that some isolated severe thunderstorms may be possible during the early portion of the afternoon, and the possibility of a QLCS (Quasi Linear Convective System) around early evening. The strongest threat at this time appears to be damaging thunderstorm winds and gusts, based on bulk shear values, and DCAPE of 500+ j/kg-1.  While CAPE values are fairly meager, based on bulk shear, 0-3km SRH values, isolated weak tornado activity could occur in association with the QLCS should it develop.  The strongest forecast indices and parameters should occur within the 2% TORNADO outline
CAPE VALUES FORECAST

DEW POINT FORECAST

Based on analysis of model animations, the current outlook, and analysis of indices, the strongest convection and indices currently should occur approximately between 2:00 p.m. CDT – 6:00 P.M. CDT DEC. 28

Indices were analyzed from the NAM 3KM, CIPS DETERMINISTIC, and SPC SREF model guidance.

The following were the forecast parameters and indices analyzed this morning.  Bear in mind, indices recorded below are for the time of peak intensity.  Some indices meanings are posted below the indices themselves, and the NWS page containing a more extensive explanation can be accessed further on in the synopsis:
SBCAPE: 10 – 500 j/kg-1                  
MLCAPE: 20 – 300 j/kg-1                   
MUCAPE: 250 – 750 j/kg-1                
SRH 0 -1 km: 200 – 300 m2/s2               
SRH 0 -3 km: 200 – 500 m2/s2        
SRH EFFECTIVE: <100 – 100 m2/s2          
L. I.: 4 to -2                                                       
SCP: 0– 1                                              
STP: 0.0 – 0.3    
0 -6 km SHEAR: 50 kts – 70 kts                  
EFF. SHEAR: 30 kts – 40 kts                        
MID LEVEL LAPSE RATE: 6.5C – 7.0C   
DEWPOINT: 55F – 64F                                    
EHI: 0.04 – 0.67                                         
TOTAL TOTALS INDEX: 49C – 50C                        
K INDEX: 26C – 33C                                          
SWEAT INDEX: 425 – 440                             
THOMPSON INDEX: 22 – 35                     
CRAVEN – BROOKS INDEX: 10,000       

CAPE

ENERGY HELICITY INDEX

K INDEX

TOTAL TOTALS INDEX

STORM RELATIVE HELICITY

LIFTED INDEX

SWEAT VALUES

THOMPSON INDEX

Craven SigSvr Parameter:
The simple product of 100mb MLCAPE and 0-6km magnitude of the vector difference (m/s; often referred to as “deep layer shear”) accounts for the compensation between instability and shear magnitude. Using a database of about 60,000 soundings, the majority of significant severe events (2+ inch hail, 65+ knot winds, F2+ tornadoes) occur when the product exceeds 20,000 m3/s3.
A little fact on SRH values and tornadoes from NOAA / NWS

A little fact on SRH values and tornadoes from NOAA / NWS
Storm Relative Helicity (m² s^-2)
SRH (Storm Relative Helicity) is a measure of the potential for cyclonic updraft rotation in right-moving supercells, and is calculated for the lowest 1-km and 3-km layers above ground level. There is no clear threshold value for SRH when forecasting supercells, since the formation of supercells appears to be related more strongly to the deeper layer vertical shear. Larger values of 0-3-km SRH (greater than 250 m² s^-2) and 0-1-km SRH (greater than 100 m² s^-2), however, do suggest an increased threat of tornadoes with supercells. For SRH, larger values are generally better, but there are no clear thresholds between non-tornadic and significant tornadic supercells.

STP ( Significant Tornado Parameter) EXPLAINED:
A majority of significant tornadoes (EF2 or greater damage) have been associated with STP values greater than 1, while most non-tornadic supercells have been associated with values less than 1 in a large sample of RAP analysis proximity soundings.

SCP (Supercell Composite Parameter) EXPLAINED:
A multiple ingredient, composite index that includes effective storm-relative helicity (ESRH, based on Bunkers right supercell motion), most unstable parcel CAPE (muCAPE) and convective inhibition (muCIN), and effective bulk wind difference (EBWD). Each ingredient is normalized to supercell “threshold” values, and larger values of SCP denote greater “overlap” in the three supercell ingredients. Only positive values of SCP are displayed, which correspond to environments favoring right-moving (cyclonic) supercells.

The following are the SCP (Supercell Composite Parameter) and STP (Significant Tornado Parameter) forecast maps from the NAM 3KM model.  Generally, the higher the values and brighter the color, indicates a greater probability of strong thunderstorm and / or tornadic activity over an area:
NAM 3KM SCP FORECAST 2:00 P.M. CDT DEC. 28 – 6:00 P.M. CDT DEC. 28

NAM 3KM STP FORECAST 2:00 P.M. CDT DEC. 28 – 6:00 P.M. CDT DEC. 28

Please use the following maps, which should update automatically, for Mesoscale Discussions and Convective Watches.  You may have to refresh your browser, or click on the graphics.  I have provided the SPC homepage link below, so you may get the updated information regarding any changes to the outlook:
https://www.spc.noaa.gov/classic.html
SPC MESOSCALE DISCUSSIONS (CLICK IMAGE FOR UPDATES)

SPC CONVECTIVE WATCHES (CLICK IMAGE FOR UPDATES)

The following sites will explain most of the severe weather and tornado values listed above, and will give you an idea of what to expect:
ENVIRONMENTAL INDICES AND PARAMETERS NWS
https://www.weather.gov/lmk/indices

THE WEATHER PREDICTION
http://www.theweatherprediction.com/severe/indices/

The following links will connect you to the Excessive Rainfall probabilities and River Flood Outlook:
EXCESSIVE RAINFALL
https://www.wpc.ncep.noaa.gov/qpf/excessive_rainfall_outlook_ero.php

SIGNIFICANT RIVER FLOOD OUTLOOK
https://www.wpc.ncep.noaa.gov/nationalfloodoutlook/index.html

The following NWS Watch / Warning map will provide local NWS information for your area.  Click the image, then once it refreshes, click on your area of interest to view any special weather statements, hazards or advisories for your area.
NWS WATCH / WARNING DISPLAY (LINKED…CLICK MAP, THEN YOUR AREA)

NWS DOPPLER RADAR LOOP (LINKED, CLICK RADAR MAP)

RAP RADAR (CLICK IMAGE THEN GO TO LOOP DURATION AND PICK LENGTH OF LOOP, THEN CLICK RADAR SITE)
WUNDERGROUND RADAR SUMMARY MAP (CLICK FOR UPDATES)

PRECIPITATION TYPE (CLICK TO ACCESS ANIMATION FEATURE)

CARIBBEAN RADAR (CLICK IMAGE TO ACCESS ANIMATION)

You may direct any questions by contacting me personally, ANYTIME, at: [email protected]

Have a blessed day!

T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST