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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 SLIGHT risk for severe thunderstorms in the current DAY 1 Outlook: FOR MIDDLE TENNESSEE AND SOUTH-CENTRAL KENTUCKY…

…SPC SUMMARY…
Scattered severe thunderstorms are possible later this afternoon through the evening across parts of the Ohio and Tennessee Valleys. A few marginally severe storms could also develop in the central Gulf Coast states late this afternoon into the overnight period.
SPC DAY 1 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:
CSU – MLP DAY 1 FORECAST (CLICK FOR LARGER IMAGE)

DAY1 PROBABILITY CONVERSION TABLE

SPC DISCUSSION EXCERPT:
Perhaps equally consequential will be mid-level cold-air advection with 500-mb temperatures forecast to significantly cool (e.g., -12 deg C at 12 UTC per the Nashville, TN 12 UTC raob to -16 to -17 deg C by 00 UTC). As a result, weak destabilization is forecast with MLCAPE ranging from 200-500 J/kg over KY to 500-1000 J/kg across the TN Valley. Model guidance continues to show scattered cellular storms developing late this afternoon initially over the KY/TN border vicinity, with storms developing farther south near the AL/TN border during the evening. Forecast hodographs will support organized storms with the stronger updrafts, including the possibility for a few supercells. A tornado risk, in addition to the threat for damaging gusts and perhaps marginally severe hail may accompany the stronger storms. A mix of linear storm modes and supercells are expected through the early to mid evening as this activity moves east. Storms and the severe risk will probably lessen over the southern Appalachians before diminishing overnight.

The following maps are from NADOCAST for tornado and hail probabilities.  The SIGTOR probability was shown to be .1%
12Z NADOCAST TORNADO PROBABILITY (CLICK FOR LARGER IMAGE)

NADOCAST SIGTOR PROBABILITY (CLICK FOR LARGER IMAGE)

NADOCAST HAIL 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 with isolated supercells early on, with a more linear mode by early to mid evening.  

SPC mentions the possibility of some isolated large to marginally severe  hail potential. Based on the increase in CAPE values and lifted indices and mid level lapse rates being moderately steep, this may be possible.  It was again noted CAPE and lifted indices appear to be strongest over the extreme southern portion of the MARGINAL risk outline, isolated over Southern AL / MS.  Deep layer shear could cause some damaging thunderstorm winds and gusts.  Any tornado and / or hail activity should be isolated.  IF any tornadoes do develop, they should be weak (EF0 – EF1).  
CAPE VALUES FORECAST

Based on analysis of model animations, the current outlook, and analysis of indices, the strongest convection and indices currently should occur approximately between 3:00 p.m. CDT – 6:00 P.M. CDT NOV. 07

Indices were analyzed from the NAM 3KM, HRRR 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: 500 – 1000 j/kg-1                  
MLCAPE: 500 – 1000 j/kg-1                   
MUCAPE: 500 – 1500 j/kg-1                
SRH 0 -1 km: 100 – 250 m2/s2               
SRH 0 -3 km: 150 – 300 m2/s2        
SRH EFFECTIVE: 100 – 200 m2/s2          
L. I.: -2 to -5                                                       
SCP: 2– 5                                               
STP: 0.4 – 1.7    
0 -6 km SHEAR: 50 kts – 60 kts                  
EFF. SHEAR: 30 kts – 40 kts                        
MID LEVEL LAPSE RATE: 6.0C – 7.0C   
DEWPOINT: 58F – 68F                                    
EHI: 0.7 – 1.4                                           
TOTAL TOTALS INDEX: 47C                      
K INDEX: 21C – 33C                                          
SWEAT INDEX: 325 – 370                             
THOMPSON INDEX: 23 – 38                     
CRAVEN – BROOKS INDEX: 10,000 – 25,000      

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 3:00 P.M. CDT NOV. 07 – MIDNIGHT CDT NOV. 08

NAM 3KM STP FORECAST 3:00 P.M. CDT NOV. 07 – MIDNIGHT CDT NOV. 08

HRRR 3KM SCP FORECAST 3:00 P.M. CDT NOV. 07 –MIDNIGHT CDT NOV. 08

HRRR 3KM STP FORECAST 3:00 P.M. CDT NOV. 07 –MIDNIGHT CDT NOV. 08

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)

IF A TORNADO WARNING IS ISSUED FOR YOUR AREA, TAKE IMMEDIATE SAFE AND STURDY SHELTER!
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)
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