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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!
My forecasts will be as an on and off basis, to help my wife in recover from the kyphoplasty procedure performed on her back.

Some changes have been made in the synopsis, as the SPC did a little upgrade as I was getting ready to distribute this synopsis

The Storm Prediction Center (SPC) has issued a MARGINAL risk for severe thunderstorms in the current DAY 1 Outlook: THE MISSISSIPPI/TENNESSEE/LOWER OHIO VALLEYS…AND PORTIONS OF COASTAL NORTH CAROLINA…

…SPC SUMMARY…
Isolated strong to severe thunderstorms capable of producing occasional damaging winds and perhaps a tornado or two may occur through this evening across parts of the lower/mid Mississippi Valley into the Tennessee Valley/Southeast, and late tonight across portions of coastal North Carolina.

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.

CSU – MLP DAY 1 FORECAST (CLICK FOR LARGER IMAGE)


DAY1 PROBABILITY CONVERSION TABLE

SPC DISCUSSION EXCERPT:
…Carolinas… 
Isolated strong to locally severe convection may occur late tonight through early Friday morning as an increasingly negative-tilt mid-level trough and a related robust strengthening of the deep-layer wind field approach eastern NC. The gradual modification and erosion of continental/cold air is a key uncertainty due to persistent surface high pressure along the East Coast into western Atlantic. Some guidance such as the 12Z NAM may be a bit too aggressive regarding late-night near-surface-based destabilization. Still, the main area of concern is for the immediate NC coastal areas/Outer Banks, where somewhat greater airmass modification/low-level moistening should occur amid strong low-level and deep-layer shear. If surface-based thunderstorms can form and spread northeastward across this area, they could pose a threat for isolated severe/damaging winds and perhaps a tornado. But, it is also possible that convectively enhanced wind gusts materialize inland (including Piedmont areas) in the predawn hours, although confidence in this occurring remains low.

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

12Z NADOCAST SIGTOR PROBABILITY (CLICK FOR LARGER IMAGE)

12Z NADOCAST HAIL PROBABILITY (CLICK FOR LARGER IMAGE)

12Z NADOCAST SIGHAIL PROBABILITY (CLICK FOR LARGER IMAGE)

Based on my analysis of the severe weather indices, the forecast calls for a stable atmosphere over the risk area.  Instability is greater much further south.  It currently appears that damaging wind gusts may be the main threat, based on 40 – 50 kts of deep layer shear, slightly veering winds, and DCAPE (Downdraft Convective Available Potential Energy) values forecast to be 500+.  Based on the current forecast indices, it appears obvious the NADOCAST and CSU – MLP maps may be somewhat inaccurate.

Based on analysis of model animations, the current outlook, and analysis of indices, the strongest convection and indices should occur approximately between 4:00 p.m. EST – 10:00 P.M. EST DEC. 18.  Given the lack of lift, hail should not be a factor, however the deep layer shear, moderate mid level lapse rate, 0-3 km SRH (Storm Relative Helicity, and veering wind profile, could possibly introduce a slim probability of and isolated, very weak tornado threat. Please visit the SPC homepage via the link provided for any changes to the forecast today.
CAPE VALUES FORECAST

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: 0 – 225 j/kg-1                  
MLCAPE: 0 – 120 j/kg-1                   
MUCAPE: 0 – 300 j/kg-1                
SRH 0 -1 km: 50 – 135 m2/s2               
SRH 0 -3 km: 100 – 225 m2/s2        
SRH EFFECTIVE: < 100 m2/s2          
L. I.: 10 to -2                                                     
SCP: 0.1 – 0.5                                            
STP: 0.0 – 0.1  
0 -6 km SHEAR: 40 kts – 50 kts                  
EFF. SHEAR: 30 kts – 35 kts                        
MID LEVEL LAPSE RATE: 6.5C – 7.5C   
DEWPOINT: 50F – 61F                                    
EHI: 0.1 – 0.2                                        
TOTAL TOTALS INDEX: 39C – 40C                      
K INDEX: 0C to -16C                                          
SWEAT INDEX: 25 – 120                              
THOMPSON INDEX: -10 to -16          
CRAVEN – BROOKS INDEX: <5000    

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 4:00 P.M. EST DEC. 18 – 10:00 P.M. EST DEC. 19

NAM 3KM STP FORECAST 4:00 P.M. EST DEC. 18 – 10:00 P.M. EST DEC. 19

HRRR 3KM SCP FORECAST 4:00 P.M. EST DEC. 18 –10:00 P.M. EST NOV. 18

HRRR 3KM STP FORECAST 4:00 P.M. EST DEC. 18 –10:00 P.M. EST NOV. 18

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)
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