Disclaimer:  This site is not affiliated with the National Hurricane Center, Hurricane Hunters, Storm Prediction Center, or National Weather Service.  ALL forecasts herein are the result of my analysis, (to which you will see me at times, insert excerpts from various agencies due to the nature of the importance of the information) and I am solely responsible for the content.  As ALWAYS, follow the National Hurricane Center, National Weather Service, and your local Emergency Management officials for emergency decisions.  In addition, this is strictly a FORECAST OFFICE.  I CANNOT make decisions regarding travel plans, etc.  My purpose, is to provide you the information, based solely on information I analyze, and the accuracy of the information at hand of the time of analysis, so you may make informed decisions.
(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 forecast center is closed on Sunday’s.

The Storm Prediction Center indicates a SLIGHT risk for severe weather on Thu., Apr. 23.  
SPC DAY 4 – 8 OUTLOOK: (LINKED TO OUTLOOK)

IF 1300Z SPC DAY 1 outlook graphics are utilized, please check the SPC site for any updates to the outline risks when they are issued.  1630Z updates post at approximately 12:30 p.m.

CURRENT DAY1 SEVERE WEATHER OUTLOOK
The Storm Prediction Center (SPC) has issued a SLIGHT risk for severe thunderstorms in the current DAY1 Outlook: OVER PARTS OF THE UPPER OHIO VALLEY TO THE APPALACHIANS…

…SPC SUMMARY…
Scattered strong to severe thunderstorms capable mainly of damaging winds will be possible today across the upper Ohio Valley and central Appalachians.
1300Z SPC DAY 1 SEVERE THUNDERSTORM OUTLOOK (LINKED FOR OUTLOOK TEXT)

TORNADO PROBABILITY

Probability of a tornado within 25 miles of a point.  Hatched area: a 10% or greater probability of  EF2 – EF5 tornadoes within 25 miles of a point
HAIL PROBABILITY

Probability of one inch diameter hail or larger within 25 miles of a point. Hatched area: a 10% or greater probability of 2 – inch diameter or larger hail 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.  Hatched area: a 10% or greater probability of 65 kt+ winds within 25 miles of a point
CSU – MLP DAY 1 AND 2 FORECAST PROBABILITIES (CLICK FOR LARGER IMAGE) NOT AVAILABLE

NSSL ML DAY 1 PROBABILITY

CSU – MLP 6 PANEL PROBABILITIES DAY 3 – DAY 8 (CLICK FOR LARGER IMAGE) NOT AVAILABLE

DAY 1 PROBABILITY CONVERSION TABLE

SPC DISCUSSION EXCERPT:
…OH Valley into the Appalachians…
Some heating combined with a gradually moistening airmass (55-60 deg F surface dewpoints) will result in weak destabilization by midday as convective development ensues near the preceding outflow/wind shift and front. Ample mid to high-level flow will aid in some potential for storm organization, mainly in the form of a few stronger cells and linear bands. Widely scattered strong to severe gusts capable of wind damage will likely be the primary hazard, but an isolated risk for hail or a brief tornado is possible with the strongest cells. This activity will likely weaken by early evening as it encounters a slightly drier and less unstable airmass with east extent.

…Central Texas…
Scattered showers and elevated thunderstorms are expected throughout much of the day as the cold front rapidly undercuts a moist and unstable air mass. The 12 UTC Del Rio, TX raob shows an 8.2 deg C/km 700-500 mb lapse rate. Forecast soundings show MUCAPE parcels rooted in the 850-700 mb layer, with effective deep-layer shear of 50-60 kt. Although an isolated risk for large hail appears to be the main hazard with the stronger cells, there has been some indication that a localized risk for severe gusts could accompany the strongest cores. For short-term details regarding a risk for hail/wind with a few stronger thunderstorms this morning extending from the Concho Valley east-northeast towards DFW, reference MCD #490.

The following maps are from NADOCAST for tornado and hail probabilities.  Click each image for a larger view.  
12Z NADOCAST TORNADO PROBABILITY

12Z NADOCAST SIGTOR PROBABILITY 

12Z NADOCAST HAIL PROBABILITY 

12Z NADOCAST SIGHAIL PROBABILITY 

Based on my analysis this morning of the current forecast severe weather indices, the forecast calls for a marginally to moderately unstable atmosphere within the SLIGHT risk outline.  The main severe risk as of analysis this morning appears to be a possibility of damaging wind gusts.  An isolated hail risk as well as a brief tornado exists with the strongest cells.  Any tornadoes that occur should remain within the weak range (EF0 – EF1), with the best probability lying within the 2% TORNADO outline

Based on analysis of mainly model animations, the current outlook, and analysis of indices, the strongest convection and indices should occur approximately between early afternoon through early evening hours over the slight risk area.  Please visit the SPC homepage via the link provided for any changes to the forecast today.
CAPE VALUES FORECAST
DEW POINT FORECAST

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

REGARDING EHI VALUES: While EHI values are calculated utilizing MLCAPE and 0 – 3 km SRH values (MLCAPE x 0 – 3 km SRH /160,000), the highest SRH values do not always fall within ample, highest MLCAPE values for the best probability of tornado activity. I utilize the SRH and MLCAPE values over the area that has the highest tornado risk potential.  Maximum EHI values are calculated within the area(s) that have the greatest probability for tornado activity.  Based on further research, (from the NWS and AMS) it was revealed that in calculation, the lower level SRH (0 – 1 km) is best for significant/violent tornado potential, while SRH (0 – 3 km) is more suited for anticipating supercell development and rotation.  This is not mentioned in the EHI calculator instructions, and these changes will be implemented.  This was brought to my attention in that the max. EHI yesterday was at 6.5, which indicated a possibility of EF4 – EF5 tornadoes, which differed greatly from the SPC actual storm reports.
AMS ARTICLE:
https://journals.ametsoc.org/view/journals/wefo/18/3/1520-0434_2003_18_530_rsatfp_2_0_co_2.xml#:~:text=These%20parameters%20are%20storm%2Drelative,3%20km%20above%20ground%20level.

The following were the forecast parameters and indices analyzed this morning within the SLIGHT risk outline.  Listed indices will always pertain to the area(s) located within the highest SPC risk outlines, based mainly on indices regarding a higher tornado potential, should multiple severe risk areas appear in the SPC forecast.  Although certain indices may appear stronger on a forecast map, given the lack of other indices does not contribute to the overall severe risk.  Bear in mind, MAXIMUM 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 – 1500 j/kg-1                  
MLCAPE: 250 – 1000 j/kg-1                   
MUCAPE: 500 – 1500 j/kg-1                
SRH 0 -1 km: 75 – 200 m2/s2               
SRH 0 -3 km: 150 – 275 m2/s2        
SRH EFFECTIVE: 50 – 100 m2/s2          
L. I.: -1 to -4                                                  
SCP: 1 – 6                                        
STP: 0.2 – 1.0
0 -6 km SHEAR: 40 kts – 50 kts                  
EFF. SHEAR: 30 kts – 40 kts                        
MID LEVEL LAPSE RATE: 6.5C – 7.0C   
DEWPOINT: 52F – 65F                                    
EHI SUPERCELL: 0.2 – 1.7 
EHI TORNADO: 0.2 – 1.3                             
TOTAL TOTALS INDEX: 48C                
K INDEX: 22C to 36C                                          
SWEAT INDEX: 330 – 390                   
THOMPSON INDEX: 23 to 40    
CRAVEN – BROOKS INDEX: 5,000 – 10,000     

The following are some severe weather parameters and indices explanations:
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
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 1:00 P.M. EDT APR. 18 – 8:00 P.M. EDT APR. 18

NAM 3KM STP FORECAST 1:00 P.M. EDT APR. 18 – 8:00 P.M. EDT APR. 18

NAM 3KM RADAR SIMULATION 1:00 P.M. EDT APR. 18 – 8:00 P.M. EDT APR. 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)

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 forecasts, any special weather statements, hazards or advisories for your area.
IF A TORNADO WARNING IS ISSUED FOR YOUR AREA…SEEK STURDY AND SAFE SHELTER IMMEDIATELY!

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: twalsh22000@yahoo.com

Have a blessed day!

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