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 office is closed on Sunday.

PLEASE visit the SPC site after issuance of this synopsis, as SPC outlook maps will often change after issuance of the synopsis.

The Storm Prediction Center (SPC) has issued a ENHANCED risk for severe thunderstorms in the current DAY 1 Outlook: ACROSS PARTS OF THE MIDWEST/OHIO VALLEY…

…SPC SUMMARY DAY 1…
Scattered severe thunderstorms are expected this afternoon and evening across parts of the Midwest and Ohio Valley. Large to very large hail, a few tornadoes, and severe/damaging winds all appear likely.
1630Z SPC DAY 1 SEVERE THUNDERSTORM OUTLOOK (LINKED FOR OUTLOOK TEXT)

TORNADO PROBABILITY

Probability of a tornado within 25 miles of a point.  Hatched Area: 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-knot (or higher) winds within 25 miles of a given location.

The following is the current CSU – MLP severe weather probability forecast map and NSSL ML probability forecast:
CSU – MLP DAY 1 FORECAST (CLICK FOR LARGER IMAGE)

NSSL ML DAY 1 SEVERE PROBABILITY 

DAY 1 PROBABILITY CONVERSION TABLE

SPC DISCUSSION EXCERPT DAY 1:
…Mid Mississippi Valley into the Midwest/Ohio Valley…
Beneath a capping inversion, moistening will continue with surface dewpoints rising into the 56-62 deg F range from the mid MS Valley east into western PA. Upwards of 500-1500 J/kg MLCAPE is likely by mid afternoon south of the front. A belt of strong, westerly 50-65 kt 700-mb flow is forecast to move from IA and expand spatially across the warm sector through early evening. This increase in flow will act to elongate hodographs despite mainly veered southwesterly surface flow. Recent convection-allowing model guidance varies considerably on the depiction of cellular versus mostly linear clusters evolving in the first few hours of the convective life cycle. Time-lagged HRRR would imply a more spatially and numerically extensive supercell hail and tornado risk than most of the 12z HREF HRW members showing less risk of these hazards. The tornado risk could focus with potential supercells near a weak low and where surface flow would locally back to southerly. However, confidence is muted regarding this specific scenario.

Regardless, current expectations are for thunderstorms to quickly develop along the length of the front from central IL eastward into IN, southern Lower MI, and northern OH by 19-22Z as diurnal heating erodes lingering convective inhibition. A mix of supercells and organized linear clusters will evolve with large to very large hail possible. A fairly quick transition to more linear structures appears likely given the frontal forcing, with an increasing threat for scattered to numerous severe/damaging winds as one or more clusters spreads east-southeastward across much of the OH Valley into western/central PA through the late afternoon and evening. Given the forecast strength of the low to mid-level flow, isolated gusts of 75+ mph may occur. There is a threat for a few tornadoes as well with both supercells and embedded mesocirculations within the linear clusters.

The following maps are DAY 1 probability maps from NADOCAST for tornado and hail probabilities.  
12Z NADOCAST TORNADO PROBABILITY

12Z NADOCAST SIGTOR PROBABILITY

12Z NADOCAST HAIL PROBABILITY 

12Z NADOCAST SIGHAIL PROBABILITY 

Based on my analysis of the preliminary severe weather indices, the forecast calls for a HIGH END moderately unstable to a borderline VERY UNSTABLE atmosphere at the moment.  Indices and current outlook maps indicate ALL severe weather threats are possible.  Large to significant hail is in the forecast, and should be located mainly within the current 45% HATCHED HAIL outline.  Based on analysis of deep layer shear, veering winds with height, 0 – 3km SRH, and EHI values, tornadoes are very likely.  Based on the maximum EHI value and maximum 0 – 3km SRH, the possibility of some strong tornadoes, (EF2+) probably isolated, could be experienced.  Currently, strongest severe weather indices should be within the ENHANCED risk, 45% HAIL outline, and darkest area of the NSSL ML probability outlines, mainly over central to eastern Illinois and over Indiana and a small portion of Ohio.  Some indices could change slightly between now and the time of peak intensity. 
CAPE VALUES FORECAST

DEW POINT FORECAST

Based on analysis of model animations, the current outlook, and analysis of indices, SPC suggests severe storms should initiate by 19Z (2:00 P.M. CDT), with the strongest convection and indices occurring by mid – late afternoon, through early evening, with current animations indicating the strongest between 3:00 P.M. – 7:00 P.M. CDT.  

Indices were analyzed from the NAM 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 MLCAPE values in order to provide the best probability for tornado activity.  Maximum EHI values are calculated within the area(s) that have the greatest probability for tornado activity. 

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: 750 – 2500 j/kg-1                  
MLCAPE: 750 – 2000 j/kg-1                   
MUCAPE: 750 – 2500 j/kg-1                
SRH 0 -1 km: 100 – 250 m2/s2               
SRH 0 -3 km: 200 – 500 m2/s2        
SRH EFFECTIVE: 200 – 400 m2/s2          
L. I.: -2 to -8                                                  
SCP: 2 – 17                                           
STP: 0.4 – 2.3 
0 -6 km SHEAR: 50 kts – 60 kts                  
EFF. SHEAR: 40 kts – 50 kts                        
MID LEVEL LAPSE RATE: 7.0C – 8.5C   
DEWPOINT: 59F – 65F                                    
EHI: 0.9- 4.1                                       
TOTAL TOTALS INDEX: 54C                       
K INDEX: 22C – 29C                                          
SWEAT INDEX: 545 – 615                             
THOMPSON INDEX: 23– 37                     
CRAVEN – BROOKS INDEX: 20,000 – 50,000 

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 2:00 P.M. CDT MAR. 26 – 10:00 P.M. CDT MAR. 26

NAM 3KM STP FORECAST 2:00 P.M. CDT MAR. 26 – 10:00 P.M. CDT MAR. 26

NAM 3KM FORECAST RADAR ANIMATION 2:00 P.M. CDT MAR. 26 – 10:00 P.M. CDT MAR. 26

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:
SPC HOMEPAGE
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…SEEK STURDY AND SAFE SHELTER IMMEDIATELY!

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 forecasts, 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