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.

IF 1300Z SPC 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.

The SPC indicates severe weather risks for Thu. through Sat.:
ALL IMAGES LINKED:
DAY 2

DAY 3
DAY 4 – 8

CURRENT DAY1 SEVERE WEATHER OUTLOOK
The Storm Prediction Center (SPC) has issued a SLIGHT risk for severe thunderstorms in the current DAY1 Outlook: FROM THE SOUTHERN PLAINS INTO THE MIDWEST AND SOUTHERN GREAT LAKES…

…SPC SUMMARY…
Severe thunderstorms posing a risk for large to very large hail, damaging winds, and perhaps a few tornadoes will be possible across parts of the southern/central Plains into the Midwest/Ohio Valley and southern Great Lakes this afternoon and evening.
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: 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)

NSSL ML DAY 1 PROBABILITY

CSU – MLP 6 PANEL PROBABILITIES DAY 3 – DAY 8 (CLICK FOR LARGER IMAGE)

DAY 1 PROBABILITY CONVERSION TABLE

SPC DISCUSSION EXCERPT:
…Iowa into Missouri
Expectations are for additional robust thunderstorms to eventually develop by 19-21Z along/near the front in IA, with steep mid-level lapse rates noted on the observed 12Z TOP sounding supporting moderate to locally strong MLCAPE even if clouds/precipitation hinder daytime heating to some extent. Various NAM/RAP forecast soundings show elongated/nearly straight hodographs at mid/upper levels and 50+ kt of deep-layer shear, which will be favorable for upper-level/anvil venting and hail production with any supercells that form. Large to very large hail will be a concern with initially discrete convection. But, some tendency for clustering and movement north of the surface front casts considerable uncertainty on the wind/tornado potential. Even so, some chance for a few tornadoes and scattered damaging winds may exist along/south of the front across IA into MO with any convection that can develop east of the dryline.

…Southern Plains into the Ozarks and Mid Mississippi Valley…
It still appears likely that surface-based thunderstorms will develop this afternoon (around 19-21Z) along/east of the dryline as MLCIN gradually erodes ahead of the ejecting upper trough. But, overall evolution remains somewhat unclear, with potential for messy storm modes/interactions fairly early in the convective life cycle given a large degree of boundary-parallel flow in low/mid levels. Initial supercells should pose a threat for mainly large to very large hail (isolated 2+ inches in diameter), before clustering and an increase in damaging wind potential occurs. The tornado threat is less clear, as stronger low-level flow will tend to remain focused farther north into the Midwest. Still, sufficient low-level shear should exist this afternoon and evening to support a threat for a few tornadoes with both supercells and embedded within clusters.

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 moderately unstable to very unstable atmosphere at the moment within the SLIGHT risk outline in the HATCHED TORNADO outlines.  The main severe risk as of analysis this morning appears to be a possibility for large to very large hail based on CAPE, steep lapse rates, and deep layer shear as well as damaging wind gusts, and the possibility for an isolated strong tornado or two within the 5% HATCHED TORNADO outlines.

Based on analysis of mainly model animations, the current outlook, and analysis of indices, the strongest convection and indices should occur approximately between 3:00 P.M. CDT – 9:00 P.M. CDT.  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, 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

The following were the forecast parameters and indices analyzed this morning.  Listed indices will always pertain to the area(s) located within the highest SPC risk outlines should multiple severe risk areas appear in the SPC forecast, however since there are 2 different SIGNIFICANT HATCHED tornado outlines with almost the same indices, indices in the left column will apply to IOWA and the ones in the right column will apply to OKLAHOMA.  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: 1500 – 3000 j/kg-1…..1500 – 4000 j/kg-1                   
MLCAPE: 1000 – 2500 j/kg-1…..1500 – 3000 j/kg-1                    
MUCAPE: 1500 – 3000 j/kg-1…..1500 – 4000 j/kg-1                 
SRH 0 -1 km: 50 – 150 m2/s2…..50 – 125 m2/s2                
SRH 0 -3 km: 150 – 200 m2/s2…..50 – 200 m2/s2         
SRH EFFECTIVE: 50 – 100 m2/s2…..50 – 100 m2/s2           
L. I.: -5 to -9…..-6 to -11                                                  
SCP: 2 – 8…..2 – 10                                         
STP: 0.4 – 2.8…..1.0 – 3.0
0 -6 km SHEAR: 50 kts – 60 kts…..50 kts – 60 kts                   
EFF. SHEAR: 40 kts -45 kts…..40 kts – 45 kts                        
MID LEVEL LAPSE RATE: 7.0C – 8.0C…..7.0C – 8.0C    
DEWPOINT: 57F – 67F…..57F – 70F                                     
EHI: 0.9 – 3.1…..0.5 – 3.8                               
TOTAL TOTALS INDEX: 59C…..57C                
K INDEX: 28C to 34C…..28C – 36C                                           
SWEAT INDEX: 565 – 605…..560 – 600                     
THOMPSON INDEX: 33 to 43…..34 – 47     
CRAVEN – BROOKS INDEX: 40,000 – 60,000…..30,000 – 80,000     

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. CDT APR. 15 – 11:00 P.M. CDT APR. 15
NAM 3KM STP FORECAST 1:00 P.M. CDT APR. 15 – 11:00 P.M. CDT APR. 15

NAM 3KM RADAR SIMULATION 1:00 P.M. CDT APR. 15 – 11:00 P.M. CDT APR. 15
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: [email protected]

Have a blessed day!

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