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 Tue., Wed., and Fri.
ALL IMAGES LINKED:
DAY 2
DAY 3
DAY 4 – 8

CURRENT DAY1 SEVERE WEATHER OUTLOOK
The Storm Prediction Center (SPC) has issued an ENHANCED risk for severe thunderstorms in the current DAY1 Outlook: ACROSS SOUTHERN MINNESOTA AND PARTS OF WISCONSIN…

…SPC SUMMARY…
Severe thunderstorms are likely across the Upper Mississippi Valley and Great Lakes region with potential for large to very large hail, damaging wind, and tornadoes, mainly late this afternoon into tonight. A more conditional and isolated risk for severe storms is possible across portions of the southern Plains late this afternoon and evening.

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 6 PANEL PROBABILITIES DAY 1 AND DAY 2 (CLICK FOR LARGER IMAGE)

NSSL ML DAY 1 PROBABILITY

DAY 3 – DAY 8

DAY 1 PROBABILITY CONVERSION TABLE

SPC DISCUSSION EXCERPT:
…Upper Mississippi Valley/Great Lakes including MN/WI…
Multiple lead mid-level disturbances over the northern High Plains will progress northeastward today toward the Upper Midwest, with strengthening winds aloft across this region particularly late today and tonight. A surface low will tend to deepen/develop east-northeastward from northeast Nebraska this morning into far southern Minnesota and Wisconsin by tonight in vicinity of a slow-moving/stalled frontal boundary. Low/middle 60s F surface dewpoints will advect north-northeastward and become increasingly prevalent along/south of the aforementioned stationary/warm front this afternoon. MLCAPE values are forecast to reach 2000-2500 J/kg by around 21z/4pm CDT.

Thunderstorm development will become increasingly probable through mid/late afternoon (21-00z) as isentropic ascent strengthens ahead of the approaching upper disturbance. Lingering inhibition coupled with 45-50 kt effective bulk shear should promote initially discrete supercells along or just north of the surface boundary. Hodograph elongation appears favorable for a large hail threat, possibly as large as 2-3 inches in diameter with the more robust cells. Additionally, enhanced low-level SRH along the frontal zone is expected to result in a corridor of relatively higher tornado potential for storms that can remain rooted immediately along the boundary.

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 very unstable atmosphere at the moment within the ENHANCED risk outline.  The main severe risk as of analysis this morning appears to be large to significant hail, based on lifted indices, very steep mid level lapse rates, and maximum SBCAPE values within the 15% SIGNIFICANT HAIL  and 30% SIGNIFICANT HAIL outline, with most favorable indices for tornado formation within the 5% HATCHED TORNADO  and 10% HATCHED TORNADO outline. Damaging thunderstorm winds / gusts, are most probable within the 10% damaging winds outline.  The possibility of an isolated (EF4 – EF5) tornado cannot be ruled out based on indices regarding tornado formation and intensity.  I cannot safely rule out a low probability of an isolated PDS (Particularly Dangerous Situation) if strongest indices materialize over a particular area.

Based on analysis of mainly model animations, the current outlook, and analysis of indices, the strongest convection and indices should occur approximately between 4:00 P.M. CDT APR. 13  – 11:00 P.M. CDT APR. 13.    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

The following were the forecast parameters and indices analyzed this morning within the ENHANCED risk outline.  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.  Although certain indices may appear stronger on a forecast map, given the lack of other indices does snot 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                  
MLCAPE: 1500 – 2500 j/kg-1                   
MUCAPE: 1500 – 3000 j/kg-1                
SRH 0 -1 km: 150 – 200 m2/s2               
SRH 0 -3 km: 200 – 300 m2/s2        
SRH EFFECTIVE: 100 – 200 m2/s2          
L. I.: -3 to -11                                                 
SCP: 5 – 18                                         
STP: 0.3 – 2.8
0 -6 km SHEAR: 40 kts – 50 kts                  
EFF. SHEAR: 30 kts – 40 kts                        
MID LEVEL LAPSE RATE: 8.0C – 9.0C   
DEWPOINT: 64F – 68F                                    
EHI: 1.9 – 4.2                                
TOTAL TOTALS INDEX: 58C                
K INDEX: 28C to 36C                                          
SWEAT INDEX: 595 – 650                      
THOMPSON INDEX: 31 to 48    
CRAVEN – BROOKS INDEX: 20,000 – 40,000     

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 3:00 P.M. CDT APR. 13 – 2:00 A.M. CDT APR. 14
NAM 3KM STP FORECAST 3:00 P.M. CDT APR. 13 – 2:00 A.M. CDT APR. 14
NAM 3KM RADAR SIMULATION 3:00 P.M. CDT APR. 13 – 2:00 A.M. CDT APR. 14

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