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(T. F. “Storm” Walsh)

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The Storm Prediction Center (SPC) has issued a MARGINAL risk for severe thunderstorms in the current DAY 1 Outlook: ACROSS PARTS OF THE SOUTHEAST AND CENTRAL GULF COAST…AND FROM NORTHERN/CENTRAL CALIFORNIA INTO SOUTHWEST OREGON…

…SPC SUMMARY…
Isolated severe storms are possible across parts of the Southeast today. A few marginally severe storms will also be possible from the Sacramento and northern San Joaquin Valleys to coastal areas of northern California and southwest Oregon.

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)

NSSL ML PROBABILITY DAY 1

The CSU – MLP and NSSL ML probabilities forecast maps still indicate probabilities for severe weather risks for DAY 6 and DAY 7 in the forecast period concerning next week.
CSU – MLP DAY 6 AND 7 VS SPC PROBABILITY FORECAST


NSSL ML DAY 6 AND 7


From the SPC DAY 6 and DAY 7 discussion:
Convective potential appears likely to increase across at least the South-Central States by late week. Guidance spread remains large with the handling of a lower-latitude shortwave trough that will initially be off the southern CA/Baja CA coast on D4/Tuesday. Non-ECMWF deterministic guidance largely eject this wave quickly east-northeastward into the southern Great Plains by late D5/Wednesday night. The ECMWF, EC-AIFS, and AIGFS maintain a slower and more reasonable scenario of progression through D6/Thursday. This will probably interact with a modifying warm-moist sector from the western Gulf, with some severe potential in a portion of the South-Central States. Spatiotemporal detail differences exist even among the preferred slower guidance and the majority of GEFS/ECENS ML probs remain below 15 percent for Thursday.

For the broad upper trough over the West, latest EC-AIFS and the ECMWF now depict potential of a negative-tilt evolution compared to prior runs and other guidance. Spread is quite large within the ECENS for both the AI/non-AI, indicative of a poorly predictable pattern for shortwave impulses embedded within the broader trough. But with potential for fast mid-level southwesterlies overlapping seasonably rich low-level moisture emanating north from the western Gulf, and some scenarios indicative of cyclogenesis over the central states, a severe area highlight may eventually be warranted on D7/Friday.

DAY1 PROBABILITY CONVERSION TABLE

SPC DISCUSSION EXCERPT:
...Southeast/Central Gulf Coast…
Early-morning satellite imagery shows a shortwave trough progressing southeastward across northeast TX towards the Lower MS Valley. Expectation is for this wave to continue southeastward through the Lower MS Valley and central Gulf Coast before eventually moving off the Southeast coast late tonight/early tomorrow. Surface analysis places a low associated with this wave over east TX, with another low farther east over central AL. A modest stationary front currently extends between these lows. This front will transition to a cold front this morning, progressing southeastward as the surface lows also move southeastward ahead of the approaching shortwave. Mid 60s dewpoints are in place ahead of this front from the Upper TX Coast through southern LA into southern MS/AL. Given the presence of the stationary front, this is likely near the northern extent of this greater low-level moisture.

Diurnal heating will be limited by cloud cover, but the general expectation is for modest buoyancy ahead of the approaching cold front. This buoyancy will support scattered thunderstorm development along the front as it moves through the region. Low-level flow will likely veer ahead of the front, limiting low-level curvature. Even so, strong mid-level westerly/southwesterly flow will extend across the region, resulting in long hodographs that could support occasional organized updrafts. Primary severe risk will be isolated damaging gusts, although a low-probability risk for a brief tornado exists as well. Some isolated hail could also occur, particularly with any storms near the surface low over southern AL and the western FL Panhandle during the late afternoon/early evening when colder mid-level temperatures are in place.

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 marginally to moderately atmosphere over the risk area.  The main threat at this time appears to be damaging thunderstorm winds and gusts, based on bulk shear values, and DCAPE of 600+ j/kg-1.  The strongest CAPE values, bulk shear, 0-3 km SRH, along with the strongest lifted index (L.I.) and mid level lapse rate values, and veering winds with height, tend to suggest isolated weak tornado activity, and the possibility of isolated hail.  The strongest forecast indices and parameters should occur within the 2% TORNADO outline and 5% HAIL outline.

Based on analysis of model animations, the current outlook, and analysis of indices, the strongest convection and indices should occur approximately between 2:00 p.m. EST – 7:00 P.M. EST.  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.

The following were the forecast parameters and indices analyzed this morning.  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: 500 – 1250 j/kg-1                   
MUCAPE: 500 – 1500 j/kg-1                
SRH 0 -1 km: 50 – 200 m2/s2               
SRH 0 -3 km: 100 – 200 m2/s2        
SRH EFFECTIVE: 50 – 100 m2/s2          
L. I.: -1 to -4                                                    
SCP: 1.0 – 4.0                                          
STP: 0.1 – 0.7  
0 -6 km SHEAR: 40 kts – 50 kts                  
EFF. SHEAR: 30 kts – 35 kts                        
MID LEVEL LAPSE RATE: 6.0C – 7.5C   
DEWPOINT: 55F – 67F                                    
EHI: 0.5 – 1.2                                        
TOTAL TOTALS INDEX: 46C – 48C                      
K INDEX: 29C to 34C                                          
SWEAT INDEX: 245 – 300                             
THOMPSON INDEX: 30 to 38         
CRAVEN – BROOKS INDEX: 10,000 – 15,000    

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 2:00 P.M. EST JAN. 03 – 7:00 P.M. EST JAN. 03

NAM 3KM STP FORECAST 2:00 P.M. EST JAN. 03 – 7:00 P.M. EST JAN. 03

HRRR 3KM SCP FORECAST 2:00 P.M. EST JAN. 03 –7:00 P.M. EST JAN. 03

HRRR 3KM STP FORECAST 2:00 P.M. EST JAN. 03 –7:00 P.M. EST JAN. 03

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 forecasts, 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