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(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 Storm Prediction Center (SPC) has issued a MARGINAL risk for severe thunderstorms in the current DAY 2 Outlook: FOR THE SOUTHEAST AND PARTS OF CA/OR…

…SPC SUMMARY…
Isolated severe storms are possible across parts of the Southeast on Saturday, and the Sacramento/northern San Joaquin Valleys to coastal northern California-southwest Oregon in the afternoon/early evening.

SPC DAY 2 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.
The following is the current CSU – MLP severe weather forecast map and NSSL ML probability forecast:
CSU – MLP DAY 2 FORECAST (CLICK FOR LARGER IMAGE)

NSSL ML PROBABILITY

DAY 2 PROBABILITY CONVERSION TABLE

SPC DISCUSSION EXCERPT:
…Southeast…
A positive-tilt shortwave trough will progress east across the Lower MS Valley to off the South Atlantic Coast by Saturday evening. An attendant weak surface cyclone should track from central AL to offshore of SC by 00Z, with a cold front trailing west-southwest to the central Gulf Coast. Low-level warm conveyor convection should increase during the mid to late morning, with a separate round of thunderstorms developing near the surface low to along the front by midday into the afternoon. Low-level hodograph curvature will be modestly enlarged within the warm conveyor as it shifts east through the day, but surface-based instability should remain weak with low-probability tornado/wind threats.

It appears probable that a corridor of moderate buoyancy with MLCAPE of 1000-1500 J/kg should extend from around the mouth of the MS River towards the western FL Panhandle by midday. However, low-level flow will be increasingly veered in this portion of the warm sector ahead of the front. Sufficient deep-layer speed shear should exist for a few supercells with mid-level rotation, which may produce isolated severe hail and eventually isolated damaging winds as storms cluster during the afternoon.

 The following maps will not be available until the SPC DAY 1 outlook.  
00Z NADOCAST TORNADO PROBABILITY (CLICK FOR LARGER IMAGE)

NADOCAST SIGTOR PROBABILITY (CLICK FOR LARGER IMAGE)
Based on my morning analysis of the severe weather indices (12Z), the forecast calls for a marginal to moderately unstable atmosphere at the moment.  Indices indicate at the moment, that some isolated severe thunderstorms and supercells may be possible during the early portion of the afternoon. The strongest 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 tend to suggest isolated, weak tornado activity, and the possibility of isolated severe hail.  The strongest forecast indices and parameters should occur within the 2% TORNADO outline and 5% HAIL outline.
CAPE VALUES FORECAST

DEW POINT FORECAST

Based on analysis of model animations, the current outlook, and analysis of indices, the strongest convection and indices currently should occur approximately between 2:00 p.m. CDT – 7:00 P.M. CDT JAN. 03

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

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: 500 – 1500 j/kg-1                  
MLCAPE: 500 – 1250 j/kg-1                   
MUCAPE: 500 – 1500 j/kg-1                
SRH 0 -1 km: 100 – 200 m2/s2               
SRH 0 -3 km: 100 – 250 m2/s2        
SRH EFFECTIVE: 100 – 200 m2/s2          
L. I.: -1 to -4                                                       
SCP: 1– 3                                              
STP: 0.1 – 1.2   
0 -6 km SHEAR: 40 kts – 50 kts                  
EFF. SHEAR: 30 kts                       
MID LEVEL LAPSE RATE: 6.5C – 8.0C   
DEWPOINT: 56F – 67F                                    
EHI: 0.6 – 1.4                                         
TOTAL TOTALS INDEX: 54C – 55C                        
K INDEX: 28C – 34C                                          
SWEAT INDEX: 415 – 475                              
THOMPSON INDEX: 29 – 38                     
CRAVEN – BROOKS INDEX: 10,000 – 20,000       

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

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)

Though the SPC does not indicate it at this time, the CSU – MLP and NSSL ML forecast probabilities are currently indicating severe weather probabilities (MARGINAL risk at the moment) for DAY 6 – 8, with the NSSL indicating the strongest probs for day 8 (JAN. 09).  I will be monitoring this during next week and will try to update if this comes to fruition.
CSU – MLP DAY 6 – 8 SEVERE PROBABILITIES FORECAST (LINKED)

NSSL – ML DAY 8 SEVERE PROBABILITIES FORECAST (CLICK FOR INTERACTIVE MAP)

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 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