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.  I will not be available until tomorrow evening, as I will be attending a friends memorial service.  Please refer to the SPC homepage for any updates to the outlook.  I will try to post an update in the evening on the upcoming Nor’easter / coastal storm which is forecast to materialize on Sunday.

The SPC has cancelled the MARGINAL risk that had been forecast for today.  From the SPC:
…NO SEVERE THUNDERSTORM AREAS FORECAST…
…SUMMARY…
Organized severe thunderstorms are not expected today.

…Discussion…
A shortwave trough will move quickly eastward across the Great Lakes into the Northeast, with a surface low developing off the coastal Mid-Atlantic. Over land, a cold front will progress eastward across Virginia and the Carolinas, with rapid drying from the west. Despite this, a few showers/thunderstorms will be possible prior to the front moving offshore. Warm profiles aloft suggest weak storms, but strong westerlies just off the surface could yield gusty winds.

The south-southwest extent of front will decelerate today and then generally stall, orienting in a west/southwest-east/northeast fashion across Louisiana, southern portions of Mississippi/Alabama and the middle part of Georgia by late today. Isolated thunderstorms may become a bit more probable into tonight as weak ascent focuses along/north of the front. That said, relatively warm mid-level thermodynamic profiles may limit the prevalence of lightning, as well as any consideration for meaningful hail magnitudes. This is even while elevated instability will quantitatively increase and hodographs will be rather long, with steadily strengthening southwesterly winds in the lowest 2-3 km AGL and 50+ kt shear through the cloud-bearing layer. While a couple of strong storms could occur tonight, thinking remains that the potential for severe storms should remain low/conditional.

The Storm Prediction Center (SPC) has issued a MARGINAL risk for severe thunderstorms in the current DAY 2 Outlook: FROM SOUTHEAST ALABAMA AND THE NORTHERN FLORIDA PANHANDLE EAST INTO SOUTHERN SOUTH CAROLINA…

…SPC SUMMARY…
Thunderstorms are possible across parts of the eastern Gulf and south Atlantic coast states Saturday, accompanied by at least some risk for damaging wind gusts.
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 DAY 2 SEVERE PROBABILITY 

DAY 2 PROBABILITY CONVERSION TABLE

SPC DISCUSSION EXCERPT:
A remnant frontal boundary will be stretched from southern North Carolina southwestward toward southeast Texas. A surface low will develop along this frontal boundary during the day on Saturday in response to the amplifying mid-level trough before quickly out to sea by Sunday morning.

Ongoing thunderstorms at the start of the forecast period should persist through the morning, as the mid-level wave amplifies and surface low develops. Along and south of the front, modest diurnal heating will result in an environment with up to 500 to perhaps 1000 J/kg of most unstable CAPE. Long, straight hodographs largely parallel to the frontal zone should favor small linear/bowing segments over supercells, despite the strong deep-layer shear present. A marginal threat for damaging wind gusts will accompany any sustained thunderstorm segment. A modest low-level jet during the morning hours may provide enough low-level streamwise vorticity to support a brief tornado or two. This threat should diminish during the afternoon as the low-level jet veers and weakens.

NADOCAST maps will not be available until the SPC DAY 1 outlook, but may be accessed through the following link:
http://data.nadocast.com/

Based on my analysis of the preliminary severe weather indices, the forecast calls for a marginally unstable atmosphere to almost borderline moderately unstable at the moment.  Indices are mixed right now as to the forecast instability of the atmosphere, and severity of the risk.  At the moment, the strongest risks appear to be the probability of tornadoes and damaging thunderstorm winds / gusts.  Based on analysis of deep layer shear, more of a zonal surface to upper air pattern, 0 – 3km SRH, and EHI values, tornadoes could be possible and develop from more of a QLCS (Quasi Linear Convective System) vice supercellular, and should remain within the weaker range of EF0 – EF1.  Currently, strongest severe weather indices should be within the MARGINAL risk, especially within the 2% TORNADO, and darkest area of the NSSL ML probability outlines.  Hail could be possible, but at the moment the probability is less than 5%. Some indices will most likely change between issuance of this synopsis, and by the onset of the DAY1 outlook, so this forecast should not be taken as absolute.  
CAPE VALUES FORECAST

DEW POINT FORECAST

Based on analysis of model animations, the current outlook, and analysis of indices, the strongest convection and indices should occur by early afternoon. The current model animations suggest that convection could be ongoing by or just before NOON tomorrow and diminishing by early evening.  The 12Z NAM 3km animations suggest the strongest storms and indices to occur between 1:00 p.m. EST – 7:00 p.m. EST.

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 – 2000 j/kg-1                  
MLCAPE: 500 – 1250 j/kg-1                   
MUCAPE: 500 – 1500 j/kg-1                
SRH 0 -1 km: 100 – 300 m2/s2               
SRH 0 -3 km: 150 – 375 m2/s2        
SRH EFFECTIVE: 100 – 150 m2/s2          
L. I.: -2 to -4                                                      
SCP: 2 – 6                                              
STP: 0.6 – 2.1  
0 -6 km SHEAR: 60 kts – 70 kts                  
EFF. SHEAR: 45 kts – 50 kts                        
MID LEVEL LAPSE RATE: 6.0C – 6.5C   
DEWPOINT: 57F – 69F                                    
EHI: 0.9 – 2.2                                         
TOTAL TOTALS INDEX: 46C                       
K INDEX: 28C – 35C                                          
SWEAT INDEX: 315 – 345                             
THOMPSON INDEX: 30 – 39                     
CRAVEN – BROOKS INDEX: 10,000 – 30,000      

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
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. EST FEB. 21 – 7:00 P.M. EST FEB. 21

NAM 3KM STP FORECAST 1:00 P.M. EST FEB. 21 – 7:00 P.M. EST FEB. 21

NAM 3KM FORECAST RADAR ANIMATION (NOON EST – 8:00 P.M. EST FEB 21.)

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

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

Elsewhere, the ECMWF and GFS models have been consistent during the past 72 hours in developing a Nor’easter / coastal storm by Sunday morning, off the Mid Atlantic coast / OBX region.  I will try to post a synopsis on this sometime Saturday evening if time permits.
ECMWF AND GFS MSLP ANOMALY ANIMATION


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: twalsh22000@yahoo.com

Have a blessed day!

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