May 23, 2024

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MODERATE SEVERE WEATHER RISK / POTENTIALLY DANGEROUS SEVERE WEATHER EVENT FORECAST SYNOPSIS…ISSUED MAY 08, 2024…10:45 A.M. EDT

8 min read

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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Good day everyone!

I will be out of the office from May 20 through June 01 as we will be traveling to Wyoming for our grandsons high school graduation.  For updates on severe weather and / or tropics, please come to this site, and use the following links for updates.  I will resume tropical outlooks on June 03.
https://www.spc.noaa.gov/classic.html
https://www.nhc.noaa.gov/


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.

The outlined maps you were used to seeing from my F5 DATA software, are no longer around and operational.  This means I have lost quite a bit of data to analyze but I will try to make the severe weather forecasts as accurate and understandable as possible.
https://www.spc.noaa.gov/new/images/SPC_outlook_final_updated.png
CATEGORICAL OUTLOOK CONVERSION TABLE FOR DAY 1 OUTLOOKS
image002day1.conv

Today’s forecast is very lengthy, but PLEASE, I recommend reading all of it.  This is the highest I’ve seen most forecast indices in quite a while!

The Storm Prediction Center (SPC), has issued an MODERATE risk of severe thunderstorms: OVER PORTIONS OF SOUTHERN/SOUTHEASTERN MISSOURI…EXTREME NORTHEASTERN AR…EXTREME SOUTHERN ILLINOIS…WESTERN/SOUTH-CENTRAL KENTUCKY…AND NORTHWESTERN TO MIDDLE TENNESSEE…

…SPC SUMMARY…
Severe thunderstorms appear likely from parts of the mid Mississippi, Ohio, and Tennessee Valleys into the southern Plains. All severe hazards, including tornadoes, very large to giant hail, and potentially significant damaging winds are possible. Some tornadoes may be strong.

SPC DAY 1 SEVERE THUNDERSTORM OUTLOOK MAPS (first image linked to current SPC outlook.  Click for any updated outlook maps)
day1otlk_1300
TORNADO PROBABILITY
day1probotlk_1300_torn
Probability of a tornado within 25 miles of a point. 
Hatched Area: 10% or greater probability of EF2 – EF5 tornadoes within 25 miles of a point.
HAIL PROBABILITY
day1probotlk_1300_hail
Probability of one inch diameter hail or larger within 25 miles of a point.  Hatched Area: 10% or greater probability of two inch diameter hail or larger within 25 miles of a point.
DAMAGING THUNDERSTORM WINDS PROBABILITY

day1probotlk_1300_wind
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.  Hatched Area: 10% or greater probability of wind gusts 65 knots or greater within 25 miles of a point

The forecast is very complex today.  SPC has classified this as a POTENTIALLY DANGEROUS SEVERE WEATHER EVENT. IF YOU ARE WITHIN THE ENHANCED, AND ESPECIALLY MODERATE RISK OUTLINE, PLEASE BE THINKING AND PLANNING YOUR ACTION FOR SAFETY. 

From the SPC 13Z update:
Ozarks to Mid Mississippi, lower Ohio and Tennessee Valleys…

A complicated, potentially dangerous severe-weather event is possible today into this evening. Multiple rounds of strong-severe thunderstorms are expected today across this region, additively contributing enough severe hazard for the “moderate” (level 4 of 5) risk area. A swath of damaging to severe gusts and at least a few embedded tornadoes are likely to accompany a complex of thunderstorms from southern MO across parts of the multi-state area near the Ohio/Mississippi River junction, to at least northern parts of the Tennessee Valley region. The main MCS should move east-southeastward to southeastward along and near the instability gradient associated with the aforementioned outflow boundary. Before and during that process, several supercells are expected, offering tornadoes (a few potentially significant/EF2+), large to very large hail, and localized severe gusts.

Based on my analysis of the current outlook, CIPS, NAM 3km, and SPC SREF forecast models, information derived from forecast indices indicate all severe threats are probable, with all having a significant potential.  Based on the complexity of the forecast, I highly recommend reading the outlook text.  Based on my analysis, this event today has the potential to become a DANGEROUS and DEADLY situation.

Tornadoes (stronger) will be a threat mainly within the MODERATE and ENHANCED outline (possibly northern half of AR.).  Based on CAPE, all SRH values, shear values, along with strongly veering winds, and extreme EHI values, lends credence to strong tornadoes within the hatched area on the SPC  tornado probability map.  While some EF2+ tornadoes COULD occur over portions of the ENHANCED risk outline, residents within the MODERATE and 10% hatched tornado risk area, could experience EF3 – E5 tornadoes.

Some PDS (Particularly Dangerous Situation) tornado watches could be issued today.  Significant large hail of 2.00″+ in diameter is possible along with severe damaging wind / gusts (60 – 70 mph),within the same general area, given CAPE, shear, lifted indices values, and moderate to steep mid level lapse rates.  Strongest severe thunderstorms may initiate from mid afternoon through the evening hours CDT.

Let me point out, this does not mean this will ABSOLUTELY occur, but that analyzed forecast conditions indicate a high POSSIBILITY.

The following were the forecast parameters and indices analyzed this morning from the 06Z model runs, with the max. values pertaining to southern portions of the ENHANCED risk area (south of the MODERATE outline), and strongest of the maximum values over the MODERATE and 10% hatched tornado risk area.  Bear in mind, indices recorded below are for the time of peak intensity which could be initiating by early to mid afternoon.  All model information had not updated as of the SPC 13Z update, and I am posting below, what the new information is from the SPC.  Indices meanings can be accessed further on in the synopsis:
SBCAPE: 2500 – 4500 j/kg-1
MLCAPE: 2500 –4000 j/kg-1
MUCAPE: 3000 – 4500 j/kg-1
SRH 0 -1 km: 100 – 200 m2/s2
SRH 0 -3 km: 200 – 350 m2/s2
SRH EFFECTIVE: 200 – 250 m2/s2

L. I.: -6 to -11
SCP: 5 – 21
STP: 10 – 23
0 -6 km SHEAR: 50 – 60 kts
EFF. SHEAR: 40 – 50kts
MID LEVEL LAPSE RATE: 7.5 – 8.0C
DEWPOINT: 62F – 76F
EHI: 4.2 – 6.8+
TOTAL TOTALS INDEX: 55 – 56C
K INDEX: 26 – 34C
SWEAT INDEX:
550 – 575

From the SPC 13Z UPDATE:
Eastern OK to AR, Mid-South and central TX…
Thunderstorms should develop by late afternoon near the front and dryline, as a combination of lift along those boundaries and strong surface heating combine with very rich low-level moisture to erode the EML cap sampled well by the 12Z FWD RAOB. Large to giant hail, occasional severe gusts, and a few tornadoes are possible as activity shifts eastward to northeastward across central/east TX, the Arklatex, and AR through the evening. The northern part of this convection may merge with or be overtaken by MCS activity moving out of MO and into parts of the Mid-South. The afternoon/preconvective environment should be characterized by steep low/middle level lapse rates on either side of the weakening cap, along with surface dewpoints commonly in the 70s F. This will contribute to strong buoyancy with the peak/preconvective MLCAPE reaching 4500-5500 J/kg, and SBCAPE values topping 6000 J/kg. Although near-surface flow generally will be 10 kt or less, limiting lowest-km hodographs/shear, effective-shear magnitudes in the 40-55-kt range indicate supercells will be possible. These will be capable of very large/destructive hail exceeding 3 inches in diameter. Clusters or upscale mergers of convection also may offer deep, precip-loaded, hail-cooled downdrafts with locally severe gusts. Cell mergers and interactions with boundaries will factor into tornado potential on the storm scale, since the environmental low-level shear appears on the margins.

The increase in MLCAPE along with analyzed 0 – 3km SRH values, will increase the EHI.
Screenshot 2024-04-26 at 19-04-32 Env Parameters and Indices
Screenshot 2024-04-27 at 08-58-07 Env Parameters and Indices
Screenshot 2024-04-27 at 08-56-33 Env Parameters and Indices
Screenshot 2024-04-27 at 08-59-15 Env Parameters and Indices
Screenshot 2024-05-01 at 08-46-17 Env Parameters and Indices
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.

SWEAT INDEX
Screenshot 2024-03-30 at 09-30-56 SWEAT Index

The following are the SCP (Supercell Composite Parameter) and STP (Significant Tornado Parameter) forecast maps from the NAM model.  Generally, the higher the values and brighter the color, indicates a greater probability of strong thunderstorm and tornadic activity over an area:
NAM 3KM SCP FORECAST (3:00 p.m. 08 MAY  – MIDNIGHT CDT 09 MAY)
nam-nest-arkansas-supercell_comp-1715169600-1715198400-1715230800-80
NAM 3KM STP FORECAST (3:00 p.m. 08 MAY  – MIDNIGHT CDT 09 MAY)

nam-nest-arkansas-sig_tor-1715169600-1715198400-1715230800-80
This is from the 00Z update from NADOCAST.  Click on the image for the updates page.  Once there, click on the time on the left (i.e. 12Z), then scroll to models-conus-sigtor abs -calib)
nadocast_2022_models_conus_sig_tornado_abs_calib_20240508_t00z_f12-35
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:
SPC MESOSCALE DISCUSSIONS (CLICK IMAGE FOR UPDATES)
Valid MD Image
SPC CONVECTIVE WATCHES (CLICK IMAGE FOR UPDATES)
Valid WW Image
IF A TORNADO WARNING IS ISSUED FOR YOUR AREA, IMMEDIATELY TAKE STURDY AND SAFE 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/

SPC HOMEPAGE LINK
https://www.spc.noaa.gov/classic.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)
canvas.radr_.us_
RAP RADAR (CLICK IMAGE THEN GO TO LOOP DURATION AND PICK LENGTH OF LOOP, THEN CLICK RADAR SITE)
CARIBBEAN RADAR (CLICK IMAGE TO ACCESS ANIMATION)
radar_comp_Eng
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

palmharborforecastcenter

2024-05-08 14:41:46

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