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March 17-18 Severe Weather Event


DanLarsen34
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Okay, okay... it looks like we're all saying pretty much the same thing now, so let's move on to actually discussing what's about to go down today. Thanks y'all

As posted above, incoming PDS watch for MS/AL. Also, WF is still currently over far N/NE MS, and cutting through or just NE of the Birmingham metro, based on SPC mesoanalysis as of 16z. Warm air advection is probably going to keep pushing it a bit farther north and northeast, but just how much remains to be seen, as the wedge might be holding on slightly longer than expected. Thoughts?

Just saw the post from @yoda as I was typing this. Wow...

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18 minutes ago, bamabonners said:

All these hype clowns keep throwing out 2011, 2011, 2011, 2011...  The more you use it, the less weight it will carry.  Then, people get tired of it or ignore it.  Then, it comes across as fear mongering or hype.  Where way, it is ridiculous.  Just give the facts and keep the hype away... Some people have a genuine fear of weather and these types of reports don't help.  

As a weather noob, but political science and policy professional, I have some survey data (pandemic disrupted plans to publish) showing that the public does not get tired or ignore stuff when it turns out to be overhyped and wrong.  We focused on hurricane warnings and preparedness and found warnings that did not live up to the hype failed to diminish peoples willingness to prepare for and believe future warnings.

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..SUMMARY  
  
A SIGNIFICANT TORNADO OUTBREAK IS EXPECTED WITH NUMEROUS STRONG AND  
A FEW LONG-TRACK, POTENTIALLY VIOLENT TORNADOES. AN INITIAL ROUND IS  
EXPECTED TO BEGIN ACROSS EASTERN MISSISSIPPI AND ALABAMA THIS  
AFTERNOON. A SEPARATE SWATH SHOULD EMANATE FROM SOUTHEAST ARKANSAS  
TO LOUISIANA THIS AFTERNOON AND SPREAD EAST ACROSS MISSISSIPPI AND  
ALABAMA THIS EVENING INTO TONIGHT.  

 

 

.DEEP SOUTH  
  
MINOR CHANGE MADE TO THE CATEGORICAL HIGH RISK AREA TO EXPAND A BIT.  
MAIN CHANGE IS TO THE UNDERLYING PROBABILITIES WITH THE ADDITION OF  
A 45 TOR AND 45 WIND. A DANGEROUS, LONG-DURATION TORNADO OUTBREAK  
EXPECTED TO COMMENCE THIS AFTERNOON AND PERSIST WELL INTO TONIGHT  
WITH MULTIPLE ROUNDS OF HEIGHTENED TORNADO POTENTIAL.  
  
ONGOING CONVECTION IS WITHIN AN ARC WITH A PRE-FRONTAL SQUALL FROM  
FAR EAST TX TO NORTHEAST AR AND THEN IN A MORE WEST/EAST-ORIENTATION  
FROM NORTHEAST AR TO THE AL/TN BORDER AREA. THE NORTHERN ACTIVITY  
WILL TEND TO REINFORCE THE SURFACE WARM FRONT APPROACHING THE TN  
BORDER WITH MS/AL THIS AFTERNOON. THE SOUTHWEST BAND WILL LIKELY  
PERSIST EAST AND SHOULD BREAKUP INTO A BROKEN BAND OF SUPERCELLS AT  
SOME POINT THIS AFTERNOON AS LOW-LEVEL SHEAR FURTHER STRENGTHENS  
ACROSS THE ARK-LA-MISS REGION. FARTHER EAST, WARM-ADVECTION SHOWERS  
IN SOUTHEAST MS TO WEST-CENTRAL AL WILL LIKELY DEEPEN BY EARLY  
AFTERNOON INTO A SEPARATE SWATH OF SEVERAL DISCRETE SUPERCELLS IN AN  
ENVIRONMENT OF STRENGTHENING LOW TO DEEP-LAYER SHEAR. BETWEEN THESE  
TWO AREAS, THE DESTABILIZING WARM SECTOR WITH WARMING BOUNDARY-LAYER  
TEMPERATURES AND MID 60S TO LOW 70S DEW POINTS, WILL SUPPORT AN  
EXPANSIVE PLUME OF 1500-2500 J/KG MLCAPE.  
  
BY LATE AFTERNOON AND INTO EARLY TONIGHT, A LOW-LEVEL JET SEGMENT  
WILL STRENGTHEN TO AT LEAST 50-60 KT ACROSS MS/AL AS THE MIDLEVEL  
TROUGH APPROACHES FROM THE WEST, CONTRIBUTING TO VERY STRONG  
LOW-LEVEL SHEAR (0-1 KM SRH IN EXCESS OF 300 M2/S2). BUOYANCY WILL  
BE SLOW TO DECREASE AFTER SUNSET AND WITH EASTWARD EXTENT BASED ON  
THE PREVALENCE OF RATHER RICH BOUNDARY-LAYER DEW POINTS, VERY  
FAVORABLE WIND PROFILES (WITH 700-MB WINDS REACHING 70-80 KT) WILL  
MAINTAIN THE THREAT FOR LONG-TRACK, INTENSE TORNADOES WITH BOTH  
WARM-SECTOR SUPERCELLS, AS WELL AS SUPERCELLS WITHIN THE BROKEN BAND  
NEAR AND AHEAD OF THE SURFACE WIND SHIFT PROGRESSING EAST ACROSS MS  
BY EARLY TONIGHT. THE STRONG TORNADO AND SIGNIFICANT DAMAGING WIND  
THREAT WHILE BECOMING MORE SPATIALLY CONFINED WITH TIME, WILL LIKELY  
PERSIST ACROSS PARTS OF AL OVERNIGHT AND SHOULD SPREAD INTO WESTERN  
GA BEFORE 12Z.  
  
..GRAMS/BENTLEY.. 03/17/2021  
  
 

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I feel like I'm watching ESPN debating MJ vs Lebron for the 1,000,000th time seeing all the comparisons to April 27 on here. 

That being said, surface based CAPE across the region at the moment is insane for 11:30 AM. This atmosphere is so ripe, looks like a classic multi-round tornado event today. 

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Just now, ATDoel said:

Those cells just west of Birmingham look to already have some broad rotation, the event wasn't supposed to start until 1...

yep..already getting that look and are discrete 

may really start  to spin  when they hit that warm front

right around the time they are over a major Metro area too

 

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Just now, janetjanet998 said:

yep..already getting that look and are discrete 

may really start  to spin  when they hit that warm front

right around the time they are over a major Metro area too

 

Check out the storm between Meridien and Hattiesburg, MS.  Local Jackson, MS news network met mentioned that the SPC is ready to issue a PDS tornado watch for most of MS, within the hour

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13 minutes ago, olafminesaw said:

Are probabilities defined as odds of a tornado within a circle who's radius is 25 miles, or as odds that a line segment 25 miles long will be crossed by a tornado?

Probability of a tornado within 25 miles of any point within the area outlined by the contour (or technically, to the right of the contour line, which is actually drawn as an arrow chasing its tail).

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RGENT - IMMEDIATE BROADCAST REQUESTED  
TORNADO WATCH NUMBER 29  
NWS STORM PREDICTION CENTER NORMAN OK  
1135 AM CDT WED MAR 17 2021  
  
THE NWS STORM PREDICTION CENTER HAS ISSUED A  
  
* TORNADO WATCH FOR PORTIONS OF   
  WESTERN AND CENTRAL ALABAMA  
  CENTRAL TO EASTERN MISSISSIPPI  
  
* EFFECTIVE THIS WEDNESDAY MORNING AND EVENING FROM 1135 AM UNTIL  
  700 PM CDT.  
   
..THIS IS A PARTICULARLY DANGEROUS SITUATION  
  
* PRIMARY THREATS INCLUDE...  
  NUMEROUS TORNADOES EXPECTED WITH A FEW INTENSE TORNADOES LIKELY  
  SCATTERED DAMAGING WINDS AND ISOLATED SIGNIFICANT GUSTS TO 80  
    MPH LIKELY  
  SCATTERED LARGE HAIL AND ISOLATED VERY LARGE HAIL EVENTS TO 3  
    INCHES IN DIAMETER LIKELY  
  
SUMMARY...NUMEROUS DISCRETE SUPERCELLS ARE EXPECTED TO DEVELOP THIS  
AFTERNOON CAPABLE OF PRODUCING STRONG TO INTENSE TORNADOES.  

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