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Severe Weather Threat April 25-26


audioguy3107

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Well, after reading FFC's discussion this afternoon, probably should have a separate thread for this event...especially with them citing March 2008 as the closest reminder when numerous supercells tracked across north Georgia into South Carolina as the evening went along.  SPC still has us only in a slight risk, but we all know the deal here.  If we don't have any junkvection to deal with and we get a good amount of sun and heating before 2 PM or so, we may have a pretty serious situation on our hands.  It doesn't look like the wedge will save us here around Atlanta this time, although may not be the case further NE into the upstate of SC.  Anyhow, here's the Day 1 convective outlook in case you haven't seen it.

 

 

post-1217-0-86395800-1429922612_thumb.gi

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Here's a part of the afternoon discussion........whenever offices in the SE start talking about long track tornadoes, we better start paying attention.  Any STP over 2 or 3 has the potential to be pretty serious.

 

12Z MODEL GUIDANCE STILL INDICATING ISOLATED TO SCATTERED
SIGNIFICANT SVR STORMS SAT 3PM-MIDNIGHT BEHIND MORE WIDESPREAD
AREA OF SHRA AND ELEVATED TSRA. PROGGED STP VALUES THE HIGHEST WE
CAN REMEMBER IN THE LAST 2-3 YEARS AND HAS WORKED WELL WITH
PREVIOUS HIGH END EVENTS. 12Z GFS HAS STP 4-6 FROM SRN AL TO NW
GA TO ERN TN AT 00Z SUN. VERY IMPRESSIVE DEEP SHEAR WITH THIS
EVENT AND EVEN THO DIRECTIONAL SHEAR NOT THAT GREAT...0-1KM BULK
SHEAR ALSO IMPRESSIVE AT 30-40KTS. THOMPSON ET AL 2003 HAD SHOWN
PREVIOUSLY THAT 0-1KM BULK SHEAR JUST AS HELPFUL AS 0-1KM SRH WHEN
PREDICTING TORNADIC SUPERCELLS. IF EVEN MORE FAVORABLE SHEAR
DEVELOPS ON STORM SCALE AND BOUNDARY WITH WEDGE FRONT INTERACTS
WITH ANY SUPERCELL...MODERATE TO LONG TRACK TORNADOES CANT BE
RULED OUT.

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The sounding posted above doesn't scream tornado to me with winds from the westerly/SSW direction at the surface. The area to watch for tornadic activity will be where the warm front/wedge boundary sets up, but still thinking the biggest threat for tornadoes will be N and NW of the area. Not ruling out a rouge supercell away from the boundary in the SE either. Other threat, in my opinion, will be large hail. Lapse rates fully support some large hail, especially out over TN. SPC has also highlighted this area in their newest update with a 30% hatched outlook.

 

A couple soundings from the 0z NAM4km for comparison..

 

Athens, GA:

vZGg5DJ.png

 

Crossville, TN:

MbYnddi.png

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5% chance of tornado's in KY/IL/IN and S GA/N FL but only a 2% chance elsewhere around the south.  Cells don't look to pop until pretty late tonight so this won't be the best chase chance unless you are planning on going to the IL/KY line (which is indeed a good place to chase since it is mainly flat).  I have been waiting for a decent threat in that area but I have a final exam in my forecasting class today so I will not be participating sadly.  If something were to pop in E TN or N GA though later tonight, I might take a little journey if it isn't too late.  I believe playing the triple point today in KY will be the best bet for anyone look for twisters with helicity favorable and a high celling.  The 6z 4km NAM shows a nice line of cells breaking out across N GA late tonight but the other short range models do not agree as much.  Cape will not be the problem in S GA as convective mode will be in full force, but shear could be marginal, not allowing full supercell mode to occur.  The atmosphere does seem to be clearing a bit though, so a few decent cells later tonight across the south cannot be ruled out.  Good luck to anyone chasing today and watch for large hail if you are headed to KY/TN!

 

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5% chance of tornado's in KY/IL/IN and S GA/N FL but only a 2% chance elsewhere around the south.  Cells don't look to pop until pretty late tonight so this won't be the best chase chance unless you are planning on going to the IL/KY line (which is indeed a good place to chase since it is mainly flat).  I have been waiting for a decent threat in that area but I have a final exam in my forecasting class today so I will not be participating sadly.  If something were to pop in E TN or N GA though later tonight, I might take a little journey if it isn't too late.  I believe playing the triple point today in KY will be the best bet for anyone look for twisters with helicity favorable and a high celling.  The 6z 4km NAM shows a nice line of cells breaking out across N GA late tonight but the other short range models do not agree as much.  Cape will not be the problem in S GA as convective model will be in full force, but shear could be marginal, not allowing full supercell mode to occur.  The atmosphere does seem to be clearing a bit though, so a few decent cells later tonight across the south cannot be ruled out.  Good luck to anyone chasing today and watch for large hail if you are headed to KY/TN!

 

 

 

Lower Ohio Valley is the place to see twisters for sure, wedge wins in SC and a lot of GA......until we see this pattern break the chances for most of Dixie Alley into the Carolinas to see a large true severe outbreak is pretty slim....

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Wedge is not much of a factor IMBY as of now

 

N GA will need to see plenty of sun to destabilize but its early so maybe you will get enough sun to help with this afternoon.......there are some decent breaks to the west headed your way......if the low had headed further south it would have been a rough day there for sure....

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Well, looks like things may not be as volatile as models showed yesterday, of course the morning AM convection has reinforced the ever present north Georgia storm shield.  Anyway, FFC has just sent up a special sounding so we may know a little more here in the next hour.  We've had plenty of breaks in the clouds and temps have warmed up into the low to mid 70's, so instability is slowly increasing so it's not over yet.  We should know more by 4 PM or so.

 

- Buck

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mcd0456.gif

 

MESOSCALE DISCUSSION 0456

NWS STORM PREDICTION CENTER NORMAN OK
0210 PM CDT SAT APR 25 2015

AREAS AFFECTED...PORTIONS OF CNTRL AL AND WRN GA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 251910Z - 252045Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...AN ISOLATED SEVERE THREAT MAY DEVELOP ACROSS PORTIONS OF
CNTRL AL/WRN GA THIS AFTERNOON. DEPENDING ON ADDITIONAL CONVECTIVE
DEVELOPMENT...WW ISSUANCE IS POSSIBLE.

DISCUSSION...ISOLATED CONVECTION THAT INITIALLY FORMED OVER E-CNTRL
MS HAS RECENTLY MOVED INTO W-CNTRL AL WHILE WEAKENING...MOST LIKELY
IN ASSOCIATION WITH LIFT ATTENDANT TO A LOW AMPLITUDE SHORTWAVE
TROUGH MOVING OVER THE LOWER MS VALLEY ALONG WITH DIURNAL HEATING. A
BROAD CIRRUS SHIELD DOWNSTREAM FROM THUNDERSTORMS ALONG THE GULF
COAST IS TEMPERING MORE ROBUST HEATING ACROSS THIS AREA...WITH
TEMPERATURES GENERALLY IN THE UPPER 70S TO LOWER 80S. CONVECTION
FROM EARLIER THIS MORNING HAS OVERTURNED THE LOW TO MID LEVEL
AIRMASS AND LESSENED LAPSE RATES SOMEWHAT. HOWEVER...18Z SOUNDINGS
FROM BMX AND FFC SUGGEST THAT THE ATMOSPHERE HAS HAD SUFFICIENT TIME
TO RECOVER...AS MLCAPE RANGES FROM 1000-2000 J/KG ACROSS CNTRL
AL...TO ABOUT 500-1000 J/KG OVER WRN GA. EFFECTIVE SHEAR OF 50-70 KT
WOULD SUPPORT SUPERCELL STRUCTURES...WITH AN ASSOCIATED THREAT FOR
DAMAGING WINDS AND LARGE HAIL. WITH LOW-LEVEL FLOW NOW MAINLY VEERED
TO THE SW PER 18Z AREA SOUNDINGS AND RADAR VWPS...THE TORNADO THREAT
APPEARS LOW AT THIS TIME. RECENT HRRR TRENDS SUGGEST ISOLATED TO
WIDELY SCATTERED CONVECTION MAY FORM ACROSS SRN PORTIONS OF CNTRL AL
THIS AFTERNOON. IF THIS OCCURS...THEN A WW MAY BE ISSUED.

..GLEASON/MEAD.. 04/25/2015


ATTN...WFO...FFC...BMX...

LAT...LON 32318780 32518831 32858829 33518704 33998542 33438474
32428466 32088503 32118679 32288737 32318780 

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Best storm of the year currently. A legit severe thunderstorm. You can tell the storms still weakened a bit though.

Where Gawx? 81mph wind gust around Savannah and that's the second severe storm of the day there.

KSAV got hit hard tonight. 9 pm obs, NW 48, peak gust 81 mph squall 1/4 mile VIS

Edit: You saw that report, my goodness, these storms missed just south of here and would have been the most severe in a long time. That's the strongest wind gust i've seen in KCHS CWA outside of a tropical cyclone.

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Yep, metal/Stormsfury, it has been quite the stormy and wet day in SAV. The SAV area got strong to severe thunderstorms with lots of thunder/lightning, moderate to heavy rains, and gusty winds this evening. My power flickered off once. This adds to the heavy rains from strong to severe thunderstorms that we got earlier today (around midday) to make for quite a weather day!

Regarding the 81 mph gust at the SAV airport: wow!! Holy sheet! I wonder how long it has been since the last gust that strong there as alluded to by Stormsfury. The last hurricane hit was by David in 1979 and I don't know if SAV airport got a gust that strong then. I may check David later.

There was widespread tree damage as well as some property damage in especially areas just west and NW of SAV proper followed very soon by that in parts of the city followed by some of that to the east over Wilmington Island and finally Tybee Island, where 60 mph gusts were measured about 20 minutes after the city of SAV got hit. So, the activity was moving eastward at near a whopping 60 mph!

Edit: I got probably close to 3" of rainfall today!

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Well, good lord was that a colossal severe weather fail. How we went from FFC's discussion yesterday to what (didn't) happen in less than 24 hrs. is beyond me. I'm embarrassed for even starting this thread :axe: . North Georgia storm shield alive and well for about the 4th straight year.

The SGA storm sheild is still alive too. That line of storms got devoured as soon as it passed us. It usually happens to the west b4 moving in. The rest held together up there by Savannah.

It been a pretty active 6 days here severe wise.

2 tornado watches, 2 severe thunderstorm watches, like 6 severe thunderstorm warnings and 1 tornado warning. Today was the only day we actually got some action though and is the only day I remember here where we have had a severe thunderstorm watch and tornado watch in one day.

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Well, good lord was that a colossal severe weather fail. How we went from FFC's discussion yesterday to what (didn't) happen in less than 24 hrs. is beyond me. I'm embarrassed for even starting this thread :axe: . North Georgia storm shield alive and well for about the 4th straight year.

No storms here. Don't worry about the fail. This has been happening since last spring. Severe storms are getting as hard to get right as snow here.

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Wow that lady sounds so dumb on twc. Did they really not know that was coming to Mobile, AL? There was warnings and everything. They say they thought it was going to be a regular storm. I'm pretty sure the skies had to be scary looking before the storm hit and not just suddenly popped up out of nowhere like they were saying.

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Wow that lady sounds so dumb on twc. Did they really not know that was coming to Mobile, AL? There was warnings and everything. They say they thought it was going to be a regular storm. I'm pretty sure the skies had to be scary looking before the storm hit and not just suddenly popped up out of nowhere like they were saying.

Well, when your sailing in a regatta , the box wine is flowing like wine, and you don't have a care in the world , til you are capsized! Money can't save you from drowning!! She did sound dumb, and first rule on the water is : know the weather, duh!
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