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Severe Weather Risk This Weekend


Jim Martin

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Looking as if some severe weather mischief is a possibility for this weekend across the Southeast. From the National Weather Service Area Forecast Discussion from Birmingham...

 Threat 2 over the weekend still has some disagreement between the
models this time out, but certainly has the potential for some
significant impacts. The GFS has better continuity than the ECMWF
this run, as the ECMWF has trended back toward solutions a few
days ago. The GFS is picking up on several impulses riding through
the flow and the potential of severe storms Saturday, Saturday
night, and Sunday. The ECMWF is a bit more limited to Saturday
night and Sunday. The flow suggest that there will be additional
impulses and am leaning toward the GFS here. Additionally, the GFS
parameters are better for a longer period. ECMWF would suggest a
better risk south. Therefore, we will keep the severe threat going
for the entire area both Saturday and Sunday and not focus
specifically on these parameters. The synoptic pattern is
favorable and the mesoscale will have impacts. Analogues have
indications that the pattern is very conducive to severe storms.
Stay tuned.

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I've been paying attention to this setup the last day or two.....FFC and BHM is really highlighting the chances for a potential severe weather outbreak over Alabama and Georgia, especially on Sunday afternoon.  The GFS has CAPE in the 1000 - 2200 range nosing into western Georgia with surface temps in the low 70's and no CAD to protect us this time which is a rarity in the heart of winter.  LI as high as -5 over parts of the area.  If some of the models are correct in showing dryer air punching in from the west giving us clearing on Sat/Sun., this has potential we haven't seen in quite awhile.

- Buck

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Potential is certainly there for a significant event, but there are some caveats. Models have been inconsistent with the timing of the 500mb trough, with 12z GFS notably faster than earlier runs (though this could easily change in future runs). Overall low-level wind profiles are also a question mark. With that said, whenever you get a decent EML and good moisture in January, it's definitely something to watch. 

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8 hours ago, MattPetrulli said:

Kinda funny when there is more discussion of this severe weather event here than the SE thread, and this isn't even the main threat area. Nonetheless, Still could be one of the more significant events in the past few years.

Large majority of the posters in the SE forum are a little North and East of the threatened area with this storm. Not many Alabama posters, and not many who live along the gulf coast. 

Im concerned for Florida, the CIPs analogs exceeding 1 tor report is at 57% of Top 15 analogs, centered just west of orlando Sun night. 

IMG_6013.PNG

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There should be a date attached to the thread title. "This weekend" is kind of ambiguous.

From RAH:

A few strong storms
remain possible from mid afternoon Sun through Sun evening, with a
70-90 kt mid level jet streak accompanying the powerful upper
divergence and steep 700-500 mb lapse rates, topping 7.5 C/km
according to the GFS. Timing will be crucial, as the ECMWF is up to
12 hrs faster than the GFS with the arrival of the mid level low.
CIPS analog guidance at this range hints at a greater threat for FL,
historically speaking, but GFS forecast soundings for central NC
showing lengthy wavy hodographs and moderate instability support at
least a modest risk of severe storms in our area, including a
tornado risk along and north of the occluding frontal system.
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1 hour ago, Jon said:

Large majority of the posters in the SE forum are a little North and East of the threatened area with this storm. Not many Alabama posters, and not many who live along the gulf coast. 

Im concerned for Florida, the CIPs analogs exceeding 1 tor report is at 57% of Top 15 analogs, centered just west of orlando Sun night. 

 

Yeah Dixie Alley usually post in the central forum during big severe weather days....you don't see a lot of folks talking about severe in the SE forum until it gets FL/GA/SC/NC....where most of us are.  Still I am much more a severe weather guy, snowstorms tracking is slow and frustrating, so I will be in whichever forum the thread sets up in on Sat and Sunday...

Florida has a bloody history of winter tornado events....Feb seems to be the worst month for it in Florida, the threat here in the Carolinas is still a pretty big question mark, it doesn't take much to mitigate the threat up this way, that said when they do work out they can be pretty rough. Jan 2011 had a couple of nasty tornados out in western NC etc....

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confirmed tornado this morning in MS

look like a multi day event with the main bang saturday night into sunday

here is the  current day 2 and day 3 outlooks outlook

WER MISSISSIPPI VALLEY FRIDAY NIGHT/SATURDAY MORNING  
  
GENERAL SCENARIO REMAINS CONSISTENT WITH PREVIOUS DAY 3 OUTLOOK,  
WITH A SERIES OF LEAD SHORTWAVE TROUGHS EJECTING FROM THE  
CENTRAL/SOUTHERN PLAINS TO THE MISSISSIPPI VALLEY, DOWNSTREAM FROM A  
STRONG MID-UPPER JET CORE FROM NEAR THE CA COAST TO NORTHERN MEXICO.  
OF GREATEST INTEREST IS A SUBTLE SPEED MAX THAT IS EXPECTED TO EJECT  
NORTHEASTWARD FROM NORTHEAST MEXICO AND SOUTH TX TO THE LOWER MS  
VALLEY FRIDAY NIGHT.  LOW-LEVEL MASS RESPONSE TO THIS MIDLEVEL WAVE  
WILL FOSTER STRENGTHENING LOW-LEVEL WARM/MOIST ADVECTION AND  
LOW-LEVEL SHEAR FRIDAY NIGHT ACROSS THE NORTH-CENTRAL GULF COAST.   
SEVERAL CLUSTERS OF THUNDERSTORMS WILL LIKELY FORM WITHIN THIS  
REGIME AND SPREAD NORTHEASTWARD INTO AL THROUGH SATURDAY MORNING.  
  
BOUNDARY-LAYER DEWPOINTS OF 65-70 F ARE ALREADY PRESENT ACROSS THE  
GULF COAST, AND SHOULD REMAIN THERE THROUGH THE END OF THIS FORECAST  
PERIOD.  STRENGTHENING VERTICAL SHEAR WITH THE APPROACH OF THE  
MID-UPPER SPEED MAX, AS WELL AS STEEPENING MIDLEVEL LAPSE RATES FROM  AY 3 CONVECTIVE OUTLOOK    
NWS STORM PREDICTION CENTER NORMAN OK  
0211 AM CST THU JAN 19 2017  
  
VALID 211200Z - 221200Z  
  
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM LOUISIANA AND  
MISSISSIPPI EASTWARD TO GEORGIA...  
  
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE  
SLIGHT RISK AREA...  
   
..SUMMARY  
  
A FEW EPISODES OF SEVERE STORMS WILL BE POSSIBLE FROM SATURDAY  
MORNING THROUGH SUNDAY MORNING ACROSS A BROAD AREA OF THE LOWER  
MISSISSIPPI VALLEY AND THE SOUTHEAST STATES.  
   
..LOWER MISSISSIPPI VALLEY TO THE NORTHEAST GULF COAST  
  
A STRONG MID-UPPER TROUGH, NOW SOUTH OF THE ALEUTIANS, WILL REACH  
THE CA COAST AND NORTHWEST MEXICO BY DAY 2 (FRIDAY), AND CONTINUE  
EASTWARD ACROSS THE SOUTHERN PLAINS TO THE LOWER MS VALLEY BY  
SATURDAY NIGHT/SUNDAY MORNING (END OF DAY 3).  THERE ARE SOME  
DISAGREEMENTS AMONG THE OPERATIONAL MODELS, WITH THE NAM APPEARING  
TO REFLECT SOME CONVECTIVE FEEDBACK AND EASTWARD DEVELOPMENT OF THE  
SYNOPTIC CYCLONE TOO FAST COMPARED TO THE GFS/ECMWF.  WITHOUT THE  
FEEDBACK, LOW-LEVEL MASS RESPONSE/FLOW SHOULD REMAIN RELATIVELY WEAK  
DURING THE DAY SATURDAY ACROSS LA/MS IN THE MAIN PART OF THE WARM  
SECTOR.  THE PRIMARY SYNOPTIC CYCLONE AND ASSOCIATED LARGE-SCALE  
FORCING FOR ASCENT WILL APPROACH THE MS RIVER BY THE END OF THE  
PERIOD.  
  
COMPLICATING FACTORS THIS PERIOD WILL BE ANY LINGERING INFLUENCE OF  
ONGOING CONVECTION SATURDAY MORNING FROM MS INTO AL, AND A SOMEWHAT  
NEBULOUS FOCUS FOR ADDITIONAL STORMS DURING THE AFTERNOON ACROSS  
LA/MS (WELL AHEAD OF THE SYNOPTIC WAVE/COLD FRONT).  ANY STORMS THAT  
FORM HERE WILL DO SO IN AN ENVIRONMENT WITH STEEP MIDLEVEL LAPSE  
RATES, MODERATE BUOYANCY, AND SUFFICIENT DEEP-LAYER SHEAR FOR  
SUPERCELLS CAPABLE OF PRODUCING LARGE HAIL (POTENTIALLY SOME VERY  
LARGE) AND DAMAGING WINDS.  THE STRONGER LOW-LEVEL WIND PROFILES ARE  
EXPECTED FARTHER EAST AND OVERNIGHT IN ASSOCIATION WITH A LEAD SPEED  
MAX PROGRESSING INLAND FROM THE GULF.  ENHANCEMENT TO LOW-LEVEL  
SHEAR/SRH FROM SOUTH/SOUTHEAST AL INTO THE FL PANHANDLE AND  
SOUTHWEST GA WILL FAVOR SUPERCELLS WITH DAMAGING WINDS AND  
POTENTIALLY SOME TORNADO RISK, DEPENDING ON THE DETAILS ON THE  
LOW-LEVEL SHEAR AND NEAR-GROUND LAPSE RATES INLAND.  
  
WILL OPT TO MAINTAIN A RATHER BROAD 15%/SLIGHT RISK AREA IN THIS  
UPDATE, THOUGH PORTIONS OF THE OUTLOOK AREA MAY NEED TO BE  
CONSIDERED FOR HIGHER COVERAGE/INTENSITY PROBABILITIES ONCE  
UNCERTAINTIES ARE REDUCED.  
THE WEST-SOUTHWEST, WILL CONTRIBUTE TO AN INCREASINGLY FAVORABLE  
ENVIRONMENT FOR SEVERE STORMS FRIDAY NIGHT INTO SATURDAY MORNING.   
SUPERCELLS WILL BE POSSIBLE WITHIN THE CONVECTIVE CLUSTERS, WITH A  
COUPLE OF TORNADOES POSSIBLE GIVEN BUOYANCY ROOTED AT THE SURFACE  
AND EFFECTIVE SRH INCREASING TO 200-300 M2/S2.  THE STEEPENING LAPSE  
RATES AND RELATIVELY COOL UPSTREAM MIDLEVEL TEMPERATURES WILL  
SUPPORT A RISK OF LARGE HAIL, ESPECIALLY WITH ANY EMBEDDED  
SUPERCELLS, AS WELL AS DAMAGING WINDS.  

--------------------------

 

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From new Day 2 outlook for primarily Friday night:

By late Friday night, forcing for ascent may become strong enough,
   southward along the 850 mb jet axis toward southeast
   Louisiana/Mississippi/Alabama coastal areas, to overcome inhibition
   and support increasing convective development.  In the presence of
   increasingly boundary layer based instability, the risk for
   supercells with potential for tornadoes, in addition to large hail
   and damaging winds, may increase by or shortly after 12Z Saturday.
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SPC outlook excerpts

 Day 1: The more pronounced mass response to the midlevel trough will occur
   tonight across the lower MS Valley, where strengthening low-level
   flow/warm advection will contribute to multiple thunderstorm
   clusters near and after midnight.  Boundary layer dewpoints in the
   mid-upper 60s will maintain surface-based buoyancy through the
   overnight hours, while the increasing low-level shear will favor
   supercells and some risk for tornadoes.
Day 2: In addition, a few tornadoes also appear likely, though stronger
   low-level shear will be maximized along the northward-lifting warm
   front, and much farther east beneath the LLJ.
Day 3: Current thinking is a squall line should migrate
   across the Gulf states, eventually progressing across the FL
   peninsula as flow strengthens from the west.  Damaging winds and
   perhaps some hail and possibly a few tornadoes can be expected with
   this activity.

 

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the lack of activity in this thread is strange

enhanced risk 3 outlooks in a row

if the atmosphere can recover after the first wave tomorrow, Saturday night into Sunday could be really nasty

 

 

new day 1

   
..NORTHWESTERN GULF COAST AND LOWER MISSISSIPPI VALLEY  
  
CONVECTIVE DEVELOPMENT, ASSOCIATED WITH LOW/MID-LEVEL WARM ADVECTION  
ON THE LEADING EDGE OF A DEVELOPING SOUTHERLY RETURN FLOW, NOW  
APPEARS UNDERWAY NEAR LOWER TO MIDDLE TEXAS COASTAL AREAS.  THIS  
STILL APPEARS LIKELY TO GRADUALLY INCREASE IN COVERAGE LATE THIS  
AFTERNOON THROUGH TONIGHT, WHILE DEVELOPING NORTHEASTWARD THROUGH  
THE LOWER MISSISSIPPI VALLEY BY 12Z SATURDAY.  THE RISK FOR SEVERE  
HAIL MAY BE THE PRIMARY THREAT WITH INITIAL DEVELOPMENT ACROSS PARTS  
OF UPPER TEXAS COASTAL AREAS INTO LOUISIANA AND MISSISSIPPI.   
HOWEVER, THE RISK FOR POTENTIALLY DAMAGING WIND GUSTS, AND  
TORNADOES, PROBABLY WILL INCREASE AS ACTIVITY GROWS UPSCALE LATER  
TONIGHT, AS THIS INCREASINGLY COINCIDES WITH INLAND BOUNDARY LAYER  
MOISTENING AND DESTABILIZATION, ACROSS PARTS OF SOUTHEASTERN  
LOUISIANA INTO SOUTHERN MISSISSIPPI.  LATEST MODEL OUTPUT SEEMS TO  
SUGGEST A GREATER LIKELIHOOD THAT COULD OCCUR CLOSER TO  
LOUISIANA/MISSISSIPPI COASTAL AREAS THAN PREVIOUSLY INDICATED. 
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2 minutes ago, janetjanet998 said:

the lack of activity in this thread is strange

enhanced risk 3 outlooks in a row

if the atmosphere can recover after the first wave tomorrow, Saturday night into Sunday could be really nasty

 

 

new day 1


   
..NORTHWESTERN GULF COAST AND LOWER MISSISSIPPI VALLEY  
  
CONVECTIVE DEVELOPMENT, ASSOCIATED WITH LOW/MID-LEVEL WARM ADVECTION  
ON THE LEADING EDGE OF A DEVELOPING SOUTHERLY RETURN FLOW, NOW  
APPEARS UNDERWAY NEAR LOWER TO MIDDLE TEXAS COASTAL AREAS.  THIS  
STILL APPEARS LIKELY TO GRADUALLY INCREASE IN COVERAGE LATE THIS  
AFTERNOON THROUGH TONIGHT, WHILE DEVELOPING NORTHEASTWARD THROUGH  
THE LOWER MISSISSIPPI VALLEY BY 12Z SATURDAY.  THE RISK FOR SEVERE  
HAIL MAY BE THE PRIMARY THREAT WITH INITIAL DEVELOPMENT ACROSS PARTS  
OF UPPER TEXAS COASTAL AREAS INTO LOUISIANA AND MISSISSIPPI.   
HOWEVER, THE RISK FOR POTENTIALLY DAMAGING WIND GUSTS, AND  
TORNADOES, PROBABLY WILL INCREASE AS ACTIVITY GROWS UPSCALE LATER  
TONIGHT, AS THIS INCREASINGLY COINCIDES WITH INLAND BOUNDARY LAYER  
MOISTENING AND DESTABILIZATION, ACROSS PARTS OF SOUTHEASTERN  
LOUISIANA INTO SOUTHERN MISSISSIPPI.  LATEST MODEL OUTPUT SEEMS TO  
SUGGEST A GREATER LIKELIHOOD THAT COULD OCCUR CLOSER TO  
LOUISIANA/MISSISSIPPI COASTAL AREAS THAN PREVIOUSLY INDICATED. 

We are just looking for snow! We score severe thunderstorms and severe , like Buffalo does Lake effect!

just saw TWC has a TORCON of 5 for most of SC and  S Ga for Sunday 

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RAH: Friday 1/20...

Severe threat: Forcing for ascent will not be lacking on Sunday
given lead disturbances aloft and the eventual 100+ meter
height falls late Sunday Deep layer shear is plenty strong in
excess of 50kt, and low-level hodographs are long and
increasingly cyclonically curved owing to a 40-50kt LLJ and the
isallobaric response to the deepening surface low. The CAD
airmass that developed this morning may still be around in the
western Piedmont, and thus the early morning convection is more
likely to be elevated than later in the day when backed low
level flow has a better chance to advection the warm sector
inland. The late day convection should evolve into a squall line
as the forcing becomes more linear. Highs in the mid 60s
northwest to mid 70s southeast, along with dewpoints potentially
in the low/mid 60s, below mid-level lapse rates of 6.5-7C/km
could definitely support CAPE values of near 1000 J/KG.
Destablization is always a tough thing for models to handle in
the pattern, and they typically over mix the eastern edges of
the CAD airmass and overestimate SBCAPE. There is always the
potential for convection along the Gulf Coast to alter the
downstream mass fields and disrupt moisture transport. However,
the strengthen of the surface low does warrant some concern for
damaging winds and a few tornadoes inland to maybe the US-1
corridor later Sunday?

QPF and Flooding: Total QPF is between 2-3 inches through the
weekend, which may not be a significant flooding threat when
spread out over a couple of days. However, PW around 1.25" and
a cutoff low to our SW are favorable for at least some minor
flooding.
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New Day 1 outlook for tonight has a 10% hatched area of tornado probabilities for S Louisiana, S Mississippi and far S Alabama (including NOLA and Mobile, AL).

In addition, a 10% tornado probability area has been included for
   parts of southern LA/MS and far southwest AL, including the Mobile
   metro area. There will be a greater potential for discrete supercell
   development with southward extent ahead of the previously mentioned
   line of thunderstorms. Forecast soundings across this region suggest
   that any tornadoes that do form in this environment could be strong
   with southwesterly winds around 850 mb strengthening to around 50 kt
   overnight, and corresponding effective SRH in excess of 300 m2/s2.
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Interestingly strong wording on this evening's day 1 outlook. Another thing to note is that they put;

   Reminder: This Day 1 Convective Outlook will be valid THROUGH 12Z
   Saturday (7 AM EST/6 AM CST). An upcoming Day 1 Convective Outlook
   will be issued around 06Z (1 AM EST/Midnight CST), which will be
   valid BEGINNING at 12Z Saturday, and continuing through 12Z Sunday.

One thing to point out;

Forecast soundings across this region suggest
   that any tornadoes that do form in this environment could be strong

Strong wording with that.

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The kinematics on Sunday over FL and GA (perhaps into the Carolinas too) look pretty ridiculous. Euro has an appreciable plume of instability into the area as well. Going to come down to the amount of convection between now and then and also the mode, but I could certainly see a widespread damaging wind event or significant tornadoes if the intensity of the low level jet being shown by the Euro/NAM verifies. Tomorrow is more clouded given the high res almost uniformly indicating a lot of contamination from MCS activity, but if anything resembling a healthy warm sector ends up being in place, effective shear is certainly high enough for a pretty broad swath of severe reports.

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The National Weather Service in Lake Charles has issued a

* Tornado Warning for...
  Northwestern Jefferson County in southeastern Texas...

* Until 815 PM CST
    
* At 748 PM CST, a severe thunderstorm capable of producing a tornado
  was located near China, or near Nome, moving northeast at 35 mph.

  HAZARD...Tornado and quarter size hail. 

  SOURCE...Radar indicated rotation. 

  IMPACT...Flying debris will be dangerous to those caught without 
           shelter. Mobile homes will be damaged or destroyed. 
           Damage to roofs, windows, and vehicles will occur.  Tree 
           damage is likely. 

 

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