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Severe Poss severe threat late this week

THIS IS FROM NWS BMX

AS OF 1400HRS 01/07/2020
A ROBUST STORM SYSTEM WITH AMPLE DYNAMICS WILL AFFECT THE AREA ON
SATURDAY AS A COLD FRONT ARRIVES FROM THE WEST. INSTABILITY VALUES
ARE FORECAST TO BE SUFFICIENT FOR SEVERE STORMS POSING A RISK FOR
DAMAGING WINDS AND TORNADOES. THE RECENT RAINFALL AND ELEVATED RIVER
LEVELS WILL RAISE CONCERNS OVER POSSIBLE MINOR FLOODING.

WHILE CONFIDENCE IS GROWING IN SEVERE WEATHER ON SATURDAY WITH GOOD
OVERALL GLOBAL MODEL AGREEMENT IN THE SYNOPTIC PATTERN AND SETUP,
MUCH OF THE CRUCIAL DETAILS REMAIN TO BE RESOLVED. THE DYNAMICS ARE
QUITE STRONG WITH THIS SETUP FEATURING A 65-75 KNOT LOW LEVEL JET
ACROSS THE AREA ON SATURDAY WITH VERY HIGH WIND SHEAR VALUES ACROSS
OUR NORTHERN AND CENTRAL COUNTIES WITH SUFFICIENT VALUES ACROSS THE
SOUTHERN COUNTIES. THE FORECAST INSTABILITY VARIES WITH HIGHER
VALUES ACROSS THE SOUTH BUT SUFFICIENT VALUES ARE DEPICTED ACROSS
MUCH OF OUR FORECAST AREA WITH THE LOWEST VALUES ACROSS THE FAR
NORTH. ALL OF THESE DETAILS WILL CONTINUE TO BECOME MORE DEFINED AND
REFINED AS WE CONTINUE TO EVALUATE NEW DATA THROUGH TIME AND AS WE
GET INTO THE 2-3 DAY TIME PERIOD WE WILL HAVE MESOSCALE INFORMATION
TO EXAMINE IN ADDITION TO THE SYNOPTIC SCALE DATA THAT IS AVAILABLE
AT THIS TIME. BOTTOM LINE IS TO EXPECT SOME ADJUSTMENTS AND FURTHER
REFINEMENTS TO THE FORECAST AS WE GET CLOSER TO SATURDAY AND TO USE
THE TIME NOW TO ADJUST YOUR WEEKEND PLANS AND TO ENSURE THAT YOU
HAVE A SOLID SEVERE WEATHER SAFETY PLAN, EMERGENCY SUPPLIES AND
MULTIPLE RELIABLE WAYS TO GET EMERGENCY INFORMATION
 
Sounding ahead of the linear convection in eastern TX/western LA, definitely the presence of a EML, also unimpressive llvl lapse rates and some weird action at 3km, and meh crit angles, these are things that will probably limit supercellular development ahead of the line, also why the amount of heating from breaks in clouds is important, but even this environment like what this sounding shows can support tornadoes due to such strong wind energy, and even with unimpressive llvl lapse rates theres solid 3CAPE, whether it’s from a rogue supercell out ahead or a QLCS tornado, also these storms are gonna b moving fast, 45-55 mph231A240F-A144-4008-8B4C-09421BB55590.png
 
NOW THEY ARE MENTIONING A DERECHO:oops:

LATEST FROM NWS BMX

.LONG TERM...
/UPDATED AT 0402 AM CST WED JAN 08 2020/

FRIDAY THROUGH TUESDAY.

FRIDAY WILL MARK THE BEGINNING OF AN EXTENDED PERIOD OF UNSETTLED
WEATHER AS A TROUGH STRENGTHENS AND BECOMES INCREASINGLY DYNAMIC
OVER TEXAS AND NEW MEXICO. STRENGTHENING SOUTHERLY FLOW WILL LEAD
TO ISENTROPIC LIFT AS A WARM SECTOR BEGINS TO ADVANCE NORTHWARD.
WIDESPREAD SHOWERS WITH ISOLATED EMBEDDED ELEVATED THUNDERSTORMS
ARE EXPECTED ACROSS MUCH OF THE FORECAST AREA ON FRIDAY.

AS THE UPPER-LEVEL TROUGH TRANSITIONS FROM A NEUTRAL TO NEGATIVE
TILT FRIDAY NIGHT, RAPID PRESSURE FALLS ARE EXPECTED NEAR THE
MISSISSIPPI RIVER AT 6 AM SATURDAY. AN EXTREMELY STRONG LOW-LEVEL
JET IS ANTICIPATED IN ADVANCE OF A WELL-ORGANIZED QLCS, WITH MID
TO UPPER 60S DEWPOINTS OVERSPREADING THE FORECAST AREA BY NOON
SATURDAY. AS IT STANDS, A SIGNIFICANT SEVERE WEATHER EVENT APPEARS
LIKELY BEGINNING AS EARLY AS 9 AM IN OUR WESTERN COUNTIES. SBCAPE
IS CURRENTLY MODELED AT 500-1000 J/KG BY MOST MODEL GUIDANCE, BUT
MY HUNCH IS THAT THESE VALUES MAY BE A LITTLE ON THE LOW SIDE DUE
TO THE EFFECTS OF ERRONEOUS-LOOKING QPF AS NOTED IN THE ECMWF
DATA. EVEN TAKING CAPE A FACE VALUE, STRONG FORCING COMBINED WITH
EXTREME LOW-LEVEL WINDS AND WIND SHEAR WOULD RESULT IN A QLCS
CAPABLE OF PRODUCING WIDESPREAD DAMAGING WINDS AND EMBEDDED
TORNADOES. THE ECMWF SHOWS A WIDE SWATH OF 70-80 KT 700MB WINDS
WITH POCKETS UP TO 100 KTS, MEANING THAT A DERECHO CANNOT BE RULED
OUT PARTICULARLY ACROSS OUR NORTHWESTERN COUNTIES. THE POTENTIAL
FOR SUPERCELLS AHEAD OF THE QLCS WILL DEPEND ON THE STATE OF THE
WARM SECTOR. IF THE WARM SECTOR IS RELATIVELY UNCONTAMINATED AND
THE CURRENT TIMING HOLDS TRUE, TEMPERATURES WOULD RISE INTO THE
70-74F RANGE DURING THE LATE MORNING AND EARLY AFTERNOON HOURS,
AIDING IN THE FORMATION OF CELLULAR CONVECTION AHEAD OF THE QLCS.
IN ORDER FOR ANY CELLULAR ACTIVITY TO BECOME TORNADIC IN THE
PRESENCE OF EXTREME WIND SHEAR, ROBUST UPDRAFTS WILL BE REQUIRED.
OTHERWISE, THESE UPDRAFTS WILL BE TORN APART.
 
Its quiet in here .... what are short range models saying for Friday ?
 
Looking at lastest models, no change in my thinking. Main threat will be a squall line with embedded supercell structures with wind being the highest threat. Things for that is the amount of wind energy close to the surface would be easier to bring to the ground in the heavier rain. There is also lots of forcing as the trough goes negative. Things against this although there is CAPE, 3/4 of it is off the surface with almost none in the lowest 3km of the Atmosphere. That along with the cap may mean that storms in the squall line remain mostly elevated which reduces the wind and tornado threat.

The other thing against it is low level lapse rates are just pitiful. That may hurt the strength of the line as it progresses east and upper level support pulls NE.

There could be possible convective development ahead of the line, but it too suffers from bad lapse rates and elevated instability. Along with the very high wind energy, which will tear the updrafts apart. Something would have to change significantly to make me believe that supercells dropping tornadoes ahead of the line is a likely threat.
 
Brad travis said a squall line with spin ups so I'm not that concerned but I'll be watching
 
Well as of now, the synoptic look almost screams widespread almost "extreme" damaging wind event, with flood concerns. As BMX AFD points out, the winds will most likely "overpower" any updrafts that do form. One thought though is what may occur should any convection form away from the strongest wind fields (Eastern Alabama, into West Georgia to Metro ATL) With QLCS moving into here later in day, a better chance at convection exists, especially if any sunshine occurs.
The other factor(as always) is any meso-features that develop.
 
gawxnative said:
Well as of now, the synoptic look almost screams widespread almost "extreme" damaging wind event, with flood concerns. As BMX AFD points out, the winds will most likely "overpower" any updrafts that do form. One thought though is what may occur should any convection form away from the strongest wind fields (Eastern Alabama, into West Georgia to Metro ATL) With QLCS moving into here later in day, a better chance at convection exists, especially if any sunshine occurs.
The other factor(as always) is any meso-features that develop.
Click to expand...

Have you had a chance to read Kirk Mellish latest blog? He also talks about it being more of a wind damage type system with flooding concerns for North Georgia.


Sent from my iPhone using Tapatalk
 
If thunder roars please go indoors. Just want to echo the official NWS. Stay off land lines and get out of the bath tub. Do not shelter under trees or use an umbrella in heavy lightning.
 
Latest NAM not very enthusiastic about CAPE. I know it does not take much in winter, but interesting to say the least.
 
deltadog03 said:
Latest NAM not very enthusiastic about CAPE. I know it does not take much in winter, but interesting to say the least.
Click to expand...

I think it doesn't take much Cape if it's in the right place. Fred told me years ago to not necessarily look at cape in winter, but look at 0-3km Cape. In this case not only is surface Cape meager, but 0-3km Cape is about zero.
 
Arcc said:
I think it doesn't take much Cape if it's in the right place. Fred told me years ago to not necessarily look at cape in winter, but look at 0-3km Cape. In this case not only is surface Cape meager, but 0-3km Cape is about zero.
Click to expand...
I wonder if there will so much shear the updrafts get ripped apart.
 
Something that caught my eye a bit, and reminds me of past setups, but you can actually get low topped convection that forms off the gulf, even with a EML/meh llvl lapses, pulled a sounding from there and actually showed the best crit angle I’ve seen modeled for this setup (even this one ain’t that good) even with solid low level cape those low level lapse rates aren’t the best for tornadoes, and I tried to get a sounding that wasn’t contaminated so you gotta account for that in this sounding, and also there’s way more MUcape vs SBCape, indicating that the environment supports more elevated convection due to trash low level lapse rates 3907FAAE-2EA9-487D-817B-E0214F313404.jpeg5EAD0CE2-5E0A-44F6-862C-F1D6A057B24F.png
 
The discussion from spc and bmx seem to focus on this being a primarily qlcs driven event. However they both point to this being a rather potent qlcs with the possibility of embedded strong tornadoes. The qlcs wording is about as potent as you can get when talking about a squall line. So the line itself will need to be taken rather seriously. Both discussions mentioned a conditional threat for supercells accompanied by strong tornadoes but mentioned it all depends on what the status of the warm sector ahead of the line looks like.
 
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Myfrotho704_ said:
Something that caught my eye a bit, and reminds me of past setups, but you can actually get low topped convection that forms off the gulf, even with a EML/meh llvl lapses, pulled a sounding from there and actually showed the best crit angle I’ve seen modeled for this setup (even this one ain’t that good) even with solid low level cape those low level lapse rates aren’t the best for tornadoes, and I tried to get a sounding that wasn’t contaminated so you gotta account for that in this sounding, and also there’s way more MUcape vs SBCape, indicating that the environment supports more elevated convection due to trash low level lapse rates View attachment 30026View attachment 30027
Click to expand...

In my experience, in these types of strong negative tilt troughs, right off the gulf is normally where you do end up seeing the highest threat especially tornado wise.
 
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