Oct. 17/18 Severe Weather Thread

by **andyhb** 2012-10-16, 2:12 am

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1244 AM CDT TUE OCT 16 2012

VALID 171200Z - 181200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE AR...SE
MO...FAR SRN IL...FAR WRN KY...WRN TN AND NW MS...

...LOWER TO MID MS VALLEY...
AN UPPER-LEVEL TROUGH IS FORECAST TO DIG SEWD FROM THE GREAT PLAINS
SEWD INTO THE OZARKS WEDNESDAY AS A 75 TO 90 KT MID-LEVEL JET DIVES
INTO THE GREAT PLAINS. AT THE SFC...A COLD FRONT WILL ADVANCE
QUICKLY SEWD INTO THE MID MS VALLEY AND ARKLATEX. STRONG LARGE-SCALE
ASCENT ASSOCIATED WITH THE UPPER-LEVEL TROUGH AND LIFT ASSOCIATED
WITH THE EXIT REGION OF THE MID-LEVEL JET WILL PROVIDE PLENTY OF
SUPPORT FOR THUNDERSTORM DEVELOPMENT ACROSS THE SLIGHT RISK AREA
WEDNESDAY AFTERNOON. AS STORMS RAPIDLY INCREASE IN COVERAGE LATE
WEDNESDAY AFTERNOON...MCS DEVELOPMENT WILL BE POSSIBLE WITH A
CONVECTIVE CLUSTER OR LINE LIKELY PERSISTING INTO THE OVERNIGHT
PERIOD.

FORECAST SOUNDINGS AT LITTLE ROCK LATE WEDNESDAY AFTERNOON SHOW
INSTABILITY PEAKING NEAR 2500 J/KG OF MLCAPE JUST BEFORE FRONTAL
PASSAGE WITH SFC DEWPOINTS IN THE UPPER 60S F. THIS ALONG WITH 0-6
KM OF AROUND 50 KT SHOULD BE FAVORABLE FOR SUPERCELLS. COLD TEMPS
ALOFT WILL HELP SUPPORT ISOLATED LARGE HAIL AND LOW-LEVEL SHEAR
SHOULD BE STRONG ENOUGH FOR A TORNADO THREAT ESPECIALLY WITH THE
MORE DOMINANT SUPERCELLS. HOWEVER...STRONG LARGE-SCALE ASCENT AND
FRONTAL FORCING COULD RESULT IN A RAPID TRANSITION TO LINEAR MODE.
THESE FACTORS COMBINED WITH STEEP LOW-LEVEL LAPSE RATES EVIDENT ON
FORECAST SOUNDINGS COULD RESULT IN AN ENHANCED WIND DAMAGE THREAT AS
MCS DEVELOPMENT TAKES PLACE EARLY WEDNESDAY EVENING. IT APPEARS
THERE IS A POSSIBILITY FOR A CONCENTRATED SEVERE THREAT EVENT
WEDNESDAY AFTERNOON ACROSS ECNTRL AR. THE SEVERE THREAT SHOULD DROP
OFF WITH NEWD EXTENT ACROSS SE MO...SRN IL AND FAR WRN KY DUE TO A
LACK OF DESTABILIZATION. A SHARP DROP OFF IN THE SEVERE THREAT
SHOULD ALSO EXIST ACROSS THE ARKLATEX DUE TO THE STRONG CAP IN
PLACE.

..BROYLES.. 10/16/2012

by **tennessee storm09** 2012-10-16, 5:38 am

looks pretty legit to me... and if the timing is off some, the 30 percent will be nudged little further east across the miss. river... spc hasnt don a good job on timing issues latley in my opinion.

by **Toot** 2012-10-16, 8:05 am

Yessir..expecting a strong squall line with this system. I will try to post more about this threat this evening!

by **skillsweather** 2012-10-16, 10:51 am

Bring it on we need some good storms. Been boring weather here for awhile and we didn't get no good spring storms so hope we have some good fall ones before the cold

by **andyhb** 2012-10-16, 3:24 pm

tennessee storm09 wrote:looks pretty legit to me... and if the timing is off some, the 30 percent will be nudged little further east across the miss. river... spc hasnt don a good job on timing issues latley in my opinion.

I think you're pushing it just a bit...

by **Eric** 2012-10-16, 4:26 pm

Honestly don't see what the big deal is: surface low pressure is straddling the MN/Canada border; progged pressures never dip below 1000mb; mid/upper level jets are lagging well behind the trough axis in the cold sector of the LP; surface dew points never rise above 60F (they're stable in the low 50s but ramp up a bit due to the LLJ); instability axis is narrow and will get trangressed quickly as the frontal forcing kicks in; warm sector is progged to be socked in, further inhibiting diurnal instability. Will there be thunder...probably...but hoping for anything more than a loud QLCS will leave some heartbroken.

by **Toot** 2012-10-16, 5:07 pm

Eric wrote: progged pressures never dip below 1000Mb

I havent seen guidance today...but I have been tracking this system for several days and its been consistently progged well into the 980Mb range..so the part I quoted above is false!

by **Eric** 2012-10-16, 5:13 pm

Toot wrote:
Eric wrote: progged pressures never dip below 1000Mb
I havent seen guidance today...but I have been tracking this system for several days and its been consistently progged well into the 980Mb range..so the part I quoted above is false!

Low pressure CENTER bombs out in the 980-990mb range, but the pressures further downstream are much, much higher. Guess I touched a nerve...not intentional. Maybe I should've made that point a bit more clear in my discussion.

by **Toot** 2012-10-16, 5:36 pm

No nerve touched...normally when a Lps is being discussed and one is talking about the mslp of the system they are talking about the stormcenter. Just a misunderstanding on my part I guess wacko

by **Adam2014** 2012-10-16, 5:53 pm

I just don't see the potential for this storm. I expect it to be a lot like Sunday in our area with some more lightning and thunder... that is it.

by **tennessee storm09** 2012-10-16, 5:59 pm

the latest nam does develop a meso type low, that would allow for more back building of the winds ... still suspect some severe in west tn... at least some boomer warnings...but wouldnt be suprised to see a tornado warning closer to the miss. river

by **andyhb** 2012-10-16, 6:33 pm

Toot wrote:No nerve touched...normally when a Lps is being discussed and one is talking about the mslp of the system they are talking about the stormcenter. Just a misunderstanding on my part I guess

He's talking about the sfc pressure trough that extends from the sfc low southward into TX.

by **Toot** 2012-10-16, 7:23 pm

andyhb wrote:
He's talking about the sfc pressure trough that extends from the sfc low southward into TX.

Yes..I realize what he is talking about...but normally when one is discussing the mean sea level pressure of a high or low pressure system the stormcenter is what we would be discussing. This is the same when you are talking about a tropical cyclone's pressure. Why would we discuss pressures a 1000 miles away from the stormcenter unless we were talking about wind gradients?

by **Toot** 2012-10-16, 7:53 pm

18z 4km nam valid 20-21:00 tomorrow yikes

Oct. 17/18 Severe Weather Thread 2reqdtg

by **Toot** 2012-10-16, 8:31 pm

Here is a quick writeup I did on my FB blog this evening!

Eyes will turn to the mid-south region tomorrow evening as a very deep upper low drops into the eastern US from the higher latitudes. An associated and very deep surface cyclone will drag an intense cold front into the region..ahead of this cold front moisture will quickly pool. Dewpoints in the Memphis area should climb into at least the mid 60's if not the lower 70's.

Plentiful sunshine during the day will help temperatures heat up into the 80's and when those surface temps mingle with cooler temps aloft provided by quickly falling heights fuel for the fire will be abundant! Upper level winds will also be more than favorable for vigorous thunderstorm growth. The shaded areas are where I think the best potential exists for severe thunderstorms.

Oct. 17/18 Severe Weather Thread 222528_318242548283504_1544739518_n

Oct. 17/18 Severe Weather Thread 222528_318242548283504_1544739518_n

by **tennessee storm09** 2012-10-16, 8:58 pm

Toot wrote:Here is a quick writeup I did on my FB blog this evening!

Eyes will turn to the mid-south region tomorrow evening as a very deep upper low drops into the eastern US from the higher latitudes. An associated and very deep surface cyclone will drag an intense cold front into the region..ahead of this cold front moisture will quickly pool. Dewpoints in the Memphis area should climb into at least the mid 60's if not the lower 70's.

Plentiful sunshine during the day will help temperatures heat up into the 80's and when those surface temps mingle with cooler temps aloft provided by quickly falling heights fuel for the fire will be abundant! Upper level winds will also be more than favorable for vigorous thunderstorm growth. The shaded areas are where I think the best potential exists for severe thunderstorms.

very well put there toot... jesus christ, no one predicted this to be a tornado outbreak or major severe outbreak at that... but for what i see on the latest models and short range stuff... there should be a few cells that will go to a severe warning, and one or two will verify... still i wouldnt rule out a storm that will have some rotation near or around the miss. river that could put out a tornado warning... should be no doubt a severe thuunderstrom watch issued to areas far east as posible the tn river... i know i get carried away some on severe.. cause i like to chase and personally i think i can chase with the best of them... i am working on getting me more equipment hopefully by the spring season 2013

by **Toot** 2012-10-16, 9:06 pm

tennessee storm09 wrote: jesus christ, no one predicted this to be a tornado outbreak or major severe outbreak at that

Exactly...no one has even mentioned the word "Tornado" not sure why people think anyone is making a big deal of anything. scratch

by **andyhb** 2012-10-16, 9:16 pm

Toot wrote:
andyhb wrote:
He's talking about the sfc pressure trough that extends from the sfc low southward into TX.

Yes..I realize what he is talking about...but normally when one is discussing the mean sea level pressure of a high or low pressure system the stormcenter is what we would be discussing. This is the same when you are talking about a tropical cyclone's pressure. Why would we discuss pressures a 1000 miles away from the stormcenter unless we were talking about wind gradients?

Because low level pressure falls, even ones that far away from the center of the low, can lead to backing/modification of LL winds and enhance convergence along/ahead of a front, creating more favorable conditions for severe storms.

by **tennessee storm09** 2012-10-16, 9:37 pm

well whatever takes place here tomorrow... i wont even see it... im going to jackson miss. tomorrow with my wife for a gospel conviction until sunday but i am carring my laptop since i dont have serive on my phone, internet that is... down in the kjan area it seems to much of a cap will be in place were i am at... and i am affraid i will be to far south of the better shear products... maybe i can still get a nice line down there.

by **Toot** 2012-10-16, 9:39 pm

andyhb wrote:
Because low level pressure falls, even ones that far away from the center of the low, can lead to backing/modification of LL winds and enhance convergence along/ahead of a front, creating more favorable conditions for severe storms.

Agreed..Now just speaking hypothetically...wouldnt these new pressure falls that are now backing the LL winds be coming from a newly formed low/mesolow? Not the one 1000 miles away?

by **tennessee storm09** 2012-10-16, 9:41 pm

Toot wrote:
andyhb wrote:
Because low level pressure falls, even ones that far away from the center of the low, can lead to backing/modification of LL winds and enhance convergence along/ahead of a front, creating more favorable conditions for severe storms.

Agreed..Now just speaking hypothetically...wouldnt these new height falls that are now backing the LL winds be coming from a newly formed low/mesolow? Not the one 1000 miles away?

i am not andy, but yeah, if nam verifies... thats what its showing

by **andyhb** 2012-10-16, 10:21 pm

Toot wrote:
Agreed..Now just speaking hypothetically...wouldnt these new pressure falls that are now backing the LL winds be coming from a newly formed low/mesolow? Not the one 1000 miles away?

It could be that, or it could be just the pressure falls associated with the front itself.

by **andyhb** 2012-10-17, 2:22 am

Oct. 17/18 Severe Weather Thread Day1probotlk1200torn

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT WED OCT 17 2012

VALID 171200Z - 181200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE OZARKS/ARKLATEX TO
LOWER/MIDDLE MS VALLEY...

...SYNOPSIS...
A SOUTHEASTWARD SURGING STRONG POLAR JET /130+ KT 300 MB/ WILL
CONTRIBUTE TO CONSIDERABLE LARGE SCALE TROUGH AMPLIFICATION THROUGH
TONIGHT ACROSS THE CENTRAL/EASTERN CONUS...WITH THE MAIN PORTION OF
THE LONGWAVE TROUGH EVOLVING OVER THE UPPER MIDWEST. MULTI-PHASED
SURFACE CYCLOGENESIS WILL OCCUR TODAY ACROSS THE UPPER MIDWEST AND
UPPER/MIDDLE MS VALLEYS...WITH AN EAST-SOUTHEASTWARD MOVING COLD
FRONT PROGRESSIVELY INTERCEPTING AN INCREASINGLY MOIST AIRMASS
TOWARD THE ARKLATEX/MS VALLEY INTO THIS EVENING...WITH SEVERE TSTMS
PROBABLE AS BELOW.

...ARKLATEX/OZARKS TO LOWER/MIDDLE MS VALLEY...
WHILE MOISTURE IS INITIALLY LIMITED AWAY FROM THE TX COAST EARLY IN
THE OVERNIGHT...STEADY MOISTURE TRANSPORT WILL OCCUR NEAR/MORE SO
ABOVE THE SURFACE EARLY TODAY IN TANDEM WITH AN INCREASINGLY STRONG
SOUTHWESTERLY LOW LEVEL JET. BY MID/LATE AFTERNOON...LOWER TO MIDDLE
60S F SURFACE DEWPOINTS ARE EXPECTED TO BECOME WELL ESTABLISHED FROM
THE ARKLATEX INTO THE OZARKS/MIDDLE MS VALLEY...WHERE A SURFACE WAVE
MAY DEVELOP IN VICINITY OF THE ADVANCING COLD FRONT THIS AFTERNOON.

STRONG/STEADY HEIGHT FALLS AND A BROADLY DIFFLUENT UPPER JET EXIT
REGION OVERSPREADING AN INCREASINGLY MOIST WARM SECTOR WILL LEAD TO
STRONG/SEVERE SURFACE BASED TSTM DEVELOPMENT TODAY ACROSS THE
REGION...PERHAPS AS SOON AS EARLY AFTERNOON OR MORE CERTAINLY BY
MID/LATE AFTERNOON. SUCH DEVELOPMENT SHOULD INITIALLY OCCUR ACROSS
PORTIONS OF THE OZARKS/PERHAPS FAR EASTERN OK...WHILE EXPANDING
SHORTLY THEREAFTER INTO THE MIDDLE MS VALLEY VICINITY AND REMAINDER
OF AR AND THE ARKLATEX VICINITY. THIS DEVELOPMENT WILL PRINCIPALLY
BE NEAR THE COLD FRONT...ALTHOUGH SOME SEMI-DISCRETE DEVELOPMENT
COULD OCCUR AHEAD OF IT ACROSS PORTIONS OF SOUTHERN/EASTERN AR AND
NORTHERN LA/NORTHWEST MS WHERE A RELATIVELY MOIST/WEAKLY INHIBITED
BOUNDARY LAYER WILL EXIST COINCIDENT WITH LOW-LEVEL CONFLUENCE.

AS AN INCREASINGLY STRONG DEEP LAYER WIND FIELD OVERSPREADS THE
FRONTAL ZONE/WARM SECTOR...A SEVERAL HOUR TEMPORAL WINDOW OF
SEMI-DISCRETE SUPERCELLS WILL BE POSSIBLE THROUGH THE
AFTERNOON...ALTHOUGH ROBUST FORCING FOR ASCENT WILL ALMOST
UNDOUBTEDLY ENSURE CELL MERGERS AND RELATIVELY QUICK LINEAR
EVOLUTION BY EVENING. IN A RELATIVE SENSE...SEMI-DISCRETE STORMS MAY
PERSIST A BIT LONGER INTO THE EVENING ACROSS THE MID-SOUTH/LOWER MS
VALLEY ON THE SOUTHERN FRINGE OF THE EVOLVING SQUALL LINE. SOME
TORNADOES WILL BE POSSIBLE WITHIN A HIGHLY SHEARED LOW LEVEL
ENVIRONMENT /STEADILY INCREASING 0-1 KM SRH TO UPWARDS OF 200-400 M2
PER S2/...EITHER VIA SEMI-DISCRETE SUPERCELLS OR EVOLVING
QUASI-LINEAR EMBEDDED MESOVORTICES. HOWEVER...DAMAGING WINDS ARE
EXPECTED TO BE THE MOST PREVALENT HAZARD. SOME HAIL IS POSSIBLE AS
WELL...ESPECIALLY IN THE PRE-LINEAR EARLY CONVECTIVE CYCLE AND/OR
ACROSS THE ARKLATEX TO WESTERN MS WHERE SUPERCELLS ARE MORE PROBABLE
AND DESTABILIZATION WILL BE A BIT STRONGER THIS AFTERNOON.

...MIDWEST/OH VALLEY...
LOWER-TOPPED CONVECTION IS LIKELY TO DEVELOP NEAR THE ADVANCING COLD
FRONT THIS AFTERNOON WITHIN A KINEMATIC ENVIRONMENT CHARACTERIZED BY
AMPLE FORCING FOR ASCENT/VERY STRONG SHEAR. EXPECTATIONS FOR MORE
MARGINAL MOISTENING/ANEMIC DESTABILIZATION SHOULD LARGELY LIMIT THE
SEVERE POTENTIAL WITH NORTHWARD EXTENT FOR AREAS SUCH AS NORTHEAST
MO AND IL/INDIANA. THAT SAID...AT LEAST CONVECTIVELY ENHANCED STRONG
WIND GUSTS MAY NONETHELESS BE POSSIBLE THIS AFTERNOON INTO EVENING.
UNANTICIPATED LOW-LEVEL MOISTENING/DESTABILIZATION WITH NORTHWARD
EXTENT...EVEN A COUPLED HUNDRED J/KG SBCAPE...WOULD WARRANT
NORTHWARD-SPATIAL ADJUSTMENTS OF THE CURRENT SLIGHT RISK ACROSS MORE
OF THE REGION.

..GUYER/ROGERS.. 10/17/2012

by **tennessee storm09** 2012-10-17, 6:53 am

spc must be buying in the nam soloution quite a bit. it clearyl shows the development of another low over oklahoma and it moves ne from there which will ramp up dew points rapidly... i really like the trends of the other models also... showing slowly even morre instabliltiy with the help of increasing lower level jet this evening... well i am off to the jackson ms area. that area is near or on the edge of the 10 percent hatched area... this may even turn out better than i thought, but i have seen some many busts the last few years or so... o well, its about time to keep eye on sref and ruc guidance.

by **tennessee storm09** 2012-10-17, 8:45 am

spc just done their morning update... nudged the 10 percent tornado chance some little east. pretty much sw corner of tn. the 10 percent hatched remains in the same spot. kjan arear