April 15th Severe weather thread Tornado outbreak possible

[janetjanet998]

this deserves it own thread at this point as the GFS and NAM are now on board, anything after 12z friday goes here

SPC day 3 outlook to get things started

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE LOWER TO

MID-MS VALLEY...CNTRL GULF COAST...TN VALLEY AND OH VALLEY...

..LOWER TO MID-MS VALLEY/CNTRL GULF COAST/TN VALLEY/OH VALLEY

A STRONG NEGATIVELY-TILED UPPER-LEVEL LOW IS FORECAST TO MOVE FROM

THE CNTRL PLAINS EWD INTO THE OZARKS ON FRIDAY. THE EXIT REGION OF A

WELL-DEVELOPED 80 TO 100 KT MID-LEVEL JET IS FORECAST TO SPREAD

ACROSS THE CNTRL GULF COAST STATES DURING THE DAY CREATING STRONG

DEEP LAYER SHEAR PROFILES FAVORABLE FOR SEVERE STORMS. THE

GFS...ECMWF AND NAM BEGIN THE DAY 3 PERIOD WITH AN MCS LOCATED IN

THE MID-MS VALLEY DRIVING THIS FEATURE EWD INTO WRN KY AND WRN TN BY

MIDDAY. SOUTH ACROSS THE WARM SECTOR...THE MODELS DEVELOP MODERATE

INSTABILITY ACROSS MUCH OF THE CNTRL GULF COAST STATES AND INITIATE

NUMEROUS THUNDERSTORMS FROM MIDDLE TN SWWD INTO NCNTRL AL...MS AND

SE LA DURING THE AFTERNOON. THE DEVELOPMENT OF A SEVERE MCS SEEMS

PROBABLE ACROSS THE CNTRL AND SRN PARTS OF THE SLIGHT RISK AREA

FRIDAY AFTERNOON AND EVENING.

FORECAST SOUNDINGS IN CNTRL MS AND WRN AL AT 21Z ON FRIDAY SHOW

IMPRESSIVE WIND SHEAR PROFILES WITH 50 TO 60 KT OF 0-6 KM SHEAR AND

0-3 KM STORM RELATIVE HELICITIES AROUND 400 M2/S2. THIS ENVIRONMENT

SHOULD SUPPORT SUPERCELL DEVELOPMENT WITH A THREAT FOR STRONG

TORNADOES POSSIBLE. HOWEVER...THE MAGNITUDE OF THE TORNADO THREAT

WILL BE CONDITIONAL UPON STORM MODE. IF A SQUALL-LINE WERE TO

DEVELOP INSTEAD OF MORE DISCRETE CONVECTION....THEN WIND DAMAGE

COULD BE THE GREATER THREAT. THE UPPER-LEVEL SYSTEM IS QUITE

IMPRESSIVE WITH A WELL-DEVELOPED LOW-LEVEL JET IN PLACE ACROSS THE

ECNTRL STATES. THE GFS AND NAM SOLUTIONS FOCUS THE LOW-LEVEL JET

FURTHER NORTH IN TN AND KY BY LATE AFTERNOON WHILE THE ECMWF SHOWS A

STRONG COMPONENT OF THE JET IN THE TN VALLEY AND CNTRL GULF COAST

STATES. IF THE ECMWF SOLUTION IS CORRECT AND MOISTURE RETURN ENDS UP

BEING STRONGER THAN FORECAST...THEN A TORNADO OUTBREAK COULD OCCUR

IN PARTS OF WRN TO MIDDLE TN...MS AND AL FRIDAY AFTERNOON. AT THIS

POINT...THE POTENTIAL FOR AN OUTBREAK REMAINS CONDITIONAL AND

DIFFERENCES IN THE MODEL SOLUTIONS RAISE UNCERTAINTIES CONCERNING

THE EXACT SCENARIO.

FURTHER NORTH ACROSS THE OH VALLEY...SEVERE STORMS WILL ALSO BE

POSSIBLE FRIDAY AFTERNOON AS THE UPPER-LEVEL LOW APPROACHES FROM THE

WEST. IN SPITE OF WEAKER INSTABILITY...A STRONG WIND FIELD IS

FORECAST WITH COLD TEMPS ALOFT. THIS WOULD RESULT IN A POTENTIAL FOR

HAIL AND WIND DAMAGE WITH THE MORE ORGANIZED CONVECTIVE CLUSTERS. A

TORNADO THREAT WILL ALSO BE POSSIBLE IN THE OH VALLEY DUE TO THE

STRONG LOW-LEVEL SHEAR FORECAST BUT THIS POTENTIAL SHOULD BE

DEPENDENT UPON MOISTURE RETURN.

[janetjanet998]

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE BIRMINGHAM AL

313 PM CDT WED APR 13 2011

DISCUSSION

EXPECTING SEVERE THUNDERSTORMS...POSSIBLY TORNADIC SUPERCELLS...BY

MID TO LATE AFTERNOON FRIDAY IN THE WEST TO PUSH THROUGH THE STATE

THROUGH THE EVENING HOURS. 12Z MODEL CONSENSUS IS TO HAVE THE

MAJORITY OF THE STORMS IN FAR EASTERN ALABAMA BY MIDNIGHT AND

POSSIBLY EAST OF THE CWA BY THEN. THE ONLY OUTLIER THIS GO ROUND

IS THE NAM WHICH IS SLOWER WITH ITS FRONTAL POSITION. OTHERWISE...ALL

THE SEVERE WEATHER PARAMETERS APPEAR TO BE FAVORABLE FOR ANOTHER

POTENTIAL WIDESPREAD EVENT.

[janetjanet998]

impressive

[Indystorm]

Certainly is impressive and much more likely to come to fruition with richer dewpoints closer to the Gulf than the 50 prob progged for a slight time with the northern IL situation April 10. Scary.

[Stebo]

impressive

Wow that's a big time 50 area.

[janetjanet998]

Jackson

CONVECTIVE INHIBITION IS FORECAST TO GIVE WAY TOTALLY FRIDAY...

ALLOWING THE DEVELOPMENT OF INTENSE CONVECTIVE UPDRAFTS AND

SUPERCELL DEVELOPMENT ACROSS THE REGION. WIDESPREAD DESTABILIZATION

WILL OCCUR. CAPE VALUES ABOVE 1000-1500 ARE FORECAST ACROSS THE

ENTIRE FORECAST AREA...PAINTED AS HIGH AS 2-3K BY THE GFS ACROSS THE

BULK OF THE REGION FRIDAY AFTERNOON. GFS BUFR SOUNDINGS SHOW VERY

HEALTHY LAPSE RATES WITH THE EURO GOING HEAVIEST WITH FORECAST LAPSE

RATE VALUES AT OR ABOVE 7 DEGREES OVER MANY NRN AND ERN AREAS.

SYNOPTIC LIFT IS ENHANCED WHEN THE DEEPENING UPPER TROUGH PIVOTS

INTO THE AREA FRIDAY AFTERNOON...MAINTAINING ITS NEGATIVELY TILTED

ORIENTATION AS A SECONDARY WAVE PIVOTS AROUND THE LOW CENTER.

HEALTHY UPPER DIVERGENCE DEVELOPS ACROSS THE ENTIRE AREA EARLY IN

THE DAY AND IS FORECAST TO PERSIST IF NOT STRENGTHEN OVER ERN ZONES

DURING THE AFTERNOON...AS DOES LOW LEVEL HELICITY AND SHEAR. INTENSE

0-1KM HELICITIES AND IMPRESSIVE VGP VALUES HIGHLIGHT THE HIGH

POTENTIAL FOR TORNADIC DEVELOPMENT FOR MUCH OF THE AREA...

PARTICULARLY OVER ERN ZONES DURING THE AFTERNOON AS THE LOW LEVEL

JET INTENSIFIES.

[tornadotony]

Yeah this one means serious business. Really serious business. We've shaved awful close a few times this year, but this one looks like a sucker puncher.

[Stebo]

Yeah this one means serious business. Really serious business. We've shaved awful close a few times this year, but this one looks like a sucker puncher.

Yeah the difference being this time its closer to the gulf, less distance for moisture return.

[Stebo]

Btw I don't know if anyone mentioned it but I wouldn't be shocked to see an enhanced tornado potential near the low on Thursday and especially Friday. One of those low CAPE high shear environments.

[Thundersnow12]

Btw I don't know if anyone mentioned it but I wouldn't be shocked to see an enhanced tornado potential near the low on Thursday and especially Friday. One of those low CAPE high shear environments.

I wouldn't be shocked either given the impressive low-level instability up into southern and parts of central IL.

[CUmet]

One thing that I really like about the Friday setup are the very cold mid-level temperatures that overspread the warm sector, even all the way down to the Gulf Coast. The 0-3km CAPE progs have been impressive as a result. The SREF significant tornado ingredients progs have been very impressive as well, and it has a pretty good track record.

However, there are a couple of significant question marks that remain. All of the models have indicated substantial precip occurring across the warm sector pretty early in the day, which is consistent with the lack of capping and the strong forcing. Also, the low-level jet axis is largely removed from the instability axis, leaving less area for the instability to overlap with the strong helicities. The caveat, though, is that the models do have a tendency to underestimate the helicity closer to the boundary.

This will be an interesting day to watch unfold, and it certainly holds potential, but I don't think this is a slam-dunk tornado outbreak by any means.

[Stebo]

One thing that I really like about the Friday setup are the very cold mid-level temperatures that overspread the warm sector, even all the way down to the Gulf Coast. The 0-3km CAPE progs have been impressive as a result. The SREF significant tornado ingredients progs have been very impressive as well, and it has a pretty good track record.

However, there are a couple of significant question marks that remain. All of the models have indicated substantial precip occurring across the warm sector pretty early in the day, which is consistent with the lack of capping and the strong forcing. Also, the low-level jet axis is largely removed from the instability axis, leaving less area for the instability to overlap with the strong helicities. The caveat, though, is that the models do have a tendency to underestimate the helicity closer to the boundary.

This will be an interesting day to watch unfold, and it certainly holds potential, but I don't think this is a slam-dunk tornado outbreak by any means.

No I totally agree, and what I meant with my post about the area's near the low is if they can break into the sun even if its only for a 4-6hr window, the potential would sky rocket.

[upsloper]

I agree about the potential along the weak instability axis near the low.

I know this a Friday thread, but I think even Saturday looks somewhat interesting along for Ohio and part of Michigan. I think low-level lapse rates on both the NAM and GFS actually look better on Saturday than on Friday over the weak instability zone as the H7 temp min moves over the area. Looking at forecast soundings for that area, it might not take much of an adjustment of things to get CAPE values over 500. Models forecast strong lift over the region, and with shear vectors nearly perpendicular to the boundary, I wouldn't be surprise to see some brief mini-supercells and an isolated tornado or two.

[Madmaxweather]

Be nice if we could get something out of this. The Sunday/Monday busted big time around here.

[Stebo]

I agree about the potential along the weak instability axis near the low.

I know this a Friday thread, but I think even Saturday looks somewhat interesting along for Ohio and part of Michigan. I think low-level lapse rates on both the NAM and GFS actually look better on Saturday than on Friday over the weak instability zone as the H7 temp min moves over the area. Looking at forecast soundings for that area, it might not take much of an adjustment of things to get CAPE values over 500. Models forecast strong lift over the region, and with shear vectors nearly perpendicular to the boundary, I wouldn't be surprise to see some brief mini-supercells and an isolated tornado or two.

With the low ejecting west of the area, wouldn't discount the chance right now probably be a low end chance but certainly not 0.

[wxsmwhrms]

One thing that I really like about the Friday setup are the very cold mid-level temperatures that overspread the warm sector, even all the way down to the Gulf Coast. The 0-3km CAPE progs have been impressive as a result. The SREF significant tornado ingredients progs have been very impressive as well, and it has a pretty good track record.

However, there are a couple of significant question marks that remain. All of the models have indicated substantial precip occurring across the warm sector pretty early in the day, which is consistent with the lack of capping and the strong forcing. Also, the low-level jet axis is largely removed from the instability axis, leaving less area for the instability to overlap with the strong helicities. The caveat, though, is that the models do have a tendency to underestimate the helicity closer to the boundary.

This will be an interesting day to watch unfold, and it certainly holds potential, but I don't think this is a slam-dunk tornado outbreak by any means.

One other thing to keep in mind is this is the Southeast - and significant tornadoes early in the day are not uncommon. When you have dewpoints near 70F, you don't really need much sun to get good instability when you have mid level cold air. That early day convection the models are showing could potentially be nasty. I would feel pretty confident about at least a moderately impressive severe/tornado event, but any really high end tornado episode, if it occurs, would probably be confined to a relatively small regional area. Parts of MS/AL and maybe W/mid TN?

[Stebo]

One other thing to keep in mind is this is the Southeast - and significant tornadoes early in the day are not uncommon. When you have dewpoints near 70F, you don't really need much sun to get good instability when you have mid level cold air. That early day convection the models are showing could potentially be nasty. I would feel pretty confident about at least a moderately impressive severe/tornado event, but any really high end tornado episode, if it occurs, would probably be confined to a relatively small regional area. Parts of MS/AL and maybe W/mid TN?

Not to say this would be anything like Yazoo City, but that is an example of an early day significant tornado.

[OceanStWx]

Quite a few of the models (UKMET and NAM in particular) are indicating a very good potential for an MCS to develop from the eastern Oklahoma convection somewhere in Arkansas. This may race on ahead an lay down a nice boundary across northern Mississippi/Alabama which also isn't uncommon for these kind of events.

[Thundersnow12]

Quite a few of the models (UKMET and NAM in particular) are indicating a very good potential for an MCS to develop from the eastern Oklahoma convection somewhere in Arkansas. This may race on ahead an lay down a nice boundary across northern Mississippi/Alabama which also isn't uncommon for these kind of events.

Yep and would only enhance the tornado threat...this day is going to be quite interesting.

21z SREF popping a 50 on the tor ingredients from 15-0z.

[Fred Gossage]

00Z NAM is much less messy in the warm sector. It moves morning activity out of the way much faster, allows for much more destabilization, and is much more potent overall... which, I hear, is a trend toward the Euro. WRF-NMM through 12Z Friday and the broadcast proprietary models support this also. The NAM is also more subtle with the forcing ahead of the cold front... which makes since with diffluent, but lower-amplitude mid to upper level jet.

[Fred Gossage]

I see you lurking Jimzzzz.... What are your thoughts?

[thewxmann]

Hey Fred! Not many thoughts right now... been pretty busy with stuff this week. On paper this looks like a pretty impressive setup, but if the low occludes faster then the LLJ displacement mentioned by CUmet will become a significant problem.

Right now I am focusing more on the threat tomorrow... AR tomorrow night looks concerning.

[SmokeEater]

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1259 AM CDT THU APR 14 2011

VALID 151200Z - 161200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL GULF

COAST STATES AND TN VALLEY...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE LOWER TO

MID-MS VALLEY...CNTRL TO ERN GULF COAST STATES...SRN APPALACHIAN

MTNS AND OH VALLEY...

...TORNADO OUTBREAK BECOMING INCREASINGLY POSSIBLE ACROSS THE CNTRL

GULF COAST STATES ON FRIDAY INTO FRIDAY NIGHT...

...CNTRL GULF COAST STATES/SRN APPALACHIAN MTNS...

AN IMPRESSIVE NEGATIVELY-TILTED UPPER-LEVEL LOW IS FORECAST TO MOVE

FROM THE CNTRL PLAINS EWD INTO THE OZARKS. THE EXIT REGION OF A 75

TO 90 KT MID-LEVEL JET ROUNDING THE BASE OF THE UPPER-LEVEL TROUGH

WILL OVERSPREAD THE CNTRL GULF STATES FRIDAY AFTERNOON CREATING VERY

FAVORABLE DEEP LAYER SHEAR PROFILES FOR SEVERE STORMS OVER A BROAD

AREA. AT THE SFC...A LOW WILL DEEPEN AND MOVE NEWD ACROSS THE OH

VALLEY AS A TRAILING COLD FRONT ADVANCES EWD ACROSS THE MS VALLEY.

ELEVATED THUNDERSTORM ACTIVITY MAY BE ONGOING ACROSS THE WARM SECTOR

FRIDAY MORNING IN AL AND MIDDLE TN WITH THIS CONVECTION BEING

SHUNTED EWD AWAY FROM THE MODERATE RISK AREA AROUND MIDDAY. AS THIS

OCCURS...MODEL FORECASTS ARE CONSISTENT WITH DEVELOPING NUMEROUS

THUNDERSTORMS ALONG THE WRN EDGE OF AN AXIS OF MODERATE TO STRONG

INSTABILITY FROM WRN TN SWD ACROSS NRN AND CNTRL MS. THIS ACTIVITY

SHOULD SPREAD EWD ACROSS THE MODERATE RISK AREA LATE FRIDAY

AFTERNOON INTO THE EVENING.

FORECAST SOUNDINGS ALONG THE INSTABILITY AXIS SHOW MLCAPE VALUES

FROM 2000 TO 3000 J/KG IN CNTRL MS TO 1500 TO 2000 J/KG ACROSS WRN

KY AND WRN TN. THIS IS COMBINED WITH 55 TO 70 KT OF DEEP LAYER SHEAR

AND STRONG LOW-LEVEL SHEAR SHOULD RESULT IN SUPERCELL DEVELOPMENT

WITH TORNADOES ACROSS THE MODERATE RISK AREA. 0-3 KM STORM RELATIVE

HELICITIES ARE FORECAST TO BE 400 TO 500 M2/S2 WITH LOOPING

HODOGRAPHS ACROSS MUCH OF ERN MS AND WRN AL SUGGESTING A POTENTIAL

FOR LONG-TRACK STRONG TORNADOES WILL EXIST. 500 MB TEMPS ARE

FORECAST TO BE FROM -12C IN SRN MS AND SRN AL TO -16C IN WRN TO

MIDDLE TN. THIS ALONG WITH THE STRONG DEEP LAYER SHEAR SHOULD ALSO

BE FAVORABLE FOR LARGE HAIL. VERY LARGE HAIL WILL BE POSSIBLE

ESPECIALLY IN ERN MS AS SUPERCELLS DEVELOP DURING THE MID TO LATE

AFTERNOON WHERE THE STRONGEST INSTABILITY IS FORECAST. ALTHOUGH

DISCRETE CONVECTION IS ANTICIPATED EARLY IN THE EVENT...LINEAR

DEVELOPMENT SHOULD INCREASE ALONG THE COLD FRONT BY EARLY EVENING

WITH A SQUALL-LINE MOVING EWD ACROSS THE REGION. DISCRETE STORMS

AHEAD OF THE LINE SHOULD CONTINUE TO HAVE TORNADO THREAT THROUGH THE

EVENING.

ONE CONCERN IS THAT THE LOW-LEVEL JET IS FORECAST TO BE MAXIMIZED

OVER KY AND TN DURING THE EARLY EVENING. LOW-LEVEL SHEAR PROFILES

WILL STILL BE VERY FAVORABLE FURTHER SOUTH IN MS AND AL BUT THE

LOW-LEVEL JET RESPONSE MAY BE FOCUSED FURTHER TO THE NORTH. ANOTHER

CONCERN IS FOR THE SRN EDGE OF THE MODERATE RISK. MODEL FORECASTS

DIFFER ON CONVECTIVE COVERAGE WITH THE NAM ISOLATED BUT THE ECMWF

DEVELOPS NUMEROUS STORMS. IN SPITE OF THE UNCERTAINTIES...WILL ISSUE

A MODERATE RISK ACROSS MUCH OF THE CNTRL GULF COAST STATES DUE TO

THE POTENTIAL FOR A HIGHER-END EVENT.

...MID-MS VALLEY/OH VALLEY...

AN UPPER-LEVEL LOW WILL MOVE ACROSS THE OZARKS FRIDAY WITH A MOIST

AXIS IN PLACE ACROSS KY...IL AND IND. THE DEVELOPMENT OF NUMEROUS

SEVERE THUNDERSTORMS APPEARS LIKELY TO THE EAST OF THE UPPER-LEVEL

LOW AS STRONG LARGE-SCALE ASCENT MOVES ACROSS THE REGION FRIDAY

AFTERNOON. FORECAST SOUNDINGS ALONG THE MOIST AXIS SHOW SFC

DEWPOINTS IN THE UPPER 50S F WITH DEEP LAYER SHEAR OF 40 TO 50 KT.

THIS ENVIRONMENT ALONG WITH COLD TEMPS ALOFT SHOULD SUPPORT THE

DEVELOPMENT OF SUPERCELLS WITH LARGE HAIL. BACKED SFC WINDS AND

STRONG LOW-LEVEL SHEAR ALSO SHOULD BE FAVORABLE FOR A TORNADO THREAT

WITH ROTATING STORMS. HOWEVER...STRONG LOW-LEVEL CONVERGENCE ALONG A

COLD FRONT MAY FORCE A LINEAR MCS. THIS WOULD RESULT IN A WIDESPREAD

WIND DAMAGE THREAT WITH THE LINE MOVING INTO IND...CNTRL KY AND

ECNTRL TN DURING THE EVENING.

..BROYLES.. 04/14/2011

[janetjanet998]

if there is indeed an outbreak over two days , It could be considered one huge outbreak if there isn't a 6 hour break between tornadoes which is very possible

overnight tonight looks bad in AR and some NWS offices are talking about storms starting in the morning during the day for friday

[Kevin Askew]

We may head to MEM area at around noon. See how things set up later tonight we would have to leave around 9am. May have morning event, then air mass recovery take place for rapid development early afternoon. AFD for KMEM is rather opmistic of a tornado outbreak in the area.

Side note. Storm motion appears 30-35 mph ENE. Very chasable

[BrentO]

http://www.spc.noaa.gov/products/outlook/day2otlk.html .......looks like they moved the MDT a bit further west.

[CUmet]

One other thing to keep in mind is this is the Southeast - and significant tornadoes early in the day are not uncommon. When you have dewpoints near 70F, you don't really need much sun to get good instability when you have mid level cold air. That early day convection the models are showing could potentially be nasty. I would feel pretty confident about at least a moderately impressive severe/tornado event, but any really high end tornado episode, if it occurs, would probably be confined to a relatively small regional area. Parts of MS/AL and maybe W/mid TN?

Yeah I pretty much concur with this. The early storms will have the benefit of being more co-located with the LLJ axis before it moves too far east. Given that the moisture is good and the mid-level temps are cold, they won't need all that much surface heating. In fact, I'm wondering if this will materialize as the main round, with scattered cells initiating around 12z near NE LA/SE AR and spreading ENE across north-central MS. Parameters appear supportive for significant tornadoes with this activity.

If the low-level jet can stay closer to the west and overlap more of the warm sector, as being hinted at by the possibility of a secondary low developing, then the threat will be substantially greater with the afternoon/early evening activity across portions of AL. I'm not completely convinced that this will happen yet, but this is a key feature of the setup that needs to be watched.

[wxsmwhrms]

Yeah I pretty much concur with this. The early storms will have the benefit of being more co-located with the LLJ axis before it moves too far east. Given that the moisture is good and the mid-level temps are cold, they won't need all that much surface heating. In fact, I'm wondering if this will materialize as the main round, with scattered cells initiating around 12z near NE LA/SE AR and spreading ENE across north-central MS. Parameters appear supportive for significant tornadoes with this activity.

If the low-level jet can stay closer to the west and overlap more of the warm sector, as being hinted at by the possibility of a secondary low developing, then the threat will be substantially greater with the afternoon/early evening activity across portions of AL. I'm not completely convinced that this will happen yet, but this is a key feature of the setup that needs to be watched.

Excellent post IMO. Completely agree. SREF has consistently been showing sig tor ingredients already maxed out at 15Z across MS, and models have been keying on development 12Z to 18Z from NC to WC MS, and spreading E from there. Will be interesting to see how things evolve.

[TheWeatherPimp]

00z NAM has me concerned about the potential for low topped sups across Illinois, Indiana and Ohio tomorrow.

[Hoosier]

00z NAM has me concerned about the potential for low topped sups across Illinois, Indiana and Ohio tomorrow.

Haven't looked at it much but I wish we had some steeper mid level lapse rates.