Severe Weather Wednesday

[jkt21787]

Still looks like Wednesday will be an active day from TX into OK, LA, AR, into the Western TN Valley and much of the Mid-South.

The SPC continues a slight risk of severe weather for most of this area, including such cities as Dallas/Forth Worth, Tulsa, Little Rock, Shreveport, Houston, Springfield, Paducah, Memphis, New Orleans, and Jackson. Most of AR, LA, Eastern Texas, Eastern OK, and Western MS have the highest risk accord to SPC with 25% noted.

First and foremost, most of the early part of Wednesday will be rather quiet as a mid level cap holds in place. Additionally, cirrus clouds will keep sunshine limited, although breaks are possible. The amount of breaks will highly depend on the exact nature of the severe weather threat.

By Wednesday afternoon, A very strong cold front along with an approaching shortwave will move into the Red River Valley and Ozarks and begin the weakening of the cap, allowing development of showers and thunderstorms. At first, discrete cells are possible, but rapid formation into a squall line is expected as the storms move towards AR and LA. On Wednesday night, the squall line will continue moving east into the Lower MS and TN Valley and by Thursday morning into AL and central TN with a decreasing severe threat.

Wind profiles and jet dynamics are VERY impressive and favorable for severe thunderstorms. A 60-75 kt low level jet and a 80 kt mid level jet are expected to be in place. Wind shear will be favorable for supercells, with helicity values over 500 m2/s2. Instability will be lacking though. Due to a lack of sunshine, cape values will remain near or under 1000 j/kg for most areas, and LIs will not be extremely low, although they will be below zero. One plus for severe weather will be steep lapse rates that increase near the front.

At this point, the best severe weather threat will be damaging winds, from a rapidly moving squall line that pushes east during Wednesday Night. Winds of 60, and perhaps over 70 mph in some places are likely, and damage from the wind could be quite widespread, especially in AR and LA back into Eastern TX. The tornado threat is low, but it is not zero. Embedded supercells are possible in broken areas of the squall line, and under the very high shear, could begin rapidly rotating and drop a tornado or two. Since the cap is unlikely to break until forcing along the front moves in, widespread supercells are not likely, thus a major tornado outbreak is not expected. Keep in mind also that strong bow echoes in the squall line could drop brief spinup tornadoes that can also be deadly and destructive. Isolated instances of hail are possible, especially early in the event, but the main focus will again be damaging winds.

If there is more widespread sun than currently forecast, instability would increase, as well as the severe threat. This could also weaken the cap a bit early and cause more supercell development. Right now, this is not likely, but needs to be watched as the day progresses. Heavy rain and localized flooding is possible, but given the rapid movement in the line, it is not a major threat. Certainly people near rivers, especially in the OH valley, should watch this aspect.

The SPC could upgrade to a moderate risk eventually, but there remains much uncertainity. As of now, a slight risk may be justified and verified from this, especially if sun is limited (which is expected as of now), but the potential for a widespread damaging wind event even without large instability should be concerning for everyone in this area.

The threat by Thursday should decrease as the front slows a bit and the squall line loses some of its dynamics as the line pushes into AL, GA, Eastern TN and the Carolinas, but some instances of damaging winds are still possible. Although no slight risk is issued as of yet, one is very possible.

Please keep up to date with SPC and NWS forecasts over the next 48 hours as this situation unfolds. Watches and warnings are likely tomorrow in some of these areas, and some could be for tornadoes. Take immediate shelter if a storm approaches.

Again, comments are welcomed.

[jkt21787]

Here one view from another published earlier today:

Henry Margusity's Column: January 11, 2005
POSTED: 11:12 a.m. January 11, 2005

TUESDAY WEATHER BRIEF

A MAJOR SEVERE WEATHER OUTBREAK WEDNESDAY!!!!!!!!!!!

Remember Henry's rule..."Thunderstorms in California, severe weather in the Plains the next Day. Ok,. we have the storms already, so where will the severe weather be Wednesday. What I find interesting this morning are the thunderstorms already occurring across the Tennessee Valley. It also thundered in the snow area here in State College. What that tells me is the atmosphere is already highly unstable and primed for a severe weather event to occur. You only need to look at the surface map this morning and see the 60s dew points across eastern Texas into the Tennessee Valley. That's only one ingredient...Wednesday, ahead of the cold front, skies will clear to allow sufficient heating all the way into the western Ohio Valley. Dew points in the 60s will surge as far north as Illinois. Severe storms will develop late in the day from Illinois to eastern Texas, along and head of the cold front. The storms will spread east through the Ohio Valley, Tennessee Valley and the deep South during the night. The potential is there for wind damage, large hail and tornadoes. This event has the potential to be a major severe weather outbreak, one with over 100 reports of severe weather.

I will be updating the severe weather issue this afternoon after the 18z ETA run comes in. I will not be surprised to see SPC upgrade the risk from Slight to Moderate today given the potential for the event.

This discussion is updated only the days that Henry is available, usually Monday-Friday. Check the date above and come back often!

I seriously don't think we will have 100 severe reports, although I have been wrong before, and could be again. But he does have the general overview of the situation handled well.

Any other thoughts? Wxguy? Anybody else? It's awfully quiet on the forums this evening.

[jeff]

There will be some severe weather, and probably a few tornadoes, but nothing I would call a major outbreak.

Damaging winds remain the main threats and as you pointed out in your discussion the amount of sun and instability is most of the key.

[jkt21787]

There will be some severe weather, and probably a few tornadoes, but nothing I would call a major outbreak.

Damaging winds remain the main threats and as you pointed out in your discussion the amount of sun and instability is most of the key.

Jeff, I read your comments on the TX Thread and we pretty much are in close agreement in regards to the situation.

Not sure who that Henry guy is, but right now this does not look like a classic severe weather outbreak. Could it be rather impressive? I think so, at least with wind potential. Isolated tornadoes are also likely. But this does not look like a repeat of Jan 1999, or Jan 2000, not by far.

Intresting to note some dry slotting here tonight, skies are actually clear in Eastern AR, N MS and SW TN. If this is here for tomorrow, then the situation will be much more volatile, but more clouds are already building from the west, although there are some noticeable breaks on satellite.

Even though this won't be a major outbreak, it has been a while for many of us since the last severe weather threat, so be alert to the sky tomorrow.

[jkt21787]

The new ETA just coming in is a little bit slower, putting the squall line into Central Arkansas around Midnight, and the MS around 12z THU. Obviously only one model, so we will see how the others follow.

I don't think it will be that much slower, the line will be moving fast, but timing is still a big question mark with this threat.

[dvdweatherwizard]

Thoroughly enjoyed reading your discussion, jkt21787! I found it very comprehensive. I feel as though Louisiana, Arkansas, Mississippi, and West Tennessee will be the most threatened areas for this upcoming event. I agree that damaging winds will be by far the most widely reported severe weather item and that this event will be modulated by instability.

The instability aspect of this event concerns me. Everything else seems favorable for a fairly significant severe weather outbreak, especially the low-level jet. (The progged strength of the low-level jet scares me.) But, if the instability turns out weak, then there will be some severe weather, but not a great deal. However, I have generally found that model forecasts of instability seem to turn out LESS than what actually occurs, although I have no solid evidence in front of me to back up that claim. If this turns out to be the case here, then watch out! As it stands now, I believe SPC will go ahead and upgrade to a moderate risk at some point tomorrow, and I do happen to believe that we will see over 100 reports of severe weather late tomorrow into Thursday like Henry suggests. But again, everything depends on that instability and how much sunshine the targeted area sees tomorrow. The greatest alignment of parameters may also come during the overnight hours, which would tend to limit somewhat the maximum potential that this thing could have otherwise reached. So, there are definitely some limiting factors as well as some very ominous factors, but I will go ahead and stick with 100 or more reports. Can't wait to see what happens!

[jkt21787]

Thoroughly enjoyed reading your discussion, jkt21787! I found it very comprehensive. I feel as though Louisiana, Arkansas, Mississippi, and West Tennessee will be the most threatened areas for this upcoming event. I agree that damaging winds will be by far the most widely reported severe weather item and that this event will be modulated by instability.

The instability aspect of this event concerns me. Everything else seems favorable for a fairly significant severe weather outbreak, especially the low-level jet. (The progged strength of the low-level jet scares me.) But, if the instability turns out weak, then there will be some severe weather, but not a great deal. However, I have generally found that model forecasts of instability seem to turn out LESS than what actually occurs, although I have no solid evidence in front of me to back up that claim. If this turns out to be the case here, then watch out! As it stands now, I believe SPC will go ahead and upgrade to a moderate risk at some point tomorrow, and I do happen to believe that we will see over 100 reports of severe weather late tomorrow into Thursday like Henry suggests. But again, everything depends on that instability and how much sunshine the targeted area sees tomorrow. The greatest alignment of parameters may also come during the overnight hours, which would tend to limit somewhat the maximum potential that this thing could have otherwise reached. So, there are definitely some limiting factors as well as some very ominous factors, but I will go ahead and stick with 100 or more reports. Can't wait to see what happens!

Thanks for the kind words dvdweatherwizard! I truly appreciate that.

The instability factor will be huge in this, as often is the case in fall/winter outbreaks. If the sun comes out in large supply tomorrow, a major event would be much more likely to happen, including a lot more tornadic potential.

Back last Nov, I do think the instability in that event was more than forecasted, although still quite limited, and thinking back to that has me more concerned.

100 events could very well happen if a long and intense squall line does form (which is VERY possible), but most of them more than likely would be wind reports. Moderate risk quite possible, just will have to wait and see how instability develops.

Many areas from TX to TN are seeing clear/ptcldy or mostly cloudy skies tonight, satellite also shows these breaks, as i mentioned earlier. If they hang around tomorrow, then we are in play for big severe weather!

[jkt21787]

Incoming GFS is faster than new ETA, brings the squall line through central AR by Midnight, around the MS River about 3 AM, and approaching the TN River/AL state line around 6 AM. That is about the timing discussed previously from the weather service.

[dvdweatherwizard]

Man, I just checked the Jackson, MS NWS office discussions to see what they were thinking since I just remembered how well they were able to identify the November threat. They are being fairly aggressive with this event as well. Here are some snippets from their discussions.

From the Tuesday early am discussion:

...SIGNIFICANT SEVERE WEATHER EVENT POSSIBLE WEDNESDAY NIGHT...
.
.
.
WED NIGHT WILL BE THE BIG SHOW! MODELS HAVE BEEN PRETTY CONSISTENT
FROM RUN TO RUN AND ARE NOW BEGINNING TO LOOK SIMILAR WITH EACH
OTHER. INTENSE FORCING WILL SPREAD ACROSS THE REGION...ESPECIALLY
ALONG A SHV TO MEM LINE. IN THE MID LEVELS...A 75 TO 90 KT JET WILL
SPREAD ACROSS THE REGION WITH THE CORE JUST TO THE NORTH!! THE LOW
LEVELS WILL RESPOND AND A 60-70 KT LLJ WILL DEVELOP AND MOVE OVER
THE AREA AS WELL! THESE WIND FIELDS WILL PROVIDE HIGH LEVELS OF
SHEAR AND SR HELICITY. SO WHAT ABOUT THE INSTABILITY? THE LATEST
TRENDS HAVE HIGHER INSTABILITY. SFC CAPE LOOKS TO BE A GOOD 800-1000
J/KG WITH THE POTENTIAL FOR 1300 J/KG. THIS MAKES SENSE NOW AS THE
MODELS HAVE CONSISTENTLY SHOWED DECENT LAPSE RATES THE PAST FEW
DAYS. SO WITH THAT...HERE IS WHAT I SEE. JUST TO MY WEST...ARKLATEX
REGION...EVERYTHING WILL FIRE AND THERE WILL LIKELY BE SUPER CELLS
OUT IN FRONT OF THE LINE. EVERYTHING WILL DEVELOP RAPIDLY AND SPREAD
EAST. A SQUALL LINE WILL DEVELOP TO THE WEST OF THE PRE-FRONTAL
SUPER CELLS AND EVENTUALLY CATCH UP WITH THEM IN THE VICINITY OF THE
NW CWA CLOSE TO MIDNIGHT. EVEN AS THE LINE CONSOLIDATES...BOWING
SEGMENTS WILL TAKE OVER. THE THREAT OF TORNADOES AND SIGNIFICANT
WIND DAMAGE WILL GOOD POSSIBILITY. THE SYSTEM WILL PUSH EAST AS THE
NORTHERN SECTION ACCELERATES TO THE NORTHEAST. THE BOTTOM END OF THE
LINE WILL STILL HAVE MORE THAN ENOUGH TO KEEP IT SVR...BUT JUST HOW
IT WILL EVOLVE IS STILL IN QUESTION. HOWEVER...SVR POTENTIAL STILL
LOOKS GOOD AS THE LINE WILL BE POSITIONED JUST TO THE WEST OF THE
I-59 CORRIDOR AROUND 12Z. SYSTEM WILL PUSH THROUGH THE REST OF THE
CWA BY NOON.

From the Tuesday mid-morning discussion:

...SIGNIFICANT SEVERE WEATHER EVENT POSSIBLE WEDNESDAY NIGHT...
.
.
.
FOR TONIGHT AND TOMORROW...OUR ATTENTION SHIFTS TO THE SOUTHWEST.
THE AMOUNT OF INSTABILITY THAT WILL BE AVAILABLE FOR CONVECTION
TOMORROW NIGHT WILL BE THE MAIN QUESTION. RIGHT NOW...DEW POINTS
OVER THE CENTRAL GULF ARE AROUND 66 DEGREES. WATER TEMPERATURES ARE
IN THE MID 70S. ONE THING TO MONITOR OVER THE NEXT 24 HOURS WILL BE
ANY TRENDS IN THE DEW POINT READINGS FROM THE BUOYS AND ALSO ANY
TRENDS THAT DEVELOP ALONG THE COAST. IF THE SURFACE AND 850 MB DEW
POINTS ARE HIGHER THAN WHAT THE MODELS ARE ANTICIPATING (WHICH ARE
CURRENTLY EXPECTED TO BE SOMEWHERE AROUND 60-63 DEGREES AT THE
SURFACE AND +11 CELSIUS AT 850 MB)...THEN THE ARK-LA-MISS
(ESPECIALLY ALONG THE MISSISSIPPI RIVER SHOULD EXPECT SIGNIFICANT
SEVERE THUNDERSTORM ACTIVITY...INCLUDING TORNADOES. AGAIN...THE MAIN
THING TO MONITOR WILL BE THE TRENDS IN THE DEW POINTS COMING FROM
THE BUOYS AND FROM THE COASTAL STATIONS. IF DEW POINTS OF 70 DEGREES
ARE REACHED IN THE CENTRAL GULF AND DEW POINTS IN THE UPPER 60S ARE
REACHED ALONG THE COAST BY TOMORROW AFTERNOON...THEN WATCH OUT. ALL OTHER
PARAMETERS NEEDED FOR WIDESPREAD...ORGANIZED SEVERE CONVECTION (FOR
TOMORROW NIGHT) LOOK GOOD TO EXCELLENT. CURRENT MODEL
PARAMETERS...LL HELICITY...LCL HEIGHTS...VEERING PROFILES...LOW,
MID, UPPER LEVEL JET SUPPORT...MOISTURE TAP...ARE ALL IDEAL FOR
SIGNIFICANT SEVERE THUNDERSTORM ACTIVITY. THE ONLY LIMITING FACTOR
COULD BE A LACK OF STRONG SURFACE-BASED INSTABILITY...WHICH WOULD
HAMPER SOME OF THE DEVELOPMENT.

AGREE VERY STRONGLY WITH THE PREVIOUS FORECAST DISCUSSION IN REGARD
TO THE DEVELOPMENT...EVOLUTION...AND TRACK OF THIS SYSTEM. IT STILL
LOOKS LIKE SHOW TIME WILL BE DURING THE OVERNIGHT HOURS...BEGINNING
AROUND MIDNIGHT AND LASTING THROUGH DAYBREAK. PLEASE STAY TUNED FOR
FUTURE UPDATES TO THIS POTENTIALLY VOLATILE SITUATION.

And finally, from the afternoon discussion:

SYNOPSIS...POTENTIAL FOR SEVERE THUNDERSTORMS STILL EXISTS FOR
WEDNESDAY NIGHT INTO THURSDAY ALTHOUGH TIMING IS SLOWER.
.
.
.
ELSE...EYES ARE ON THE POSSIBILITY OF SEVERE WEATHER
WEDNESDAY NIGHT. LATEST ETA12 SUGGESTS A SLOWER SCENARIO THAN GFS
AND PREVIOUS ETA RUNS...AND IS CLOSER TO THE EUROPEAN MODELS. OUR
UNSEASONABLY WARM AND MOIST AIRMASS WILL BE FURTHER AIDED BY
INCREASING SOUTHERLY FLOW OVER THE NEXT 24-36 HOURS. BREEZY
CONDITIONS ARE ALREADY OCCURRING OVER THE DELTA THIS AFTERNOON. A
TIGHTER SFC PRESSURE GRADIENT AND DAYTIME MIXING SHOULD RESULT IN
EVEN HIGHER WINDS OVER THE WESTERN PORTION OF THE CWA WEDNESDAY. WL
ISSUE A LAKE WIND ADVISORY FOR AREAS WEST OF I-55. AS A FAIRLY
AMPLIFIED UPPER TROUGH MOVES INTO THE CENTRAL U.S. WEDNESDAY A SFC
LOW WILL DEEPEN OVER THE CENTRAL PLAINS AND MOVE TO THE NORTHEAST
TOWARD THE GREAT LAKES REGION WEDNESDAY NIGHT. THIS WILL SEND A
TRAILING COLD FRONT IN OUR DIRECTION. A SQUALL LINE IS EXPECTED TO
DEVELOP ALONG THE FRONT AND PROGRESS EASTWARD. IN OUR REGION AHEAD
OF THE FRONT A STRENGTHENING LOW LEVEL JET COMBINED WITH THE
ENTRANCE REGION OF AN UPPER JET WILL PROVIDE STRONG DEEP LAYER SHEAR
AND HELICITIES TO SUPPORT SEVERE STORMS. PLENTY OF AVAILABLE DEEP
MOISTURE WILL BE IN PLACE AS WELL. TODAY'S CAP WILL BE SLOW TO ERODE
WEDNESDAY BUT BY WEDNESDAY NIGHT INTO THURSDAY MORNING...THE CAP
SHOULD BE GONE AND ENOUGH INSTABILITY WILL BE PRESENT TO MAINTAIN
THE SQUALL LINE WITH ISOLATED TORNADOES...LARGE HAIL AND DAMAGING
WINDS POSSIBLE ACROSS THE CWA. THE MOST LIKELY PLACE FOR SEVERE
WEATHER AT THIS TIME APPEARS TO BE OVER OUR WESTERN CWA THURSDAY
MORNING.

[jkt21787]

Jackson again has been probably been the most aggressive of the offices, although both Memphis and Shreveport are hitting it hard as well.

Their technique has been working well lately I must say, see if the pattern continues tomorrow.

0Z models overall not much different, but there are surely are some things I missed LOL.

[TexasSam]

I haven't seen the National map with this much color in a long time!

It's from the NOAA web site:
http://www.weather.gov/

[Tornado_Chaser2005]

Well im particulary interested in the Eastern Oklahoma area, Tulsa down to McAlester somewhere aruond 12PM tomorrow afternoon Central Time. Reason I am, is beause I have family there, and friends, so I will forecast that area. Yes i see that between Tulsa and McAlester will be probably the best place for tornadoes, and severe weather at this time forecasted. a 60knt LLJ, 110knt ULJ, with a powerul boundary at the 500mb vort level, good dewpoints, and some instability. This area just 6hrs before will have a giant cap, however, it just releases sometime around 11AM CST or so..60-65 degree temps as well ,so its all set up.

Also I am trying a little experiment out...This will be to locate the areas to start a vorticy for a tornado so to forecast a bit better perhaps...Ok, well I see indiviual areas of vorticy in Northeast oklahoma Over Tulsa, and a bit Southeast of there near the Arkansas border..So that area will be where i expect the tornadoes to be around...So if I was chasing, id place myself, smack there in Tulsa Oklahoma tomorrow morning.

NOTE
By about 6 hrs later, I see the vorticies getting 6 times stronger than in Northeast Oklahoma, across West Central Arkansas

TC

[jeff]

Severe Weather threat today from SE TX through mid MS valley. Damaging winds will be the main threat.

Am soundings from Fort Worth and Norman show strong capping in the 800mb to 700mb over the southern plains (850mb of 19.6C and 18.8 C respectively). KCRP shows even a greater cap. Water vapor shows the powerful upper low dropping into New Mexico and heading rapidly E. Impressive surface pressure falls over NW TX have greatly increased the PGF over TX with stations easily gusting over 30 and a few over 40 (KGPD gusting to 64mph). West TX NEXRADS have 50-60kts at 3000 and 4000 ft and much of this will be mixing down this afternoon. The dust will fly over W TX.

With the visible showing a large cirrus shield over the state and the stout cap on the soundings, the little amount of heating will not do the trick. However, mid level cooling and ascent this evening should weaken the cap and then the low level forcing along the front should be able to break it. This will likely occur east of the I-35 corridor where the deepest moisture lies into E OK. Morning surface analysis from OU ARPS shows:

Helicity of 300 over E OK with lower amounts of TX and AR
CAPE: 500-1000 over NC TX into E OK and W AR.
MUCAPE: 1000-2000 over central TX through AR
LI: -2 to -4 over N TX and E OK. (matches well with the KFWD sounding of -1.42)
A low level jet of 55-60kts extends from the TX coastal bend to the ARKLATX with a 120kt jet racing in from the WSW.

Much of E OK and NE TX into AR will lie within the left front quad of an upper level jet streak by this evening.

Linear forcing along the front should fire the storms by late afternoon and early evening from E of OKC to E of Dallas to E of Austin. Cells will quickly form into a squall line and race ENE into AR, E TX, LA and southern Ill overnight. Bows and LEWPS within the line will produce widespread damaging winds as some of the wind energy is mixed down from above. I expect the main brunt of the line across NE TX, E OK, and AR as this area is most favorable dynamically and has less capping to overcome. Southward in SE TX capping may prevent more than a line of thunderstorms and showers south of I-10.

[misty]

So, do you think it will be a squall by the time it reaches southwest arkansas with damaging winds being the primary threat. Thanks for the information. You always break it down where even I can understand it. What do you think the ETA will be. I am thinking somewhere around 6-7 pm.

[jeff]

So, do you think it will be a squall by the time it reaches southwest arkansas with damaging winds being the primary threat. Thanks for the information. You always break it down where even I can understand it. What do you think the ETA will be. I am thinking somewhere around 6-7 pm.

Probably a solid line ETA between 7-10pm

[misty]

Sorry to ask so many questions, but I amtrying to learn about models and caps and helicity and stuff by reading the post on this board. Plus I get very, shall we say...concerned anout severe weather.

[PurdueWx80]

Misty and others in the Arklatex region -

I think you are in the heart of what could be the most severe weather of this event. The dynamics associated with the upper jet and the powerful upper low coming out of the SW should easily break the cap by this evening. Something I didn't see happening a few days ago is now showing up on a few of the mesoscale models and I think it has a good chance of verifying. They are progging the surface winds to back to the SSE or even SE ahead of the surface low in the Plains. If this verifies, the threat of tornadoes (some F2-F4's) would greatly increase. Hail is already likely once the initial storms develop, and many of these will become supercells. We'll have to watch surface pressure falls and the resulting backing of the winds to the SE or SSE - if this occurs, look out. Stay alert late this afternoon because this will be a rapidly developing situation. The severe weather in the COLD sector (near KC, MO) should tell us that the atmosphere is primed for severe weather today once the cap gets out of the way. The window for tornadic supercells to develop is relatively narrow, as the forcing suggests rapid squall line development. With the low level helicities increasing along the squall line overnight, rapid spinups are possible anywhere from IL, IN down to the Gulf Coast - but particularly out ahead of the surface low as it weakens and moves NNE/NE. The prospects of widespread wind damage still seem high as well given the 60-80 kt jet just off the surface. The moisture profile at the surface suggests these winds can mix down at times since there will be no low-level temperature inversion overnight. Stay alert!

[jeff]

Norman and Fort Worth will be launching 200pm soundings. ARPS sounding animation for KOUN shows cap weakening rapidly within the past 2-4 hours with roughly 25 to 50 J/KG CIN left. However it reamins strong over N TX and areas south of there.