Widespread Severe Weather Outbreak Monday, Tornadoes Likely

[jkt21787]

GFS and Euro have both been indicating a possible severe weather event/outbreak since last Sunday. This morning's 12z run looks very ominous. Strong low pressure develops and moves across Northeast Oklahoma into Southeast Missouri then into Central Illinois. A warm front extends east of the low putting most of the Southeast US in the warm sector. A cold front trails the low pressure and moves across the Southeast from Monday Night into Tuesday.

There is a strongly negatively tilted trough, along with a strong shortwave approaching with a lot of energy present. Strong jet winds greater than 65kts are also expected with veering winds with height, supporting supercells. Instability will likely be there in some fashion. GFS also indicates a strong squall line along the cold front. NAM at 84hr indicates a similar pattern setting up at the time the outbreak would be beginning most likely.

Timing looks to be West of the Mississippi River Monday afternoon and evening, and east of the Mississippi River Monday Night into Tuesday, before exiting GA by Tuesday Afternoon.

This is something that needs to be watched closely. Most the NWS offices are making mention of this, and several meteorologists who have online blogs are also saying this could be big. Keep an eye out for this one.

Anybody else watching this?

[jeff]

Looks like it could be rough over AR, LA, MS, AL, TN early next week.

Your post sums it up nicely so I will not add anything. It is still several days out and convective developments this weekend will have to be watched for influences early next week.

[jkt21787]

Looks like it could be rough over AR, LA, MS, AL, TN early next week.

Your post sums it up nicely so I will not add anything. It is still several days out and convective developments this weekend will have to be watched for influences early next week.

Thanks. It could be rough one over this region come Monday and Tuesday. The 18z NAM is in and still showing a favorable set up. It is a quite bit slower than the GFS, and I have a feeling it is more accurate in its timing. We will wait and see though.

There is still plenty of time to watch this though and several things can change. People in these areas though watch the forecasts over the weekend. Also with Spring Break beginning for many, keep an eye out if you have any outdoor plans or are planning travel to this region.

[Brent]

Hopefully not coming through at night.

[ALhurricane]

It is definitely an event that needs to be monitored closely. Personally, I like the consistency of the GFS on this and feel the NAM is trying to play catch up. While the GFS may be a little too fast, I do not like the NAM depiction of the surface low.

For instance... here is the new 18z NAM for 72hrs...

http://www.nco.ncep.noaa.gov/pmb/nwprod ... _072.shtml

Notice how the surface low is vertically stacked with the 500mb shortwave? In the case of a negatively tilted trough, it does not make synoptic sense for the low to be in that position. I have noticed the NAM doing this a lot this winter and it takes it till about 48 hours out from the event to adjust the surface low position.

If the GFS verifies, then it is would be a fairly significant severe weather outbreak.

[Guest]

It appears even sections of south-central Nebraska and norht-central Kansas may even see a little action. It will probably not be severe in that area, but they do mention only one ingredient for a svr event is missing: deep layer shear. Non-the-less, it looks rough further south and east. I will definitely be monitoring this.

[jkt21787]

It is definitely an event that needs to be monitored closely. Personally, I like the consistency of the GFS on this and feel the NAM is trying to play catch up. While the GFS may be a little too fast, I do not like the NAM depiction of the surface low.

For instance... here is the new 18z NAM for 72hrs...

http://www.nco.ncep.noaa.gov/pmb/nwprod ... _072.shtml

Notice how the surface low is vertically stacked with the 500mb shortwave? In the case of a negatively tilted trough, it does not make synoptic sense for the low to be in that position. I have noticed the NAM doing this a lot this winter and it takes it till about 48 hours out from the event to adjust the surface low position.

If the GFS verifies, then it is would be a fairly significant severe weather outbreak.

Thanks for the input AL. I definitely see the NAM issue there, with it being vertically stacked. I am sure it is having some problems there, especially since it has had it before.

Are you thinking more tornadic supercell here or squall line? GFS shows the squall line pretty well, but noticed some veering winds on the output that could be favorable for supercell development out ahead of it. Noticed the Jackson NWS is mentioning this as well.

[ALhurricane]

There could definitely be some supercells if the GFS comes to fruition. I would be even more concerned near the warm front...as any storms that develop along it would be able to ingest the enhanced helicity along the boundary.

The key for the day will be instability. GFS is rather vigorous with it and given the GFS is a global model, it doesn't always depict the instability strong enough. Even if there is clouds around, the mid level lapse rates will likely be pretty good with this system.

As always this far out, it comes down to the questions of the boundary layer. Only time will tell on that.

[ChiTownMC]

Latest NAM (00Z) is a close call here in Chicago. Looks like a definate mixed bag. Definately something to watch.

[jkt21787]

There could definitely be some supercells if the GFS comes to fruition. I would be even more concerned near the warm front...as any storms that develop along it would be able to ingest the enhanced helicity along the boundary.

The key for the day will be instability. GFS is rather vigorous with it and given the GFS is a global model, it doesn't always depict the instability strong enough. Even if there is clouds around, the mid level lapse rates will likely be pretty good with this system.

As always this far out, it comes down to the questions of the boundary layer. Only time will tell on that.

Yep, I was thinking about some action on the warm front as well, as it comes in late Sunday and early Monday. Sometimes you can get pretty strong tornadic development there.

Instability will be the key, as upper air support is definitely there with strong jet dynamics. Being we are now in spring, the cloud cover should hopefully be less of a factor than what we deal with during the winter threats.

00z NAM looking pretty favorable for this area. Still maybe having some problems though as far as being vertically stacked. I think the GFS has NAM beat on this one, at least in the synoptic pattern being presented. You have to give it credit, because its had this system in some way since last Sunday that I've tracked it.

ChiTown: Being from the south, I am not an expert on thundersnow by any means. I'd ask someone else. Sorry.

[jkt21787]

The early morning model runs continue to indicate a significant severe weathet threat beginning in Eastern Oklahoma and Texas late Sunday Night and early Monday, expanding to the Lower Missisippi Valley and Mid South on Monday Afternoon and Night, and into the remainder of the southeast including Alabama and Georgia Tuesday.

The models still differ on timing, between faster GFS and slower NAM/DGEX. Right now the NAM solution has the best chance of verifying in term of timing.

The Storm Prediction Center has put Eastern OK, Eastern TX, LA, AR, MO, MS, and Western TN in a slight risk of severe weather with a 25% risk of severe, the highest they issue that far out. I fully expect some area to be upgraded to moderate on the day 2 outlook.

Also, yesterday's DGEX run was very interesting, painting portions of the Southeast late Monday into Tuesday with Lis as low as -10, SWEAT values between 300-500, and Totals Totals 50 and above. With expected high Cape and directional wind shear also, there COULD be a high risk for an area of the Southeast either Monday or Tuesday. Right now I still say moderate risk, as high risks are rare and only when the set up is PERFECT. However, we won't be far from it.

Most of the region gets into the warm sector, and becomes very unstable Monday afternoon. Supercells should begin firing in the warm sector and could rapidly begin rotating and become tornadic. They also have a risk of large hail and damaging downburst winds. The supercell threat COULD extend well east of the front/dryline depending on a potential cap along with several other factors. The supercells will gradually become linear in nature and form a squall line with damaging winds, widespread possible. Isolated tornaodes remain possible here as well in bowing segments or LEWPs, or in broken segments along the line where they can retain supercell characteristics. As the line moves into TN, AL, and GA Tuesday, it should remain severe. Depending on the timing and heating that can occur before the front reaches, the supercell threat could again be maximized. At any rate, this area can also expect damaging winds and isolated tornadoes, and perhaps a higher tornado and hail threat if supercells do indeed develop.

The confidence is continuing to increase that this will in fact be a major outbreak of severe thunderstorms and possible tornadoes. I won't call this a true tornado outbreak yet with many changes still possible, but we are working towards that direction. If you have any plans in this region Monday and/or Tuesday, keep a very close eye on the forecasts from the National Weather Service, and also review your severe weather safety rules in the event they are needed.

One more note...here is the discussion this morning from Jackson NWS.

NOW FOR MON/MON NIGHT. ALL I HAVE TO SAY IS WOW!! THERE SEEMS TO BE
ONLY ONE MINOR PARAMETER THAT IS A NEGATIVE AND THAT WOULD BE THE
SOMEWHAT LOW LEVELS OF 850MB MOISTURE. AFTER THE PRECIP EXITS OUT
THE THE CWA SOMETIME MON AFTERNOON...WE WILL BEGIN TO PRIME UP. VERY
STEEP LAPSE RATES WILL SPREAD OVER THE REGION AND WE WILL WARM UP
QUICKLY. INTENSIFYING SFC LOW WILL CONTINUE TO PULL BETTER LOW LEVEL
MOISTURE NORTHWARD AND WINDS AT ALL LEVELS OF THE ATMS WILL QUICKLY
INCREASE IN RESPONSE TO LARGE HEIGHT FALLS MOVING OUT OF THE S
PLAINS. ALL INGREDIENTS WILL BE IN PLACE FOR A SIGNIFICANT SVR WX
OUTBREAK LATE MON AFTERNOON INTO MON NIGHT. SUPERCELLS AND EVEN A
SQUALL LINE LOOK TO BE POSSIBLE. THERMODYNAMIC PROFILES WILL SUPPORT
VERY LARGE HAIL...ESPECIALLY WITH ANY SUPERCELLS. VEERING AND
INCREASING WIND PROFILES WILL SUPPORT ROTATING UPDRAFTS AND THE
LIKELIHOOD OF TORNADOES. I'LL BE HONEST...WE HAVEN'T SEEN THIS
COMBINATION OF REALLY STEEP LAPSE RATES...INSTABILITY AND WIND SHEAR
IN QUITE SOME TIME. I CAN'T GIVE YOU ANY EXACT INSTABILITY
VALUES...BUT JUST LOOKING AT HOW STEEP THE LAPSE RATES WILL
BE...2000-2500 JOULES OF MLCAPE WILL BE VERY REASONABLE. THIS SET UP
WILL BE EXPLOSIVE! THESE EXPLOSIVE UPDRAFTS COMBINED WITH STRONG
SHEAR WILL SUPPORT AT LEAST STRONG TORNADOES. REMEMBER...THIS IS
STILL 3 DAYS AWAY AND THE DETAILS WILL DETERMINE WHAT MODE OF
CONVECTION WE WILL HAVE AND IF SIG SVR STORMS WILL OCCUR. STAY
TUNED!

[jkt21787]

A snippet of the Jackson HWO from this morning...

THE MAIN TIME PERIOD FOR SEVERE STORMS WILL BE MONDAY AFTERNOON THROUGH MONDAY NIGHT. THE SEVERE ACTIVITY WILL BEGIN TO OUR WEST AND STEADILY PUSH EAST ACROSS THE REGION MONDAY EVENING AND DURING THE OVERNIGHT HOURS. AT THIS TIME...CERTAIN PARAMETERS ARE COMING TOGETHER TO SUPPORT A SIGNIFICANT SEVERE WEATHER EVENT. THE MAIN RISK DURING THIS EVENT WILL BE FROM SUPERCELL THUNDERSTORMS PRODUCING VERY LARGE HAIL...STRONG TORNADOES AND DAMAGING WINDS. A VERY STRONG SQUALL LINE WILL ALSO BE LIKELY THAT WILL BRING AN ADDITIONAL DAMAGING WIND THREAT.

ALHurricane: Whenever you're back on, could you give us your latest thoughts about this? I'm obviously interested in your opinion since your working for the NWS here. Also, With both Shreveport and Jackson both mentioning significant/strong tornadoes in their HWO, do you think this type of therat will reach this far north?

Thanks a lot, as always, for your excellent input into the discussion. I did notice Memphis also beefing up the wording in the AFD and HWO, saying the "T" word, and that's not thunderstorms.

[Guest]

Though I am away from the action up north (and probably will be), the phrase "STRONG TORNADOES" caught my eye! It is especially interesting that this event is about two days away!

[jeff]

Potential for long tracked violent tornadoes Monday afternoon through Tuesday from E TX/ OK into the Mid MS valley and deep south.

Ingredients appears to be coming together for a major severe weather outbreak including the threat of large and damaging tornadoes.

Severe storms should erupt E of the surface dry line over OK and TX early to mid afternoon Monday as low pressure moves ENE across OK. Surface heating will increase instability over LA, MS and as far N as AR and MO. Low level shear will be favorable for supercells especially over LA, AR, and MS and of course near the surface warm front.

Intense squall line will form by early evening and race E overnight across the mid and lower MS valley driven by strong mid level winds and a good low level inflow of the low level jet. Tornadic supercells will be possible ahead of this line throughout the night, although instability may decrease with cooling and the further E you go. I would place the main threat of tornadoes over LA, AR, MS and W TN Monday afternoon and overnight.

We are still over 48 hours out, so fine tuning with respect to timing and severity should be expected.

[jkt21787]

Potential for long tracked violent tornadoes Monday afternoon through Tuesday from E TX/ OK into the Mid MS valley and deep south.

Ingredients appears to be coming together for a major severe weather outbreak including the threat of large and damaging tornadoes.

Severe storms should erupt E of the surface dry line over OK and TX early to mid afternoon Monday as low pressure moves ENE across OK. Surface heating will increase instability over LA, MS and as far N as AR and MO. Low level shear will be favorable for supercells especially over LA, AR, and MS and of course near the surface warm front.

Intense squall line will form by early evening and race E overnight across the mid and lower MS valley driven by strong mid level winds and a good low level inflow of the low level jet. Tornadic supercells will be possible ahead of this line throughout the night, although instability may decrease with cooling and the further E you go. I would place the main threat of tornadoes over LA, AR, MS and W TN Monday afternoon and overnight.

We are still over 48 hours out, so fine tuning with respect to timing and severity should be expected.

Yep Jeff, this is really starting to look like a deadly and dangerous situation. The threat of large and strong tornadoes has already been mentioned by two offices, see my posts above, and I think you are hitting the nail on the head in regard to the storm initiation and threat. I think we are going for a rather widepsread supercell event then transitioning to a massive squall line with strong damaging winds and isolated tornadoes. Also the threat of supercells even after the line has formed is still there into Middle and East TN, AL, and GA as we move into Tuesday.

Not a good situation at all. Again, urge all in this area to being preparing and reviewing safety rules. And as Jeff said there are still some timing issues as we are 48 hours out, and instability amount is not set in stone either.

[Skywatch_NC]

Chance of thunderstorms here by Tuesday afternoon and evening as well.

Eric

[Indystorm]

Upper dynamics look very favorable for a significant severe weather event on Monday afternoon and night as has been mentioned. I think the key ingredient with this system with respect to tornadoes will be the amount of low level moisture. If Td's are >60 within a large geographical area of Louisiana, Arkansas, and Mississippi this could be quite dangerous with initial tornadic supercells followed by a squall line. Watch the Td's and helicity along the warm front that afternoon and night.

[jeff]

Potential for significant severe weather outbreak Monday

Parameters coming together for long lived supercells capable of producing large and destructive tornadoes. See SPC Day 2 Outlook

Trough over the W US will eject into the S plains late tonight spawning surface low pressure over C OK early Monday. 850mb low level jet will rapidly increase this evening from coastal TX to C AR in response to pressure falls over the plains. Strong WAA regime will be underway by late tonight with low to mid 60 degree dewpoints spreading N into NE TX, SE OK, S AR, and N LA. Surface dry line over W OK into WC TX will sharpen and begin to track E early Monday. I feel the GFS and NAM are underforecasting CAPE over the concerned area and values of 1500-2500 J/kg will be possible by early afternoon west of elevated convection on the nose of the low level jet. Steep lapse rates, cooling mid leve temps., LI's of -4 to -8 and increase dynamics support the development of severe thunderstorms by midday over E OK into EC TX ahead of the surface dry line.

KSHV forecasting ETA sounding has helicity values of 592 by late afternoon over NW LA and 339 at Little Rock. Low level winds will back to the ESE and SE along and south of the surface warm front and SE of the surface low over OK. Winds will veer to south and increase to near 50kts at 900 to 850mb and then veer to WSW in the mid levels with a 120-140kt jet max punching across NE TX and SE OK by mid afternoon. Left front quad. of jet streak wil be over NE TX, SE OK, and AR during max heating along with favorable shear (0-1km 30-40kts).

Supercells will fire first from EC TX to NE OK ahead of surface dry line in a strongly shear atmosphere. Storms will go quickly severe with all severe modes possible including a few high end wind, hail, and tornado events.

Storms will gradually congeal into a large intense squall line or MCS over W LA into MO and move E to ESE overnight across the MS valley and the south US. Tornado threat will shift to the tail end of the line over LA and MS after dark where best low level inflow will exist and ahead of the main squall line with any supercells rooted in the low level jet.

Review tornado safety rules and act quickly if a warning is issued for your area

JL

[jkt21787]

Thanks for updating Jeff. Slept in a little today so was a bit late. Defintiely outbreak in the works for Southern AR, Northern LA, and Eastern TX, where long track supercells could cause deadly tornadoes. If you live in these areas pay especially close attention to the situation.

There is a moderate risk up for a rather large area of the region Tomorrow. However, I do have some concerns with the northern and eastern part of that risk.

I feel we may have some major problems with Instability further North and East into Arkansas, on to Mississippi, into West TN. The NAM indicates precip over much of this region during the day and this would severely limit instability. NAM never shows any unstable air working into this area as the main precip moves through. If this is the case, the best bet is a squall line with severe gusts and maybe a tornado or two across Central and East AR, TN, Northern MS, into AL late Monday into early Tuesday, overall it wouldn't be that bad at all.

The GFS indicates a lot less precip, and would be more indicative of instability devleoping across this region. Which one is right? Too soon to say now.

Also of concern is moisture return, as dewpoints may not get too high outside of the Arklatex region into West Central MS. This of course will also help to limit things. I feel right now the southern portion of the moderate will likely verify, but the northern remains in much question because the models are not clear on this situation. I would say the supercell threat will be much lower across Northern AL, West and Middle TN, Central and North AR and any threat would likely be from the squall line. Maybe a couple of discrete cells form out ahead of it.

Tuesday AL and GA are in game for the squall line which will likely restrengthen and there could be another maximization in the supercell threat here. Back west there could be another round of severe thunderstorms in AR, TN, MS and surrounding areas as instability really pumps up in. Here it is mainly a hail threat with most shear leaving with the main squall line.

Outbreak still looks likely, with tornado threat best in Southern AR, Northern LA, and Eastern TX, with a lesser threat North and East of there.

Jeff, what's your thinking about the moisture and instability return this far north and specifically here in Memphis?

[jeff]

Moisture will probably be somewhat limited, but it all depends on how quickly the return flow sets up.

Winds already swinging around to South here in SE TX much sooner than I thought they would.

We will know by early Monday.