April 1st-4th Severe Weather Thread

[andyhb]

Looks like we have a D6 issued so probably best to get a separate thread going so the mid range thread can be left for the period after this.
 

 

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0400 AM CDT FRI MAR 28 2014

VALID 311200Z - 051200Z

...DISCUSSION...
MODELS HAVE BEEN FAIRLY CONSISTENT MAINTAINING A PROGRESSIVE AND
ACTIVE PATTERN IN THE 4-8 PERIOD WITH A SERIES OF RELATIVELY
LOW-AMPLITUDE WAVES TRAVERSING THE COUNTRY.

WED /DAY 6/...SHORTWAVE TROUGH FORECAST TO MOVE THROUGH THE PLAINS
DAY 4 AND EVENTUALLY THE GREAT LAKES DAY 5 WILL BE STARVED OF
MOISTURE. HOWEVER...THE NEXT IN A SERIES OF SHORTWAVE TROUGHS IS
FORECAST TO MOVE INTO THE CNTRL/SRN PLAINS AS A NEUTRAL TILT OR
SLIGHTLY POSITIVE TILT FEATURE LATER DAY 6. MODELS INCLUDING MOST
ENSEMBLE MEMBERS HAVE DEMONSTRATED RUN-TO-RUN CONSISTENCY AS WELL AS
CONSISTENCY AMONG THEMSELVES REGARDING THIS FEATURE. AN AXIS OF
PARTIALLY MODIFIED GULF AIR WILL LIKELY RETURN NWD BENEATH STEEP
LAPSE RATES THROUGH THE SRN PLAINS AND LOWER-MID MS VALLEY AREA AS A
LLJ DEVELOPS AHEAD OF ATTENDANT LEE CYCLONE. MEANWHILE WIND PROFILES
WILL INCREASE AHEAD OF THE UPPER TROUGH. IT APPEARS THAT CLOUDS AND
EARLY CONVECTION WILL BE POSSIBLE ALONG THE CONVEYOR BELT. HOWEVER
IN WAKE OF THIS ACTIVITY POTENTIAL WILL EXIST FOR ADDITIONAL MORE
ISOLATED STORMS TO DEVELOP ALONG THE DRYLINE...ESPECIALLY FROM OK
INTO NRN TX AND SUBSEQUENTLY MOVE THROUGH WARM SECTOR. GIVEN
SLIGHTLY POSITIVE TILT NATURE OF THE UPPER TROUGH...CAPPING COULD BE
A CONCERN...ESPECIALLY WITH SRN EXTENT INTO TX. THOUGH MESOSCALE
DETAILS REMAIN UNCLEAR AT THIS TIME...OVERALL PATTERN APPEARS
SUFFICIENT FOR A HIGHER END SEVERE THREAT FROM A PART OF THE SRN
PLAINS INTO THE LOWER-MID MS VALLEY REGION.

MODELS BECOME INCREASINGLY DISPERSIVE AND UNCERTAINTY INCREASES
BEYOND DAY 6.

..DIAL.. 03/28/2014

[HM]

The CPC day 6-10 analogs were duds mixed with some rather eye-opening years:

http://www.cpc.ncep.noaa.gov/products/predictions/610day/610analog.off.gif

In the Tropics, the El Nino-dominate Walker Cell takes a hit over next 10 days from intraseasonal oscillations (a complex network of kelvin waves/migrating Walker) before likely returning into a strengthened state 10-20 days out.

The El Nino-touch is giving us our "duds" in the analog list while this brief "relaxation" from that is bringing us a strong "outbreak" signal too in the analogs. Not a bad LR signal right now.

[HM]

 

The CPC day 6-10 analogs were duds mixed with some rather eye-opening years:

http://www.cpc.ncep.noaa.gov/products/predictions/610day/610analog.off.gif

In the Tropics, the El Nino-dominate Walker Cell takes a hit over next 10 days from intraseasonal oscillations (a complex network of kelvin waves/migrating Walker) before likely returning into a strengthened state 10-20 days out.

The El Nino-touch is giving us our "duds" in the analog list while this brief "relaxation" from that is bringing us a strong "outbreak" signal too in the analogs. Not a bad LR signal right now.

I should point out that many LR forecasters highlighted the end of March / early April for an uptick in activity over the last couple of weeks due to intraseasonal oscillations (of course most were late to the party recognizing the signal). Weakening subsidence over Indonesia, where El Nino likes to put subsidence, seems to have delivered the more active days this winter as well:

11/17, 12/20-21, 2/20-21.

[Thundersnow12]

Both Tuesday and Wednesday look quite nice on the 12z GFS. 

 

The more obvious area is on Weds but Tues could hold chances anywhere from DRT northward along the leading edge of the better moisture return up to ABI or so.

 

Have always liked chasing well south around Sonora/DRT area with nobody around. 

 

Weds just looks solid as pressures fall all day and winds back really nicely along the DL from SPS down to I-20 with really nice moisture and dews. 

[Chicago Storm]

Both Tuesday and Wednesday look quite nice on the 12z GFS. 

 

The more obvious area is on Weds but Tues could hold chances anywhere from DRT northward along the leading edge of the better moisture return up to ABI or so.

 

Have always liked chasing well south around Sonora/DRT area with nobody around. 

 

Weds just looks solid as pressures fall all day and winds back really nicely along the DL from SPS down to I-20 with really nice moisture and dews. 

Tuesday actually really doesn't look that good at all now.

 

The GFS came in much slower, and the ECMWF has also now come in slower. Both to the point where Tue is just about a lost cause verbatim. We'll see if things trend back the opposite direction being 4 days out still.

 

Wed and Thur are the days on both models, though Thur is in about the same place as yesterdays event...jungles.

[thewxmann]

12Z Euro is very impressive next week.

[brettjrob]

Major slowdown continues on the Euro... trying to make me eat my words from last night about Tue vs. Wed. It's so slow that Wed 4/2 now looks like a relatively high-end threat for tornadic supercells over central and western OK/KS. Depicting a 990 mb low over SE CO with the warm front roughly along I-70, and a dryline trailing roughly along 100 W. Close to textbook, with slightly better moisture being about all one could ask for.

 

Probably represents a best-case scenario against which future runs will be compared, but hopefully the general idea WRT timing is correct. Tuesday is kaput, so slower is better at this point.

[ZackH]

I'm fine if Tuesday is kaput if the 12z Euro verifies for Wed... I would love the threat hanging out in south central/SW KS... so begins the agonizing wait from run to run of the first potentially big setup of the year.

[OKpowdah]

Same trends from all model centers today ... more consolidated, sharper, amplified s/w trough, and more s/w ridging downstream. Slower. Stronger sfc low placed a little NW, with low level winds backed. All around very favorable trends for Wednesday.

[andyhb]

00z GFS follows the 18z pretty closely for Wednesday's threat, ejecting a low amplitude ULL from the southern Four Corners through the TX and OK Panhandles on Wednesday morning through 00z Thursday. Quite a broad warm sector out ahead of it with widespread 1500-2500 J/kg of CAPE and 65+ Tds.

[brettjrob]

00z GFS follows the 18z pretty closely for Wednesday's threat, ejecting a low amplitude ULL from the southern Four Corners through the TX and OK Panhandles on Wednesday morning through 00z Thursday. Quite a broad warm sector out ahead of it with widespread 1500-2500 J/kg of CAPE and 65+ Tds.

 

The roller coaster ride continues -- Tuesday looks better again for SW OK and NW TX, though not spectacular.

 

Wednesday you have a high-quality warm sector (for early April) in place with a beautiful trough approaching. Trouble is, it's a lot more pinchy and compact than the 12z ECMWF, and its axis is still back in AZ. So we end up with a weak, veered LLJ in between shortwaves, and likely a nontornadic supercell case. Not going to lose sleep over it until the ECMWF blinks, but not the most encouraging.

[andyhb]

The best threat on the GFS would be further east towards 00z, but obviously that wouldn't be favorable for chasing.

 

Currently, this appears to be a North American vs. European guidance deal.

[OKpowdah]

The roller coaster ride continues -- Tuesday looks better again for SW OK and NW TX, though not spectacular.

 

Wednesday you have a high-quality warm sector (for early April) in place with a beautiful trough approaching. Trouble is, it's a lot more pinchy and compact than the 12z ECMWF, and its axis is still back in AZ. So we end up with a weak, veered LLJ in between shortwaves, and likely a nontornadic supercell case. Not going to lose sleep over it until the ECMWF blinks, but not the most encouraging.

 

Yeah the 850 jet races off east early Wednesday and just like you said, with the trough still further west, the 850 and 700 winds are pretty meager and veered until Thursday morning.

[andyhb]

Despite slowing down and with a positively tilted trough, the 00z Euro verbatim looks rather impressive for Wednesday with rather strong, southerly low level flow and excellent deep moisture return to the east of the dryline, yielding widespread 2000-3000 J/kg of CAPE. In addition to that, there is a 993 mb low in SE Colorado/OK Panhandle and a pretty favorable look in the upper levels with the RRQ of the northern stream jet and the LFQ of the ST jet in place over OK. Discrete storms look to develop (on the precip maps) between 21z and 00z and then are moving into increasing low level shear and deep BL moisture through the evening hours. Capping would be a bit of concern with the slower evolution (as highlighted by SPC in the latest outlook), but this would also help keep things more discrete well into the later evening hours.

 

Also the 12z GGEM was trying to bring a more substantial trough through on Wednesday but kind of got stuck in between the Euro and GFS solutions.

[andyhb]

Also another thing of note, the GFS lowballed instability yesterday, with many areas seeing in the range of 500-1500 J/kg higher than forecast by it, more along the lines of the NAM.

 

Edit: 12z UK still continues with a much stronger solution than the GFS.

[brettjrob]

GFS and ECMWF are no closer to ironing out differences in trough orientation and shortwave dominance. The 12z GGEM is way out in left field with yet another solution. About all we can do for now is to define a wide distribution of possible solutions.

In terms of practical implications, I'd place the highest probability on this scenario: the lead wave is too late for surface-based initiation Tuesday, and Wednesday is also a cap bust along the dryline due to near-neutral height tendencies and the EML. Both 2010 (4/4-4/6) and 2013 (4/7-4/9) featured slow-moving early April troughs that looked very impressive, but failed to do anything worth mentioning over the Plains even in the presence of seasonably impressive moisture return. I can very easily see this one joining that list. Of course, the probability distribution is still wide, and one or both days still have a chance.

Surface-based convection over the open warm sector (i.e., the jungle) is probably a more noteworthy threat late Wednesday into Wednesday night, as several models have consistently signalled. The solutions for Thursday vary so wildly between American, Canadian and European guidance that it's futile to speculate for now.

[andyhb]

In terms of practical implications, I'd place the highest probability on this scenario: the lead wave is too late for surface-based initiation Tuesday, and Wednesday is also a cap bust along the dryline due to near-neutral height tendencies and the EML. Both 2010 (4/4-4/6) and 2013 (4/7-4/9) featured slow-moving early April troughs that looked very impressive, but failed to do anything worth mentioning over the Plains even in the presence of seasonably impressive moisture return. I can very easily see this one joining that list. Of course, the probability distribution is still wide, and one or both days still have a chance.

 

That system also had anafrontal problems and issues with the vertical wind profile that won't be ironed out until we get down to the nitty-gritty, I think it easily could've turned out significantly different. It's not that storms didn't initiate that day.

[Chicago Storm]

0z GFS brings yet another solution to the table.

 

Sig differences between it and the ECMWF continue.

[ZackH]

0z GFS bring another solution to the table.

 

Sig differences between it and the ECMWF continue.

 

Yup, Thursday turning into the big day via the GFS... and much further west than initially forecast... if it could go a bit further west, it would be pretty... however just too much uncertainty with this system to make me comfortable.  I've almost decided to sit this setup out... I think Tues and Wednesday are looking less and less attractive and Thursday is a tough day for me.  00z GFS is just crazy different and the the ECMWF is a whole different solution.

[Chicago Storm]

Yup, Thursday turning into the big day via the GFS... and much further west than initially forecast... if it could go a bit further west, it would be pretty... however just too much uncertainty with this system to make me comfortable.  I've almost decided to sit this setup out... I think Tues and Wednesday are looking less and less attractive and Thursday is a tough day for me.  00z GFS is just crazy different and the the ECMWF is a whole different solution.

Indeed...Riding the edge for Thur regarding decent chase terrain, with the DL sitting just west of 35 through the afternoon/evening.

 

The difference between the 0z and 18z GFS runs aloft are day and night...Laughable difference in how it handles the wave.

[Stebo]

Indeed...Riding the edge for Thur regarding decent chase terrain, with the DL sitting just west of 35 through the afternoon/evening.

 

The difference between the 0z and 18z GFS runs aloft are day and night...Laughable difference in how it handles the wave.

 

Yeah I don't know how much stock I would put into the GFS solution, not saying it is wrong but it literally has shown something new every 6 hours.

[brettjrob]

Euro is at least giving the illusion that it's locked onto a solution -- differences between tonight's run and last night's are negligible out to Thursday, and all the while the other globals are flailing in the wind run-to-run. Barring an uncharacteristic Euro meltdown at relatively short range, this should be strong evidence for discarding the other guidance tonight that shows positive-tilt slop Wed-Thu that struggles to progress.

 

Wed would clearly be the best dryline threat of the three days, even though the 00z GFS says it's the least impressive of the three. I'm noticing the Euro has been adamant run after run that supercells develop over the warm sector around 00z Thu and march from I-35 into the Ozarks overnight, which would be unfortunate for both chasers and the general public. It's fairly rare to see that type of initiation away from boundaries in the Plains, so I'm still hopeful that the real storms (if any) will focus along the dryline, but it's something to keep a close eye on.

 

EDIT: Wundermap is doing that thing where it plots QPF for a bunch of 3-hour periods together as it updates, and it has an ominous ESE-directed streak from the tri-state region into N AR overnight Wed. Crazy stuff.

 

[andyhb]

From the looks of the 00z suite, the Euro and UK solutions show a conditional, but impressive threat on Wednesday later on as Brett highlighted nicely above, with the potential for a nocturnal tornado event given the rapidly strengthening low level shear, discrete storm mode, coupled boundary layer and strong instability. Meanwhile, Thursday appears to have the most confident (across the full suite) potential for a widespread severe event. Both the Euro and UK solutions again are leading the pack in terms of threat level on Thursday (UK probably the highest potential with keeping the trough as an open wave while the Euro closes it off by 120 hrs), with both of them looking like higher end events depending on leftover convection and other mesoscale factors that obviously won't be locked down yet. The GFS and GGEM, considering their wild inconsistencies, still show notable threats on Thursday although probably not quite to the degree of the former pair (kind of laughing right now at the North American model performance with this so far, frankly). 

 

I would think that a risk area for Thursday might be upcoming either in about an hour or tomorrow once greater model consensus develops (if it does, lol).

[andyhb]

And just as an added note, the warm sector the GFS is showing at 00z Friday is pretty incredible for early April, widespread 3000+ J/kg SBCAPE (and this is the rather thermodynamically conservative GFS keep in mind).

[thewxmann]

Interestingly, despite their differences, the CMC/Euro/GFS all have been somewhat consistent in breaking out convection around the Red River around 0Z Thur (Wed aftn). It's quite possible that the key to initiation on Wed might lie in a disturbance embedded in the STJ that noses into the warm sector over N TX around that time. I think the trend is evident that the main system and larger-scale forcing will not arrive until overnight Wed.

 

Agree with the nocturnal threat and the likelihood of extreme instability with this one.

[andyhb]

These anomalously cold 500 mb temperatures (showing -15˚C over parts of the warm sector) are really going to help steepen mid level lapse rates and increase instability to more than it otherwise might be.

[andyhb]

Good to know I haven't gone insane, lol.

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0357 AM CDT SUN MAR 30 2014

VALID 021200Z - 071200Z

...DISCUSSION...
DAY 4-5/

MODELS APPEAR TO BE CONVERGING TOWARD A SLOWER...MORE AMPLIFIED
SOLUTION REGARDING THE UPPER TROUGH FORECAST TO MOVE THROUGH THE
CNTRL AND SRN PLAINS AND MID MS VALLEY AREA BY THURSDAY /DAY 5/ WITH
ECMWF ALSO TRENDING SLOWER...BUT STILL REMAINS THE FASTER MODEL.
PRECEDING THIS FEATURE...RICHER GULF MOISTURE /LOW-MID 60S
DEWPOINTS/ WILL ADVECT THROUGH THE WARM SECTOR UNDERNEATH STEEP
MID-LEVEL LAPSE RATES RESULTING IN MODERATE-STRONG INSTABILITY OVER
THE SRN PLAINS AND A PORTION OF THE LOWER MS VALLEY BY WEDNESDAY
/DAY 4/. IT STILL APPEARS A FEW SEVERE STORMS COULD DEVELOP ALONG
THE DRYLINE DAY 4 OVER THE SRN PLAINS AND NEAR THE DRYLINE/FRONT
INTERSECTION OVER NWRN OK/SWRN KS. HOWEVER...CAPPING WILL BE A
CONCERN FOR SEVERE STORM COVERAGE ALONG THE DRYLINE AS WELL AS
FARTHER EAST IN WARM SECTOR. CONFIDENCE IN WHERE TO PLACE A 30% OR
GREATER SEVERE AREA REMAINS LOW FOR DAY 4...BUT A CATEGORICAL RISK
AREA WILL PROBABLY BE NEEDED FOR THE NEXT DAY 3 UPDATE.

GIVEN MODEL TRENDS...IT NOW APPEARS A MORE SUBSTANTIAL SEVERE THREAT
MIGHT DEVELOP FROM THE SRN PLAINS INTO THE LOWER-MID MS VALLEY
REGION THURSDAY /DAY 5/ AS THE SHORTWAVE TROUGH EJECTS ENEWD
RESULTING IN HEIGHT FALLS ACROSS THE WARM SECTOR AND A STRENGTHENING
LLJ. STORMS MAY DEVELOP ALONG THE DRYLINE AND DRYLINE/PACIFIC FRONT
MERGER OVER THE SRN PLAINS AS WELL AS FARTHER EAST IN THE WARM
SECTOR. SEVERE THREAT WILL LIKELY SPREAD EWD INTO THE LOWER MS
VALLEY AREA BY LATER THURSDAY AFTERNOON AND EVENING.

DAY 6/

SEVERE THREAT WILL PROBABLY DEVELOP FARTHER EAST INTO THE OH AND TN
VALLEYS AS WELL AS A PORTION OF THE SERN STATES BY FRIDAY /DAY 6/.
IF CURRENT TRENDS PERSIST...A PORTION OF THIS REGION MAY BE INCLUDED
IN A CATEGORICAL RISK IN THE NEXT UPDATE.

..DIAL.. 03/30/2014

[blizzardof96]

The 0z Euro looks quite impressive with PWAT's nearing 2.0" in the warm sector along with backing sfc winds across SE TX, E OK and NW AR. DP's are generally in the low to mid sixties across most of the area which is pretty nice(albeit more confined and not as impressive as the 12z run) coupled with the strengthening LLJ ~50kts at initiation. Highest CAPE values do seem to be displaced slightly west of the nicest shear/convergence w/ a max of ~3500j/kg across central Texas and OK.

[andyhb]

Looks like the 12z GFS is coming into better agreement with the European guidance regarding a significant threat on Thursday and now Friday as well. Notice how it has done this as the lead trough has come ashore this morning.

 

Edit: GGEM as well.

[NTXYankee]

Looks like the 12z GFS is coming into better agreement with the European guidance regarding a significant threat on Thursday and now Friday as well. Notice how it has done this as the lead trough has come ashore this morning.

 

Edit: GGEM as well.

You seem very knowledgable regarding severe weather and me a newbie to southern plains systems, it seems as though the DFW area may just miss this Thursday event, Euro and GFS seem to push through quicker now, early afternoon.