April 6-10th Severe Potential

[Chicago Storm]

Several issues on any given day, but there is potential.

[Indystorm]

At least we are moving into a more active pattern.  Many here do recall JB's concern for mid April till the end of May.

[Chicago Storm]

At least we are moving into a more active pattern.  Many here do recall JB's concern for mid April till the end of May.

That really isn't much of a call.

[andyhb]

12z Euro/GFS looked pretty robust for 4/9 in the Southern Plains/perhaps Ozarks.

[1900hurricane]

Starting to dig on Wednesday and Thursday a bit. It would be nice to have something worthwhile in my driving range for a change.

[ZackH]

Today's GFS runs make Wednesday look like the most desirable chase day to me (big day Thursday too, but messy)... in eastern KS and the north half of MO.  But the 12z Euro looks high end potential wise for Thursday in OK . I'm sure we still have quite a few changes before getting a clear idea on the evolution, but it certainly looks like an active week coming up.

[jojo762]

KTOP already went all out with their AFD for next week. Specifically, on Wednesday, they mention that supercells are likely including tornadoes... Seems really early to go all in.

[Chicago Storm]

Wednesday and Thursday are the best looking days at this point, as the trough finally starts to eject out.

18z GFS has come in faster and with more northern stream influence, which takes Friday out of the equation chase wise. Then Monday will likely be a cap bust, and Tuesday will have similar issues.

[Superstorm93]

KTOP already went all out with their AFD for next week. Specifically, on Wednesday, they mention that supercells are likely including tornadoes... Seems really early to go all in.

 

For posterity 

 

 

 

Wednesday through Wednesday night, the upper level trough will move

east across AZ into NM. Ahead of the upper trough a lee surface low

and trough will develop across eastern CO and western TX. the

veered 850mb winds will back to the south across central OK into

eastern KS. Severe thunderstorms will develop along the surface

dryline across south central KS and central OK. The ECMWF slowly

brings the surface front northward towards the southern counties

of the CWA. This would be another area of convergence where

severe thunderstorms may develop in the afternoon and evening

hours. The low-level vertical wind shear profiles will increase

significantly through the afternoon and into the evening hours.

Any storms that develop along the drying across south central KS

and the warm front across southeast and east central KS will most

likely be supercells, and with sufficiently strong low-level

vertical wind-shear, some of these supercells may be capable of

producing tornadoes along with large hail and damaging wind guts.

Any supercells that move north of the boundary will be capable of

producing large hail and isolated severe wind gusts. This forecast

may change over the next few days, depending on how far north the

surface warm front will move during the afternoon hours of

Wednesday. 

[andyhb]

Seems like the model consensus as of now is for the mid/upper flow with this event to be a tad weaker than we're used to seeing this time of year (although instability also looks like it will be rather robust and over a large area). This might help with storm motions as far as chasing prospects go, although there's obviously a lot of things to be worked out. There are still a lot of inconsistencies with what day will end up being over which area, which I think will remain for the next couple of days at least.

 

Either way, a broad, relatively low amplitude trough (provided it actually ejects properly) such as this one with favorable cross-boundary flow should provide a solid background forcing environment at least for supercells, we just have to see what else we have to work with.

[Superstorm93]

00z GFS starting to like Wednesday a bit more than its previous run. 

 

A lot remains up in the air about the evolution of the this system, however it does look rather decent for a chase event in the Plains. 

 

 

 

 

 

 

[brettjrob]

I've been extremely skeptical of this whole period for the past few days. This whole business of a stalled, slowly filling wrn CONUS trough holding back just a smidge too far... I'll take it from mid May into June, but not so much in early April. We don't have the luxury of 15-hour daylight to mitigate shortwave timing issues, remnant outflow boundaries galore, etc. In the vast majority of cases this early in the spring, you really just want one obvious, moderately- or strongly-forced day; not a string of "interesting days." Because most of those end up not being very interesting in the end.

With that being said, I'm happy to see the GFS and Euro begin to converge some tonight, with Wednesday appearing to offer decent potential on the southern Plains. I'm still quite concerned about the potential for a cap bust, at least along the dryline, even on "the day" (whichever that ends up being). Thursday in the trees is currently looking like the obvious, synoptically-forced day... but I think everyone in this subforum knows by now how much those setups interest me.

[andyhb]

Hell I would like to see at least just one solid day without a rather grungy mess somewhere, just to show that 2015 has some form of life.

[brettjrob]

Looking at the full output of the 04/00z ECMWF, hard to complain about the solution for Wednesday, particularly this time of year. All the ingredients for a respectable dryline supercell event appear to be there across western into central OK, with seasonably rich moisture and good low-level shear. Glad to see both the GFS and Euro convect on tonight's runs, but we've got plenty of squirming to do during subsequent runs, methinks.

[thewxmann]

This setup kinda reminds me of a less potent version of mid-April 2012. A lot of somewhat interesting days before the main event.

[andyhb]

Looking at the full output of the 04/00z ECMWF, hard to complain about the solution for Wednesday, particularly this time of year. All the ingredients for a respectable dryline supercell event appear to be there across western into central OK, with seasonably rich moisture and good low-level shear. Glad to see both the GFS and Euro convect on tonight's runs, but we've got plenty of squirming to do during subsequent runs, methinks.

 

Of course it's putting storms right over the OKC metro with a strengthening southerly LLJ and backed near-sfc flow at 00z. I have a funny feeling (not really based on anything concrete right now) we might be going through that rodeo again before this is all said and done in some form or another.

[brettjrob]

This setup kinda reminds me of a less potent version of mid-April 2012. A lot of somewhat interesting days before the main event.

 

I had that exact thought earlier today. Plenty of similarities, but given the likely lower-amplitude nature of the longwave trough, I suspect the ceiling is lower.

 

Of course it's putting storms right over the OKC metro with a strengthening southerly LLJ and backed near-sfc flow at 00z. I have a funny feeling (not really based on anything concrete right now) we might be going through that rodeo again before this is all said and done in some form or another.

 

Wouldn't surprise me, since virtually every significant OK event for years now has snapped right to the metro OKC counties. I'm slightly optimistic that the ECMWF convective signal starts a few counties W of here, particularly since the global models commonly have an eastward bias in dryline placement. No doubt the threat would extend into the metro area at some point during the evening taking this all literally, but perhaps we'd be fortunate enough for the main show to be over wheat fields.

[thewxmann]

Of course it's putting storms right over the OKC metro with a strengthening southerly LLJ and backed near-sfc flow at 00z. I have a funny feeling (not really based on anything concrete right now) we might be going through that rodeo again before this is all said and done in some form or another.

 

It's kinda ridiculous how if a risk area is even remotely close to OKC metro Moore gets in the crosshairs. I'm getting that funny feeling as well.

[andyhb]

15% for Wed and a rather large 30% risk for Thursday in the latest D4-8.
 

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0358 AM CDT SAT APR 04 2015

VALID 071200Z - 121200Z

...DISCUSSION...
LATEST RUNS OF THE MEDIUM-RANGE MODELS EXHIBIT DECENT AGREEMENT INTO
THE DAY 6 /THU. 4-9/ TIME PERIOD...PROJECTING THE WRN U.S. TROUGH TO
BECOME PROGRESSIVE AND TRAVERSE THE ROCKIES THROUGH DAY 5 BEFORE
SHIFTING INTO THE PLAINS DAY 6. FROM LATE IN THE DAY 6 PERIOD
ONWARD...SPREAD IN THE MODEL SOLUTIONS INCREASES SUCH THAT LOW
FORECAST CONFIDENCE PREVAILS DAYS 7 AND 8.

SEVERE-WEATHER RISK APPEARS RELATIVELY LOW EARLY IN THE PERIOD --
BUT A GRADUAL RAMP-UP IN RISK EACH AFTERNOON/EVENING THROUGH DAY 6
APPEARS LIKELY ACROSS THE U.S. AS THE WRN TROUGH APPROACHES -- AND
EVENTUALLY REACHES -- THE CENTRAL CONUS. THOUGH AIRMASS ACROSS THE
OK/ERN KS/MO/AR/N TX VICINITY DURING THE AFTERNOON ON DAY 4 /TUE.
4-7/ WILL LIKELY BECOME STRONGLY UNSTABLE...WEAK RIDGING PERSISTING
ALOFT -- AND ASSOCIATED/WEAK SUBSIDENCE -- SHOULD PERMIT CAPPING AT
THE BOTTOM OF THE EML LAYER TO PERSIST IN MOST AREAS. THIS SUGGESTS
THAT STORM INITIATION /AND ASSOCIATED SEVERE RISK/ SHOULD REMAIN
RELATIVELY ISOLATED.

SLIGHTLY MORE WIDESPREAD STORM DEVELOPMENT WILL BE POSSIBLE DURING
THE AFTERNOON ON DAY 5 /WED. 4-8/...AS WEAK HEIGHT FALLS BEGIN AHEAD
OF THE APPROACHING UPPER SYSTEM. WHILE EJECTION OF ANY APPRECIABLE
LEAD WAVE IS NOT EVIDENT ATTM...A LESS SUBSIDENT/MORE NEUTRAL
BACKGROUND LARGE-SCALE UVV SUGGESTS GREATER POTENTIAL FOR CAP
BREACHES/STORM INITIATION -- PRIMARILY ACROSS THE ERN KS/MO/OK
VICINITY. WITH STRONG INSTABILITY AND MODERATELY STRONG SHEAR
EXPECTED...ENVIRONMENT WILL FAVOR SUPERCELLS...AND ASSOCIATED RISK
FOR LARGE HAIL...DAMAGING WINDS...AND POSSIBLE TORNADOES.

WHILE ONGOING CONVECTION OVERNIGHT DAY 5 AND INTO EARLY DAY 6
LIKELY...ASCERTAINING DEGREE AND LOCATION OF SEVERE RISK DAY 6
PRESENTS SOME DIFFICULTY ATTM. WITH THAT SAID...THE ADVANCE OF THE
WRN TROUGH AND ASSOCIATED UVV INTO THE INTO THE CENTRAL PLAINS
DURING THE AFTERNOON AND EVENING WILL PERMIT WIDESPREAD CONVECTIVE
INITIATION -- FOCUSED INVOF THE COLD FRONT FORECAST TO BE ADVANCING
ACROSS ERN KS/CENTRAL OK NEAR PEAK HEATING. WITH SUBSTANTIAL
INSTABILITY LIKELY TO BE PRESENT AND A FAVORABLY SHEARED
ENVIRONMENT...A FAIRLY BROAD AFTERNOON AND EVENING ZONE OF RISK FOR
LARGE HAIL AND DAMAGING WINDS ALONG WITH A FEW TORNADOES IS EVIDENT
-- EXTENDING FROM IL SWWD ACROSS MO/AR INTO SERN KS/ERN OK AND
POSSIBLY INTO N CENTRAL/NERN TX.

..GOSS.. 04/04/2015

CIPS analogs lighting up the Plains for Wednesday already (some notable dates in there for sure).

 

[huronicane]

Seeing May 3, May 8, April 14 are probably not what a lot of plains folk want to see...but it's definitely something the chasers want to see.

[vwgrrc]

00z GFS starting to like Wednesday a bit more than its previous run.

A lot remains up in the air about the evolution of the this system, however it does look rather decent for a chase event in the Plains.

Right above dfw metro too? But I guess the cap should hold everything here again... Like it always

[andyhb]

12z GFS really looks like it has ramped up the strength of the trough/surface reflection compared to previous runs. It initiates in KS near the triple point on Wednesday with 3000+ J/kg CAPE and strong low level shear east of the dryline. There's also no problem with the wind profile aloft either, at least as of now.

[ZackH]

Comparing the 12z GFS/12z ECMWF... they appear to be in fairly good agreement by Wednesday afternoon synoptically. Trough orientation/location and surface low strength are very similar. However, the GFS ejects out a stronger piece of mid-level energy Wednesday afternoon than the more subtle ECM impulse. The thermo fields in the ECM solution are also not quite as robust as the GFS.

 

As far as the trough placement by Tuesday night... WPC seems to think that the GFS is the one out to lunch, per their 12z model diagnostic discussion... that it is too progressive, which would meld with usual GFS biases. I will say that the Euro's thermodynamic profile looks a bit unrealistic to me... the moisture should be there and in plenty.  

 

As of now, the GFS holds the highest ceiling, and the 12z solution would be quite a high end event verbatim (on Wednesday) as well as in the previous few runs. The ECM still maintains a potentially significant solution, but it is not quite as robust... the ECM also still seems to have the highest ceiling on Thursday with a decent day before the day setup on Wednesday. Hopefully we will get some further agreement in the coming days. 

[brettjrob]

On the whole, we're converging on a timing solution where the H5 map I'd most like to see at 21z-00z for a high-end Plains dryline day is valid at 12z Thu. I feel like I say that at least once every year in March or April, usually more like 2-3x. For now, the Euro manages to convect Wednesday and delays vertically stacking the cyclone long enough that Thursday looks good, albeit east of 35. But truthfully, ignoring the details of any one model solution, the pattern gives me that "too late for D1, too early for D2" vibe -- at least for areas W of 35. If shortwave timing is impeccable and the structure of the longwave trough evolves just right, both days could be good. More likely, IMO, we're looking at limited (if any) CI on Wednesday, and then trying to will a narrow window of favorable CAPE-shear overlap Thursday into the easternmost chaseable areas (E KS, etc.). Think 4/5-6/10, 4/2-3/14, 4/26-27/14, etc. (recognizing that those had vastly different outcomes downstream; I'm talking strictly for the true Plains).

To be fair, comparing this specifically to 4/26-27 last year, we don't have stubborn downstream troughing encouraging the upstream cyclone to pinch off and go barotropic on us. So if the timing settles roughly around the current progs *and* the trend toward a more negative-tilt orientation (by Thursday) advertised on this morning's runs holds, I like the chances for a high-end threat across E KS/SE NE and surrounding areas a little more than last year's case. If the more energetic, negative-tilt solution doesn't materialize, I kind of doubt Thursday works out for chasers.

[ZackH]

On the whole, we're converging on a timing solution where the H5 map I'd most like to see at 21z-00z for a high-end Plains dryline day is valid at 12z Thu. I feel like I say that at least once every year in March or April, usually more like 2-3x. For now, the Euro manages to convect Wednesday and delays vertically stacking the cyclone long enough that Thursday looks good, albeit east of 35. But truthfully, ignoring the details of any one model solution, the pattern gives me that "too late for D1, too early for D2" vibe -- at least for areas W of 35. If shortwave timing is impeccable and the structure of the longwave trough evolves just right, both days could be good. More likely, IMO, we're looking at limited (if any) CI on Wednesday, and then trying to will a narrow window of favorable CAPE-shear overlap Thursday into the easternmost chaseable areas (E KS, etc.). Think 4/5-6/10, 4/2-3/14, 4/26-27/14, etc. (recognizing that those had vastly different outcomes downstream; I'm talking strictly for the true Plains).

To be fair, comparing this specifically to 4/26-27 last year, we don't have stubborn downstream troughing encouraging the upstream cyclone to pinch off and go barotropic on us. So if the timing settles roughly around the current progs *and* the trend toward a more negative-tilt orientation (by Thursday) advertised on this morning's runs holds, I like the chances for a high-end threat across E KS/SE NE and surrounding areas a little more than last year's case. If the more energetic, negative-tilt solution doesn't materialize, I kind of doubt Thursday works out for chasers.

 

I can't argue with those concerns. I love the GFS timing wise... but I'm not confident that piece of energy that its throwing out early will materialize.

[andyhb]

Seems like the models went towards this stronger solution as soon as the lead wave came ashore this morning and was fully sampled. This is probably a good sign going forward. While not over prime terrain (yes I must speak not just for chasers), the 12z Euro is a potentially high end outcome over E OK and the Arklatex region/Ouachitas. It reminds me a bit of 4/12/1945 in that regard. If you are familiar with pre-1950 severe climo west of the Mississippi, that should ring a bell.

[ZackH]

18z GFS holds serve with a significant threat from ICT to OKC along the I-35 corridor on Wednesday.

[KSWx]

A bit off-topic, but is the COD weather lab page extremely slow to load models today for anyone else?

[andyhb]

A bit off-topic, but is the COD weather lab page extremely slow to load models today for anyone else?

 

Yes they were having technical difficulties earlier.

[Thundersnow12]

Yes they were having technical difficulties earlier.

 

They should be fixed now. 

 

I'd argue the 18z GFS is even more significant than the 12z run for Weds. Big convective signal just after 0z in southern KS with a pretty stellar environment as p-falls really back the sfc winds along the dryline leading to what I call the "skittle composite" environment.

 

Great crossovers