Severe weather risk 4/30 - 5/3

[JasonOH]

FWIW the 12z FV3 was very bullish with the LLJ for Wednesday.  I’m not sure how well it verifies since it’s brand new.

 

0z GFS improves the 850mb flow compared to earlier runs today for Wednesday. Not quite up to the level of the FV3 but it’s close.  Long range NAM is still on an island. 

[Radtechwxman]

11 minutes ago, WhiteoutWX said:

I'm not going to be trusting the long range NAM for synoptic details over the GFS/Euro. While a subtle slowing trend has been evident on the global models the past couple days, they still have plenty of QPF signal, indicating initiation is not a problem.

0z GFS has moderate/strong height falls 18-0z on Wednesday afternoon, plenty of low level shear, and upper 60s/near 70 dewpoints. I'm not gonna panic yet over some slight downtick of the threat on the 12z Euro and the long range NAM out on an island.  The threat still looks fairly robust to me. 

I couldn't agree more. The difference in trough orientation between GFS and NAM is unreal. NAM has a strong positive tilt which holds the jet back and GFS is more neutral which allows the better height falls and jet winds to overlap dryline and warm sector earlier

[jojo762]

Not saying it is happening here really. But putting so much thought into the 84/78/72 hour NAM for Wednesday seems silly given how much tuesday has shifted on it over the last several runs.

[jojo762]

After having gone into more detail looking at forecast soundings, etc. from the 00z GFS I am coming out quite impressed.

Along and east of the entire dryline from Southern Kansas and into southwest Oklahoma GFS forecast soundings indicate an impressively moist BL with dewpoints in the upper 60s to even low 70s, instability is forecast to be quite strong with the GFS currently indicating MLCAPE of 2500-3500+ J/KG along most of the dryline with 3500+ value being especially prevalent across west-central Oklahoma. Mid/Upper level flow is quite favorable on the GFS across the highest-risk area with 50-70kt mid-level H5 southwest flow perhaps veering to WSW at H25. Current indications from the GFS are that an expansive and relatively impressive S/SSW'ly 35-45kt LLJ will reside along and east of the dryline with surface flow becoming increasingly backed by 00Z across western Oklahoma and southern KS, and especially by 03Z. Effective shear values should hover in the 55-70kt range, which is ideal for supercells and updraft maintenance. 0-3km helicities values along and east of much of the dryline are progged in the 200-300 m2/s2 range, and low-level CAPE should be in the 80-140 J/KG range... both of which are favorable for mesocyclones and tornadogenesis. Lastly, the GFS indicates that at least some CIN should still exist by 00Z, paving the way for scattered discrete supercells along much of the dryline. (as is indicated in the precip fields of both the euro and the GFS) These supercells will be capable of very large hail, damaging winds, and tornadoes - some of which could be strong and long-tracking. 

[jojo762]

DAY 2 CONVECTIVE OUTLOOK    
NWS STORM PREDICTION CENTER NORMAN OK  
1239 AM CDT MON APR 30 2018  
  
VALID 011200Z - 021200Z  
  
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL  
AND NORTHERN KANSAS...MUCH OF SOUTHEAST NEBRASKA...AND FAR SOUTHWEST  
IOWA/NORTHWEST MO...  
   
..SUMMARY  
  
SEVERE STORMS ARE EXPECTED MAINLY ACROSS NORTH-CENTRAL KANSAS INTO  
SOUTHEAST NEBRASKA TUESDAY FROM LATE AFTERNOON THROUGH EVENING.  
LARGE HAIL, DAMAGING WINDS, AND A FEW TORNADOES ARE POSSIBLE. MORE  
ISOLATED SEVERE STORMS ARE POSSIBLE FROM CENTRAL KANSAS INTO WESTERN  
OKLAHOMA.  
   
..SYNOPSIS  
  
A BROAD BELT OF SOUTHWESTERLY FLOW ALOFT WILL REMAIN OVER THE PLAINS  
AS AN UPPER TROUGH AMPLIFIES ACROSS THE SOUTHWESTERN STATES. AT THE  
SURFACE, A COLD FRONT WILL MOVE EAST ACROSS THE UPPER MS VALLEY  
DURING THE DAY WITH A WEAK TROUGH DEPARTING TO THE NORTH, WHILE THE  
TAIL END OF THE FRONT BECOMES QUASI-STATIONARY ACROSS SOUTHEAST NE  
INTO NORTHWEST KS. STRONG HEATING WILL OCCUR OVER THE SOUTHERN  
PLAINS WITH LOW PRESSURE ACROSS SOUTHEAST CO AND SOUTHWEST KS.  
DEWPOINTS IN THE 60S F WILL EXIST SOUTH OF THE COLD FRONT, AND EAST  
OF A DRYLINE THAT WILL EXTEND FROM CENTRAL KS INTO WEST CENTRAL TX.  
STRONG SOUTHERLY WINDS WILL DEVELOP ACROSS THE PLAINS, WITH A 50+ KT  
LOW-LEVEL JET DURING THE EVENING. THE COMBINATION OF STRONG  
INSTABILITY AND SHEAR WILL RESULT IN AREAS OF SEVERE STORMS, MAINLY  
FROM NORTHERN KS INTO SOUTHEAST NE, WITH A CONDITIONAL SEVERE THREAT  
FARTHER SOUTH INTO WESTERN OK.  
  
...CENTRAL AND NORTHERN KS, SOUTHEAST NE, FAR SOUTHWEST IA AND  
NORTHWEST MO...  
SUPERCELLS ARE EXPECTED TO FORM BY LATE AFTERNOON ACROSS CENTRAL TO  
NORTH CENTRAL KS, NEAR THE DRYLINE/FRONT INTERSECTION, AND WITH  
ADDITIONAL ACTIVITY DEVELOPING INTO SOUTHEAST NE ALONG THE FRONT.  
WIND PROFILES WILL FAVOR SUPERCELLS, WITH LARGE HAIL AND A FEW  
TORNADOES POSSIBLE. WITH TIME, A COMPLEX OF STORMS IS EXPECTED ALONG  
THE FRONT, PERHAPS WITH EMBEDDED SUPERCELLS CAPABLE OF DAMAGING  
WINDS AND HAIL, AND A BRIEF TORNADO.  
   
..SOUTH-CENTRAL KS INTO NORTHWEST OK  
  
STRONG INSTABILITY WILL DEVELOP ALONG THE DRYLINE AS DEWPOINTS RISE  
INTO THE 60S F AND HEATING OCCURS. THE AIR MASS SHOULD BE UNCAPPED  
AFTER ABOUT 21Z, AND WIND PROFILES WILL VEER WITH HEIGHT AND CLEARLY  
FAVOR SUPERCELLS. COOLER AIR EAST OF THE DRYLINE, AND THUS  
CONTAINING MORE CIN, WILL BACK WESTWARD AFTER 00Z. THIS SETUP LENDS  
UNCERTAINTY AS TO HOW MANY STORMS WILL OCCUR AND FOR HOW LONG. IN  
ADDITION, MIDLEVEL SUBSIDENCE IS FORECAST ESPECIALLY OVER SOUTHERN  
AREAS. CONDITIONALLY, VERY LARGE HAIL AND EVEN TORNADOES WILL BE  
POSSIBLE AS SRH INCREASES LATE IN THE DAY.  
   
..MAXIMUM RISK BY HAZARD  
  
TORNADO:  10% SIG - ENHANCED  
WIND:     30%     - ENHANCED  
HAIL:     30% SIG - ENHANCED  
  
..JEWELL.. 04/30/2018  

[bjc0303]

2 hours ago, WhiteoutWX said:

I'm not going to be trusting the long range NAM for synoptic details over the GFS/Euro. While a subtle slowing trend has been evident on the global models the past couple days, they still have plenty of QPF signal, indicating initiation is not a problem.

0z GFS has moderate/strong height falls 18-0z on Wednesday afternoon, plenty of low level shear, and upper 60s/near 70 dewpoints. I'm not gonna panic yet over some slight downtick of the threat on the 12z Euro and the long range NAM out on an island.  The threat still looks fairly robust to me. 

Euro with yet another potent run. Maybe one day, just maybe, chasers will learn to wait for the 48-60 hour range to seriously consider the NAM. Ah who am I kidding. 

[jojo762]

3 minutes ago, bjc0303 said:

Euro with yet another potent run. Maybe one day, just maybe, chasers will learn to wait for the 48-60 hour range to seriously consider the NAM. Ah who am I kidding. 

GFS seemed potent, but the euro really one-up'ed it IMO. A bit confused by the MCS the Euro develops in KS by 21Z, doubt that happens. But nevertheless, backed surface flow along the entire dryline in OK with strong instability and deep-layer shear, along with a 30-45kt LLJ (that is not displaced from the dryline). Get that maybe slightly considering what the NAM is showing might play a role in it, but wouldn't be surprised to see SPC go bombs away with the D3 given the consistency and agreement of the GFS/Euro. 

[OUGrad05]

6 hours ago, jojo762 said:

GFS seemed potent, but the euro really one-up'ed it IMO. A bit confused by the MCS the Euro develops in KS by 21Z, doubt that happens. But nevertheless, backed surface flow along the entire dryline in OK with strong instability and deep-layer shear, along with a 30-45kt LLJ (that is not displaced from the dryline). Get that maybe slightly considering what the NAM is showing might play a role in it, but wouldn't be surprised to see SPC go bombs away with the D3 given the consistency and agreement of the GFS/Euro. 

Hindsight is obviously 2020 but they kept the enhanced risk with a smaller hatched area than I would have guessed.  However, I can't blame them at this point.  Timing of the shortwave, possibilities of a displaced jet (NAM guidance, probably wrong but still) and other issues preclude the upgrade at this time.  

I think they made the right call given the data we currently have.  00NAM runs this evening will be crucial (assuming we don't lose the GFS and Euro).

[WhiteoutWX]

D3 outlook lacked much detail, which I’m fine with for now until details become clearer. I do think the sig risk area should extend to southwest Oklahoma given the GFS/Euro agree on quite the potent environment here. But again, D3, not worth nitpicking at this point.

[tornado_junkies]

1 minute ago, WhiteoutWX said:

D3 outlook lacked much detail, which I’m fine with for now until details become clearer. I do think the sig risk area should extend to southwest Oklahoma given the GFS/Euro agree on quite the potent environment here. But again, D3, not worth nitpicking at this point.

I would like to see the 12z and especially 0z NAM runs today trend more towards a GFS/ECM solution. I'm okay with a vauge Day 3 as well. Plenty of details to work out still.

[Radtechwxman]

15 minutes ago, tornado_junkies said:

I would like to see the 12z and especially 0z NAM runs today trend more towards a GFS/ECM solution. I'm okay with a vauge Day 3 as well. Plenty of details to work out still.

I couldn't agree more. Def would feel better to see NAM trend that way. NAM has sniffed out trends before but also equally has been wrong. Hard to say

[Drz1111]

NAM/WRF sniffs out what its powered to sniff out - things where its resolution lets it see things that a global misses, where its convective scheme is more accurate, or where its the first model to run with new information when features move onto the observational network.  I certainly don't expect it to be better with upper features than the Euro or even the GFS, unless those features are being driven by smaller-scale processes. (WRF was always a good check on the GFS convective feedback . . .)

[Radtechwxman]

Looks like 12z nam trended more towards a GFS/Euro compromise with trough orientation and better timing 

[OUGrad05]

1 minute ago, StormChaser4Life said:

Looks like 12z nam trended more towards a GFS/Euro compromise with trough orientation and better timing 

Yes it did but still leaves quite a bit to be desired.  But you kind of expect this from the NAM, it'll continue to move toward the others.  

[CheeselandSkies]

3 minutes ago, OUGrad05 said:

Yes it did but still leaves quite a bit to be desired.  But you kind of expect this from the NAM, it'll continue to move toward the others.  

Despite its solution's shortcomings vs. the globals in the timing quality for Wednesday, it still has that massive spike in EHI from 00 to 03Z Thursday.

[OUGrad05]

6 minutes ago, CheeselandSkies said:

Despite its solution's shortcomings vs. the globals in the timing quality for Wednesday, it still has that massive spike in EHI from 00 to 03Z Thursday.

Yes it does.  I'm not really giving anything on the NAM much credence until the 00Z run this evening.  At that point we'll be within range for it to perform adequately.  

[Radtechwxman]

24 minutes ago, OUGrad05 said:

Yes it does.  I'm not really giving anything on the NAM much credence until the 00Z run this evening.  At that point we'll be within range for it to perform adequately.  

Yea at this range only looking at Tues on it. But at least it is firing storms at or just before 0z now on Wed. Lol

[hlcater]

If trends on the HREF and even the GFS hold serve, one could justify a 15% hatched tor for NC KS into SE NE.

[andyhb]

The triple point in KS on the majority of guidance (including every member of the HREF) tomorrow looks absolutely nasty. Assuming we get those mid 60s dewpoints into there, wouldn't be shocked at all to see a significant tornado/hail risk starting in the late afternoon.

The setup reminds me a lot of some of the things we saw in later May in 2016, only this time with slightly less instability/moisture, but a much stronger low level flow regime.

Should note that further south down the dryline isn't a total write-off either, albeit more conditional.

[the ghost of leroy]

yeah i'll be there along with 1500 of my pals

[jojo762]

CAM/HREF output for tomorrow is quite impressive. Especially across NC/NE KS and SE NE. HRW-NSSL and HRW-ARW are particularly impressive showing dual discrete supercells propagating east/northeastward along the KS/NE border. Most HREF members hint at the development of a couple of discrete supercells further south along the dryline, the HRW-ARW is particularly aggressive with this idea depicting several scattered supercells east of the dryline by 00Z. 12hr HRW-NMMB also hints at the possibility of development down into OK, not sure that that would happen, but such aggressive supercell development along the entire dryline such as that would certainly make tomorrow a very interesting day.

[CheeselandSkies]

Interesting aside, I've noticed SPC has started breaking down the expected probabilities by hazard within the text of the Day-2 outlooks, although the graphic doesn't explicitly do so.

[Chicago Storm]

Interesting aside, I've noticed SPC has started breaking down the expected probabilities by hazard within the text of the Day-2 outlooks, although the graphic doesn't explicitly do so.

It eventually is coming graphic-wise.


.

[yoda]

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1235 PM CDT Mon Apr 30 2018

   Valid 011200Z - 021200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE
   CENTRAL PLAINS/MID MISSOURI VALLEY AREAS...

   ...SUMMARY...
   Severe storms are expected mainly across north-central Kansas into
   southeast Nebraska Tuesday from late afternoon through evening.
   Large hail, damaging winds, and a few tornadoes are possible.

   ...Synopsis...
   As an upper low near the New England Coast departs eastward across
   the Atlantic, a large, slow-moving upper trough over the western and
   north-central U.S. will prevail, with ridging east of the trough
   encompassing much of the southern and eastern portions of the
   country.

   At the surface, a northeast-to-southwest cold front -- extending
   initially from Minnesota to western Kansas/eastern Colorado will
   make very slow/minor southeastward progress through the period. 
   Meanwhile, a dryline will mix east across western Kansas and the
   Texas and Oklahoma Panhandles through the afternoon, before
   retreating back westward after sunset.

   ...Central Plains/mid Missouri Valley area and vicinity...
   With only minimal movement of the large-scale western U.S. upper
   trough expected Tuesday, and mid-level heights thus neutral if not
   slightly rising downstream across the Plains, large-scale ascent
   across the broad warm sector -- defined by the cold front across the
   central Plains and a dryline over the High Plains -- will remain
   minimal away from the immediate boundaries.  As such, capping is
   expected to hinder convective development.

   The exception will be where ascent focuses along the cold front,
   particularly near the cold front/dryline intersection expected to
   reside in the north-central Kansas vicinity during the afternoon,
   and to a lesser degree northeast along the front and southward for a
   short distance along the dryline.  Here, steep lapse rates aloft
   combined with a modestly moist, deeply mixed boundary layer will
   result in moderate mixed-layer CAPE on the order of 1500 to 2500
   J/kg.  

   Widely scattered to isolated storms are forecast to develop by late
   afternoon, and given the available CAPE, should quickly grow into
   robust updrafts.  Aided by background veering/increasing flow with
   height yielding shear supportive of updraft rotation, storms will
   become supercellular initially -- with very large hail, and locally
   damaging winds possible.  A couple of tornadoes may also occur --
   particularly near the front/dryline intersection and northeastward
   along the front across southeast Nebraska into southwest Iowa and
   northwest Missouri, with a strong tornado possible.

   Later, storms should grow upscale into clusters, with an increase in
   elevated storms also expected through the evening still farther
   northeast, north of the front.  Large hail will be the main risk
   north of the boundary, with risk for hail and wind both possible
   from roughly Iowa southwestward to northern Kansas into the
   overnight hours.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:  10% SIG - Enhanced
   Wind:     30%     - Enhanced
   Hail:     30% SIG - Enhanced

   ..Goss.. 04/30/2018

[jojo762]

12Z Euro continues to follow suit with a sig-threat on Wednesday along most of the dryline in KS/OK. A bit concerned by the lack of a solid precip signal in Oklahoma, but the GFS shows a fairly good precip signal there, so not too worried. Deep-moist PBL amidst a strongly unstable and favorably sheared environment, 40kt LLJ juxtaposed to backed SSE'ly surface flow by 00z. 

Still wonder if storms may fire a bit too early on, as hodographs will not become particularly favorable until around 23-00z and thereafter. 

[bdgwx]

There's just not a lot of low level wind shear until close to or even after dark on Wednesday especially in Kansas where odds are the highest for convective activity per the EPS and GEFS. And FWIW the SREF from the 9Z and 15Z runs is more bullish with tornadoey activity on Thursday in far eastern Kansas and into Missouri.

[OUGrad05]

1 hour ago, jojo762 said:

12Z Euro continues to follow suit with a sig-threat on Wednesday along most of the dryline in KS/OK. A bit concerned by the lack of a solid precip signal in Oklahoma, but the GFS shows a fairly good precip signal there, so not too worried. Deep-moist PBL amidst a strongly unstable and favorably sheared environment, 40kt LLJ juxtaposed to backed SSE'ly surface flow by 00z. 

Still wonder if storms may fire a bit too early on, as hodographs will not become particularly favorable until around 23-00z and thereafter. 

Interesting synopsis, I just sent a buddy of mine a similar text.  Euro seems to try to cap off OK, latest NAM guidance blows up a few cells at dusk on the TX/OK border rest of the state stays dry.  

I think even if storms fire early they may be disorganized and a bit messy but will remain discreet or semi discreet, by 5 or 6pm they'll start getting their act together.  I am a bit concerned with the lack of precip on the euro as well but its not its strong suit.  

[tornado_junkies]

2 minutes ago, OUGrad05 said:

Interesting synopsis, I just sent a buddy of mine a similar text.  Euro seems to try to cap off OK, latest NAM guidance blows up a few cells at dusk on the TX/OK border rest of the state stays dry.  

I think even if storms fire early they may be disorganized and a bit messy but will remain discreet or semi discreet, by 5 or 6pm they'll start getting their act together.  I am a bit concerned with the lack of precip on the euro as well but its not its strong suit.  

Both the 12z and 18z NAM look better than 0z last night as well.

[weatherextreme]

Some of Jeff Duda's thoughts regarding Wednesday

 

 

[Upper Level LOL]

I for one am shocked to see Jeff downcasting a setup. Shocked I tell you.