May 16th Severe Potential

[andyhb]

18z GFS ramps things up even further in W OK, axis of instability got wider + extreme low level turning. Looks like a bit stronger mid level flow across the dryline too.

[Thundersnow12]

18z GFS ramps things up even further in W OK, axis of instability got wider + extreme low level turning. Looks like a bit stronger mid level flow across the dryline too.

 

Bingo, stronger mid-level flow for sure and continues to show discrete CI signal in western OK. 

 

18z GFS is also much more favorable in digging the late week jet 

[Jim Martin]

 

18z GFS sounding Monday evening at 7:00 PM CDT near Bridgeport, Oklahoma.

[Jim Martin]

 

18z NAM Sounding for Sunday Evening at 7:00 PM CDT near Prague, Oklahoma.

[jojo762]

18z GFS sounding Monday evening at 7:00 PM CDT near Bridgeport, Oklahoma.

Basically uncapped, and completely amazing in the lower-levels, hodographs from SFC-700mb are really about as good as it gets for tornadoes... and sufficient but not overpowering in the mid-levels... Upper-levels are border line really for what you would like to see as far as speed goes... Probably going to see most stuff be HP given 50-60kts at H25, and PWATS of ~1.3in, and a DP in the upper 60s. Given the recent trends in model forecasts for W OK/E TX, would expect to see an ENH risk for that area by the 06Z D2, not that it matters really. Best thing is that this is all pretty great chasing territory, still have in the back of my mind how notorious this area is for terrible busts.

[Jim Martin]

 

Impressive look at the potential for Monday here with the crossover/CAPE setup...

[OUGrad05]

If the trend holds I could see an enhanced risk for Day2, they may wait till their midday update tomorrow but the latest GFS is pretty impressive.  the 00Z should be available within the next 20 minutes.

[Quincy]

Live and die by model forecast reflectivity, but FWIW, the 4km NAM continues to show no storms initiating in the region of favorable instability/shear. I talked to Andy about how while I'm skeptical, the latest EC and RGEM bring appreciable moisture and instability into SW OK.

[bjc3395]

Live and die by model forecast reflectivity, but FWIW, the 4km NAM continues to show no storms initiating in the region of favorable instability/shear. I talked to Andy about how while I'm skeptical, the latest EC and RGEM bring appreciable moisture and instability into SW OK.

going by reflectivity on a model such as the NAM and nam 4km is asking for trouble.

[Chinook]

I don't see why there would be zero convective storms (as per the 4km NAM) on Monday evening. I think there will be some storms. Given the information I'm seeing, I think there's a reasonable chance for EF-1+ tornadoes in a somewhat small space/time window. Convective inhibition (CINH) will increase significantly after 00z in the threat region. Before 00z, the storm-relative helicity and LCLs may not be highly favorable for tornadoes, but supercells may form. The question is, determining the threat window. Then, there's the fact that the synoptically-evident outbreaks have been overhyped, while May 9 (last Monday) was sort of an "oops" tornado day.

[jojo762]

Live and die by model forecast reflectivity, but FWIW, the 4km NAM continues to show no storms initiating in the region of favorable instability/shear. I talked to Andy about how while I'm skeptical, the latest EC and RGEM bring appreciable moisture and instability into SW OK.

the 4K nam is garbage with CI. It barely showed any storms on 4/26 a couple days out if I remember right, and on 5/8, along with a few other events. a 40-50kt mid-level jetcore overspreading a seasonably moist and unstable environment will be more than sufficient for at least a few supercells. If LLVL wind fields verify with the amount of turning-- and decent speed models are showing, then tornadoes--some possibly strong--are going to be pretty probable within a certain time period.

[brettjrob]

Lots of positive trends the past 24-36 h, but the degree of cold air in play still bothers me. Of tonight's 00z suite, only the GFS has an MSLP field I can get excited about. Other models, to varying degrees, have more of a "saggy" frontal boundary with tightly-packed isobars over the PHs and SW KS. In turn, the sfc low does not look prototypical for a high-end event, and it would be tough to get surface based supercells riding the WF. Down the dryline, my experience has been that it's tough to get CI when the sfc low is so "pinched," at least in the absence of considerable forcing (this is more of a subtle embedded shortwave scenario). However, CI has yet to be a problem all year, despite several days where it appeared to be a concern. I can't bring myself to stop sitting on the fence yet about whether this is a big deal or not, even 48 h out. Doesn't help that I was pretty wrong about last Sunday and Monday.

[Quincy]

I'm not basing my concerns solely upon NAM CI. In fact, I've been skeptical about Monday for several days now. We can address cold air leading up, wind fields, moisture return, location of warm front, early day cloud debris and about the fact that the GFS has been hitting this hard while other models have been more skeptical/timid. (Admission that the other models have stepped up the threat a bit) so many things have to come together and even then, there's bust potential. (Some would half-heartedly say that western OK is known for being boom or bust too)

Having high expectations about every event is going to lead to frequent disappointment. It's taken a lot of busts with under-achieving events for me to conclude that a rationally skeptical approach works best in most cases. I'll consider the red flags and not assume that simply because a model shows shear and instability that we'll have tornadoes.

It's a fine line. We thread the needle. More often than not, things don't come together quite right and I'll play the odds to some degree. I also brought up the point that, take tornado counts for example. 2/3 of the time, May has finished with "below average" tornadoes, but in that other 1/3, tornado activity has been above and sometimes considerably above average. More severe events bust than overperform, but there are rare times that an event just goes nuts because some mesoscale things lined up just right.

I still haven't made a decision about chasing on Monday yet, but I'll have to be darn sure the setup looks likely to produce before I chase. I've driven upwards of 1,000 miles in one day to chase a lower end setup, so I'm not just being skeptical here to rain on the parade.

I think we've learned from this season that you must have very strong confidence in an event 24-48+ hours in advance to start calling for specifics. (Tornado counts/intensity, aerial coverage of convection, etc.)

My guess is that SPC stays with SLGT in the upcoming update. Why pull the trigger when we're still two days out and subtle changes could kill off the threat almost entirely? The last thing we need is premature hype that leads to busts and public complacency.

[Indystorm]

Sunday's 06Z NAM coming more to agree with the GFS for NW OK and also including more of central OK in play.  Will have to see what further model runs bring.

[David Reimer]

Well the 12Z 4KM NAM has convective initiation in the Oklahoma Panhandle and eastern Texas Panhandle tomorrow afternoon. It shows a very volatile enviornment with UH tracks pretty much at the top-end of what I've ever seen produced out there. 

[Thundersnow12]

Near Canadian, TX on the 4km NAM just SE of a strong supercell

 

[jojo762]

Upgraded to a small ENH risk.

 

...THERE IS AN ENH RISK OF SVR TSTMS NERN TX PANHANDLE AND PORTIONS  
OF NWRN/WRN OK...  
 
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF OK/NORTHWEST TX  
AND ADJACENT SOUTHERN HIGH PLAINS...  
   
..THERE IS A MRGL RISK OF SVR TSTMS ACROSS THE SOUTHERN PLAINS  
 
   
..SUMMARY  
 
SEVERE THUNDERSTORMS WILL BE POSSIBLE MONDAY AND MONDAY NIGHT ACROSS  
THE SOUTHERN PLAINS...PRIMARILY FROM SOUTHEAST COLORADO AND  
NORTHEAST NEW MEXICO TO THE TEXAS PANHANDLE AND INTO WESTERN AND  
NORTHERN OKLAHOMA.  
   
..SYNOPSIS  
 
SPLIT UPPER-LEVEL WESTERLIES WILL PERSIST OVER THE WESTERN HALVES OF  
THE CONUS AND CANADA FEATURING A SLOW-SOUTHWARD-MOVING UPPER LOW  
OVER THE GREAT BASIN. A DISTURBANCE IS FORECAST TO MOVE THROUGH THE  
BASE OF THE WRN U.S. TROUGH AND EJECT EWD INTO THE SRN HIGH PLAINS  
MONDAY AFTERNOON. A FRONTAL ZONE INITIALLY NEAR THE RIO GRANDE  
MIDDAY SUNDAY WILL ADVANCE NWD AS A WARM FRONT AS A SURFACE LOW  
DEVELOPS OVER THE SRN HIGH PLAINS WITH AN ATTENDANT DRYLINE ARCING  
SWD. AFTER DARK...A COLD FRONT WILL MOVE SWD THROUGH PORTIONS OF  
THE SRN HIGH PLAINS AS THE LOW MOVES SLOWLY ESEWD AND MOVES TO NEAR  
THE RED RIVER VALLEY BY EARLY TUESDAY.  
   
..SERN CO ESEWD INTO TX/OK PANHANDLES AND WRN/NRN OK  
 
APPRECIABLE LOW-LEVEL MOISTURE --CONFINED TO S TX MIDDAY SUNDAY--  
WILL STREAM NWD ON STRENGTHENING SLY FLOW ACROSS THE SRN PLAINS  
DURING THE DAY. A LOW-LEVEL WAA REGIME ONGOING AT THE START OF THE  
PERIOD WILL LIKELY LEAD TO WIDESPREAD CLOUDS/POSSIBLE PRECIP NEAR  
AND N OF THE RED RIVER MONDAY MORNING. HOWEVER...STRENGTHENING SLY  
LOW-LEVEL FLOW WILL ADVECT LOWER 60S DEWPOINTS IN A CORRIDOR E OF A  
SHARPENING DRYLINE BY MID-LATE AFTERNOON OVER THE ERN TX PANHANDLE.  
STORMS ARE EXPECTED TO INITIALLY DEVELOP BY EARLY-MID AFTERNOON IN  
AN UPSLOPE REGIME NEAR THE FRONT ACROSS ADJACENT CO/NM/OK. A STRONG  
CAP DUE TO AN INVIGORATED EML /H7-H5 LAPSE RATES 8+ DEG C PER KM/  
WILL OVERSPREAD THE WARM SECTOR AND LIKELY INHIBIT STORM DEVELOPMENT  
ALONG THE DRYLINE UNTIL STRONG HEATING AND STRENGTHENING FORCING FOR  
UPPER ASCENT --ASSOCIATED WITH THE AFOREMENTIONED IMPULSE-- ARRIVES  
BY LATE AFTERNOON. YET...APPRECIABLE UNCERTAINTY IS DEPICTED IN  
OPERATIONAL GUIDANCE IN STORM COVERAGE ALONG THE DRYLINE.  
HOWEVER...WITH THE STORM COVERAGE CAVEATS IN MIND...AN EROSION OF  
MLCINH IS EXPECTED WITH AT LEAST ISOLD TO PERHAPS WIDELY SCTD STORMS  
DEVELOPING ALONG THE DRYLINE OVER THE ERN TX PANHANDLE. 40+ KT H5  
FLOW ATOP A VEERING LOW-LEVEL WIND PROFILE COUPLED WITH MLCAPE IN  
EXCESS OF 2000 J/KG WILL SUPPORT SUPERCELLS. LARGE TO VERY LARGE  
HAIL WILL BE POSSIBLE WITH ANY ROBUST STORM/SUPERCELL AND ISOLATED  
TORNADOES MAY OCCUR AS STORMS MOVE INTO AN AREA WHERE HODOGRAPHS  
ENLARGE BY EARLY EVENING.  
 
BY EARLY TO MID-EVENING...STRONG AGREEMENT EXISTS AMONGST SUITE OF  
DETERMINISTIC MODELS IN SHOWING A TSTM CLUSTER DEVELOPING NEAR AND  
NORTH OF THE NWD ADVANCING FRONTAL ZONE OVER NRN OK DURING THE  
EVENING AND TRACKING ESEWD AS THE LLJ STRENGTHENS AND VEERS DURING  
THE OVERNIGHT HOURS. THE THREAT FOR ISOLATED LARGE HAIL/SEVERE  
GUSTS MAY LINGER WELL INTO THE OVERNIGHT WITH THIS ACTIVITY. 

[Thundersnow12]

Little surprised they didn't back up the ENH a little further NW given 12z NSSL WRF and the NMM/ARW but oh well. 

[jojo762]

Near Canadian, TX on the 4km NAM just SE of a strong supercell

 

4km NAM mon.png

GFS is not that different either for the same location... just a bit less robust than 4NAM, as you'd expect. 

[andyhb]

Looking like another setup with excellent mid level lapse rates tomorrow. This year's EML advection has been very efficient, especially compared to the junk last year. One of the main reasons why there has been many discrete supercells vs. MCS activity.

[brettjrob]

I think the crucial factor tomorrow will be the timing of CF advancement southward. The ECMWF still starts sweeping it south between 21z-00z (covering 3 counties in that timespan), which is not good. Any CI signal from CAMs in the warm sector has been right near the triple point, so we need the front to hold steady until at least 00z-01z to have a window before undercutting. Even then, a lot of the CAM runs I've seen appear to show big UH tracks right along or on the immediate N side of the boundary, so I'm not sure how much confidence in true surface based storms I'd glean from that.

 

Assuming we're fortunate enough for a storm to initiate a county or two S of the triple point, the other thing I'd watch for, similar to last Sunday, is CI timing. Later is better, since hodographs look questionable before 23z-00z.

[OKpowdah]

Waiting for this to suddenly change day-of, but at least for the time being, this is one of very few events this year where the wind profile isn't so much a concern. These forecast hodographs have been pretty.

[jojo762]

No real reasoning as to why most CAMs do not show CI further south from the triple-point, in the eastern TX PH/ W OK... Forecast soundings in this area show very little to no cap. Cyclogenesis and associated pressure-falls will create sufficient convergence along much of the dryline given the impressively backed SFC winds east of the dryline in W OK/E TX PH... Along with the convergence...the ejection of the 40-50kt H5 S/W at 21-00z should be sufficient for at least a few supercells southward along the dryline in the E TX PH and into W OK...

 

Makes no sense why the only CI would occur along the triple point. CAMs for the most part have struggled in this range it seems this year with CI along the DL, even in what seemed like obvious CI situations. Very little to no CI was shown on 5/8 south of NW OK due to supposed capping concerns, despite that all models showed an impressive MLVL jet-streak ejecting into the warm sector by as early as 21Z, which is roughly when numerous storms erupted along much of the DL... Same situation goes for this, just with a less strong MLVL jet (perhaps that could be good for keeping storms more isolated)... Seems like CAMs do not have a good grasp on the effects of large-scale forcing created from a S/W along a dryline. 

 

Now, the environment these storms will actually encounter really depends on the timing of CI like Brett mentioned... Likewise, the environment along and east of the DL/triple-point will become markedly more impressive toward 23-02Z... Prior to 23Z, LLVL winds will likely be pretty meh, basing off of current progs. If we get any supercells and not just a semi-disorganized mess by that time, then tornadoes would be a good possibility given current model forecasts of 0-1KM and 0-3KM SRH. Any more appreciable tornado threat would be probably be realized with any supercells that develop along the DL, since it appears that undercutting and a messier storm-mode will prevail further north...

[OKpowdah]

I think the crucial factor tomorrow will be the timing of CF advancement southward. The ECMWF still starts sweeping it south between 21z-00z (covering 3 counties in that timespan), which is not good. Any CI signal from CAMs in the warm sector has been right near the triple point, so we need the front to hold steady until at least 00z-01z to have a window before undercutting. Even then, a lot of the CAM runs I've seen appear to show big UH tracks right along or on the immediate N side of the boundary, so I'm not sure how much confidence in true surface based storms I'd glean from that.

 

Assuming we're fortunate enough for a storm to initiate a county or two S of the triple point, the other thing I'd watch for, similar to last Sunday, is CI timing. Later is better, since hodographs look questionable before 23z-00z.

 

I'm also wary of the UH streaks up there being associated more with bowing segments. Clearly strong storms, but undercutting + wind profile gets junkier

[andyhb]

One issue I'm seeing in many soundings for tomorrow is that critical angles look like they are significantly exceeding 90˚ given the progged storm motions. Not ideal streamwise vorticity ingestion if so. 18z NAM/NAM 4 km also a bit lacking in the 0-1 km SRH department.

[brettjrob]

One issue I'm seeing in many soundings for tomorrow is that critical angles look like they are significantly exceeding 90˚ given the progged storm motions. Not ideal streamwise vorticity ingestion if so. 18z NAM/NAM 4 km also a bit lacking in the 0-1 km SRH department.

 

It's not terrible by 00z, but I generally agree. However, anecdotally, I would rather suffer questionable llvl shear in the PHs into E CO than most other areas. The Canadian event last May had very lackluster values on the progs, only for a jaw-dropping carousel mesocyclone and sigtor to form. Events like that, Wray, Campo, etc. lead me to suspect that the rough topography and upslope flow can make the low-level shear very horizontally heterogeneous and unpredictable. If we manage a discrete supercell well S of the baroclinic boundary and mid 60s Tds materialize in the PH, my hunch is that low-level shear won't be a huge limiting factor.

[andyhb]

It's not terrible by 00z, but I generally agree. However, anecdotally, I would rather suffer questionable llvl shear in the PHs into E CO than most other areas. The Canadian event last May had very lackluster values on the progs, only for a jaw-dropping carousel mesocyclone and sigtor to form. Events like that, Wray, Campo, etc. lead me to suspect that the rough topography and upslope flow can make the low-level shear very horizontally heterogeneous and unpredictable. If we manage a discrete supercell well S of the baroclinic boundary and mid 60s Tds materialize in the PH, my hunch is that low-level shear won't be a huge limiting factor.

 

Yeah that's a good point. ESRH is still projected to be quite healthy, enough for strong mesocyclones assuming supercells form in the environment. I'm noticing there's a substantial cap at the base of the EML on some soundings by 00z, but the models what to bring a shortwave through around 21z when it is uncapped. I have a hard time believing there won't be at least isolated initiation then if that ends up happening.

[Chicago Storm]

I won't be chasing tomorrow, as it does not look to be worthy of a 15 hour drive for a one day event.

A few things concern me, some of which have already been discussed. Initiation south of a Dumas-Canadian line is questionable, then you have the crashing front issue. I've been burned with crashing fronts in both instances I've chased days with them. No thanks.

[jojo762]

Pretty good 20Z AFDs from AMA/OUN...

OUN

 

 

Most locations will remain dry during the day tomorrow as
shortwave ridging passes overhead and another mid to upper
shortwave trough moves into SE CO and NE NM. Low level moisture
transport will increase as a lee sfc low deepens in response to
the approaching wave. A dryline is still expected to surge
eastward to near the western OK/TX border by 00Z. Strong CIN
should keep storm coverage limited during the afternoon, but at
least a couple of storms along the dryline will be possible before
the sun sets especially across NW OK where sfc convergence will be
maximized. If afternoon/early evening storms manage to develop,
they will likely be discrete for a bit and will be capable of
producing ALL types of severe weather. There is still some
uncertainty regarding how far north the warm front will make it
tomorrow but the overall agreement is somewhere near or just
south of the KS/OK border. Then, later in the evening, storm
coverage should increase near the triple point (NW OK) as the mid
to upper trough moves near the KS/OK border and the cold front
begins its surge to the south. Bowing line segments will then be
possible through the overnight hours as a complex of storms moves
into central/north central OK. A large hail threat will also
continue with very steep mid level lapse rates remaining in place.
The complex should decrease in intensity close to sunrise.

AMA... There is more to the AMA discussion, but this is the meat of it.

 

 

Current thinking is that convective development should occur mid
afternoon over Southeast Colorado and far Southwest Kansas first.
These storms and consolidate fairly quickly before accelerating
southeastward through late afternoon and evening bringing a
wind/hail threat to much of the Oklahoma Panhandle and far northeast
Texas Panhandle. At least a couple supercells should form mid-late
afternoon further east of the surface low along the sharpening dry
line by late afternoon. Steep mid-level lapse rates contributing to
over 1,000 J/kg of CAPE in the hail growth zone, along with 60 knot
flow at the top of the HGZ should be favorable for large hail,
potentially very large/giant hail in the most organized and
persistent updrafts. The window for a tornado or two would be
generally northeast of a line from Hooker to Perryton to Canadian in
the evening with the supercells before they consolidate and/or are
overtaken by the MCS expected to move east-southeast across the
region. LCL heights as low as 500m along with quickly veering low-
level flow are present across this area. At this time it appears the
strengthening low-level jet will be misplaced and mistimed
precluding a more significant tornado threat but we will need to
monitor trends in the short term guidance and obs closely between
now and then as it is possible that a narrow corridor of increased
tornado risk may evolve.

[jojo762]

Well today's the last day for about a week or so of any interest... Not that great really, but might get a few nice panhandle supercells. FWIW, 00Z WRF-NMMB shows an intense isolated supercell across the far southern TX panhandle moving into SW OK by the evening.