May 15-20 Severe Threat

[Quincy]

Lower than average confidence at this range (in my opinion) for storm mode and evolution this afternoon. The HRRR and NCAR ensembles are wildly different, with the latter favoring a more classic outbreak with numerous intense UH tracks across western/central/southern Kansas, while the HRRR goes from initiation to an MCS mess extremely quickly. The SSEO guidance appears to lean toward NCAR. Either way, the parameter space is high end and it will be interesting to see what SPC does with the upcoming update. 

The 12z OUN sounding certainly has the look of an outbreak given low-level moisture, veering winds with height and relatively steep lapse rates aloft. 

[1900hurricane]

I'm still in the Texas Panhandle this morning, but I'll be headed to near the OK/KS border in an hour or two. Thinking Coldwater, Medicine Lodge, or Alva at the moment.

[1900hurricane]

The new SPC Day 1 is a very good read.

 

SPC AC 181243

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0743 AM CDT Thu May 18 2017

   Valid 181300Z - 191200Z

   ...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
   CENTRAL AND SOUTHERN KANSAS TO NORTHWESTERN OKLAHOMA...

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   HIGH RISK FROM WESTERN OKLAHOMA TO CENTRAL KANSAS...

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   MODERATE RISK FROM PARTS OF NORTHWEST TEXAS TO PARTS OF SOUTHEASTERN
   COLORADO...NORTHERN KANSAS AND EXTREME WESTERN MISSOURI...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   ENHANCED RISK AND EXTENDING INTO EASTERN COLORADO...WESTERN
   MISSOURI...EXTREME SOUTHERN NEBRASKA...AND THE TEXAS RIO GRANDE
   VALLEY NEAR DEL RIO...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTHEASTERN
   INDIANA TO WESTERN NEW ENGLAND...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING BOTH
   SLIGHT RISKS AND BETWEEN THEM OVER THE MID MISSISSIPPI VALLEY...

   ...SUMMARY...
   An outbreak of severe thunderstorms with tornadoes, very large hail
   and wind damage is expected to develop across parts of the southern
   and central Plains from this afternoon into this evening and
   overnight.  Some strong, long-lived tornadoes are expected, along
   with hail to near 4 inches in diameter, over parts of Kansas and
   Oklahoma.  Large hail, tornadoes and wind damage also will be
   possible outside of these areas across parts of the southern and
   central Plains.  Damaging gusts and sporadic hail also are expected
   across parts of the lower Great Lakes region to western New England
   this afternoon and early evening.

   --- Technical Discussion ---

   ...Synopsis...
   In mid/upper levels, broadly cyclonic flow will cover much of the
   western and central U.S., anchored by a major cyclone now centered
   over UT.  The 500-mb low is expected to dig southeastward across the
   Four Corners through the period, reaching northwestern NM by the end
   of the period.  As this occurs, the leading lobe of an 85-100-kt
   250-mb jet will spread over the southern High Plains and western/
   central KS through tonight.  A leading shortwave trough -- currently
   apparent on moisture-channel imagery over WI, western Lake Superior
   and the MN Arrowhead -- will weaken and eject east-northeastward
   across southern QC to northern ME by 12Z.

   At the surface, 11Z analysis showed a cold front from southern QC to
   a low over the MI/WI border, southwestward across IL, becoming
   quasistationary over MO and the KS/OK border region, to a weak low
   over southeastern CO.  The low is expected to move erratically
   eastward along the KS frontal segment (becoming a slowly northward-
   moving warm front) through the period.  Today, the richer low-level
   moisture now over north TX and southern/central OK will advect
   northwestward over the outlook area.  The dryline will sharpen this
   afternoon from northern Coahuila northward across west-central TX to
   southwestern KS.  The cold front will move southeastward across the
   Great Lakes region, reaching parts of NY, New England and the Ohio
   Valley region overnight.

   ...Central/southern Plains...
   Scattered thunderstorms, including multiple supercells with
   significant-tornado, giant-hail and damaging-wind potential, still
   appear probable this afternoon anywhere over the moderate- and
   high-risk areas, and possible farther south where coverage should be
   more widely scattered to isolated.  The progged ingredient/parameter
   space is ideal for a multi-hazard severe-weather outbreak from the
   warm-frontal zone southward for 250-300 nm ahead of the dryline:
   *  Moderate to strong moisture and instability:  moist advection of
   a rich Gulf air mass with 60s to near 70 deg F surface dew points,
   diurnally heated along/ahead of the dryline to remove CINH, beneath
   roughly 8 deg C/km midlevel lapse rates, yielding 3000-4500 J/kg
   MLCAPE.  CAPE will diminish northward through the warm-frontal zone
   but the cut-off of surface-based inflow should be gradual, not
   abrupt.
   *  Favorable lift along the dryline and in the "bent-back" zone of
   deep forcing closer to the surface and upper lows,
   *  Favorable low-level and deep-layer shear, especially near the
   warm front and low, but also southward across the moist sector. 
   Low-level vorticity and hodograph size each will be maximized along
   and somewhat north of the warm front, with 300-400 J/kg effective
   SRH and 50-65 kt effective-shear magnitudes common.
   Any discrete/sustained supercells in this environment will be
   capable of cyclic, significant-tornado production as well as giant,
   destructive hail.

   A note of caution on this forecast:  Some uncertainties still exist,
   however, precluding any greater probabilities at this time -- mainly
   involving density and timing of convection.  Initiation of too many
   cells in early/middle afternoon (before warm-sector hodographs and
   CAPE each are biggest), and/or too close to each other at once, is
   possible in some parts of the current moderate/high risks.  This
   scenario, which some guidance suggests, would lend a greater wind
   threat and somewhat suppressed hail/significant-tornado risk with
   eastward extent, due to messier storm modes amidst strengthening
   deep-layer flow.  Evidence for such a quick transition still is
   inconsistent in the bulk of numerical guidance, and of course
   observationally.  While not compelling enough to modify the high or
   moderate risk-driving probabilities yet, this is a possibility to be
   monitored for potential adjustments to the outlook during the day.

   Regardless of timing, storm mergers and ultimate upscale growth of
   convective clusters appear likely, with embedded supercells, bows,
   and mesobeta- or smaller-scale damaging-wind swaths.  Therefore,
   wind probabilities have been offset eastward somewhat, relative to 
   the others.

   ...Northeast to mid Mississippi Valley...
   Widely scattered to scattered thunderstorms are expected to develop
   along and ahead of the front this afternoon as diabatic surface
   heating and low-level convergence zones (including the baroclinic
   zone) act against already weak MLCINH.  Well-mixed subcloud layers
   beneath 1000-1500 J/kg MLCAPE, and the presence of 30-40 kt
   effective-shear magnitudes will support enough multicellular
   organization, and perhaps transient supercell structures, for a
   hail/wind threat.  Nearly unidirectional prefrontal wind profiles
   are forecast, and some bowing clusters could develop that would
   enhance the wind-damage potential on smaller scales, especially over
   parts of NY or western New England, however, it is too soon to be
   specific enough with mesoscale details for a greater categorical
   corridor within the existing, somewhat eastward-expanded lines.  The
   severe wind/hail threat will be more isolated, marginal and
   transient this afternoon and early evening southwestward toward the
   middle Mississippi Valley where warm-sector surface winds and
   frontal convergence each should be weaker.

   ..Edwards/Dial.. 05/18/2017

[the ghost of leroy]

Dis gon be good

 

[bjc0303]

To be honest I'm doubting HRRR solutions of rapid upscale growth and think this is an issue with an extreme instability solution.. 

 

And is it just me or did Edwards suggest possible upgrades in percentages? 

[MUWX]

1 minute ago, bjc0303 said:

To be honest I'm doubting HRRR solutions of rapid upscale growth and think this is an issue with an extreme instability solution.. 

 

And is it just me or did Edwards suggest possible upgrades in percentages? 

It was mentioned in the previous outlook also, I believe. 

[hlcater]

6 minutes ago, bjc0303 said:

To be honest I'm doubting HRRR solutions of rapid upscale growth and think this is an issue with an extreme instability solution.. 

 

And is it just me or did Edwards suggest possible upgrades in percentages? 

Also mentioned in the outlook, but the biggest thing causing uncertainty is the convective evolution today, until that becomes clear, I can't foresee the SPC changing much, however it could go either way if things trend upscale or discrete.

[jojo762]

12Z HRRR is quite a bit more discrete than previous runs (albeit still with some clusters), shows numerous discrete/semi-discrete supercells between 21-01Z across SC KS/N OK, and even a lone-ranger in south-central OK. 12Z HRRR would be rather concerning... especially for the Wichita area, brings two discrete supercells with fairly impressive UH tracks right into the general vicinity of ICT around 00-01Z.

[OceanStWx]

That moisture pool is nice and deep. 1 km deep at FWD this morning, 0.5 km deep at OUN, shallow by the time you reach DDC. But it's coming.

[the ghost of leroy]

16 minutes ago, jojo762 said:

12Z HRRR is quite a bit more discrete than previous runs (albeit still with some clusters), shows numerous discrete/semi-discrete supercells between 21-01Z across SC KS/N OK, and even a lone-ranger in south-central OK.

you headed out today?

[jojo762]

1 minute ago, cmasty1978 said:

you headed out today?

Probably. Favoring the Enid area, wait for stuff to develop and see how it evolves and move on from there.

[David Reimer]

OUN launching a 15Z special sounding and a TBD special sounding this afternoon. 

[OUGrad05]

Going out today but there's some things I don't like about this setup and I hate the CAM solutions.  Really disgruntled in that regard.  Moisture is going to be top shelf fantastic today.  If we can get enough of a cap to hold off convection for a bit then that would be ideal.  

They caveated this high risk with the possibility of a downgrade later...I'm thinking that's just because they didn't want to remove the high risk only to add it back at 11:30 if conditions warranted.  

[bjc0303]

*Be very cautious with CAMs* they are likely underforecasting cap (reference FWD, OUN soundings) and initaiting too early, numerous. Significant day ahead.

[Santa Clause]

Today literally has every solution on the table,  storm mode will be make or break.

[OceanStWx]

8 minutes ago, bjc0303 said:

*Be very cautious with CAMs* they are likely underforecasting cap (reference FWD, OUN soundings) and initaiting too early, numerous. Significant day ahead.

That's true enough. RAP had OUN cap around 20-20.5C, but in reality it is more like 22.5-23C.

[WhiteoutWX]

15z sounding should hopefully shed a little more light on if the cap is being underdone by models.

We should have a pretty good idea by 18-19z either way.

[Weatherdemon]

Norman Discussion interesting:

 

.DISCUSSION...
Determining exactly when and where storms occur today remains a
challenge. Latest guidance overall has been suggesting an earlier
start for storm initiation with first storms forming across
southwestern Oklahoma and western north Texas around noon.

Overall, based on latest model guidance (particularly the
HRRR/RAP) and incoming data from a special 15 UTC KOUN sounding,
confidence is growing that storms will form earlier and somewhere
over southwestern Oklahoma or western north Texas around noon
today. The 15 UTC KOUN sounding depicted that the base of the low
level inversion has lifted about 40 mb (from around 900 mb to 860
mb) and low level moisture deepening below the inversion. Based on
latest HRRR/RAP guidance, this lifting is expected to continue in
the next few hours, which would allow for storms to form earlier
than previously expected once surface temperatures reach the 
lower to mid 80s near or just east of the dryline across 
southwestern Oklahoma and western north Texas. A weak mid level 
disturbance may be causing the lift, though the exact cause for 
the lift remains uncertain.

If these storms form around noon in southwestern Oklahoma and
western north Texas, they may at first be slighlty elevated with
giant hail as the main hazard. However, these storms would likely
become surface-based due to daytime heating no later than 3 pm as
they move northeast. This could increase the tornado potential
across western north Texas, southwestern and central Oklahoma this
afternoon and evening while slightly decrease the tornado
potential in northwestern Oklahoma. Again, the exact details 
remain uncertain today.

The bottom line is that the combination of shear, instability, 
and moisture support significant severe storms with giant hail 
and tornadoes this afternoon and evening somewhere over the 
western two thirds of Oklahoma and western north Texas

[OUGrad05]

What an interesting discussion, sounds like they may expand the MDT some to the east based on that and more south.

[OceanStWx]

HRRR still insisting on CI next hour down S of CDS (and then the rest of the dry line by 20z at the latest).

[janetjanet998]

2 minutes ago, OceanStWx said:

HRRR still insisting on CI next hour down S of CDS (and then the rest of the dry line by 20z at the latest).

there appears to be some CU growing in that area at this time

[OceanStWx]

2 minutes ago, janetjanet998 said:

there appears to be some CU growing in that area at this time

Definitely becoming agitated Cu down there, maybe even some towering Cu.

And based on 16z obs, there is at least a meso low in the OK Panhandle.

[jojo762]

 

000
FXUS63 KICT 181601
AFDICT

Area Forecast Discussion
National Weather Service Wichita KS
1101 AM CDT Thu May 18 2017

.UPDATE...
Issued at 1059 AM CDT Thu May 18 2017

Its still looking like a volatile setup this afternoon, as low
level moisture rapidly returns to the area. Warm frontal boundary
has surged north to along highway 50, with mid to upper 60 dewpoints
into srn KS.  Even seeing some dewpoints around 70 in nrn OK. SBCAPE
values have already surged into the 3000-3300 j/kg range just to the
southwest of the forecast area, with areas SW of the area slowly
becoming uncapped. Latest NAM/WRF showing SBCAPE of 4000 possible by
this afternoon. Of significant note is the short range models
depiction of 0-1km shear values of 35-40kts with 0-8km shear of 60-
70km.  Both of these parameters suggest a threat of long track
supercells with significant tornadoes.  With the cap eroding a
little faster than previous thoughts, could see convection develop
by 20-21z in the warm sector or just south of the warm front.
Certainly think by 21z severe convection will be ongoing.

One "fly in the ointment", is the hi-rez models, composite radar
depictions showing a messy storm mode, with a couple of discrete
supercells then lots of multicell clusters. This would diminish
chances of an outbreak of severe weather/tornadoes, but think a few
strong/violent tornadoes still look possible.  The ingredients are
certainly there. So typical for a "high risk" day, there is
potential for a high end severe day, but there is always something
to make us pause.

Ketcham

[Superstorm93]

There's some developing CU near Snyder, Texas, but otherwise things look pretty capped for now (at least where the HRRR initiates things)

Waiting on the 15z special sounding still. 

 

[CGChaser]

15z OUN ..

[jojo762]

Still MLCIN of -200+J/KG. If things are anything like that further west into N TX, those early storms shouldn't form imo. Especially since the likely forcing mechanism is only a very subtle mid-level disturbance.... or at least they shouldn't sustain, I'd think.

[Superstorm93]

6 minutes ago, jojo762 said:

Still MLCIN of -200+J/KG. If things are anything like that further west into N TX, those early storms shouldn't form imo. Especially since the likely forcing mechanism is only a very subtle mid-level disturbance.... or at least they shouldn't sustain, I'd think.

I'd argue it would be hard to sustain them...but that area could also rapidly destabilize as the moisture continues to advect northward. 

 

[Quincy]

Convective initiation is likely within the next hour or two with minimal remaining CINH. 

[jojo762]

3 minutes ago, Quincy said:

Convective initiation is likely within the next hour or two with minimal remaining CINH. 

Looks like the RAP is also underdoing CIN, shows 0 SBCIN, whereas 15z oun still showed 30+J/KG. Curious to see if SPC goes with consistency in the forecast and gut feeling or caves to the CAMs with new outlook. 

[1900hurricane]

I think we're still 1.5-2 hours away from anything firing in Texas. The cumulus field still looks fairly suppressed to me. Also, the 12Z NCAR Ensembles start displaying echoes around 18Z.