2018 Short to Medium Range Severe Thread

[ChrisBray]

Been eyeing N IL/E IA for some possible warm front action, but NAM is very inconsistent with Euro and other CAMs in regards to what exactly will happen.  Looks like overall there are some nice parameters in place, but week surface pattern and possible height rises due to wave timing have me concered.  

[Chicago Storm]

Enhanced Risk was expanded in northern MO/southern IA, with a moderate risk farther west.
Also noticed this probabilistic breakdown at the end of the day 2 outlook.  Wonder if they are going to be doing this from now on.  It used to be sort of a guessing game on what the individual probabilities were for day 2.
 

...MAXIMUM RISK BY HAZARD...  Tornado:  10% SIG - Enhanced  Wind:     45% SIG - Moderate  Hail:     30% SIG - Enhanced

 

My guess is they’re doing it until the full spread of D2 graphics eventually come.


.

[hlcater]

The triple point looks interesting in Iowa tomorrow. SPC even has a 10% hatched there on the D2. Of course triple point concerns apply, upscale growth, storm motions into the cool sector etc. but if it looks good enough, I’ll see if I can find time to head to south central Iowa tomorrow. Regardless, convection seems to organize into 1 or 2 MCSs with time.

[ChrisBray]

Regarding Today, it is interesting the SPC has that 5% tornado extended way across Illinois, but yet they don't really address the storms that pretty much every model fires across E IA/W IL this afternoon.  Based on the wind profiles I am seeing, I have to imagine that percentage is based on the overnight squall line that fires in Kansas today?

[snowlover2]

Appears severe weather returns by Wednesday. SPC has a day 4 area outlined for E MO/S half of IL/SW IN/W KY. They also mention chances for severe for the OV beyond day 4.

Quote

Day 4-8 Convective Outlook 
   NWS Storm Prediction Center Norman OK
   0357 AM CDT Sun May 06 2018

   Valid 091200Z - 141200Z

   ...DISCUSSION...
   ...Wednesday/Day 4 to Friday/Day 6...
   The ECMWF, GFS, Canadian and UKMET models are in general agreement
   for Wednesday, moving an upper-level trough into the mid Mississippi
   Valley. Surface dewpoints ahead of the trough are forecast to be in
   the 60s F. As surface temperatures warm during the day, a pocket of
   moderate instability may develop across the mid Mississippi Valley
   by afternoon. This combined with 30 to 40 kt of deep-layer shear
   should be enough for an isolated severe threat from parts of
   Missouri into Illinois and western Kentucky where a 15 percent
   contour has been added. On Thursday and Friday, the medium-range
   models move the upper-level trough eastward into the Northeast and
   off the Atlantic Coast. The models suggest a front will be located
   from the north-central U.S. into the Ohio Valley. This would be the
   favored corridor for thunderstorm development each afternoon, along
   which an isolated severe threat can not be ruled out. Any severe
   threat would depend upon the timing of shortwave troughs and the
   magnitude of destabilization.

   ...Saturday/Day 7 to Sunday/Day 8...
   On Saturday, the models suggest that an upper-level trough will be
   located in the western U.S. with west to southwest mid-level flow
   over the central and northeastern states. The ECMWF shows a corridor
   of maximized low-level moisture from the lower Mississippi Valley
   into the upper Ohio Valley while the GFS has the moist sector
   further west. Severe thunderstorms will be possible Saturday
   afternoon along the northern edge of the moist sector where
   mid-level flow is forecast to be stronger. The models vary
   considerably on how far north the moist sector will be on Saturday.
   On Sunday, the models move the upper-level trough across the Rockies
   and maintain west to southwest mid-level flow from the Mississippi
   Valley eastward. The models suggest a front could be located from
   the southern Plains extending northeastward to the Ohio Valley.
   Severe thunderstorms would be possible along the boundary where the
   greatest instability develops Sunday afternoon. However, uncertainty
   is considerable at this range in the forecast period.

   ..Broyles.. 05/06/2018

 

[nrgjeff]

12Z GFS (Tue) resurrects some hope for Illinois Wednesday iff the slower front solution verifies. Euro is faster like the NAM. I infer the ICON is slower toward the GFS but I do not have complete ICON charts. Anyway we have all seen Illinois go from meh to yea!

Morning rain is forecast, which is fine long as it gets on out. Outflow should remain. Previous forecasts looked like southern IL jungle. Now appears central/northern IL is in play, which is a world better terrain and roads. Again all this requires the CF hang back, not sweep through early. Slower CF would allow a DL-like feature, or at least pre-frontal trough, to get into central IL. Target would be its intersection with the the remnant outflow. 

Much needs to happen for the chasing scenario. Of course I wish all chasers and enthusiasts the best of luck to enjoy it safely and successfully.

[Hoosier]

While Wednesday doesn't look big, it may be one of those days that becomes good enough for anyone who lives in the area to do some local chasing.  The wind profiles aren't overly intense but there could be some decent directional shear, especially if there's something near 180 at the surface.  

[ChrisBray]

Take this FWIW but latest NAM has this around 25 miles south of Valpo on Wednesday evening

 

Will be interesting to see if NAM keeps trending out of Illinois for this event.  Low levels look amazing, its upper levels and bulk shear that aren't so hot.

[bjc0303]

The propensity for updrafts to collapse on themselves thanks to weak effective bulk shear have this looking like a non-event. Still could get some brief spinup out of a cluster or something, but I see this as a cluster/multicell storm event with low level shear leading to upscale growth in the early evening hours. Storm rotation will be possible and I suppose you'll see some interesting looking clouds at times, but tendency will be for updrafts to be choked off by cold pools. Largely a wind event.

The lone exception is if you get enhanced wind shear along any remnant outflow boundaries. I think that is a pretty big if, and won't be discernible at this range. 

 

[snowlover2]

Day 2 risk areas shifted east and north.

Quote

Day 2 Convective Outlook 
   NWS Storm Prediction Center Norman OK
   1229 PM CDT Tue May 08 2018

   Valid 091200Z - 101200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS
   SOUTHERN/EASTERN IL...WESTERN IN...AND SOUTHWEST LOWER MI...

   ...SUMMARY...
   Scattered thunderstorms associated with wind damage and isolated
   severe hail will be possible across parts of the mid Mississippi and
   Ohio Valleys on Wednesday.

   ...Synopsis...
   Shortwave trough currently moving through the northern and central
   Plains is expected to continue eastward into the upper Midwest
   today, continuing across the Upper Great Lakes on Wednesday. Another
   shortwave trough, currently moving through southern Alberta, will
   follow quickly in the wake of the first, eventually catching up to,
   and phasing with, the lead system as it moves across the mid MS and
   lower/mid OH Valleys. Surface low associated with the lead shortwave
   will take a similar path to the parent upper system, moving across
   the upper Midwest and through the upper Great Lakes.

   Farther west, upper ridging initially in place from the Four Corners
   into the northern Rockies will dampen somewhat as a low-amplitude
   shortwave trough ejects across the Interior Pacific Northwest and
   into the northern Rockies late in the period. Predominately
   westerly/northwesterly flow aloft across the Rockies and into the
   Plains will favor a sharpening lee trough across the High Plains.
   Thunderstorms may develop across the higher terrain and move out
   into the High Plains, particularly across portions of western MT and
   eastern CO.

   ...Mid MS Valley...Lower OH Valley...Lower MI...
   Complex forecast scenario is anticipated across the region
   Wednesday. Showers and thunderstorms will likely be ongoing at the
   beginning of the period within the warm-air advection zone from the
   upper Midwest into the mid MS Valley. This antecedent precipitation
   and resulting cloud cover casts some doubt as to whether
   destabilization will be able to occur across these areas (i.e.
   southern MN and western IL) before the surface trough moves through.
   Most of the latest guidance, both parameterized and
   convection-allowing (i.e. HREF), keep this area free of storms.
   Current expectation is for convective initiation to occur farther
   east from central IL into southeast lower MI as the surface trough
   and approaching shortwave trough interact with a modestly moist and
   unstable airmass.

   Given the generally weak mid to upper level flow, vertical shear
   profiles support a predominately multicell storm mode. Occasional
   bowing segments are likely given the linear nature of the forcing
   for ascent and relatively stronger low-level flow with a resulting
   threat for damaging wind gusts. A brief tornado cannot be ruled out,
   especially across portions of northern IN and adjacent southwest
   lower MI where slightly stronger low-level flow and more backed
   surface winds are anticipated. Hail is also possible, especially as
   a result of brief updraft intensification resulting from cell
   mergers.

   ...High Plains...
   Orographically enhanced lift may result in a few storms over the
   higher terrain upwind of the southern High Plains while more
   synoptically evident forcing for ascent will likely contribute to
   thunderstorm development farther north. In either case, eastward
   progression into a more mixed low-level airmass may contribute to
   the potential for a few strong gusts. This is especially true across
   southeast CO where there boundary layer will likely extend to around
   10 kft amidst modest upslope flow.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:   2%     - Marginal
   Wind:     15%     - Slight
   Hail:      5%     - Marginal

   ..Mosier.. 05/08/2018

 

[snowlover2]

New day 1 has most of IN in the slight risk now.

Quote

  Day 1 Convective Outlook 
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Wed May 09 2018

   Valid 091200Z - 101200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
   THE MIDWEST VICINITY...

   ...SUMMARY...
   Scattered thunderstorms -- with embedded/isolated severe
   thunderstorms capable of producing damaging winds and hail -- will
   be possible across parts of the Midwest today.  Isolated severe
   storms with attendant risk for gusty/damaging winds may also occur
   across the Kansas vicinity late this afternoon.

   ...Synopsis...
   While upper troughs linger near both the West and East Coasts, a
   short-wave trough crossing the Missouri and Mississippi Valleys into
   the Midwest region will be the primary feature associated with the
   bulk of the convective/severe risk this period.

   At the surface, a weak low/trough associated with the aforementioned
   short-wave trough will advance into the Midwest by afternoon --
   focusing convective development.  Otherwise, high pressure will
   prevail across the southern and eastern U.S. while a weak cold front
   advances across the West.

   ...Southern Upper Great Lakes and Midwest region...
   Weak early-period convection will likely be moving eastward across
   portions of the risk area, gradually dissipating through the day.
   Meanwhile, as a plume of steeper mid-level lapse rates spreads into
   the Midwest, at least some heating in the wake of the dissipating
   convection/cloud cover should provide an amply unstable environment
   for convective redevelopment to occur near the eastward-moving
   surface trough crossing the Illinois/Wisconsin vicinity during the
   afternoon.  While mid-level flow will remain somewhat modest through
   peak heating, enhanced low-level flow suggests potential for some
   storm organization -- and attendant risk for damaging winds and hail
   -- and possibly a brief tornado.  Low-level veering with height may
   increase during the early evening hours, but any enhancement to the
   tornado risk as a result should be mitigated by a gradually cooling
   boundary layer, and some tendency for upscale growth of the
   convection linearly.  As such, the primary severe risk lingering
   into the evening hours appears likely to be gusty/damaging winds.

   ...Kansas area...
   As a weak/subtle short-wave trough shifts east-southeast toward the
   central High Plains above weak low-level southeasterly upslope flow,
   isolated/high-based convection may develop across the northwest
   Kansas vicinity by late afternoon/early evening.  Though CAPE should
   remain modest, a multi-model signal for isolated storm development
   is noted.  Given the deep/dry mixed layer, potential exists for
   evaporatively aided downdrafts, which may produce gusts to severe
   levels in a few locales -- particularly if some weak upscale growth
   occurs resulting in a ragged cluster of storms shifting southeast
   across Kansas.  However, with late convective initiation expected,
   and thus a gradually stabilizing boundary layer likely to limit more
   appreciable wind risk, will introduce only MRGL risk across the
   area.

   ..Goss/Leitman.. 05/09/2018

 

[IWXwx]

I may be mistaken, but I'm not seeing the parameters for severe in the FWA area this evening. The CAMS look much better for NW IN/ORD than over here. Can anyone tell me what SPC is seeing that I'm missing to have the slight risk extend into our area?

[Hoosier]

1 hour ago, IWXwx said:

I may be mistaken, but I'm not seeing the parameters for severe in the FWA area this evening. The CAMS look much better for NW IN/ORD than over here. Can anyone tell me what SPC is seeing that I'm missing to have the slight risk extend into our area?

Probably giving credit to the increasing wind profiles by then.  But yeah, models aren't bullish on things holding together.

[Chinook]

The HRRR really doesn't have too many storms in IL/IN. That's kind of a bad sign, I guess. I would have expected many more storms on the HRRR.

[Hoosier]

The 18z ILX sounding had a cap around 850 mb

 

[Indystorm]

1 hour ago, Hoosier said:

The 18z ILX sounding had a cap around 850 mb

I wonder if there will be enough insolation or forcing to break the cap later this evening.  My cousin in Highland just told me she had a brief shower so I looked at radar. Grandkids have practices and baseball games scheduled for later this evening in the area.    Meso discussion now out for ne IL and Chi town with svr watch possible.

 

[snowlover2]

Tornado on ground just NW of Milwaukee WI.

Quote

Severe Weather Statement
National Weather Service Milwaukee/Sullivan WI
506 PM CDT WED MAY 9 2018

WIC131-092230-
/O.CON.KMKX.TO.W.0003.000000T0000Z-180509T2230Z/
Washington WI-
506 PM CDT WED MAY 9 2018

...A TORNADO WARNING REMAINS IN EFFECT UNTIL 530 PM CDT FOR
SOUTHEASTERN WASHINGTON COUNTY...

At 504 PM CDT, a confirmed tornado was located near Jackson, moving
east at 30 mph.

HAZARD...Damaging tornado.

SOURCE...Weather spotters confirmed tornado. At 458 PM, a tornado
         was reported just west of Hubertus by a trained spotter.

IMPACT...Flying debris will be dangerous to those caught without
         shelter. Mobile homes will be damaged or destroyed. Damage
         to roofs, windows, and vehicles will occur.  Tree damage is
         likely.

Locations impacted include...
Richfield and Hubertus.

 

[Hoosier]

Might get the splitsky here unless things fill in, but did have a cell pass through earlier.

[Chicago Storm]

Today kind of went as expected...Nothing too significant, and just scattered severe storms.

The lack of shear prevented things from getting going earlier severe wise, and storms being sustained as well...Especially prior to this evening.

[hardypalmguy]

The tornado on the ground yesterday in Wisconsin was only 15 minutes from me.

[CheeselandSkies]

Yeah that totally came out of left field for us. Didn't even occur to me to chase.

[Hoosier]

23 hours ago, snowlover2 said:

Tornado on ground just NW of Milwaukee WI.

 

Confirmed as EF0 with path length of 5+ miles.

[geddyweather]

Looks like we may see some activity along the quasi-stationary front tomorrow. Nothing eye-popping, likely just some severe clusters here and there, but....it is something!

[snowlover2]

23 minutes ago, geddyweather said:

Looks like we may see some activity along the quasi-stationary front tomorrow. Nothing eye-popping, likely just some severe clusters here and there, but....it is something!

Day 2 was just updated and an enhanced area was added for eastern Ohio and eastward.

Quote

Day 2 Convective Outlook 
   NWS Storm Prediction Center Norman OK
   1237 PM CDT Fri May 11 2018

   Valid 121200Z - 131200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE UPPER
   OHIO VALLEY TO THE NORTHERN MID ATLANTIC REGION...

   ...SUMMARY...
   Severe thunderstorms producing damaging winds and some hail will be
   possible through Saturday night near and south of the Great Lakes
   through the upper Ohio Valley and portions of the northern Mid
   Atlantic Coast region.

   ...Synopsis...
   Models remain consistent with the evolution of the mid/upper level
   flow pattern across the contiguous U.S. for the Day 2 forecast
   period.  A large upper low will encompass much of the Intermountain
   West and adjacent portions of the Rockies and Pacific Coast states.
   At the same time, seasonably strong northwesterly mid/upper flow is
   expected to persist across much of Canada into the Northeast and Mid
   Atlantic States.  A series of midlevel perturbations translating
   through the base of the western upper low will track from the upper
   Mississippi Valley through the southern Great Lakes and Ohio Valley
   to the Mid Atlantic region Saturday and Saturday night.  At the
   surface, a front is expected to advance south through the Ohio
   Valley into western/central PA, while the eastern extent of this
   boundary shifts north from MD into southeast PA, and extend into NJ.
   Farther west, this front is expected to remain nearly stationary
   from central IL to far northern MO, and southwest through KS,
   intersecting a dryline in the eastern OK Panhandle and adjacent
   southern KS.

   ...Ohio Valley to the Mid Atlantic States...
   Severe probabilities and categorical risk have been upgraded across
   the upper Ohio Valley to the Mid Atlantic region.  Boundary layer
   moistening is expected in advance of the southward advancing surface
   boundary, while strong diabatic heating and the eastern extent of a
   steep midlevel lapse rate plume contribute to moderate instability
   across the warm sector Saturday afternoon.  Mainly elevated storms
   are expected to be ongoing north of the surface front at the start
   of Day 2, with activity becoming surface based as the boundary
   advances south into the destabilizing environment.  Moderately
   strong deep-layer west-northwesterlies suggest line segments/bowing
   structures will be the primary storm mode, though effective bulk
   shear of 35-45 kt indicates embedded supercells will also be
   possible.  There is increasing concern and confidence for several
   swaths of damaging winds across the upper Ohio Valley to the
   northern Mid Atlantic region, as suggested by several CAMs.  A
   midlevel perturbation is expected to move through these areas during
   peak heating increasing the likelihood for thunderstorm development.
   A tornado threat will be possible across northern MD into southeast
   PA and adjacent NJ and DE, as low-level shear increases to the east
   and northeast of a surface low tracking into MD and along the warm
   front.

   ...IA to the southern Great Lakes region...
   Elevated strong to severe storms may be ongoing across IA into
   northern IL and IN Saturday morning.  This activity should become
   surface based and track to the east-southeast with a severe
   hail/wind risk possible in response to forcing associated with
   lower/mid tropospheric warm advection through Saturday afternoon and
   evening.  Elevated storms may persist well after dark across parts
   of this region north of the front, within zone of strong warm
   advection, with hail being the main threat Saturday night.

  

   ...MAXIMUM RISK BY HAZARD...
   Tornado:   5%     - Slight
   Wind:     30%     - Enhanced
   Hail:     15%     - Slight

   ..Peters.. 05/11/2018

 

[Chicago Storm]

The slight risk this far west is definitely overdone.

[Stebo]

4 hours ago, Chicago Storm said:

The slight risk this far west is definitely overdone.

3km/12km NAM and Euro disagrees, it is more so for stuff Saturday evening, at the very least elevated hailers as a nose of the next LLJ moves in tomorrow evening.

[Chicago Storm]

3km/12km NAM and Euro disagrees, it is more so for stuff Saturday evening, at the very least elevated hailers as a nose of the next LLJ moves in tomorrow evening.

I agree with elevated hailers for Saturday night, as well as tonight...but it’s more marginal worthy.


.

[Stebo]

1 hour ago, Chicago Storm said:

I agree with elevated hailers for Saturday night, as well as tonight...but it’s more marginal worthy.


.

Decent pocket of MUCAPE coming in tomorrow, higher than tonight, along with stronger LLJ. I can see why they went SLGT.

[Hoosier]

14 minutes ago, Stebo said:

Decent pocket of MUCAPE coming in tomorrow, higher than tonight, along with stronger LLJ. I can see why they went SLGT.

To me it's one of those that could go either way.  I wouldn't be surprised if it verifies as marginal and I wouldn't be surprised if it verifies as slight.  How's that for committing?  

[Stebo]

46 minutes ago, Hoosier said:

To me it's one of those that could go either way.  I wouldn't be surprised if it verifies as marginal and I wouldn't be surprised if it verifies as slight.  How's that for committing?  

Wishy-washy Hoosier