2020 Short/Medium Range Severe Thread

[CheeselandSkies]

Go figure, the best chase season (and potentially, with it the most dangerous tornado season) in quite a few years would occur in the midst of this pandemic and all the logistical, legal and moral complications it has placed around interstate travel.

[Hoosier]

3 hours ago, CheeselandSkies said:

Go figure, the best chase season (and potentially, with it the most dangerous tornado season) in quite a few years would occur in the midst of this pandemic and all the logistical, legal and moral complications it has placed around interstate travel.

I don't see how it's going to affect chasing in a big way unless out of state travel gets banned.  Perhaps the biggest concern is if law enforcement catches you outside of your vehicle filming/taking pics, but even then, they would probably just tell you to go home. 

[outflow]

1 hour ago, Hoosier said:

I don't see how it's going to affect chasing in a big way unless out of state travel gets banned.  Perhaps the biggest concern is if law enforcement catches you outside of your vehicle filming/taking pics, but even then, they would probably just tell you to go home. 

 as a chaser and or spotter your doing a public service by helping the nws know of hazards to life and property during svr weather so would some be considered essential?

[Hoosier]

1 hour ago, outflow said:

 as a chaser and or spotter your doing a public service by helping the nws know of hazards to life and property during svr weather so would some be considered essential?

Good point

[Hoosier]

No surprise Indiana schools cancelled for the rest of the school year. 

[Chicago Storm]

1 minute ago, Hoosier said:

No surprise Indiana schools cancelled for the rest of the school year. 

Preparing for the next severe event? 

[Hoosier]

54 minutes ago, Chicago Storm said:

Preparing for the next severe event? 

Swore I was in the coronavirus thread lol

[Indystorm]

10 minutes ago, Hoosier said:

Swore I was in the coronavirus thread lol

It's starting to get to all of us.

[Jackstraw]

I've forgotten what day it was twice this week lol

[Chinook]

8 hours ago, Hoosier said:

I don't see how it's going to affect chasing in a big way unless out of state travel gets banned.  Perhaps the biggest concern is if law enforcement catches you outside of your vehicle filming/taking pics, but even then, they would probably just tell you to go home. 

Will storm chasers even be able to stay in hotels? I guess campgrounds could be open. 

[kevlon62]

There's always Aunt Meg's.

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[RCNYILWX]

Liking Tuesday for a potential NW flow severe event somewhere in N/C IL. Wind/shear profiles provisionally would favor supercells and models in good agreement on strong EML with plume of very steep lapse rates overhead (near or above 8C/km 700-500 mb). 12z ECMWF verbatim would support a potentially sig hail threat. Boundary layer moisture and thus LCL heights are somewhat questionable for for tor threat. There's been variance on warm frontal progress, though 12z op runs favored area getting solidly into warm sector ahead of cold front. Warm front getting hung up some would probably elevate tor potential.

 

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[wisconsinwx]

16 hours ago, RCNYILWX said:

Liking Tuesday for a potential NW flow severe event somewhere in N/C IL. Wind/shear profiles provisionally would favor supercells and models in good agreement on strong EML with plume of very steep lapse rates overhead (near or above 8C/km 700-500 mb). 12z ECMWF verbatim would support a potentially sig hail threat. Boundary layer moisture and thus LCL heights are somewhat questionable for for tor threat. There's been variance on warm frontal progress, though 12z op runs favored area getting solidly into warm sector ahead of cold front. Warm front getting hung up some would probably elevate tor potential.

 

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Is better forcing still indicated in Wisconsin?  Last I checked that was the case, thinking Monday's emphasis on convection was in N/C Illinois and Tuesday's was a bit to the north due to expecting the warm front to lift north.

[Indystorm]

Lapse rates still look very good over northern IL and IN for Tuesday afternoon and evening  (over 8)/  per GFS this evening.  Will have to watch how this progresses as we get closer.

[cyclone77]

11 minutes ago, Indystorm said:

Lapse rates still look very good over northern IL and IN for Tuesday afternoon and evening  (over 8)/  per GFS this evening.  Will have to watch how this progresses as we get closer.

Yeah there's definitely some conditional potential there.  00z NAM showing some capping around H8 that would limit potential.  Would make sense with warm southwesterly flow feeding into the area above the BL.  Not much in the way of height falls either to help.  EC has been consistent in breaking out precip/convection around 00z late Tue, so that is encouraging.  Previous runs of the NAM have less capping compared to the new 00z, so hopefully trends reverse with subsequent NAM cycles.

[Indystorm]

From Chicago discussion this Sat, concerning Tuesday evening.

 

Aforementioned set-up with temps in 70s and around 60/lower 60s
dew points could yield moderate instability of 1000-2000 j/kg
MLCAPE. This is concerning as strengthening northwest flow aloft
with approaching wave later in the day/early evening may support
40-50+ kt of deep layer bulk shear and a strongly veering profile.
This period will be one to watch for northwest flow strong to
severe thunderstorm risk Tuesday PM. The above described wind
profiles would potentially be supportive of supercells with a
large to very large hail risk given steep lapse rates and large
CAPE in hail growth zone. Steep low level lapse rates may also
develop, posing a threat for damaging downburst winds. Looming
uncertainty with this threat pertains to the potential for EML
capping to hold if there is less insolation and/or forcing and
frontal convergence is not enough to erode the MLCINh. ECMWF has
been most consistent in favoring convective initiation, with GFS
more capped, though ECMWF does have solid ensemble support
including from GEFS. Capped PoPs in mid to high chance range due
to uncertainty, and did add some 3-hourly temporal detail to PoPs
Tuesday afternoon.

[cyclone77]

3km NAM looks to be way under-doing surface temps compared to the Euro.  It looks like it has extensive cloud cover that limits heating throughout the day, and resulting in a stout EML above the cooler surface temps.  The Euro has been advertising a much more mixed, warmer surface regime for many days, and results in surface temps 10+ degrees warmer.  It continues to insist on convection taking off later Tue afternoon over northern IL, in a fairly impressive thermodynamic environment.  It will be interesting to see which model wins out.  

[Sydney Claridge]

This isn't my subforum, but I was wondering some things about the severe potential for Tuesday 4/7.  The NAM3k runs (12z and 06z) seem to be ramping up parameters for tornadoes in the eastern parts of the Day 3 Slight risk area (Ohio in particular), although they are not initiating convection.  Plain NAM (12z run) may be trying to pop something in central Ohio with some good CAPE/helicity overlap; I'm taking this with a grain of salt though.  I know tornadoes are less likely in northwest-flow regimes even with favorable parameters, but seeing relatively-high 0-3 km EHI values on model runs (GFS shows somewhat-elevated EHI slightly further west too) does catch my eye.  I would post the imagery but my Internet connection has been painfully slow with the COVID-19 situation and all.

I also recall back on March 28th, models (NAM-based, RAP, and HRRR mainly) were showing elevated EHI near the OH/PA/WV border region, and some of that verified with severe thunderstorm reports (and a tornado warning) around Pittsburgh that day, well east of what was expected to be the "main" outbreak in IA/IL (which as we know largely busted).  I was wondering if this might be a similar situation where much of the main action occurs further west, but with a few storms possibly going severe further east.

[Indystorm]

As with 3/28 I think the issue will be how far north the WF gets and how high the dews progress geographically.  Our surface temps here in IN have been slow to reach max guidance the past couple of days, but I see what you are talking about, Brandon, on the models.

[snowlover2]

ILN has a very detailed disco in the new afd. They say they wouldn’t be surprised to see an upgrade from the slight risk.

.LONG TERM /TUESDAY THROUGH SATURDAY/...
The long term period is going to start off on an active note, with
several forecast items that warrant a thorough discussion and will
certainly require a close eye as we progress into the beginning of
the workweek.

The first item of concern will be associated with the expectation
for ongoing convection Tuesday morning across at least a portion of
the local area through daybreak. The region will be positioned on
the lee side of a broad mid/upper level ridge axis initially
positioned across the mid-Mississippi River Valley Monday night.
A weak midlevel impulse/disturbance will round the peak of the
aforementioned ridge axis Monday night, with a surface warm front
becoming established from NW to SE across the heart of the Ohio
Valley. With the arrival of increasing forcing for ascent and some
low level convergence becoming established with the aforementioned
frontal boundary generation/frontogenesis, anticipate that a
corridor of NW-to-SE convection will develop initially N/W of the
ILN FA before working its way S/E Monday night into Tuesday morning.
The instby at this point will be mainly elevated in nature,
suggesting that any severe threat would remain rather minimal, even
with a non-zero potential for some small hail as ML instby increases
through the night. The main concern will be the potential for some
heavy rain/training convection, owing to a nearly-parallel
orientation of the low level boundary with the deeper-layer flow.
Additionally, moisture transport into the region will intensify by
late Monday night with the arrival/development of a 30-35+kt H8/H9
jet nosing northeast through the area. The juxtaposition and
parallel orientation between the low level convergent axis and mean
deeper-layer flow, and ingestion of increasingly moist BL air, all
suggest the potential for training storms to develop/become
established -- with early indications favoring a corridor from west-
central into central Ohio. This training activity and potential for
heavy rain/flooding may linger into Tuesday morning before the S/W
energy pulls east and forcing begins to wane by late morning into
the afternoon hours, with a trend toward drier/clearer conditions
possible by mid/late afternoon.

By later Tuesday afternoon into the evening, the setup/environment
expected to develop into the region becomes even a bit more
concerning, for several reasons.

1. The mainly elevated instby working into the area Monday night
into early Tuesday will become surface-based by Tuesday afternoon
into the evening with the influx/advection of moisture-rich BL air
with dewpoints reaching into the low/mid 60s. This will occur
coincident with cooling in the midlevel, yielding a
corresponding steepening of midlevel lapse rates. All of this
adds up to a development of SB/ML CAPE on the order of 1500-2000
j/kg+, depending on your model of choice. Suffice to say that
with ample instby, which will be rooted in the BL, large hail
and translation of strong winds aloft may become increasingly
efficient/possible with any stronger cores that develop by late
Tuesday afternoon into the evening/overnight.

2. Fcst sounding analysis shows long/slightly-curved hodographs
amidst quasi-zonal/WNW deep-layer flow with some /albeit not overly
strong/ low level directional/speed shear developing into the
central part of the Ohio Valley by Tuesday evening/night. This would
tend to suggest, especially in an environment characterized by the
aforementioned instby, that any stronger core/storm that develops
may be able to become supercellular in nature, especially on the
edge of the nosing LLJ moving back into the region by this time.
This being said, the forcing to initiate such development maybe
somewhat lacking late Tuesday afternoon into the evening, lending
itself to at least some uncertainty into how widespread re-
initiation will be /if any/ before the arrival of the stronger S/W
forcing and height falls late Tuesday evening from the west. While
confidence on development of storms late Tuesday afternoon into the
evening in the open warm sector is rather meager at this point,
should a storm be able to develop, it/they would be doing so in an
environment conducive to supercellular formation, of which could
produce any and all severe hazards. This is why the setup will be
monitored so closely, even before the arrival of the main
forcing/most widespread convection late Tuesday evening into the
overnight.

While open warm sector storm initiation during the daytime period on
Tuesday remains somewhat in question, despite the increasingly
favorable environment for intense storms should development occur,
confidence remains much higher in widespread activity moving through
the region by late Tuesday evening into the overnight period. This
activity may initially erupt well to the N/W of the ILN FA even by
early Tuesday evening, courtesy of the aforementioned arrival of
height falls/forcing as the S/W progresses east into a very
thermodynamically- and kinematically-favorable environment. Any
activity later in the evening into the overnight period may be
exhibit more of a cluster/bowing structure, one that potentially
becomes somewhat cold-pool driven the further into the nighttime we
progress. With this in mind, the late evening/overnight activity may
certainly pose a strong/damaging wind threat above all else, but
again all hazards may come into play at one time or another from
late Tuesday afternoon through the nighttime period.

This is certainly a situation and an environment that will be
monitored and analyzed closely, both from a temporal and spatial
perspective. But based on overall pattern setup/recognition, one
which shows support from CIGs analogs, as well as overall
expectation for favorable thermodynamic evolution, we may be dealing
with several rounds of strong to severe storms from Tuesday
afternoon/evening through the overnight period. And this is a
separate concern from the heavy rain/flooding risk that was
mentioned for Monday night/Tuesday morning. Will highlight all of
these risks/threats in the HWO, but would not be surprised at all to
see a convective category upgrade (from SLGHT) for Tuesday/night
should current data trends continue.

[cyclone77]

18z 3km NAM continues to show expansive cloud cover that severely limits surface heating for most of the risk area Tuesday.  Will be interesting to see if the HRRR shows this as well when we get within 36hrs.  If the NAM verifies this one is DOA.

[Indystorm]

LOT still  hanging its hat on the King for the Sunday AFD.

 

Heading into the day on Tuesday, there could be some residual
cloudiness/ACCAS, but expect temperatures to still manage to get
up into the 70s across the area thanks to southwesterly flow at
the surface advecting warm moist air into the region. The ECMWF
continues to indicate highs in the upper 70s are possible,
especially for our far southwestern zones. This will help set the
stage for potential strong to perhaps severe storms Tuesday
evening. The big question is whether there is enough forcing to
break the strong capping inversion in place. Models are not
consistent with timing and location of convective initiation, with
many suggesting things develop after 00Z and farther to the
southeast. The ECMWF has been consistently developing a line of
convection across our NW by 21-22Z run after run, so cannot fully
discount this. It is worth noting the ECMWF has a stronger 500mb
speed max reaching the area prior to 00Z which could explain why
convection is able to initiate prior to 00Z. With such a robust
EML, it is possible that lower dewpoints could mix down to the
surface, however, if there is sufficient clearing during the day,
temps could reach into the mid to upper 70s which could provide
sufficient surface destabilization to provide additional lift to
overcome this. Given these uncertainties, thunderstorm coverage
would likely be isolated/discrete. If storms are able to form,
steep lapse rates exceeding 8C/km and MUCAPE over 2000+J/kg and
sufficient shear suggest strong to severe thunderstorms would be
possible if they are able to form. Will continue to evaluate as
things get closer.

A stronger cold front pushes through the area on Wednesday.
Thunderstorm potential is highly dependent on how things
ultimately evolve on Tuesday, but if the atmosphere is able to
recover, there is a window for thunderstorm development again
Wednesday evening, especially for areas south of I-80. If
dewpoints struggle to get back into the 50s, thunderstorm
development may be limited.

[Indystorm]

IND agrees with SPC currrent outlook.

Tuesday the aforementioned upper wave will be moving off to the
east and as the day commences a capping inversion will build over
the area under weak upper ridging. Central Indiana will remain in
the warm sector with a warm front to the north as a system
approaches from the west. Some uncertainty regarding how long it
will take the cap to break, how long earlier clouds from the
Monday night rain and storms will take to move out, and the exact
timing of the upper wave and front. However, shear with the
incoming system is solid. Temperatures should reach into the 70s
(and possibly upper 70s if skies clear out) and models show
dewpoints climbing into the lower to middle 60s with southwesterly
flow. If these features can come together, the potential for
severe weather is there. Steep mid level lapse rates look to
advect in over the area late in the day as well. Looking at all of
the above and checking out forecast soundings, current thoughts
are cap will hold most of the day and best chances for development
of storms will be early evening into the night. Large hail and
damaging winds the main threat at this time. SPC slight risk looks
reasonable.

[LansingWeather]

8 hours ago, cyclone77 said:

3km NAM looks to be way under-doing surface temps compared to the Euro.  It looks like it has extensive cloud cover that limits heating throughout the day, and resulting in a stout EML above the cooler surface temps.  The Euro has been advertising a much more mixed, warmer surface regime for many days, and results in surface temps 10+ degrees warmer.  It continues to insist on convection taking off later Tue afternoon over northern IL, in a fairly impressive thermodynamic environment.  It will be interesting to see which model wins out.  

My money would be on the NAM being correct. Just based on climatology and the preceeding even which was halted by a large amount of clouds.

I really can see clouds being a major problem with this set up. Hope I am wrong though, looks like (here at least) a large hail threat.

[Chicago Storm]

4 hours ago, cyclone77 said:

18z 3km NAM continues to show expansive cloud cover that severely limits surface heating for most of the risk area Tuesday.  Will be interesting to see if the HRRR shows this as well when we get within 36hrs.  If the NAM verifies this one is DOA.

NAM's have been overzealous with cloud cover, and in turn have underdone temps on almost every warm day thus far this season.

So easy toss material there.

[madwx]

the 0z  3km NAM is a step in the right direction, slowing down the wave and having slightly more realistic boundary layer heating.  The WRFs seem to be convecting over Southern Wisconsin/Iowa in the late afternoon.  Slightly intrigued by the setup.  Think there could be some severe in Wisconsin, especially if the wave stays a bit slower.

[Sydney Claridge]

21 hours ago, snowlover2 said:

ILN has a very detailed disco in the new afd. They say they wouldn’t be surprised to see an upgrade from the slight risk.

12z HRRR lends some credibility to ILN's discussion from yesterday, as it depicts the initiation of scattered cells in NW Ohio around 18z (with motions to the SE), and some of this activity could move across the northern part of ILN's area of responsibility (Dayton and Columbus areas mainly).  If taken verbatim the risk would be higher in Columbus (storms in metro area) than Dayton, but you should never take a model run verbatim.

South of I-70 the 12z HRRR seems to depict greater mixing with larger T/Td spreads (upper 70s/lower 80s with mid-to-upper 50s dewpoints).  Along and north of I-70 the T/Td spreads (lower 70s with lower-to-mid 60s dewpoints) suggest isolated tornadoes are a possibility with any supercells given lower LCLs and sufficient EHI.

As with respect to other models, 12z NAM3k and NAM still struggle to initiate storms, however.  12z HRW WRF-ARW shows cellular activity in NE OH (lower dewpoints however); 12z HRW NMMB has higher dewpoints and cellular activity in N/NE OH (and ramps things up a little in the MO/IL border region later on, though highest EHI values depicted are in OH); 12z HRW WRF-NSSL tries to send up cells in E OH but they struggle to get strong.

The new Day 2 SPC convective outlook seems to think that morning convection in Ohio will cause subsidence in its wake, which may cast doubt on cellular storms in the Ohio vicinity starting around 18z as depicted by the HRRR.

The Slight risk now extends from the Ohio Valley to the Southeast (Carolinas) and Mid-Atlantic (VA) coast.  There is also a broad 2% tornado risk shaded across this area (although it would not surprise me to see upgrades in a few areas, especially if that early-afternoon cellular storm mode in OH verifies, and maybe further west in IL/IN too, since some of the models show higher parameters over there too).

[Chicago Storm]

Looks like an elevated hailer threat this evening/tonight, and then a more interesting threat tomorrow afternoon/evening.

[cyclone77]

SPC removed most of north IL from the day 2 threat.  Euro and RGEM both continue to develop some precip over the area, so I guess we'll have to see how things evolve.  

[geddyweather]

That D2 outlook is one of the goofier updates I've seen lately. Went from localized in the OH Valley to almost 5 whole states completely covered in SLGT including basically all of the lower/mid Appalachians...