Jump to content

  • Member Statistics

    17,607
    Total Members
    7,904
    Most Online
    ArlyDude
    Newest Member
    ArlyDude
    Joined

June 11-17 Severe Threats

Quincy

By Quincy,
in Central/Western States

Recommended Posts

Quincy

Quincy

Posted
Posted

After an unusually slow stretch of severe weather across the Plains since late May, during the season's climatological peak, changes are likely in the coming days. 

A modest northwest flow pattern will give way to a vigorous shortwave trough, exiting from the Great Basin into the northern High Plains early in the coming week. Appreciable low level moisture, i.e. upper 60s to lower 70s F dew-points, beneath steep mid-level lapse rates, will support strong instability across the Nebraska/South Dakota vicinity (including surrounding states) through the period. As weak impulses transverse around the approaching trough, isolated to scattered thunderstorm development can be expected each day. Deep layer shear profiles suggests supercell potential and all severe hazards are anticipated. 
 
Sunday:
Large scale forcing appears to be negligible, as 500mb heights should largely remain steady  across the central/northern Plains. Convergence along a nearly stationary front draped from Nebraska into the upper Mississippi Valley may be great enough to support isolated storm development. While this day does not scream anything widespread, it's one of those "sleeper" days that could result in an intense supercell or two. Conditional, yes, but it's the subtle forcing days that can sometimes produce something noteworthy, given the degree of instability and sufficient shear. 
 
Monday:
Perhaps the most interesting day of the bunch, in my perspective. The upper air pattern is very similar to 6/17/14, based on model progs. (Although it should be noted that the overall multi-day evolution of this year's threat is not the best match from 2014's mid-June tornado outbreak sequence, but nonetheless, similarities are clear for at least Monday.) The most apparent focus for storm development will be close to a surface cyclone over the central/northern High Plains, but storms could develop farther east along a surface front, and possibly south immediately ahead of a dryline, should boundary layer heating prove sufficient enough to locally breach a capping inversion. 
 
Tuesday:
Another day with elevated severe potential, a bit farther east from previous days, as the system transverses across the northern Plains. Details are less clear with time, given model variability, but one modest limiting factor may be the tendency for the trough to become negatively tilted. Either way, a severe threat should evolve across some segment of the north-central states. 
 
Note that while 6/17/14 has been referenced, this thread is not being posted under the expectation of a multi-day tornado outbreak. Still, the pattern looks favorable for at least a seasonably active stretch of severe weather across portions of the region. 
Link to comment
Share on other sites
  • Replies 146
  • Created
  • Last Reply
CheeselandSkies

CheeselandSkies

Posted
Posted

I was originally focused on the Dakotas, but SE MN is starting to look pretty good for tomorrow. That's a plus in that it's not as far a drive, but a negative in that the terrain is bad along the MS river, and crossing it becomes a logistical concern.

4K NAM wants to plow a big MCS through and SPC seems to agree with that thinking, but then it initiates more discrete cells with strong UH tracks on its southern flank, presumably along the outflow/WF intersection.

Link to comment
Share on other sites
bjc0303

bjc0303

Posted
Posted
4 minutes ago, CheeselandSkies said:

I was originally focused on the Dakotas, but SE MN is starting to look pretty good for tomorrow. That's a plus in that it's not as far a drive, but a negative in that the terrain is bad along the MS river, and crossing it becomes a logistical concern.

4K NAM wants to plow a big MCS through and SPC seems to agree with that thinking, but then it initiates more discrete cells with strong UH tracks on its southern flank, presumably along the outflow/WF intersection.

If it is that close to the MCS, then they would likely be undercut rapidly by that outflow.. Better odds at something worth watching will be in the wake of the MCS, should atmosphere recover, or in Nebraska where the cold front may be able to initiate a few storms. 

Link to comment
Share on other sites
Quincy

Quincy

Posted
  • Author
Posted

The morning MCS appears to blow through far too early to amount to much. A conditional severe threat may still exist on the southwestern flank of the remnants of the MCS and/or across the central Plains near the outflow boundary/effective front intersection with a surface low. 

Link to comment
Share on other sites
CheeselandSkies

CheeselandSkies

Posted
Posted
9 hours ago, bjc0303 said:

Monday on the other hand looks potent...

Too far away considering I have to work the next day (and anything beyond about 3 hours away qualifies since work starts at 3AM for me). Shouldn't have taken tomorrow off so I could chase today, but at the time it looked great over SD on the GFS.

 

#2017fail

Link to comment
Share on other sites
Chinook

Chinook

Posted
Posted

NAM forecast sounding near Douglas, WY for tomorrow says 3444 J/kg, 243 m2/s2 effective helicity, 59 kt of effective shear. Convection-allowing models show supercells in eastern Wyoming. Models show an increase in SRH and shear from 21z to 00z !

Link to comment
Share on other sites
Quincy

Quincy

Posted
  • Author
Posted
11 minutes ago, Chinook said:

NAM forecast sounding near Douglas, WY for tomorrow says 3444 J/kg, 243 m2/s2 effective helicity, 59 kt of effective shear. Convection-allowing models show supercells in eastern Wyoming. Models show an increase in SRH and shear from 21z to 00z !

You probably have more objective stats on this, but it appears like the CAPE profiles being modeled are climatologically high-end for the area. Shear is not hard to come by, but 50 knots of deep layer shear plus >3000 J/kg MLCAPE in the CO/NE/WY border area? Such a parameter space can't be very common. 

Link to comment
Share on other sites
andyhb

andyhb

Posted
Posted

Looks like a pretty classic upsloping severe event tomorrow with enhanced convergence INVOF the Front Range. Thing that sets this apart as Quincy already touched on is the projected parameter space. The mention of 6/17/2014 intrigues me since I could very well see something like what happened in SE MT that day happen again tomorrow further south (and then perhaps further E along the WF in SD/NE). IIRC, that was a very similar shear/instability combination to some of the forecast soundings tomorrow.

12z CIPS analogs featured a number of events in this region including 6/12/2001, 6/15/1992 (albeit this was generally further E), the aforementioned 6/17/2014, 6/6/1993, 6/10/2004 (Chappell/Big Springs, NE tornado), 6/23/1998 (Columbus, NE wedge), 6/6/2005 and 6/16/2010 (Dupree, SD tornadofest). That's quite a compilation.

Link to comment
Share on other sites
MattPetrulli

MattPetrulli

Posted
Posted

Long but juicy discussion from NWS Cheyenne 

  

...Widespread Severe Weather Outbreak Likely on Monday...Including
Potential for Several Tornadoes...Very Large Hail...and Damaging
Winds...


Our attention then shifts to what very well could be one of the most
significant severe weather episodes we have seen in recent years for
southeast WY and the western NE Panhandle. Models have been in great
agreement over the last several days w/ a significant upper low over
the Great Basin/Intermountain West at 00z Tuesday. The net result is
impressive upper-level difluence over the entire area along with sfc
cyclogenesis over northern CO. This 992 mb low then proceeds to lift
NNE across southeast WY and western NE through the day, which should
be a classic track for a potential tornado event. Thunderstorms will
become numerous along/e of the Laramie Range by 00z with the help of
low-level upslope, excellent convergence along w/steadily increasing
large scale ascent. Biggest remaining question is storm mode as some
models have trended toward a weak, almost negligable cap with no CIN
to be had which could be messy with too much forcing. However, GFS &
NAM soundings both show at least a shallow low-level inversion at 5k
feet AGL or so which could promote discrete cells early. It also may
help that the stronger dynamic support does not arrive until late in
the afternoon which could keep early storms from merging too quickly
and limiting storm intensity to some degree. By mid/late evening, we
expect storms to merge into one or more clusters across east central
WY or the northern NE Panhandle.

This convection, especially if discrete, will be associated w/a high
threat for severe weather. Steep mid-level lapse rates, coupled with
strong surface heating is expected to yield a moderately to strongly
unstable air mass characterized by MLCAPE over 2000 J/kg. Impressive
forecast soundings remain with 0-6 km shear over 50 knots across all
of our high plains zones. Very large, curved, and even a few sickle-
like hodographs are common along/n of the warm front between 00z-03z
as the low-level jet rapidly strengthens with 50 knot flow at 850 mb
and resulting 0-1 km/effective SRH over 400 m2/s2. This will support
intense supercells with low-level mesocyclones, likely being capable
of all facets of severe weather including tornadoes, extremely large
and damaging hail, flash flooding, and destructive winds. Any storms
which can become rooted in the boundary layer by evening will almost
certainly have the potential to produce a strong/violent, long-track
tornado given 0-1 km EHI of 2-4. SREF and NCAR Ensembles suggest STP
values of 3+ as well, which is impressive. Dew points in the 60s may
help promote low LCLs under 1000 meters, perhaps under 500 meters in
the early evening. Expect this to support a threat for tornadoes, as
long as the storm mode can at least stay quasi-discrete.
Link to comment
Share on other sites
Chinook

Chinook

Posted
Posted
9 hours ago, Quincy said:

You probably have more objective stats on this, but it appears like the CAPE profiles being modeled are climatologically high-end for the area. Shear is not hard to come by, but 50 knots of deep layer shear plus >3000 J/kg MLCAPE in the CO/NE/WY border area? Such a parameter space can't be very common. 

I checked the climatology for KDNR upper-air soundings. The 3000-4315 J/kg range is the top tier for all CAPEs measured at Denver. (Max of all time might be 4315 J/kg.) Those type of CAPEs only happen in June and July in Denver. By similarity of the foothills/plains topography, this would also apply to areas near the foothills of Wyoming. CAPEs of 3000 J/kg would happen a few times per year in the region of Torrington-Sindey-Scottsbluff-Pine Bluffs, since these are at lower elevations.

Link to comment
Share on other sites
nrgjeff

nrgjeff

Posted
Posted

Cheyenne Ridge is a nice geographic feature within the broad upslope flow Monday. It can behave similar to the Palmer Divide in Colorado. Speaking of Colorado, CAMs have a big cell on the lifting synoptic front in CO. Storm coverage should be greater in Wyoming, esp coming off the Laramie Mtns. Cheyenne ridge coverage looks in between which may be chaser friendly.

Tuesday looks more synoptic vs Monday. Warm front, east of Dakotas surface low, should enter southwest Minnesota which is still good chase territory. CAMs show some storm mode issues, but pattern recognition is at least a few supercells on that warm front initially. Shear and instability are there down into Nebraska and maybe even Kansas, but no quality boundary intersections that far south. CF and DL is always questionable.

Link to comment
Share on other sites
Quincy

Quincy

Posted
  • Author
Posted

Some regionally impressive observations already, considering it's still late morning MDT:

-Upwards of 4000 J/kg SBCAPE in east-central CO

-2000 to 3000 J/kg SBCAPE in southeastern WY

-67 to 69F dew-points as far west as NW Kansas/SW Nebraska

(CAPE based on mesoanalysis)

Link to comment
Share on other sites
jojo762

jojo762

Posted
Posted
12 minutes ago, Quincy said:

SPC will issue a PDS Tornado Watch shortly for portions of CO/NE/WY. First PDS tor watch on record for Wyoming. 

90/80 probs for 2+ tornadoes/1+ significant tornado 

Rare to see such a potent setup in this area. Terrain is pretty much ideal for chasing too, road network is meh I'd assume... but should be an interesting next few hours.

Link to comment
Share on other sites
weatherextreme

weatherextreme

Posted
Posted

PDS watch issued

 

 

Particularly Dangerous Situation (PDS) Tornado Watch 317

 

 

WW0317 WOU

  

The NWS Storm Prediction Center has issued a

   * Tornado Watch for portions of 
     Northeast Colorado
     Western Nebraska Panhandle
     Southeast Wyoming

   * Effective this Monday afternoon and evening from 110 PM until
     800 PM MDT.

   ...THIS IS A PARTICULARLY DANGEROUS SITUATION...

   * Primary threats include...
     Several tornadoes and a few intense tornadoes likely
     Widespread large hail expected with scattered very large hail
       events to 4 inches in diameter likely
     Isolated significant damaging wind gusts to 75 mph possible

   SUMMARY...Isolated intense supercell thunderstorms are expected to
   develop across the watch area this afternoon.  Giant hail and strong
   tornadoes will be possible in the most intense storms.

   The tornado watch area is approximately along and 60 statute miles
   east and west of a line from 50 miles north northeast of Douglas WY
   to 55 miles southeast of Fort Collins CO. For a complete depiction
   of the watch see the associated watch outline update (WOUS64 KWNS
   WOU7).
Link to comment
Share on other sites
CheeselandSkies

CheeselandSkies

Posted
Posted
3 minutes ago, NWLinnCountyIA said:

The southern most cell looks extremely promising with a very strong midlevel meso, a massive BWER, 50kft+ ET and no interference to the south. Could put down a big one.

Not even warned yet and has one of the best hooks I've seen all year.

*Edit: There it is, but interestingly they went with a SVR first.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...