andyhb

2 hours ago, bjc0303 said:

Just a note.. Tornado ratings don't mean anything when evaluating the quality of events. You're basically equating the quality of the season with the number of damaging tornadoes...doesn't make sense. The Wyoming event was pretty wild even if most of the tornadoes were 'weak' in the sense that they didn't have much to hit out there. Just an odd comment..

If we wanna harp on chaseability that's a different story. 2017 did suck in that regard.

Well that's quite the tone to come back to this site with.

10/15 of the EF3+ tornadoes occurred before April last year. EF3+ tornadoes occur when the setups are most favorable for classic supercells most of the time, regardless of biases in terms of buildings to hit/etc. Was 2011 a great chase season? No, but that was mainly because the setups were in unfavorable locations. 2017 had a number of Plains "potential events" that underperformed or just were generally not that great in terms of photo/video opportunities. Removing the subjectivity of ratings, 6/12 was basically the only above average chase day during the AMJ period last year.

33 minutes ago, cmasty1978 said:

i just want something fatty and high contrast. the 3 tornadoes i saw this year were underwhelming af compared to 2016.

Cosigned.

Well it's about that time of year again with just over two months until meteorological spring begins.

Closest to first high risk date last year -> Stebo: March 13th (actual: January 22nd)

Closest to number of tornadoes last year -> lookingnorth and hurricaneman: 1300-1400 (actual: 1359 as per December 27th)

As mentioned in the previous thread, last year was one with a generous amount of tornadoes overall, yet very few intense (EF3+) tornadoes, yielding a very strong contrast between overall numbers and "quality" of events. There were four high risks that generally underperformed due to various factors, one being the hangover sub-tropical influence from the 2015-16 super Nino, despite the presence of weak La Nina SSTAs in the tropical Pacific.

Looking forward to the coming year, it appears we'll have lingering La Nina influence in place once again, but this time with a less prominent sub-tropical jet. The analogs presented below in Anthony Masiello's tweet represent years with a good QBO/ENSO match to the current winter.

As one can see, the current December regime is a close match to the December 250 mb geopotential height anomalies, although a sample size of just three winters is not ideal. Other years that have been mentioned in analogs from various winter forecasts include 1954-55, 1995-96, 2005-06, 2007-08 and 2013-14 (I've seen some other bigger years thrown around, although they don't appear to be as good matches to the SSTA patterns, QBO structure, etc). We've also seen a dominant East Siberia/Sea of Okhotsk standing wave vortex as of late, whose downstream effects have generally encouraged a persistent -EPO via wavebreaking (something that hopefully eases a bit later in the season). The southeast ridge has also been fairly suppressed.

The PDO has also fallen into a more neutral state lately, as opposed to the positive conditions of the past few years, which is at least somewhat promising. We also currently have a -TNI in place with cooler SSTAs in Nino 1+2 vs. Nino 4, and a positive state has shown some correlation to increased chances for larger outbreaks. The PDO and weakened sub tropical jet appear to be two factors favouring an uptick in activity vs. the mean of the past 5 or so years. It remains to be seen how much La Nina will influence the upcoming late winter and spring (MEI has been relatively weak), although I'd tend to lean towards at least cold neutral forcing come peak season.

Number of tornadoes: 1225

First High Risk: March 16th

D3 ENH, partially hatched for N TX and a good chunk of OK. Given the forcing near the cold front and it's rather fast motion, convection will almost certainly be linear/undercut with time in that area (damaging winds, etc.). I'm a bit curious to see if we can get a few discrete cells popping out ahead given the degree of forecast low level shear and considerable BL moisture content (into the upper percentile for this time of year in this area) across guidance.

This prospect would be more likely in a case where a more well developed secondary surface low can develop along the low pressure trough extending southward from the primary low over the Prairies, which would then amplify low level convergence/surface backing ahead of the front. Such a low is spurned on by the southern in a pair of vorticity maxima that emerges from the Four Corners region through the morning and afternoon Saturday. There is also a bit of a coupled upper jet structure overhead enhancing divergence aloft, which would also imply increased large scale ascent ahead of the front.

Pretty strongly worded AFD coming out of DDC with regards to tomorrow's severe threat.

Quote

National Weather Service Dodge City KS
355 PM CDT Thu Oct 5 2017

...Updated Short Term and Long Term Section...

.SHORT TERM...(This evening through Friday)
Issued at 354 PM CDT Thu Oct 5 2017

The main interest in the forecast is severe weather potential
tomorrow. This may be the best fall severe weather setup for
southwest Kansas this year (and perhaps the last several years). A
compact mid level potential vorticity anomaly will be at the base of
a sharp trough over Colorado late in the day, and this will induce
low level cyclogenesis just out ahead of it over far southeast
Colorado. Intense low level convergence will develop at the surface
low as well by late afternoon. Initially veered out surface winds
will slowly back to due south, if not slightly east of due south in
a very small area just ahead of the low. This is clearly the area of
greatest concern for the most vigorous severe local storm anytime
after 21z. This could be as far west as the Colorado border,
initially.

All ingredients from available moisture, convergence, deep layer
shear, low level shear, mid level cold advection, etc. are pointing
to aggressive severe storms, including supercells. The most vigorous
supercell storm could produce baseball size hail. Tornado potential
would be greatest early in the event, through about 00z or so, as 0-
1km bulk shear will be about 20-25 knots. Early CAMs runs of WRF-ARW
and WRF-NMM show supercell development at the greatest surface
convergence in southwest Kansas, not far from Dodge City. A
supercell may very well be underway, as mentioned earlier, well to
the west of Dodge City and even Garden City. The main question will
be how long supercell phase would last.

Wedge tornado reported N of Scott City per SN moving NE.

70-80 kts of effective shear and 400-500+ m2/s2 ESRH for that storm SW of Leoti to work with.

MCD out for an imminent tornado watch in the High Plains.

   Mesoscale Discussion 1678
   NWS Storm Prediction Center Norman OK
   0239 PM CDT Sun Oct 01 2017

   Areas affected...Central High Plains

   Concerning...Severe potential...Tornado Watch likely 

   Valid 011939Z - 012045Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Severe threat is increasing across the central High
   Plains. Tornado Watch is warranted for this region and will likely
   be issued by 2030z.

   DISCUSSION...Large-scale forcing for ascent is spreading across the
   central Rockies with high-based convection increasing across the
   northern CO Rockies into the High Plains where boundary-layer
   moisture is somewhat limited at the time. This activity is expected
   to mature over the next few hours as it encounters increasingly
   moist air mass from extreme northeast CO into southwest NE. Bow-type
   structures may ultimately evolve from this activity as it propagates
   northeast along a boundary draped across this region.

   Farther south, strong boundary-layer heating has contributed to a
   substantial dry line surge into northwest KS. CU field is increasing
   in areal coverage both west and east of the dry line, indicative of
   convective temperatures being breached. It appears thunderstorms
   will evolve across northwest KS over the next few hours and
   shear/instability favor discrete supercells. Latest HRRR model
   guidance supports this idea with two distinct scenarios evolving
   this evening. While storm mode may favor wind/hail with activity
   spreading across northeast CO into southwest NE, higher
   moisture/instability across northwest KS into south-central NE
   suggests a few tornadoes may evolve from supercells across this
   region. Tornado watch will likely be issued within the hour to
   account for this threat.

   ..Darrow/Guyer.. 10/01/2017

Also, couple of potentially tornadic supercells W of the ABQ metro right now.

Could be a window for a nice sup or two in the central High Plains (specifically NW KS and SW NE) late tomorrow afternoon/evening. Strong flow aloft and good veering in the lowest 3 km will make for favorable shear profiles, although moisture may be a bit on the marginal side for tornadic potential especially if mixing is more than forecast. There is a fairly strong signal amongst the CAMs for supercell development and modest upsloping associated with the backed low level flow near the lee cyclone should allow for it along with moderate large scale forcing for ascent.

Pending enough moisture return, Tuesday (9/19) could offer a fairly substantial severe risk across the Dakotas mainly. Consensus for a strong, negatively tilted shortwave pivoting east/northeast out of that large trough in the northwest with a broad, 40-50 kt southerly/south-southeasterly LLJ axis becoming established by 21z Tuesday. Don't see many problems with forcing for ascent (so much so that fairly quick linear transition is more of a concern than a cap bust), and if enough southwesterly 500 mb flow can overlap the LLJ axis, deep layer shear shouldn't be an issue either.

Seems to me like it could be the first healthy risk of the "second season". Also, the primary trough/ULL remains in the west in behind, which could lead to further potential later in the week, although that's still TBD.

Not a bad call. Initiated about 15 miles E of Mitchell.

I get the sense that there may be a surprise or two in E SD (perhaps somewhere in the Mitchell vicinity) this afternoon/evening looking at the overall synoptic setup. Pretty healthy dynamically in the low levels with favorable proximity to the triple point, although deep layer shear is a bit marginal for supercells.

Evening model runs looking pretty interesting over the E TX Panhandle and west-central/SW OK tomorrow. 00z soundings show high quality BL moisture in place over the source regions (FWD, CRP, BRO). Even OUN has an 11-12˚C H85 dewpoint. Most of the VBV showing up in the soundings by 00z looks to be above 500 mb, which is another plus. Steep lapse rates showing up over the EML source regions for this setup.

Barring a very significant increase in convective coverage tonight, I think we should see a fairly healthy warm sector tomorrow afternoon. Going to be dependent on the western branch of the low level jet strengthening sufficiently for higher tornado chances though, but synoptically speaking, it looks like one that could yield a few tubes.

Georgia has gotten absolutely raked this year. It has fit with an overall SE shift closer in to verification with a lot of the threats through April.

12z CAMs, particularly the NSSL WRF, highlighting the possibility of intense supercells INVOF the I-10 corridor through the afternoon tomorrow.

Surprised there hasn't been a bit more discussion for tomorrow in SE TX and LA. The GFS, Euro and NAM variants are all suggesting a relatively high end (particularly in the low levels) parameter space in place centered on the Sabine Valley and then shifting E towards the Lower MS Valley later on, especially nearer to the warm front. Assuming the MCS along/ahead of the southeastward moving front doesn't completely take over, seems like there would be potential for tornadoes out ahead in the open warm sector. 00z NCAR ensembles did show a number of members with more discrete cells going up out ahead of this feature.

Looks about ready to go in the NE TX Panhandle (GOES 16 data via COD).

17 minutes ago, WhiteoutWX said:

Currently winds are out of the SW in northwest OK and the TX panhandle. Doesn't exactly get me enthused about tornado potential 

That should change later on as the vort over the NM/CO border shifts east and the surface low deepens over the western OK Panhandle. Mid 60s dewpoints over SW OK right now via the mesonet, should be game on if those get anywhere near the triple point.

NCAR ensemble (which performed quite well yesterday) was also pinpointing that area for a heightened risk. Sitting right on the southern periphery of the vort max passing to the north with slightly strengthened flow aloft as a result. There's a plume of low 60s dewpoints lurking to the south with 8.5-9+ C/km 700-500 mb lapse rates over the region currently, those two combined should yield some impressive CAPE later on. Low level flow doesn't look quite as favorable (strength wise) as it was yesterday, although there is certainly some decent veering in the lowest km.

15 minutes ago, SmokeEater said:

It's produced many tornadoes, some up to a mile wide. Insane storm.

That big one was down for at least half an hour unless it cycled in between scans. Certainly not something I saw coming today, but favorable low level winds can lead to strange things when combined with 2500 J/kg MLCAPE. Noteworthy that the 500 mb flow was only around 15 kts in the area where this cell set up shop.

Yeah I'd say this cell is enjoying its environment just a bit.

160+ kts GTG, wedge in progress from Daniel Shaw's stream.

Little bit of Panhandle magic going on W of Dimmitt right now, already one short-lived tornado confirmed and looks to be cycling to the south.

Overall synoptic setup today reminded me a lot of 5/22 last year, which yielded several slow moving tornadic supercells (thermos obviously not quite up to that level).

Positioning of subtropical ridging is going to have to change here. It's anchored too much over the central US shunting the storm track north (almost reminiscent of a late June/July-type pattern) before any shortwave can eject into the Plains. Need to get that shifted east.

So far this year, the Pacific jet has been overwhelming these western/central US ridging episodes with time. The cycles in AAM/MJO activity have been driving jet extensions generally towards the tail-end of the months. Some of the mid-range ensembles are generally indicative of this occurring again, but probably don't want that ridge to become too dominant in the meantime.