Central/Western Summer Medium/Long Range Discussions

[brettjrob]

Tomorrow should be a fairly decent severe setup by autumn standards on the High Plains. I'm thinking similar caliber to the 2012-10-12 event last year that featured intense supercells and some brief spin-ups near Plainview. In this case, I see the bullseye setting up more northeast -- perhaps bounded by GUY-PPA-AMA-DUX.

 

Moisture return is underway and should only accelerate through the night, thanks to an intense LLJ. With low-mid 60s surface dewpoints along and east of the Caprock by late afternoon, buoyancy should be sufficient for intense supercells when combined with the moderate to strong deep-layer shear. There's been some talk of an insta-squall line evolution, but I don't really agree -- I think the shear magnitude and orientation should enable supercells for several hours, admittedly messy if too many initiate quickly. The main limiting factors appear to be: 1) poor mid-level lapse rates (as expected this time of year), and 2) marginal low-level shear until near to after dark. If the low-level shear ramps up quicker than anticipated, a "decent" tornado is certainly possible. If the trough were ejecting more cleanly and we could realize 2500-3000 J/kg SBCAPE, this might be a pretty significant day in hypothetical land.

[tornadotony]

Tomorrow should be a fairly decent severe setup by autumn standards on the High Plains. I'm thinking similar caliber to the 2012-10-12 event last year that featured intense supercells and some brief spin-ups near Plainview. In this case, I see the bullseye setting up more northeast -- perhaps bounded by GUY-PPA-AMA-DUX.

 

Moisture return is underway and should only accelerate through the night, thanks to an intense LLJ. With low-mid 60s surface dewpoints along and east of the Caprock by late afternoon, buoyancy should be sufficient for intense supercells when combined with the moderate to strong deep-layer shear. There's been some talk of an insta-squall line evolution, but I don't really agree -- I think the shear magnitude and orientation should enable supercells for several hours, admittedly messy if too many initiate quickly. The main limiting factors appear to be: 1) poor mid-level lapse rates (as expected this time of year), and 2) marginal low-level shear until near to after dark. If the low-level shear ramps up quicker than anticipated, a "decent" tornado is certainly possible. If the trough were ejecting more cleanly and we could realize 2500-3000 J/kg SBCAPE, this might be a pretty significant day in hypothetical land.

Agree with most of this.  But I think that the tilt of the trough (neutral/going neg) plus the NAM's tendency to undermodel low-level winds and shear hints toward a pretty good setup, definitely significant by Sept standards.  The SPC WRF has quite an evening modeled for the Liberal to Lubbock corridor...

 

[brettjrob]

Agree with most of this.  But I think that the tilt of the trough (neutral/going neg) plus the NAM's tendency to undermodel low-level winds and shear hints toward a pretty good setup, definitely significant by Sept standards.  The SPC WRF has quite an evening modeled for the Liberal to Lubbock corridor...

 

In line with the scenario on the SPC 4 km WRF, I think the potential for anything "significant" would lie just after dark, during the 8-10pm timeframe. Whether storms remain discrete through that window -- and if so, are able to draw surface parcels in the face of increased CINH via storm-scale perturbation pressure forces -- will be key.

 

These last-minute moisture return scenarios seem more likely than average to be productive during the mid-late evening timeframe, based on experience. Also, I've been noticing relatively modest capping even on 03z model soundings across the eastern Panhandles. So I definitely agree with your assessment of the ceiling, even though my actual expectations are somewhat lower.

[tornadotony]

In line with the scenario on the SPC 4 km WRF, I think the potential for anything "significant" would lie just after dark, during the 8-10pm timeframe. Whether storms remain discrete through that window -- and if so, are able to draw surface parcels in the face of increased CINH via storm-scale perturbation pressure forces -- will be key.

 

These last-minute moisture return scenarios seem more likely than average to be productive during the mid-late evening timeframe, based on experience. Also, I've been noticing relatively modest capping even on 03z model soundings across the eastern Panhandles. So I definitely agree with your assessment of the ceiling, even though my actual expectations are somewhat lower.

Look at San Angelo's dewpoint rise between 0600 UTC and 1200 UTC.  In that time, the dewpoint jumped 13°F, from 54°F to 67°F.  That's one of the most impressive sfc dewpoint rises I can honestly recall.  Some of that gradient is obviously going to mix out with daytime heating, but I really have no doubt now that the low-level moisture will be there in time.

 

 

[Ed Lizard]

Anybody see a tornado, or at least a cool supercell yesterday?

[andyhb]

Various model guidance appear to be indicating the ejection of a rather substantial upper trough (with varying geometries in the different depictions) around the 132 hr time frame. The Euro suggests a more favorable large scale pattern for moisture return into the Plains setting up rather far in advance of this feature, which may enable a more widespread potential for severe than yesterday's system. The GFS partially complicates things with the evolution of a tropical system in the eastern Gulf around the same time frame. Also, depending on what the trough does initially, it could lead to threats further east as well.

[thewxmann]

0Z GFS was completely different from 12Z GFS, not that either was very favorable for a major widespread severe wx outbreak.

 

Trough geometry is going to be fairly important since lapse rates are da suck this time of year and a more negatively-tilted system will advect colder mid-level temperatures through the warm sector. 12Z was lacking in this aspect.

 

0Z simply phases the trough too late and meaningful cyclogenesis doesn't occur until the front passes the Appalachians.

 

Neither GFS nor Euro have been particularly consistent with the synoptic setup, so a lot is still up in the air. I do think the ceiling for this system is higher than the last one since the Gulf won't be scoured out in the days before.

[tornadotony]

It's just nice to actually be talking severe wx right now, just any prospect.

[OKpowdah]

Personally, I'm more interested in the prospects of an early season winter storm in the northern Plains. Always a challenge to get all the right factors together this early in the season though.

[Minnesota Meso]

Personally, I'm more interested in the prospects of an early season winter storm in the northern Plains. Always a challenge to get all the right factors together this early in the season though.

 

Count me in your camp.  I've been rolling this around in my mind as well.  Up here all the best forcing has been along the International Border.  I've been toying with the idea that as fall storm systems start to impact the PAC NW, how far south will they be able to dig? Will they stall out causing a few strong CO lows to develop which than will move to the NE? and of course how much cold air could dam up in southern Canada?  Since the 1st of March it's been a wild ride up here.  No spring to speak of with a historic winter storm south of MSP in May, to many MN lakes recording record late ice out's or very close to a record as several northern lakes were still iced in for the fishing opener on Mothers Day weekend.  June brought mostly cool wet days with some just warm enough for severe storms, at one time our power company reported a record amount of power outages.  July started off very warm, thus allowing the crabgrass seeds to germinate only to be followed by a stretch where lows dropped into the upper 40's to lower 50's thus killing off said crabgrass.  Aug. and

Sept. have been very warm and dry, as a matter of fact in the last twelve months we have gone from drought to almost surplus and back to drought.  I wonder if the other shoe will drop quickly and the right factors could align bringing another sudden change.

 

It will be interesting when it comes out to compare the average H5 anomalies from Sept 2013 versus the long term average, versus 1991.  Now I would never suggest a repeat of the Halloween storm of 1991, but the overall pattern could suggest the possibility of a surprise late Oct. winter storm of some sort.

[brettjrob]

It's just nice to actually be talking severe wx right now, just any prospect.

 

I feel like I shouldn't talk about it at all, given the veracity of my above posts on this past Friday.

 

As modeled, this next trough feels like a classic mis-timed waste of potential, overall. I really like the shape and orientation, as well as the moisture return, progged by today's runs. The problem is that everything seems to come together about 12z Friday. Prediction: Thursday has very nice kinematics over the central to southern Plains, but cap busts. Friday will probably be the bigger day (not saying much if the aforementioned verifies) around the Ozarks/Arklatex, but the increasingly positive tilt doesn't necessarily bode well.

 

Technically enough time for a save still, but in my opinion, the timing needs to shift +/- 8-12 hours for something substantial. Hopefully I'm as wrong as I was last time.

[thewxmann]

If you ask me, based on tonight's runs, the better severe potential is in the Upper-Mississippi Valley where the 500mb temps are a bit cooler and the mid-level flow might be oriented slightly more perpendicular to the cold front. Actually, the 0Z runs of the GFS and Euro aren't looking too bad, and are an improvement to previous runs. Tony is right that we're lucky to have severe wx to talk about given the abysmal tropical season... and this trough is probably the best looking thing we've seen since late May.

[Thundersnow12]

6z GFS had a very impressive system across the northern plains with 850mb winds of 80kts in the CCB. 

 

[Ian]

GFS looks decent for some sort of svr wx event in latest runs. Timing better on Fri.

[baroclinic_instability]

First winter event of the year for the plains becoming quite likely. I feel so out of the loop after being in Fairbanks the past 3 weeks.

[thewxmann]

SPC is very bullish in their latest Day 4-8 outlook:

 

 

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0232 AM CDT TUE OCT 01 2013

VALID 041200Z - 091200Z

...DISCUSSION...
...FRIDAY D4: NEB...IA...MN...WI...
MODELS HAVE COME INTO BETTER ALIGNMENT AND CONFIDENCE IS HIGH FOR A
SEVERE WEATHER EPISODE ON FRI/D4 ANYWHERE FROM FAR ERN NEB INTO
IA...SRN MN...AND SWRN WI.

THE WRN TROUGH IS FORECAST TO MOVE INTO THE PLAINS ON
FRIDAY/D4...WITH A RAPIDLY DEEPENING SURFACE LOW NEAR THE NEB/IA
BORDER FRIDAY LATE AFTERNOON...CONTINUING NEWD INTO MN OVERNIGHT.

BOUNDARY LAYER DEWPOINTS ON THE ORDER OF 65-68 F WILL ALREADY BE IN
PLACE ACROSS THE WARM SECTOR...E OF THE DEVELOPING COLD FRONT
TRAILING S FROM THE SURFACE LOW...AND S OF A WARM/STATIONARY FRONT
WHICH WILL BE ACROSS SRN MN INTO CNTRL WI.

DUE TO COOLING ALOFT WITH THIS STRONG SYSTEM...MIDLEVEL LAPSE RATES
WILL BE STEEP FOR THIS TIME OF YEAR...PERHAPS NEAR 8.0 C/KM...ATOP A
MOIST BOUNDARY LAYER RESULTING IN CLASSIC LOADED GUN PROFILES.
HODOGRAPHS WILL BE VERY LARGE NEAR THE SURFACE LOW TRACK...AND WILL
FAVOR SUPERCELLS PRODUCING TORNADOES...SOME POSSIBLY STRONG...AND
VERY LARGE HAIL. A FASTER MOVING FRONT OR EARLIER INITIATION COULD
LEAD TO MORE OF A LINEAR MODE WITH DAMAGING WINDS...BUT DETAILS SUCH
AS THESE HAVE LOW PREDICTABILITY THIS FAR OUT.

...FRIDAY D4: ERN KS...OK...WRN MO...
THE COLD FRONT IS FORECAST TO RAPIDLY SURGE SEWD ACROSS THE REGION
WITH THE MORE FAVORABLE FORCING FARTHER N. STILL...SCATTERED TO
NUMEROUS STORMS IN THE FORM OF A SQUALL LINE IS EXPECTED ALONG THE
COLD FRONT. INTERROGATION OF FORECAST SOUNDINGS SUGGEST CAPPING WILL
BE A FACTOR AWAY FROM THE FRONT. AS A RESULT...ANY CHANCE OF
SUPERCELLS WILL LIKELY BE IN A VERY SHORT TIME WINDOW UNTIL THE
FRONT UNDERCUTS THEM...ACROSS WRN AREAS WHERE HEATING IS STRONGEST.
LOCALLY DAMAGING WINDS AND PERHAPS MARGINALLY SEVERE HAIL WILL OCCUR
WITH THE SQUALL LINE.

...SATURDAY D5: MI INTO THE LOWER OH/MID MS VALLEY...
THE COLD FRONT IS EXPECTED TO BECOME OCCLUDED INTO SAT/D5 AS THE LOW
ROTATES NWD ACROSS THE UPPER MS VALLEY. STRONG FLOW NEARLY PARALLEL
TO THE FRONT AND MARGINAL INSTABILITY WILL RESULT IN SCATTERED
STRONG STORMS...SOME OF WHICH COULD BE SEVERE WITH DAMAGING WINDS OR
HAIL...BUT THE THREAT IS NOT EXPECTED TO BE HIGH END.

..JEWELL.. 10/01/2013

[tornadotony]

SPC is very bullish in their latest Day 4-8 outlook:

This one is pretty much a no brainer...seasonably deep trough + 65-68°F sfc Td = trouble

[Thundersnow12]

12z NAM pretty impressive taking a sfc low across north central IA on Friday with 90's in the warm sector. Also would be quite the snowstorm for the northern plains which the Euro has ABR getting smashed with snow. 

[tornadotony]

I'm starting a Friday thread...it really deserves it at this point.

[icebreaker5221]

NAM is almost certainly overdone - boundary layer looks too cool - but the dynamics are certainly there for that cold-air conveyor belt to really get cranking for a while Fri-Sat.  Could be a real pasting of heavy wet snow. 

[andyhb]

Operational 00z GFS/Euro and a decent chunk of the 00z ensembles say we repeat the general western troughing pattern similar to now again at some point later next week.

[andyhb]

Drought conditions vs. this time last year.

 

[andyhb]

Also, seeing the 00z Euro is getting my attention for Monday in western portions of KS and perhaps southward into the OK and TX Panhandles with a trough eerily like the one last Friday and at least some moisture return despite troughing off the SE coast resulting in moderate instability over a rather decent area longitudinally (strong shear seems a likelihood as well in the Euro's depiction with backing sfc winds east of the dryline and a fairly robust and well developed LLJ by 00z). Also has the left exit region of a 110-120 kt 200 mb jet over the region.

 

The GFS suggests a bit of a lesser threat with a more rapidly veering LLJ and increasingly strung out/positively tilted H5 trough, although it would still suggest some potential.

 

That said, SPC does mention a good point in the D4-8, with the maturity of this warm sector, there is likely going to be a lot of WAA cloud cover and precip that could limit the extent of destabilization.

[brettjrob]

Monday is slated to be a really frustrating day for chasers and severe enthusiasts. Getting low-mid 60s dew points up to NE this time of year ahead of a dryline and beneath a 40-50 kt LLJ is no easy feat, but it will likely be all for naught. An early wave ejecting 09z-15z Mon looks to induce the mother of all washouts over the warm sector, overturning what might otherwise be a primed environment.

 

Late recovery immediately along the dryline/cold front is plausible, but these situations almost never bear fruit in terms of a substantial supercell threat. Using the current model consensus, if renewed initiation even occurs late in the afternoon, I'd expect veered low-levels and marginal instability to keep any meaningful tornado threat at bay. If there's any spatiotemporal window for an exception, I'd bet on 21z-00z up near the sfc low in NE at this point. Will continue to monitor. At least this will help to beat down the slight resurgence of the Plains drought of late.

[Chinook]

It has been cool in the Rockies and West in the past week, and also somewhat cool in Texas, with warmer than normal in the East. Most places west of the Mississippi are near normal or below normal right now.  Models show the mean trough will move to the Midwest, then Northeast. GFS ensembles have positive PNA pattern from October 19 to the end of the run, so weather should be much improved on the West Coast by that time period. I have been noticing that the temps have failed to hit 70 here since Tuesday.

 

once again, South Dakota seems to be the magnet for weird weather. from 100 degree and 90 degree temperatures late in the summer, to the recent blizzard and tornadoes. Now the NAM forecast is for 3" of rain in South Dakota from this next storm.

[andyhb]

Monday is slated to be a really frustrating day for chasers and severe enthusiasts. Getting low-mid 60s dew points up to NE this time of year ahead of a dryline and beneath a 40-50 kt LLJ is no easy feat, but it will likely be all for naught. An early wave ejecting 09z-15z Mon looks to induce the mother of all washouts over the warm sector, overturning what might otherwise be a primed environment.

 

Late recovery immediately along the dryline/cold front is plausible, but these situations almost never bear fruit in terms of a substantial supercell threat. Using the current model consensus, if renewed initiation even occurs late in the afternoon, I'd expect veered low-levels and marginal instability to keep any meaningful tornado threat at bay. If there's any spatiotemporal window for an exception, I'd bet on 21z-00z up near the sfc low in NE at this point. Will continue to monitor. At least this will help to beat down the slight resurgence of the Plains drought of late.

 

Unfortunate considering there likely won't be anymore chances for the foreseeable future considering this strong +PNA pattern and huge blocking ridge on the West Coast upcoming.

 

Furthermore, this trough for tomorrow has been growing more impressive with each run (as in, tornado outbreak/high risk if we didn't have the flood of initial wave/WAA-induced junk convection/cloud cover), all for not though. The wind fields in Eastern NE are off the charts, even better than they were on 10/4.

[thewxmann]

Monday is slated to be a really frustrating day for chasers and severe enthusiasts. Getting low-mid 60s dew points up to NE this time of year ahead of a dryline and beneath a 40-50 kt LLJ is no easy feat, but it will likely be all for naught. An early wave ejecting 09z-15z Mon looks to induce the mother of all washouts over the warm sector, overturning what might otherwise be a primed environment.

 

Late recovery immediately along the dryline/cold front is plausible, but these situations almost never bear fruit in terms of a substantial supercell threat. Using the current model consensus, if renewed initiation even occurs late in the afternoon, I'd expect veered low-levels and marginal instability to keep any meaningful tornado threat at bay. If there's any spatiotemporal window for an exception, I'd bet on 21z-00z up near the sfc low in NE at this point. Will continue to monitor. At least this will help to beat down the slight resurgence of the Plains drought of late.

 

 

Just saw this. Kinda crept up on me.

 

Tragic. Waste of a beautiful H5 map, and it will be our last chance for awhile I think.

[andyhb]

Lol all of Eastern NE is covered in 400+ m²/s² 0-1 km SRH...some areas as high as 700-800 m²/s².

[brettjrob]

You guys said it right. One of the most depressing days in awhile, given the god-awful pattern we're entering. Cold and dry with a chance of absolutely nothing redeeming!

[Chinook]

If this high-latitude blocking were occurring in winter, some of the northern states would be 0 or -10.