andyhb Posted October 27, 2013 Share Posted October 27, 2013 Since we have been discussing this in detail in the medium range thread, figured it was time to start this given we are beginning to enter the nitty-gritty period. The models are still at some odds regarding timing the ejection of this strong jet streak/ULL that is currently dropping through the Pac NW. The GFS suggests a potentially greater threat on Tuesday in the Plains, while the 00z/06z NAM suggests a potential show on Monday evening in Western OK and vicinity (which I'll say looks quite robust, with some very impressive soundings at 00z and 03z). The Euro appears to edging along the NAM's lines, especially considering the slower timing of the two respective models. Meanwhile, SPC has also highlighted a D4 and D5 area despite the potential for a washout of leftover cloud cover, junk convection and WAA precip limiting instability in an otherwise strongly sheared environment on both days. DAY 4-8 CONVECTIVE OUTLOOK CORR 1 NWS STORM PREDICTION CENTER NORMAN OK 0411 AM CDT SUN OCT 27 2013 VALID 301200Z - 041200Z CORRECTED FOR INCORRECT DAY OF THE WEEK ...DISCUSSION... A MULTI-DAY SEVERE RISK REMAINS POSSIBLE ESPECIALLY ON DAYS 4-5 WEDNESDAY/THURSDAY AS A CONSIDERABLE UPPER TROUGH AND ASSOCIATED COLD FRONT SPREAD GENERALLY EASTWARD OVER THE CENTRAL CONUS AND INTERCEPT A SEASONALLY MOIST LOW-LEVEL AIRMASS. ABOVE-AVERAGE GUIDANCE VARIABILITY STILL CONTINUES /FASTER GFS VERSUS SLOWER ECMWF/...SUCH THAT SPATIAL/SCENARIO VARIABILITY EXISTS AND AREAL ADJUSTMENTS OF THE RISK AREAS WILL UNDOUBTEDLY BE NEEDED. ON DAY 4/WEDNESDAY...CURRENT THINKING IS THAT SEVERE TSTMS WILL BE POSSIBLE WITHIN A GENERAL CORRIDOR FROM OK/NORTH TX TO THE LOWER MO RIVER VALLEY/MIDDLE MS VALLEY...AND POTENTIALLY AS FAR NORTH AS PARTS OF THE UPPER MIDWEST/UPPER MS VALLEY PENDING SUFFICIENT DESTABILIZATION. AS THE UPPER TROUGH POTENTIALLY TAKES ON A MORE NEGATIVE TILT INTO DAY 5/THURSDAY...A SEVERE RISK SHOULD SPREAD EASTWARD TO THE ARKLATEX AND LOWER/MIDDLE MS VALLEY. SOME SEVERE RISK ON DAY 5/THURSDAY COULD EVEN POTENTIALLY EXIST AS FAR NORTH AS THE OH VALLEY AND THE GREAT LAKES REGION SHOULD SUFFICIENT /ALBEIT MODEST/ DESTABILIZATION MATERIALIZE AHEAD OF THE COLD FRONT. ..GUYER.. 10/27/2013 Link to comment Share on other sites More sharing options...
brettjrob Posted October 27, 2013 Share Posted October 27, 2013 Usual disclaimer about the reduced thresholds applies, but... Link to comment Share on other sites More sharing options...
thewxmann Posted October 27, 2013 Share Posted October 27, 2013 I think Tuesday is the biggest day for tornadic supercells. Wednesday/Thursday look like washouts + convective messes due to the tropical fetch from Hurricane Raymond. Link to comment Share on other sites More sharing options...
andyhb Posted October 27, 2013 Author Share Posted October 27, 2013 If the NAM/Euro are on the right track, I think Monday evening has better potential for tornadic supercells in Western OK and West Central KS. Tuesday is likely going have problems with capping. Link to comment Share on other sites More sharing options...
brettjrob Posted October 27, 2013 Share Posted October 27, 2013 NAM environment for tomorrow evening is simply impressive for late October. Timing of initiation is the biggest concern -- given sunset is now a little before 00z, initiation by 22-23z is probably needed for a substantial tornado threat. The secondary concern will be moisture return, because while the NAM soundings at 00z look nice, instability is practically nonexistent throughout the affected area as late as 18z. True last-minute return situation. Link to comment Share on other sites More sharing options...
tornadotony Posted October 27, 2013 Share Posted October 27, 2013 I think Tuesday is the biggest day for tornadic supercells. Wednesday/Thursday look like washouts + convective messes due to the tropical fetch from Hurricane Raymond. Idk. Thursday is not completely dissimilar to 11/24/01 in a lot of ways. 1) H5 T on 11/24/01 where only about -10°C across the warm sector, even at JAN which has a 12z CAPE of 2000 J/kg with a 73/67 sfc temp. 2) Incredibly intense LLJ >50 kt. 3) Sfc low displaced from the main warm sector convective region. 4) General similarity in the overall synoptic pattern. If you remember 11/24/01, the tornadic supercells that day were largely embedded in a large mixed convective/stratiform rain mass, not what one might normally expect. But that outbreak still produced 68 tornadoes, including 18 F2s, 3 F3s, and 3 F4s, two of which were high-end F4/near F5 intensity. Those were in MS predawn on the 24th prior to the big convective mess. I'm not sure that we'll have a period like that Thursday. But even in AL, where the entire outbreak was a big convective mess, we had 36 tornadoes (the largest outbreak on record in AL until 4/15/11), 12 of which were F2-F4 intensity. I guess my main takeaway is that the biggest details with this are going to be sfc conditions as long as the H5 temps are around -10°C. If we can get into the 70s in the warm sector, then I think we're in business, maybe big-time business given the wind fields. All it would take to get thinks going down here is CAPE of ~500 J/kg, which I think is well within the ballpark of reasonable. FWIW, HUN's forecast high for Thursday as it stands right now is 77. Not sure we get that warm, but who knows... 11/23-11/24/01 tornado outbreak map 1930 UTC radar comp: Link to comment Share on other sites More sharing options...
andyhb Posted October 27, 2013 Author Share Posted October 27, 2013 11/24/01 was easily one of the more impressive November outbreaks on record, of course only to be outdone less than a year later... Link to comment Share on other sites More sharing options...
tornadotony Posted October 27, 2013 Share Posted October 27, 2013 FYI, this morning's #3 CIPS analog for the SE at 120h was 11/10/02... Link to comment Share on other sites More sharing options...
andyhb Posted October 27, 2013 Author Share Posted October 27, 2013 I also saw the morning of 11/15/89 on the 96 hr frame. Link to comment Share on other sites More sharing options...
brettjrob Posted October 28, 2013 Share Posted October 28, 2013 NAM backs off on moisture return for tomorrow and moves toward the model consensus. Those of you on the "screw the NAM outside 36" train have been spot on this month. It completely blew 10/4 too. If tomorrow is a cap bust until SBCINH fills in, I can easily see this whole system being for naught in the Plains. Tuesday and Wednesday both have that awful anafrontal, right-exit-region, no-convergence-on-the-boundary look that historically leads to hazy sunsets in 5-10 EHI environments. Link to comment Share on other sites More sharing options...
andyhb Posted October 28, 2013 Author Share Posted October 28, 2013 SPC hitting Thursday hard with the new D4... DAY 4-8 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0359 AM CDT MON OCT 28 2013 VALID 311200Z - 051200Z ...DISCUSSION... A SEVERE RISK REMAINS APPARENT ESPECIALLY ON DAY 4/THURSDAY. THIS WILL BE AS A CONSIDERABLE UPPER TROUGH AND ASSOCIATED EASTWARD-ACCELERATING COLD FRONT SPREAD EASTWARD AND INTERCEPT A SEASONALLY MOIST LOW-LEVEL AIRMASS FROM THE ARKLATEX/LOWER MS RIVER VALLEY INTO THE TN/OH RIVER VALLEYS. WHILE EARLY-DAY CONVECTION IS AN UNCERTAINTY FACTOR...CURRENT THINKING IS THAT THE MOST FAVORABLE /OR CERTAIN/ COMBINATION OF MODEST INSTABILITY/STRONG VERTICAL SHEAR WILL BE ACROSS PORTIONS OF THE ARKLAMISS/TN VALLEY...ALTHOUGH MID-LEVEL LAPSE RATES WILL BE WEAKER WITH SOUTHERN EXTENT. GIVEN A VERY MOIST LOW-LEVEL AIRMASS AND AMPLE LOW-LEVEL/DEEP-LAYER SHEAR...DAMAGING WINDS AND SOME TORNADOES /POTENTIALLY A FEW STRONG/ WILL BE POSSIBLE. FARTHER NORTH ON DAY 4/THURSDAY...ALTHOUGH THE EXACT DEGREE OF DESTABILIZATION IS UNCERTAIN...A SEVERE /DAMAGING WIND AND PERHAPS TORNADO/ RISK CANNOT BE DISCOUNTED FOR ADDITIONAL PORTIONS OF THE OH VALLEY/NEARBY GREAT LAKES. THIS INCLUDES THE POSSIBILITY OF A STRONGLY FORCED/LOW-TOPPED CONVECTIVE LINE IN ASSOCIATION WITH ROBUST VERTICAL SHEAR/FORCING FOR ASCENT. Link to comment Share on other sites More sharing options...
andyhb Posted October 28, 2013 Author Share Posted October 28, 2013 As for today, lol @ the NAM is all I can say... Link to comment Share on other sites More sharing options...
tornadotony Posted October 28, 2013 Share Posted October 28, 2013 I said it yesterday, but it bears repeating. The H5 temps are going to be critical on Thursday. The GFS has H5 temps above -10°C, which would probably minimize the threat. But the NAM is a different story, with H5 temps near -10°C in the warm sector. Yeah, it's the NAM, and it's probably way too slow/far west right now, but the GFS has a major problem with saturation above 500 mb, which forces mid-level temps to be too warm due to excess trapping of heat caused by phantom excess water vapor. As long as the NAM has temps near -10°C, the SE is definitely in play for a potentially significant severe weather event on Thursday. Link to comment Share on other sites More sharing options...
Stebo Posted October 28, 2013 Share Posted October 28, 2013 I said it yesterday, but it bears repeating. The H5 temps are going to be critical on Thursday. The GFS has H5 temps above -10°C, which would probably minimize the threat. But the NAM is a different story, with H5 temps near -10°C in the warm sector. Yeah, it's the NAM, and it's probably way too slow/far west right now, but the GFS has a major problem with saturation above 500 mb, which forces mid-level temps to be too warm due to excess trapping of heat caused by phantom excess water vapor. As long as the NAM has temps near -10°C, the SE is definitely in play for a potentially significant severe weather event on Thursday. The other problem with the GFS with respect to the excess water vapor, is that the GFS is keeping the surface temperatures too cool and over-precipitating, the NAM is at least somewhat reasonable with respect to temperature profiles through the column. Link to comment Share on other sites More sharing options...
Chinook Posted October 28, 2013 Share Posted October 28, 2013 As for today, lol @ the NAM is all I can say... What feature are you laughing at? Link to comment Share on other sites More sharing options...
andyhb Posted October 28, 2013 Author Share Posted October 28, 2013 What feature are you laughing at? The overestimation of BL moisture return by runs as late as 18z yesterday/00z today. Link to comment Share on other sites More sharing options...
brettjrob Posted October 28, 2013 Share Posted October 28, 2013 What feature are you laughing at? See the forecast sounding I posted yesterday from the 18z run, showing a primed environment for tornadic supercells over NW OK/SW KS. The verification is likely to be 250-750 J/kg SBCAPE and strongly capped, with no surface-based convection before dark. I know the NAM has a bad rap, but this one was pretty bad even by its standards (from 24-36 hours out, at least). Link to comment Share on other sites More sharing options...
Thundersnow12 Posted October 28, 2013 Share Posted October 28, 2013 FWIW, the 12z 4km WRF has a long lived helicity updraft signal going up in the nrn TX PH. Link to comment Share on other sites More sharing options...
Chicago Storm Posted October 28, 2013 Share Posted October 28, 2013 I'm sitting this one out, but if chasing today I'd target the Guymon-Borger-Woodward triangle. Right on the nose of the best moisture return and nice differential heating zone with the cloud deck to the SE. Link to comment Share on other sites More sharing options...
brettjrob Posted October 28, 2013 Share Posted October 28, 2013 I'm sitting this one out, but if chasing today I'd target the Guymon-Borger-Woodward triangle. Right on the nose of the best moisture return and nice differential heating zone with the cloud deck to the SE. I had every intention of trying if I thought the odds of daytime convection were even 40/60, but chose to sit it out. The HRRR is adamant that nothing significant happens. Only favorable guidance I've seen so far is the 12z SPC WRF and a few runs of the RAP, though the latter isn't even worth looking at for QPF/CI. Maybe some of the Panhandle chasers will get a backyard surprise at sunset... they deserve it after how this decade has gone so far for them. Link to comment Share on other sites More sharing options...
brettjrob Posted October 28, 2013 Share Posted October 28, 2013 Initiation W of AMA. If it intensifies and moves into the air along the Caprock, we may have a show after all. Link to comment Share on other sites More sharing options...
tornadotony Posted October 28, 2013 Share Posted October 28, 2013 Initiation W of AMA. If it intensifies and moves into the air along the Caprock, we may have a show after all. It's got a 60 dBZ core. Link to comment Share on other sites More sharing options...
tornadotony Posted October 28, 2013 Share Posted October 28, 2013 It's got a 60 dBZ core. Make that 66 dBZ. Wow. Link to comment Share on other sites More sharing options...
brettjrob Posted October 28, 2013 Share Posted October 28, 2013 Yep. And the 19z HRRR was like a switch got thrown... all the sudden a broken line of supercells from W KS down to CDS that persists into the evening. The environment just E of I-27 is quite primed, especially in a couple hours with an increasing LLJ. Link to comment Share on other sites More sharing options...
tornadotony Posted October 28, 2013 Share Posted October 28, 2013 Yep. And the 19z HRRR was like a switch got thrown... all the sudden a broken line of supercells from W KS down to CDS that persists into the evening. The environment just E of I-27 is quite primed, especially in a couple hours with an increasing LLJ. Yeah, part of the SVR watch coming out may very well have to get upgraded to a TOR watch later this evening. Storm near Hereford about to split. Link to comment Share on other sites More sharing options...
Buckeye05 Posted October 28, 2013 Share Posted October 28, 2013 Hereford storm seems to be struggling, but something is trying to fire near Guymon as well. Something to watch at least. Edit: Decent looking core on the Hereford storm again. Link to comment Share on other sites More sharing options...
Chicago Storm Posted October 28, 2013 Share Posted October 28, 2013 Hereford storm seems to be struggling, but something is trying to fire near Guymon as well. Something to watch at least. Edit: Decent looking core on the Hereford storm again. We'll see what happens once it hits the boundary that curves through AMA. Link to comment Share on other sites More sharing options...
thewxmann Posted October 28, 2013 Share Posted October 28, 2013 Lol, 60F dewpoints aren't extending anywhere north and west of CDS as of 23Z. NAM Fail. Link to comment Share on other sites More sharing options...
tornadotony Posted October 28, 2013 Share Posted October 28, 2013 Lol, 60F dewpoints aren't extending anywhere north and west of CDS as of 23Z. NAM Fail. You've got 60 at Gage and 63 at Altus AFB, 59 at CDS, and the NAM verification is for 00z, at which point Tds will likely be slightly higher due to slight shutdown of turbulence at aft-eve transition. I wouldn't call it a slam dunk for the NAM, but I wouldn't hedge it as a total failure yet. EDIT: That's comparing to today's NAM runs. If we're talking yesterday's, that's another story. Link to comment Share on other sites More sharing options...
thewxmann Posted October 28, 2013 Share Posted October 28, 2013 You've got 60 at Gage and 63 at Altus AFB, 59 at CDS, and the NAM verification is for 00z, at which point Tds will likely be slightly higher due to slight shutdown of turbulence at aft-eve transition. I wouldn't call it a slam dunk for the NAM, but I wouldn't hedge it as a total failure yet. EDIT: That's comparing to today's NAM runs. If we're talking yesterday's, that's another story. Yes, I was talking about yesterday's. My bad, should've made that clearer. Link to comment Share on other sites More sharing options...
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