andyhb Posted May 3, 2012 Share Posted May 3, 2012 Thread for the ongoing potential this weekend and beyond. Both the NAM and GFS indicate some serious juice building up across the Central portion of the country (which has already begun, essentially). Not seeing very much agreement at all, however, regarding evolution of possible upper level waves during this period. Latest SPC D4-8: DAY 4-8 CONVECTIVE OUTLOOKNWS STORM PREDICTION CENTER NORMAN OK 0358 AM CDT WED MAY 02 2012 VALID 051200Z - 101200Z ...DISCUSSION... MODELS HAVE CONVERGED ON SOLUTION THAT AN UPPER TROUGH FORECAST TO AMPLIFY OVER THE WRN STATES WILL MOVE INTO THE NRN PLAINS DAY 4 /FRIDAY/ WITH DOWNSTREAM RIDGING FROM THE UPPER MS VALLEY INTO THE GREAT LAKES. QUASI-STATIONARY FRONT WILL REMAIN FROM THE OH VALLEY WWD INTO THE CNTRL PLAINS. SOME THREAT FOR A FEW SEVERE STORMS MAY PERSIST IN VICINITY OF THIS BOUNDARY GIVEN MODERATE TO STRONG INSTABILITY EXPECTED IN THE WARM SECTOR...ESPECIALLY FROM THE CNTRL PLAINS INTO THE MID MS VALLEY REGION. HOWEVER...IT APPEARS THE STRONGER WINDS ALOFT WILL REMAIN IN COOL SECTOR...AND TOO MUCH UNCERTAINTY EXISTS REGARDING HOW ONGOING CONVECTION WILL MODULATE WHERE A HIGHER COVERAGE SEVERE THREAT MAY EVOLVE. IMPULSE EMBEDDED WITHIN THIS TROUGH IS FORECAST TO EJECT INTO SRN QUEBEC BY DAY 6 WITH REMAINING PORTIONS OF THE POSITIVELY TILTED TROUGH GRADUALLY SHIFTING SEWD. THIS WILL FORCE WRN PORTION OF THE FRONT TO ADVANCE SEWD THROUGH THE PLAINS AND MID MS VALLEY. SEVERE POTENTIAL WILL LIKELY PERSIST AS THIS BOUNDARY INTERACTS WITH THE UNSTABLE WARM SECTOR. HOWEVER...IT APPEARS THE STRONGER FORCING FOR DEEP ASCENT WILL LAG THE SFC FRONT WHICH INCREASES UNCERTAINTY REGARDING THE EXTENT OF STORM COVERAGE GIVEN LIKELIHOOD OF A CAP. THE GREATEST SEVERE COVERAGE MAY EVOLVE OVER PORTIONS OF THE MID MS VALLEY INTO THE OH VALLEY BY DAYS 6-7. Link to comment Share on other sites More sharing options...
Thundersnow12 Posted May 3, 2012 Share Posted May 3, 2012 Not liking the long range at all after mid week next week. I'll be out for 10 days so hoping it changes. Link to comment Share on other sites More sharing options...
andyhb Posted May 3, 2012 Author Share Posted May 3, 2012 Man does that ridge ever need to go... And what on earth is the NAM blowing up in Northeast NE on Saturday evening? Link to comment Share on other sites More sharing options...
wxsniss Posted May 3, 2012 Share Posted May 3, 2012 thanks for starting the thread andy... chasing in the Plains next week so I'm counting on your thread-starting juju Agree models have been all over the place, but most target May 8-9 in the Plains. Best GFS solution in this regard was from 12z 5/1 shown here (but since has trended away from this sharp southwestern trough with more emphasis on large ULL diving over Ontario): comments from my PM replies for others interested, thanks baro: As for 6-11, it does seems the numerical global guidance has trended away from a deep, slow moving closed low across the west...and they mostly track the main parent upper low across the northern Rockies into the northern plains. The big discrepancies develop day 4 on as the global guidance really struggles with the potential development of a basal closed low across the 4 corners. ECMWF has almost nothing whereas the CMC/UKMET/GFS all suggest some sort of developing closed low across the west. The good news is all scenarios still have nice return flow off the GOM advecting high boundary layer theta-e into the southern plains. I think right now ANY solution including the crappy ECMWF will shunt any threats into the southern plains/southern high plains along the dryline...at least at this juncture. KICT long-range discussion today: Monday-Wednesday the GFS has maintained somewhat better continuity over the European model (ecmwf) in past runs and is preferred in its maintenance of a deeper upper trough or closed low hanging back across the southwest Continental U.S. Through early next week. While forecast consensus supports maintaining precipitation chances through Wednesday...chances look relatively smaller after Monday as better moisture gets shunted across the Southern Plains. If trends continue to support this scenario...later forecast adjustments and refinements to probability of precipitation or removal may be needed. Link to comment Share on other sites More sharing options...
andyhb Posted May 3, 2012 Author Share Posted May 3, 2012 00z GFS looks even weaker with the 8th/9th system than the 12z run, upper flow looks ok, but I'd like to see a stronger LLJ (still plenty of time to go)...and the upper air pattern is absolutely terrible all the way to the end of the run (regarding Thundersnow's concerns)... Link to comment Share on other sites More sharing options...
wxsniss Posted May 3, 2012 Share Posted May 3, 2012 Day 4 up... best shear is in cold sector, expecting mostly hail/wind threat best features for tornadoes still appear to be May 8-9 but still widely varying model solutions ZCZC SPCSWOD48 ALL ACUS48 KWNS 030853 SPC AC 030853 DAY 4-8 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0353 AM CDT THU MAY 03 2012 VALID 061200Z - 111200Z ...DISCUSSION... MODELS CONTINUE TO INDICATE THAT UPPER TROUGH CURRENTLY IN PROCESS OF AMPLIFYING OVER THE WRN STATES WILL MOVE THROUGH THE NRN PLAINS ON SATURDAY INTO SUNDAY. COLD FRONT ACCOMPANYING THIS FEATURE WILL CONTINUE SEWD THROUGH THE PLAINS AND MID-UPPER MS VALLEY SUNDAY /DAY 4/. SOME THREAT FOR A FEW SEVERE STORMS WILL UNDOUBTEDLY PERSIST ALONG THIS BOUNDARY AS IT INTERACTS WITH THE MODERATELY TO STRONGLY UNSTABLE WARM SECTOR...ESPECIALLY FROM THE CNTRL PLAINS INTO THE MID MS VALLEY REGION. IT APPEARS THE STRONGER WINDS ALOFT WILL REMAIN IN COOL SECTOR. DESPITE THE WEAK VERTICAL SHEAR...THE THERMODYNAMIC ENVIRONMENT WILL BE SUPPORTIVE OF SEVERE MULTICELLS THAT SHOULD ORGANIZE ALONG THE SEWD ADVANCING FRONT. SOME SEVERE THREAT WILL PERSIST INTO MONDAY /DAY 5/ FROM THE OH VALLEY SWWD INTO THE SRN PLAINS AS THE COLD FRONT CONTINUES SEWD. BEYOND THIS TIME...PREDICTABILITY DECREASES AS DETERMINISTIC MODEL SOLUTIONS AND ENSEMBLE MEMBERS BECOME INCREASINGLY DISPERSIVE. ..DIAL.. 05/03/2012 Link to comment Share on other sites More sharing options...
brettjrob Posted May 3, 2012 Share Posted May 3, 2012 The medium range looks absolutely ugly for any organized convective potential, with the jet retreating into Canada. Shades of 2009, which was record-breaking in its quietness (I believe we went something like 10 days in mid-May without a single watch issued by SPC). Hopefully this dreadful pattern breaks by May 20 or so, instead of waiting til June like that year. Link to comment Share on other sites More sharing options...
Ian Posted May 3, 2012 Share Posted May 3, 2012 The medium range looks absolutely ugly for any organized convective potential, with the jet retreating into Canada. Shades of 2009, which was record-breaking in its quietness (I believe we went something like 10 days in mid-May without a single watch issued by SPC). Hopefully this dreadful pattern breaks by May 20 or so, instead of waiting til June like that year. i'll vote for that. Link to comment Share on other sites More sharing options...
wxsniss Posted May 3, 2012 Share Posted May 3, 2012 00z GFS looks even weaker with the 8th/9th system than the 12z run, upper flow looks ok, but I'd like to see a stronger LLJ (still plenty of time to go)...and the upper air pattern is absolutely terrible all the way to the end of the run (regarding Thundersnow's concerns)... 12Z 5/3 GFS continues this... trend is not my friend. Ridge re-establishes in west with jet into western canada, decent trough in east by late next week. Can't back out of my chase trip at this point, but this is not looking good. Link to comment Share on other sites More sharing options...
nrgjeff Posted May 3, 2012 Share Posted May 3, 2012 Let your heart not be troubled. Plenty to chase this year. Next 10-14 days does not show a major classic outbreak; however, I can almost guarantee about 1/3 of the days will be chase days. A dirty flow looks to set up with shortwaves rippling through. While the pattern will require patience and flexibility, along with better than average day ahead forecasting skill, it will deliver. Hopefully in open areas and definitely not in towns ravaged recently. This year is nowhere near as bad as 2009 for chasers. So far 2012 has included a couple major outbreaks, at least on pace with normal. I'm thinking March 2 and April 14. Plus I can think of 4-5 other days with good local events. In 2009 there were 3-4 chase days in April, but nothing huge. Believe there was only one big day early. May was a disaster in 2009 before June recovered. This May just looks nowhere near as dismal. So far this year is ahead in both majors and locals. I forecast it to continue, especially the locals. Good luck! Link to comment Share on other sites More sharing options...
Amped Posted May 3, 2012 Share Posted May 3, 2012 WNY and WPA looks possible day 5. I don't see any deep low pressures on the map though which may mean only an isolated severe threat through the period. Link to comment Share on other sites More sharing options...
ZackH Posted May 3, 2012 Share Posted May 3, 2012 I must be the only one in the world kind of excited about next week. Sunday and Monday look isolated but decent if the cap can break on the southern parts of the dryline and Tuesday/Wed both have some real potential in the southern plains. The upper level support kind of sucks and there's not much low level jet to work with in the best areas, but the projected CAPE is ridiculous and a couple of those days are coupled with 40-50 knot SFC-500mb bulk shear (especially in the TX panhandle and western OK on Tuesday... according to last nights 00z GFS... I haven't had time to look at the 12z stuff today). Like was stated above, there is no obvious big system and there will probably not be any major outbreak... but there will definitely be 3-4 days of potential next week (starting Sunday) with these subtle shortwaves rippling through the southern Plains... and any storms that can break the cap on the dryline should be gorgeous and discrete. Models at this range will be able to get a handle on directional shear as we get to better resolution and closer to the events. I don't know, maybe I just have blinders on because I will be out next week for my Plains trip... but I see potential, just nothing major. Ehh... 12z run looks much less fun for Tues/Wed Link to comment Share on other sites More sharing options...
Buckeye05 Posted May 3, 2012 Share Posted May 3, 2012 Keep in mind that "surprise" tornado outbreaks happen fairly frequently. The 2010/2011 New Years outbreak, November 15-16 2011 outbreak, 2012 Leap Day outbreak, and April 3 2012 Texas outbreak were all fairly unexpected and recent. Link to comment Share on other sites More sharing options...
Ian Posted May 3, 2012 Share Posted May 3, 2012 Saturday could be good SD/NE tho I lean climo a bit that far north even with a July pattern. Potential could be there for a strong tornado or two regardless. Link to comment Share on other sites More sharing options...
andyhb Posted May 3, 2012 Author Share Posted May 3, 2012 What Ian just mentioned was what I saw on the NAM the other day (which it continues to have), showing some kind of large convective complex/supercell blowing up in Northeast NE/Southeast SD with enhanced LL shear (owing to strongly backed LL/sfc flow) in the area and certainly no shortage of instability. Link to comment Share on other sites More sharing options...
wxsniss Posted May 4, 2012 Share Posted May 4, 2012 I must be the only one in the world kind of excited about next week. Sunday and Monday look isolated but decent if the cap can break on the southern parts of the dryline and Tuesday/Wed both have some real potential in the southern plains. The upper level support kind of sucks and there's not much low level jet to work with in the best areas, but the projected CAPE is ridiculous and a couple of those days are coupled with 40-50 knot SFC-500mb bulk shear (especially in the TX panhandle and western OK on Tuesday... according to last nights 00z GFS... I haven't had time to look at the 12z stuff today). Like was stated above, there is no obvious big system and there will probably not be any major outbreak... but there will definitely be 3-4 days of potential next week (starting Sunday) with these subtle shortwaves rippling through the southern Plains... and any storms that can break the cap on the dryline should be gorgeous and discrete. Models at this range will be able to get a handle on directional shear as we get to better resolution and closer to the events. I don't know, maybe I just have blinders on because I will be out next week for my Plains trip... but I see potential, just nothing major. Ehh... 12z run looks much less fun for Tues/Wed 18Z GFS even less favorable... Sat/Sun might be best days of the week on this latest run Link to comment Share on other sites More sharing options...
baroclinic_instability Posted May 4, 2012 Share Posted May 4, 2012 If the GFS/ECMWF verify, we are looking at a significant severe weather outbreak across portions of NE into SD. EC has all the classic features of big easterly upslope outbreaks here. Toss in the late eening and overnight bowing line segments/LEWP and we may be busy here. EC/GFS support multiple rounds of upslope enhanced supercells before the cold front plows through. Maybe the only minor negative is the weakness in the mid level flow, but if that easterly flow sets up as progged, we will still have loopy clockwise hodographs and some extreme CAPE in excess of 3500+ j/kg. Link to comment Share on other sites More sharing options...
andyhb Posted May 4, 2012 Author Share Posted May 4, 2012 NAM would probably support this as well, with some crazy backing of the LL winds...0-3 km SRH in excess of 300 m2/s2 across several areas. Link to comment Share on other sites More sharing options...
baroclinic_instability Posted May 4, 2012 Share Posted May 4, 2012 Sorry had to post this MCD. Link to comment Share on other sites More sharing options...
andyhb Posted May 4, 2012 Author Share Posted May 4, 2012 I knew something looked fishy about that Link to comment Share on other sites More sharing options...
reber500 Posted May 4, 2012 Share Posted May 4, 2012 Why does the Cap have to be so strong.. Otherwise this week would have had a bit more of potential... Link to comment Share on other sites More sharing options...
Amped Posted May 4, 2012 Share Posted May 4, 2012 Why does the Cap have to be so strong.. Otherwise this week would have had a bit more of potential... Same goes for all ofJuly and August. Also a strong Cap does let the shear and instabilty build up higher than it normally would if there was no CAP. Link to comment Share on other sites More sharing options...
andyhb Posted May 4, 2012 Author Share Posted May 4, 2012 00z NAM has some seriously beefy parameters for NE and SD on Saturday afternoon/evening...along with 50-70 kts of upper flow overspreading the area... Link to comment Share on other sites More sharing options...
brettjrob Posted May 4, 2012 Share Posted May 4, 2012 LCLs are the one aspect of this setup I'm questioning right now. That's some awfully hot air lurking over most of the warm sector (>90 F at GRI). The NAM verbatim indicates a narrow zone on the northern fringe that might be okay, but a look at forecast soundings shows that likely to be a result of convective parameterization. Link to comment Share on other sites More sharing options...
andyhb Posted May 4, 2012 Author Share Posted May 4, 2012 LCLs are the one aspect of this setup I'm questioning right now. That's some awfully hot air lurking over most of the warm sector (>90 F at GRI). The NAM verbatim indicates a narrow zone on the northern fringe that might be okay, but a look at forecast soundings shows that likely to be a result of convective parameterization. The NAM does show some nice deep layer moisture across the region though, which could lower the LCL heights further than one might think with the sfc temps as high as they are shown. The best parameters seem to also be north of GRI and the Platte Valley as well, where sfc temps aren't quite as high (namely North Central/Northeastern portions of NE and adjacent areas of SD). Link to comment Share on other sites More sharing options...
brettjrob Posted May 4, 2012 Share Posted May 4, 2012 The NAM does show some nice deep layer moisture across the region though, which could lower the LCL heights further than one might think with the sfc temps as high as they are shown. The best parameters seem to also be north of GRI and the Platte as well, where sfc temps aren't quite as high (namely North Central/Northeastern portions of NE and adjacent areas of SD). Yeah, the focus for this setup is definitely north of GRI. I just get nervous when widespread 90+ temps are lurking close by to the south. At 21z, the NAM has the 85 F isotherm cutting from Sioux Falls to Valentine, with the more reasonable LCLs seen in that corridor at 00z attained at least partially through precipitation. The most interesting threat may be more in the wrapped-around area in south-central SD. Link to comment Share on other sites More sharing options...
ZackH Posted May 4, 2012 Share Posted May 4, 2012 If the NAM is correct, then there is some potential in east KS and west MO on Sunday. 0-3 km EHI values approaching 6... however, 0-1 km EHI is not very impressive and there seems to be some very warm midlevels. There should be substantial forcing, however, and soundings look like the cap can be broken in late afternoon. Wish the midlevel flow would put its big boy pants on. Link to comment Share on other sites More sharing options...
andyhb Posted May 4, 2012 Author Share Posted May 4, 2012 The high 0-3 km EHI there though appears to be working primarily off of the very strong instability, generally when you get 4000-5000 J/kg CAPE, even relatively minimal SRH can churn out large numbers (which is why May 24th last year had such insane values east of the dryline with 0-1 km SRH in excess of 400 m2/s2 and MLCAPE in the 3500-4500+ range...same with 5/3/99 and 5/10/10). Link to comment Share on other sites More sharing options...
ZackH Posted May 4, 2012 Share Posted May 4, 2012 The high 0-3 km EHI there though appears to be working primarily off of the very strong instability, generally when you get 4000-5000 J/kg CAPE, even relatively minimal SRH can churn out large numbers (which is why May 24th last year had such insane values east of the dryline with 0-1 km SRH in excess of 400 m2/s2 and MLCAPE in the 3500-4500+ range...same with 5/3/99 and 5/10/10). Yes, but when you have CAPE values that high and you can get at least just a little bit of shear, surprises can happen. In no way was I saying it could be a major event, but there is potential. Link to comment Share on other sites More sharing options...
andyhb Posted May 4, 2012 Author Share Posted May 4, 2012 Yes, but when you have CAPE values that high and you can get at least just a little bit of shear, surprises can happen. In no way was I saying it could be a major event, but there is potential. True enough (eg. Jarrell, Roanoke and Plainfield, although the CAPE was probably about 1500-3000 j/kg higher for those three events). Link to comment Share on other sites More sharing options...
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