Hoosier Posted March 24, 2012 Share Posted March 24, 2012 Looks like some severe potential may spill over into our subforum on Tuesday. Recent runs of the GFS are indicating about 1000 CAPE nosing into Illinois on Tuesday evening with sufficiently strong deep layer shear. It's worth noting that mid level lapse rates look fairly decent so any underestimation of surface temps by the GFS could result in somewhat better instability than currently shown. Link to comment Share on other sites More sharing options...
cyclone77 Posted March 24, 2012 Share Posted March 24, 2012 Yeah, nice little setup from the looks of things. The surface low is a bit further north towards the Canadian border in recent runs, and that does veer the surface/near surface a bit, but still not too bad. Verbatim the GFS would suggest at least a brief period of supercellular action early on. We'll have to keep an eye on how much instability we can get in the warm sector. The GFS looks pretty meager right now, but as we get closer I wouldn't be surprised to see some of the other short-term models crank that up a notch or two. Link to comment Share on other sites More sharing options...
andyhb Posted March 24, 2012 Share Posted March 24, 2012 00z GFS definitely gets better sfc moisture advection than the other runs of the GFS today, I'm liking the H5 shear vectors too, almost perfectly perpendicular with the incoming boundary. That said, sfc flow veering too early and moisture depth problems are still definitely showing up. Link to comment Share on other sites More sharing options...
Thundersnow12 Posted March 24, 2012 Share Posted March 24, 2012 low clouds, ongoing precip, veered sfc flow in the "warm sector". Reminds me of 4/3/11 Link to comment Share on other sites More sharing options...
andyhb Posted March 24, 2012 Share Posted March 24, 2012 Pretty substantial snippet from the AFD from ARX, basically backs up cyclone's thoughts: 23.12 MEDIUM RANGE FORECAST MODELS CONTINUE TO INDICATE THE POTENTIALFOR STRONG TO SEVERE THUNDERSTORMS TUESDAY AFTERNOON INTO TUESDAY EVENING AS A STRONG LOW PRESSURE SYSTEM MOVES EAST INTO THE REGION FROM THE DAKOTAS. THE MAJOR LIMITING FACTOR IS INSTABILITY. MODELS ARE STRUGGLING TO GENERATE HIGH CAPE VALUES...WITH CAPE RANGING FORM 200 TO 800 J/KG IN A VERY NARROW CORRIDOR RIGHT ALONG THE COLD FRONT. SHEAR IS RATHER STRONG WITH THIS SYSTEM WITH 0-6 KM BULK SHEAR OF 45 TO 55 KT. 0-1 KM BULK SHEAR VALUES ARE VERY STRONG...WITH VALUES OF 30 TO 50 KTS. GIVEN THE STRENGTH OF THE SOUTHERLY FLOW...HIGHER DEWPOINTS AND WARMER AIR SHOULDNT HAVE ANY PROBLEMS ADVECTING NORTHWARD INTO THE FORECAST AREA AHEAD OF THE LOW. IF ANY SUNSHINE IS SEEN TUESDAY AFTERNOON...INSTABILITY SHOULD INCREASE LEADING TO RAPID THUNDERSTORM DEVELOPMENT ALONG AND AHEAD OF THE COLD FRONT TUESDAY AFTERNOON ACROSS SOUTHEAST MINNESOTA AND NORTHEAST IOWA. THESE STORMS SHOULD THEN PUSH INTO WESTERN WISCONSIN LATE TUESDAY AFTERNOON INTO TUESDAY EVENING. WILL HAVE TO CONTINUE TO CLOSELY MONITOR SEVERE THUNDERSTORM POTENTIAL THE NEXT FEW MODEL RUNS. IF THE THUNDERSTORMS CAN DEVELOP...STRONG WINDS AND ISOLATED TORNADOES WOULD BE THE PRIMARY CONCERNS. Link to comment Share on other sites More sharing options...
andyhb Posted March 24, 2012 Share Posted March 24, 2012 DAY 4-8 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0216 AM CDT SAT MAR 24 2012 VALID 271200Z - 011200Z ..DISCUSSION ON TUE/D4...A POTENT SHORTWAVE TROUGH WILL BE LOCATED OVER THE DAKOTAS EARLY...EJECTING NEWD ACROSS MN AND PERHAPS INTO WRN ONTARIO BY 00Z WED. SOME SHOWERS AND STORMS ARE LIKELY TO BE ONGOING...ELEVATED ABOVE A WARM FRONT. THERE IS MODEL VARIABILITY WITH HOW FAR N THIS WAVE WILL EJECT DURING THE DAY...WHICH WILL AFFECT HOW MUCH INSTABILITY FORMS OVER A NARROW WARM SECTOR. IT APPEARS LIKELY THAT THUNDERSTORMS WILL FORM ALONG THE TRAILING COLD FRONT FROM WI INTO NRN AND WRN IL TUE AFTERNOON...HELPED BY 850 MB CONFLUENCE AND DEWPOINTS IN THE MID TO UPPER 50S F. FORECAST SOUNDINGS INDICATE UP TO 1000 J/KG MUCAPE...BUT WITH RELATIVELY POOR LAPSE RATE PROFILES IN THE LOW TO MID LEVELS WELL S OF THE MIDLEVEL SPEED MAX. VEERING FLOW WITH HEIGHT WOULD CONDITIONALLY FAVOR SUPERCELLS...BUT AT THIS TIME THE THREAT LOOKS TO BE ISOLATED. THIS TROUGH WILL FLATTEN THE RIDGE AND MOVE INTO THE NERN STATES AS A FRONT TRAILS SWWD ACROSS THE OH VALLEY WITH MARGINAL INSTABILITY AND ISOLATED SEVERE STORMS WITH SOME HAIL AND WIND. LITTLE SEVERE THREAT IS EXPECTED THROUGH THE REST OF THE PERIOD WITH GENERALLY ZONAL FLOW ALONG THE NRN CONUS AND WEAK FLOW OVER THE CNTRL AND SRN STATES. ..JEWELL.. 03/24/2012 Link to comment Share on other sites More sharing options...
Hoosier Posted March 24, 2012 Author Share Posted March 24, 2012 FWIW, the NAM has CAPE values exceeding 1500 J/kg edging into extreme southern Wisconsin. Link to comment Share on other sites More sharing options...
Hoosier Posted March 24, 2012 Author Share Posted March 24, 2012 I don't know if I necessarily agree with that lapse rate comment in the day 4-8 outlook. Models are advertising 700-500 mb lapse rates around 7C, which isn't bad. That being said, there are things that can go wrong which you guys have outlined. Link to comment Share on other sites More sharing options...
cyclone77 Posted March 24, 2012 Share Posted March 24, 2012 Already took the day off, marginal as it may be. Time to shake the cobwebs off. As expected now that it's in the NAM range it's showing much better instability. Unfortunately it places the surface low even further north, which really veers the lower levels. The GFS actually looks pretty nice to me, although lacks instability. Overall I still have some hope for this setup. Link to comment Share on other sites More sharing options...
PatrickSumner Posted March 25, 2012 Share Posted March 25, 2012 Looks like severe threat may extend into Central/Northern IN overnight Tuesday... Link to comment Share on other sites More sharing options...
IWXwx Posted March 25, 2012 Share Posted March 25, 2012 Sigh....Yet another severe threat bifurcating two subforums. I really wish there was a way to keep it all in one place, but I don't have an answer. I'll just keep reading multiple threads. Link to comment Share on other sites More sharing options...
Hoosier Posted March 25, 2012 Author Share Posted March 25, 2012 DAY 3 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0226 AM CDT SUN MAR 25 2012 VALID 271200Z - 281200Z ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE INDIANA/IL VICINITY SWWD INTO FAR SERN KS/NERN OK... ...SYNOPSIS... A SMALL BUT POTENT UPPER LOW INITIALLY OVER THE NRN PLAINS IS FORECAST TO CONTINUE MOVING ENEWD ACROSS NRN MN AND EVENTUALLY INTO THE NRN UPPER GREAT LAKES REGION. MEANWHILE...AN UPPER LOW IS FORECAST TO REMAIN OFF THE BRITISH COLUMBIA/PAC NW COAST...THOUGH A LEAD IMPULSE IS FORECAST TO MOVE ONSHORE LATE. AT THE SURFACE...THE PRIMARY FEATURE OF INTEREST WILL BE A COLD FRONT FORECAST TO SHIFT ACROSS THE MIDWEST/UPPER GREAT LAKES/OH VALLEY REGION THROUGH THE PERIOD...S OF A SLOWLY FILLING LOW WHOSE TRACK IS PROGGED TO ROUGHLY COINCIDE WITH THE ASSOCIATED UPPER SYSTEM. A COLD FRONT IS ALSO FORECAST TO SHIFT INLAND ACROSS THE PAC NW...AHEAD OF THE AFOREMENTIONED UPPER IMPULSE. ...MIDWEST WSWWD ACROSS THE MO OZARKS... WHILE MODEST LOW-LEVEL MOISTURE IS AGAIN EXPECTED AHEAD OF THE ADVANCING CENTRAL U.S. COLD FRONT...ISOLATED STORMS ARE EXPECTED TO DEVELOP ALONG THE FRONT FROM SERN IA/WRN IL SWWD INTO THE NERN OK VICINITY...AS GENERALLY 1000 TO 1500 J/KG MIXED-LAYER CAPE EVOLVES DURING THE AFTERNOON. WITH FLOW ALOFT VEERING/INCREASING WITH HEIGHT TO NEAR 40 KT AT MID LEVELS...SHEAR SUPPORTIVE OF A FEW ORGANIZED/ROTATING STORMS SUGGESTS THREATS FOR LOCALLY DAMAGING WINDS AND HAIL. WHILE THIS THREAT SHOULD DIMINISH DURING THE EVENING WITH THE LOSS OF DIURNAL HEATING...A FEW STORMS -- AND ISOLATED SEVERE POTENTIAL -- SHOULD SPREAD EWD INTO THE LOWER LAKES/UPPER OH VALLEY WITHIN THE ZONE OF WARM ADVECTION AHEAD OF THE ADVANCING FRONT. ..GOSS.. 03/25/2012 Link to comment Share on other sites More sharing options...
Hoosier Posted March 25, 2012 Author Share Posted March 25, 2012 Although the low level flow veers with time, mid/upper level winds are out of the W/WSW which results in some directional shear. Looking at the NAM, I think there could be a window for a tornadic supercell or two around late afternoon/early evening Tuesday. Link to comment Share on other sites More sharing options...
Thunder Road Posted March 25, 2012 Share Posted March 25, 2012 Doesn't the SLGT seem a bit far to the east? I agree that N IL and N IN may be in play well after sunset for the byproduct of what happens farther west during he afternoon, but CI seems like it could definitely occur west of the Mississippi (and west of the SLGT risk area), since at 21z Tue the majority of the warm unstable region is in Iowa. It doesn't shift into IL until almost 0z per the 12z NAM. Link to comment Share on other sites More sharing options...
Hoosier Posted March 25, 2012 Author Share Posted March 25, 2012 Doesn't the SLGT seem a bit far to the east? I agree that N IL and N IN may be in play well after sunset for the byproduct of what happens farther west during he afternoon, but CI seems like it could definitely occur west of the Mississippi (and west of the SLGT risk area), since at 21z Tue the majority of the warm unstable region is in Iowa. It doesn't shift into IL until almost 0z per the 12z NAM. Yeah I could see it getting pulled west some later. To be honest, I'm not really excited about the threat east of I-57 or so. Storms should be outrunning the instability axis by then. Perhaps things flare up again farther south/east on Wednesday but haven't really looked at it much. Link to comment Share on other sites More sharing options...
tornadotony Posted March 25, 2012 Share Posted March 25, 2012 Yeah I could see it getting pulled west some later. To be honest, I'm not really excited about the threat east of I-57 or so. Storms should be outrunning the instability axis by then. I'm just becoming less and less excited about the whole setup from run to run. It's not even that I think moisture's going to be a problem. Where's the forcing? What's going to get things going on Tuesday? It's not going to be AVA behind a lead impulse, or null vorticity advection south of the shortwave, or the right-exit region of the jet, that's for sure. Link to comment Share on other sites More sharing options...
Hoosier Posted March 25, 2012 Author Share Posted March 25, 2012 I'm just becoming less and less excited about the whole setup from run to run. It's not even that I think moisture's going to be a problem. Where's the forcing? What's going to get things going on Tuesday? It's not going to be AVA behind a lead impulse, or null vorticity advection south of the shortwave, or the right-exit region of the jet, that's for sure. I agree with the forcing concern. Will probably serve to keep things rather isolated/scattered. Link to comment Share on other sites More sharing options...
cyclone77 Posted March 25, 2012 Share Posted March 25, 2012 Yeah not as optimistic with this system either. Low levels are pretty veered, not much surface convergence. Low is way up in Canada now as well. Will keep an eye on things, but confidence/hope is slowly on the decline run to run. Link to comment Share on other sites More sharing options...
chase_stormz Posted March 25, 2012 Share Posted March 25, 2012 Well, as unimpressive as this threat looks lol, I may still gamble and chase cause it's close and I have yet to chase since March 2 when i had a horrible day. Not a fan of the veering surface winds, lack of moisture, and forcing. However, if dews can manage to get into the low 60s across e/ne IA into extreme sw WI, nw IL there may be a chance at a brief, weak tornado where the surface winds are not so much veered and the shear overlaps the instability. Link to comment Share on other sites More sharing options...
Thunder Road Posted March 26, 2012 Share Posted March 26, 2012 The NAM is even weaker tonight with the SLP. It seems the weakening trend is significant. We went from a broad area of sub-992 at 0z Wed on the 1200/24 run, to a small area of sub-992 on the 0000/25 run, to a broad area of sub-996 on the 1200/25 run, to now only a small area of sub-996 on the current (0000/26) run. The only advantage is that it's also trended southward a bit, but that's not going to be enough to compensate for a greater than 4 mb weakening (realistically closer to 6 mb given the amount of area covered by the 992 isobar on the 1200/24 run compared to the amount of area covered by the 996 isobar on the latest run), especially given that it was already looking like a marginal set-up. There might still be enough juice for some convection in that skinny warm sector, but with the even more reduced turning it seems like the tornado threat is rapidly decreasing. Link to comment Share on other sites More sharing options...
andyhb Posted March 26, 2012 Share Posted March 26, 2012 My attention is rapidly drawing away from this system to the big one the GFS has been consistently showing for the past several days. Euro/CMC have hinted at it as well at times. More importantly, the models seem to be consistently ejecting lead anomalies ahead of this larger scale trough, which would help create a more zonal flow pattern in between systems and perhaps a more progressive upper level trough. Link to comment Share on other sites More sharing options...
cyclone77 Posted March 26, 2012 Share Posted March 26, 2012 The low-level shear is pretty pathetic now that the lower level winds are veered as much as they are. Above 850mb the shear increases a bit, but with instability at 1000j/kg or less, that's not gonna get it done. With the lack of low-level shear in place we would need something to dig in hard and take a turn to the right of the mean flow. That usually takes decent instability, which is clearly lacking with this setup. Assuming we can actually get something to fire, anything that does try to get something going will probably quickly occlude given the crappy low-level shear. Link to comment Share on other sites More sharing options...
cyclone77 Posted March 26, 2012 Share Posted March 26, 2012 My attention is rapidly drawing away from this system to the big one the GFS has been consistently showing for the past several days. Euro/CMC have hinted at it as well at times. Meh. This system looked impressive as well several days ago. Link to comment Share on other sites More sharing options...
PatrickSumner Posted March 26, 2012 Share Posted March 26, 2012 My attention is rapidly drawing away from this system to the big one the GFS has been consistently showing for the past several days. Euro/CMC have hinted at it as well at times. What time frame are we talking about here? I see a storm chance for the weekend, and then a big trough entering Central U.S. after that on the GFS... Link to comment Share on other sites More sharing options...
andyhb Posted March 26, 2012 Share Posted March 26, 2012 What time frame are we talking about here? I see a storm chance for the weekend, and then a big trough entering Central U.S. after that on the GFS... The second point you mentioned. Meh. This system looked impressive as well several days ago. Yes, but this is a much different type of upper/mid level system than the one being shown after. I sense a bit of frustration in your posts That said, the 00z Euro/GGEM are nothing like the GFS...although the GFS ensembles actually have some pretty impressive agreement along the lines of the GFS OP. Link to comment Share on other sites More sharing options...
Hoosier Posted March 26, 2012 Author Share Posted March 26, 2012 Call me crazy but I still feel like there could be a window (few hours maybe just before/after 0z?) where we have to watch for some tornadic potential. Yes, the low level flow veers but I will go back to my earlier point about mid level winds basically being due west, which results in about 50-60 degrees of turning. That is not overwhelming by any means but it has produced before. Overall I do think hail/wind are bigger threats though. I guess one good thing is that we probably won't have to worry too much about storm competition/interaction lol Link to comment Share on other sites More sharing options...
cyclone77 Posted March 26, 2012 Share Posted March 26, 2012 A few of the forecast soundings off the 12z NAM aren't too bad around the Dubuque area tomorrow afternoon. Surface winds are slightly more backed this run it seems, at least to me. Not much precip showing up on many of the models, so initiation may not even happen, or wait till after dark. This has been a pretty frustrating system to look at in many ways lol. If it weren't so close to home I probably wouldn't be spending much time looking at it, but alas... Link to comment Share on other sites More sharing options...
chase_stormz Posted March 26, 2012 Share Posted March 26, 2012 A few of the forecast soundings off the 12z NAM aren't too bad around the Dubuque area tomorrow afternoon. Surface winds are slightly more backed this run it seems, at least to me. Not much precip showing up on many of the models, so initiation may not even happen, or wait till after dark. This has been a pretty frustrating system to look at in many ways lol. If it weren't so close to home I probably wouldn't be spending much time looking at it, but alas... Yea, I'm from Peoria, IL. Really frustrating setup to look at, however, with it being so close, can't help it lol. Based off the last few 12/00z NAM and GFS runs (which are in excellent agreement) I feel like the most likely area for storm initiation/coverage is going to be somewhere between Dubuque, IA to Davenport, IA staying North of I-88 in Illinois. This is due to the best forcing available being located in this area where 1000-1500 sb cape seems achievable. We'll see.. Link to comment Share on other sites More sharing options...
wisconsinwx Posted March 26, 2012 Share Posted March 26, 2012 New slight risk extends a bit farther north up to about Madison. A bit surprised, but perhaps if parts of the area can get some sun to the west of Milwaukee, the atmosphere will be primed. Link to comment Share on other sites More sharing options...
Hoosier Posted March 26, 2012 Author Share Posted March 26, 2012 DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1228 PM CDT MON MAR 26 2012 ...PLAINS/MS VALLEY INTO GREAT LAKES REGION... THE STRONGEST MID/UPPER FORCING FOR UPWARD VERTICAL MOTION APPEARS LIKELY TO SPREAD INTO AREAS NEAR/NORTH OF THE CANADIAN/U.S. BORDER IN ADVANCE OF THE BETTER LOW-LEVEL MOISTURE RETURN. THIS IS EXPECTED...IN GENERAL...TO LIMIT THE OVERALL SEVERE WEATHER THREAT FOR THIS PERIOD. HOWEVER...MODELS ARE SUGGESTIVE THAT COOLING ASSOCIATED WITH UPPER LOW MAY WEAKEN INHIBITION SUFFICIENTLY TO SUPPORT INCREASING THUNDERSTORM ACTIVITY AS IT OVERSPREADS THE PRE-FRONTAL LOW-LEVEL MOIST AXIS ...ACROSS PARTS OF EASTERN KANSAS AND NORTHWEST MISSOURI INTO EASTERN IOWA AND WESTERN WISCONSIN. LOWER/MID TROPOSPHERIC WARM ADVECTION MAY SUPPORT ADDITIONAL STORM DEVELOPMENT JUST AHEAD OF THE SOUTHERN FLANK OF THIS NARROW BROKEN CONVECTIVE BAND...ACROSS PARTS OF NORTHERN INTO WEST CENTRAL MISSOURI...WHICH SHOULD BE MOSTLY BASED ABOVE THE BOUNDARY LAYER...WITH LIMITED SEVERE POTENTIAL...AS IT SPREADS EAST SOUTHEASTWARD BEFORE DIMINISHING DURING THE AFTERNOON. IN THE WAKE OF THIS INITIAL ACTIVITY...MODERATE BOUNDARY LAYER DESTABILIZATION /CAPE OF 1000-2000 J PER KG/ IS EXPECTED BENEATH STEEP LAPSE RATES...ALONG AN AXIS FROM SOUTHEASTERN KANSAS INTO NORTHWESTERN ILLINOIS. VERTICAL SHEAR IS EXPECTED TO REMAIN AT LEAST MODESTLY STRONG ALONG THIS AXIS...EVEN WITH THE STRONGER LOW AND MID-LEVEL JET CORES SHIFTING THROUGH THE UPPER MISSISSIPPI VALLEY AND GREAT LAKES REGION. WHILE FORCING FOR LARGE-SCALE ASCENT IS EXPECTED TO WEAKEN AT THE SAME TIME... MID-LEVEL INHIBITION SHOULD REMAIN WEAK ENOUGH FOR SCATTERED STRONG/SEVERE STORM DEVELOPMENT LATE TUESDAY AFTERNOON. THIS MAY INCLUDE A FEW SUPERCELLS...PARTICULARLY ACROSS PARTS OF NORTHEAST MISSOURI INTO NORTHWEST/WEST CENTRAL ILLINOIS...BEFORE CONVECTION WEAKENS/DIMINISHES DURING THE EVENING HOURS. ..KERR.. 03/26/2012 Link to comment Share on other sites More sharing options...
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