baroclinic_instability Posted April 24, 2011 Share Posted April 24, 2011 Yesterday's runs... while having a very impressive synoptic system... were very forced in a linear fashion for Wednesday. Upward velocities were extremely strong and with a very linear configuration. This, combined with the low-level jet axis being just ahead of the surface boundary on yesterday's runs... restricting the low-level convergence to just ahead of the surface cold front... really screamed a linear storm mode. With this lower amplitude trough configuration, we have trended toward a situation where low-level convergence associated with the western side of the low-level jet is spaced significantly ahead of the surface front... and the upward velocities on the synoptic scale are also more spaced out and subtle. Also, while this won't really back the surface winds toward a southeasterly direction... we're seeing the 850-mb winds trend more SSW to SW, overtop the due south surface winds... which is a more classic configuration for our big tornado days in this part of the country. We often don't see events with a SE sfc flow work out because of the trajectories of the low-level air mass. In fact, all four of Alabama's F5 tornadoes in history happened with surface winds ranging from due S to SW... and an 850-mb flow out of the SSW to SW. While the synoptic system isn't quite as strong on today's model runs... we've stepped away from more of a forced, linear storm mode... and toward more subtle forcing overtop a weakly capped LLJ axis with significant instability. Any veering of the 850-mb jet toward the SSW to SW is going to rapidly ramp up 0-1 km storm relative helicity values... and 0-3 km values are already progged to be sky high. My main concern with Wednesday down here is actually that we may have a little bit of a problem with LCL heights if we reach some of the progged surface temperatures shown in some of the model guidance. Edited for typo. Thanks for the info Fred. I won't lie I know little of southeast severe climo. I guess I was mostly referencing farther N, but all your points make good sense. Link to comment Share on other sites More sharing options...
Thundersnow12 Posted April 25, 2011 Share Posted April 25, 2011 Just got home from Louisville awhile so just now really digging into the severe threat the next few days, but just looking at these images for weds is ringing off alot of bells..some serious juice coming in/sitting on the gulf, look at high theta-e air. Link to comment Share on other sites More sharing options...
hannie Posted April 25, 2011 Share Posted April 25, 2011 How is Louisville, Ky lookin for the next few days? Is there any chance the worst may stay south of us? Link to comment Share on other sites More sharing options...
nwohweather Posted April 25, 2011 Share Posted April 25, 2011 Hey guys we are literally swamped here - never been this busy with any event What do some of you think about the Tuesday night into Wednesday time frame for southern IL and western KY - some mets are thinking further east of here - wondering if anyone can give me specific thoughts Thanks ahead of time Nahh it seems like on the models the storm keeps showing itself a little bit stronger than the one before although I'll admit I haven't had a chance to really look today. Plus the winds aloft will be absolutely screaming in that vicinity. I think it'll be about a little bit west of where current thoughts are but who knows Link to comment Share on other sites More sharing options...
nwohweather Posted April 25, 2011 Share Posted April 25, 2011 I hope not This is a mess - I have multiple friends and family that may be threatened now by flood waters. Talked to some local meteorologists and needless to say there is a lot of discouragement here - most have not been able to even put together forecasts like highs and low temperatures - they are just grabbing straight off raw model numbers. It has been non-stop for the last few days. This is a once in a lifetime series of events down here. Defin appreciate any thoughts on the TUE/WED event because it is important. Yeah those numbers the HPC were throwing out of 10+" down there in 5 days in insane. Up here we've seen major flooding the last few years from 2-4" on top of a snowpack, I can't imagine what that amount of rain would do, nor would anyone want to. I'll admit though there are so many variables still up in the air it's scary considering the potential this storm has Link to comment Share on other sites More sharing options...
Indystorm Posted April 25, 2011 Share Posted April 25, 2011 From this evening IND AFD with respect to Wed. system... VARIANCE STILL EXISTS IN THE EVENTUAL TRACK OF THIS FINAL SYSTEM...WITH THE ENSEMBLES CONVERGING ON A TRACK FROM SOUTHERN ILLINOIS THROUGH WESTERN INDIANA ON THE WESTERN END...TO ACROSS SOUTHEAST INDIANA INTO WESTERN OHIO ON THE EASTERN END. APPEARS THERE MAY BE STRONG DEEP SHEAR OVER THE WARM SECTOR WITH GOOD ALIGNMENT OF THE LOWER AND UPPER LEVEL JETS POSSIBLE...SO THE TRACK OF THIS LOW WILL HAVE TO BE WATCHED. Link to comment Share on other sites More sharing options...
Superstorm93 Posted April 25, 2011 Share Posted April 25, 2011 Wow... For the short time I have been using the SREF, I have never seen STI this high for so long. From tomorrow morning until Wednesday, there is a "50" for the exception of one frame. Check this out: Link to comment Share on other sites More sharing options...
on_wx Posted April 25, 2011 Share Posted April 25, 2011 Wow... For the short time I have been using the SREF, I have never seen STI this high for so long. From tomorrow morning until Wednesday, there is a "50" for the exception of one frame. Check this out: Once again that pocket of 5% is back over my regional municipality Link to comment Share on other sites More sharing options...
Superstorm93 Posted April 25, 2011 Share Posted April 25, 2011 Once again that pocket of 5% is back over my regional municipality Supercell Probs for 48 hours Link to comment Share on other sites More sharing options...
on_wx Posted April 25, 2011 Share Posted April 25, 2011 Supercell Probs for 48 hours Well good! If trends continue I may get my first chase in of the season. Link to comment Share on other sites More sharing options...
Stebo Posted April 25, 2011 Share Posted April 25, 2011 At glance the NAM is taking the low over or to our west GFS is way southeast of us That is as far as I have gotten lol Yeah Beau right now the GFS is on its own with the further SE track, all the rest are to the West of it. Link to comment Share on other sites More sharing options...
Calderon Posted April 25, 2011 Share Posted April 25, 2011 Wow... For the short time I have been using the SREF, I have never seen STI this high for so long. From tomorrow morning until Wednesday, there is a "50" for the exception of one frame. Check this out: hey, works well for me Link to comment Share on other sites More sharing options...
Stebo Posted April 25, 2011 Share Posted April 25, 2011 Day 2 Moderate risk DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0100 AM CDT MON APR 25 2011 VALID 261200Z - 271200Z ...THERE IS A MDT RISK OF SVR TSTMS ACROSS FAR NORTHEAST TEXAS...SOUTHERN AND EASTERN ARKANSAS...WESTERN TENNESSEE...NORTHWEST MISSISSIPPI...AND NORTHERN LOUISIANA... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGER PORTION OF THE EASTERN U.S. FROM THE NORTHEAST/E COAST STATES TO THE LOWER MS VALLEY/SRN PLAINS... ...SYNOPSIS... VERY LARGE UPPER TROUGH WILL REMAIN IN PLACE OVER THE CENTRAL CONUS...AS ONE SHORTER-WAVELENGTH FEATURE SHIFTS INTO THE GREAT LAKES AND A SECOND DIGS SEWD OUT OF THE ROCKIES. A SURFACE BAROCLINIC ZONE IS EXPECTED TO EXTEND FROM THE GREAT LAKES/OH VALLEY SWWD INTO N TX...AND WILL SERVE AS A FOCUS FOR WIDESPREAD SEVERE CONVECTION -- INCLUDING THE POSSIBILITY OF A LOCAL SEVERE WEATHER OUTBREAK FOCUSED FROM THE ARKLATEX REGION INTO THE MID MS VALLEY REGION. ...ARKLATEX REGION ENEWD INTO THE LOWER/MID MS VALLEY... COMPLEX -- BUT POTENTIALLY SIGNIFICANT/DANGEROUS -- SEVERE WEATHER EVENT IS UNFOLDING FOR THIS AREA FOR DAY 2 /TUE. AND EARLY WED./. STORMS WILL LIKELY BE ONGOING AT THE START OF THE PERIOD...SHIFTING EWD/ENEWD INTO THE OH/TN VALLEYS ALONG WITH ONGOING SEVERE POTENTIAL. GREATER SEVERE THREAT FOR THIS REGION HOWEVER WILL EVOLVE LATER IN THE DAY...AS AN INITIAL SHORT-WAVE TROUGH DEPARTING NEWD IS FOLLOWED BY A SECOND/DIGGING FEATURE SHIFTING QUICKLY SEWD OUT OF THE ROCKIES AND INTO THE SRN PLAINS. AS THIS OCCURS...BACKING/INTENSIFYING LOW-LEVEL FLOW FIELD IS FORECAST...WITH A 70-PLUS KT LOW-LEVEL JET TO SHIFT EWD FROM NE TX ACROSS AR/LA DURING THE EVENING...BENEATH MID-LEVEL WLYS INCREASING TO 70 TO 80 KT. AS THE UPPER SYSTEM APPROACHES...SURFACE CYCLOGENESIS WILL OCCUR ALONG THE WARM FRONT...SHIFTING EWD ACROSS N TX AND AR TOWARD THE MID MS VALLEY LATE. STORMS SHOULD INITIATE DURING THE AFTERNOON ACROSS NE TX AND QUICKLY BECOME SUPERCELLULAR...WITH LARGE HAIL...DAMAGING WINDS...AND TORNADOES EXPECTED. A SUBSTANTIAL TORNADO THREAT APPEARS LIKELY TO EVOLVE -- SPREADING ACROSS NRN LA/AR AND THEN INTO WRN TN/NWRN MS LATE. ALONG WITH TORNADO POTENTIAL...DAMAGING WIND/LARGE HAIL THREAT WILL ALSO ACCOMPANY THE STORMS THROUGH THE END OF THE PERIOD -- POSSIBLY EXTENDING AS FAR E AS MIDDLE TN/NRN AR/NWRN GA BY 27/12Z. ...LOWER GREAT LAKES REGION/OH AND TN VALLEYS... THUNDERSTORMS ONGOING AT THE START OF THE PERIOD WILL CONTINUE SHIFTING NEWD ACROSS THE TN/OH VALLEYS AND INTO THE LOWER GREAT LAKES REGION. THIS WILL OCCUR AS STRONG SHORT-WAVE TROUGH SHIFTS ACROSS THIS AREA FOCUSING LARGE-SCALE UVV ALONG A SURFACE COLD FRONT EXTENDING SWWD ACROSS THE MID MS VALLEY INTO TX. WHILE AFTERNOON HEATING MAY BE HINDERED BY WIDESPREAD PRECIPITATION/CLOUD COVER...LOCAL AREAS OF GREATER DESTABILIZATION WILL SUPPORT AFTERNOON INCREASE IN STORM COVERAGE AND INTENSITY -- AS FAR NE AS PA AND NY NEAR THE SURFACE WARM FRONT. WITH A STRONG SWLY FLOW FIELD ALOFT ACROSS THIS ENTIRE AREA /LOW-LEVEL FLOW INCREASING FROM 50 TO 65 KT IN THE 850 TO 500 MB LAYER/...SHEAR WILL SUPPORT ORGANIZED/ROTATING STORMS...ALONG WITH LINEAR/BOWING SEGMENTS. ALONG WITH SOME THREAT FOR HAIL...DAMAGING WINDS WILL BE LIKELY ALONG WITH THE POTENTIAL FOR ISOLATED TORNADOES. THE THREAT SHOULD SPREAD EWD WITH TIME AS THE FRONT SLOWLY ADVANCES...WITH SOME THREAT LIKELY LINGERING INTO THE OVERNIGHT HOURS INTO NY/PA/WV. ...CAROLINAS/VA... WEAK SHORT-WAVE FEATURES SHIFTING NEWD ACROSS THIS REGION -- EMBEDDED WITHIN CYCLONIC FLOW FIELD AHEAD ON THE ERN FRINGE OF THE LARGE CENTRAL U.S. TROUGH -- WILL SUPPORT A BROAD ZONE OF AFTERNOON THUNDERSTORM DEVELOPMENT ACROSS THIS AREA. WITH HEATING OF THE MOIST BOUNDARY LAYER AIRMASS OCCURING THROUGH THE DAY...INSTABILITY WILL BECOME SUFFICIENT -- IN CONJUNCTION WITH MODERATE/VEERING FLOW WITH HEIGHT -- TO SUPPORT ORGANIZED/LOCALLY SEVERE STORMS...INCLUDING THREATS FOR HAIL AND DAMAGING WINDS...AND AN ISOLATED TORNADO. WITHOUT A CLEAR LOW-LEVEL FOCUSING MECHANISM...WITH MAINTAIN ONLY 15%/SLIGHT RISK FORECAST ATTM -- GIVEN THE BROAD/UNFOCUSED THREAT AREA. Link to comment Share on other sites More sharing options...
tornadotony Posted April 25, 2011 Share Posted April 25, 2011 I don't have a lot of time to type, but man is this going to be a long 3-4 day stretch. Gotta feel for MEG, LZK, TSA, etc. Link to comment Share on other sites More sharing options...
Stebo Posted April 25, 2011 Share Posted April 25, 2011 I don't have a lot of time to type, but man is this going to be a long 3-4 day stretch. Gotta feel for MEG, LZK, TSA, etc. Yeah what I would pay to have Tuesday off so I could leave for Memphis after work today for 3 days. Link to comment Share on other sites More sharing options...
baroclinic_instability Posted April 25, 2011 Share Posted April 25, 2011 What a complicated setup for each day through Thursday. Each event will have a cascading effect on both the synoptics as well as the storm environments. Not an easy set of forecasts for SPC or the local forecast offices. Link to comment Share on other sites More sharing options...
Jebman Posted April 25, 2011 Share Posted April 25, 2011 I hope this outbreak is less severe than progged. I also hope that no tornadoes hit the Mid Atlantic, namely northern VA. Everyone stay safe, including the storm chasers. Link to comment Share on other sites More sharing options...
thewxmann Posted April 25, 2011 Share Posted April 25, 2011 lol... off the charts anyone? Link to comment Share on other sites More sharing options...
baroclinic_instability Posted April 25, 2011 Share Posted April 25, 2011 lol... off the charts anyone? Yeah I saw that too. Euro, CMC, UK and NAM all suggesting some sort of mesoscale complex rapidly propagating northward associated with that low amplitude leading wave ahead of the main anomaly overnight Tuesday into Wed and some sort of freak nasty theta-e inflow. Honestly never seen soundings or wind fields like that before. Link to comment Share on other sites More sharing options...
Stebo Posted April 25, 2011 Share Posted April 25, 2011 lol... off the charts anyone? Amazing shear, but not a terribly high amount of instability in the sounding. Link to comment Share on other sites More sharing options...
thewxmann Posted April 25, 2011 Share Posted April 25, 2011 Amazing shear, but not a terribly high amount of instability in the sounding. Obv convective feedback induced, but that 75kt at H85 is nonetheless impressive. 1000 m2s-2 0-3 helicity to boot. I've just never seen a hodograph that was literally "off the charts" on twisterdata like that. Link to comment Share on other sites More sharing options...
baroclinic_instability Posted April 25, 2011 Share Posted April 25, 2011 Amazing shear, but not a terribly high amount of instability in the sounding. It is propagating along the warm front--you can see it in the theta-e fields. It is definitely feeding off the moist inflow. It is definitely convective in nature--no other way to explain 90 kt 850 wind fields. Oddly enough Euro, CMC, UK all suggest this type of feature. Link to comment Share on other sites More sharing options...
baroclinic_instability Posted April 25, 2011 Share Posted April 25, 2011 Obv convective feedback induced, but that 75kt at H85 is nonetheless impressive. 1000 m2s2 0-3 helicity to boot. I've just never seen a hodograph that was literally "off the charts" on twisterdata like that. I don't think there is any "convective feedback" here. Typically convective feedback is produced by overcooked convection--usually in situations with massive CAPE fields and weak shear. Old GFS displayed that when it tried to develop sub-grid scale convection under those scenarios. Classic convective feedback is a mass amount of unrealistic latent heat released by the models in the mid-troposphere which then unrealistically warms the mid levels and cripples the dynamic/thermal fields. NAM/GFS had this on full display during the Groundhogs Day storm. The old GFS bullseyes in the VV/vorticity fields were another example. Link to comment Share on other sites More sharing options...
Stebo Posted April 25, 2011 Share Posted April 25, 2011 It is propagating along the warm front--you can see it in the theta-e fields. It is definitely feeding off the moist inflow. It is definitely convective in nature--no other way to explain 90 kt 850 wind fields. Oddly enough Euro, CMC, UK all suggest this type of feature. Oh you are talking about that NAM meso low that formed? Yeah that definitely had a convectively induced look to it, although it is interesting that the other models all show it. Might be something to monitor the potential of as we move through next few days. Link to comment Share on other sites More sharing options...
baroclinic_instability Posted April 25, 2011 Share Posted April 25, 2011 Oh you are talking about that NAM meso low that formed? Yeah that definitely was convectively induced, although it is interesting that the other models all show it. Might be something to monitor the potential of as we move through next few days. Yeah I was guessing that was where thewxmann pulled the crazy soundings. I saw those too earlier--interesting to see if/how that feature develops. Link to comment Share on other sites More sharing options...
thewxmann Posted April 25, 2011 Share Posted April 25, 2011 I don't think there is any "convective feedback" here. Typically convective feedback is produced by overcooked convection--usually in situations with massive CAPE fields and weak shear. Old GFS displayed that when it tried to develop sub-grid scale convection under those scenarios. Classic convective feedback is a mass amount of unrealistic latent heat released by the models in the mid-troposphere which then unrealistically warms the mid levels and cripples the dynamic/thermal fields. NAM/GFS had this on full display during the Groundhogs Day storm. The old GFS bullseyes in the VV/vorticity fields were another example. Gotcha. What I really meant was a "convective response", which you alluded to in earlier posts. Thanks for the clarification. Link to comment Share on other sites More sharing options...
Stebo Posted April 25, 2011 Share Posted April 25, 2011 Yeah I was guessing that was where thewxmann pulled the crazy soundings. I saw those too earlier--interesting to see if/how that feature develops. Yeah, if it were to develop you'd have a severe backing of the winds at the surface, and the potential of significant tornado action would skyrocket. Link to comment Share on other sites More sharing options...
Stebo Posted April 25, 2011 Share Posted April 25, 2011 Day 3 Mod too DAY 3 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0230 AM CDT MON APR 25 2011 VALID 271200Z - 281200Z ...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF CENTRAL AND EASTERN KENTUCKY...MIDDLE AND EASTERN TENNESSEE...NORTHEAST MISSISSIPPI...CENTRAL AND NORTHERN ALABAMA...AND NORTHWEST GEORGIA... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PORTION OF THE ERN U.S. FROM THE LOWER AND MID MS/OH VALLEYS EWD... ...SYNOPSIS... A LARGE UPPER TROUGH WILL CONTINUE SHIFTING EWD ACROSS THE U.S. THIS PERIOD...WITH A POTENT SHORT-WAVE TROUGH/SPEED MAX SHIFTING EWD INTO THE MID SOUTH REGION INTO THE AFTERNOON. AS THIS OCCURS...SECONDARY SURFACE LOW DEVELOPMENT IS EXPECTED ALONG THE COLD FRONT S OF THE MAIN GREAT LAKES REGION LOW. THIS SYNOPTIC-SCALE SETUP FAVORS SIGNIFICANT SEVERE WEATHER POTENTIAL E OF THE MS VALLEY. ...PA/NW SSWWD TO THE GULF COAST... YET ANOTHER DAY OF POTENTIALLY VERY SIGNIFICANT SEVERE WEATHER IS EXPECTED DAY 3 /WED. AND EARLY THU. APR. 27 AND 28/ -- WITH ELEVATED THREAT FOR A TORNADO OUTBREAK EVIDENT ACROSS THE MID SOUTH AND INTO PORTIONS OF THE CENTRAL GULF COAST STATES. STRONG/SEVERE STORMS SHOULD BE ONGOING AT THE START OF THE PERIOD ACROSS THE NWRN PORTIONS OF THE SLIGHT RISK AREA...AS THE POTENT SHORT-WAVE TROUGH AND ASSOCIATED MID-/UPPER-LEVEL SPEED MAX ROUNDS THE BASE OF THE LARGER-SCALE TROUGH. WHILE AN INITIAL SURFACE LOW SHOULD SHIFT NNEWD ACROSS THE OH VALLEY/MIDWEST...SECONDARY SURFACE LOW DEVELOPMENT IS FORECAST DURING THE AFTERNOON IN THE KY/TN VICINITY...WITH LOCALLY-BACKED SURFACE FLOW VEERING/INCREASING SUBSTANTIALLY WITH HEIGHT RESULTING IN SHEAR PROFILES VERY SUPPORTIVE OF SUPERCELLS AND TORNADOES. THE MOST FAVORABLE COMBINATION OF RICH LOW-LEVEL MOISTURE...STRONG SHEAR...FOCUSED LARGE-SCALE ASCENT...AND ANTICIPATED LACK OF APPRECIABLE PRIOR CONVECTION INDICATES A RELATIVELY HIGH-CONFIDENCE AREA OF CONCENTRATED SIGNIFICANT THREAT FOR POTENTIALLY STRONG TORNADOES AND WIDESPREAD WIND DAMAGE CENTERED OVER THE MID SOUTH/TN VALLEY REGION. THEREFORE...WILL INTRODUCE MODERATE RISK FORECAST ATTM -- INDICATIVE OF OUTBREAK POTENTIAL. ALONG WITH FAIRLY SUBSTANTIAL SEVERE POTENTIAL EXTENDING FARTHER NNEWD INTO PA/NY -- INCLUDING THREATS FOR DAMAGING WINDS AND ISOLATED TORNADOES...SEVERE STORMS WILL LIKELY ALSO EXTEND E OF THE APPALACHIANS INTO THE ATLANTIC COAST STATES. ALONG WITH THE LIKELIHOOD FOR AFTERNOON SEVERE CONVECTION...SEVERE CONVECTION MAY CONTINUE INTO THE OVERNIGHT HOURS AS THE SURFACE FRONT CRESTS THE APPALACHIANS. ..GOSS.. 04/25/2011 Link to comment Share on other sites More sharing options...
thewxmann Posted April 25, 2011 Share Posted April 25, 2011 Wow, has a MDT on Day 1, 2, AND 3 ever happened before? Link to comment Share on other sites More sharing options...
Stebo Posted April 25, 2011 Share Posted April 25, 2011 Wow, has a MDT on Day 1, 2, AND 3 ever happened before? I'm guessing no. Link to comment Share on other sites More sharing options...
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