CheeselandSkies Posted March 5, 2020 Share Posted March 5, 2020 9 hours ago, frostfern said: Yea. Tornado outbreaks in March and April are usually going to coincide with abnormal warmth and humidity for the time of year. That doesn't mean you need summer-like temperatures though. Shear is far more important, and low cloud bases / high relative humidity is very beneficial because evaporative cooling from nearby precip won't completely stabilize surface-based storm-inflow. I think Dr. Leigh Orf's work provided some pretty strong evidence that violent tornadoes ingest a lot of surface-based parcels that are more stable than average, yet still realize some positive buoyancy once lifted into the middle levels of the storm by the upward vacuum-suction force of the rotating meso. Hot weather brings you the highest surface based CAPE, but that CAPE can be completely neutralized by just a little bit of precip if the boundary layer is characterized by low relative humidity. The result is many hot-day summer supercells have elevated inflow, and thus never produce tornadoes. Early spring supercells are very good at producing tornadoes because they often form in an environment where instability is more than adequate for strong convection despite high boundary layer relative humidity. Good insight, I need to get better about remembering this. Being based further north (like you) I've seen many an early season (even well into May for us) potential setup get quashed by insufficient instability, so I'm a CAPE guy. I get really geeked out to chase on those 86/77 days, then wonder why the updrafts weren't going up like atom bombs. This mindset cost me on 4/9/2015, when I was bumming around IN OGLE COUNTY, IL until about 4:30 PM, then threw in the towel and started for home. Got there just in time to pull up GR Level 3 and see the debris ball about 10 miles from where I'd just been 90 minutes before. Link to comment Share on other sites More sharing options...
frostfern Posted March 6, 2020 Share Posted March 6, 2020 11 hours ago, CheeselandSkies said: Good insight, I need to get better about remembering this. Being based further north (like you) I've seen many an early season (even well into May for us) potential setup get quashed by insufficient instability, so I'm a CAPE guy. I get really geeked out to chase on those 86/77 days, then wonder why the updrafts weren't going up like atom bombs. This mindset cost me on 4/9/2015, when I was bumming around IN OGLE COUNTY, IL until about 4:30 PM, then threw in the towel and started for home. Got there just in time to pull up GR Level 3 and see the debris ball about 10 miles from where I'd just been 90 minutes before. Yea. I think sometimes intense sunshine is unhelpful because it produces a deep dry adiabatic layer. Supercell tornadoes tend to like areas where there the low-level lapse rate isn't too steep. Downdrafts don't become too dominant then. You also get more backing near the ground when the first 1000 feet is a little more stable because there aren't as many dry thermals mixing westerly momentum down from above. The most likely place for big tornadoes usually isn't in the middle of a bubble of high SBCAPE. It's usually around the edge of the SBCAPE bubble (i.e. where there's a sharp SBCAPE gradient). I think tornadic supercells are often pulling in the most unstable air from a slightly elevated layer, but the meso is able to "dig" down and pull in surfaced based air as well. For example, you might have a MUCAPE of 1400 j/kg for a layer rooted around 900 hPa on the "cool" side of an old outflow boundary, but the storm is also pulling in surface parcels with CAPE around 700 j/kg. The surface parcels probably have a fairly high LFC, but the vacuum effect of the meso can get them up there. These parcels have a lot more "backed" momentum profile than those entering the storm from the 900 hPa level, so they can contribute a lot of extra spin to the meso, helping to reinforce the upward vacuum effect. On the warm side of the outflow boundary you might have SBCAPE of 2500 j/kg, but meso's are all weak and elevated due to strong cold pools and lack of near-surface backed flow. 1 Link to comment Share on other sites More sharing options...
Indystorm Posted March 8, 2020 Share Posted March 8, 2020 It's a week out with usual caveats, but 12z GFS on March 8 continues its trend of producing a storm around St. Patrick's Day that could be a svr wx producer for the southern Midwest and mid south. New ERTAF outlook issued the evening of March 8 also mentions this possibility. 1 Link to comment Share on other sites More sharing options...
Hoosier Posted March 11, 2020 Author Share Posted March 11, 2020 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Wed Mar 11 2020 Valid 121200Z - 131200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE OZARKS TO THE LOWER OHIO VALLEY/MID-SOUTH VICINITY... ...SUMMARY... Severe thunderstorms are possible across parts of the lower Ohio Valley and Mid South into parts of the southeastern Plains Thursday afternoon and evening. ...ArkLaTex Vicinity to the Ohio/Tennessee Valley Region... A shortwave impulse embedded in larger-scale upper trough over the central U.S. will deepen and eject eastward from the central Plains to the Great Lakes on Thursday. The main surface low associated with this system will track eastward across Ontario with a surface cold front extending south/southwest from the Upper Midwest to western portions of the southern Plains during the morning. A warm front will extend eastward from a weak surface low over northern OK into northern AR/western TN early Thursday, lifting northward toward the Ohio River during the day. Strong warm advection ahead of the east/southeastward progressing cold front will allow low-to-mid 60s F dewpoints to overspread the south-central U.S. from eastern OK/TX into parts of KY/TN. Surface heating likely will be limited by cloud cover and areas of ongoing showers, and strong warm advection between 850-700 mb will result in pockets of stronger capping. However, a 40-50 kt southwesterly low level jet will develop by late afternoon/early evening and pockets of MLCAPE up to 1000 J/kg are forecast along/just ahead of the cold front/triple point near the MO/AR border southwestward into southeast OK, as well as eastward near the warm front across KY/TN. Semi-discrete cells in the warm sector are possible initially, but clusters are expected to grow upscale into during the evening as vertical shear become aligned with the frontal boundary. All severe hazards appear possible, with hail more likely earlier in storm evolution where midlevel lapse rates are expected to range from 7-7.5 C/km across western portions of the Slight risk area. SRH values greater than 250 m2/s2, and enlarged low level hodographs will support tornado potential in both discrete cells and within any bowing line segments. Furthermore, intense low level wind field will support damaging winds through the evening hours as convection spreads eastward into the OH/TN Valley vicinity. ...Central/Southern Appalachians Vicinity... Several forecast models indicate isolated storms may develop across parts of northern GA into Upstate SC/western NC. Dewpoints in the lower 60s will increase across the region, and backed southeasterly surface winds are forecast as a surface trough develops near higher terrain. There is indication that subtle impulses will eject across the region ahead of the main upper trough, leading to weak upper forcing and low level convergence along the surface trough. Stronger heating is likely this far east, and MLCAPE could climb to near 1000 J/kg with marginal low-to-mid level lapse rates forecast withing an adequately sheared environment. While conditional, any cells that develop could pose a risk for marginal hail/gusty winds. ...Lower Colorado Valley Vicinity... An upper low off the coast of southern CA will pivot eastward toward the Lower CO Valley on Thursday. Surface dewpoints near 60F will spread northward along the CA/AZ border beneath steep midlevel lapse rates. Low level shear will be weak, but effective shear will support some organized cells with strong flow expected in mid and upper levels. Instability will be limited, but a couple of strong cells are possible. If trends continue, probability may become warranted in later outlooks, mainly for a marginal hail risk. ..Leitman.. 03/11/2020 Link to comment Share on other sites More sharing options...
andyhb Posted March 11, 2020 Share Posted March 11, 2020 Definitely a few similarities with the setup that yielded the deadly TN tornadoes on 3/3. Strong westerly flow aloft with similar hodograph structure and I'm going to bet that the NAM/NAM 3 km are too cold at the surface. Any southerly component to the surface wind will yield large 0-1 km SRH when your 850 mb jet is 50 kts out of the WSW. 1 Link to comment Share on other sites More sharing options...
Indystorm Posted March 11, 2020 Share Posted March 11, 2020 I attended a sv wx spotter session last Sat. and asked the met about the TN tornadoes with dews only in the 50's and he said the stronger shear compensated for that. Concern for PAH and lower Ohio Valley area in particular for Thursday evening Mar. 12. Link to comment Share on other sites More sharing options...
CheeselandSkies Posted March 11, 2020 Share Posted March 11, 2020 1 hour ago, andyhb said: Definitely a few similarities with the setup that yielded the deadly TN tornadoes on 3/3. Strong westerly flow aloft with similar hodograph structure and I'm going to bet that the NAM/NAM 3 km are too cold at the surface. Any southerly component to the surface wind will yield large 0-1 km SRH when your 850 mb jet is 50 kts out of the WSW. 18Z HRRR sim ref/UH looks ugly for MO bootheel/southern IL/KY tomorrow, but we saw that have a tendency to overhype particularly with some of the OK setups last May. Of course, tomorrow will feature a rather different set of conditions than those did. Link to comment Share on other sites More sharing options...
Stebo Posted March 11, 2020 Share Posted March 11, 2020 2 hours ago, CheeselandSkies said: 18Z HRRR sim ref/UH looks ugly for MO bootheel/southern IL/KY tomorrow, but we saw that have a tendency to overhype particularly with some of the OK setups last May. Of course, tomorrow will feature a rather different set of conditions than those did. Yeah I think the Paducah area is in for it tomorrow. Another of these low amplitude waves with great speed shear and low level directional shear. Link to comment Share on other sites More sharing options...
Indystorm Posted March 12, 2020 Share Posted March 12, 2020 18z NAM for PAH area for late Thursday afternoon Link to comment Share on other sites More sharing options...
Jim Martin Posted March 12, 2020 Share Posted March 12, 2020 Could the risk for severe weather tomorrow be extended a bit further north than previously forecast? Link to comment Share on other sites More sharing options...
Chinook Posted March 12, 2020 Share Posted March 12, 2020 19 minutes ago, Jim Martin said: Could the risk for severe weather tomorrow be extended a bit further north than previously forecast? The 00z models are in the process of finishing up the forecasts for tomorrow. At this time, I don't think there's a need to extend the slight risk much north of Cincinnati OH. The 00z HRRR may be unrealistic about deep convection near Indianapolis. I'm not sure. Maybe elevated CAPE could produce some hail near Indianapolis. 1 Link to comment Share on other sites More sharing options...
Indystorm Posted March 12, 2020 Share Posted March 12, 2020 00z NAM coming in a smidgeon weaker for PAH area but still intense. I think it all depends on the strength of the WAA northward and the available near surface moisture. We still have strong shear, helicity, and jet. The fact that andyhb has chimed in on this concerns me since he is such a good svr wx met. Link to comment Share on other sites More sharing options...
andyhb Posted March 12, 2020 Share Posted March 12, 2020 6 hours ago, CheeselandSkies said: 18Z HRRR sim ref/UH looks ugly for MO bootheel/southern IL/KY tomorrow, but we saw that have a tendency to overhype particularly with some of the OK setups last May. Of course, tomorrow will feature a rather different set of conditions than those did. Why do you keep tagging me with the weenie emoji? Link to comment Share on other sites More sharing options...
Chinook Posted March 12, 2020 Share Posted March 12, 2020 Here's an interesting slightly new plot type from SPC HREF- Max and Min (highly negative) updraft helicity tracks. As has been discussed, there is a range of possibilities with supercells/ elevated supercells tomorrow. The SPC may move the risk area farther north into parts of Indiana. Link to comment Share on other sites More sharing options...
Indystorm Posted March 12, 2020 Share Posted March 12, 2020 Day one outlook is out from SPC. Enhanced risk for se MO, PAH environs, and east to Louisville and a 10% hatched tor. Link to comment Share on other sites More sharing options...
CheeselandSkies Posted March 12, 2020 Share Posted March 12, 2020 4 hours ago, andyhb said: Why do you keep tagging me with the weenie emoji? Because it's a severe event to weenie out over. Link to comment Share on other sites More sharing options...
cheese007 Posted March 12, 2020 Share Posted March 12, 2020 Watch just issued with high tor probs Link to comment Share on other sites More sharing options...
SmokeEater Posted March 12, 2020 Share Posted March 12, 2020 Tornado Watch out. High end too, probs 70/40. Sent from my SM-G973U using Tapatalk Link to comment Share on other sites More sharing options...
Indystorm Posted March 12, 2020 Share Posted March 12, 2020 As of 1:20 CDT most storms seem elevated in southern IL and west KY as the surface CAPE is along the Arkansas-TN northern border. Helicity up to 600 is found near St. Louis and slightly lower values into southern Illinois. If that higher surface CAPE continues to move northward to intersect the eastward moving high helicity values things should get very active. Numerous 3/4 inch hail reports in PAH area. Link to comment Share on other sites More sharing options...
Indystorm Posted March 12, 2020 Share Posted March 12, 2020 Mesoscale Discussion 0170 NWS Storm Prediction Center Norman OK 0128 PM CDT Thu Mar 12 2020 Areas affected...Southern IL...Far Southwest IN...Western KY...Far Southeast MO/MO Bootheel Concerning...Tornado Watch 46... Valid 121828Z - 122030Z The severe weather threat for Tornado Watch 46 continues. SUMMARY...The threat for damaging wind gusts and line-embedded tornadoes is expected to increase over the next few hours. DISCUSSION...Bowing segment moving across far southwest MO into southern IL has recently shown slightly improved linear structure. Striated velocity signatures from KLSX suggest this more linear structure is currently resulting from a bore elevated atop the stable surface layer and not surface-based outflow. However, as the cluster continues to move downstream, the air mass is expected to become increasingly supportive of surface-based convective, particularly once it moves into western KY. Low/mid-level wind fields will also increase as the jet max currently extending from northern AR into southern MO spreads eastward. Expectation is for the effective SRH to increase to over 400 m2/s2 ahead of the line over western KY by 20-21Z. As a result of these environmental changes, the threat for damaging wind gusts and/or line-embedded tornadoes is expected to increase. A more discrete storm also exists ahead of the line. More cellular nature of this storm and the improving downstream air mass suggests potential exists for this storm to develop into a mature supercell capable of producing damaging wind gusts and/or a tornado. Link to comment Share on other sites More sharing options...
Indystorm Posted March 12, 2020 Share Posted March 12, 2020 ..A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 300 PM CDT FOR POPE...NORTHEASTERN JOHNSON...WILLIAMSON...SALINE...SOUTHEASTERN FRANKLIN AND SOUTHERN HAMILTON COUNTIES... AT 224 PM CDT, SEVERE THUNDERSTORMS WERE LOCATED ALONG A LINE EXTENDING FROM NEAR WEST FRANKFORT TO NEAR CRAINVILLE, MOVING SOUTHEAST AT 45 MPH. HAZARD...TWO INCH HAIL AND 60 MPH WIND GUSTS. SOURCE...TRAINED WEATHER SPOTTERS. WIND DRIVEN 2 INCH HAIL WAS REPORTED ALONG I-57 SOUTH OF WEST FRANKFORT. IMPACT...PEOPLE AND ANIMALS OUTDOORS WILL BE INJURED. EXPECT HAIL DAMAGE TO ROOFS, SIDING, WINDOWS, AND VEHICLES. EXPECT WIND DAMAGE TO ROOFS, SIDING, AND TREES. LOCATIONS IMPACTED INCLUDE... MARION, HARRISBURG, ELDORADO, JOHNSTON CITY, GALATIA, GOLCONDA, PITTSBURG, CREAL SPRINGS, THOMPSONVILLE, LAKE OF EGYPT AREA, CARRIER MILLS, RALEIGH, HANAFORD, STONEFORT, WHITEASH, WILLIAMSON COUNTY REGIONAL AIRPORT, NEW BURNSIDE, SPILLERTOWN, BROUGHTON AND EDDYVILLE. Link to comment Share on other sites More sharing options...
Indystorm Posted March 12, 2020 Share Posted March 12, 2020 Mesoscale Discussion 0171 NWS Storm Prediction Center Norman OK 0231 PM CDT Thu Mar 12 2020 Areas affected...Portions of southeast MO and northern AR Concerning...Severe potential...Tornado Watch likely Valid 121931Z - 122100Z Probability of Watch Issuance...80 percent SUMMARY...Thunderstorms are expected to develop over the area and will be capable of severe hail, damaging winds, and a few tornadoes. A Tornado Watch is likely in the next 1-2 hours. DISCUSSION...Strong forcing for ascent associated with a mid-level speed max and a cold front will contribute to thunderstorm development over the MCD area in the next 1-2 hours. Storms are expected to develop first over southeast MO, then southwestward along/ahead of the cold front into northern AR. The airmass over southeast MO has been slow to destabilize because of abundant clouds, but temperatures warming into the mid 60s to low 70s near the AR/MO border will quickly advect northward to near Farmington prior to storms developing. Steep mid-level lapse rates of 8.5 C/km sampled by the 18z SGF sounding, dewpoints in the low 60s, and continued heating will contribute to a corridor of 1000-1500 MLCAPE along/ahead of the front. Supercell modes will be supported by effective shear magnitudes of 50-60 kt, favorable angles between the deep-layer shear and the front, and storm speeds that will be fast enough to remain ahead of the front. Although surface winds have veered to south-southwesterly, storm motions forecast to be 270-290 deg and strong 850-700-mb wind speeds should still result in 0-1-km SRH of 200-300 m2/s2 over the area, contributing to some tornado potential in the evening. Given the steep lapse rates and 50-kt winds in the 850-700-mb layer, severe hail and damaging wind gusts are also possible. A tornado Watch is likely to be issued. Link to comment Share on other sites More sharing options...
Jackstraw Posted March 12, 2020 Share Posted March 12, 2020 Isolate supercells popping along the MO/AR border, they all are showing rotation and a couple TOR warned. Link to comment Share on other sites More sharing options...
Chinook Posted March 12, 2020 Share Posted March 12, 2020 There could be a TDS near Ash Flat, AR. It's kind of tough to say, with all radars being far away from that area. Link to comment Share on other sites More sharing options...
Jackstraw Posted March 12, 2020 Share Posted March 12, 2020 Storms becoming more cellular in central KY. Was a possible debris ball on CC on the one warned just N of Bowling Green but it's also showing a nasty hail core so don't know. Link to comment Share on other sites More sharing options...
mob1 Posted March 12, 2020 Share Posted March 12, 2020 PDS warning for the storm approaching Popular Bluff. Link to comment Share on other sites More sharing options...
Jackstraw Posted March 12, 2020 Share Posted March 12, 2020 I would think that cell approaching Bowling Green needs TOR warned. Nice hook, rotation and inflow notch on radar. Was warned 30 min ago Link to comment Share on other sites More sharing options...
Indystorm Posted March 12, 2020 Share Posted March 12, 2020 BULLETIN - EAS ACTIVATION REQUESTED TORNADO WARNING NATIONAL WEATHER SERVICE PADUCAH KY 536 PM CDT THU MAR 12 2020 THE NATIONAL WEATHER SERVICE IN PADUCAH HAS ISSUED A * TORNADO WARNING FOR... CENTRAL BUTLER COUNTY IN SOUTHEASTERN MISSOURI... * UNTIL 615 PM CDT. * AT 536 PM CDT, A CONFIRMED LARGE AND EXTREMELY DANGEROUS TORNADO WAS LOCATED NEAR POPLAR BLUFF, MOVING EAST AT 50 MPH. THIS IS A PARTICULARLY DANGEROUS SITUATION. TAKE COVER NOW! HAZARD...DAMAGING TORNADO. SOURCE...LAW ENFORCEMENT CONFIRMED TORNADO. IMPACT...YOU ARE IN A LIFE-THREATENING SITUATION. FLYING DEBRIS MAY BE DEADLY TO THOSE CAUGHT WITHOUT SHELTER. MOBILE HOMES WILL BE DESTROYED. CONSIDERABLE DAMAGE TO HOMES, BUSINESSES, AND VEHICLES IS LIKELY AND COMPLETE DESTRUCTION IS POSSIBLE. Link to comment Share on other sites More sharing options...
WeatherMonger Posted March 13, 2020 Share Posted March 13, 2020 CPC still with a rather large severe area in the 8+ day range. SPC and WPC have nothing delineated in the 7-8 day range, SPC with predictability too low. New thing for CPC? Usually the delineate the SPC and WPC areas of notez but now they are going out on their own beyond warmer/colder than average. 1 Link to comment Share on other sites More sharing options...
Indystorm Posted March 17, 2020 Share Posted March 17, 2020 Thursday March 19 late afternoon and evening could be somewhat interesting across MO, IL. and IN per this evening's NAM. Had to look at something else beside Coronavirus news to restore my sanity. But we certainly don't need any type of svr wx anywhere with all these restrictions in place. And it is the first day of astronomical spring, one of the earliest dates on record on March 19. Link to comment Share on other sites More sharing options...
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