Chase Discussion for 2007-05-05 Chase Discussion for May 5, 2007. Valid: 05/04/2007. Target Area: Elk City/Sayre Departure Time: 14:00 CDT Current Risk Area: Moderate Discussion: 00z NAM brings back some major deja vu for Saturday, reference the 23rd/24th. First, a lone supercell developed in the Texas panhandle this evening and moved into Northwest Oklahoma. This storm split a few times and produced at least two tornadoes. Very similar to what happened on April 23rd, other than those storms developed in Oklahoma. Now, the 00z NAM wants to develop a squall line along the dryline Saturday morning and move it across the region. It fails to develop convection behind this line tomorrow afternoon/evening. This continues to complicate matters given prior issues this year. I'm a big on model trends and this is one I don't like, because it would greatly reduce the threat tomorrow. I'm not completely sold on this solution for a few reasons: 1) no energy moving across the dryline to light it up from Kansas to Mexico, which the NAM does and 2) the 00z NAM under initialized 700mb temps. If this is carried through to later forecasts, then it may explain how the NAM can develop a 600 mile long squall line with seemingly little support. It should be noted that the cap strength is much stronger than the 24th. Midland sounding had 12C 700mb temps at 00z, that air is moving this way. Point sounding for Clinton yields something I wouldn't expect given NAM precip fields, it does not saturate the environment. Another consideration is that the NAM has 0.01 to 0.10 QPF, any thing that develops will produce much more than 0.10. Therefore, I'm (at the risk of insanity) going to use my prior reasoning from 1.5 weeks ago. I think the NAM is struggling with the deep layer tropical moisture and is convinced there has to be convection. It appears that once the convective parameterization turns on, it goes to town all the way to Mexico. Long story short, we're still in the wait and see mode. The forecast sounding for tomorrow afternoon at Clinton is impressive with CAPE values around 4500 J/Kg and ML CAPE 3500 J/Kg. LI -6, EHI 5.5, supercell potential 77%. Some of these numbers are likely to change, but look pretty impressive at this point. The chase is still scheduled and we'll see what happens in the morning. I am happy that as 10pm approaches, all is quiet in western OK/TX. Severe Weather Discussion 2007-9-4 Severe Weather Discussion for May 5 - 7, 2007. Valid: 05/05/2007. *Significant Severe Weather Event Today* Highlights: - Outbreak of tornadoes and severe thunderstorms appears likely today, especially in Kansas and Nebraska. Across western Oklahoma activity should be more isolated, but still very intense. Primary threats with any activity will be strong tornadoes, destructive hail, and damaging winds. - Active severe weather day is possible on Sunday from central Texas into Kansas. - Severe thunderstorms are possible in central Texas on Monday. Discussion: Little time for a discussion today as my main focus has been on the developing weather situation for today. SPC has a PDS tornado watch up for northern KS/southern Nebraska and this is certainly a good idea. The high risk is also well placed. The threat for Oklahoma is conditional once again today. The atmosphere is in a very similar condition today as yesterday. This means that CAPE values will again approach 5000 J/Kg with LIs to -10. This extreme instability, when combined with decent speed/directional shear will allow any storm that develops to rapidly form into a supercell. The main question is IF storms will develop and then how many. My thinking is that two, maybe three storms will form in western Oklahoma later today. OUN has a moderate risk for much of northwest Oklahoma and this looks good. I think it should come farther south, but not gonna worry about it. Storms should move northeast through the region tonight as the dryline retreats to the west. Storms may form late tonight on the dryline as a shortwave trof impinges on this feature and the very unstable atmosphere. Even though temperatures will be at min values for the day, CAPE values should still be 3500 J/Kg, more than enough for intense activity. Question again is IF storms can develop. Sunday has huge potential if there isn't widespread overnight convection. Models are worthless here as none of them have the current environment correct. Conditions will be similar with the dryline farther east into Oklahoma. A chase is possible on Sunday, depending on what happens today. Monday looks to be in central Texas and SPC Day 3 seems to have a good handle on it. A heavy rain event appears possible across parts of the region, but model disagreement makes that tough to forecast. Both Day 1 and 2 risk areas are very conditional on activity in the morning and the prior evening. Probabilities: Risk area for any part of OK/TX (valid: 05/06 Day 1, Day 2): Slight: 100%, 100% Moderate: 75%, 35% High: 5%, 0% Chase Status: Level 4 - Heading to Arnett at 13:00. Severe Weather Discussion 2007-9-3 Severe Weather Discussion for May 4 - 8, 2007. Valid: 05/04/2007. Highlights: - Active severe weather day is likely in western KS into NW OK/SW Nebraska. Destructive hail and tornadoes are the main threats. Isolated severe thunderstorms are possible farther south into Oklahoma and the TX/OK panhandles; however, this threat is conditional. - Active severe weather day is expected on Saturday, this is a potentially dangerous weather situation with numerous supercell thunderstorms expected across Nebraska, Kansas, and Oklahoma. - Severe thunderstorms are possible Sunday - Tuesday across much of the region. It remains difficult to isolate a particular day or location that has higher potential than the other days. Forecast details are quite muddied by expected activity today and tomorrow. - Chase Status is increased to Level 3. Discussion: Very exciting and potentially significant severe weather situation is developing for the region today through the weekend. First off, I know better than to not trust my forecasting skills. I had today nailed a few day ago. Such as it is, we're all on board at this point. 12z NAM/GFS runs continue prior trends of developing extreme instability across the region today with CAPE values above 4000 J/Kg expected. The dryline is located along the TX/OK border at 17:40z per the Oklahoma Mesonet. 17z CAPE values are 2500 J/Kg and higher across the region and this should increase during the day. LIs are -5 to -8 with dewpoints in the mid/upper 60s. Storm initiation remains iffy today due to a strong cap across the region. CIN values are 25 J/Kg and higher with near 100 J/Kg along the dryline. The strongest surface heating is occurring away from the dryline ATTM. As the day progresses, the convective inhabitation along the dryline should decrease and the question becomes can storms develop. Little in the way of upper support will be available in this area, so it is a tough call. Additionally, the cap should strengthen today with the NAM showing 10C 700mb temperatures at 00z in NW Texas. OUN is doing a 19z sounding to assess cap strength and thermodynamics. Wind fields aloft are more than favorable for supercell thunderstorms should any develop. Storms will remain discrete and likely produce high-end severe weather across western OK. More numerous activity may occur in Kansas and Colorado up to Nebraska. SPC Day 1 has this will covered. Elevated thunderstorms are possible tonight across parts of the region as 40-60kt low-level jet develops. How widespread and intense will how an impact on Saturday. Many of us forecasters are still licking our wounds from the 24th. The new Day 2 is somewhat of a disappointment and I'll say I disagree with it. The moderate risk should cover into northwest Texas, why Goss pulled it north to I-40 is very odd. There is little new model data that argues changing the risk area. Additionally, I'm not sure what he's looking at regarding meridional flow. I do agree that mid-level and especially upper-level flow will be more backed than usual, but I don't see anything limiting rotation potential. In fact the 12z NAM helicity values are much higher than I typically expect from this model. 12z GS has 3500 J/Kg CAPE along the dryline Saturday afternoon and this looks good. NAM instability is a little off mainly due to it tracking a supercell east across southern Oklahoma tonight into tomorrow. I'm not saying it won't happen, just saying I'm not convinced of it. And, that it will have that big of an affect on the thermodynamics. As with last week, if storms develop in the morning, it will greatly reduce the severe weather threat. Models are not as aggressive with widespread activity as they did last week and this would make sense given the location of the upper system, as compared to the system last week that was lifting northeast into the region in the morning. Another note about Day 2, there is meridional flow in KS/Nebraska but I see little impact here. The best winds are in NW OK, but the extreme instability farther south should compensate for marginally reduced wind fields. There isn't that big of a difference. My chase location is Sayre/Elk City area right now. I like the north-south options and this allows coverage in both quadrants. This is not a tail-end Charlie day or to avoid such, T/Td spreads will be quite low along with LFC's and LCL's. If the atmosphere is not worked over today, there should be plenty of thermodynamics for widespread severe thunderstorms (supercells) Saturday afternoon. Another consideration for a southern location is potential for anvil seeding. Given 300-200mb flow less than 60kts across much of the area, this could be a problem. The southern storms however should not have that issue. Sunday is technically within the forecast range, but very tough at this point. 12z GFS/NAM agree that a large chunk of the upper system will have lifted out by Sunday afternoon. Wind fields will remain favorable for severe thunderstorms. The question remains how unstable can the atmosphere get. SPC has a slight risk up and this looks good. The threat looks to shift to eastern Oklahoma and points east on Monday. It does not look like a moderate or high-end day, more on the high side of a slight risk. I'll put probabilities in for it at this point given the potential. Tomorrow is one of those almost classic outbreak days. Whether or not SPC does a high risk will depend on forecaster bias and especially if convection occurs in the morning. I'm going with 50% mainly due to the latter issue, otherwise I'd give it a 75% rating. Probabilities: Risk area for any part of OK/TX (Valid: 05/05 Day 1, Day 2, Day 3): Slight: 100%, 100%, 75% Moderate: 100%, 50%, 0% High: 50%, 0%, N/A Chase Status: Level 3 - Looking to go Saturday, location Elk City/Sayre, target time 13:30 CDT. Severe Weather Discussion 2007-9-2 Severe Weather Discussion for May 4 - 8, 2007. Valid: 05/03/2007. Highlights: - Severe thunderstorms are possible in western Oklahoma on Friday, but confidence is low. - Active severe weather day is expected across western Oklahoma into the Texas/OK Panhandles on Saturday. - Severe thunderstorms are possible each day through Tuesday, at this time confidence is too low to pick a day that has more potentially than any other. - Chase Status increased to Level 2. Discussion: Little change to thinking from Tuesday. Evolution of the weather situation for this weekend into next week is very complex due to the presence of a closed/cutoff low in the SW U.S. and a 582dm ridge in the eastern U.S. Said low should hang around for several days, potentially moving northeast around Tuesday. 00z ECMWF is a little different than the GFS on how this system will evolve and makes the forecast rather frustrating. On Friday, models remain consistent on developing high instability values across the region as mid 60s dewpoints are in-place. Current indications are that CAPE values will be 3000 - 4000 J/Kg along the dryline Friday afternoon. Mid-level winds will be favorable for severe thunderstorms, however a strong cap will be in-place across the region. The dryline should be slightly east of the TX/OK border. Models show little QPF Friday afternoon, but I wouldn't be surprised if one storm developed. Anything that does go will be severe. Saturday looks very interesting with improving wind fields across the area and high instability. NAM CAPE values are again reduced in favor of the GFS. Not saying it can't happen, but I'm not biting on 5500 J/Kg CAPE. GFS is around 3500 J/Kg and this looks good to me. Both models develop QPF on Saturday and it looks like a wild day across the region. As such, the Chase Status is increased to Level 2. Beyond Saturday there is just too much model disagreement on the evolution of this system. NAM has more veered winds aloft than the other models, which would seem to provide a decent severe threat for the region again on Sunday. The downside is this same model develops lots of QPF over the area during the day Sunday. Tough call on it and not sure how much rainfall will occur given what should be a strong cap. Either way, the next week seems to continue an active severe weather season for the region. Question is, will Oklahoma finally get in on the action... SPC already has a slight risk up for KS/NE tomorrow and this looks good. They may extend it down into TX/OK, but the threat is rather conditional. The Day 2 for Saturday should get a moderate for the eastern half of the panhandles into western Oklahoma and northward to Nebraska. Some part of that area may get a higher risk depending on the ultimate evolution of this event. I'd like to see 250/200mb wind speeds higher, but can't get everything. That may be a limiting factor on the risk area. Probabilities: Risk area for any part OK/TX (valid: 05/04 Day 1, Day 2, Day 3): Slight: 30%, 100%, 100% Moderate: 0%, 75% 25% High: 0%, 0%, N/A Chase Status: Level 2 - Watching Saturday Severe Weather Discussion 2007-9-1 Severe Weather Discussion for May 4 - 8, 2007. Valid: 05/01/2007. Highlights: - Severe Thunderstorms are possible across parts of western Oklahoma into Kansas on Friday. - Severe Thunderstorms are possible across the Texas/Oklahoma panhandles northward into CO/KS on Saturday. - Isolated severe thunderstorms are possible across Texas/Oklahoma panhandles northward into Nebraska on Sunday and Monday. Discussion: Active and low-confidence weather situation appears to be developing for parts of the region later this week. The activity appears to be confined mainly to the western part of the region. However, combination of high instability values and upper system to the west yields potential for at least one medium-end event. Models continue to be at odds on how this will evolve, but I'm seeing better agreement on the general features. Friday is the first day on this set-up and is rather subtle. I have to wonder if I'm grasping here given the lack of interest by NWS offices on anything this day. 12z NAM/GFS create a rather large warm sector across KS/OK/TX on Friday. The dryline looks to be in western Oklahoma during the afternoon, this location also fits with the 00z ECMWF. Low/mid level winds will be on the weak side but will turn with height. And, progged instability would seemingly be sufficient for organized severe thunderstorms. Issue then becomes, can storms develop. GFS develops one storm near Enid while the NAM is dry. Given GFS CIN values around 30 J/Kg at peak heating in central/southern Oklahoma this would make sense. For now it is something to monitor. I'm not crazy enough to jump on the NAM's 5500 J/Kg CAPE prog...I'm going to put that in the "we'll see" drawer. Saturday looks quite interesting for the Texas/Oklahoma panhandles, assuming the models don't shift things again. Dryline should surge west late Friday into Saturday as a surface low redevelops in Colorado. Tropical moisture should spread west to the I-27 area during the day. Models differ on QPF with the GFS near the Caprock. Not sure about that prog, especially given model dryline bias issues. However, CAPE values should be around 3000 J/Kg with LIs to -8. Wind fields are starting to back at 850/700mb during this time period as western U.S. closed low cuts off from the northern jet and settles in over the SW U.S. 0-1km shear looks weak but 0-3km and 0-6km shear look decent. Mesoscale events can compensate for these issues. It is certainly something to watch. By Sunday the winds are strongly backed and unidirectional across this area. While I can't rule anything out, would not expect much more than low-end type severe weather. 12z GFS is at odds with the 00z ECMWF on when the SW U.S. cutoff low will eject northeast. If the 12z GFS verifies, then the severe threat will translate east on Monday, otherwise Monday will be more like Sunday for western areas. I'm still not sure what to think about Friday, so I'll throw a token 50% in for a slight risk. Probabilities: Risk area for any part of OK/TX (valid: 05/02 Day 3): - Slight: 50% - Moderate: 0% - High: N/A Chase Status: Level 1 - Normal