Friday, May 21, 2010

FCST: May 22, 2010 NE/SD

Initial Target: O'Neill, NE to Plankinton, SD (Based on a blend of the NAM-WRF, GFS, SREF and ECMWF)

Forecast Discussion: A trough is digging onto the west coast with severel shortwaves visible at the midlevels.  Several of these shortwaves will round the base of the trough and eject into the northern plains during the period.  One thing to note is the trough remains well west of the modest instability axis leaving any forcing to occur along the dryline Saturday afternoon and evening. 

Another concern is the EML forecasted to be strengthening over the target area throughout the day on Saturday.  Absent any large scale ascent this could be problematic for convection to initiate. However, the NAM is breaking precipitation out over south central SD and north central NE at 0Z/23, albeit it has been pushed further north from run to run.  Any storms that do form will quickly go severe and with a warm front in the area and the potential for outflow boundaries the tornado risk should be enhanced with the more robust supercells.

Another concern for this forecast period is the on-going thunderstorms over the high terrain of eastern Wyoming and the residual cloud cover. These parameters will need to be resolved with tomorrow mornings forecast and nowcasting throughout the morning on Saturday.



Areas of surface low pressure are forecasted to be over eastern Montana (992mb) and NE Colorado (1000mb) with a developing surface low (996mb) over central Nebraska Saturday afternoon and evening.  This developing surface low is forecasted to deepen by 0Z/23. 

A warm front will be draped southeastward from the developing central Nebraska low back across south central and southeastern Nebraska.  A dryline will be positioned along and south of the low pressure center from the central Dakota's into Kansas.  These areas of low pressure and attendant boundaries will interact with a very broad warm sector and will provide the focus for severe thunderstorm development from north central Kansas into the Dakota's Saturday afternoon and evening.






Warm air advection is currently on-going over the target area with deep gulf moisture being transported northward into the forecasted warm sector.  A very broad warm sector will develop from central Kansas all the way into the Dakota's tomorrow afternoon and evening.   Surface temperatures are forecasted to be in the upper 70's to low 80's across the target area.  Here is a look at current dewpoints and forecasted dewpoints over the target area (0Z/22):




Surface based CAPE is forecasted in the 3000 to 3500 J/kg range over the target area by the NAM-WRF and GFS.  There will be a moderate to strong cap over the target area most of the day with 700mb temps in the 12C-14C range.  Howevver, the NAM-WRF and GFS show the cap begining to erode between 18Z/22 and 0Z/23 over the target area with 700mb temps dropping to the 9C range as well.



Modest shear values are also present with bulk shear in the 40 to 50 kt range with shear vectors being perpindicualr to the dryline/boundary.  SRH and EHI values are maximized across the target area at 0Z/23.  Low level shear, 0-1km, is also appreciable for an attendant tornado threat with large, looping hodographs in the target area.




Thursday, May 20, 2010

Sedalia, MO tornado May 20, 2010


News Chopper 9 Pilot Johnny Rowlands live streamed tornadogenesis southwest of Sedalia, MO on May 20, 2010 at approximately 6:45 p.m.   http://www.kmbc.com/video/23626976/

Discussion:  A surface area of low pressure was passing near Kansas City, MO and an H7 upper level low was positioned just northwest of the surface low.  A cold front trailed back into southeastern Kansas and northeastern OK from the surface low with a boundary draped along and just south of the the I-70 corridor. 
 
A bit of sunshine this afternoon allowed temperatures to reach the upper 60's to lower 70's and dewpoints were in the low to mid 60's.  In addition, surface and upper level shear was maximized near the low pressure centers.

As thunderstorms formed, they encountered the boundary and storm relative helicities were enhanced allowing the atmosphere to reach the correct parameters for tornadic thunderstorms.  Once the thunderstorms crossed the boundary, they weakened considerably, thus eliminating the tornado threat.

In addition to the parameters already mentioned, cold air aloft at the 500mb level, crossed over the Johnson and Pettis County areas near the time of peak afternoon heating. 500mb temps were on the order of -13C to -14C. This has similar characteristics to a CC500L tornado event, but I am not versed well enough in this phenomenon to accurately discuss it. Jon Davies has a great paper, which I continue to read over and over, at this link for review: http://www.jondavies.net/DaviesWAF_coldcoretors_dec06.pdf.

SPC MesoAnalysis indicated 500 J/kg of CAPE and SRH 0-1 and 0-3 in the 150-200 m^2/s^2 range in the area of the tornadoes this afternoon.  The 0Z/21 SPC Mesoanalysis references are below:




Sunday, May 16, 2010

Tornado Warning Seneca, MO 5-16-10


Just finished a chase from my house.  Got a call from my family in Seneca, MO saying they were under a tornado warning.  When I opened GRlevel sure enough there was a tornado warning. BRV was showing a definite area of rotation just to the NE of Seneca moving SE at 20MPH.  My cousins could see a lowering but could not confirm if it was reaching the ground to the east of Seneca approx. 5 to 7 miles.  Was on the phone with 3 different people telling them the location of the possible tornado and hail core.  There were a few reports of hail but as I write this no reports of wall clouds or rotation on SN. GR never showed MESO's or TVS's which surprised me. By the time one of the chasers got to the area the storm had diminished considerably.  I laughed when my cousin said it was sad that they had to call KC to see what their weather was doing! ~ TB

Here are some screen shots from GRLevel3 I took during the "Chase".


 






Saturday, May 15, 2010

May 12, 2010 - OK Storm Chase summary

This was probably the most unexpected outcome of the day type chases, since when I woke I was not expecting to chase. It was 2 days after my big bust in Kansas so I really didn't have the confidence to chase. Around 4pm, I noticed storms had fired to my east and had some great looking updraft structures. I noticed it was a line, but that southern storm looked great visually. After contacting a couple people about the parameters and what the radar looks liked, I decided to leave work @ 5pm, get my equipment, and jet east on I-40. I got to Groom, TX, when the first storm went tornado warned. I thought we were going to miss the show, but the storm near Wellington was looking really good, both visually and on radar. That was our storm, the tail-end charlie. We got to Shamrock, and made a quick decision to dive south to Wellington, then back east to Magnum, then north to be in a decent position. But by the time we got to Wellington, the storm was pretty far away, at least another 30 miles. We got to Magnum, and the storm further east was going insane on radar, but I knew we were a good 30 miles from that storm. My hopes were diminishing. I decided to stay on the furthest south storm, and see what we could get out of it.

I called my buddy Corey Sloan for a quick nowcast and he gave me the good news that we were in some good dynamics. We kept traversing north and east to get ahead of the storm. We were 7 miles south of Elk City on SH-6 about 2 miles south from the SH-6/SH 152 intersection. We saw a clearing in the clouds to our NE, and saw the edge of a nice wall cloud. Just then what looked like a funnel became clear, but we were sure if it was just scud or not. Then we noticed a large dust cloud forming under it, right then I knew it was a tornado. I pulled over, and tried getting as many pics as I could. Unfortunately, the lighting was crap, and I tried getting my tripod set up, but that didn't help. I still managed to get a couple pics, and after adjusting the contrast, the tornado is very evident. I couldn't confirm it as a tornado, simply because we were far away and couldn't tell if it was just scud or if it was rotating. Finally after calling Norman NWS and David Drummond, I could confirm it as a tornado.


After grabbing some quick McD's in Elk City, we attempted to core punch a couple storm coming out of Hemphill County, TX. We travelled up US 283 to Crawford, OK, but by then the storms had weakened and only got dime sized hail. We called it a day, drove home, and arrived around 1am.

Total miles for this chase: ~366

Friday, May 7, 2010

FCST: May 10 KS,MO,OK,TX


UPDATED Sunday 10 a.m. CDT

The storm system is forecasted to eject faster now....this was a concern of mine when I made this forecast Friday night....I mentioned the target area may need to be adjusted 150 to 200 miles further east, and it has materialized.  The atmosphere is poised for a significant weather event Monday afternoon and evening.  Instability and shear profiles create the potential for a very violent environment across the target area.  The Storm Prediction Center has this area highlighted for a moderate risk on their SWODY2 outlook.  Overnight convection and the ability of the atmosphere to recover will be the key to how violent the storms are Monday afternoon and evening. 

I will update my target location tonight and/or tomorrow on the blog as well as www.stormchaselive.com.


Initial Target Location: Wichita, KS to Muskogee, OK (Additional adjustments will be made as we get closer to the event)  In addition, there appears to be a secondary target shaping up, at least early, from Hays, KS to the NW.

Forecast Discussion: This forecast is based on a blend of the NAM-WRF, GFS, SREF, and ECMWF.


A strong storm system is poised to take aim on the southern and high plains beginning late Sunday and into Monday evening. There will be a marginal/conditional threat for elevated severe thunderstorms Sunday evening across the target area, with large hail the main threat. Overnight convection and any remnant outflow boundaries will need to be nowcasted during the Monday morning forecast. 

The negatively tilted trough will eject into the plains on Monday and the associated areas of low pressure will bring the potential for a significant severe weather event across the southern and high plains during the Monday afternoon and evening time frame.  A strong thermodynamic and kinematic environment will be in place for a few significant, long track tornadoes accompanied by very large hail.  Here is a look at the significant tornado parameter values greater than 5 as progged by the SREF at 0Z/11:



A 100kt jet stream is forecasted over the area with a 90kt jet streak embedded in the flow.  This jet streak is forecasted to be nosing into south central and southeast KS at 0Z/11.  The right entrance region of the jet streak appears to be over north central OK and the left exit region looks to be over southeast KS at 0Z/11.  This strong, upper level flow will create significant divergence aloft and convergance at the surface which will aid in storm growth, maturity, and duration.


A strong mid level shortwave, at the 500mb level, is forecasted to be quickly ejecting into the plains overnight Sunday and into the afternoon hours on Monday.  This mid-level disturbance, accompanied by 70 to 80kt SWLY 500mb winds, will be the triggering mechanism for potentially violent weather across the plains states.  This disturbance is forecasted to be over SC KS by 0Z/11.





A strong southerly flow at the surface and low level jet at 850mb, of 40 to 50 kts, will provide an efficient WAA regime to pump rich Gulf moisture into the region during the day on Monday.  Surface and 925mb dewpoints are forecasted to be in the low to mid 60's across the target area by Monday afternoon, with some progs showing lower 70's in south central KS ahead of the dryline.   Moisture depth and quality are indeed not an issue with this setup!







This southerly flow will continue during the day on Monday and continue to provide a very moist and significantly unstable airmass across the region.  SBCAPE values approaching 3000 J/KG and MUCAPE values over 3500 J/kg in the warm sector. 







SREF CAPE values over 2000 J/kg at 0Z/11:



There is moderate capping inversion, which has lessened on the last few model runs, in the target area at the H85 and H8 layer, along with H7 temps in the 5C to 8C range. The CAP may now be in the favor of more discrete supercells during the event.  Nonetheless, I belive the forcing and convergence along the dryline and warm front, along with the convective temperature being realized will quickly erode the CAP and rapid thunderstorm development will occur with the storms quickly becoming supercellular/tornadic.







At the surface a strong and deepening area of low pressure, on the order of 992mb, is forecasted to be in central KS at 0Z/11. This area of low pressure will quickly progress to the east/northeast overnight.  A warm front is forecasted to be draped from south central KS into central Oklahoma putting the target area in the warm sector by Monday afternoon, albeit a very small warm sector.  While a dryline will be setting up from south central KS to the Red River Valley.



Here is a quick look at the surface feature locations from the NAM-WRF, GFS, UKMET and ECMWF for timing comparisons.  The UKMET is indeed the outlier on these models runs.










Surface temperature are forecasted to be in the upper 70's to lower 80's. Surface winds are out of the south/southeast and backed in the target area at 20+ kts.  This warm front and dryline will be the focusing mechnsism for severe thunderstorms, some potentially tornadic, during the Monday afternoon and evening time frame.





The GFS and NAM-WRF are showing a THETA-E ridge nosing into SE KS at 0Z/11.





Storms will fire north and east of the warm front , near the triple point, as well east of the dryline late Monday afternoon into the evening hours.  The strong forcing and low level wind shear, overall bulk shear of 60 to 70kts and shear vectors perpindicular the boundaries, should not allow the atmosphere to decouple and keep the storms surface based well after dark.  This indicates the tornado threat may well extend into the overnight hours across the target area before the atmosphere decouples. 

Storm motions could be an issue with forecasted motions being in the 35 to 40kt range:



In addition, midlevel lapse rates on the order of 8C to 9C will promote a large hail threat, with some hail stones being fairly substantial.

Helicity values are very high, with most models forecasting, over 300+ m2/s2 0-1 and 0-3km Helicity values over much of the warm sector Monday afternoon.  EHI values are forecasted to be 4+ in the target area, some model progs are putting EHI's in the low teens.  These shear values/upper air dynamics have the models progs producing long, curved hodographs with added SRH's along the attendant warm front in the target area.  Here are the 36 hour NAM-WRF forecasted soundings from Bartlesville, OK and Wichita, KS: