Chase Target for Thursday, August 19
Madison, SD
Timing and storm mode:
Storms will develop after 6 PM CDT, with supercell structures early in convective evolution. All modes of severe weather are possible before about 9 PM, including a tornado or two. Later in the evening, storms will evolve into one or more large complexes and track east though southern MN
Discussion:
By late afternoon, a shortwave trough will arrive in western MN. Models disagree on the details of this feature. At the surface, a diffuse warm front will develop along the SD/NE boarder. A temperature gradient will be enhanced somewhat by differential insolation due to high clouds over SD throughout the afternoon hours.
Capping should prevent surface-based convection until 00Z with a stout EML in place. H7 temperatures in excess of 12C south of I-90 will result in large amounts of CIN until after 00Z at which time cooling in association with the aforementioned trough overspreads the region. Once initiation finally takes place, strong shear parameters will couple with steep lapse rates to favor supercells with initial storm development. Deep layer shear should increase to 60 kts as the shortwave overspreads the area. Backing flow with enhanced hodograph curvatures should exist along and north of the warm front in southeastern SD, especially after 00Z when the southwesterly LLJ increases to 40 kts. The SPC SREF ensemble indicates a significant tornado parameter in excess of 4, suggesting the possibility of strong tornadoes with storms that remain discrete.
During the evening hours, storms will expand in coverage along and north of the warm front as the LLJ noses into the area. This MCS will track east across southern NM overnight, with heavy rainfall the primary hazard.
Bill Schintler
KD0DJG
www.twistertoursusa.com
1:13 PM CDT, 08/18/10
Chase Target for Saturday, July 17
Farming, MN (15 miles west of St. Cloud).
Timing and storm mode:
Storms should develop by 5 PM CDT, with storm motion towards the east at 20 mph. All modes of severe weather seem probable; including supercells, very large hail, and a tornado or two.
Discussion:
Another in a series of shortwaves embedded within a strong belt of westerlies will amplify over NRN MN on Saturday. Southerly flow will strengthen ahead of the system, with dewpoints increasing into the lower 70s by Saturday afternoon. Strong instability will develop along the eastern fringe of steep mid-level lapse rates in excess of 8C/km. Elevated storms should develop to the north and east of the WF by mid afternoon. Severe hail will be the primary threat with these storms.
Later, surface-based convection should initiate along the WF just E of the SFC low along the ERN fringe of an advancing CI shield. Capping will persist S and W along the advancing CF owing to strong mid-level WAA, limiting SRLY extent of convective development until the evening hours. H7 temperatures will increase to nearly 15C by late afternoon in SWRN MN and locations to the south. Convection will eventually fire along the CF in ERN NEB and WRN IA after 03Z as the CF surges eastward.
SFC-3km SRH will increase to AOA 300m2/s2 after 00Z as an increasingly veered LLJ strengthens to 40kts over backing LLVL flow along and N of the WF. Additionally, deep layer shear will increase between 00Z and 06Z as the compact H5 shortwave overspreads the region. LCLs will lower as the evening progresses, enhancing tornado probabilities. Storms will evolve into one or more severe MCS(s), which should track towards the SE as the LLJ strengthens overnight.
Chase Target for Sunday, June 13:
Coldwater, KS
Timing and storm mode:
Storms should develop by 5 PM CDT. Early in convective development, supercells and a tornado or two will be possible. By early evening, convection will evolve into a large storm complex and track through KS and northern OK.
Discussion:
The forecast is challenging, as location and timing of outflow boundaries are key to Sunday’s setup. Outflow and the approach of the upper low are expected to begin to push the front towards the southeast. Strong instability should exist with MLCAPEs of 2000-2500J/kg and surface-based LIs of -4 to -5C. Deep-layer shear will increase through the early evening hours as upper-low shifts slowly east. Tornado probabilities will remain modest given large dewpoint spreads in excess of 25F by late afternoon. The SPC SREF ensemble indicates a significant tornado index of 1 to 2 at 03Z. Overnight, storms should evolve into a large convective complex which will track east through KS and northern OK as a cold pool becomes established and the LLJ increases to 40 kts.
- Bill
8:51 PM CDT, 06/12/10
Chase Target for Saturday, May 29:
10 miles west of Mullen, Nebraska (60 miles north-northwest of North Platte).
10 miles west of Mullen, Nebraska (60 miles north-northwest of North Platte).
Timing and storm mode:
Storms will fire from north to south along an advancing cold front, with convection initiating in the target area between five and six PM CDT. Initial storm mode will be high-based supercells and discrete storms, with a transition into linear segments by early to mid-evening. Storm motion will be towards the northeast at 30 mph.
Synopsis:
Changes are on the way for the recent blocky synoptic pattern. A persistent ridge dominating the eastern CONUS will finally deamplify and shift to the east. Meanwhile, the last in a series of disturbances will eject from the western trough into the central and northern Plains. This will push a cold front east into the area, with storms firing north to south from the Canadian boarder into central Nebraska. Low pressure will organize over northeast Colorado, and a diffuse dry line will mix eastward into western Kansas and southwest Nebraska. Convection should remain inhibited areas south of I-80 due to a thermal ridge aloft.
Discussion:
Storms will fire along much of the cold front, and the chase target is at the southern extent of convective development, the “tail-end Charlie” storm. This is also near the triple point of the cold front and dry line and in a region of locally backing surface flow. The target area is also along the southern periphery of the strongest upper-level flow. SFC-6km deep-layer shear of 30 to 40 kts will be sufficient for storm organization. Strong capping will once again be the rule; however, convection is certain along the front in Nebraska due to strong forcing. The warm sector will remain largely cloud free save for some scattered CU. Along and west of the front, thick CI will reach the eastern Colorado boarder, to a Valentine, Nebraska line by 22Z; but this post-frontal cloud band will not inhibit insolation.
Once storms fire during the late afternoon hours, ample instability will be available for vigorous updrafts. Steep mid-level lapse rates in excess of 8.5 C/km and a 150mb deep well-mixed boundary layer with dewpoints approaching the mid-60’s will contribute to strong instability with as much as 3000 J/kg of MLCAPE. Discrete supercells are likely early in evolution, with an upscale evolution into a linear storm mode. Cloud bases will be relatively high, suggesting photogenic storms while limiting tornado potential.
- Bill
Chase Target for Thursday, May 27:
Jordon, MT (115 miles northeast of Billings).
Timing and storm mode:
Storms should initiate between 6 and 7 PM MDT. Storm motion will be towards the northeast at 20 mph. Supercell storms and a tornado or two is likely.
Synopsis:
The ERN CONUS ridge should amplify slightly over the next 24 hours, which will slow eastward progression of a WRN CONUS ULVL system. Upstream 00Z soundings (SLC, GJT, and RIW) indicate nearly dry-adiabatic mid-level lapse rates. The 00Z NAM has initialized slightly high with regard to SFC dewpoints, which were verifying in the low- to mid-50’s F in ECNTRL MT. MDLs do appear to have a handle on present convective trends in ERN MT.
Discussion:
A WF in ERN and NERN MT will provide the focus for a variety of severe WX Thursday afternoon. Capping will remain strong through 22Z, especially over the SERN portion of MT, owing to subtle H5 ridging and a ridge of 10C plus H7 temperatures. By late afternoon, however, large-scale assent increases as the exit region of a 60kt H5 streak ejects form the WRN CONUS trough and overspreads the area. H7 omegas locally increase to -6uB/s after 00Z. A band of AC cloudiness will edge eastward from CNTRL MT after 23Z. Virga from this cloud deck may cool mid-levels through evaporative cooling enough to aid in weakening of the cap. S of I-94 in SERN MT, diurnal convection should remain inhibited due to capping.
Once storms initiate, moderate to strong instability and shear will support a wide spectrum of severe WX. Steep mid-level lapse rates of 8-8.5 C/km and SFC dewpoints of 60-65 F will support SBCAPEs AOA 2000 J/kg. Deep-layer shear will increase to 40-50 kts with the approach of the aforementioned H5 streak. SFC-3km SRH AOA 200m2/s2 will exist along and N of the boundary as southerly H8 flow surges over easterly or northeasterly SFC flow. LLVL directional shear will slowly increase between 00Z and 03Z as the LLJ strengthens and shifts W into ERN MT. Storms will travel parallel to and along the boundary instead of crossing over to the cool side and becoming elevated as often occurs. Therefore, cells should continue to tap into moist BL air in an environment with large clockwise-curved hodographs and LCLs of 1000-1200m AGL.
- Bill
KD0DJG
www.twistertoursusa.com
9:34 PM CDT, 05/26/10
Chase Targets for Wednesday, May 26
South: Las Animas, CO (65 miles east of Pueblo).
North: Lindon, CO (80 miles east of Denver).
Timing and storm mode:
Isolated storms should initiate over the Front Range of southeastern Colorado by late morning, and then develop east into the target areas between 1 and 2 PM MDT. Primary storm mode will be multicell, however a few high-based supercells are possible, especially during the first few hours following initiation. Storms will track towards the east at 20 mph.
Discussion:
At the SFC, an OFB extended along an arc extending from Springfield to Rocky Ford to Limon in SERN CO at 05Z. Convection is ongoing along the NRN extent of this boundary. The SRN end of the boundary should stall out, and will be a focus for renewed convection on Wednesday. Modest shear parameters will exist over much of ERN CO; however, orographic features and the OFB may locally enhance hodograph curvatures. Additionally, MDLs indicate a compact H5 shortwave well E of the primary WRN CONUS long wave trough. SFC-6km shear locally in excess of 40 kts by 21Z will be juxtaposed with a helicity bulls-eye and moderate MLCAPEs. Regarding the north target, winds should back in response to a Denver cyclone.
AMS recovery is a concern with SFC dewpoints currently AOB 50 F in much of ERN CO except the far SE where the 04Z Springfield observation was 62/60. 00Z soundings and UA analysis indicates a developing LLJ with a region of 16C H85 dewpoints surging N towards the area from the SRN TX Panhandle. Dewpoints should slowly increase with time. Additionally, the elevation of the target area is 4000ft, and lower dewpoints are necessary for sufficient instability then at sea level. Capping will be weak, with convective temperatures generally between 70-75F in SERN CO. Convection should initiate along the ERN Front Range by late morning with the approach of the aforementioned shortwave. By early afternoon, storms will develop east into the Foothills.
- Bill
Chase Target for Monday, May 24:
20 miles south of North Platte, NE
Storms will initiate between 2 and 3 PM and track towards the north-northeast at 35-40 mph into the Sand Hills region, where the road network is generally poor. Supercells will be likely early in storm evolution, with a transition to a linear squall line after 6 PM.
Synopsis:
UA analysis indicates a couple of closed circulations with attendant cold temperatures aloft embedded within a broad, positively-tilted WRN CONUS trough. The first ULVL low is located over SRN CA and NV, while an upstream circulation is tracking S out of WA. Associated with the SRN CA system was a 12-hr H5 height fall of 70 m bulls-eye over extreme SRN CA, suggesting that the trough will continue to dig and become negatively-tilted through 00Z, 05/24. At the SFC, low pressure is centered over WCNRTL CO, with associated pressure falls centered over SERN WY. A nearly stationary front extends E and then NE, bisecting both NEB and MN from SW to NE. A DL extends from ECNTRL CO across extreme ERN NM.
Discussion:
A large area of convection will be ongoing over much of ND and SRN SD N of I-90 during the morning hours. This WAA precipitation will lift N of the area by early afternoon. A DL will sharpen in extreme WRN NE, KS, and the panhandles; with dewpoints generally in the low-60’s E of this feature. Low pressure will track from the Black Hills area into SWRN ND between 21Z and 00Z, while a secondary wave organizes along the KS/NEB border along the DL. SC will cover most of the warm sector; however, breaks in the cloudiness will allow for sufficient insolation during the afternoon hours. Capping is weak, storms should quickly develop by mid-afternoon.
Renewed convection should initiate first over NWRN NEB and the Black Hills between 18 and 19Z as H7 temperatures cool several degrees with the approach of the ULVL system. Further S, convection will fire along a DL bulge in SWRN NEB as the RRQ of the 80kt H5 streak overspreads the area and H7 omegas increase to -10ub/s .
Moderate instability will couple with impressive shear parameters, supporting a full spectrum of severe WX. MLCAPEs should increase to 2000J/kg along a narrow axis immediately E of the DL. Bulk shear will increase to 60 kts as the mid-level streak approaches. Additionally, hodograph curvatures will be maximized N of the secondary low/DL bulge in SWRN NEB. MDL soundings at North Platte indicate an increasing clockwise hodograph curve between 21Z and 00Z, with SFC-3km SRH AOA 300m2/s2 by early evening.
- Bill
KD0DJG
www.twistertoursusa.com
12:10 AM CDT, 05/24/10
Chase Target for Monday, May 10
Enid, OK
Timing and storm mode:
Supercell storms should develop along a dryline after 4 PM CDT. All modes of severe weather is likely, including tornadoes. Storm motion will be at least 30 mph towards the northeast during initiation, and increasing to 50 mph or more by early evening.
Discussion:
A transition to an increasingly amplified jet stream will take place over the next 72 hours as a series of disturbances embedded within this flow eject from the trough base into the Plains. On Monday, a lead 100kt H5 streak will overspread the panhandles and then OK. At 00Z, a 100m H5 12hr height drop was centered over SRN CA. Looking ahead, another potent shortwave will pivot through the trough Wednesday, with the system transitioning from neutral to negatively tilted. At the SFC, low-pressure over WCNTRL KS will track slowly towards the east Monday. A synoptic WF will extend ESE of this feature. One or more mesoscale outflow boundaries will likely exist S of the main WF because of the departing MCS. Timing and location of this convection is key to the degree of AMS recovery in the target area, especially towards the N in KS. A DL will mix rapidly EWD and sharpen during the afternoon, reaching I-35 in NCNTRL OK shortly after 00Z.
Moisture return is a concern, with H85 dewpoints AOA 16C currently confined to SRN TX, however strong NWD moisture transport will take place between 06 and 12Z as the LLJ increases to 60 kts. OUN and FWD soundings both indicate increasing moisture in the H8-H9 layer. The 00Z NAM has initialized well to SFC and H85 moisture in this area. Elevated convection will increase overnight over much of OK at the nose of the strengthening LLJ. This precipitation will lift NE of the area during the morning; however, with SC lingering into early afternoon. Low cloudiness should erode from W to E by 21Z, allowing for moderate to strong insolation. Upstream 00Z soundings (AMA, EPZ, ABQ, and TUS) all indicate nearly dry-adiabatic mid-level. lapse rates. Differential advection of this EML with moisture from the S will result in strong instability with MLCAPE’s increasing to 2000J/kg along a narrow axis immediately E of the DL.
Once storms initiate, this instability coupled with impressive shear parameters and low cloud base heights will be supportive of a full spectrum of severe WX, including supercells and tornadoes. SFC-H7 shear vectors in excess of 50 kts, nearly perpendicular to the DL, will promote a discrete storm mode. LCL levels AOB are also indicated E of the DL. Extremely rapid storm motion is expected, with storm speeds increasing to more then 50 Kts as the ULVL streak approaches.
- Bill
Timing and storm mode: