Archive for the ‘Storm Chase Forecasts’ Category

Forecast for March 23, 2009

March 22, 2009

Forecast Made: March 23, 2009 – 5 Z

Target for Possible Tornadoes: Bassett, NE

Target for Severe Weather in General: Wichita, KS

Initiation Time: Early Afternoon across Nebraska, with initiation in Kansas between 3 and 5pm. Initiation across Oklahoma in the 5 to 7pm timeframe.

Discussion: This appears to be the first major Plains severe weather event of the season. As is typical of March severe weather setups, fantastic dynamics (mainly NE/KS) will be tempered by less than stellar thermodynamics. Usually when this occurs, the best place to chase from a tornado-viewing standpoint is near the upper-level low pressure center. North central Nebraska and possibly southern South Dakota offer the best combination of the cold air aloft and marginal dewpoints in the low to middle 50’s. Low topped supercell development looks possible in this area given the intense wind field associated with the low. A few tornadoes and large hail appear to be the main threat here. Further south, in Kansas, the dynamics still appear to be pretty good. However, the further south you go, the more the winds take on a unidirectional nature. This suggests any discrete supercell development in southern Kansas or northern Oklahoma will probably be short-lived. Better moisture values could allow CAPE’s to reach ~1000-1250 by late afternoon, which would be on the low end of what is needed to sustain an updraft given the amount of shear. Across southwestern Oklahoma and northwest Texas, where the best moisture exists, mid-level capping should hold off storm development until late in the day. However, by 19-23Z, the dryline and cold front are expected to be advancing quickly towards the east. This could maximize surface convergence for storm initiation, while unidirectional flow would suggest any storms that do develop will quickly become linear. Areas across the Rolling Plains and Big Country of Texas will see an isolated shot of a supercell or two along the sharpening dryline, as the forcing from the cold front will not arrive until after sunset. However, the cap in this area will be quite strong, so the likely scenario would only include storms after sunset as the cold front advances.

Conclusion: I suppose the first ‘big-looking’ severe weather event every year is well hyped, but in my opinion this one is being way over-hyped. I have been on many early Spring chases with low moisture / high dynamic events that have not turned out well. Overall, any tornado threat will be rather isolated / short lived because of the lack of low level moisture. Hail appears to be the main threat, with high winds becoming more of an issue across southern Kansas / OK / TX with the possible formation of a squall line.

Forecast for April 9, 2008

April 8, 2008

Forecast Made: April 8, 2008 – 20Z

Target: Roby, TX

Initiation Time: Showers/non-severe thunderstorms will likely be ongoing across the area Wednesday morning in advance of the warm front. Severe weather becomes more likely between 20-23Z near target area.

Discussion: The big question 36 hours out is how models are resolving a warm front that will move northward across west central Texas during the morning/early afternoon hours on Wednesday. Models have been in better agreement in recent runs that the front will be near the I-20 corridor by 12Z Wednesday. However, early morning drizzle/showers north of this front may slow the progression northward during the morning hours. Both the NAM and GFS are in reasonable agreement that a well defined triple point will set up early Wednesday afternoon near or just south of the Lubbock area. Initial storms should develop along this dryline by mid-afternoon. Primary threats initially with these supercells will include large hail, and possible some gusty winds. The tornado threat along/near the warm front will increase by about 0Z Thursday, as all models indicate 60 degree plus dewpoints pooling along the warm front. In addition, 0-3 km storm-relative helicity values ~500 m^2/s^-2 suggest that a couple of strong tornadoes may form after 0Z north of the Abilene area. Eventual loss of daytime heating will likely be overcome by stronger dynamics entering west Texas. Therefore, initial discrete storms should form a severe MCS by late Wednesday evening / overnight into Thursday for OK/north TX. Another potential target area during the day is near Childress, TX, but uncertainty with respect to strength/movement of the warm front in the area precludes mentioning a tornadic threat at the current time.

Conclusion: Impressive dynamics and moderate instability suggest supercellular storms will occur across parts of Texas on Wednesday. I like the area around Roby, TX / Abilene, TX tomorrow afternoon and evening.