Brett Roberts
EF5
The significant western CONUS longwave trough that is forecast to drop into the Pac NW tomorrow and Thursday should continue digging into S CA on Friday, setting the stage for a possible day-before-the-day opportunity somewhere in the southern Plains. Important timing differences still exist between the medium-range models, but I figure we're only three days away and the ceiling of potential is high enough to warrant a thread.
Tonight's 05/00z GFS offers the most progressive -- and perhaps most appealing -- scenario, with the 500 mb low centered roughly over Death Valley by Friday evening. While this idea is generally supported by the GFS's own ensembles, the operational runs of the GGEM and ECMWF dig the trough a bit more to the SW, with the upper-level low centered along the S CA coastline at the same time. Even despite the more westward evolution of the trough on the foreign models, they still indicate nice lee cyclogenesis over CO and resultant backing of low-level winds.
By 09/00z, the GFS depicts a warm front extending east from the surface low across N KS and N MO, with a dryline intersecting it somewhere near I-135 and draped down across W OK and NW TX. To the east, SSE surface winds and widespread surface dew points of 65-68 F exist, resulting in >2000 J/kg SBCAPE. Both low-level and deep-layer shear are somewhat modest, but adequate for the threat of supercells and possibly tornadoes across portions of OK/KS should other ingredients fall into place. SBCINH is shown to erode immediately ahead of the dryline, but is still formidable over much of the open warm sector.
While Friday currently looks like the best chase opportunity so far this season on the GFS, I have two main concerns. First, the slower and more positively-tilted ECMWF/GGEM solution could lead to more capping issues, as well as weaker flow throughout the low- and mid-levels, should it verify. It does seem like so far this year, there's been a tendency for west coast troughs to stall or even retrograde before weakening as they progress east, so I wouldn't be surprised if this happens again to some extent. Second, if last weekend's system is any indication, low-level moisture is likely overdone on current progs. Replacing the mid-upper 60s surface dew points on the GFS with more reasonable values of, say, 61-64 F, LCL's become a somewhat-bigger concern (though not a dealbreaker by any means).
Will be anxious to see what the NAM has to say about this in the morning, since it seems to be performing significantly better than any of the global models this year even towards the end of its range.
Tonight's 05/00z GFS offers the most progressive -- and perhaps most appealing -- scenario, with the 500 mb low centered roughly over Death Valley by Friday evening. While this idea is generally supported by the GFS's own ensembles, the operational runs of the GGEM and ECMWF dig the trough a bit more to the SW, with the upper-level low centered along the S CA coastline at the same time. Even despite the more westward evolution of the trough on the foreign models, they still indicate nice lee cyclogenesis over CO and resultant backing of low-level winds.
By 09/00z, the GFS depicts a warm front extending east from the surface low across N KS and N MO, with a dryline intersecting it somewhere near I-135 and draped down across W OK and NW TX. To the east, SSE surface winds and widespread surface dew points of 65-68 F exist, resulting in >2000 J/kg SBCAPE. Both low-level and deep-layer shear are somewhat modest, but adequate for the threat of supercells and possibly tornadoes across portions of OK/KS should other ingredients fall into place. SBCINH is shown to erode immediately ahead of the dryline, but is still formidable over much of the open warm sector.
While Friday currently looks like the best chase opportunity so far this season on the GFS, I have two main concerns. First, the slower and more positively-tilted ECMWF/GGEM solution could lead to more capping issues, as well as weaker flow throughout the low- and mid-levels, should it verify. It does seem like so far this year, there's been a tendency for west coast troughs to stall or even retrograde before weakening as they progress east, so I wouldn't be surprised if this happens again to some extent. Second, if last weekend's system is any indication, low-level moisture is likely overdone on current progs. Replacing the mid-upper 60s surface dew points on the GFS with more reasonable values of, say, 61-64 F, LCL's become a somewhat-bigger concern (though not a dealbreaker by any means).
Will be anxious to see what the NAM has to say about this in the morning, since it seems to be performing significantly better than any of the global models this year even towards the end of its range.
Feel free to add/correct...
