1/29/2006 FCST: Gulf Coast and Southeast U.S.

Added Thursday 1/26/05 1600Z:

Latest NAM output valid 1/30 00Z seems to be trending towards deeper moisture ahead of the developing shortwave, but has the system farther west on Sunday. Surface dewpoints approaching 65 in central LA resulting in a pocket of CAPE ~1500 J/kg with 0-3 km helicities approaching 300 m^2/s^2. NAM and GFS output for the period both show a surface low developing near Joplin, MO during the day Sunday, at 1005mb and 1006mb respectively. The NAM's solution has a deeper shortwave than the GFS, but both currently show the leading edge of a 60+ kt 500mb streak approaching the Arklatex area 00Z 1/30. Based
on the current guidance of these two models, I'd target central LA near Alexandria for Sunday, with plans to move in any direction as convection fired. But unless the action area moves to points farther east towards AL and GA I'll be chasing this one from my PC. About 10 hours one way is the most I can allot for a Sunday chase, given work at 8am on Monday.

Figure I will go ahead and put a jinx to the promising 144hr GFS model output. Currently, it has the closed upper low now over Baja filling and moving out, but with another system on its heels developing into a negatively tilted shortwave as it cuts across the upper Tennessee Valley area on Day5-6. Surface cyclogenesis forecast by 120 hr over western OK with the surface low progged to deepen to sub-1000mb by 144hr and then bomb out at below 985mb as it moves ene into the Ohio Valley by 156 hr. Deep boundary moisture with 65+ dps looks to stay confined to offshore in the western GoM, however the strength of the progged dynamics would likely be more than sufficient for deep convection given even low 60s dps. Storm mode, given current output of mean 0-6km flow being normal to the cold front/dryline feature, would likely be supercellular in nature, at least during the first 4 to 6 hours of storm evolution. More than likely the GFS is overforecasting the strength of the shortwave, but it sure looks good on paper as of now, 1/24/06 1510Z.

ECMWF is pretty much in agreement with the GFS thru late Day3, and also has the Baja closed upper low rapidly filling as it moves through the central plains. However, ECMWF Day4-6 is more or less contradicts the the GFS solution, with the new system moving out of the four corners region late Day4 and deeping slightly as it crosses the southern plains on day 5, but rapidly filling by Day 6 as it moves offshore middle Atlantic. ECMWF looks awful but to me more probable, given the recent pattern of weak (and quite boring) systems with no significant deep moisture to work with.