TX and LA forecast

[jeff]

Impressive MCS off the upper TX coast has dropped greater than 10 inches of rain this evening (more like 14.0 in). Good thing it is off the coast, if it were inland somebody would be in a world of hurt. Low level flow feeding this complex is robbing some of the moisture over the area. Convection has recently fired along the appraoching cold front from E of CLL to NW LA. Conditions are favorbale for increasing convection tonight as the front moves S into increasing moisture and some instability (CAPE 500 J/kg). The severe threat should be minimal and limited to tornadic supercells right along the coast and isolated high wind events (downburst and microbursts) inland. Threat increases Wed over LA where better moisture and instability can be found, but remains in the SPC slight risk range.

Newest guidance tonight continues the trend of a little more precip over N TX wed with a little better chance of accumulation. Currently going with 1.0 inches along the Red River counties with a dusting over the metro areas. May have to up the QPF a little as the isentropic lifting is looking fairly strong. Could see more than just a dusting over the metro areas, depending on surface temps.

Guidance has also swung back to the original idea of the Gulf low forming and heading into the Gulf coast late this week. Differences develop between the models as to what to do with the energy in the SW over old Mexico. The trend today has been for a more slower and cut-off solution of the energy and a better chance of overrunning moisture along the Gulf coast. Indications are more of a wintery mix from north of Brownsville to New Orleans Thursday PM through early SAT AM. Given the setup I like to start the precip as snow then transition to freezing rain as warm air advection increases over the TX and LA coast. Very difficult forecast WRT P-type and demarcation lines along the coast. It is still just possible that the coastal trough forming under the forcing of the upper level energy remains far enough offshore to keep the coastal areas dry.

I actually believe the best areas for frozen precip. may be from Matagorda Bay south to north of Brownsville and then over toward SE LA. These two areas will be closest to the deeper moisture and have favorable profiles for either freezing or frozen precip.

As with any winter weather forecast in the south forecast confidence is extremely low and the simple fact is, nobody including the most expert forecasters will know what the outcome will be until the event is underway or the forecast models come into very good agreement. If it were not cold I seriously doubt there would be any talk about the expect mositure levels and QPF amounts.

Jeff L

[jeff]

Forgot to mention.

Cold front just passed KCLL which is about 6-8 hours ahead of model forecast times. Front should be passing KIAH by 200am and at the coast by 500am then into W LA after daybreak.

Cold air is lagging the wind shift by about 50-80 miles with the arctic air north entering central KS. Surface low over the coastal bend should help move these colder air masses southward faster than what we are currently seeing.

[ktulu909]

So in english this is good or bad for snow watchers in New Orleans?

[Steve]

Latest model guidance from the 00z GFS seems to indicate that South Texas, East Texas Coastal Regions, SW LA and a line to about the River Parishes (St. John/Ascension/St. Charles/St. James) might be below the freezing line. But since jeff notes that the cold is actually coming a little faster, it's possible. The 00z run backs off on the extreme cold for SE LA but puts in much more preceipitation.

Steve

[MGC]

I would say good if you want snow. Several of the models have questionable temps for snow. If the cold air arrives ahead of schedule that will allow for colder temps Friday. For a good snow in NO the low would have to track on a NE trajectory into the Fla panhandle thus keeping the NO area in the cold air.....MGC