Jeff Lindner email update I got about an hour or so ago:
Sorry for the delay, I wanted to look over the 18Z guidance and forecast soundings to help nail down P-type and totals...not sure it changed the thinking much.
Winter Storm Watch in effect for all of coastal Texas and have been expanded into central TX and SW LA.
Historic snow and ice event within 24 hours of onset.
Record snowfall totals may be challenged by this event.
Discussion:
Little has changed with the overall pattern which conitnues to exhibit a classic TX winter storm profile. Deep upper trough digging into northern MX at this time will develop a NW Gulf of Mexico surface low which throws copious moisture NW into the frigid arctic air mass in place. While aloft the sub-tropical jet stream will bring moisture in from the Pacific. While the low levels are dry, the snow falling through the air column will gradully moisten the surface layer starting early Thursday. Widespread snow/sleet will develop by Thursday evening with heavy snow likely overnight.
Timing:
Models have trended a little faster today with the onset timing. In fact a few models suggest we could begin to see flurries along the coast before noon on Thursday, but this would be very light as the surface layer saturates. Wet bulb effects and ongoing cold air advection will likely keep temperatures below freezing. Light snow and sleet should develop along the coast and begin to spread inland around the noon-100pm time period. Light snow will expand northward over the rest of SE TX by 300-400pm with accumulations starting about an hour after the snow begins...possibly sooner if the temperatures are in the upper 20's at the onset. Thursday night weak warm layer tries to advance toward the coast and may push inland resulting in sleet and freezing rain and ice accumulations...I continue to be wary of this P-type change given how cold the air column is and the fact that the models may be overdoing the 1-2 degree above freezing warm nose (around or above the 850mb level) above a very cold surface. Will cut back on the ice accumulations around Galveston Bay and favor more sleet/snow instead...I may end up being wrong on this, but I just think this air mass is colder than the models show it to be.
Accumulations:
I am going with a 10:1 ratio but it could be closer to 12:1 given the very cold/dry air mass in place. This means an inch of liquid would produce 10-12 inches of snow. These are very high ratios for coastal TX, typical ratios are usually closer to 7:1 and in Dec 09 were around 5:1. Other aspect with accumulation is that the ground will be very cold, so what falls will not melt adding to the amounts.
I am very confident that snow will fall, I am not as confident on accumulations as much depends on what P-type is falling and for how long at a given location. Freezing rain will mean more ice, while freezing rain and sleet will also cut down on snow accumulations. With all that said here is my best try at accumulations right now:
Southeast of a line from McAllen to Alice offshore to Bay City to Kemah to High Island:
Light snow early changing to freezing rain/sleet Thursday afternoon/evening. Accumulations of ice of 1/10th to 1/4th of an inch. Mix changing to sleet/snow early Friday...snow accumulations of 1-2 inches.
Southeast of a line from San Antonio to Hempstead to Conroe to Livingston:
Snow/sleet will start the event with all snow likely after 600pm Thursday. Accumulations of 1-3 inches is likely with isolated totals of 4-5" possible. This area will be the favored location for meso scale snow bands and these bands may produce very heavy snow in this corridor including Wharton, Fort Bend, Harris, Montgomery, San Jacinto, Waller, Austin, and Colorado counties.
North of the line from San Antonio to Hempstead to Conroe to Livingston:
Snow for the entire event will accumulations of 1-3 inches likely with isolated amounts up to 4". While snow is favored the entire event, the moisture will be greater closer toward the coast which may cut back on totals this far north.
Meso Banding:
NAM and GFS both show convective precipitation with this event which was seen in Dec 2004 resulting in the banding of very heavy snow. Strong isentropic ascent combined with frontgenic forcing in the favorable baroclinic zone greatly enhances the threat for this meso banding along and about 50 miles N of the US 59 corridor. This is the area that could really get hammered with some impressive totals and the NAM has been hinting at this over NE Harris, N Liberty, San Jacinto, Polk, and E Montgomery counties the last few runs, I like that idea and will also include Waller, Fort Bend, Wharton and Austin to mesh where this zone may setup. It is impossible to forecast where these bands will form and how long they will remain over a certain location...so it is impossible to know where some of the higher totals will be. Under these bands snowfall rates of 1-2 inches will be possible per hour with visibilities falling to less than 1/4th of a mile.
Preparations:
Looks like much of the area will fall below freezing tonight and not get back above freezing until maybe midday Saturday. This extended period of sub-freezing temperatures may freeze pipes as happened last night at some locations. Make sure pipes are protected and check your water pressure regularly to ensure pipes are not frozen.
Travel conditions on area roadways is going to go downhill very quickly Thursday afternoon/evening. Not sure if we wil get the evening rush hour complete before roads begin to accumulate ice/snow. Best estimate now is onset of precipitation over the heavy metro areas in the 300-500pm time period with accumulations starting 30 minutes to an hour after snow begins to fall...this really does not get us through the rush hour and feel by 600pm snow will start to accumulate on bridges/overpasses and some surface streets. After 700pm expect travel to be extremely dangerous and by Friday morning nearly impossible as all roadways will be ice covered and snow packed. Road crews are going to be overwhelmed with the event and will not be able to spread snad fast enough to keep most roadways open. Travel after 600pm Thursday is being strongly discouraged through all day on Friday and likely through noon on Saturday.
School Closings:
Early Release on Thursday:
Wharton ISD: noon
Lamar CISD: around noon
Additional ISD's will likely release early on Thursday especially southwest and many schools will likely be closed on Friday.
The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or 
my Cowboys 
