Analysis: Winds across Texas have turned out of the south or southwest in response to a developing trough of low pressure along the lee of the Rocky Mountains. This has resulted in temperatures this morning being slightly warmer than they were this time yesterday. In the upper levels, a cut-off low is noted over northern Mexico. This low should move northeast across Texas during the next 36 hours. Despite the enhanced lift from this upper-level low, deep dry air is noted on all Texas soundings, meaning little in the way of precipitation is expected, though a few showers and perhaps a thunderstorm will be possible along the coast.
Forecast: The first upper-level low should depart the region by Saturday morning, with ridging expected to build in behind. This should lead to pleasant weather on Saturday. By Sunday morning, a high-amplitude trough will dig into the Desert Southwest. Cyclogenesis along the lee of the Rockies will result in a deep fetch across the Gulf of Mexico. Precipitable water values are forecast to increase in excess of 1.50 inches across much of southern and eastern Texas by Monday morning. Per yesterday’s discussion, this would rank amongst the highest precipitable water values ever recorded in Texas during the month of February. Right now, it appears that the heavy rain threat will be a much bigger concern than for severe weather. Instability should be limited, and deep southerly flow parallel to the Pacific cold front should cause any convection to “line out” quickly. There continues to be some uncertainty regarding where the axis of highest precipitable water values will set up, which will be key to determining where the heaviest rainfall occurs. Yesterday, this was roughly along the I-35 corridor, whereas today, the GFS pegs it roughly along I-45, placing Houston under the heaviest rainfall. The Weather Prediction Center Days 4-5 Quantitative Precipitation Forecast (QPF) graphic shows a bullseye of 3.60 inches just off the coast of the Bolivar Peninsula, with most of the Houston area in the 2.50-3.00 inch rainfall totals. Given the 1.90 inches of precipitable water seen on forecast soundings northeast of Houston, higher amounts will certainly be possible if not likely. Based on climatology from Lake Charles, LA (there is no upper-air site in Houston), if 1.90 inches verified, it would be the highest value ever recorded in February.
The bottom line is that confidence continues to increase that heavy rainfall (perhaps very heavy rainfall) along with flash flooding and river flooding will be possible somewhere in East Texas beginning late Sunday and into Monday. As already mentioned, there is uncertainty where this heaviest rainfall will occur, but people in, or who will be traveling to, East Texas, especially Houston, should continue to monitor forecasts.