GFS/ECM Trending MUCH Wetter in Texas in 6-10-Day Forecast

Fig. 1-2: The 12Z GFS and ECM 6-10-day precipitation amount forecasts for ERCOT.

Discussion: The GFS produced a consistent tropical cyclone risk in their medium/extended-range forecasts since late last week. However, the GFS has dropped that idea late last night and today. Instead, GFS produces an excessive rainfall episode as an upper trough entrains western Gulf of Mexico moisture next week producing >10 in. of rain in some spots based on today’s 12Z GFS (Fig. 1). The following 12Z ECM is not as wet but is similar thematically with a 3-5 in. rainfall episode projected in the 6-10-day forecast (Fig. 2). The most recent rainfall needed to neutralize dry Palmer Drought Severity Index (PDSI) analysis from NOAA reveals an impressive and widespread 9-12 in. deficit across Texas (Fig. 3). The rainfall indicated for next week could cut that deficit in half. Rainfall amount as buoyant as indicated by GFS would normally require influence of the Madden Julian oscillation (MJO) shifting across the equatorial Pacific Ocean. Interestingly, Australia Bureau of Meteorology made a comment yesterday that surface wind has turned into the west to the north of Australia suggesting a strengthening MJO episode to the east. Forecast models are vague but there is the suggestion that an eastward-shifting MJO could be involved with the Texas rainfall event next week and if so, the higher amount forecasts could be correct. There is potential for a significant dent in the Texas drought.

Fig. 3: Rainfall needed to neutralize dry Palmer Drought Severity Index.