Fig: 1-4: NOAA/SPC indicates an unusually strong severe weather event on Friday in the East-central U.S. while NOAA/CPC adds extreme rainfall risk (which includes severe weather) at times during the first third of April (top). Unusually warm SSTA across the Gulf of Mexico increases low-level atmospheric moisture entrained into an energetic subtropical jet stream causing the heavy weather risk.
Discussion: Another round of unusually intense severe weather is forecast for late this week and again in the extended-range across the East-central and Mid-south U.S. according to NOAA (Fig. 1-2). The unusual intensity of severe weather has already began given several episodes so far during early spring most recently in the Southeast U.S. The catalyst to the exceptionally strong severe weather is the increased low atmospheric moisture across the somewhat warmer than normal Gulf of Mexico (Fig. 3) and the persistent negative Pacific North America (-PNA) pattern propelling an energetic jet stream across Mexico to the Mid-south U.S. (Fig. 4). Short-wave troughs embedded within the energetic jet stream entrain the buoyant moisture from the Gulf of Mexico creating the dynamics to produce heavy convective storms. After cooling off 2 weeks ago, the Gulf has regained warmth (+0.5C) during the past 7 days. The -PNA pattern remains in the forecast through the first third of April (at least). Adding more fuel to the excessive rain/severe weather risk in the extended-range is presence of the Madden Julian oscillation (MJO) shifting eastward across the equatorial Pacific as indicated by most operational models.