Bad drought developing in the Southeast U.S.
Fig. 1: Rainfall needed to neutralize negative PDSI across the U.S.
Southeast/Mid-Atlantic U.S. drought discussion: The Southeast U.S. to Mid-Atlantic States continue to dry-out RAPIDLY. A significant drought is devloping in these regions. Rainfall needed to neutralize strong negative PDSI values is over 15 in. across eastern Georgia and now 12-15 in. in southern Alabama (Fig. 1). Rainfall deficits of 6-9 in. are now common in West Virginia, Virginia and Delaware. The dryness is extending westward to northern Louisiana and the central Ohio Valley. The Southwest U.S. dry pattern is broad and strengthening. Interesting is the feast or famine nature of the climate pattern as in-between the two dry zones described Imelda brought near 40 in. of rain to southeast Texas last week. Contributing to the dryness (in the Northwest and Southwest U.S. plus the eastern states) is the tendency for upper level warm/dry high pressure ridging over the poleward oceans during late northern hemisphere summer 2019 (Fig. 2).
Fig. 2: Mid-latitude drought is caused by subtropical high pressure ridging stretching across warm SSTA regions which are plentiful the past 2 months.
The FEEDBACK Loop: The anomalous warm ocean and attendant 500 MB high pressure ridging is difficult to replace. The best way to impinge on the late summer pattern is by the influence of evolving cool season climate. The dryness in the Southeast is producing a feedback mechanism to the upper atmosphere sustaining the ridge, causing over-achieving maximum temperatures and blocking approaching tropical cyclone activity. The GFS ENS indicates this feedback mechanism to sustain the pattern continues (Fig. 3-4).
Fig. 3-4: The GFS ENS 15-day temperature anomaly and percent of normal precipitation forecast.
However, we’re out of the summer season now and the atmosphere is compensating for very warm areas by producing upstream cold zones featuring early season snows. The cold anomalies are bold due to the presence of snow cover developing in the Northwest U.S. and southwest Canada into early October.
The boundary between the cold and snowy Northwest climate pattern and the persistent warmth in the Southeast is located over the Western Corn Belt where frequent rainfall events occur the next 15 days (and well into October).