Highlight: Great Plains drought is worsening.
Discussion: During the past 7 days the U.S. precipitation pattern observed a widening dry regime featuring little or no precipitation across most of the U.S. including the ongoing D3/D4 drought in the central and southwest Great Plains to Texas (Fig. 1). The only recent wet periods in the Central U.S. were Feb. 26-Mar. 4 and Mar. 19-25 when heavy amount stayed just east of the drought zone. Consequently, the drought condition is increasingly aggressive from Nebraska to Kansas to northwest and west-central Texas (Fig. 2). The lack of precipitation in April has caused a soil moisture drying trend from Oklahoma to Nebraska and eastward across the Missouri Valley to the northern Mid-Atlantic States (Fig. 3). The NOAA constructed analog system (CAS) has identified the early-to-mid-spring dry soil trend in the established drought area and maintained drought through the summer of 2023 (Fig. 4-5). Once we’re into the warm season (MAY/JUN), eroding drought becomes more difficult, and the CAS forecast gains credibility if the ongoing dryness persists a few more weeks. Another evolving issue regarding forecasts is the precipitation bias all models are developing for the medium-range which is too wet in the Central and East-central U.S. (Fig. 6-7). The last 2 GFS 15-day percent of normal precipitation forecasts across the U.S. AG Belt demonstrates the below average confidence to critical forecasts. The 00Z GFS 15-day outlook is drier than normal for most of the Great Plains (Fig. 8) with wet risk concentrated over the Upper Midwest U.S. However, 6 hours later, the 06Z GFS produced a much wetter forecast for the Upper Midwest, Great Lakes region, and westward into Kansas (Fig. 9). The change in the forecast is based on a deep low pressure off the Northwest U.S. Coast maintaining a downstream dry ridge over the Central U.S. (00Z GFS) or the trough weakening and transferring attendant energy to the Midwest U.S. trough to cause a wetter forecast (06Z GFS). Persistence and model (forecast) bias supports drier Great Plains forecasts for now.
Fig: 1: U.S. percent of normal precipitation observed April 8-14, 2023.
Fig: 2-3: Current soil moisture anomalies and change in April (so far).
Fig: 4-5: The NOAA CAS U.S. soil moisture anomaly forecast for the end of May and end of August.
Fig: 6-7: The GFS ENS precipitation bias for the past 7 days with medium-range forecasts.
Fig: 8-9: The last two GFS model runs, and their percent of normal precipitation 15-day forecast for the U.S. AG Belt.