U.S. soil moisture/rainfall deficit discussion: Beginning in the Northeast U.S. rainfall needed to neutralize dry Palmer Drought Severity Index (PDSI) remained moderate-to-high as of June 26, 2021 (Fig. 1). Conditions worsened in Connecticut and central Pennsylvania where rainfall shortages are now in the 3-6-inch range. In the Northeast, the worst rainfall shortages (9-12 in.) are in coastal Maine, central New Hampshire, northern New York and southwest Pennsylvania.
In the Mid-Atlantic region to the Carolinas patchy drought areas continue. Last week, central South Carolina turned drier now with a 6-9 in. rainfall deficit while south-central Georgia gained some helpful rainfall. The passage of weak Tropical Storm Danny did little to help rainfall shortages in the Georgia/South Carolina region.
The Florida drought went from bad to worse last week as Southern Florida now has nearly 15-inch rainfall deficits.
The northwest/north Gulf of Mexico region to the Mid-south States and eastern Kansas/Missouri Valley remain in a rainfall surplus. Across these locations PDSI is unusually to extremely moist.
Far southern Illinois turned drier last week but central and northern areas lost their marginal drought signature due to heavy rainfall. The rainfall also affected southeast Iowa. However, west/north Iowa drought worsened last week despite the nearby rains.
North and South Dakota into western Minnesota rainfall shortages also increased last week. Rainfall shortages are now >12 in. across parts of North Dakota where torrid drought is in effect. Eastern Nebraska rainfall shortages eased due to rainfall last week.
In the Southwest U.S., drought continues although rainfall shortages eased slightly due to thundershowers in southeastern California to the Las Vegas, NV area. Unchanged are the steep rainfall shortages across coastal and northern California to the Oregon/Washington Cascades and westward to the coast.
The outlook: The 15-day forecast by the most reliable model, the ECM ENS reveals the combination of dry and hot climate to accelerate drought conditions is well-fortified across the West, Northwest and North-central U.S. (Fig. 2-3). This hot and dry region acts as a source region for pulses of heat eastward into the Northeast U.S. in July. The heavy rain pattern is locked-in over Texas to New Mexico occasionally stretching across the East U.S. which encounters frequent thunderstorms for mid-summer. The wet climate zone causes suppressed heat risk.
Fig. 2-3: ECM ENS 15-day percent of normal rainfall and temperature anomaly forecast.