Minimal soil moisture recharge expected this fall
GRACE’s Groundwater Drought Indicator shows some wetter soil conditions for the Northeastern Plains, eastern Midwest and Delta during this fall season, along with the Pacific Northwest Coast and part of the southwestern US, where very active monsoon rains have recently occurred. Elsewhere there are indications of a sharp decline in soil moisture supply. The western Midwest, Northwestern, Central and Southwestern Plains, the rest of the western US and the entire Atlantic Seaboard have virtually nothing to offer in terms of groundwater improvements this fall.
La Nina’s continued presence in the Pacific Ocean certainly contributes greatly to this bleak prospect. La Nina, where sea temperatures along the equator between South America and the International Date Line have consistently been at least 0.5 degrees Celsius (0.9 degrees Fahrenheit) below normal, is entering its third straight year. Jet stream pattern changes due to La Nina have diverted moisture away from the US interior and will sustain this drying effect for the next few months. In addition, a hot late summer brought further dehydration and moisture loss. For example, Nebraska and Kansas had August precipitation totals that were the second-driest and seventh-driest on record. Montana and Wyoming had August temperatures that were 8 to 10 degrees Fahrenheit above normal, according to a NOAA weather report for the summer season. Additionally, the USDA in its September 20 Weekly Weather and Crop Bulletin noted that overall US drought coverage ended the summer with more than 40% of the contiguous US in 101 consecutive weeks of drought – a 21st century record. That’s almost two full years going back to late summer 2020.
Looking towards the end of the month, the short to medium term forecasts don’t offer much rainfall. A move towards more tropical system activity in the Atlantic Basin implies that moisture in the Gulf of Mexico will be seized by the development of tropical storms or hurricanes. Additionally, continental North American weather systems are centered on the Canadian prairies, which usually means little rainfall for the interior of the US — the sun’s angle — is getting under way.
Bryce Anderson can be reached at [email protected]
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