Western Heat/Drought Focus Continues, Expands to Northwest

Rainfall Deficits Increasing Midwest, Northeast and Southeast
06/15/2021, 5:14 am EDT
Weak La Nina Trying to Return
06/21/2021, 12:15 pm EDT
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Historic heat continues to worsen the extreme California/Great Basin/Southwest drought region. Longer-term, the anomalous heat and dryness is likely to focus on the Northwest States.

Highlight: Fierce heat in California/Southwest States eases into mid-next week. Northwest hot/dry focus to increase. Early fire season!

Fig. 1: Today’s western U.S. drought monitor identifying the extreme dry conditions affecting most of the region.

Discussion: The western U.S. drought (Fig. 1) is worsening beneath an extreme heat dome of high-pressure which continues to sustain a plethora of heat warnings and advisories most-focused on California, the Great Basin and the Southwest States (Fig. 2). The current heat wave features consistent daily records in the 104-118F range for the regions listed. The extreme heat will last through Saturday and ease only slightly early next week. Temperatures ease back toward normal in California and Arizona into mid-next week. However, anomalous heat returns in the 11-15-day period this time most-focused on the northern half of California.

In the 11-15-day period the ECM ENS includes the Northwest in the hot pattern. This hot forecast for the Northwest may represent the new focus of anomalous heat for July. During mid-summer D3/D4 drought is likely to develop and spread in the Northwest States.

The dryness and attendant heat (increase) during July is due to the projection (by Climate Impact Company) of a wet monsoon pattern into the southern deserts of the Southwest U.S. The wet pattern is driven by thunderstorm activity. The increased low-level moisture caused by the evolution of the wet monsoon will spread into the Great Basin and across California. Increased low-level moisture supports incidence of air mass thunderstorms and attendant lightning strikes without much (if any) rainfall. Expect an early and hostile start to the West U.S. fire season.

Fig. 2: Latest NOAA/NWS weather watch, warning and advisory areas.

Fig. 3: ECM ENS day 11-15 temperature anomaly forecast.