U.S. Climate Extremes Driven By Regional Warm and Cool Ocean Temperature “Blobs”

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Warm and cool "blobs" of ocean temperatures southwest of the U.S. and in the northwest/northern North Atlantic are helping to drive a climate pattern producing extreme wet events AND expanding drought.

Warm/Cool Oceanic “Blobs” Driving Extreme Weather Events in U.S.

Discussion: Another gully-washer historic rainfall event yesterday in the Mid-Atlantic U.S. This time radar estimates indicate up to 6-7 in. of rain east-northeast of Richmond, VA on Saturday. The event follows 8 in. in 3 hours in Ellicott City, MD last weekend. Meanwhile drought is strengthening in the Great Plains foreshowing excessive heat ahead.

Fig. 1: The Daily Progress photo (Ryan Kelly) of flooding roadways in Charlottesville, VA May 2, 2018.

Helping to explain (and predict) these events are dramatic regional sea surface temperature anomaly (SSTA) regimes/trends. The observations are outside the normal climate predictors El Nino southern oscillation (ENSO), Pacific decadal oscillation (PDO) and Atlantic multi-decadal oscillation (AMO). They are what climate scientists are increasingly referring to as “blobs” of not well understood emergence of regional SSTA extremes that affect local climate.

Last weekend a “1-in-1000 year flood event” occurred in 3 hours in Ellicott City, MD. Another not quite as extreme flooding rainfall took place yesterday in northeast Virginia. Contributing to these historic rainfall episodes is the effect on climate by a vast area of cooler than normal SSTA south of Greenland (which continues to cool) and the recent rapid warming of the ocean surface off the Mid-Atlantic Coast (Fig. 2-5).

Fig. 2-5: The northwest North Atlantic off the Mid-Atlantic coast is warm and warming while the cool pool south of Greenland is turning colder.

The atmosphere reacts to the cool pool south of Greenland with a persistent large upper cold trough that on occasion propels cold fronts southward into the Northeast U.S. clashing with very moist air supplied by the rapidly warming ocean surface off the Mid-Atlantic Coast. The set-up described is driving these historic late spring excessive rainfall events.  This pattern may last awhile and more excessive rainfall events affecting parts of the East are likely well into summer 2018.

Concern of a bad drought in the central/southwest U.S. expanding and intensifying is increasing. Established dryness in this zone entering meteorological summer with extreme heat ahead in the forecast is a recipe to cause a feedback mechanism to evolve whereas persistent surface heating causes a high pressure ridge pattern aloft to persist.

Fig. 6: Max/min forecast by all models the next 15 days in Dodge City, KS.

A look at temperature forecasts for Dodge City, KS indicates persistent 100+ maximum temperature forecasts emerging for the first half of June (Fig. 6). If this forecast verifies drought not only intensifies but spreads further north toward the Corn Belt.

The dryness and heat risk is a northeastward expansion of the already established Southwest U.S. drought.  The Southwest U.S. drought is attributed to a persistent warm “blob” of SSTA southwest of California present for the past 2 years (Fig. 7).

Fig. 7: Global SSTA analysis for the past 90 days identifying the warm “blob” southwest of California correlated to the persistent upper ridge of high pressure causing Southwest U.S. drought. The warm blob has been present since last year.

There are other “blobs” affecting regional climate as June 2018 arrives including southeast and east of China/Southeast Asia, east of Argentina and across the central/east Mediterranean Sea. Possibly a sign of climate change, climate controllers outside of the normal climate regulators such as ENSO, PDO and AMO.

Late last week NOAA/USDA updated the U.S. Drought Monitor which identifies intense drought in the Southwest U.S. to Central Great Plains (Fig. 8). There is increasing concern this dryness could expand farther north during summer ahead.

Fig. 8: U.S. Drought Monitor updated May 29 indicates harsh drought in the Southwest U.S. to southern California and also across the central/south Great Plains to Texas. Fear of northward expansion is increasing.