Latest Seasonal Assessment -
La Niña conditions continue over the equatorial Pacific, with a 95-percent chance of persisting through the end of March 2021. The MJO is also active, with an Indian Ocean event underway. While the MJO may influence the midlatitude pattern, especially early in the outlook period, climate anomalies associated with the La Niña response will likely play the dominant role throughout the Boreal winter months. Due to this, the CPC monthly outlook for December 2020 and the December 2020 - February 2021 seasonal outlook both closely resemble composites of previous La Niña events.
During the past month, drought conditions expanded rapidly across much of Texas as the central and southern parts of the state received less than 25 percent of normal rainfall. Drought and abnormal dryness also slowly expanded across parts of the Southwest, Plains, and Midwest, but a swath of heavy precipitation associated with the remnants of Hurricane Delta and a potent midlatitude system brought drought relief to Oklahoma, southern Missouri, parts of the Ohio River Valley, and the Northeast. Overall, nearly half (45.9 percent) of the Contiguous U.S. was experiencing drought conditions as of 10 November 2020, with the greatest coverage and most intense drought conditions located over the southwestern quadrant of the CONUS.
La Niña winters frequently result in a dipole of above (below) average precipitation across the Northwest and north-central US (southern tier and the central Plains), and these conditions are anticipated to play out during the upcoming winter months. Therefore, drought reduction is favored for the Northwest and northern Rockies, while persistence or expansion of drought is favored for California, the Four Corners region, the central and southern Plains, and parts of the Southeast that are currently experiencing growing precipitation deficits. Additionally, the La Niña response tends to shift the favored winter storm track towards the Ohio Valley through interior New England, favoring continued drought improvements for Illinois, Indiana, and the Northeast. While the climate signal favors above-average snowfall for the northern Plains and upper Midwest, little change to drought conditions is forecast, as frozen soils and streams will inhibit absorption of moisture until the spring thaw commences. Elsewhere, abnormal dryness and warmth have promoted drought expansion across much of Hawaii, but given the oncoming wet season and enhanced tradewinds in association with La Niña, drought improvements are forecast, especially across the leeward sides of the islands. No drought conditions are currently present or expected to develop during the winter months across Alaska and Puerto Rico.
Forecaster: Adam Allgood
Next Seasonal Drought Outlook issued: December 17, 2020 at 8:30 AM EST.
Seasonal Drought Outlook Discussion