Dry soil conditions are widespread in the West and Central U.S. most profound in California, Utah, Texas and the Western Corn Belt. The driest seasonal change is across the Mid-South U.S. Fortunately, a wetter and more snowy pattern change is ahead for the Wet and Central U.S.

A busy NOAA/NWS weather watch, warning and advisory map? A major Christmas Eve storm erupts in the East today/tonight bringing severe thunderstorms to the coastal Mid-Atlantic region, high wind causing poser outages for the northern Mid-Atlantic into New England and flash flooding caused by heavy rain from Virginia to Maine. Heavy snow on the back side of the storm targets West Virginia to Ohio.

Mid-to-late summer regional soil moisture deficit in the deep layers (10-200 CM) are a key diagnostic for monitoring potential flash drought risk. If a period of 7-10 days (or more) of dry and anomalous hot weather occur over these regions a fast-emerging drought will develop.

The Pacific decadal oscillation cool phase strengthened in November. Meanwhile the warm phase of the Atlantic Multi-decadal oscillation ended last month. The -PDO pattern is not expected to last long becoming neutral in 2021 while the AMO pattern should rewarm for the 2021 North Atlantic tropical cyclone season.

The SSTA pattern is very warm. Easterly component of wind will increase the amount of moisture flowing into the developing storm. Heavy rain causing a flood risk is likely in east/northeast Virginia to southeast Maryland while well inland where temperatures stay cold over-achieving snowfalls will occur.

The Nino34 SSTA cool peak for La Nina was late last October. Since that time La Nina is less intense and choppy. Subsurface water in the equatorial East Pacific is not quite as cool as October.

A vigorous negative phase of the arctic oscillation (-AO) is ahead. In the Dec. 11-25 period, forecast models agree on a -2.2 signature of the AO. The GFS identifies the attendant high-pressure block near the polar region. Interestingly, the polar vortex split which results in 4 northern mid-latitude upper troughs are all located farther north than usual for a full-throttle -AO episode.

In North America nearly the entire continent trended drier during SEP/OCT/NOV most notably across the Southwest U.S., Great Basin and California. Additional drying took place in Alaska and much of Canada. The catalyst to the drier climate is the warm SSTA pattern either side of North America promoting anomalous dry/warm high pressure. The Southeast U.S. wet pattern was fueled by tropical cyclone activity. Central America also reversed much wetter due to late season tropical cyclones.

The midday GFS indicates two important trends/changes. The axis of the heaviest rain shifts east and includes Richmond, VA to Dover, DE and across Rhode Island/southeast Massachusetts to coastal Maine. Many areas receive 3 in. of rain. The snowfall forecast increases. In New England 10-20 in. of snow is forecast with >2 feet in northern New England mountain areas.

The Australian Bureau of Meteorology indicated November 2020 was the hottest on record. Additionally, the Bureau indicated spring 2020 was the warmest on record for minimum and mean temperature. Rainfall was well below normal in many parts of Australia but not as dry as last year. The November 2020 national average temperature was +2.9C according to the Bureau breaking the record of +2.4C in November 2014.