Based on the latest 8 – 14 day temperature outlook from the Climate Prediction Center the end of the the month will feature above average temperatures, and likely spring-like warmth, for the eastern two thirds of the country.
Most of the ensemble guidance, such as the GEFS, is indicating that the Arctic Oscillation (AO), which is currently positive, will remain that way during the second half of this month and that the Pacific-North American Pattern (PNA) will go negative – at least for a time.
The AO and PNA are teleconnections. The American Meteorological Society’s Glossary of Meteorology defines a teleconnection as a “linkage between weather changes occurring in widely separated regions of the globe.” We can use these established linkages/correlations in making forecasts – especially in the long range. The El Niño-Southern Oscillation (ENSO) is another example of a teleconnection.
When the the AO is positive it is difficult to get intrusions of continental arctic (cA) air into the contiguous United States. Meanwhile, when the PNA is negative, below normal geopotential heights (low pressure) are favored in the western U.S. with above normal geopotential heights (high pressure), and therefore above normal temperatures, in the east.
Another teleconnection that has a significant influence on weather in the U.S., the North Atlantic Oscillation (NAO), has been positive for all of the month so far and looks to stay that way through the end of the month at least. This too favors above normal geopotential heights and temperatures in the eastern half of the country.
Hints of this warmer weather can already be seen in the operational/deterministic runs of the GFS and ECMWF in the 7 – 10 day period.
While above average temperatures are favored through the end of the month across the central and eastern U.S., this does not mean there won’t be a cold front or two that brings a shot of cooler/colder air. But any intrusions of anomalously cold arctic air appear unlikely.
In fact, looking ahead to late this week/this weekend, a cold front is expected to bring some colder temperatures. It will also bring the potential for severe weather during the Wednesday-Thursday timeframe.
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