Caribbean disturbance no threat; winter coming back?

The tropical disturbance that formed in the western Caribbean yesterday is moving ashore over Belize, and is not a threat to become a tropical depression. Heavy rains of 4-8 inches are expected in Belize today in association with the intense thunderstorms of the disturbance. The disturbance developed in an area of low wind shear (5-10 knots) caused by a temporary split in the flow of upper-level winds over the Caribbean. This split is closing up again, and shear values are quickly rising to the very high values we are used to seeing in the tropics in winter. Computer forecast models are predicting that wind shear will remain high over the tropics the remainder of January, and no further tropical disturbances are expected this month.



Winter coming back?
The 10-14 day forecast of the GFS computer model has been consistently showing a return to a more normal wintertime pattern the past several runs. If this verifies, it means that winter will return to the eastern half of the country by the second week of February, with temperatures below normal for the first time since mid-December. The Arctic air that has numbed Russia this January is forecast to slosh across the North Pole into Canada and plunge southwards into the eastern U.S. shortly after Super Bowl Sunday--February 5. There is some doubt whether this latest forecast will verify, since the GFS model made a similar forecast back on January 10. However, the run-to-run consistency of the model is greater this time, and a "resonance" in Earth's climate system called the North Atlantic Oscillation (NAO) appears poised to switch from its positive phase to its negative phase. The negative phase is typically associated with a jet stream pattern that brings cold Arctic air to the eastern U.S., and this is the pattern seen between mid-November and mid-December, when cold air gripped much of the Eastern U.S. We have been in the positive phase of the NAO ever since, which is typically associated with very warm winter conditions across the eastern U.S.

Siberian cold hits Greece
Siberia has likely seen its coldest weather of the winter already, as temperatures have warmed considerably from the readings as low as -70 F seen last week. However, the extreme cold air from Siberia pushed into Greece today as a "back door" cold front swept in, bringing severe winter conditions to that nation. Temperatures as low as -4 F (-20 C) were recorded this morning, and high winds and heavy snows created a travel nightmare across much of Greece, Turkey, and neighboring nations. This is probably a taste of things to come for the U.S. after Super Sunday, when the Siberian Express may head our way.

Jeff Masters