A PATTERN ADJUSTMENT FOR FEBRUARY

This update to the February forecast is driven by a change in positioning of tropical forcing during the middle of this month. The expectation near the end of January was for tropical forcing to focus primarily across the Maritime Continent. This forcing would have supported the building of a ridge near Alaska, increasing the risk of Arctic air returning to portions of the Midwest and East. However, tropical forcing is now forecast to retrograde back to the Indian Ocean, which would displace the ridge near Alaska towards the Aleutian Islands.

The downstream impacts to this pattern adjustment are sizable. As opposed to a -EPO ridge near Alaska, the pattern configuration will be a -WPO ridge near the Aleutians being paired with a +EPO trough across much of mainland Alaska. This would cut off the flow of Arctic air to the US and allow for milder Pacific-based air to be more prevalent across the Central/Eastern US. The warming will be more pronounced across the Central US during the second and third weeks of February, as a -NAO ridge near Greenland will push back on this warmer airmass from fully extending through the Northeast. Meanwhile, the ridge providing the warm start to February in the West will transition over to a trough by the latter half of the second week of February, allowing for below normal temperatures to begin to spread across the West. The trough in the West should remain a persistent feature for the remainder of February, keeping the cooler pattern in place. Extreme cold is not anticipated, however. The bulk of the warmest anomalies through mid-February will focus across the Rockies through the Upper Midwest. A ridge should form during the second half of February across the Southeast, which will produce more persistent warm anomalies across the South. Temperatures should become more volatile during the second half of February from the Midwest through the Northeast, aided by what should become a more active pattern. Mild stretches will be interrupted by brief cooler spells, but cold should not be intense and is unlikely to last long before milder conditions should return.

It is still anticipated that rain and mountain snow will begin to increase across the Pacific Northwest during the second week of February and this will gather more momentum moving into the third week of February. With a stronger trough developing in the West, this will provide some opportunities for systems to extend into the Southwest at times, especially by the third week of the month. Precipitation should remain more persistent across the Northwest. This should mostly continue into the final week of February, though chances for rain and mountain snow may ease a bit in the Southwest. A clipper system or two could produce snow or a wintry mix later in week two from the Great Lakes towards the Northeast/Mid-Atlantic, but this is unlikely to be anything major. The risks for larger systems to eject out of the Rockies and through the Central/Eastern US should increase during the second half of February. The favored storm track should be from the Mid-Mississippi Valley towards the Mid-Atlantic. This will produce snow risks across the northern tier of the US, particularly from the Great Lakes to the Northeast. Thunderstorms will become a concern across the South and the Gulf Coast with this pattern, but storms are likely to weaken approaching Florida and the Southeast Coast.