Hoping you all are well and have a very blessed day! -Kirk
Temperatures:
- No major changes in the December forecast with data and analog talking fairly well for this month.
- While the month starts off pretty steady with warmth across the northern tier of the US and cooler air south and east, the second half of the month could start to become more volatile as the atmosphere tries to revert back to a more La Niña-like base state.
- Long-range data is trying to hint at low frequency MJO phase 5 forcing which would bring the risk of warmer weather the last 7-10 days of the month in the E. US. The risk of MJO phase 5-6-7 mid-month and a +SOI, however, would allow for continued cooler risks from the Midwest to East Coast.
- With that being said, given the relatively steady pattern the first 10 – 15 days of the month at least, we feel fairly confident that the Northern Plains to the Rockies average out well above normal with temperatures averaging out slightly cooler on the East Coast (even with the risk of a warm-up to end December). Top analogs for this pattern are 1988, 1999, 2003 and 2017.
Precipitation:
- Precipitation continues to look abnormal for a normal moderate to strong La Niña base state. We currently have a strong +PMM (warmth off of the Mexican coast extending towards the equator) which is more typical of El Niño years and can aid the sub-tropical jet.
- Given this signal combined with MJO phase 5 and the +SOI, we feel as though the southern and eastern US average wetter than normal with some additional wintry chances at times especially northeast of the Ohio Valley.
- We also continue to see strong split flow signals the first ~2-3 weeks of the month which will tend to favor drier risks in the Central US. If there is a storm system to watch, we need to keep an eye on Dec. 14 – 16 for perhaps a better setup for the Midwest for a winter storm.
- With the split flow the risk is drier the first half of the month, but if the eastern ridge can emerge as we work later into December, we could get a bit wetter late month in the OHV to Midwest.