Posted at 8:33 AM on November 5, 2009
by Paul Huttner
Twin Cities NWS graphical forecast showing 60s Saturday.
Many are welcoming a change to warmer temperatures this weekend. There is a history of Indian Summer in early November in the past few years. Three of the past 4 Novembers have featured warm spells early in the month with temperatures reaching above 70 degrees in the Twin Cities at least one day.
While early November warm spells seem to be more common, there are several unusual and remarkable aspects to the warm spell this year.
It is interesting to note that the sun angle and intensity at this time in November is about equal to the first week in February. Yet temperatures will be much warmer in November even with the same amount of solar energy coming in. There are some obvious reasons why this happens.
-The ground is free of snow cover right now. That means that instead of solar energy reflecting back into space on higher albedo (more reflective) snow cover, more incoming solar energy is available to heat the lower atmosphere in November than February.
-There is still plenty of warm air to the south in late fall to be moved (advected) into the Upper Midwest.
-Overall, the atmosphere at this latitude is warmer in November than in February due to the seasonal lag (residual heat) of late summer and fall.
It is also interesting to note that while it was in the upper 20s in the Twin Cities this morning, it was in the 50s in Denver at over 5,000 feet elevation. Why is this? Denver is getting downslope flow, which warms the air mass east of the Rockies. Also, some of the air mass moving into Colorado is being transported form Arizona which saw record highs in the 90s again Wednesday.
Our warm up this weekend will also feature some remarkably warm overnight minimum temperatures. It may not drop below freezing again in the metro overnight until the middle of next week. That is remarkable for November, when our average low is now running about 29 degrees in the metro this weekend. In fact, the minimum Saturday morning may be in the mid 40s. That's our average high for this time of year.
Enjoy the warm up!
Posted at 12:28 PM on November 5, 2009
by Paul Huttner
CPC graphic shows Tropical Pacific SST's warmed rapidly the past few weeks.
An updated monthly report today from NOAA's Climate Prediction Center shows El Nino is gaining strength in the Pacific Ocean. Sea surface temperatures in the tropical Pacific rose as much as 1 degree Celsius in October. Large areas of the tropical Pacific Ocean are now +1.5 degrees Celsius above average.
The CPC forecast for this winter remains for at least a moderate strength (3-month Niño-3.4 SST index of +1.0°C or greater) El Nino. According to the CPC, the anticipated effects of this level El Nino include:
"For the contiguous United States, potential impacts include above-average precipitation for Florida, central and eastern Texas, and California, with below-average precipitation for parts of the Pacific Northwest. Above-average temperatures and below-average snowfall is most likely for the Northern Rockies, Northern Plains, and Upper Midwest, while below-average temperatures are expected for the southeastern states."
The latest CPC three month outlook for Dec-February highlights the anticipated warmth in the northern states.
The various CPC models show wide disagreement on the eventual strength of El Nino this winter. From the CPC discussion:
"There continues to be disagreement among the models on the eventual strength of El Niño, but the majority indicate that the three-month average Niño-3.4 SST index value will range between +1.0°C and +1.5°C during the Northern Hemisphere winter (Fig. 5). Consistent with the historical evolution of El Niño, a peak in SST anomalies is expected sometime during November-January. At this time, there is a high degree of uncertainty over how long this event will persist. Most of the models suggest that this event will last through March-May 2010, although the most likely outcome is that El Niño will peak at least at moderate strength (3-month Niño-3.4 SST index of +1.0°C or greater) and last through at least the Northern Hemisphere winter 2009-10."
It will be interesting to see how strong this El Nino will be as it reaches maturity in the coming months.