WRAL WeatherCenter Blog

Weather to Watch?

Posted December 8, 2008

Outlook for mid-December temperatures from the Climate Prediction Center, showing the effects of a possible warm ridge aloft developing across the southeastern U.S. - if this pattern change verifies, we should see several days next week with above normal temperatures.

We finished the weekend off with temperatures well below normal (a frequent occurrence lately) along with breezy northwest winds that gusted to around 20-25 mph, but it appears we have both short-term and possibly longer term temperature swings in our near to mid-term future.

The first of those comes over the next two days as high pressure over the state shifts east of us and a developing frontal system over the nation's midsection moves into place to our west. Southeast to southwest flow should develop across the area during that period, and we'll see late day highs on Tuesday push into the mid 50s to around 60. Southerly flow may strengthen even more after that as the cold front west of us draws closer, and temperatures may end up climbing through the night into Wednesday.

On Wednesday itself, we now appear to have a decent chance to reach or exceed 70 degrees, at least for parts of our viewing area, with gusty southwest winds, and there could be enough instability later Wednesday or at night for some thunderstorms to form - right now it appears instability may be limited due to warm temperatures aloft, but vertical wind shear may be quite strong and it will be worth keeping an eye on the small potential for strong or severe storms, and also some periods of heavy rain, with one model projection indicating as much as 2-4 inches over the course of Wednesday and Thursday.

Our brief round of warmer temperatures may end with authority on Thursday as much colder air pours right back in behind the frontal system, but there remain subtle but very significant differences in projections from various computer models (and within ensemble members from the same model) regarding how fast that front moves through and the degree to which it may stall and support an additional or extended round of light to moderate precipitation, and how mild or cold it may be when that happens. Bottom line is that for Thursday, there is a fairly wide range of possible outcomes (which could involve thunder toward the southeast and a wintry mix to the northwest as the precipitation tapers off, for example) even as I write this on Monday morning, so keep checking in as we refine that forecast over the next day or two.

The longer term changes I alluded to above involve a larger-scale pattern shift that extended range models are now advertising more consistently for the period beginning late in the weekend and extending into mid-December, where it appears we may see a reversal of the recent trend toward a warm ridge of high pressure over the western U.S. and a persistent cold trough in the east. This reversal is indicated in the current 8-14 day outlooks from the Climate Prediction Center (image attached) which indicates a tendency toward above normal temperatures for that period across the southeast.

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