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|Even though we have some bitterly cold air in place over the region during these first few days of 2008, it looks like the cold won't last too long. |
Temperatures will climb to well above normals during the second week in January. (Just in time for the PA Farm Show?) This kind of a warm-up is usually termed a "January Thaw." See the graphics below for more detailed information.
The first graphic is a box-and-whiskers plot of the possible daily highs and lows (maxes and mins), and probability of precipitation from many different computer models. The dates on the plot are labelled at Midnight UTC (aka Greenwich Mean Time/London UK), which equates to 7 PM EST (the day before).
These different model runs all seem to agree quite well that Monday and Tuesday (7th and 8th) will be quite warm for this time of year. The graphic below is the summary of prognostications for Altoona, Blair County Airport (KAOO). But, similar results will be found looking at other locations across the region.
There is also a possibility for some light rain (perhaps freezing rain if the surface temperatures are cold enough) as the warmer air moves in over the weekend. Then, a stronger signal shows up in the plot for (possibly heavy) rain/showers during the middle of next week.
See other box-and-whiskers plots like this one by clicking here. These plots are available through our Computer Models link (on the left), too.
The second graphic is the expected upper-air flow (jet stream pattern) at 500 hPa (mb) for Tuesday Morning. Take a close look at the second panel (with the green contours and yellow/blue shading). Note the large-amplitude ridge that is over the Eastern U.S. This is a very warm signal for the region, as the general wind flow (at the surface and aloft should be from the southwest. The yellow and orange shading shows that this will be a somewhat unusual event, with these upper heights most abnormal over New England and Eastern Canada.
The top panel is a "spaghetti plot" that shows the individual outcomes of the different models in the Ensemble Prediction System - and their color coded lines. The grey shading on this panel shows how well the different solutions are correlated. In this case, there is some disagreement on the speed/placement of the next trough moving in from the west (very dark shading over the upper midwest), but very good agreement (light shading) on the high heights (big ridge) in the East. If the solutions are close together (in timing and/or magnitude), the shading will be light, if they are disparate, the shading will be dark.
Good agreement between the ensemble members leads to a high confidence forecast. See more ensemble plots like this on the following page: http://nws.met.psu.edu/ensembles/index.html
So, putting it all together: There is a high confidence that the temperatures will warm up early/mid next week as the pattern shifts to a mean upper ridge over the Eastern U.S.
If you read into this a bit further, the really warm weather does not last long. Does a January Thaw ever last very long?
|GFS Ensemble MOS Graphic of possible Temperatures, and Probability of Precipitation for KAOO (Altoona, Blair County Airport) for Jan 2-8, 2008|
|Ensemble Plot of Upper Heights (Jet Stream level) for Tuesday Morning, Jan 8th, 2008.|
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