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About LarryCosgrove

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  1. Weather satellites can help reveal the various features which will dictate conditions in North America as we get closer to the holiday period. What stands out the most on the mosaic view is the renewed vigor of the subtropical jet stream. Note the linkage with the current storm in the Great Lakes region originates just above Papua/New Guinea! The phasing of the two entities helps to energize the mid-latitude cyclone. Downwind of an emerging West Coast ridge, strong cold advection occurs which will be a factor in forecasts for the eastern 1/2 of the nation. It is the storm exiting the Japanese Archipelago which may be the ultimate system in setting up the longer term pattern. This gigantic area of low pressure, or other such disturbances succeeding it, will find a home between the Aleutian Islands and Hawaii. The broad cyclonic circulation will continue to pump up a ridge complex over the eastern Pacific Ocean, Alaska and northernmost Canada. So an argument for drainage of cAk values into the USA may exist periodically through the rest of December. TX and Dixie will see occasional turns to warmer air (subtropical high nearby in the Greater Antilles). Energy and moisture transport from below Baja California may also send along a storm just before Christmas.
  2. With talk of the first meaningful Arctic intrusion of the season increasing for next week, I wanted to point out two concerns that have arisen as to viability of the numerical model predictions which show much colder air. One issue is snow cover, with the lower 48 states being mostly barren of the white stuff. If you look north of the border, Canada, the Arctic Islands and nearly all of Russia has an impressive snowpack and ice sheet. This frigid display is necessary for generation of cAk regimes. So all that is needed to drain any chilled values into the U.S. would be an emphatic high-latitude ridge and deep, digging trough and storm. Note the development of an impressive subtropical jet stream, with embedded storm energy, on the GOES WEST image attached here. Yes, this is related to the high-elevation snow event in Hawaii. More important to mainland concerns, the southern branch wind field will supply energy and moisture to the large storm complex covering the northern Pacific Ocean. Once that feature digs into the U.S. (after December 5), the potential for cold advection, and snow-generating disturbances tracking through the lower Great Plains and the Eastern Seaboard, should increase markedly.
  3. Commodity and energy traders, along with winter weather enthusiasts, got something of a morale boost from the most recent CFS and ECMWF model forecasts heading for the second week of December. Viewed from the 500MB level, the American climate series showed a fairly amplified pattern with a deep trough across the eastern half of North America. The European weeklies had a stronger surface temperature reflection, trying to set up a warm West vs. cold Central/East alignment. I always check such radical turns in numerical model forecasts against analog summaries compiled for the DJFM period. Taking December 10 as an example, there are decent, though not overwhelming, similarities between the comparison test mean for the date and what the longer term predictions say. What to make of the chances for a genuine cold snap heading into mid-month? Good potential for a winter type storm tracking from TX and LA into E ON and QC. Milder temperatures along the Eastern Seaboard should get pushed out for a few days, but the strongest risk of true wintry cold will be from the High Plains through the Great Lakes and Mississippi River watershed. Hope that all of you are having a great weekend.
  4. A caution I would like to throw out to the group is that while many are clamoring for a colder winter with lots of snow and ice along the Eastern Seaboard, none of the model forecasts or analog collection seems favorable to such a scenario. You will notice on the ensemble platforms in the 11 - 15 day plenty of positive 500MB height anomalies within the Arctic Circle. But the actual contour depiction has -no- signatures (closed ridge contours above 534dcm north of 45 N Latitude). That can change, but more and more the first month of the DJFM sequence looks to have southwest flow aloft and warm anomalies. That eastern Pacific Ocean trough/Gulf of Alaska Low must retrogress to between the Hawaiian and Aleutian Islands for winter to show its true (crystal and white) colors along the Interstate 81 and 95 corridors. Happy Thanksgiving, everyone!
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