MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)
Moderate-Sized Winter Storm Brings New Surge Of Bitter Cold To Midwest, Northeast....
I suspect that the ECMWF series has the best handle on the track, structure, and intensity of a shortwave digging southeast from Alberta later this week. Since the cAk vortex is so strong and far south, the idea of a recurvature of the impulse through the lower Great Lakes (and a warmer, rainy result fro the Eastern Seaboard) seems inferior to a more classic path of a surface low through the Ohio Valley into the Delmarva Peninsula and then towards Nova Scotia (by late January 26). The more southern track I envision carries two main risks: one for a significant rain to ice accretion in parts of the Corn Belt (Interstate 70 corridor from St. Louis MO to Breezewood PA) as well as a band of moderate or heavy snow from parts pf PA and NJ through central/eastern New England. Once again I emphasize that the ECMWF panels have another significant push of brutally cold air filling in behind the disturbance which may sag as far south as GA and the Carolinas next weekend.
....But New Disturbance Hitting West Coast January 28 - 29 Could "Shake Things Up"!
Plymouth State University Weather Server (3)
The numerical models have been fairly consistent in showing an alteration or "reload" in the 500MB longwave pattern starting around January 28. As a pool of very cold Arctic values buckles north and east into Quebec and Atlantic Canada, storm energy now over the central Pacific Ocean will begin to link with the equatorial moisture axis to the south and west of Mexico. Following (mostly) the scenario put forth by the three ensemble groups (GFS, GGEM, and ECMWF; the operational American version captures the intensity but probably not the ultimate path of the surface low), moderation of the air mass should occupy the eastern half of the nation through January 30. This could be a big severe weather producer with heavy rain in parts of Texas and Dixie, and I think ultimately another snow and ice grinder fro the central Great Plains, Ohio Valley, and the Northeast. Very cold air that drops into the West will make its presence felt over the eastern two-thirds of the U.S. in the 11 - 15 day period.
EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)
Brief Warm-Up Over Eastern Half Of Nation Quickly Gives Way To Brutal Realm Of Arctic Cold Air In +PNA, -AO, -NAO Configuration....With Maybe A Winter Storm Threat!
Plymouth State University Weather Server
University Of Illinois
Pennsylvania State University
This being a truly neutral ENSO episode (as opposed to the "leaning toward El Nino or La Nina positive/negative tilt), we can look back in the calendar some years for comparisons. This type of SST anomaly regime in the equatorial Pacific Ocean was common in the period 1959 - 1963, noted for mostly erratic winter seasons that had their share of intense frozen precipitation events and sometimes breathtaking Arctic blasts. In some respects the current DJF period may resemble 1960-61, perhaps delayed by 6 - 10 days. With tropical forcing evident near the International Dateline (and a hook-up with a sub-Aleutian Low), it seems clear to me that the U.S. will be entering a very rough period for weather. As in cold and stormy.
The intense storm threatening the lower Great Plains on January 29 is actually a key player in the evolution of the 500MB longwave pattern for much of February (maybe the first two or three weeks; I think what transpires in the extended period will NOT carry over into March). My current thinking is the low takes a path into lower Appalachia, then moves along a frontal structure into the VA Capes with a chance for a major intensification. Keep in mind how consistent the ensemble groups have been now for FIVE days worth of runs! With the establishment of a highly amplified +PNA, -AO, -NAO configuration, the cAk vortex looks to expand and drop into Ontario and Quebec. I think the storm ejecting from the Southwest will help with drainage of colder values and expansion/digging of the motherlode. Hence the argument is in place that the coldest weather of the winter will occur over the U.S. to the right of the Rocky Mountains between January 31 and February 5.
There could be another storm in the mix as we end the first week of February, but I suspect that many will have their hands full with the January 28 - February 1 feature and the cold intrusion that follows. Under the ridge out West, mild and mostly dry conditions will be in stark contrast to the weather further east.
Aren't you excited about this pattern?
Prepared by Meteorologist LARRY COSGROVE on
Saturday, January 19, 2013 at 7:20 P.M. CT
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Copyright 2012 by Larry Cosgrove
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