TODAY’S FUN LINKS:
Remembering the October 2007 Severe Weather Outbreak – YouTube
October 2010 North American storm complex – Wikipedia, the free encyclopedia
The Stratospheric Sudden Warming Website – Home
WEATHER HAZARDS (During The Next 24 Hours)
SEVERE WEATHER OUTLOOK
(potential for tornadoes, damaging winds, and large hail within the next 24 hours)
Some Thunderstorms May APPROACH Severe Limits
(Pressure Gradient Derived)
MB….N, C ON….QC
Some Thunderstorms May APPROACH Severe Limits
S ID….N UT….W WY….SW MT
HEAVY RAINFALL OUTLOOK
(potential for an inch or more total rainfall within the next 24 hours)
Isolated Locations In
(QPF 1 – 2″)
WINTER WEATHER OUTLOOK
(potential for maximum temperatures below 25 deg F within the next 24 hours; snowfall in excess of 4 inches over a 24 hour period; or other frozen precipitation exceeding trace amounts)
Scattered Locations In
E MB….N ON….NW QC
(Snow; Blizzard; 4 – 12″)
GLOBAL WEATHER SUMMARY
(a review of important weather features around the world)
The western and central Pacific Ocean have become tropically quiet, with no evidence of a Kelvin Wave or any warm-core cyclogenesis. The polar westerlies are, on the other hand, active but showing fairly little connection with equatorial convection. The storm over Hokkaido is important in the sense that as it heads toward the Aleutian Islands and points eastward, its track could determine just how strong and cold a cyclonic event over North America may be in the extended period. Cold air is now building across Siberia but so far is not drifting southward into Mongolia or the PRC.
The westerlies are quite strong in all phases now, from subtropical to polar and Arctic (seen near the Aleutian Islands). Note the low latitude of the storm west of California; this feature may be implicated in severe weather, strong gradient-derived winds, and cold advection over the eastern half of the U.S. by the middle of the new week.
The area near the Americas is the most tropically active, with Tropical Storm Irwin southwest of Mexico, a broad disturbance centered over the Yucatan Peninsula, and a rogue ITCZ wave across the equatorial Atlantic Ocean. What may be the most important feature is an equatorial breach from Colombia and Peru into Florida. Should this path of cross-tropical moisture and energy links with the tropical low and an oncoming storm in the polar westerlies, a significant weather event could occur along the Eastern Seaboard on Tuesday and Wednesday.
While tropical cyclone formation form a “Cape Verde” scenario is unlikely, it is worth noting that a singular convective grouping has acquired a circulation between the Windward Islands and western Africa. Otherwise the ITCZ continues to drift southward with a huge thunderstorm grouping over and north of the Congo Delta. Thunder is also occurring over South Africa, indicating a weakening of the Kalahari heat ridge complex.
The lack of a cohesive signal from the Madden-Julian Oscillation is evident here, as convection continues to be scattered across the equatorial Indian Ocean. Thunderstorms are heavy enough to trigger cases of flooding in parts of India, Burma, and Vietnam. You can see a formative cAk vortex over far northern Russia with an Arctic cold front approaching the Ural Mountains. This signals an upcoming period of long-lived cold for much of the Russian Commonwealth.
SHORT RANGE OUTLOOK
(Through The Next 72 Hours)
Cooler, Variable Cloudy Pattern Before The Gathering Storm
Plymouth State University Weather Server
The elements which may come together to trigger a very powerful storm are evident in the GOES EAST imagery (tropical disturbance over Yucatan Peninsula; cold cyclonic energy over Ontario and Hudson Bay; approaching jetlet from storm over the eastern Pacific Ocean). Colder profiles are becoming more dominant across the northern half of U.S.; later in the new week a fairly pronounced drop in temperature is likely through the eastern two-thirds of the nation. It does appear, however, that the most important precipitation will not occur until later Wednesday. Note that the NAM version PTOT chart is still rain-free in much of the Mid-Atlantic region early on October 19.
Windy, Warm Pattern Continues For Much Of The West
Plymouth State University Weather Server
Despite the fact that a sizable storm complex is lurking offshore of California, the forecast for the southwestern states will be largely dry and quite warm over the near term. As a Sonoran heat ridge reforms over the southwestern states, the disturbance will be forced to track into the Pacific Northwest, then drop southeastward into the Great Plains. The ridge complex, in conjunction with a downslope wind profile, could boost temperatures and winds in the Golden State into a “Santa Ana” like condition on Tuesday and Wednesday.
MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)
Polar, Not Arctic, Regime Follows East Coast Storm
Plymouth State University Weather Server (2)
While the drop in temperatures expected to occur across the eastern half of the nation may seem shocking (remembering our devilishly hot summer….), the air mass involved in the cooling will be a polar (cPk) variety and NOT and Arctic regime (as has been posted on some Internet and other media sources). I suspect that the gusty winds which will be concurrent with the cold advection will heighten its chill sensation somewhat. There may be some snow showers or flurries in parts of the Great Lakes and Appalachia in the October 18 – 20 time frame, but most of the precipitation concerns will be in the forms of severe thunderstorms and heavy stratiform rains along the Eastern Seaboard. With no blocking to speak of, this is a transient cold period, as can be clearly seen on the GFS 850MB thermal chart for Friday morning. The coldest part of the domain will be exiting across New England by that time.
Flat Ridge Keeps Southwestern States Warm And Dry
While I emphasize the +PNA nature of the jet stream configuration (see return to Sonoran heat ridge across California and the Southwest), the lack of blocking implies that disturbances from the mean negative 500MB height anomaly in the Gulf of Alaska will continue to target the Pacific northwest with rain and cool (not cold) temperatures. By October 25, the depth of the 500MB trough across the Great Plains against the subtropical high will allow for an extensive surface high pressure cell to form over the Salt Lake Valley. Anticyclones in this position that exceed 1025MB are invariably associated with high wind events in California and the lower Colorado Valley. It seems likely that readings in the coastal cities in California will soar well above normal, accompanied by strong winds and fire threats.
EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)
Progressive Pattern Allows For Storm, Cold Intrusion Across Eastern U.S. In Last Week Of October
Penn State University E-Wall
A key rule to remember as winter approaches in North America: as long as no signs of high-latitude blocking mechanisms are apparent in Alaska, Canada, and Greenland, any cold air that appears in the U.S. will be strictly transient. If you examine numerical models for the longer term, none show any signals that would approach characterization as a block. In fact, the jet stream configuration after 360 hours is best described as semizonal.
However, I should be emphatic that a strong storm and cold intrusion IS likely to occur in between October 25 and 29 over the eastern half of the nation. A negative 500MB height anomaly drops out of the persistent Gulf of Alaska Low, creates a neutral or negative tilt trough complex, with a deep tropical moisture and energy connection. This seems to be a repeat of what will happen in the near term, and should the various elements come together a huge rain event, possibly ending as flurries, could occur across Appalachia and the Atlantic Coastal Plain.
A thought for the upcoming winter: if you recall, the deep negative height anomaly has drifted steadily south-southeast from its position over Alaska in June and July. Further loss of latitude will be likely with this feature, with a probably location near or just west of California by January. Teleconnections on a deep low between 40 and 35 N Latitude off of the West Coast strongly support a Rex block over AK and BC. Linkage on such a ridge, in turn would promote a cAk vortex across the Great Lakes in the dead of winter.
That doesn’t sound like a formula for a mild winter season, now does it?
Prepared by Meteorologist LARRY COSGROVE on
Saturday, October 15, 2011 at 6:30 P.M. CT
The previous statements are my opinions only, and should not be construed as definitive fact. Links provided on this newsletter are not affiliated with WEATHERAmerica and the publisher is not responsible for content posted or associated with those sites.
Copyright 2010 by Larry Cosgrove
All rights reserved.
This publication may not be reproduced or redistributed in whole or in part without the expressed written consent of the author.