WEATHERAmerica Newsletter, Saturday, March 22, 2008 at 8:30 P.M. ET
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)
HEAVY RAINFALL OUTLOOK
(potential for an inch or more total rainfall within the next 24 hours)
Isolated Locations In
(QPF 1- 2")
Isolated Locations In
W BC....W WA....W OR
(QPF 1 - 3")
FROZEN PRECIPITATION OUTLOOK
(potential for accumulation of ice rime, freezing rain, sleet or more than 3" total snowfall within the next 24 hours)
Isolated Locations In
Lower MI....ON Peninsula
(Snow; In Squalls; 3 - 6")
Numerous Locations In
(Snow; 4 - 12"; Blizzard)
Isolated Locations In
C MB....W ON
(Snow; 3 - 6")
Isolated Locations In
BC....WA Olympic Peninsula
(Snow; Above 5000 Feet; 4 - 12")
SHORT RANGE OUTLOOK
(Through The Next 72 Hours)
Snow For Easter? If Not Snow, Then Cold!
While it is really not that rare to have an Easter holiday with snow in the Midwest or Northeast (especially with the date occurring in late March this year), it is a tad unusual to be talking about the possibility for frozen precipitation reaching into Dixie. It could happen on Sunday, what with the 0 C isotherm reaching as far south as the Interstate 10 corridor. With so much cold air and vorticity aloft, I would not be surprised if some locations in the Ohio Valley and middle Appalachia receive accumulations of the white stuff. The cold air will likely be a factor in forecasts east of the Mississippi River through Tuesday morning.
Warmer Air Will Build Northward From Mexico
Of course, this being spring, cold air cannot be pervasive across the entire U.S. True to form, build-ups of warmer (cT) air have occurred periodically in the past two weeks over Mexico. Some of the hotter readings occasionally reach the Southwest and parts of the lower Great Plains. This should be the case on Tuesday, with the warm and dry domain slowly pushing north and east ahead of a large storm complex along the West Coast. Parts of NM and W TX have a decent shot at reaching 100 deg F on the afternoon of March 25.
Pacific Northwest About To Get Hit Again
There is a particularly menacing storm lurking offshore from the Pacific Northwest, and this feature should make landfall over Vancouver Island BC on Sunday night or Monday morning. Snow elevation levels are forecast to be fairly low ahead of the storm, so the coastal and inland ranges of BC, WA, OR and eventually ID are likely to see a good dump of snowfall to start the new week. Rain and wind will also be an issue in the coastal and valley locations. In time this disturbance could have a profound impact on much of the lower 48 states during the medium range.
MEDIUM RANGE OUTLOOK
(Four To Ten Days From Now)
Is There A Violent Spring Storm In Your Future?
There may actually be TWO important storms to target the U.S. in the medium range, if satellite views and the operational GFS output from 12z and 18z are taken into consideration. While the latest ECMWF model data suggest no extreme conditions from the disturbances over the eastern Pacific Ocean (which are VERY impressive looking on GOES WEST images), the ensemble runs of bother American and European schemes are nothing less than scary, showing a full-latitude impact from a storm sequence between the 96 and 192 hour time frames.
Keep in mind that unlike previous systems, the emerging threats in play are 1) severe thunderstorms and tornadoes and/or 2) heavy rainfall with flooding. Give the GFS version credit for doing better than the ECMWF panels with recent systems; the tornado and flood situations, followed by sharp attacks of cold, have been well documented by the American equation and its variants. Surface convergence is a key factor with risks from the Great Plains into the Midwest and Old South; note a perfect quadra-convergence of cP, cT, mT and IcP values on Days 5 - 7. If I lived in the communities hit by torrential rains last week, I would be very concerned about the danger of a severe+flood event arising later next week.
Volatile Temperature Swings Are Indicated (Again)
In what may be blamed as an effect of a "La Nina vs. Madden Julian Oscillation battle" (see below), the U.S. will again be visited by a rather extreme temperature change next week. The cT and mT regimes ahead of the aforementioned major storm will be replaced by a biting cA domain. If model forecasts are correct, that colder air mass will itself be short-lived, replaced by warming ahead of yet another storm at the start of the extended period.
Will Blocking In The NAO Position Keep The Cold In Place?
There is strong agreement among all of the numerical models and the respective ensemble members of a period of blocking in the NAO position (in this case Greenland and Iceland) during most of the medium range and extended period. While a positive height anomaly of this type is NOT a universal suppressant of the jet stream at this time of year, through April such a ridge can maintain cold profiles over the Midwest and Northeast. So while the southern tier of the U.S. may see meaningful periods of warming, temperature trends from the upper Missouri Valley into New England and the Mid-Atlantic states will remain mostly below seasonal normals through April 7.
EXTENDED PERIOD FORECAST
(Between Day 11 And Day 15)
Western Pacific Ocean Storm Sequence Still The Main Factor In Longer Term
The active storm sequence that has been the calling card fro the winter of 2007-2008 continues to be the driving force in weather for the first part of the spring season. One particularly troublesome feature to note: when the disturbances (perhaps linked to the now-weakening La Nina episode) interact with the equatorial convective belt that straddles the Indian Ocean and Oceania (tied to the Madden-Julian Oscillation). This sequence is happening again, and may ultimately be responsible for periodic rise in atmospheric heights in the PNA and EPO positions. If so, we will probably see another important, albeit temporary, cold intrusion across Canada and much of the lower 48 states at some point during the first week of April.
Huge Snow Cover Spells Potential For Widespread Flooding In Great Lakes, Corn Belt
In case anyone has not noticed, there has been an extraordinary amount of snowfall in parts of the Upper Midwest, Great Lakes and interior Northeast this winter. With an active storm track and a gradually warming landscape at work, the slowly melting snowpack will be a catalyst for widespread flooding. Between now and April 7, here is potential for perhaps THREE impressive overrunning events, with implication of heavy rain, for localities along and above Interstate 80. This rainfall could present a threat for widespread flooding affecting metro areas such as Minneapolis MN; Milwaukee WI; Chicago IL; Detroit MI; Cleveland OH; Buffalo NY; and Toronto ON even with few cases of warm sector penetration.
Fading La Nina, Warming Gulf Of Mexico Favor Severe Weather, Excessive Rains In Mississippi, Tennessee, And Ohio River Valleys Through Most Of The Spring
As one can see my checking out the narrowing corridor of cold SST anomalies in the equatorial pacific Ocean, the La Nina episode of 2007-2008 is steadily weakening. But the -ENSO event is still having an impact on the synoptic pattern, with stronger than normal westerlies, and storms, forming near the Ural Mountains and carrying inclement weather as far east as the United Kingdom. Not until the 3,4 sector has warmed to near climatic normals will the U.S. see a substantially different weather pattern.
I should also mention the rise of water temperatures over the western Atlantic Basin. Against a cold pool near Mexico and the West Coast of North America, teleconnections favor an active and moist subtropical jet stream running from below Baja California into Nova Scotia. With this windfield in mind, there is increased confidence in the forecast of flooding rainfall starting anew in the inundated areas stretching from OK through the Ohio Valley.
Prepared by Meteorologist LARRY COSGROVE on
Saturday, March 22, 2008 at 8:30 P.M. ET
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 2008 by Larry Cosgrove
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