A GUIDE TO BAROCLINIC DISTURBANCES AFFECTING NORTH AMERICA; Part 1B; Revised, Edited Thursday, November 4, 2021

[Larry Cosgrove]

GREAT LAKES BACKDOOR STORMS

(Slang: Manitoba Maulers, Saskatchewan Screamers)

 

Region Of Cyclogenesis: Eastern Saskatchewan, Manitoba, or western Ontario

 

Lowest Range Of Central Pressure At Surface: 990 to 1014MB

 

Forward Speed: Rapid; cross-continent sequence within 72 hours

 

Season of Occurrence: November 15 to April 1

 

500MB Structure: Shortwave in conjunction with vortex over Hudson Bay or James Bay

 

Associated Sensible Weather: Resembles an Alberta Clipper in terms of structure, forward speed, and precipitation array. Causal mechanism is purely dynamic, however, with the shortwave NOT undergoing leeside reformation. Instead, the surface low deepens as the 500MB vorticity maximum digs southeastward between a +PNA ridge in western Canada and a cA or cAk motherlode in the vicinity of Hudson Bay. Many times this type of track signifies the start of a southeastward displacement of the circumpolar vortex, implying a surge of bitter cold air affecting sections of the Midwest and/or Northeast.

 

Forecast Considerations for Great Lakes Backdoor Storms are:

 

1) Advection of cA or cAk values from NU AR and N MB into a relatively small corridor through the Great Lakes, Mid-Atlantic, or New England regions

 

2) Moderate to heavy synoptic snow (with some ice) across extreme SE ON, S QC, NY, and New England; a few cases may even see the deepest snowfall as far south as OH, PA, and NJ. This is accomplished by a strong spike in UVV concurrent with dewpoint advection from the Atlantic Ocean

 

3) Lake-enhanced blizzards along the lee shores of the Great Lakes

 

4) Poor prediction ratio due to infrequent occurrence; NWP data may portray seemingly harmless paths through QC Eastern Townships and ME as little as 48 hours before impact.

 

Classic Case: February 5-6 1984 ground blizzard which was accompanied by -70 F wind chills and zero visibility from MB into IA. Note the southward path of the 500MB low and the compact pressure array at 1000MB.

 

PUGET SOUND TO GREAT BASIN STORMS

 

Region Of Cyclogenesis: Gulf Of Alaska

 

Lowest Range Of Central Pressure At Surface: 970 to 1012MB

 

Forward Speed: Rapid; sequence finishes within 72 hours

 

Season of Occurrence: October 15 to April 1

 

500MB Structure: Shortwave ejecting from mPk, mA, or mAk vortex in Aleutian Islands or southern coastline of Alaska

 

Associated Sensible Weather: Bursts of heavy rain and/or snow lasting 3 - 6 hours, concurrent with passage of 500MB vorticity maximum; intense convection possible with microbursts, hail, and isolated funnels; overall precipitation shield is quite small, about 400 miles. These storms can bring snowfall to lower latitude locations such as Las Vegas NV; Phoenix AZ; and Albuquerque NM.

 

Classic Case: February 26, 1996 snowfall affecting Las Vegas NV metro.

 

MOGOLLAN RIM STORMS

 

Region Of Cyclogenesis: Mojave or Sonoran Deserts (southern California, southern Arizona or northern Mexico)

 

Lowest Range Of Central Pressure At Surface: 988 to 1004MB

 

Forward Speed: Very slow; sequence may take as much as six days to complete before system fills or is displaced by a kicker shortwave

 

Season of Occurrence: November 15 to April 15

 

500MB Structure: Longwave (smaller scale cutoff low); cold core low becomes trapped below +PNA type ridge over the Intermountain Region, and slowly begins to weaken through a filling process.

 

Associated Sensible Weather: Profuse production of heavy snowfall in the mountains of the southwestern U.S., with worst effects in northern Arizona and northern New Mexico. Some communities may receive as much as 4 feet of snow. Stratiform rain or scattered convection possible along the Mexican border, If cA values become entrained into the circulation of the low, snow may fall in locations such as Phoenix and Tucson in Arizona and El Paso, Texas. Precipitation may continue until the upper low fills or is kicked out, which may take nearly a week.

Classic Case: December 13 - 17, 1967; state record for snowfall in Arizona set at Heber Ranger Station

 

PANHANDLE HOOK "A" CYCLONES

 

Region Of Cyclogenesis: Eastern New Mexico or the Texas/Oklahoma Panhandle Region

 

Lowest Range Of Central Pressure At Surface: 986 to 1014MB

 

Forward Speed: Normal to rapid; sequence may last as much as four days 

 

Season of Occurrence: October 15 to May 1

 

500MB Structure: Shortwave; may begin or end its life cycle as a longwave (closed) low

 

Associated Sensible Weather: Noted for production of heavy stratiform or overrunning precipitation in the northern quadrants of the cyclone. This track is one of two that are favored to bring heavy snowfall to Midwestern cities (Des Moines IA, Kansas City MO, Milwaukee WI, Chicago IL and sometimes Minneapolis MN). Crippling ice storms may also occur just north and east of the track (perhaps involving Wichita KS, Columbia MO, Quincy IL, Gary IN, as well as Lansing, Flint and Detroit in MI and Sarnia ON). Strong convection is possible in the warm sector, but tornadic supercell signatures are rare.

 

Classic Case: January 12 - 14, 1979 blizzard which brought 20 - 26 inches of snow to Chicago IL metro area.  

 

 

 

PANHANDLE HOOK "B" CYCLONES

 

Region Of Cyclogenesis: Eastern New Mexico or the Texas/Oklahoma Panhandle Region

 

Lowest Range Of Central Pressure At Surface: 970 to 1004MB

 

Forward Speed: Normal to rapid; sequence may last as much as four days 

 

Season of Occurrence: October 15 to May 1

 

500MB Structure: Hybrid; defined low center in a progressive, full-latitude trough; may originate as an ejecting shortwave in the High Plains; almost always exhibits a neutral or negative orientation through much of its lifetime

 

Associated Sensible Weather: Two major complications from this type of cyclone are excessive production of tornadic supercells over a wide geographic area and also widespread generation of  strong winds derived from a deep surface low within a compacted pressure gradient. In some cases, snow and ice may be a problem within the cold sector.

 

Classic Cases: Two stand out as variations of the same family: the April 3 - 4, 1974 system associated with the "Super Outbreak" of tornadoes; and the November 10, 1975 "Edmund Fitzgerald" storm affecting the Great Lakes  

SOUTHLAND TEMPEST (Slang: "El Nino Express")

 

Region Of Cyclogenesis: Central or Eastern Pacific Ocean between 30 - 40 N Latitude

 

Lowest Range Of Central Pressure At Surface: 982 to 1000MB

 

Forward Speed: Normal; sequence may last three to five days 

 

Season of Occurrence: October 1 to May 15

 

500MB Structure: Shortwave deepening to a hybrid-type signature

 

Associated Sensible Weather: May mimic other types of storms, but occurs only during an El Nino episode. Cyclogenesis usually occurs when the polar westerlies split into two streams just to the northwest of the Hawaiian Islands. Energy then digs, and captures a fetch of mTw values from the equatorial Pacific Ocean. The low and its moisture plume then target C and S CA with heavy rainfall, thunderstorms, landslides, and snowfall (which in a few cases may be seen even in the lower elevations close to San Francisco, Los Angeles, and San Diego in the Golden State).

 

Redevelopment or center jump relocations can occur as much as twice during the lifetime of a Southland Tempest: to the lee of the Rocky Mountains in NM and again over the Piedmont or Atlantic Coastal Plain in GA or the Carolinas. Snow may develop at unusually low latitudes within the cold sector of the cyclone, while severe thunderstorms, tornadoes and torrential rainfall are common complications within the overrunning and warm advection quadrants. Roughly 1 out of 4 disturbances of this type will recurve to the north-northeast upon reaching the vicinity of Cape Hatteras NC, with resultant concerns for strong winds, excessive rains, and beach erosion from VA into New England, the Maritime Provinces, and Atlantic Canada.

 

Variations: In some El Nino events, jet stream splitting may be depressed as far south as the Rio Grande River and Gulf of Mexico, resulting in unusually cold conditions with frozen types in the Deep South (excepting portions of the FL Peninsula, which may experience severe weather). At the same time, northern latitudes could see a very mild and dry trend.

 

As the +ENSO event wanes and spring arrives, a gradual but noticeable northward shift in the storm track will occur, with potentially devastating effects from tornadoes and severe weather. Convective episodes with the stronger El Ninos may actually persist into May.

 

Classic Cases: December 14, 1997 heavy snow event affecting Louisiana and Mississippi; January 3 - 5 1982 storm affecting California; April 15 - 16, 1998 severe weather outbreak