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STORM TRACK CLIMATOLOGY for the U.S.+


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Larry Cosgrove posted this over at EUSWX on December 5 2004.

 

I am posting it here for educational purposes only.

 

 

 

Friends

 

A primer that I wrote on recognizable storm tracks was available until recently on the Florida State University graduates website. I was informed that the link was no longer operable. So below, until I can get a new page with graphics describing the subject, is a rundown on STORM TRACK types seen across North America. This may explain some of the titles for midlatitude cyclones that you hear frequently in technical discussions.

 

Larry Cosgrove

STORM TRACK CLIMATOLOGY

For The United States

 

Glossary: Designations Of 500mb Cyclones

 

Shortwave Usually a free-moving impulse that follows the mean jet stream wind field rather than changing the flow pattern. Noted on upper air charts by lack of closed height contours, though some intense shortwaves may exhibit a closed signature temporarily.

 

Longwave A semi-stationary disturbance that affects the general weather for a synoptic-scale area. Circulation is always closed, and often shows up in seasonal means for the territory which it is located in.

 

Hybrid Seen as a steadily moving, geographically large storm that combines the coverage of longwave storms with short-term impacts of the shortwave family of disturbances. May not have a closed-contoured 500mb low center, but usually is widely difluent at the midpoint.

 

Trough Any upper disturbance that covers a synoptic-scale area without a dominant maximum center of vorticity. Often, the emphasis of energy is with frontal boundaries and not the surface low pressure center. Height contour field shows little separation, just a noticeable ‘U’ or ‘V’ signature in accordance with pressure falls at the surface.

 

Subtropical Cyclones Disturbances which combine some aspects of a tropical feature with those of cold-core mid-latitude cyclones.

 

Remnant Cutoff Lows Best described as northern stream energy that becomes stationary, weakens, and may later rejoin the westerlies as an active disturbance.

 

Bombogenesis Rapidly intensifying storm systems that exhibit a pressure drop of at least 25 millibars in less than twelve hours time. The process, colloquially termed ‘bombing out’ happens when dynamic and synoptic parameters for cyclone development are ideal. This may include: extremely high velocities in the upper jet stream; cross-polar flow into the cold sector of the storm; equatorial 'breach', whereupon mTw air transverses the equator and flows into the disturbances warm sector; and topographic/oceanographic enhancement of the thermal and pressure fields (lee of mountains or over a particularly warm body of water). Bombogenesis also signifies the development of a new longwave feature.

 

Notable examples of Bombogenesis:

 

1) January 23-24 1978 Atlanta GA….Dayton OH

2) March 13 1993 Central Gulf of Mexico

3) November 10 1998 Concordia KS….St. Cloud MN

4) April 3 1974 Dodge City KS….Cedar Rapids IA

5) January 8 1996 Coastal SC, NC

 

 

Surface Storm Families

 

 

Gulf Of Alaska Cyclones

 

Cyclogenesis Aleutian Islands

 

Lowest Surface Pressure To Be Expected 958mb to 992mb

 

Speed Of Motion Very Slow, Semistationary; May last up to 10 days

 

Typical Storm Track Attu Island AK….250 mi S Anchorage AK….300 mi W Juneau AK

 

Upper Air Structure Longwave, Closed Low; emits numerous small shortwave-type lows that slam into coastal sections from AK southward to near San Francisco CA

 

Apparent Weather Extremely high winds within 400 miles of surface center; heavy rains with resultant flooding/mudslides along and west of coastal mountains ranges from AK Panhandle to Bay Area of CA. Mountain snows tend to vary with height, dependent upon positions of associated shortwave impulses. Some convection in highly unstable marine environment after passage of related impulses (diurnal-dependent). If the vortex and its associated trough link with the subtropical/southern branch jet stream, rainfall can be torrential. The worst-case scenario for these eastern Pacific Ocean systems is to tap mTw values from south of the Hawaiian Islands chain. This is often called the 'Pineapple Express'.

 

Likelihood Of Occurrence September 1 to May 1

 

 

Aleutian Lows

 

Cyclogenesis Kamchatka Peninsula

 

Lowest Surface Pressure To Be Expected 958mb to 992mb

 

Speed Of Motion Very Slow, Semistationary; May last up to 20 days

 

Typical Storm Track Karaginsky Island Russia….Amchitka Island AK

 

Upper Air Structure Longwave, Closed Low; emits numerous small shortwave-type lows that dig southeastward into coastal sections from OR southward to near Tijuana Baja CA Norte

 

Apparent Weather Extremely high winds within 400 miles of surface center; heavy rains with resultant flooding/mudslides along and west of coastal mountains ranges from OR to Baja CA. Mountain snows tend to vary with height, dependent upon positions of associated shortwave impulses. Some convection in highly unstable marine environment after passage of related impulses (diurnal-reactive). The Aleutian low is a semi-permanent feature during El Nino events, and may reappear with frequency during the entire low-sun period. Classic ENSO signature split flow at 500mb derives its energy from the Aleutian low.

 

Likelihood Of Occurrence September 1 to May 1

 

 

Grand Banks Vortex

 

Cyclogenesis Coastal regions of Maine or Maritime Provinces

 

Lowest Surface Pressure To Be Expected 946mb to 990mb

 

Speed Of Motion Very Slow, Semistationary; May last up to 20 days

 

Typical Storm Track Gander NWF to position 200 mi NE St. John NWF

 

Upper Air Structure Longwave, Closed Low; emits numerous small shortwave-type lows that dig southeastward into Maritime Provinces of Canada, then continuing toward Europe.

 

Apparent Weather Extremely high winds within 400 miles of surface center;). The Outer Banks vortex can be a semi-permanent feature during El Nino events, and may reappear with frequency during the entire low-sun period. This vortex forms the eastern anchor of an ENSO ‘split flow’ signature. Presence of vortex translates to raw, cold weather for most of Atlantic Canada, and may pose huge problems for shipping and fishing concerns over the far northern Atlantic Ocean.

 

Likelihood Of Occurrence September 1 to May 1

 

 

Hudson Bay Vortex

 

Cyclogenesis Northwest Territories

 

Lowest Surface Pressure To Be Expected 966mb to 1000mb

 

Speed Of Motion Very Slow, Semistationary; May last up to 20 days

 

Typical Storm Track Yellowknife NWT….Port Churchill MB….Belcher Islands

 

Upper Air Structure Longwave, Closed Low. May spin shortwave energy from Arctic Circle southeastward into Canada and the Lower 48 states of the U.S. Often this vortex will anchor steering 500mb trough over North America.

 

Apparent Weather In itself, the Hudson’s Bay vortex is not known as a major weathermaker. Rather, the importance of this feature lies in its role as a steering mechanism for shortwave-based storms and for delivering cold air. The farther south this vortex is situated, the colder it will be in the U.S. east of the Continental Divide. For instance, during extended cA outbreaks in winters of 1976-77 and 1983-84, the mean position of this system was over MI. In El Nino years, the Hudson’s Bay vortex is often nonexistent (exception: the unusual 1976-77 cold season!).

 

Likelihood Of Occurrence Year round; chief importance of feature is September 1 through May 1.

 

 

 

Kona Low

 

Cyclogenesis Central Pacific Ocean

 

Lowest Surface Pressure To Be Expected 976mb to 1004mb

 

Speed Of Motion Very Slow, Semistationary; May last up to 10 days

 

Typical Storm Track Meandering east-southeast path along and north of Hawaiian Island Chain

 

Upper Air Structure Longwave, Closed Low. May gradually take on characteristics of subtropical disturbance as system intakes mT air and structurally warms at upper levels.

 

Apparent Weather Kona-type lows are important for two reasons. One, they represent one of the few systems to threaten HI with severe convection (a result of mPk air moving so far south into the tropics) and persistent heavy rains (normal trade wind relationships over the Hawaiian Islands are reversed). Secondly, a deep Kona signature (500mb heights lower than 555dcm) will favor amplification of western North America blocking ridges. Cold-core lows at this latitude teleconnect well to very warm Omega signatures over AK and the Yukon Territory.

 

Likelihood Of Occurrence October 1 through April 1.

 

 

Bermuda Low

 

Cyclogenesis Anywhere along the eastern seaboard of North America

 

Lowest Surface Pressure To Be Expected 966mb to 1004mb

 

Speed Of Motion Erratic, Looping and very slow; May last up to 10 days

 

Typical Storm Track Savannah GA….100 mi E Myrtle Beach SC….125 mi E Cape Hatteras NC….300 mi W Bermuda (then stationary)

 

Upper Air Structure Longwave, Closed Low; emits isolated small shortwave-type lows that tend to move northward or northwestward toward Northeast U.S. May also absorb tropical features, or even convert to subtropical status (e.g., Halloween 1991 storm).

 

Apparent Weather There is a counterpart to the famed ‘Bermuda High’, but the rate of occurrence for this feature is relatively rare, usually once every 9 years. The most common synoptic setup for a Bermuda Low is a cold season ‘Gulf Coaster’ that evolves into a longwave feature after leaving the U.S. (e.g. March 1967). But other scenarios involve retrogressive Nor’easters (October 1968) and remnant cutoff lows that incorporate polar shortwaves and/or tropical features (October 1991). Key forecast feature to look for is Omega block ridge in vicinity of NWF. A variety of weather types can be expected, dependent upon season. Heavy, almost unexpected snowfalls may reach the Mid-Atlantic states during the winter; usually a prolonged rain/drizzle episode for eastern seaboard is the norm for such an event. Deep cyclogenesis (combinant structures) can sometimes produce a dazzling outburst of gradient wind and beach erosion.

 

Likelihood Of Occurrence Year-round, though most likely September 1 to May 1.

 

 

California/Great Basin Storms

 

Cyclogenesis Northeast Of Hawaiian Islands

 

Lowest Surface Pressure To Be Expected 976mb to 1008mb

 

Speed Of Motion Normal to Rapid; Sequence Lasts About 4-5 days

 

Typical Storm Track 300 mi E Honolulu HI….400 mi W Los Angeles CA….Santa Barbara CA…Winslow AZ

 

Upper Air Structure Shortwave evolving to Hybrid Type

 

Apparent Weather Extremely heavy rains for S, C CA, S NV, AZ; Mountain snows of up to 2 feet in those regions. Tornadoes and microbursts are possible along and south of storm track, with or without apparent sunshine. Snow level after passage may drop to near 1000 feet temporarily. Storms tend to dissipate after they reach S UT.

 

Likelihood Of Occurrence October 1 to April 15

 

 

Washington/Great Basin Storms

 

Cyclogenesis Coastal Islands Of British Columbia

 

Lowest Surface Pressure To Be Expected 990mb to 1012mb

 

Speed Of Motion Rapid; Sequence Lasts About 2-3 days

 

Typical Storm Track Victoria BC….Portland OR….Lake Tahoe NV….Phoenix AZ….Santa Fe NM

 

Upper Air Structure Shortwave

 

Apparent Weather Bursts of heavy rain or snow that last 3-6 hours, concurrent with passage of 500mb vorticity maximum. Convection quite likely, with risks of microbursts, hail, and isolated tornadoes. Precipitation area usually quite small, no more than 400 miles. These storms may bring snow to very low latitude locations such as Las Vegas NV, Phoenix AZ, Albuquerque NM.

 

Likelihood Of Occurrence October 15 to April 1

 

 

Mogollan Rim Storms

 

Cyclogenesis Northern Mexico, Extreme West Texas, New Mexico

 

Lowest Surface Pressure To Be Expected 988mb to 1004mb

 

Speed Of Motion Very Slow; Sequence Lasts About 5-6 days

 

Typical Storm Track San Jose CA....Sonora Mexico….El Paso TX

 

Upper Air Structure Longwave (Smaller scale cutoff low)

 

Apparent Weather Profuse heavy snow over mountains of southwestern U.S.; worst effects N AZ and N NM. Some locations may receive upwards of 4 feet of snow. Rains or scattered convection possible along Mexican border, though if cA air becomes entrained snow may reach cities such as Phoenix AZ, Tucson AZ, and El Paso TX. Precipitation lasts until upper low fills, which may take a number of days. Cold cutoff low becomes stationary beneath trapping ridge and slowly fills.

 

Likelihood Of Occurrence November 15 to April 15

 

 

Colorado/Limon Cyclones

 

Cyclogenesis Colorado Front Range between Denver and Fort Collins

 

Lowest Surface Pressure To Be Expected 960mb to 994mb

 

Speed Of Motion Very Slow; Sequence Lasts About 5-6 days

 

Typical Storm Track Boulder CO….Limon CO….Colby KS….Grand Island NE….Huron SD….Redwood Falls MN….Virginia MN….Kenora ONT

 

Upper Air Structure Longwave (Large scale cutoff low); usually starts out as digging shortwave over WA state and closes off over CO

 

Apparent Weather Varies wildly with respect to low center, which is usually vertical with 500mb core. Along and 200 miles to left of storm path, blizzard conditions with up to two feet of snow and gale-force winds are likely. Westward variant of this type can produce incredible snows over Black Hills region (up to 90 inches not out of question). If cA air is being displaced northeast of low center, portions of N IA, MN, and WI may receive heavy freezing rain and sleet. Warm sector characterized by strong southerly winds (30-50 mph), large squall lines with damaging winds (though dry intrusion will greatly limit rainfall amounts. A secondary cold front convective episode may occur near the low center, where snow area meets sun-warmed parcels.

 

As the low moves northeastward it slowly fills, leaving only light/moderate stratiform rains from NE KS/NW MO through much of IA, WI, and N IL. Systems such as these seldom affect the eastern third of the nation as they aid in pumping up downstream ridging. The first appearance of this storm track type is usually an indication that winter season pattern is over and that a new, springlike weather trend is starting.

 

Likelihood Of Occurrence February 1 to May 1

 

 

Great Plains Dusters

 

Cyclogenesis Wyoming or Colorado Front Range

 

Lowest Surface Pressure To Be Expected 968mb to 992mb

 

Speed Of Motion Normal; sequence takes 3 to 4 days

 

Typical Storm Track Cheyenne WY….Scottsbluff NE….Council Bluffs IA….LaCrosse WI….Cadillac MI….Timmins ONT

 

Upper Air Structure Hybrid (Large scale trough with identifiable 500mb low center); usually starts out as digging shortwave over WA and deepens over WY or CO

 

Apparent Weather One of the worst types of storm types, in that anything and everything is possible. Difluence in upper air structure usually accompanies very high velocities in associated jet stream, creating massive array of precipitation. Tendency for low central pressures offers a like inclination to strong surface gradient wind field. Moderate to heavy snows, near blizzard conditions north of track; sleet and freezing rain on southern edge of snow area. Stratiform rains of moderate intensity in overrunning sector. Dust storms in dry slot. Numerous severe thunderstorms in warm sector. A storm of this type caused the famed ‘Palm Sunday’ outbreak of tornadoes in 1964.

 

Likelihood Of Occurrence October 1 through June 15

 

 

Panhandle Hook (A)

 

Cyclogenesis Eastern New Mexico, Texas/Oklahoma Panhandles

 

Lowest Surface Pressure To Be Expected 986mb to 1014mb

 

Speed Of Motion Normal to Rapid; sequence takes 2 to 4 days

 

Typical Storm Track Roswell NM….Amarillo TX….Chanute KS….Springfield MO….Effingham IL….Lafayette IN….Adrian MI….London ONT….Amos QB

 

Upper Air Structure Shortwave, though may begin or end life cycle as closed upper low

 

Apparent Weather Noted for precipitation in cold and overrunning sectors. This track is one of two that are climatologically favored to bring heavy snowfall to cities such as Kansas City MO; Des Moines IA; Milwaukee WI; Chicago IL. Can also generate crippling ice storms just north and east of path (Wichita KS; Columbia MO; Quincy IL; Gary IN; Lansing MI; Detroit MI; Flint MI; Sarnia ONT). May also exhibit strong warm-sector convection, though normally does not favor tornadic signatures. Classic Panhandle Hook 'A' storm was the Great Chicago Blizzard of January 1979.

 

Likelihood Of Occurrence October 15 through May 1

 

 

Panhandle Hook (cool.gif

 

Cyclogenesis Eastern New Mexico, Texas/Oklahoma Panhandles

 

Lowest Surface Pressure To Be Expected 968mb to 1008mb

 

Speed Of Motion Normal to Rapid; sequence takes 2 to 4 days

 

Typical Storm Track Tucumcari NM….Perryton TX….Wichita KS….Omaha NE ….Newton IA….St. Paul MN….Ishpeming MI….Wawa ONT….Moosonee ONT

 

Upper Air Structure Hybrid Cyclone through lifetime

 

Apparent Weather Similar in structure and character to Great Plains Duster storms, though much larger in geographic scope. Notable for two historical storms: Tornadic Super Outbreak system of April 3,4 1974 and ‘Edmund Fitzgerald’ disaster of November 10, 1975. Also seen recently in November 10, 1998 storm where new records were set for lowest barometric pressure across portions of SD, IA, and MN. Panhandle Hook B cyclones are the ultimate generators of severe thunderstorms and tornadoes, characterized by extremely high jet stream velocities.

 

Likelihood Of Occurrence October 15 through May 1

 

 

Colorado/Trinidad Storms (A)

 

Cyclogenesis Southern Colorado, Northern New Mexico

 

Lowest Surface Pressure To Be Expected 984mb to 1010mb

 

Speed Of Motion Normal; lifetime of 3-4 days after cyclogenesis

 

Typical Storm Track Trinidad CO….Anthony KS….Springfield MO….Effingham IL….Muncie IN….Toledo OH….St. Catherines ONT….Alma QB

 

Upper Air Structure Usually starts as a remnant 500mb cutoff low, evolves into shortwave structure

 

Apparent Weather Major snow producer during winter and spring for sections of the West and Midwest. Usually starts out life as a cutoff low over southwestern states, then lifted out as additional energy from BC/AB digs southward as a ‘kicker’, and eventually phases with the older system to produce a large-scale, accelerating shortwave that may mimic the Panhandle Hook A storms. Not known for damaging warm-sector convection, but may produce incredible ice storms and even blizzards. Two Colorado/Trinidad A storms produced massive snows in Chicago IL during January 1967.

 

Likelihood Of Occurrence November 1 through April 15

 

 

Colorado/Trinidad Storms (cool.gif

 

Cyclogenesis Southern Colorado, Northern New Mexico

 

Lowest Surface Pressure To Be Expected 978mb to 1004mb

 

Speed Of Motion Normal to slow; lifetime of 5-6 days after cyclogenesis

 

Typical Storm Track Trinidad CO….Liberal KS….Independence KS….Paducah KY….Hazard KY….Roanoke VA….Wicomico VA….200 mi S Nantucket MA

 

Upper Air Structure Usually starts as shortwave, evolves into closed longwave structure

 

Apparent Weather Different from Case 'A' Trinidad cyclones in upper structure and general effects. More southerly track results in heavy snow/ice band affecting these cities: Denver CO; Kansas City MO; St. Louis MO; Indianapolis IN; Columbus OH; Pittsburgh PA; and all major cities of the Northeast U.S. Unlike the ‘A’ signature storms, intense convection may occur, especially over the South (deepening trough intersects mT air). May be prone to coastal redevelopment off VA Capes (about 1 in 4 cases). Precipitation amounts may be extremely heavy over Mid-Atlantic states as the low may utilize deep Caribbean mTw air as well as mP Atlantic parcels.

 

Likelihood Of Occurrence November 15 through April 1

 

 

Border Trackers

 

Cyclogenesis British Columbia

 

Lowest Surface Pressure To Be Expected 988mb to 1000mb

 

Speed Of Motion Rapid; coast-to-coast sequence in 2 to 3 days

 

Typical Storm Track Victoria BC….Banff AB….International Falls MN….Quebec City QB….Bathurst N Br

 

Upper Air Structure Shortwave or Hybrid, transitional from semizonal flow to building trough

 

Apparent Weather High winds along and north of about 40 deg N Latitude; Very strong warm advection south of main storm track; Sparse precipitation in warm sector, excepting ‘January Thaw’ period. Border Tracker storms in mid-January draw up huge reserves of mT air from the Gulf of Mexico; as a result numerous heavy showers and thunderstorms may occur. Locales close to storm track may experience sleet or freezing rain; snow relegated to Canadian sectors of storm.

 

Likelihood Of Occurrence Year-round

 

 

Alberta Clippers

 

Cyclogenesis Alberta or Montana, to lee of Rocky Mountains

 

Lowest Surface Pressure To Be Expected 982mb to 1018mb

 

Speed Of Motion Rapid; 1-3 day life of system

 

Typical Storm Track Edmonton AB….Miles City MT….Pierre SD….Shenandoah IA….Ouincy IL….Fort Wayne IN….Akron OH….Buffalo NY….Quebec City QB….Labrador City LBR

 

Upper Air Structure Shortwave rotating around circumpolar vortex over Hudson’s Bay or James Bay

 

Apparent Weather One of the most misunderstood of all storm tracks. Alberta Clipper systems exhibit a rapid, parabolic motion accompanied by great deepening and intense bursts of wind at surface and aloft. While moisture may be lacking, a typical ‘Clipper’ may generate ground blizzards with tremendous advection of cold air. Typical cold sector snows are in the order of 1-3 inches, though up to 8 inches is not entirely unheard of. Unlike many mid-latitude cyclones, the heaviest snowfall occurs along and just north of the path of the 500mb vorticity maximum.

 

There can be a wide range of deviation from the ‘typical’ Alberta Clipper path. Some ‘clippers’ imitate the Border Tracker storms. But all have this one feature in common: they are a product of leeside cyclogenesis in AB or MT. One subfamily may take a more south and east path (Miles City MT….O’Neill NE….Kirksville MO….Evansville IN….Bluefield WV….Ocean City MD….200 mi SE Martha’s Vineyard MA), resulting in heavy snows over portions of the Northeast U.S.; the Atlantic Ocean is used as a moisture source while cA air presses toward the coast.

 

Likelihood Of Occurrence November 15 through April 1

 

 

Great Lakes Backdoor Storms

 

Cyclogenesis Manitoba or extreme northwest Ontario

 

Lowest Surface Pressure To Be Expected 990mb to 1014mb

 

Speed Of Motion Rapid; 1-3 day life of system

 

Typical Storm Track Port Churchill MB….Thunder Bay ONT….Lansing MI….Steubenville OH….Baltimore MD….Cape May NJ….100 mi SE Provincetown MA

 

Upper Air Structure Shortwave rotating around circumpolar vortex over Hudson’s Bay or James Bay

 

Apparent Weather Resembles an Alberta Clipper in terms of structure, speed, and precipitation array; but causal mechanism is purely dynamical, along leading edge of deep cA air mass. Often, this storm type signals a southward displacement of the circumpolar vortex. Practical forecast considerations are advection of deep cAk air; lake-enhanced blizzards along the southeast shore of all major lakes; and sometimes surprise heavy snows for the Northeast U.S., using Atlantic Ocean as a moisture source. Rarity of occurrence may make for poor prediction odds.

 

Likelihood Of Occurrence November 15 through April 1

 

 

Southland Tempest (a.k.a. El Nino Express)

 

Cyclogenesis Central or Eastern Pacific Ocean

 

Lowest Surface Pressure To Be Expected 982mb to 1000mb

 

Speed Of Motion Normal (3-5 day life cycle)

 

Typical Storm Track 300 mi NE Honolulu HI….300 mi W Los Angeles CA….Santa Barbara CA….Flagstaff AZ….Albuquerque NM….Muskogee OK….Tupelo MS….Atlanta GA….Myrtle Beach SC….250 mi E Cape Hatteras NC

 

Upper Air Structure Shortwave that deepens into a hybrid 500mb signature

 

Apparent Weather Mimics other storm types but occurs only during an El Nino episode. Cyclogenesis usually occurs when jet splits into two branches north of Hawaiian Islands. Then system gather huge fetch of mTw air from equatorial Pacific Ocean and crash into S or C CA. Redevelopment of main surface low can occur as much as twice in lifetime of this storm category (lee of Rocky Mountains in NM, lee of Appalachian Mountains in SC). Forecast concerns are heavy rain (5-10 inch amounts not uncommon in CA west-facing slopes of mountains; further east 2-4 inch totals are likely); severe weather (tornado/wind damage a frequent result anywhere along or south and east of track); elevation and nocturnal snows (frequently can create heavy snowfall even over Deep South, as in December 1997 storm over LA/MS); and gradient-produced wind and beach erosion (CA as well as Atlantic coast). 1 in 4 Southland Tempests will turn up Atlantic seaboard as Nor’easters.

 

Likelihood Of Occurrence October 1 through May 15

 

 

Gulf Coasters

 

Cyclogenesis Southern or central Texas

 

Lowest Surface Pressure To Be Expected 978mb to 1004mb

 

Speed Of Motion Normal to slow (3-7 day life cycle)

 

Typical Storm Track Austin TX….Leesville LA….McComb MS….Montgomery AL….Augusta GA….Charleston SC….300 mi S Cape Hatteras NC

 

Upper Air Structure Shortwave that deepens into a longwave signature

 

Apparent Weather Track is superficially similar to El Nino-related storms, but differs in region of cyclogenesis, speed, and air mass structure. This type of low may create widespread heavy snow/ice even without regard to elevation or time of day, and can draw cA values into the Gulf of Mexico. Also notorious for severe weather in its warm sector, namely over Florida, which can experience numerous supercell tornadoes. 1 out of 4 Gulf Coasters will make a northward recurvature and become a Nor’easters.

 

Likelihood Of Occurrence October 15 through May 1

 

 

Peninsula Storms

 

Cyclogenesis Eastern Gulf of Mexico

 

Lowest Surface Pressure To Be Expected 972mb to 1000mb

 

Speed Of Motion Normal (2-5 day life cycle)

 

Typical Storm Track 100 mi N Key West FL….75 mi W Tampa FL….Cedar Key FL….Brunswick GA….100 mi E Charleston SC….300 mi E Wilmington NC

 

Upper Air Structure Longwave storm that eventually phases with higher-latitude trough

 

Apparent Weather Rare track has origins in thermal boundary over eastern Gulf of Mexico. Stationary (but relatively deep) upper low is kicked out by digging full-latitude trough, eventually phasing with dominant system east of NC by the end of its life. Because of often extreme baroclinicity (high SSTs vs. incoming cA air), Peninsula Storms can deepen dramatically. It is this track which will bring the FL Peninsula anything from numerous tornadoes to ice storms (e.g., December 1990). A subtropical variant during the fall is capable of large-scale severe weather outbreaks as well (October 1992).

 

Likelihood Of Occurrence October 1 through April 15

 

 

Galveston Bay Spin-Ups (a.k.a. Western Gulf Cyclones)

 

Cyclogenesis Western Gulf Of Mexico, East Texas, Louisiana

 

Lowest Surface Pressure To Be Expected 980mb to 1008mb

 

Speed Of Motion Normal to Rapid (2-4 day life cycle)

 

Typical Storm Track Galveston TX….Coushatta LA….Jackson TN….Lexington KY….Cleveland OH….Plattsburgh NY….Schefferville QB

 

Upper Air Structure Shortwave, sometimes evolving into a longwave feature over QB

 

Apparent Weather Cyclogenesis occurs on a stationary cP/mT front along TX Gulf Coast; thermal relationship with warm SSTs are suspected as a causal mechanism. Impulse is picked up in broad 500mb trough and swept toward Lower Great Lakes and St. Lawrence Valley. Realm of high dewpoints expanding rapidly northeastward favors extreme overrunning, with heavy rain likely along and to right of storm track. If cPk or cA air masses are dislodged, considerable snow and ice may result.

 

Likelihood Of Occurrence November 1 through April 15

 

 

Chattanooga Choo-Choos

 

Cyclogenesis Northern Alabama, Northwest Georgia, Eastern Tennessee

 

Lowest Surface Pressure To Be Expected 988mb to 1008mb

 

Speed Of Motion Normal to Rapid (2-4 day life cycle)

 

Typical Storm Track Chattanooga TN….Raleigh NC….Salisbury MD….200 mi S Nantucket MA

 

Upper Air Structure Shortwave

 

Apparent Weather Odd name (often credited to New York City television weathercaster Tex Antoine) is of course derived from familiar song and the region of cyclogenesis. Notorious for not behaving according to forecast guidance. Some storms of this type will move directly over the large cities of the Northeast U.S., bringing rain. Others tend to stay south of prediction schemes, thus drawing in cold air and bringing unforeseen heavy ice and snow. Chattanooga storms may also provide intense convection to the Carolinas.

 

Likelihood Of Occurrence October 15 through May 1

 

 

Piedmont Cyclones

 

Cyclogenesis Florida, Georgia, South Carolina

 

Lowest Surface Pressure To Be Expected 968mb to 1000mb

 

Speed Of Motion Varies (anywhere from 2-8 day life cycle)

 

Typical Storm Track Valdosta GA….Greenville SC….Roanoke VA….Lancaster PA….Albany NY….Bangor ME….Gander NWF

 

Upper Air Structure All types; longwave 500mb low has the most impact

 

Apparent Weather Often confused with Nor’easters, this is actually a unique inland storm variety that owes its genesis to the Appalachian Mountains as opposed to the Gulf Stream. A wave develops on a stationary front over the Southeast, then moves along the east slopes of the Blue Ridge and into New England. Piedmont cyclones are noted more for heavy rain production than anything else, but occasionally will produce an outbreak of severe thunderstorms across the Atlantic coastal plain (e.g., November 15, 1988 in the Northeast). Heavy snows may also develop in cold sector; this is favored heavy snow track for Pittsburgh PA, Buffalo NY, and Toronto ONT.

 

Likelihood Of Occurrence October 1 through May 1

 

 

Nor’easters (a.k.a. Hatteras Lows, Coastal Lows)

 

Cyclogenesis Coastal waters of South Carolina, North Carolina, or Virginia

 

Lowest Surface Pressure To Be Expected 962mb to 1004mb

 

Speed Of Motion Varies (anywhere from 2-8 day life cycle)

 

Typical Storm Track 100 mi E Charleston SC….Cape Hatteras NC….100 mi E Wallops Island VA….150 mi E Atlantic City NJ….50 mi E Nantucket MA….200 mi S Halifax NS

 

Upper Air Structure Shortwave transforming to closed longwave low

 

Apparent Weather Classic storm of the eastern seaboard, there are actually three subfamilies comprising the type:

 

1) Those disturbances purely related to activities in the southern branch of the jet stream, where El Nino Express and Gulf Coaster lows simply turn up the coast by recurving in a north-northeast direction. Such storms are noted for flooding rains, high winds, and coastal flooding/erosion.

 

2) Another scenario occurs when a deep 500mb cutoff low is kicked out and phased with an incoming northern stream shortwave. An example of this scenario is the March 1993 Superstorm. It is this category which can produce weather extremes in all storm quadrants, and also variations in track such as northwest recurvature upon reaching the Northeast.

 

3) The last, and classic, type of Nor’easter is when a polar or Arctic stream shortwave digs southeastward from the Great Lakes, reforming into a surface low off the coast of the Carolinas. This form represents the best potential for heavy snowfall across the Mid-Atlantic and New England regions. Caveat: if a cPk or cA anticyclone is not present over ONT or QB, holding cold profile in place, precipitation will likely change to rain over the Atlantic coastal plain.

 

Likelihood Of Occurrence Year-round; most likely span of occurrence is October 15 through May 1.

 

Disclaimer:

 

The previous statements are my opinions only, and should not be construed as definitive fact.

 

Copyright 1998 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.

 

 

 

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