Corfidi, et al. 2008 – convection where air parcels originate from a moist absolutely unstable layer above the PBL. Can produce severe hail, damaging.

Elevated ConvectionMike July

2011 Severe Weather Seminar

Elevated vs Overrunning

Colman – first coined the term “elevated” in 1990. His research found that forcing for these storms does not typically come from convectively unstable air ascending a sloped surface (implying overruning).

Occur above frontal zones and are isolated from diabatic effects Assumed air above the frontal surface has previously existed as a surface boundary

Colman Composite

Occurs northeast of a surface low North of a surface warm frontNortheasterly surface windsPBL is generally stableUsually found in the left exit region of a low-level wind maximaStrong low-level veering of winds/large vertical wind shearRegion of warm air advection (another convert )Frequently without CAPEMost likely the product of frontogenetical forcing

AHN

Elevated Convection vs ACCAS

Corfidi, et al. 2008 – convection where air parcels originate from a moist absolutely unstable layer above the PBL. Can produce severe hail, damaging surface wind and excessive rainfall well removed from surface-based instability. Frequently located near (north of) a warm or stationary front.

Not synonymous with accas as these clouds can also arise from surface-based convection.

These storms evolved into supercells which produced a tornado in northwest MO (25 June 1994)

Transition Events

Surface heating greatly reduced CIN . Storms became surface-based in the afternoon.

Classic Warm Air Advection

Cells line up parallel to isentropic surfaces north of a warm or stationary front. Strong warm air advection near fronts sometimes results in regularly spaced storms parallel to the isentropic surfaces. Factors governing this spacing is not currently understood.

Conceptual Cross Section Composite

Elevated MCS ~100 miles north of frontssw LLJ transports high-θe air northward along and above cool stable layerswly mid trop flow advects lower-θe air over the warm moist high-θe air resulting in a layer of elevated convective instabilityLarge –scale isentropic ascent (suggested by the lower –trop ospheric warm air advection and frontogenesis within the entrance region of the ULJ) aids in lifting the layer to saturation

Moore, et al

Moore, et al

Key Composite Low-level Features/Parameters

East-west quasi-stationary front South-southwesterly LLJ directed nearly normal to the boundary Moisture convergence within the left exit region of the LLJ helps to initiate deep

convection in the unstable layer along or above the frontal zone . Maximum θe advection nearly centered over the MCS centroid

θe

Mstr convergence maxima

MCS centroidMax thetae advection

Moore, et al

Key Composite Mid-level Features

• Broad southwesterly mid tropospheric flow• Moderately high mean surface-500 mb RH• MCS forms under the right entrance region of the ULJ

1202 UTC

Lower 50s surface temperatures near storm Supercell moving into a region of surface temperatures in the mid 40s with

dewpoints in the upper 30s

Elevated Supercell with Damaging WindMarch 12, 2006 (Thompson et al)

1503 UTC

Widespread wind damage with winds to 78 knots in Lawrence and baseball size hail in Lawrence and Kansas City

1413 UTC

Lawrence

14 – 15 UTC

Elevated Supercell with Damaging WindMarch 12, 2006 (Thompson et al)

MUCAPE – 600 J/kg MUCAPE – 2800 J/kg

Favors elevated supercells with very large hail rich low level moisture near top of sharp surface-based inversion nearly dry mid trop layer with nearly dry adiabatic lapse rates atop inversion strong vertical wind shear through lower half of storm depth Large DCAPE > 900 J/kg supports strong saturated downdrafts originating in the dry, steep lapse rate layer above the surface-based inversion

Lawrence, KS

850-500mb MUCAPE

East of Rockies - identify severe reports 1 degree latitude (111 km) on the cool side of a surface front (excludes convection which may occur above a surface-based nocturnal inversion

129 severe storm cases….1066 reports: 58% hail (3/4”)…..37% wind…..4% tornado Focuses on the occurrence of severe wind events ……(tornadoes are rare and

forecasting large hail not as significant of a forecast challenge)

5 Year Climatology (1983-87) Horgan, et al

2 inch dia.

65 knots

Nov - GA

Shallow near surface stable layer (< 100mb thick)

Relatively deep moist layer above the inversion

Dry air at mid levels (allows for evaporational cooling which can enhance strong downdraft potential DCAPE)

Occurred north of east-west front

4 of 5 cases warm sector MUCAPE > 2000 J/kg

Weak e to se near surface winds

Vertical wind shear-sometimes quite strong

Dec – GA/SC

Feb – MS

Nov – IA Jul - TN

Nocturnal inversion