Severe Weather Forecasting Tip Sheet: WFO Louisville.
критерии опасных явлений, pdf
https://www.weather.gov/media/lmk/soo/SvrWx_Fcstg_TipSheet.pdfНесколько примеров.
Vertical Wind Shear & SRH–0-6 km bulk shear > 40 kts – supercells
–0-6 km bulk shear 20-35 kts – organized multicells
–0-6 km bulk shear < 10-20 kts – disorganized multicells
–0-8 km bulk shear > 52 kts – long-lived supercells
–0-3 km bulk shear > 30-40 kts – bowing thunderstorms.
Large Hail– -10 to -30°C layer is the hail growth zone; look for a large CAPE
within -10 to -30°C layer
– Rotating updraft – the longer hail resides within hail growth zone, the
greater the potential for large hail
Supercells & Hail– Large boundary layer moisture
– 700-500 mb lapse rates > 7.0°C km-1
– Moderate to large CAPE, including “fat” CAPE for rapid acceleration
– 0-6 km shear > 40-50 kts (includes speed and directional)
– 0-3 km SRH > 150-200 m2 s-2.
Non-supercell hail events– Large boundary layer moisture
– 700-500 mb lapse rates > 7.0°C km-1
– Large CAPE, including within hail growth zone
– Freezing level and Wet Bulb Zero level < 10500 ft.
Melting issues– Large depth between LCL and freezing level (i.e., deep warm cloud
zone to promote melting)
– Freezing level and wet-bulb zero levels are > 10500 ft
– High RH in the lowest several km’s
– Lapse rates 850-500 mb are moist adiabatic
– Hail falling within heavy rain core; limited vertical wind shear.
Tornadic Supercells– Unstable warm sector air mass, with well-defined warm and cold fronts (i.e., strong extratropical cyclone)
– Strong mid and upper-level jet observed to dive southward into upper-level shortwave trough, then
rapidly exit the trough and cross into the warm sector air mass.
– Pronounced upper-level divergence occurs on the nose and exit region of the jet.
– A low-level jet forms in response to upper-level jet, which increases northward flux of moisture.
– Intense northwest-southwest upper-level flow/strong southerly low-level flow creates a wind profile which
is very conducive for supercell development. Storms often exhibit rapid development along cold front,
dryline, or pre-frontal convergence axis, and then move east into warm sector.
– Most intense tornadic supercells often occur in close proximity to where upper-level jet intersects low-
level jet, although tornadic supercells can occur north and south of upper jet as well.
Hodograph:
– The 0-1 km hodograph spike is relatively straight (no curvature). Above the spike, the hodograph then
displays stronger turning and curvature.
– 0-1 km bulk shear > 20 kts
– 0-1 km SRH > 150-300 m2 s-2
– Boundary layer RH > 65%
– LCL heights ≤ 1000 m (3000 ft)
– Most of the 0-3 km SRH is concentrated in 0-1 km layer
– Low LCL heights (large boundary layer RH) favor warm RFDs and tornadogenesis
– High LCL heights (low boundary layer RH) favor cold RFDs and tornadogenesis-failure
Importance of Boundaries:
– Horizontal vorticity enhancements necessary for low-level mesocyclogenesis as air rapidly accelerates
into updraft, which appears to precede tornadogenesis if other key structures develop (e.g., warm RFD).
– Tornadogenesis requires augmentation of the horizontal vorticity associated with the mean shear by the
baroclinic vorticity generated by preexisting boundaries.
– Storm-boundary interactions may not be necessary when the environmental shear is very large.
Mergers:
– Watch for cells merging into the inflow flank of supercells. This is often a precursor to tornadogenesis.
