cyclone.html

Real time Laplacian fields to diagnose Mid-latitude precursors to cyclogenesis

How to use this page: In order to track midlatitude disturbances I examine the Laplacian of the geopotential
height field. This quantity is the un-normalized geostrophic vorticity. this field is less noisy than absolute vorticity
and lets us see which vorticity center is growing or dissipating. By looking at the Laplacian of the virtual temperature
we can identify frontal zones at 500 hPa. In addition, this quantity represents the vertical distribution of geostrophic
vorticity. Thus by examing these fields at one level we can identify:

frontal zones
vorticity centers
vertical tilt of the disturbance
horizontal tilt of the system based on the major axis of the Laplacian of the height field
and, the potential for the disturbance to grow or decay

This last point is assessed by the relative location of the maxima in both fields. If they are juxtaposed then it is likely
that the disturbance is growing. Usually the loss of the maxima in the Laplacian of the virtual temperature means the
disturbance has already reached maximum amplitude.

Fields examined at 500 hPa (with 80 km resolution):

Laplacian of the geopotential height (contoured)
Laplacian of the virtual temperature (shaded)
Geopotential height (blue contour)
Surface lows and highs (blue L and black H)

Link to a paper that explains what to look for in these fields and their interpretation will be appearing soon.

AVN: (current day -1 00UTC ) top left panel, (current day -1 ) top right panel, (current day 00UTC) bottom left panel, (current day 12 UTC) bottom right panel.

AVN forecast from 12 UTC: top left panel 00hr forecast, top right panel 12 hr forecast, bottom left panel 24 hr forecast, bottom right panel 36 hr forecast

additional diagnostics:

Q-vector convergence at 500 hPa (shaded)
Thermal vorticity advection using the 700 - 300 hPa winds and absolute vorticity at 500 hPa (contoured)

ETA model omega equation forcing: top left panel 00 hr forecast, top right panel 12 hr forecast, bottom left panel 24 hr forecast, bottom right panel 36 hr forecast

Measures indirectly the effect of temperature advection that is left out of the thermal vorticity advection to relate to the omega equation forcing.

Frontogenesis Tendency: shown is the magnitude of the potential temperature gradient (blue), stretching term (shaded according to color bar) and tilting term(contoured black solid {positive} and black dashed {negative}) at 500 hPa from the ETA model.

Vorticity Tendency: same as above except convergence term (shaded according to color bar) and tilting(contoured).

Conditional Symmetric Instability Forecast from Clark et al. (2002):

Depicts the -5 and +5 (*10^-7) isopleth of the Moist Potential Vorticity (red contour) as shown by as equation 7.
Also, the Sz term (10^-11 , shaded) from equation 13, which if this term is negative within a region of low MPV means CSI is likely.
The surface pressure is shown along with surface lows and highs.

ETA model CSI forecast: top left panel 00 hr forecast, top right panel 12 hr forecast, bottom left panel 24 hr forecast, bottom right panel 36 hour forecast.

CSI event log

Date location what remarks

03/06/03 ? Northern IA enhanced snowfall in 3 counties 1 ft snow / other areas 6 inches

03/26/03 NW IA enhance rainband nearly stationary +.5" / 6hr

3/28/03 Upstate NY enhanced snowband mesodis issued/ well predicted

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updated March 27, 2003

Date	location	what	remarks
03/06/03 ?	Northern IA	enhanced snowfall in 3 counties	1 ft snow / other areas 6 inches
03/26/03	NW IA	enhance rainband	nearly stationary +.5" / 6hr
3/28/03	Upstate NY	enhanced snowband	mesodis issued/ well predicted