Experimental TC Forecast System at RENCI (Gentry, Hill, Lackmann)

Winter Precipitation Type Tools

Partial Thickness Charts

Note: The partial thickness technique is best suited for sites located inland from the immediate coast where the elevation is less than 1,500 ft.

Addtional information on the visualization of vertical temperature structure using the partical thickness technique.

New! Interactive nomogram visualizer

The above plots show 1000-850 mb thickness (blue) and 850-700 mb thickness (red) with the precipitation forecast for the previous 6-hour period from the model (color shading) ending at the time displayed. Critical thickness values are shown as a thick solid and dashed lines. Other thickness values that imply that the layer is entirely below freezing (partially above freezing) are shown as dashed (solid).

The above plots are available from the following models:

GFS 00Z, 06Z, 12Z, 18Z daily, 95-km grid spacing

NAM 211 00Z, 12Z daily, 80-km grid spacing

NAM 212 00Z, 06Z, 12Z, 18Z daily, 40-km grid spacing

Nine trend areas, each indicated by symbols representing p-type element(s), are shown on the nomogram. Each trend area describes the expected occurrence of the various p-type elements during a six-hour forecast period. Where more than one element is shown, a simultaneous mixture or changeover in p-type is indicated. The first type indicated is exptected to be the predominate type during that period, and the trend toward or away from the second p-type indicated or any other p-type will depend on the trend in the thickness values for the next 6-h period.

For example, IP/S would indicate that the predominant p-type during this period would be sleet, but with the potential for snow mixing or briefly changing over to snow. By accounting for the trend (i.e., colder or warmer) in the thickness values for the next 6 hour period, any change from sleet to another predominant p-type can be anticipated.

Forecast Soundings