COLD FRONT IN COLD ADVECTION - TYPICAL APPEARANCE IN VERTICAL CROSS SECTIONS

by ZAMG


All typical parameters seen in vertical cross sections are now illustrated with help of one case; the position of the vertical cross section line is indicated below.

22 January 1999/06.00 UTC - Meteosat IR image; position of vertical cross section indicated
22 January 1999/06.00 UTC - Vertical cross section; black: isentropes (ThetaE), red thick: temperature advection - WA, red thin: temperature advection - CA, orange thin: IR pixel values, orange thick: WV pixel values
This vertical cross section shows the typically Cold Front - like inclined zone of isentropes (crowding zone at the frontal surface), and widespread CA throughout the front and surrounding region, although there are some areas of WA embedded.

The position of the zero line in relation to the frontal cloud band and TA can be used as a tool to determine whether further development is possible (see below)

22 January 1999/06.00 UTC - Vertical cross section; black: isentropes (ThetaE), dark violet thick: humidity advection - moist advection, dark violet thin: humidity advection - dry advection, orange thin: IR pixel values, orange thick: WV pixel values
The combination of temperature advection with humidity advection shows the following situation: Far in front of the CF in CA there is WA together with moist advection; then, closer to the CF in CA, there is a zone of cold but still moist advection which is most pronounced in levels between 800 and 500 hPa. Below the frontal surface CA and Dry Advection prevails. Therefore a main characteristic of a CF in CA is the difference in moisture between the two air masses involved, which might be even more significant than temperature (see Cold Front In Warm Advection - Typical appearance in vertical cross section ).

22 January 1999/06.00 UTC - Vertical cross section; black: isentropes (ThetaE), cyan thick: vertical motion (omega) - upward motion, cyan thin: vertical motion (omega) - downward motion, orange thin: IR pixel values, orange thick: WV pixel values
The vertical cross sections are an effective tool for the forecaster: fronts which show the combination of cold advection throughout all levels and a cloud band which is dominated by negative humidity advection are usually (in 85%) decaying even if there is quite strong upwards motion at the time of observation.

The decay of a front under the influence of cold and dry advection, as described above, is illustrated below.

22 January 1999/18.00 UTC - Meteosat IR image; red: temperature advection 700 hPa, blue dashed: humidity advection 700 hPa - negative values, blue solid: humidity advection 700 hPa - positive values
23 January 1999/00.00 UTC - Meteosat IR image; red: emperature advection 700 hPa, blue dashed: humidity advection 700 hPa - negative values, blue solid: humidity advection 700 hPa - positive values
The front is completely under cold and dry advection. The sequence of the two images show the decay of frontal cloudiness.

SUB-MENU OF COLD FRONT IN COLD ADVECTION
KEY PARAMETERS
WEATHER EVENTS