Page:CAB Accident Report, TWA Flight 891.pdf/14

 (b)

_14._

(5) A band of relatively low and more or less leveled-off pressure, connecting the two low-pressure zones mentioned above through the British Isles, the Benelux countries, North—Eastern France, West Germany, the Italian peninsula and its surrounding waters, Greece and the central Mediterranean.

(6) A disturbance over the Atlantic connected with the low mentioned in (3) above and located between the 10° and the 15° Meridian West, still too far away to affect our regions;

(7) A disturbance featuring a cold front and extending from the Spanish Mediterranean shores to the French Side of the Western Alps, the Rhineland, the Benelux countries, and the North Sea;

This disturbance, which was held back dUring the entire morning by the Alps, in the early afternoon overcame the obstacle and penetrated the Po Valley, veering toward the East and remaining active; the passage of the disturbance was accompanied by the usual phenomena comected with a cold front, namer vast and imposmg formations of cumulus clouds, heavy showers, storm actinty; at 6:00 p.m. the front, in so far as our regions were concerned, was located along a line running approadmately from La Specie to Piacenza and thence to Bolasno.

NOTE:

(8} Another rather weak and uncertain disturbance was located on a line running from Turnaia to Sardinia, and thence to Latium, Dalmatia and

Hungary.

Actual conditions (cloud formations, wind and temperature) over the area at the time of the crash

While a study of the general Situation affords a quite clear identifica- tion of the cold front mentioned in (7) above, which at 12:00 noon seemed still to be hovering over the French Side of the Alps, an analysis of

the behaVior of this front on the afternoon of the 26th in the Po

Valley, after it had crossed the Alps, becomes a particularly difficult and uncertain problem.

The baric and thermic fields assoaated With the front were veryr weak and spread-out and the slight differences between the pro-frontal and post-frontal air masses were not apparent through a clear-cut frontal area but through a zone that was rather large and difficult to identify.

The momtain chain to the west and north of the Po Valley tends to slow down the front systems advancing from the west and the sheltering

effect of the mmmtains themselves tends to disperse the frontal characteristics of the system, making analysis uncertain. If the differ- ences in pressure and temerature pertaining to the front are slight,

as they were in this case, often the front passes by at a great height and does not reach the ground in the Po Valley until it has passed

over numerous weather stations in the westernmost part.