May 27.] THE NEW ZEALAND GAZETTE. 1475

METEOROLOGICAL SUMMARY FOR APRIL, 1909.

The rainfall of April was below the average north of East Cape and Kawhia, but above in most other parts of the North Island, and especially on the east coast. The total rainfall was above the normal in the South Island, except in the Nelson and Marlborough Districts, where it was less than usual.

The weather was, on the whole, mild and genial, but frosts were general after the storm on the 22nd and 23rd. A westerly area of low pressure prevailed for the first six days in the month, and rainfall was very heavy on the west coast, with high westerly winds, but over Northern and Central Canterbury, and also between East Cape and Napier, at this time dry and hot winds were experienced. The humid winds which had swept across the ocean had their vapour precipitated on the western slopes of the Alps, thus at Otira the heaviest rainfall was at this time, and 13·01" were recorded from the 1st to the 5th. The dried air, from which the vapour had been precipitated, was still comparatively warm when it passed over the top of the mountain ranges, and became squeezed as it descended into lower regions. The heat is, as it were, put into smaller compass, and the nor'westers—“foehn winds,” as they are called—are warmed by compression at the rate of 0·58 of a degree Fahrenheit for every 100 ft. of descent from the mountains. The north-west wind has then great capacity for moisture, and dries up the vegetation and fields, apart from which its general effect upon man is very depressing. Some of the air ascends at a distance from the mountains, and is cooled into a cloud, which forms the well known “north-west arch,” and stretches apparently motionless along the Canterbury Plains—i.e., on the eastern side of the mountain range. Between this cloud and the Alps is a clear expanse of sky.

In the southern parts of Canterbury and Otago cold winds and rain were experienced while the hot north-west winds prevailed, and interesting details are already to hand, but more observations are desirable from the different stations. On a future occasion we hope to deal with these phenomena at greater length, and show on a weather-map the relationship of barometric pressure, temperature, humidity, &c., with these winds.

On the 7th barometric pressure reached 30·30" in the extreme north and 30·00" at the Bluff, but was unstable, falling quickly in the South for a small westerly, with two waves in the isobars, which were followed by a cyclonic disturbance in the North. This disturbance brought considerable rain in the North Island from Good Friday to Easter Monday.

High pressure and good weather prevailed everywhere for a few days, and the barometer at Wellington reached 30·30", but on the 17th a small westerly passed over the South Island. A rapid recovery took place on the 18th, and fell as rapidly in the South on the 19th and 20th for an antarctic depression. A disturbance of a cyclonic nature followed on the 23rd, and blended with the westerly or antarctic low pressure, as shown in the chart in the Meteorological Journal. Much snow fell on the mountain ranges, and very high tides were experienced on the west coast and in Cook Straits at this time. Southerly winds followed, and rainfall was general.

On the 26th there was a heavy sea on the east coast, and an observer fourteen miles inland remarked he could hear it roaring.

Another westerly area of low pressure was due at the end of the month, but came to little, as it was pushed off by the anticyclone which held sway at the time. There were heavy frosts at night, but the days at this time were fine, bright, and warm.

D. C. BATES.

Meteorological Office, Wellington.