By early July, in most years, atmospheric adjustments
produce a mean westerly airflow over Labrador, and a southwesterly one over the
island. This marks the onset of summer conditions.
The character of the summer then
depends upon the position and relative strengths of two weather systems:
a low pressure area centred near
Ungava Bay (northwest of Labrador), and the western portion of the North Atlantic
anticyclone, centred near Bermuda. Since Labrador is under the
influence of the former system it has changeable summer conditions. The influence of the warm Bermuda
anticyclone is increasingly likely in the southeast of the island.
On the island, the spatial pattern of summer temperatures is strongly influenced by the
prevailing (SW) wind direction, and distance from open salt water.
Average air temperature for July.
Image modified by Duleepa Wijayawardhana with permission, 1998. Reproduced by
permission of Gary E. McManus and Clifford H. Wood. From Atlas of Newfoundland and Labrador
(St. John's, Newfoundland: Breakwater, ©1991 MUNCL) Plate 6.5(b).
Southern coastal areas are relatively cool overall, because the prevailing
onshore winds are chilled by sea surface temperatures of 10-13°C. Sea
fog is a regular occurrence. However, these onshore winds also moderate the nighttime
temperatures near the southern and southwestern coasts, which extends their frost-free season
to almost five months.
Annual number of frost-free days.
Courtesy of Gary E. McManus and Clifford H. Wood, Atlas of
Newfoundland and Labrador (St. John's, Newfoundland: Breakwater, ©1991 MUNCL) Plate 6.4.
Image modified by Duleepa Wijayawardhana with permission, 1998.
Average temperature decreases towards the north.
The frequency of very warm days (maxima above 25°C) is greatest over central
and western lowland districts of the island, such as the lower Exploits and Humber
valleys, including the Corner Brook area. These locations will typically experience a few
daily maxima near 30°C each summer. Being removed from the
threat of coastal sea fogs and low cloud, these are also the areas of most
frequent summer sunshine, although the inner reaches of the east coast bays also experience
a relatively high number of bright sunshine hours.
Summer in St. John's.
Located in the heart of St. John's, Quidi Vidi Lake is a popular attraction for the city's residents.
Reproduced by permission of Ben Hansen. From Ben Hansen,
St. John's, Newfoundland (Dartmouth, N.S.: James Stonehouse Publications,
1991 ©1996), 72.
The relative dryness of the April to June period is continued into July over eastern
sections of the island, especially on the Avalon peninsula, due to the influence of the
Bermudan sub-tropical anticyclone to the south (see climagraphs:
legend). However, a trend to increasing rainfall for July and August characterizes
areas further west and north, where more frequent low pressure systems, combined with
stronger daytime heating over inland sections, produces more frequent rain.
Indeed, over central and western Labrador, July and August are normally the wettest
months of the year (see climagraphs:
Toward the end of August,
and into September, the possibility exists for a tropical storm to approach southern
Tropical Storm "Eduardo" and Hurricane "Fran"; September 1996.
The visible wavelength GOES satellite image for the afternoon of 4 September, 1996 shows
two tropical storm systems at differing stages in their life cycle.
©1996, Environment Canada.
If these warm air
track close enough to the island, intense rain can fall over a short period. Such was the
case on September 11, 1995, when tropical storm Luis was responsible for approximately
100mm of rain over parts of the Burin peninsula, causing land slips and damaging roads.
©1999, Newfoundland and Labrador Heritage Web Site Project