Rain­fall num­bers: Not al­ways an ac­cu­rate mea­sure of the sea­son

The Western Star - - WEATHER - Chief Me­te­o­rol­o­gist Cindy Day

Like it or not, Au­gust is wind­ing down. As far as me­te­o­rol­o­gists go, so too is sum­mer; me­te­o­ro­log­i­cal sum­mer is June, July and Au­gust.

It’s been a hot one for sure; records were set in terms of du­ra­tion of high heat and hu­mid­ity. As far as the rain sit­u­a­tion goes, anec­do­tally, most would say it’s been very dry. If we turn to the num­bers, we’ll find that July was very dry, but a very wet June brought up our sum­mer rain to­tals. The ex­cep­tion is west­ern New­found­land and Labrador

where the rain­fall to­tals re­main well be­low nor­mal.

Buried within the rain­fall snap­shot, are in­ter­est­ing facts that are not ob­vi­ous. For ex­am­ple, while the three-month rain­fall for Syd­ney, N.S., was near nor­mal, they re­ceived twice as much rain on Satur­day as they did dur­ing the en­tire month of July.

Now peo­ple are al­ready ask­ing what fall is go­ing to be like. Be­fore I com­ment on that — and I don’t usu­ally make sea­son-long pre­dic­tions — I want to quickly look back on why it’s been so hot and muggy.

This sum­mer, the Ber­muda High, that large sub­trop­i­cal semi-per­ma­nent cen­tre of high at­mo­spheric pres­sure typ­i­cally found south of the Azores in the At­lantic Ocean, sits much far­ther north than it usu­ally does. The po­si­tion of the sys­tem and the wind-field around it re­sulted in “On­tario heat” set­tling over At­lantic Canada.

Over the next few weeks, I ex­pect the con­trol­ling sys­tem to slowly sink south­ward. That more typ­i­cal lo­ca­tion for the sys­tem will al­low the jet stream to flat­ten out and also sink south­ward, in turn al­low­ing weather sys­tems ap­proach­ing from the west to move across At­lantic Canada. That will see pe­ri­ods of rain in­stead of hit-and-miss show­ers and will put an end to the flow of air from the trop­ics. Over­all, I be­lieve our fall will be a lit­tle on the wet side, with near or above sea­sonal tem­per­a­tures.

Time will tell.

Mea­sured rain­fall doesn’t al­ways tell a com­plete weather story. (Sub­mit­ted photo)

Newspapers in English

Newspapers from Canada

© PressReader. All rights reserved.