The Weather Expert

So just how hot is a typical Boise Summer?

     Every year as the cool spring days get warmer and warmer, I am often asked two questions.  "Will it be hot this summer" and "will it be dry this summer"?  My answers are almost always the same.  "Yes... it's always a hot summer" and "yes... we live in a desert... it never rains in the summer".

     So let's look at the actual numbers.  Boise's hottest days average 91 for the high temperature during the first 6 days of August. Despite the longest day being the first day of summer in the third week of June, the hottest temperatures lag behind the seasons because it takes time for the sun to warm the air.  This is the same reason that the highest temperature of the day is in the late afternoon and not when the sun is overhead at noon.

     Over the past 67 years Boise on average has seen 5.6 days with the mercury topping 100.  However since the turn of the century we have seen an average of 14 days at 100+ with 2003 recording a record 20 days.

     So if you think 100 degree days are not normal... think again.  Our hottest days are likely right around the corner and 100 degree heat is almost ineveitable. It's been since 1982 that Boise did not see temps topping the century mark..... Keep cool !

A rare soaking

     With temperatures soaring into the mid 80s on Saturday it was hard to believe that Sunday afternoon would be THIRTY-TWO degrees colder with heavy rain!  I knew it would rain but Boise officially received .79"... not a record day but close...  1.11" of rain fell on June 10th 1977. The average rainfall in Boise for all of June is .74"!

     Sunday's rain pushed our June total to .95". We are still behind for the water year which started on October 1st.  Since then we have had 7.49" of rain which is still 2.81" below normal. You can see more of Boise's climate and weather records here.

     Did you notice all the low clouds and fog on Monday morning?  When heavy rain keeps the temperature down during the day then the skies clear around sunset, conditions are ripe for fog to form.  This is because to get fog you need the temperature to fall to its dewpoint which causes 100% humidity.  Cloud cover acts as a blanket keeping the air warmer so when the sky clears it allows the temperature to fall more at night.  That's why lots of fog formed Sunday night.

     All that rain also affected our temperature on Monday.  The sun does not heat the air, rather it heats solid objects like the ground.  The warmed ground in turn heats the air in contact with it.  That warmer air then rises and is replaced by cooler air. This process continues to steadily warm the air temperature. Monday however, the energy from the sun was evaporating all that moisture leftover from the widespread rain on Sunday.  So our temperature did not rise as quickly or as high as it would have if we had a dry Sunday.

Why was it so windy & cold?

     Early Wednesday morning my 2 year old son Jett looked outside and said "Daddy... is windy" If you stepped outside and wondered WHY is it was so windy & cold, you were likely not alone.  Gusts topped 50mph and combined with unseasonably chilly temperatures to cause wind chill factors in the 40s. 

     Wasn't it just 100 degrees? Welcome to spring in Idaho.  During the spring time the atmosphere is undergoing changes.  The sun warms the icy cold air mass over the northern hemisphere. This relaxes the jet stream (or storm track) and forces it to move north allowing the warmer air to follow.  But this process is not very consistent.  So the biggest temperature swings are possible in the spring.

     So why all the wind?  When you have big temperature contrasts, you have big pressure contrasts. (if you like math... pressure is directly proportional to temperature).  When ever you have a major temperature swing, you can expect some wind with it.

     Wind blows from high pressure to low pressure.  Imagine a room pressurize with a lot of air. Then someone opens the door.  The air will rush out of the room because the air pressure is higher in the room than out of the room....so there is a big blue H in the room and a big red L outside the room.

     When you look at my weather maps and you see and L next to an H, it is likely at least breezy between them.

     If you have any weather questions, feel free to post a comment or send me an email at sdorval@todays6.com .