Showers and Storms this Week

The last week of July is (on average) the hottest week of the summer.  We are looking at 90s Mon-Thu this week, so this may be following the pattern.  The longest day of the year is June 20th, with 16 hours of daylight in Spokane.  By the end of July, we've already lost just over an hour of that.  Not that the length of day is the only factor of hot weather, but it obviously has an effect.  The days noticeably get shorter in August, losing about 3 minutes of sunshine each day.

We were talking in the last blog about the potential for showers and thunderstorms this week.  As usual, things are becoming a bit clearer on timing and coverage.  

Afternoon and evening thunderstorms will increase over the next few days over eastern Oregon, slowly creeping north each day. By Tuesday, the southern Washington Cascades could see an isolated storm.  Wednesday will see the potential for afternoon thunderstorms over most Washington mountains. Here’s the European ensemble rainfall forecast for Wednesday afternoon, compliments of PivotalWeather.com:




After that things get interesting. Here’s a summary look at the rainfall chances at Deer Park for the next 10 days. You can see that very small rain chances get started after Wednesday and peak around Thursday night and Friday.  It's not unusual for this kind of pattern to feature a stray morning sprinkle or even a clap of thunder, but at this point I can't see those kinds of details.


Thursday has a better chance for thunderstorms than Wednesday, mainly in the afternoon and evening hours.  Don't get too hung up on the amounts.  Focus more on the coverage.


 
This activity could continue Thursday night.  There should be more showers and thunderstorms on Friday, but at this point, the majority of them will be north and east of Spokane.



Initially, these storms will mostly be dry; more lightning than rain.  But as the event continues, more moisture moves into our area from the south, so that by Friday morning, our atmospheric moisture is about double what it should be for this time of year.  The image below shows the areas that are more moist than normal, which includes all of the Inland Northwest.


Another factor we often look at is how fast the storms will be moving.  In this case, the winds aloft (which steer the storms) will be rather weak, about 5-10 mph.  This gives a thunderstorm more time to dump rain in any one location.  

If you're trying to bale some 2nd cutting before the rain arrives, dew conditions should be good for Monday and Tuesday morning.  Wednesday morning is a bit more iffy as northeast winds will develop in the morning and could hinder dew formation.  After that, our dew point gets unusually high (near 60 by Friday morning, which is muggy for our area).  But there will be lots of cloud cover at night that could keep our low temperature rather balmy (in the 60s).

Looking beyond this event, temperatures should remain in the 80s for the first part of next week with a continued low threat of showers.  By the end of next week we should start to get hot again.






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