A COOLER THAN AVERAGE SUMMER...

May 16, 2020

It's been another chilly, late breaking spring around the Midwest, a trend we've seen far too much of in recent years. These are the temperature departures over the last 2 months, going back to March 13th.

The departures are even greater the past 30 days dating back to April 13th

With meteorological summer just a couple weeks away (June-August) one has to wonder if this cool pattern will hold in the months ahead. One of the long range outlooks that I find useful that does not get the credit it deserves is the CAS model (constructed analog on soil moisture)

 

CAS - is based on empirical functions from data over the lower 48 states going back to 1932. This tool constructs a soil moisture analog from a weighted mean of past years. The weights are determined from the similarity of soil moisture conditions in prior years to a combination of recent soil moisture observations and a medium range forecast of soil moisture out to 14 days based on temperature and precipitation outlooks. Then the temperature and precipitation observed in subsequent seasons in those past years are weighted in the same proportion to produce a forecast that is consistent with current soil moisture conditions. Although available throughout the year - the CAS is primarily used during the warm half of the year from April to September when their effects are the most pronounced and skillful. I think it does a pretty job.

 

The recent CAS runs do not bode well for a hot summer, Here's what the model shows for temperature departures June through August. There's a strong chance the 3 months will average cooler and wetter over the central Midwest.

Here's the individual breakdown of the 3 summer months.

 

June is actually pretty close to normal on temperatures and above average on rainfall.

 July looks quite cool compared to the averages but rainfall is below normal

 August looks especially cool and is wetter with near to above average rainfall. 

All three summer months based on soil moisture analogs and forecast temperatures and precipitation point towards the NW flow that's dominated spring to remain in place much of summer. I'm not sure it will be as cool as CAS shows but I like the general idea.of below normal temperatures by a at least a couple degrees. That's not a bad thing at the hottest time of the year!

 

As for rainfall the next 3 months. I expect near normal totals for the majority of my area

 

The next round of rain and renewed cool temperatures arrives late Saturday. A well organized upper air and surface low along with a good moisture feed will make this another wet storm. At this time instability looks to be on the low end in my area so the severe weather threat appears limited. With the surface cyclone passing right over eastern Iowa Saturday night the heaviest rains are anticipated in my northwestern counties where amounts could exceed an inch in spots. The southeastern 2/3rds of my region get dry slotted and that should keep amounts more manageable, a good thing with all the rain that;s fallen the past few days. The EURO has this for total rain. I think it has the right idea with the trends and northward placement of the heavy rain band.

The worst of the rain should be over by mid-morning Sunday but the upper air low closes off and is slow to depart the Ohio Valley. That could result in some wrap around showers later Sunday that could linger into Monday in my far eastern counties in Illinois. Temperatures should start mild Sunday before falling into the 50s by late afternoon on gusty west winds. The cool air remains in place Monday before moderation begins on Tuesday. Highs midweek on should be in the 70s and 80s. Looking good in the neighborhood! 

 

By the way, we had a strong thunderstorm in Portland, Maine Friday evening with sharp lightning, wind, and torrential rain. It was a dang good storm and reminiscent of the the type we get in the Midwest. It made me feel like home. Have a good weekend and roll weather...TS

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© 2019 Terry Swails