First the April pattern recap:
High pressure was dominant over the northern Pacific and the north Atlantic. This drove temperatures well above normal during the first half of April. We had snow on April 1 in northern Ohio. 6-7 days late we reached 80 degrees!
"The new version of the MEI (MEI.v2) has been created that uses 5 variables (sea level pressure (SLP), sea surface temperature (SST), surface zonal winds (U), surface meridional winds (V), and Outgoing Longwave Radiation (OLR)) to produce a time series of ENSO conditions from 1979 to present"
The evolution of La Nina in years which are similar to the current event's development.
Now summer temperatures (June, July and August) vs normal
What are we expecting this summer?
Based on top analogs looking at past La Nina summers along with other variables, we expect an above number of 90 degree days this summer especially in late July and August. A few 90s are highly possible into early September.
The ground moisture is running slightly below normal as of this writing (May 4). For comparison, last year we were running a rain surplus.
* Wet ground/above normal rainfall in May/early June will limit the expansion of heat and ease of reaching 90 degrees for multiple days. Drier ground over multiple states will enhance ridges of heat in summer making 90+ easier to attain deep into summer.
What are we watching?
* The position and strength of the Sonoran Ridge (high pressure) and the Bermuda high will dictate the position of the summer storm systems.
* Our analysis shows that these ridges especially the Bermuda High will develop by mid June and pulsate north frequently. The relaxation of the ridge periodically (flattening along the northern periphery) will allow storms to drift over the ridge and into the Ohio Valley especially in late June and July.
* We expect a more active July with storms.