Monday, May 31, 2021

Angry Lake Erie and Unseasonably Cold Temperatures

 


Strong NE winds developed Thursday and Friday which piled up water in the western basin of Lake Erie. Video above is from Kelley's Island Friday courtesy Todd Neu.

Wave heights reached 10-15 feet before they settled down Saturday and Sunday


The low resembled a late fall, cut-off system. You can see how it developed over the upper midwest and then stalled in the southern Great Lakes.


Temperature started out 20+ degrees below normal Saturday morning across the Great Lakes.



High temperatures Saturday stayed in the lower 50s north and upper 50s south. Temperatures this cool (under 55) don't happen very often this late in the year.



Monday, May 17, 2021

What Drove the COLD End of April/Early May?

Seven Hills, April 20, 2021

The first 2 days of April featured snow and cold. We forget about how warm April the second full week of April was (highs in the 70s and 80s). 


Here's what most of us said on April 10th: "Winter is over. Spring is here!"

Then the bottom fell out.

Late April/early May cold was significant across the northern half of the US.  Slushy snow fell (which melted off fast) on May 9 along with 2-4" of rain Mother's Day.  Temperatures for most days were running well degrees below normal from April 15th through last week. 


So what happened?

The MJO (Madden Julian Oscillation) headed into a high amplitude phase 7,8,1


This connects well to colder than normal temperatures across the eastern US.

You can see how the surface temperatures & 500mb (upper level pressure pattern) vs normal evolved over the period. I circled the Greenland High Pressure/Block. This was responsible for locking in the pattern set up by the MJO.

April 24-30 temperatures vs normal

Upper Level Pressure Pattern vs normal

May 1-9 temperatures vs normal

Upper Level Pattern vs Normal

May 10-14 Temperatures vs Normal

Upper Level Pattern vs Normal

Notice how the Greenland Block started to weaken last week. As it weakened the cooler pattern started to break down.

Here's what the general public was say on May 9-10th: "What is going on here? Snow in May. Seriously? I can't remember the last time this happened this late."

In reality, we had a COLDER early May last year (2020) with even later snowfall.


In late April we started to see signs of warmth the last 2 weeks of May.


The pressure pattern still strongly suggests the Bermuda High to pulsate north through the end of the Month/early June as the MJO amplitude goes down/heads into phase 3,4,5,6.




Temperatures from May 17 through May 27


This WARMER pattern is a harbinger of what is to come this summer!

I can hear the cries of viewers saying "The weather is going from winter to summer again".  

(In reality this has happened many times before in weather history but I digress). Our spatial and recency bias is strong when it comes to weather.

Tuesday, May 04, 2021

How Many 90 Degree Days This Summer? Check Out The Northern Ohio Summer 2021 Outlook


After an up and down, La Nina driven winter (cold mainly from late January through February) with slightly below normal snowfall with nearly 50 inches (our snowfall prediction was 55-65"), the question is: Will the same La Nina drive this summer's pattern?

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!


Since the middle of the month, the pattern flipped.  The northern Pacific ridge shifted over Alaska. The ridge over the north Atlantic shifted north over Greenland.  Both ridges linked together over the North Pole. The trough developed underneath and across the eastern 2/3rd of the US with widespread below normal temperatures.  We had snowfall on April 20th in northern Ohio, the 3rd most this late in the season ever (2005 was the most).



Much of this was influenced by the high amplitude MJO in April rotating through phases 5 through 8.


April 2021 high temperatures vs normal in Cleveland.


Late this winter and into early April the cooler water along the equator (La Nina) has been steady but slowly warming. 


The depth of cool water is also becoming more shallow.



The MEI is another great measure of the ENSO state. It takes into account multiple oceanic and atmospheric variables (not just the ocean water temperatures) to produce an overall number either positive or negative. The current MEI is at 0.8. The MEI site's description here:

"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.


The model projections show weakening with some intensification of the La Nina late this summer/early fall. Since it take time (months) for the ocean/atmospheric state to completely transition out of its current state, I think this will have only small effects on the overall summer pattern.
Here is a great tutorial on La Nina from NOAA:

What do some of the similar past La Nina summer look like?

These are overlapping months (May through September) showing the upper level pattern. 

2018

2012

1999

1996

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.

Over the last 3 weeks, the rainfall deficit has dropped across the state.




Crop moisture is only slightly below normal but trending to near average
...same with the longer term Palmer Drought Severity Index (PDSI)


* 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.