Friday, June 29, 2012

Summer Heat, Our Dry Ground and the July Outlook

Over the last several weeks, we've been watching the heat dome gain strength in the middle of the country. Given the ocean surface temperatures in the Pacific Ocean both in the tropical and in the higher latitudes (off of the California coast and north of Hawaii) they all strongly drive the trough/cool pattern along the west coast with a central ridge/warmer conditions in the middle of the country.

Like any recipe from grandma you try to replicate, put too much or too little of one ingredient that seems
insignificant at the time can drastically alter the taste of the dish.  The atmosphere is no different.  The conditions for a warmer than normal summer were ready in the middle of the county, cooler in the west and near normal in the east.  Throw in a newly developed condition or conditions unforeseen a few months ago and the overall pattern can change drastically for us in Ohio and in other places. 

The "newly developed conditions" this early summer originate from two completely separate, totally
disconnected regions of the world.  The first condition, the Ohio Valley drought/dry ground, is the easiest to visualize because it is effecting everyone right now and will effect more of us in the pocketbook come harvest time. How does your lawn look? Not very good I would imagine.

Look at the recent drought indicator map. Notice the two spheres of extreme drought; one out west and one in the Ohio Valley.

The dry ground in Ohio and in the state west through Illinois and south to Arkansas is getting severe. The drier the soil, the more the heat dome/ridge in the central US deepens. The hot atmosphere is feeding off of the dry soil making the ridge stronger. Highs temps on Thursday reached 100+ in western Ohio

Compare the temps for the first 24 days of June to the temps on the 24th itself. See how the heat was out west then it moved east into Ohio.
Look at last June. The drought was in Texas.

The extreme heat was in Texas in June of 2011

Remember, the dry ground isn't the primary driver but an enhancer. The bigger question will be whether or not the drought conditions in the central US into Northeastern Ohio will fuel more heat into July.

This summer, unlike 2011, 2010 and 2009, we have no El Nino or La Nina (although El Nino is showing strong signs of building). Instead of using those Pacific markers to determine overall patterns across Ohio and the US, we need to use other tropical drivers.  These are called the Madden Julian Oscillation. Every 30-40 days, tropical disturbances originate in the western Indian Ocean and move east into the tropical Pacific.

When El Nino or La Nina is present, they dampen the effects of the MJO. Absent of any El Nino/La Nina, the MJO has a chance to work its magic.  The strength and position of the disturbed MJO area greatly alters the pressure patterns in the tropical Pacific which can mimmick El Nino or La Nina conditions for a much shorter period of time. These changes cause a shift in the position of the troughs/ridges across the US and the speed at which they move across the continent

If the MJO becomes weak, the steering currents across North America can relax which can result in persistent ridging/quiet/hot weather in spots. Guess what the conditions are in the Pacific here in late June/early July?  No El Nino, No La Nina and a very weak MJO. 

This all means that we are stuck on the edge of the heat wave in the central US.

Until the MJO budges, expect the heat to continue into early July.  If the MJO comes around to a phase like we had in the middle of June, we might have a return to highs in the 70s. As of this writing, the chances are small.

Like I said earlier, long range forecasts are like trying to make your grandma's signature soup. You might have all of the ingredients lined up.  Forget to add something or add too much of another and you get a completely different soup. This summer's forecast is tasting alot like that soup! 

No comments: