Fall and Early Winter Outlook

It’s been a cool, relatively dry summer so far. Many areas including the Quad Cities in eastern Iowa saw a top 5 coolest month. Here is some of the coolest July’s in recorded history in Eastern Iowa:

COLDEST JULY AVERAGE TEMPERATURE
==================================
COOPERATIVE OBSERVER STATIONS

IOWA CITY, IA WWTP  CEDAR RAPIDS NO 1, IA    BURLINGTON MUNI AP, IA
——————- ———————- ————————
1.2014 –69.9        1 2009 – 68.6           1 2009 – 70.2
  2009- 69.9        2 1992 – 70.0           2 2014 –70.4
3 1915- 70.1        3 2014 –70.2            3 1950 – 71.2
4 1950 – 70.2         1958 – 70.2           4 1971 – 71.3
5 1951 – 70.3         1950 – 70.2 5           1915- 71.8
  1924 – 70.3       6 1924 – 70.3           6 1958- 71.9
7 1958 – 70.8       7 1971 – 70.6           7 1967 – 72.0
8 1962 – 71.1       8 1967 – 71.1           8 1924 – 72.5
9 1945 – 71.6         1962 – 71.1 9           1992 – 72.6
 1920 – 71.6       10 1915 – 71.9           10 1905 – 72.8
 1904 – 71.6

 

 

(Courtesy of the NWS Quad Cities)

Many of you have been asking what this will mean going forward into this fall and winter. To simply answer this, it should continue to be cooler than average, with slightly more precipitation than normal. Why you ask? There are a bunch of different factors.

First, in the near future(1-2 weeks), an atypically placed Rex block to our Northeast will keep the chances for small amounts of rain, as well a near normal temperature profile throughout most of Iowa. An Rex block is simply a High Pressure block with a Low pressure system stuck below it. This is what a typical Rex block looks like:

Rex Block

This time of year, when this happens all “normal pattern” jet stream impulses get stopped from moving to the east, resulting in a similar type of weather for up to a month in a row, with very little change. This setup is what caused the cooler month of July, and since it has only moved about 200 miles east over the course of the month, a similar pattern will stay in place, but with slightly more moisture available for the coming month.

As to the Fall-Winter time frame, it is also looking to be cooler than normal. This deuction is being made from a couple of different sources of information. The fist is the Great Lakes Water temperature monitoring, which has shown much cooler water on the GL than normal. Here is last week’s readings, with temps averaging 4-15 degrees below average.

NOAA Great Lakes Coastal Forecasting System

What does average lake temperature have to do with long term outlooks? Simply put, is a gauge that we use to compare past years to this year, and what the similarities between years could mean. The last time that the lakes as a whole were this cool was 1992, one of the coldest and wettest winters that the Midwest has seen. This could be an meteorological sign of what is to come this winter.

The second source of information is the medium range models (From NOAA), which have been consistently been showing a cooler trend:

One Month Temperature Outlook

Above is the 1 month probability for temperature, and below is the 3 month probability for temps.

Three Month Temperature  Outlook

When you combine this information with similar El Nino patterns in 1992-1993, 1997-1998, 2002-2003, and 2009-2010, we should be prepared for a 4-8° cooler average temps over the next 6 months, and average to above average precipitation amounts.

While this is an look into the patterns and probabilities of certain weather patterns, this is just an outlook, and not a forecast. There are many components that could change certain parts of the outlook.

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