MAY/SUMMER 2017 WEATHER UPDATE
RECENT WEATHER HEADLINES:
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Four month period of December 2016 through March 2017 ranked as the 4th warmest such period since 1895 for the
lower 48 states as a whole. Through late April, monthly average temperatures were running above normal in much of
the central and eastern U.S., but there more days later in the month with below normal readings especially in some
northern and a few central areas.
April weather did provide periods of time favorable for corn planting in the Midwest, but rain also slowed progress at
times. By late in the month planting progress was ahead of the 5 year average in some states, but also behind these
numbers in several states.
Growing conditions during April were generally favorable for Hard-Red Winter Wheat crop in Central and Southern
Plains. Some favorable weather earlier in April allowed some fieldwork and planting to increase in the Northern
Plains, but more days with below normal temperatures later in the month unfavorable. By late April spring wheat
planting ahead of 5 year average in SD, but behind these numbers elsewhere.
Spring weather led to winter wheat development and spring crop planting to average near to ahead of normal in
much of the Delta and Southeast. Some heavier rains made return to some of these areas later in April.
After a long period during which sea surface temperatures in the NINO3.4 region of the Tropical Pacific averaged below normal,
extending back into the summer of 2016, these values warmed above normal during February. Except for a brief period, these
sea surface temperatures have since then been warmer than normal, with overall neutral conditions occurring. Below is a
graph from the U.S. Climate Prediction Center showing the trend in sea surface temperature departures from normal in the
NINO3.4 region. The latest weekly value was +0.5 degrees C, which is on the borderline between positive neutral and weak El Nino
conditions. There are now fairly large areas of the Pacific in which sea surface temperatures are near to above normal.
Sea Surface Temperature Anomalies for NINO 3.4 Region in Degrees C.
In the past few weeks there has been a tendency for some weather models to slow or lessen further warming of the sea surface
temperatures in NINO3.4 region of the Tropical Pacific, with no more than weak El Nino conditions developing mid to late this year.
This is a cooler over trend in this area than was being forecast earlier this spring. Latest indications are that positive neutral or very
week El Nino conditions may the most likely trend for this upcoming summer. Below is the U.S. Climate Forecast System2 forecast
for the NINO3.4 region showing expected sea surface temperatures farther into 2017. The dark black line shows past temperature
data, the dashed black line shows the ensemble forecast, and red and blue line show the forecasts of the individual model members
making up the ensemble forecast. Latest versions of the Australian model have also backed off on continued warming of sea surface
temperatures in the NINO3.4 region, while others continue to show further warming, resulting in more variance in model solutions.
For the past, few months I have been looking at some years in which the trends in the Tropical Pacific were similar to trends we
have seen since the fall of 2016 into early this year, and the expected trends into later 2017. That being a period of negative
neutral or weak La Lina conditions transitioning to positive neutral conditions into the spring of the following year and
eventually to El Nino. This list of years has included 1951, 1957, 1963, 1965, 1972, 1997 and 2002, with more borderline
candidates being 1986, 2006 and 2009. The exact path from negative neutral or weak La Nina to warmer than normal sea
surface temperatures varies in timing among these years compared to 2016-17, but in all cases an El Nino of varying intensity
eventually developed the following year. The most recent trends in forecasts for the NINO3.4 region make 1957,1965, 1972 and
1997 the least favorable matches, as in these years El Nino was fairly well established by summer. Refining these years based
on the average weather during the previous December through March period for the lower 48 states as a whole quickly
eliminates many of the years as favorable matches. A few are matches based on temperature, a few on precipitation, but very
few on both criteria. 1997 is generally the best match when looking at both criteria. There is not one of these years I would use
exclusively for an analog, and some will likely be dropped from this list as it becomes more clear how conditions in the Tropical
Pacific actually do develop over the next few months.
I did not rely on any single year in these latest updates. The summer outlook is not changed a great deal and is primarily based
on some correlations based on summers following warmest December through March periods for the lower 48 states and also
on some correlations following similar periods that were both warmer and wetter than normal for the lower 48, as well as some
consideration for a few of the years above. The May update was more based on our current longer range forecasts and climate
model updates. My confidence is lowest on the summer rainfall outlook, as is usually the case, as this feature is very difficult to
predict at best.
Looking ahead to May:
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The late April and early May weather pattern will keep spring planting progress behind the 5 year average in
sections of the Northern Plains and Midwest. Some heavy near term rain into the first week of May in parts of the
Midwest, will result in significant amount of dry time needed before fieldwork can resume. Past the first week of
May it is likely that overall conditions will improve again, but planting progress will likely still run behind 5 year
average in some areas.
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Heavy rain in Delta and some western parts of the Southeast slow fieldwork and saturate some fields also.
Improving conditions here also after first week of May. Need for some rain increases in southeastern parts of
Southeast in the near term, then rain chances do increase during first week of May.
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Late April and early May precip should keep up soil moisture for Hard-Red Winter wheat areas, but unfavorably
cool conditions also expected at times. Milder overall pattern starts later in first week of May, but still at least
some brief times when temps are below normal.
April 26, 2017
Dan Hicks/Meteorologist
Freese-Notis Weather
515-282-9310 [email protected] IM: weathertrader89 Twitter: @freesenotis