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Posted at 10:00 AM ET, 05/21/2009

Summer Outlook: Less Hot Than Recent Years

By Matt Ross

* Forecast: Warm Sunshine | NatCast | D.C.'s New Stormwater Fee *

Despite a somewhat cool May, the heat and humidity that epitomizes summer in the D.C. metro area is an inevitable reality. As such, we present our annual Summer Outlook. This summer we're predicting average to slightly above average temperatures. If this holds true, it will turn out to be the 'coolest' summer in several years.

The task of doing a summer outlook is no easy one. First, with few exceptions, summer in the D.C. area is mainly hot. Do we really care if it's 88 and humid or 93 and humid? Also, the weather varies less during the summer than it does during the the rest of the year (especially compared to winter), with the vast majority of summer months finishing within a few degrees of normal. So, it follows that when putting together a summer outlook we're less likely to see the signals for extreme warmth or cold that we sometimes see in advance of winter.

Nevertheless, we will do our best to convey what we expect for summer 2009...

Keep reading for more details on what to expect this summer...

OUTLOOK SUMMARY

This summer has a good chance to be our coolest since 2004. We do not think we will see any of the lengthy or extreme heat waves that have marked some of our more recent summers. While we should reach the 95-100 range a number of times, these extremes will be short-lived events of only 2-3 days. Nevertheless, expect plenty of hot humid days with highs in the upper 80s and low 90s, especially during the 6-7 week stretch from late June to mid-August that marks the core of our summer heat. Though summer temperatures should be close to normal and unmemorable, we do think the chances for a heavy multi-day rain event and/or remnants from a tropical cyclone are higher than normal this summer.

OUTLOOK DETAILS

Temperatures:

June: 1 degree above average
July: 1 degree above average
August: average

Overall: Average to 1 degree above average

Number of 90-degree days for June/July/August: 35 (Normal is 31.3)

Number of 100-degree days: 1

Longest Streak of 90+: 7 Days

Precipitation: Slightly above average with June most likely to be the wettest month and July most likely to be the driest.

METHODOLOGY

The main methodology for creating the outlook was the use of analog years. Analog years are past years in which conditions leading up to summer most closely resemble conditions leading up to summer 2009. Analog years are far from a perfect predictor due to the complexities of weather, as no two years are exactly alike. However, they can be of considerable value in giving us a general idea of what to expect.

The following factors were given the most consideration in preparing the outlook. It should be noted that any one factor does not necessarily correlate with a particular kind of summer (e.g., warm, cool, dry or wet).

El Niño/La Niña:

We are currently rapidly transitioning out of a 2-year La Nina event and into weak El Niño conditions. El Niño is indicated by warmer than average sea surface temperatures in the Equatorial Pacific Ocean. Currently, the water temperatures in the this region of the Pacific are only slightly above normal, but there are a number of indicators that suggest that we may be facing a moderate or even strong El Niño event as we head into fall and winter. Despite the numerous models that predict El Niño/La Niña events, there is still a lot of uncertainty and inaccuracy in these predictions. However, our outlook is predicated on the idea that El Niño will continue to strengthen throughout the summer.

This Spring's Conditions:

Despite some notable temperature swings (the most noteworthy being the late April extreme heat), temperatures have been close to normal over the past several months. Precipitation is also now near normal thanks to the rapid transition out of drought-like conditions that developed earlier in the year.

Across the rest of the U.S., the most noteworthy weather patterns we considered included the cold in the Northern Plains from March through Mid-May and the extreme May heat in southern California and the Desert Southwest.

Additional considerations

*This year, temperatures each month have been near normal except for January, which finished more than 2 degrees below normal.
*The previous four summers all finished 1-2 degrees above normal.

Analog Years

The Analog Years, or the years where many of the above factors were also apparent, are: 1951, 1957, 1968

The weather during these summers served as the basis for our outlook.

Enjoy summer 2009 and stay cool!

By Matt Ross  | May 21, 2009; 10:00 AM ET
Categories:  Capital Weather Gang, Local Climate  
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Comments

Oh don't toy with me! A lovely normal summer with no major heatwaves sounds just perfect. I, my heat hating dog, and my AC bill love this notion.

But how accurate have your predictions been in the past?

Posted by: hereandnow1 | May 21, 2009 11:35 AM | Report abuse

Actually the past two summers haven't been all that bad, though I got a new A/C unit at the beginning of last summer.

The big problem remains: Annoying evening thunderstorms on those nights I'm trying to get to a dance. It's better if Augusta Jim gets these rather than me on dance nights.

IMO transition to an El Nino should LOWER the risk of getting a tropical storm remnant this summer. El Nino conditions generally mean less tropical activity on the Atlantic side.

What I'm currently hearing is hot June, cool July and August this summer. Precipitation should largely depend on frontal placement, though this wet spring wiped out our drought.

Posted by: Bombo47jea | May 21, 2009 12:03 PM | Report abuse

NOAA's hurricane season outlook was issued this morning.

Posted by: CapitalClimate | May 21, 2009 12:18 PM | Report abuse

@hereandnow1

See our grading of last year's summer outlook here.

Posted by: CapitalWeatherGang | May 21, 2009 1:19 PM | Report abuse

Seven straight days of 90+ is a pretty sizable heat wave.

Posted by: Bombo47jea | May 22, 2009 12:03 AM | Report abuse

The comments to this entry are closed.

 
 
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