wpostServer: http://css.washingtonpost.com/wpost

The Post Most: Local

Posted at 09:45 AM ET, 05/24/2011

Capital Weather Gang’s 2011 Summer Outlook

Spring actually behaved like spring through much of May, with only two 80-degree days during the month’s first 20 days. But we racked up three 80+ days the past three days, and we cannot stave off the inevitable. If there is one season we can count on to behave according to form, it is summer.

The good news is that it doesn’t look like we’ll be making any run at last year’s record hot summer. The bad news? Like most summers, it will almost certainly be another hot and humid one in the D.C. area. The silver lining is that we may be in line for quite a few brief periods of respite from high heat and humidity, whereas last summer we got almost none.

Keep reading for the full summer outlook...

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 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 (relative to average) that we sometimes see in advance of winter.

Nevertheless, we’ll do our best to convey what we expect for summer 2011...

OUTLOOK SUMMARY

With the exception of June/July 2009, every summer month since 2005 has been at or above normal with 13 of the 18 months at least one degree above normal. We expect this summer to be no different with all three months predicted to be warmer than average. However, unlike last year’s record-breaker, we predict this summer will only be slightly above normal, and much of that may be due to warm overnight lows rather than consistently oppressive afternoon heat.

Additionally, we expect to see at least normal and perhaps slightly to somewhat above-normal precipitation, via a combination of showers/thunderstorms and longer-duration rain events. As we head into August, we may also add in rain associated with tropical systems. Overall, we predict a standard-issue hot and humid D.C. summer, but with mitigating factors that make it tolerable and even pleasant for some stretches. In other words, we expect an overall variable pattern to keep most heat waves brief, with relief by way of temporary cool shots and/or rain right around the corner.

OUTLOOK DETAILS

Temperatures:

June: 1 degree above average
July: 1 degree above average
August: 1 to 2 degrees above average
Overall: Around to just over 1 degree above average
Number of 90-degree days for June/July/August: 25-30 (Normal is 31, and we had 52 last summer)
Number of 100-degree days: 0-1
Longest Streak of 90+: 7-9 days

Precipitation:

Slightly to Somewhat Above Normal

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 2011. 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 exiting what was a 9 to10 month La Nina episode (cooler than average waters in the equatorial Pacific Ocean) that peaked as moderate during the winter. Observations and models suggest that the El Nino/Southern Oscillation should continue to move toward neutral conditions - neither El Nino (warmer than average waters) nor La Nina - as we head into summer. Though it is possible that a weak La Nina may linger or restrengthen somewhat as we progress through the summer months.

This Spring’s Conditions:

Since early February, on average we’ve had a trough (dip in the jet stream) in the west/northwest part of the U.S. resulting in cooler-than-normal weather, and a ridge (bulge in the jet stream) in the east/southeast with warmer-than-normal weather. As March and April progressed the warmer anomalies spread further south and west, especially into the drought-stricken areas of Texas.

Analog Years:

The analog years, or the years where many of the above factors were also apparent, are:1955, 2001 and 2008

The weather during these summers served as general guidance for our outlook.

Hope everyone has a wonderful summer. Despite our likely fair share of hot and humid days, in the big picture we don’t think this will be a memorable one as far as temperatures, and that’s a good thing for those still sweating from the last summer.

PAST OUTLOOKS

CWG’S 2010 Summer Outlook (post-summer evaluation)
CWG’s 2009 Summer Outlook (post-summer evaluation)

By  |  09:45 AM ET, 05/24/2011

Categories:  Local Climate, Latest

 
Read what others are saying
     

    © 2011 The Washington Post Company