April 2013: Slightly warm and dry in Washington, D.C.

After a chilly March, our middle month of the meteorological spring ended slightly warmer and slightly drier than normal.

The average temperature of 58.9F ties for fourth warmest of the 2000s and 18th warmest of the long-term history.  It is also slightly warmer than last year’s 58.3F result.

About 2.8 inches of rain fell, which is about 0.26 inches drier than normal and almost an inch wetter than last year.  The result is the 5th driest of the 2000s and 66th driest of the long-term history.  You can see the 2000s rankings in the table below.

aprilrankingsThere are many years in the 2000s where the average temperature fell in the 58F degree range.  But the month was quite volatile with periods of both much above and much below normal temperatures.

The slightly warmer-than-normal average temperature reflects the fact that 57 percent of the days were warmer-than-normal (red!) while 43% were cooler-than-normal (blue!).

Our warmest anomaly day was way back on April 10 when we hit 91 degrees, an impressive 22 degrees warmer than normal.  Our coolest day was on April 4 with  a high of only 50F, 12 degrees cooler than normal.

Speaking of high temperatures, here is the variety of high temperatures and their percentage of occurrence in this volatile April:

aprilhighsWe spent most of our time in the 60s and 70s, but had a healthy 20% of the month stuck in the cool 50s too.

April 2013 Records

April 3: Record low 27 F tying 1985 and 1965  (Baltimore-Washington, BWI)

April 4: Record low 22F tying 1965 (Washington Dulles, IAD)

April 10: Record high 91F beating 1922′s 89F (Washington National, DCA and BWI)

April 10: Record high 89F beating 1992′s 78F (IAD)

April 10: Record high minimum 58F beating 1969′s 56F (IAD)

April 20: Record daily rainfall of 1.2 inches beating 1998′s 0.75 inches (IAD)

Pattern Drivers

Both warm and cool patterns influenced our area during the month, but the primary pattern type was one with a cold upper level trough stuck over Canada and warm ridging toward the coasts.  This allowed the East Coast to see occasional warm spells and then also be influenced cool to cold pushes from the mid-continent. You can see the pattern setup on the map below.   That warm ridging also prevented us from getting as wet as we could have throughout the overall month. The cold in the middle of the U.S. helped to support record high snow levels in place in many spots. This is very different from the prevailing pattern last month when record levels of high latitude blocking sent significant cold air into most of the U.S., not just the central portions.

aprilpatternComparing to 2012

With April behind us, how is 2013 comparing to last year and the 2000s in general? Well, we’re easily cooler and wetter compared to last year.  We’re in the middle of the pack as far as the 2000s are concerned as warm and cool periods have averaged out for the most part.  Here are the temperature and precipitation rankings for the 2000s to put 2013 in perspective:

yeartodatetempyeartodateprecipWe’re about five degrees cooler and over two inches wetter than last year, which is probably better news since last year was quite extreme on both fronts!

Look Ahead

What is on deck for us in May? The National Weather Service is not offering us much of any significant guidance by favoring equal chances of wetter/drier/normal precipitation and warm/cool/normal temperatures as can be seen here.  The National Weather Service runs a long-lead model called the CFS and it is showing a cooler-than-normal month (here) and a drier-than-normal month (here).

My thinking is that we are poised to see a May that is fairly close to seasonal averages like April, but we could lean slightly cooler on temperature (maybe a degree below normal) and near normal on precipitation (anywhere from a half an inch drier to wetter)- being cooler and wetter vs. last year which has been the 2013 trend.

For Further Information:

The National Weather Service publishes nice monthly assessments usually within a week of the close of each month (should be available shortly):

You can click on your closest airport location here:

Reagan National (DCA)

Dulles Airport (IAD)

Baltimore-Washington (BWI)

Also on Capital Weather Gang

D.C. area forecast: Out with the drizzle, in with the sun