Wednesday, July 25, 2012

Washington Still on Track for 3rd Consecutive Top-3 Hottest July/Hottest All-Time Month

Image (click to enlarge): Hottest July average temperatures vs July 2012 to date (TD) and projected (PROJ) at Washington DC; CapitalClimate chart from National Weather Service data

Forecast Actual Projected
Date High Low High Low Average
27 97 77 95 77 83.8
28 94 73 97 74 83.9
29 91 72 90 72 83.9
30 89 69 89 75 83.9
31 88 71 90 74 84.0
July 31, PM Update: Once again, the temperature has outperformed expectations, with another high of 90°. This gives a final monthly average of 84.0°, the second hottest month in Washington climate history.

July 30, PM Update: The preliminary high/low temperatures are enough to keep the projection at 83.9°, even if the high tomorrow is only 84°. A high of 85° or higher would push it up to 84.0° as long as the low is at least 74°.

July 29, PM Update: The daily high underperformed the original forecast by 1°, but the current outlook for the next 2 days keeps the projected monthly average at 83.9°.

July 28, PM Update: Today's preliminary average temperature exceeds the forecast by 3.5° and raises the projected monthly average to 83.9°.

July 27, PM Update: Today's high of 95° underperformed the forecast by 2°, but the projection remains the same.

July 26 Update: Today's high/low temperatures of 100°/74° raise the month-to-date average to 84.1°, while the projected average is back to 83.8°.

In order for the final average to avoid being the second hottest month on record, the next 5 days would have to be at least 4.5° below the forecast (see table above).

5:30 PM Update: Since the chart was made, today's preliminary daily high has reached 89°, pushing the projected monthly average temperature up another tenth of a degree to 83.9°.

Original Post:
As noted last week, the first half of July put Washington firmly on track for a top-3 hottest July (and therefore top-3 hottest all-time month) for the third consecutive year. Despite a daily record low maximum temperature, the monthly average to date of 84° is still within half a degree of last year's record and well above the second place 2010 (tied with 1993).

With forecast temperatures near a possible monthly record 7th 100° reading tomorrow and upper 90s on Friday, even a return to more seasonable levels by the 31st puts the projected monthly average at 83.8°, halfway between July 2010 and 2011. At this point, temperatures for all of the next 6 days would have to average at least 4° below the forecast in order for this July to drop below second place on the all-time hottest list.

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