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Severe T-Storm Threat This Afternoon and Evening

Josh Larson @ 2:25 PM

An approaching front combined with moderate instability in the atmosphere has prompted a severe thunderstorm watch for the area, with the potential for strong winds and heavy rain, through 10pm this evening. The overall chance of precipitation is fairly high (in the 70% range) with the chance of severe weather at about 30-40%. After tonight, relatively benign early-fall weather looks to resume for the next week to 10 days, with below normal temperatures and a chance of rain on Sunday. Somewhat milder and drier conditions are expected most of next week. The forecast details follow ...


Forecast Confidence: Medium-HighChangeable ... PM T-storms. Look for mostly sunny skies for the first half of the day, but clouds will quickly stream in from the west ahead of an approaching cold front by the mid-afternoon. Highs will be in the mid to upper 70s in most places. By early evening, expect mostly cloudy skies with scattered showers developing (and perhaps a gusty thunderstorm). Showers may linger through the overnight hours, with lows in the upper 50s. Some spots may see a over a half-inch of rain by dawn Friday.


Forecast Confidence: Medium-HighClearing and cooler. Though clouds, and even a stray shower, may persist through the morning hours, expect clearing skies and breezy conditions by the afternoon hours. In the wake of the cold front, high temperatures will struggle to make it out of the mid 60s in most spots. Expect mostly clear and crisp conditions Friday night, with lows from the low 40s across the coolest suburbs to near 50 downtown.

The Weekend

Forecast Confidence: Medium-HighNot bad overall. The weekend will feature one very nice day (Saturday), and one not-so-nice day (Sunday). If you have outdoor activities, you're probably better off scheduling them for the first half of the weekend.

Saturday will be a gorgeous day with full sunshine and fall-like highs near 70 and lows in the upper 40s to mid 50s. Unfortunately, a cold front arriving on Sunday is likely to bring more clouds than sun, with at least a 40% chance of showers, especially over the northern suburbs. Highs will again be near 70, with overnight lows in the 50s.


Pattern Overview
If we take a look at two particular modes of climate variability, the North Atlantic Oscillation (NAO) and the Pacific North-American Oscillation (PNA), we see signals from both that suggest the current pattern of a trough over the eastern US and ridge over the western US, is beginning to break down.

As the NAO starts to become positive, and the PNA becomes less positive, we'll likely see a pattern switch to a trough favored over the western US and a ridge over the eastern US by next week. As such, while cooler than normal conditions are likely to linger through the weekend for our area, appreciably milder and drier conditions are likely to develop next week.

Pictured above: the GFS forecast model suggests that the current pattern of a eastern trough/western ridge will flip to a western trough/eastern ridge by next week, bringing milder temperatures to our area.

Next week's forecast
Forecast highs/lows: 75/57 (normal = 73/54)
Forecast precip: Below-normal

Forecast Confidence: Medium-HighRelatively cool conditions will linger on Monday, with mostly sunny skies and high in the low 70s with overnight lows in the mid 50s. However, as flow becomes more out of the west and southwest on Tuesday and Wednesday, we can expect temperatures to rebound to the upper 70s to lower 80s for mostly sunny afternoon highs with milder overnight lows in the upper 50s to low 60s under mostly clear skies. Thursday and Friday will likely feature fairly similar temperatures (in the mid to upper 70s for highs and the 50s for lows) but more in the way of cloud cover as a frontal system approaches. Scattered showers may develop by late Thursday into Friday.

Redskins vs. Jaguars
October 1, 2006 -- 4:15 p.m. -- FedEx Field
Kickoff2-Min. WarningWeatherChance of Precip.
70F66FPartly Cloudy30%
A passing cold front could trigger a shower or two, though much of the precipitation associated with the front may stay north of the District.

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