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10-Day Outlook: Fall Arrives -- Stormy and Cooler

Josh Larson @ 10:00 AM

Today's Weather

Today will feature overcast skies with widely scattered showers and occasional drizzle; watch out for potentially slick roads (due to oil) as it has not rained in quite a while. With dense cloud cover, expect cooler temperatures than yesterday, reaching the upper 70s in most locations. Overcast and breezy tonight with scattered showers developing overnight. Lows will be in the low to mid 60s.

Pattern Overview: Drought-busting time

In one word: over-active. The next 7-10 days will present us with a VERY active weather pattern as the atmosphere firmly transitions into a fall pattern, though the tropics still continue to broil. For instance, while temperatures over the past 10 days have averaged near 80/60, temperatures over the next 10 days will be closer to 70/50 -- a quick drop-off. As I suggested last week, the tropics are ABLAZE with activity at the moment, and developing mean troughing over the East over the next week will add energy to the systems in the tropics (as well as guide them up the East Coast) and bring us a heavy rain event Friday into Saturday and the potential for one or two more tropical, heavy rain events next week. Fasten your seat belts!

The next 5 days (Oct 6-10)
Forecast high/low: 70/53 (normal = 71/53)
Forecast precip: *above* normal

Today's weather will be the calm before Friday's storminess. The remnants of tropical storm Tammy will interact with a very potent cold front and upper-level dynamics approaching from the west. The result will be the first heavy rain event in almost two months! Expect showers to develop overnight tonight and increase in coverage and intensity on Friday. Friday will be a COMPLETE WASHOUT with moderate rain punctuated by periods of pouring rain. Expect overcast highs near 72, with lows near 60. It now appears that showers, and overcast skies, will continue on Saturday -- so not a good day for outdoor activities. I expect most of the area will have seen at least 1-3" of rain by Saturday evening.

(At right, the Hydrometeorological Prediction Center (HPC) forecasts a drought-busting 3+ inches to fall Friday and Saturday.)

With overcast skies on Saturday, temperatures will struggle to get out of the mid 60s; expect overnight lows in the 50s. Sunday's forecast is a tough one, but I'll call for variably cloudy skies, breezy conditions, and temperatures near 68/48; more importantly, I believe we have a 50/50 shot of showers redeveloping by late in the day as another wave of low pressure (the remnants of our would-be Tropical Storm Vince in the Gulf of Mexico) may crawl up the Eastern Seaboard; thus, another moderate to heavy rain event (1-3") is possible Sunday into Monday. Expect a chance of lingering showers on Monday, with temperatures near 67/50.

The following 5 days (Oct 11-15)
Forecast high/low: 67/48 (normal = 69/51)
Forecast precip: above normal

A very low confidence forecast for the following five days due to the frenetic level of activity in the tropics -- specifically the Gulf of Mexico and southwestern Atlantic. However, I believe that we have a decent shot for at least one more heavy rain event, the result of a tropical feature, sometime next week. Models suggest that some semblance of troughing will remain over the eastern US, leading to near or below-normal temperatures during the period as well as providing a conveyor belt for any storms in the aforementioned regions to crawl up the East Coast.

For next Tuesday through Saturday I expect highs generally in the mid to upper 60s and overnight lows in the upper 40s to lower 50s. Highest chance for rain is during the Wednesday/Thursday period. Note, cloud cover is also a tricky forecast, and I have a feeling the balance of the week may be mostly cloudy; if this is the case, then daytime highs might bit a bit cooler, with overnight lows a bit milder. A rouge East Coast hurricane landfall is not out of the question during this period.

Pictured above, an infrared satellite image showing at least two tropical features that are likely to impact our area over the next week.

Verification of Last Week's Outlook

I am very pleased with the performance of last week's outlook as the majority of the larger and smaller details in my forecast unfolded as I predicted. For temperatures, my forecast highs were only off by only 1.3 degrees, which is a high A on's grading scale.

But, as importantly, I said last week that the upcoming week would feature, "the highest risk this entire season for tropical systems/hurricanes to target the East Coast; essentially, the pattern will be such that any system that develops in the southwest Atlantic is likely to head straight for either the Southeast or Mid-Atlantic coast." This idea worked out very nicely as Tropical Storm Tammy will target us with heavy rain tomorrow, and the remnants of (would-be) Tropical Storm Vince, currently in the Gulf of Mexico, may very well do the same by Sunday.

Pictured: View looking towards Alexandria from the Potomac River as clouds break during the early afternoon yesterday. By photographer Kevin Ambrose.

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