Impressive 30 Day Rainfall Totals with Over a Foot in Some Locations

As we close out July 2017, some locations in the Washington Metropolitan Area have picked up between 10 and 15″ of rain!

My hope is that the rain will increase our odds of spectacular fall foliage as we head into mid to late October.

This morning’s 5 AM temperatures across the DC Area are absolutely “New England-like” with mid 50s in our outer suburbs (image courtesy WUSA9) .

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Historic Flooding Likely Across Portions of the DC Region: Turn Around Don’t Drown!

Flash Flood Watch in effect through Sunday for good reason as PWATS increase above 2.5″ this afternoon into this evening.

  • Strong frontogenetic forcing (strong upward lift at the surface), along a warm front aided by strong divergence aloft (lift) with the approach of a potent upper-level low pressure system will all aid in repeated rounds of strong to possibly severe thunderstorms containing torrential rainfall rates of 2″ per hour at times.

 

  • I can’t stress enough how dangerous conditions will become later this afternoon through the overnight hours as rain gauges across parts of our area will have already picked upwards of 3-5″ of rain with an additional 1 to 3″ of rain possible in spots through Sunday afternoon as the steady rain associated with the back side of the exiting upper-level low pressure system only exacerbates swollen creeks and streams.

 

  • If you live in a flood prone area, you need to be prepared to move to higher ground this afternoon through Sunday.

Latest Rainfall Estimate from the High Resolution Rapid Refresh Model through midnight tonight (doesn’t include the rain that will continue falling overnight through Saturday:

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Isolated Tornadoes Possible Friday

Wind shear (winds that change direction with height) values will be increasing on Friday afternoon and evening.  While strong thunderstorms with torrential rain and gusty winds will be the primary threats, enough low-level spin in the atmosphere will be present for some rotating super cells.  According to the latest NAM model, the area with the highest risk may be from Fredericksburg Virginia across the Potomac into southern Maryland. With that said, everyone should pay close attention to the weather tomorrow as much of the region is under a slight risk for Severe Thunderstorms.

The image below, courtesy pivotal weather shows wind shear values increasing throughout the day on Friday

The 18Z NAM model shows that while much of the region could pick up between one and three inches of rain, locations picking up “training thunderstorms”, that is multiple storms that develop over the same areas could easily pick upwards of 5 or more inches of rainfall.

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