Latest Rainfall Forecast & Timing of the Severe Storms

Latest North American Model Future-Cast Radar

Thunderstorms are possible overnight between 12am and 4am with a lull likely thereafter.

The worst of the weather arrives between 2PM Wednesday and 2AM Thursday when strong to severe thunderstorms are expected with torrential rain causing flash flooding. The risk of tornadoes is elevated tomorrow afternoon and evening as a warm front lifts through the area and wind shear from Ida’s remnants pass overhead.

The afternoon rush hour tomorrow is looking like a complete shit show, I wouldn’t be surprised to see school systems offer early releases.

The worst combination for DC Area drivers is to become trapped in flash flooding on clogged roadways with potential tornadoes. That could be a reality tomorrow if the Federal Government doesn’t offer a staggered early release. Plan accordingly!

Regional Rainfall Totals

Forecast models have been very consistent with 2-4” in The DC Metro, 1-3” south and east and 3-6” + north and west of the Capital Beltway.

River flooding is likely to continue through Saturday as it will take some time for the trillions of gallons of water to make its way down all of the streams creeks and tributaries that feed into the Rappahannock, Potomac, Shenandoah, and Susquehanna Rivers.

Breaking: Significant Tornado Parameters are High across Portions of DC Area on Wednesday Afternoon

Significant Tornado Parameter (STP)

A majority of significant tornadoes (F2 or greater damage) have been associated with STP values greater than one.

The latest data suggests the greatest area of concern on Wednesday afternoon and evening will be across the following areas:

Northern Virginia, east of the Blue Ridge

Washington, DC

Baltimore, central and southern Maryland

Have a plan of action of what to do in a tornado, especially for those of us without basements.

Excellent information here:

Tornadoes Possible Wednesday Afternoon across DC Region

Threat for Tornadoes Increasing Wednesday Afternoon & Evening

Wind shear is defined as winds in the atmosphere that change direction and speed with height. Shear values are forecast to increase across the DC Region Wednesday afternoon & evening as the remnants of Fred move through West Virginia.  The image below shows shear values increasing above 40 knots across the Metro Area on Wednesday afternoon increasing the odds of some super cells developing that will be capable of producing large destructive hail, damaging winds and tornadoes.

Tropical Systems and Wind Shear

Land falling tropical systems begin to weaken as their circulation in the lower-levels of the atmosphere begin to interact with ground friction.  However, the mid and upper level winds remain stronger allowing for increasing wind shear along/east of the system’s main center of circulation, increasing the threat for rotating updrafts and tornadoes.

Energy Helicity Index (EHI) Values Impressive on Wednesday

0-1 km AGL EHI values greater than 1-2 have been associated with significant tornadoes in super cells.  The blue and especially yellow colors in image below suggest that the threat of some storms becoming tornadic will remain elevated Wednesday afternoon continuing through the late evening.

Timing Wednesday’s Thunderstorms

A broken line of thunderstorms (some potentially becoming rotating super cells) will move through during the peak heating of the afternoon, likely approaching the western suburbs after 3pm and clearing the eastern shore after midnight. (time stamp in upper left corner of image below).

Have a plan on Wednesday, know what to do during a tornado and have a weather radio or local media outlet available in case tornado warnings are issued for your area.