Tracking a Squall Line Expected to Push through the Washington Area Late This Afternoon

The Storm Prediction Center has placed the Washington Region under a slight risk for severe storms this afternoon.

A strong cold front will push through the Washington Area between 4 and 7PM ushering in the coldest air of the season.  The high-resolution forecast models have consistently depicted a developing squall line out ahead of the cold front.

The image below (courtesy WxBell) shows the squall line pushing through the Washington Area between 23z (5pm) and 00z (7pm).

In addition to torrential rain, the squall line will have the potential to produce cloud to ground lightning and wind gusts of 50 to 60 mph.

Feeling More Like January and First Widespread Hard Freeze

Wednesday will be the coldest day of the upcoming work week as high temperatures struggle to rise out of the middle 40s in Washington.

Wednesday night will feature clear skies and calm winds — perfect conditions for radiative cooling.  Temperatures on Wednesday night will tumble into the middle to upper 20s in the suburbs with downtown Washington dropping to near 30 degrees.

The Washington Region’s First Widespread Hard Freeze is Likely Next Week

After what has been a year with record rainfall, allergens such as mold spores are coming in very high across our region. To kill the mold spores we need a hard freeze and while our outer northern and western suburbs (Leesburg, Gainesville, Frederick, Germantown) have dropped close to the freezing mark, many of us have not had a hard freeze — characterized by four consecutive hours of temperatures below 32 degrees.  A hard freeze is capable of killing the the mold spores and officially putting and end to the growing season.

A cold front will slide through our region on Sunday afternoon, ushering in much cooler temperatures and at least two opportunities for a hard freeze on both Wednesday and/or Thursday morning.

The image below (courtesy WxBell) shows the forecast low temperatures on Wednesday morning with many locations likely dropping to at or below freezing especially north and west of Washington.

Highs on Wednesday will struggle to reach 50 degrees in Washington with most locations holding in the middle to upper 40s. As high pressure begins to build across the area during the overnight hours, clear skies and calm winds will set up

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Squall Line could deliver threat of damaging wind gusts this Evening

A cold front accompanied by a squall line will approach the Washington Region late this evening.  Damaging wind gusts are possible, especially just south and west of the Washington Region across north-central Virginia and the Shenandoah Valley.  A strong low-level jet stream and wind shear (winds changing direction and speed with altitude) would typically indicate the potential for severe thunderstorms (some containing a tornado threat) however the missing ingredient will be instability (CAPE) as the sun will have set well before the arrival of the cold front.  Regardless, the Storm Prediction Center has placed the DC Region under a marginal risk for severe thunderstorms with damaging wind gusts being the primary threat between 9 PM and 1 AM late this evening.

Timing the arrival of the squall line (a line of convection containing gusty winds and heavy rainfall):

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