Update on Saturday’s Squall Line

Want to cool off from the February heat wave? Head to the western shore of the Chesapeake Bay (Annapolis).

Image below (courtesy WxBell) shows today’s high temperatures (according to the latest high-resolution-rapid-refresh HRRR model):

  • Mid to upper 70s likely at Dulles while Annapolis holds near 60 when the Chesapeake Bay breeze kicks in! Pretty cool to visually see the local effects of the colder Chesapeake Bay waters and how convection currents work (rising warm air over land, with cooler air over water replacing it). 

hrrr_t2m_washdc_12

Moving on to Saturday’s Storm potential:

Latest NAM model shows marginal CAPE (Convective Available Potential Energy).  Simply put, think of a boulder sitting at the edge of a cliff ready to fall (potential energy is available as the boulder could fall).  In the atmosphere we measure available energy for thunderstorms utilizing CAPE values.  At times the energy can be available without storms actually firing.  The cold front will provide the “spark” to release the available energy as colder air begins moving in from the west initializing convection. The main threat continues to be gusty winds with some isolated storms potentially containing pea sized hail.

Latest NAM model below shows CAPE values running near/below 1000 j/kg along portions of the 95 corridor on Saturday afternoon (image below is the forecast for 1PM):

hires_cape_ne_37

Next ingredient we look at is Wind Shear (helicity): Wind shear is simply wind direction that changes with height. So at the surface tomorrow, winds should be blowing out of the south but just above the surface, winds will be blowing in from the southwest (mid-levels) and then from the west/northwest (upper levels).  

  • Notice the purple colors moving along the squall line that should be moving out of the Blue Ridge around 1PM. The two images below are showing Helicity (wind shear) with Northeastern Maryland being the favored location of highest values as this line crosses the Region during peak daytime heating.

hires_helicity3_washdc_37_1pm hires_helicity3_washdc_40_4pm

Temperatures along and east of interstate 95 will climb into the upper 60s to lower 70s if skies do not become overcast out ahead of the front. Image below show’s temperatures at 1PM on Saturday before the front races through the DC Region:

hires_t2m_washdc_37

Finally here is the latest high-resolution future cast simulated radar for Saturday:

ade72a5c-e5d5-4ef1-ac72-cf3aa305ea2b

Taking everything above into account, here is my current thinking on timing and highest risk for a pop-up severe thunderstorm (remember to get a severe thunderstorm warning all you need are wind gusts reaching 58 mph). 

  • Warrenton – Leesburg – Frederick (squall line should arrive between 11AM and 2PM)

 

  • Fredericksburg – DC – Baltimore (squall line should arrive between 2 and 4PM)

 

  • Northern Neck of Virginia – lower southern Maryland – Annapolis (squall line should arrive between 4PM and 6PM)

metro_dc_t-storm_timing_threat_dcstorms-com

 

One Reply to “Update on Saturday’s Squall Line”

  1. Looks like pattern flips back to quite cold in early March. This is a typical false spring, with a heatwave in late February, but when real spring comes, the warm air is often missing in action.

    I am wondering how the rather extreme change will affect the cherry blossoms. Hope they don’t get nipped in the bud.

    Like

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