The watch spans from central Virginia by central Pennsylvania, the place the storms are growing and sweeping southward. It doesn’t embody counties alongside the Chesapeake Bay the place storms are projected to be considerably much less quite a few and intense.
Do not forget that a extreme thunderstorm watch means circumstances are favorable for intense storms, however not a assure. Keep climate conscious. If a extreme thunderstorm warning is issued in your location, it means a extreme storm is imminent and that it’s best to search shelter.
An preliminary spherical of showers and storms has already handed by the realm and radar suggests one other wave growing in southern Pennsylvania — which can be extra intense — arriving in the course of the late afternoon.
We’ll publish a brand new replace in one other hour — round 3:10 pm
Authentic article from noon
The blissfully dry climate of the previous a number of days has departed; a really heat, humid sample is taking its place. However cooler air lurks to our northeast and northwest. We’re caught within the transition zone the place these contrasting air lots meet, a ripe setting for intense thunderstorms.
Storms are most possible between about 3 and 11 pm, and a few could also be extreme — containing damaging winds and hail along with heavy downpours and harmful lightning. Some areas may very well be hit by heavy storms repeatedly — rising the danger of flooding.
The Nationwide Climate Service has issued a flood look ahead to a lot of the area, apart from Southern Maryland and counties subsequent to the Chesapeake Bay, the place showers and storms will in all probability be much less quite a few.
Tea #Flood Look ahead to potential flash flooding this afternoon and night has been expanded eastward into the I-95 hall. Heavy #rain from thunderstorms could result in speedy rises of water in creeks, streams, and in poor drainage areas. pic.twitter.com/MtfzQDadcQ
—NWS Baltimore-Washington (@NWS_BaltWash) June 22, 2022
The heaviest rain and biggest flood menace will probably focus between Interstates 95 and 81. “Rainfall quantities of 1 to three inches are potential inside the span of a few hours, with regionally greater quantities potential,” the Climate Service cautions.
Rain totals will likely be extremely variable all through the realm, relying on the place the heaviest storm cells monitor — which may’t be predicted earlier than they begin to kind. Some areas may see lower than a tenth of an inch whereas some fashions present most totals over 5 inches, which is a severe quantity of rain. This quantity of rain would require heavy storms forming and reforming whereas monitoring over the identical space repeatedly — a phenomenon generally known as coaching. The best menace of coaching storm cells is west of Route 15, operating from Frederick to Warrenton.
The Climate Service has positioned the western half of our area in a Stage 2 out of 4 danger zone for extreme rain; our jap areas are beneath a Stage 1 danger.
The flooding menace could also be mitigated considerably by the very fact June has been dry thus far — but when 2 or extra inches falls briefly period of time, that would shortly trigger streams to overflow and for poor drainage areas to be overwhelmed.
“Extreme runoff could lead to flooding of rivers, creeks, streams, and different low-lying and flood-prone places,” the Climate Service writes.
Bear in mind to by no means try to drive throughout a flooded highway because the water stage is troublesome to evaluate. Flip round, do not down.
Along with the heavy rain menace, the Climate Service’s Storm Prediction Heart has positioned the realm in a Stage 2 out 5 danger for extreme storms that would produce “damaging winds and remoted massive hail.” An remoted twister additionally can’t be dominated out.
Probably the most possible timing for extreme storms could be within the late afternoon and early night earlier than the menace wanes towards darkish. Nevertheless, the danger of heavy rainfall may proceed till 10 or 11 pm in components of the realm.
An uncommon sample is coming collectively for the following 12 to 18 hours.
As proven within the forecast floor chart (legitimate 8 pm) beneath, now we have an approaching chilly entrance from the west. Over the Bay and I-95 hall, one other slow-moving frontal boundary is approaching from the east: an odd route, in truth, a course of that is referred to as retrograding. Alongside this boundary, a weak space of low strain is anticipated to develop.
So the area will likely be positioned in a zone during which the humid, unstable air mass in between the fronts is getting squeezed from each instructions. That is referred to as convergence of air, and the end result will likely be a big mass of air compelled to ascend.
Including to the efficiency is a really excessive humidity content material of the air. The morning climate balloon at Dulles revealed aggressive moistening of the deep ambiance is underway, to the purpose the place the “precipitable water” (whole liquid equal depth of water vapor) will likely be between 2 to 2.5 inches — a worth that’s fairly extreme for our area in late June—close to document ranges. These abnormally excessive values at 8 this night are proven by the ribbon of pink colours within the map beneath.
So now we have very excessive moisture content material, getting squeezed upward over the area between two fronts, in an environment unstable sufficient to generate thunderstorms. These elements will intensify late this afternoon and sure be sustained till about midnight.
The deep airflow aloft can be anomalous for this time of yr, from due north — so storm cells will develop in Pennsylvania and drift south into the Baltimore-Washington area.
We expect the retrograding entrance draped alongside I-95 will act as a conduit alongside which storm cells will repeatedly hearth and monitor from north to south. It is troublesome to say a priori the precise counties/locales impacted, however this “coaching” impact may result in spectacular rain totals for some, upward of two to three inches. One of many high-resolution forecast mannequin simulations of radar protection for by tonight is proven beneath — you possibly can pick the improved hall of storm cells alongside and west of I-95.
One other space of targeted, heavy rain could also be close to or simply west of the I-81 hall, the place enhanced lifting of humid air by the mountains and the approaching chilly entrance could wring out additional atmospheric moisture. Notice, nonetheless, the above radar simulation is just a tough information as to how storms could evolve; the precise timing and placement of storms may find yourself being fairly completely different.
Domestically extreme storm cells may additionally generate damaging wind gusts, intense lightning and, maybe, even a weak twister. We do not anticipate the extreme climate protection to be as widespread because the flood menace. However the wind shear (or improve in wind velocity and alter in route with altitude) is ample, together with native “spin” generated alongside the retrograding entrance, for the specter of an remoted twister.
Damaging straight-line winds are extra probably, within the type of downbursts, during which the heavy mass of descending water in cell downdrafts drags the air all the way down to the floor in a high-velocity impression.