For Mother's Day Forecast, you see: Cloudy with much cooler temperatures Sunday
5:30 PM update
The heavy thunderstorm that was previously used for The counties of Loudoun and Frederick (Md.) was issued, was extended to the east and now includes Fairfax County, Prince George's County, Montgomery County and the District.
In the east, a tornado watch is available until 1am for Howard and Anne Arundel districts and sites to the north and east.
Strong In the southwest and south of central Pennsylvania, heavy thunderstorms break out and move east / southeast. In addition, during the evening, new storms can come closer to the immediate subway area.
In both the severe thunderstorm and tornado wake zones, storms are possible that can produce damaging winds and hail. Especially in the Tornadowatch Zone, the National Weather Service says: "A few heavy tornadoes are possible." This is a situation where storms are likely to be hit or missed … not everyone will see storms, but storms that form can be intense
Based on radar and short-term modeling, the main frame for observing storms is between 7 and 7 and 23 o'clock this evening. If you're out tonight, stay weather-aware and watch out for warnings.
If a severe thunderstorm warning is issued, seek shelter.
When a tornado warning is issued, go into an interior in the lowest level of a strong building, away from windows.
We will post our next update at 18:45, or if storms get closer to the region, whichever comes first.
3:10 am update
The National Weather Service has issued a heavy thunderstorm for Frederick and Loudoun counties and locations in the Northwest until 11am. Storms that form in this zone can generate winds up to 70 km / h and reach the size of golf balls.
Some storms are beginning in eastern Ohio and southwestern Pennsylvania. These storms should increase in the next few hours as they go from east to southeast.
The short-term modeling shows that we probably will not see too much storm activity in the Washington area until at least 6 pm. and whatever form of storm you may take until after dark. But stay tuned for additional updates as it's possible the heavy thunderstorm will be extended east this afternoon or early evening.
The temperatures are rising on this summery Saturday. The humidity is high and there is a cold front near our region. These are the usual ingredients for a recipe from severe to severe storms, and we are watching this risk for today and until this evening.
Heavy storms today are likely to be located closer to the border between Maryland and Pennsylvania, but arrears could affect the impact DC region, especially tonight. We can not rule out that a scattered storm appears on site. All in all, it seems that our best chance of rain and rumble in the immediate area comes in the hours after sunset.
- Approximate window when storms are most likely:
- 6 to 10 o'clock. Loudoun, Frederick, and Howard Counties
- 19-23 pm Montgomery County and the District
- 8pm to 12pm Fairfax and Prince George's Counties and the South East
- Storm Duration: 30 up to 60 minutes at each location
- Measurable rainfall per location:
- 60 percent in the north of Maryland.
- 50 percent in the immediate vicinity (within a county of DC).
- 40 percent in southern suburbs.
- Storm movement: Northwest to Southeast
- Probable storm effects: rain, lightning
- Possible storm effects: Storm winds, small to medium hail
- Very low chance of: Great hail, isolated tornado  19659025] Precipitation potential: On average 0.1 to 0.5 inches, but locally higher levels possible
The DC region will continue to experience a hot day when the humidity on the uncomfortable side of this afternoon rises slightly. These conditions will also create a lot of hovering air to the point that late-day thunderstorms can fire. It is expected that the storms will be limited to the frontal border slowly slipping out of Pennsylvania, as shown below. A weak low-pressure wave will develop along the front near Harrisburg and slide eastward overnight.
The high winds are also rising outside the west at the same time as this low surface takes shape. This will increase wind shear in our region during the rest of the day. The combination of buoyant air, wind shear and the approach of a frontal boundary creates the conditions for potentially heavy weather.
Accordingly, the National Oceanic and Atmospheric Administration's Storm Prediction Center has the outlook for the immediate DC region as a "low risk" of severe thunderstorms (level 2 on a 5-point threat scale, see below). For Washington and its immediate suburbs, there is a 15 percent harmful wind probability, along with 15 percent for hail and 2 percent for tornado. The risk of damaging the straight-line wind increases to 30 percent in the small extended Outlook zone.
In North Central Maryland (north of Montgomery County) and including Baltimore, the risk has been increased (Level 3).
One factor that can mitigate widespread heavy activity near Washington is a westerly wind in the low levels of the atmosphere, as revealed by the morning weather balloon launch at Dulles International Airport. This means that the airflow approaching Washington has reached the Appalachians, which tends to dry the air and suppress the lift needed to initiate storms. Predictive models also suggest that the atmosphere may stabilize somewhat by the afternoon (caused by descent from higher altitudes), which could inhibit convective cloud growth.
These predictive models show a series of showers and thunderstorms limited to early evening along the Mason-Dixon line (animation below). After 19-20, this band sags southeast as the cold front advances southward, and activity eventually begins to affect Loudoun, Frederick, Montgomery, and Howard districts. At about 10 o'clock or so the activity could reach Washington. The intensity of convection, however, seems to drop lower as we lose the destabilizing influence of the sun.