9:40 p.m. update: Heavy storms continue to train through northern Montgomery and central Howard counties to around Baltimore, and have already produced 2-2.5 inches of rainfall. About to 2 inches of additional rain could fall in this area prompting flash flood warnings through midnight. Here’s the obligatory reminder to not drive across a flooded road: turn around, don’t drown. As these storms are slow movers and more storms are forming along the same path, conditions may not improve until after 11 p.m.
We are getting a slew of reports of lightning in the region, but what everyone is seeing is the frequent lightning from the Montgomery and Howard county storms. There are no other storms in the region, although we cannot rule out a few new storms popping up overnight.
8:50 p.m. update: The severe thunderstorm has been trimmed back and only remains in effect for southern suburbs, where it will expire at 9 p.m.
The only activity in the region is currently – ironically – in the northern suburbs: a strong-to-severe thunderstorms is tracking through northern Montgomery and central Howard counties. That storm, producing heavy downpours and gusty winds, will move off in the next hour as it tracks off towards Baltimore.
After that storm passes, we’ll still need to watch for the possibility of isolated storms (20-30 percent chance) that could develop with little notice for the next few hours.
4:40 p.m. update: So far, no real signs of storminess in the region. Showers have skirted by to the north, and a few storms have formed to the south, since the severe thunderstorm watch was issued. Most of the activity moving this direction from the west has decreased or disappeared. However, some additional storms to the west and northwest are worth watching.
Hi resolution short term models tend to indicate that we won’t see much thunderstorm activity the rest of the day, or we’ll see a weakening line approaching sometime after sunset. Given the trends of the day, it’s not hard to think that’s the most likely solution. But given the high instability in the area, we’ll continue to watch in the hours ahead.
1:15 p.m. Overview: The National Weather Service’s Storm Prediction Center (SPC) has issued a large severe thunderstorm watch for the region until 9 p.m. this evening. Abundant heat and humidity remains over the area today as a cold front approaches. This combination should lead to an increasing threat of storms as we get through the afternoon into evening. While we don’t anticipate widespread damage from storms, any one might be quite intense, with heavy rain, plentiful lightning, damaging winds and perhaps hail.
SPC technical discussion:
DISCUSSION…INITIALLY LOOSELY ORGANIZED BELT OF TSTMS FROM NRN WV ACROSS SRN OH…AS WELL AS SEPARATE AREA OF CONVECTION OVER CENTRAL INDIANA…MAY ORGANIZE AND INTENSIFY TO SVR LEVELS AS THEY MOVE ESEWD INTO DIABATICALLY DESTABILIZING AND FAVORABLY MOIST AIR MASS…NEAR SRN EDGE OF FAVORABLE MID-UPPER LEVEL FLOW. MULTICELLULAR BANDS AND CLUSTERS WILL OFFER DAMAGING GUSTS AND SPORADIC LARGE HAIL BEFORE WEAKENING EARLY THIS EVENING.