A hot and humid air mass in place led to increasing amounts of instability across the region. This fostered the development of a few showers and thunderstorms, a couple of which became locally severe.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS LWX wrote it up.
A hot and humid air mass in place led to increasing amounts of instability across the region. This fostered the development of a few showers and thunderstorms, a couple of which became locally severe.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Baltimore/Washington wrote its last area forecast discussion before the first event at Aug 18, 8:38 AM EST, 4 hours 36 minutes earlier.
Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 938 AM EDT Sun Aug 18 2019 .SYNOPSIS... High pressure off the East Coast will continue to build through Monday, providing a southerly flow of hot, humid air across the region. A front will approach from the northwest during the middle of the week. High pressure will return from the northwest by week's end. && .NEAR TERM /THROUGH TONIGHT/... 9 AM temperatures are running 1-3 degrees warmer than the same time yesterday, ranging from the 60s at higher elevations to near 80 in the urban corridor and close to 85 along the bay. Lots of sunshine for most of the area, and I already updated the forecast earlier this morning to show that. The main exception are some morning showers and storms that formed just north of the area over Pennsylvania. Visible satellite shows a trailing line of cloud cover from that into NE Maryland. Although radar hasn't shown anything south of the Mason-Dixon line yet, an isolated shower can't be ruled out as heat builds (though the immediate window seems to be closing as of 9:30 AM). Convective temp off the KIAD 12z sounding was 91 degrees, and that should be reached in many areas around noon. As previous forecaster noted, the added heat today yields greater CAPE than yesterday so once cumulus clouds form they could (should?) grow vertically fairly quickly. However, there is less of a forcing mechanism today so my gut feeling is that convective initiation is more dependent on existing boundaries and terrain than yesterday. Of course we have terrain and, at a minimum, the boundary in NE MD and bay/river breeze boundaries. With that in mind, I raised PoPs about 5 percent from the previous forecast; and will be closely looking at the 12z hi-res guidance for potential further refinements late this morning. As for temperatures/heat index values: adding 1-3 to yesterday's highs gives highs 90-95 almost everywhere outside of the higher elevations. I tweaked areas west of the Blue Ridge down a degree or two from the previous forecast (but still following the +1 to +3 trend). It looks like we mix down slightly lower dewpoints during the heat of the day (like we did yesterday) and that should keep us from reaching heat advisory criteria on a widespread basis...though a few locations that don't mix down quite as low could get close/exceed. We should stabilize after sunset. Models are more robust with fog development tonight compared to this morning, but that's dependent on convection today. The NAM in particular also has some overnight convection in the northern third of the area. Although I tweaked overnight PoPs upward, I kept them below 20 percent. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... General consensus is for Monday to be the hottest day of the period, though Tuesday won't be far behind. The only thing likely to hold Tuesday back will be increased cloud/storm coverage in the afternoon, before it has a chance to get as hot or hotter than Monday. Given both days will be close, and Monday has a good chance of reaching heat advisory criteria, inserted this potential into the HWO. Will allow next shifts an additional look before issuing advisory. Highs will be in the 90s both days with heat indices more likely to hit 105 east of the Blue Ridge, and 100 west of the Blue Ridge, especially Monday. Nighttime lows will be mostly in the high 60s to low 70s. Storm coverage Monday looks pretty low, similar to today, given weak forcing aloft despite plenty of CAPE. Things start to change Tuesday as a stronger, deeper shortwave approaches, not to mention a cold front from the northwest. CAPE remains plentiful Tuesday and PW's near 2 inches. Thus, decided it was prudent to insert a mention for severe weather and flooding into the HWO for this day, given the higher potential compared to prior days. The SPC has also placed us in a marginal risk for severe weather Tuesday. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... A cold front will near the Ohio Valley on Wednesday as weak high pressure situates itself over the Mid Atlantic region. At the same time, an upper level trough will dig across the Great Lakes into Thursday. This will allow for the front to approach the area late Wednesday, lingering nearby Thursday, before the primary trough axis pivots east of the Great Lakes late Thursday and the front sinks to our south and east. This will result in unsettled weather Wednesday into Thursday, with showers and thunderstorms expected. There is some model discrepancy on where the best large scale lift will reside, either over our area or just to the north, so this will play a role in the coverage and strength of convection during this period. Additionally, the timing of the front, currently projected to arrive overnight Wednesday, would miss out maximizing daytime heating and potential instability for storm coverage. Despite ample cloud cover, will continue to advertise above normal temperatures and humidity until the front pushes through the area on Thursday. In the wake of the front, large Canadian high pressure appears poised to setup shop over the Great Lakes Thursday night through Friday, tracking overhead through Saturday. This will deliver dry conditions and falling temperature/humidity levels for the region. Near normal temperatures return Friday and Saturday with highs in the low to middle 80s and lows in the 60s. && .AVIATION /13Z SUNDAY THROUGH THURSDAY/... Generally VFR through the TAF period and beyond through Tuesday night. Main concerns are limited mist reducing vsby in the AM hours, and afternoon/evening t-storms with gusty winds and heavy rain. Both risks are limited today and Monday, but the t-storm risk increases markedly Tuesday, along with the fog risk Tuesday night. A cold front will be approaching the region late Wednesday, delivering unsettled conditions over the terminals into Thursday. Periods of sub VFR conditions will be possible in passing showers/thunderstorms. The front will push through the terminals later Thursday, delivering dry conditions and light northerly breezes in its wake. && .MARINE... Winds generally sub-SCA through Tuesday night; however, there are some increasing indications of southerly channeling late this afternoon/evening. It's hard to tell in the models whether the SCA-level gusts come from storms or from channeling. Not issuing a SCA at this time, but monitoring closely. Otherwise, main concern through Tuesday is gusty afternoon/evening t-storms which may require special marine warnings. Best odds will be Tuesday, with lesser chances today and Monday. Increasing southerly flow ahead of an approaching cold front may yield SCA conditions over the waters Wednesday and Wednesday night. The front will linger nearby on Thursday before sinking to the south Thursday night. Gusty showers and thunderstorms will also be possible over the waters late Wednesday and Thursday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && SYNOPSIS...RCM NEAR TERM...JE SHORT TERM...RCM LONG TERM...BKF AVIATION...RCM/BKF MARINE...JE/RCM/BKF
Hazardous Weather Outlook National Weather Service Baltimore MD/Washington DC 508 AM EDT Sun Aug 18 2019 ANZ530>543-DCZ001-MDZ011-013-014-016>018-508-VAZ052>057-190915- Chesapeake Bay north of Pooles Island MD- Chesapeake Bay from Pooles Island to Sandy Point MD- Chesapeake Bay from Sandy Point to North Beach MD- Chesapeake Bay from North Beach to Drum Point MD- Chesapeake Bay from Drum Point MD to Smith Point VA- Tidal Potomac from Key Bridge to Indian Head MD- Tidal Potomac from Indian Head to Cobb Island MD- Tidal Potomac from Cobb Island MD to Smith Point VA- Patapsco River including Baltimore Harbor- Chester River to Queenstown MD-Eastern Bay- Choptank River to Cambridge MD and the Little Choptank River- Patuxent River to Broomes Island MD- Tangier Sound and the inland waters surrounding Bloodsworth Island-District of Columbia-Southern Baltimore-Prince Georges- Anne Arundel-Charles-St. Marys-Calvert-Southeast Harford- Prince William/Manassas/Manassas Park-Fairfax- Arlington/Falls Church/Alexandria-Stafford-Spotsylvania- King George- 508 AM EDT Sun Aug 18 2019 This Hazardous Weather Outlook is for the Maryland portion of the Chesapeake Bay, Tidal Potomac River, and adjacent counties in central Maryland and northern Virginia as well as the District of Columbia. .DAY ONE...Today and Tonight An isolated gusty thunderstorm is possible over the waters today. .DAYS TWO THROUGH SEVEN...Monday through Saturday Heat indices may exceed 105 degrees on Monday and Tuesday. A heat advisory may be required. Thunderstorms may produce isolated damaging wind gusts and isolated instances of flooding on Tuesday. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. MDZ003>006-501>507-VAZ025>031-036>040-050-051-501>508-WVZ050>053- 055-501>506-190915- Washington-Frederick MD-Carroll-Northern Baltimore- Extreme Western Allegany-Central and Eastern Allegany- Northwest Montgomery-Central and Southeast Montgomery- Northwest Howard-Central and Southeast Howard-Northwest Harford- Augusta-Rockingham-Shenandoah-Frederick VA-Page-Warren-Clarke- Nelson-Albemarle-Greene-Madison-Rappahannock-Orange-Culpeper- Northern Fauquier-Southern Fauquier-Western Highland- Eastern Highland-Western Loudoun-Eastern Loudoun- Northern Virginia Blue Ridge-Central Virginia Blue Ridge- Hampshire-Morgan-Berkeley-Jefferson-Hardy-Western Grant- Eastern Grant-Western Mineral-Eastern Mineral-Western Pendleton- Eastern Pendleton- 508 AM EDT Sun Aug 18 2019 This Hazardous Weather Outlook is for eastern West Virginia, northern and central Virginia, and central and western Maryland with the exception of Garrett County. .DAY ONE...Today and Tonight No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Monday through Saturday Heat indices may exceed 105 degrees on Monday and Tuesday east of the Blue Ridge/Catoctins. They may also exceed 100 degrees on both days west of the Blue Ridge. A heat advisory may be required. Thunderstorms may produce isolated damaging wind gusts and isolated instances of flooding on Tuesday. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
The Sterling radar (KLWX), 81 km away, was scanning. The volume nearest the first event began at 18:11 UTC.
10 thunderstorm wind, 2 hail. Local standard time, as filed.
A tree was split in half with large branches down on Washington Boulevard near South Monroe Street.
Trees and wires were blown down near Ivy Terrace and Athol Avenue.
A tree was blown down on Arnoldtown Road near Mountain Church Road.
A tree was blown down on South Maple Avenue near Brunswick Campground.
Trees were blown down across Park Mills Road near the intersection with Dickerson Road. A tree was also blown down on Tuscarora Road near Pleasant View Road.
Two utility poles and wires were blown down in the 21000 block of Beallesville Road near Big Woods Road. Multiple trees were also blown down at a residence of Mouth of Monocacy Road.
A large tree was blown down at a residence in the 3900 block of Ridge Road.
Poles and wires were blown down near Fingerboard Road and Green Valley Road.
Multiple trees were uprooted and snapped, and damage occurred to vinyl siding on a few homes on Penn Shop Road between Ridge Road and Fingerboard Road.
A tree branch was blown down on wires at Pocock Road and Jarrettsville Pike.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Maryland in 2019Every state in 2019This day in weather historyWarnings in Maryland, August 2019
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 850115, 850116, 850113, 850114, 850117, 850118, 850119, 850120, 850121, 850125, 850122, 850124.