High pressure both at the surface and aloft caused hot conditions. A southerly flow caused high humidity, which led to high heat indices.
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The episode as NWS LWX wrote it up.
High pressure both at the surface and aloft caused hot conditions. A southerly flow caused high humidity, which led to high heat indices.
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 Jul 14, 9:31 AM EST, 1 hour 29 minutes earlier.
Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1031 AM EDT Fri Jul 14 2017 .SYNOPSIS... A stalled front will remain to the north of the region through today while a Bermuda High persists. The front will push south through the area as a cold front tonight. Weak high pressure will influence the weather over the weekend, before another cold front moves in from the north and stalls over the area next week. && .NEAR TERM /THROUGH TONIGHT/... Showers and thunderstorms continue this morning across Pennsylvania, in an air mass that has decent shear and somewhat uncapped instability. With eastward propagation, the forecast area has been largely unaffected, except for a few showers that have snuck south of the Mason-Dixon line. Additional showers/storms in West Virginia have weakened as they have trekked across the Appalachians, due mostly to meager but effective CINH. While clouds remain across northern Maryland, much of the remainder of the area receiving filtered insolation. Triggers remain as previously analyzed: a prefrontal trough over the Piedmont, and the actual cold front, which won't be approaching until late afternoon. Modified 12z LWX RAOB suggests near 1400 J/kg MLCAPE and 25-30 kt of mean layer shear...about what was expected from previous forecast. For that reason, and with support from recent runs of the RAP/HRRR, have not made many changes to that forecast. Parameters will be in place for the potential of severe storms. Weak mid level lapse rates will limit hail potential, with damaging wind gusts being the primary threat. Given the slow movement to the front and the moist atmosphere, some locally heavy rain will also be possible. Do not see a widespread flash flood threat in the cards as precipitable waters "only" 1.7 inches, but will have to keep an eye on localized issues. The best signal for storm coverage and thus QPF is currently in the Baltimore metro area. Envision showers/storms developing in the Potomac Highlands early afternoon, driven by instability and shear feeding off of differential heating boundaries. The storms would then be spreading south/east through the day. The target time for the most numerous coverage will be late afternoon/early evening, but interactions likely will be complicated due to outflows/numerous boundary collisions. Showers and storms may take until well into the night to exit southern MD. There are also some indications a second boundary could have a few showers and storms with it, although these should dissipate in the diurnal minimum as they reach the Potomac Highlands and northern MD. The cloud cover/storm initiation balance will also impact the temperature forecast. Latest LAMP supports going forecast in the upper 80s to mid 90s, a little cooler than yesterday. This keeps heat indices in the 95-103 range, but slight differences in temperatures or dew points could nudge values into advisory territory. Overnight temperatures will be slow to cool, with 70s still likely for most locations east of the Blue Ridge. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... It looks like the front will push far enough south on Saturday that the forecast area should be dry. While it will be cooler, temperatures will still remain near normal for this time of year, in the mid 80s to around 90. Low pressure developing along the front may nudge it back toward southern MD Saturday night, though have kept the forecast dry for now. Winds should back to the south again on Sunday as a shortwave trough aloft swings into the Great Lakes. It looks like the prior front and its deep moisture remain to the south, so potential for convection looks limited. If there is a chance, it would be over the mountains (closer to trough) and southern MD (should front try to pivot north due to the prior low pressure). Temperatures should rebound a few degrees over Saturday. && .LONG TERM /MONDAY THROUGH THURSDAY/... A new shortwave will approach from the northwest early next week, possibly cutting off into a closed low, before lifting back out later on the week. At the surface, this will result in the front stalled to our south over the weekend to dissipate as another front approaches from the northwest. This front will also end up stalling in the vicinity, though it is unclear if it will actually reach portions of the CWA, or simply stall just to our north, before lifting back north late in the week. The presence of the upper trough/possible closed low means that at least early in the week, the potential for showers and t-storms will be present, aided by the nearby surface front. Later in the weak, this threat will likely diminish as heights build and the front lifts back north. Similarly, temps are likely to be cooler early in the week before warming up later on. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... VFR flight conditions continue across the terminals through early afternoon. The main opportunity for thunderstorms will come later this afternoon and evening as a cold front drops into the area. Coverage/timing concerns still preclude a detailed TAF delineation at this time. Amendments will likely be needed. Gusty winds and heavy rain will be possible. Storm threat should diminish by mid evening. At this time, no significant aviation impacts are expected Saturday and Sunday with weak high pressure behind the cold front. Main concern as we head into next week is potential for showers and t-storms and resultant intermittent sub-VFR conditions, mainly Monday and Tuesday. This risk will diminish later in the week. && .MARINE... West to southwest flow expected today. Storm threat will increase again especially late this afternoon, and potentially extending well into the night in southern MD. SMWs are likely. NW behind the cold front for Saturday. At this time, gusts fall just short of SCA criteria, but will need to be monitored for potential issuance. Winds eventually become southerly again by late Sunday as the weak high pressure moves offshore. As a front stalls in the vicinity early next week, flow is likely to remain fairly weak, with relatively low risk of SCA conditions. Higher concern will be due to scattered thunderstorms and attendant gusty winds, which could require special marine warnings. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && SYNOPSIS...ADS NEAR TERM...HTS/ADS SHORT TERM...ADS LONG TERM...RCM AVIATION...HTS/ADS/RCM MARINE...HTS/ADS/RCM
Hazardous Weather Outlook National Weather Service Baltimore MD/Washington DC 521 AM EDT Fri Jul 14 2017 ANZ530>543-DCZ001-MDZ011-013-014-016>018-508-VAZ052>057-150930- 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- 521 AM EDT Fri Jul 14 2017 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 Isolated severe thunderstorms with damaging wind gusts are possible today into tonight. Scattered incidents of flooding are also possible. .DAYS TWO THROUGH SEVEN...Saturday through Thursday No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is possible Friday. MDZ003>006-501>507-VAZ025>031-036>040-050-051-501>508-WVZ050>053- 055-501>506-150930- 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- 521 AM EDT Fri Jul 14 2017 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 Isolated severe thunderstorms with damaging wind gusts are possible today into tonight. Scattered incidents of flooding are also possible. .DAYS TWO THROUGH SEVEN...Saturday through Thursday No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is possible Friday.
The national radar mosaic for the moment the first event began.
5 heat. Local standard time, as filed.
Heat indices around 105 degrees were reported at observations nearby.
Heat indices around 105 degrees were reported at observations nearby.
Heat indices around 105 degrees were reported at observations nearby.
Heat indices around 105 degrees were reported at observations nearby.
Heat indices around 105 degrees were reported at observations nearby.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Virginia in 2017Every state in 2017This day in weather historyWarnings in Virginia, July 2017
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: 717300, 717301, 717302, 717303, 717304.