Area Forecast Discussion

WHAT HAS CHANGED

There were no changes to the forecast for today, with things still on track at this time.

KEY MESSAGES

- 1) Hot and humid conditions persist through Friday with a daily threat for strong to severe thunderstorms.

- 2) Shower and thunderstorm chances return late Sunday into next week as a cold front moves through the region.

DISCUSSION

KEY MESSAGE 1...Hot and humid conditions persist through Friday with a daily threat for strong to severe thunderstorms.

Shortwave ridging will pivot overhead later this morning into the first part of the afternoon in the wake of an early morning MCS over PA. This should allow for a fair amount of sunshine and heating of a humid low-level airmass. After a start in the mid 60s to lower 70s, temperatures are expected to quickly rise this morning, approaching the upper 80s to lower 90s by midday. Highs this afternoon likely top out in the lower to middle 90s for the lower elevations. A lingering surface trough near I-95 may keep more of a westerly component to the wind for areas to the west, with slightly less humid conditions likely resulting in heat index values just shy of criteria (which is 100 west of Blue Ridge, 105 east of Blue Ridge). Near and east of I-95, slightly more humid air to the east of the trough and closer to the Chesapeake Bay is expected to result in heat index values near 105, peaking mid afternoon. It will be hot regardless, so make sure to stay hydrated and avoid strenuous activity during the heat of the day.

With the heat and humidity comes some rather strong instability. The subsidence may keep things from firing given weak/negligible forcing into the afternoon hours. But another subtle shortwave approaching from the west, combined with daytime heating, terrain circulations, the lingering surface/lee trough, and bay/river breezes, will probably touch off at least widely scattered thunderstorms by late afternoon. Timing is a bit uncertain, but it seems to be at least a few hours later than storms that formed Wednesday afternoon. Given the strong instability and low-level lapse rates as well as mid-level dry air, any storms that do develop will have the potential to produce very gusty winds. Thinking that convection approaching from the west may tend to struggle crossing the mountains with a relative minimum in storm chances east of the Appalachians and west of the Blue Ridge. As weak height falls encroach upon the more theta-e ridge boundary layer near I-95, storms may become more vigorous, possibly congealing into small clusters with a damaging wind and sporadic large hail threat.

On the mesoscale, will have to monitor the evolution of an MCV associated with severe early morning storms over IL/IN as it moves east toward the region late this afternoon, and how that interacts with the above mentioned lifting mechanisms (not to mention any residual outflow from the early morning PA MCS). It is plausible that these features enhance convective development by resulting in slightly higher forcing and perhaps some subtly enhanced mid-level flow. This would result in more widespread storms and an uptick in damaging wind potential locally.

Thunderstorm activity should wind down late this evening, though with the residual warm and humid airmass in place a pop up shower or even a bit of thunder can't be ruled out overnight.

Heat and humidity lingers Friday, and unless there is a lot of morning cloud cover it looks to be a bit hotter. There is the potential for a bit more mixing down of lower dew points given lingering westerly flow, but heat index values likely approach 100 to 105 again in the afternoon.

Stronger forcing associated with an upper trough glancing by to the northwest and an approaching cold front lends to higher certainty of more numerous thunderstorms Friday afternoon and evening. Flow aloft will tick up slightly, though still modest. But with abundant instability in place once again thunderstorms may produce some rather gusty winds. Severe/damaging wind gusts are plausible, especially with the added forcing that should help force storms into bands. Isolated large hail is possible with the most intense updrafts.

Following the Friday night cold frontal passage, high pressure will briefly pivot over the Mid-Atlantic for Saturday. This results in notably lower humidity and temperatures several degrees cooler (relatively speaking) as well.

More sun than clouds amid light northwest breezes are expected. Temperatures falling into the 60s Saturday night with dew points around 60 will feel like a stark contrast to the more oppressive humidity in the preceding couple of days/nights.

KEY MESSAGE 2...Shower and thunderstorm chances return late Sunday into next week as a cold front moves through the region.

A deep upper-level trough will form over the Great Lakes towards the end of the weekend, resulting in a cold front that will track through the East Coast between late Sunday and going into Monday. There are a couple of ML models that show a severe risk for this front, bringing back severe chances after a brief pause on Saturday.

Once this cold front moves through, we could begin to see a brief dip in temperatures, with highs for Monday currently ranging largely in the 80s. Although the low pressure system associated with this front will push north by late Monday, another area of low pressure could build towards the south and push north on Tuesday, bringing additional chances for rain and showers. By this point, severe chances become much more uncertain as instability looks modest, but shear will increase. Overall, expect a repeating pattern of frontal boundaries tracking through the region bringing several opportunities for precipitation.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Prevailing VFR conditions are expected through Friday. Thunderstorm coverage is uncertain this afternoon and evening, but any storm could contain very gusty winds or even some hail. Storms look to fire later today relative to yesterday. The 06Z TAFs have a broad 6-hour window of highest potential from late afternoon through mid evening. There is a higher chance of strong to severe thunderstorms Friday afternoon and evening as a cold front approaches. Winds will be fairly light out of the west or southwest both days. Will continue to hone in on the window of greatest TS risk in AMDs and future forecast cycles.

VFR conditions are predominantly expected through the weekend, with some reduced conditions possible beginning Sunday evening associated with potential showers and thunderstorms. Periodically reduced conditions associated with a low pressure system could continue through early next week. Gusts between 15-20 knots are possible Sunday afternoon/evening before falling again Monday, with southwest winds shifting easterly by Monday evening.

MARINE

Generally light west to southwest winds are expected through Friday, becoming northwest Friday night through Saturday. There is a potential of at least brief near SCA conditions behind a cold front Friday night into Saturday morning. Ahead of this front, potential showers and thunderstorms bring a risk of lightning and strong winds to the waters each afternoon/evening.

SCAs will likely be needed Sunday evening with gusts up to 20 knots possible, but should go back below SCA thresholds by Monday morning. Southwest winds shift northerly Monday afternoon before shifting southeast.

CLIMATE

Temperatures are expected to soar to as much as 15 to 20 degrees above average through Friday. This approaches or exceeds daily record values at some sites.

Below is a list of record daily high and warm low temperatures for June 11th and 12th (Thursday and Friday).

================================================================= June 11th Record Daily Highs and Warm Lows ================================================================= Site Record High Record Warm Low DCA 101 F (set in 1911) 74 F (set in 2020 +6 others) IAD 95 F (set in 2016) 72 F (set in 2005) BWI 99 F (set in 1911) 75 F (set in 1914) DMH 100 F (set in 1984) 79 F (set in 1984) NAK 96 F (set in 2000) 79 F (set in 1973) HGR 97 F (set in 1911) 73 F (set in 2005) MRB 101 F (set in 1911) 71 F (set in 1927 and 1922) CHO 99 F (set in 1911) 76 F (set in 2020)

================================================================= June 12th Record Daily Highs and Warm Lows ================================================================= Site Record High Record Warm Low DCA 95 F (set in 2017 +6 others) 77 F (set in 2015) IAD 96 F (set in 1986) 72 F (set in 1986) BWI 96 F (set in 1986 and 1914) 77 F (set in 1947) DMH 96 F (set in 2025 +2 others) 77 F (set in 2017 and 2015) NAK 98 F (set in 1914) 77 F (set in 2000 and 1973) HGR 92 F (set in 2017 +5 others) 71 F (set in 2010 +5 others) MRB 97 F (set in 1938 and 1933) 73 F (set in 1914) CHO 98 F (set in 1914) 72 F (set in 1947 +2 others)

LWX WATCHES / WARNINGS / ADVISORIES

DC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for DCZ001. MD...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for MDZ008-011-013-014-016>018-508. VA...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for VAZ054-057. WV...None. MARINE...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for ANZ530.