Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
077 FXUS61 KLWX 230132 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 932 PM EDT Sat Jun 22 2024 .SYNOPSIS... Broad high pressure offshore will continue to drive excessive heat and humidity into the region through Sunday. A stationary front over the Great Lakes and Upper Midwest will drop south into the area late Sunday and Monday bringing increased chances for thunderstorms. High pressure briefly returns Tuesday before another cold front crosses the area Wednesday and Thursday next week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Very warm and muggy tonight with lows struggling to drop below 80 along and east of I-95 due to increasing high clouds and scattered mid clouds. Some record warm minimums are expected, particularly at IAD and DCA. Some scattered convection has developed in the vicinity of Winchester, but hopefully, these storms will wane by midnight with increasing convective inhibition. Adjusted minimums upward tonight by several degs and tomorrows`s highs just a touch, keeping them just shy of the century mark. Also, increased PoPs for Sunday-Sunday evening given better signal for convection in model guidance, although the best chance may not be until evening, but multiple rounds are not out of the question. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... One last hot day is on top for the Mid-Atlantic region on Sunday. Despite a gradual lowering of heights as the ridge buckles, net warming in the lower troposphere will make for another toasty one. Forecast highs rise into the mid/upper 90s again, accompanied by dew points which will hold steady in the upper 60s to low 70s. Profiles appear moister on Sunday which suggests it may be more difficult to scour out the moisture by convective mixing processes. Consequently, Heat Advisories will again go into effect, but this time for the Blue Ridge eastward from 11 AM until 7 PM. Heat indices start pushing into the 104 to 107 degree range. The biggest question mark will be whether any sizable increase in mid/high clouds can offset surface heating effects. Additionally, the guidance does show some light shower activity firing up near the lee trough. This could further hinder temperatures from hitting the century mark. Unlike today/Saturday, lift in the column should be more robust as the area is grazed by a shortwave trough over New England. The glancing blow of height falls combined with better moisture transport should allow for greater shower and thunderstorm coverage on Sunday afternoon through portions of the overnight hours. Multiple rounds of such convection is possible, some of which could become strong to severe in nature. The Storm Prediction Center has upgraded areas north of U.S. 50 into a Slight risk for severe weather on Sunday. Elsewhere, a Marginal risk persists. There is also a non-zero risk for flash flooding for locations that see multiple rounds of activity. The flash drought which has ensued from the lengthy heat wave will help mitigate some of the flood risk though. A cold front sweeps through the area late Sunday night into Monday morning. This slowly brings an end to the shower and thunderstorm activity. The new work week will yield slightly cooler temperatures and less humidity. Mid 80s to low 90s are expected during the afternoon, while 70s are more commonplace over mountain locales. Any shower activity largely ends up farther south to around the I-64 corridor. Northwesterly winds persist through the day with afternoon gusts up to 20 mph at times. Dry weather continues into the night with forecast lows falling back into the 60s, locally in the mid/upper 50s over the higher terrain. && .LONG TERM /TUESDAY THROUGH SATURDAY/... A one day reprieve in the humidity before the heat surges again midweek. More widespread thunderstorm chances and much needed rain expected across the area Wednesday into Thursday. Surface high pressure briefly builds back over the area Tuesday giving us a brief reprieve in humidity as drier air settles in. Dewpoints will fall back into the mid to upper 50s and low 60s with light west to northwest breezes. The drier air combined with a downslope component to the wind will allow high temperatures to surge back into the low to mid 90s especially east of the Allegheny Front. Overnight lows Tuesday night will fall back into the upper 60s and low 70s. Unfortunately, high pressure quickly pushes offshore Wednesday allowing for increased southwesterly return flow and our next shortwave trough/front to move in. This will allow temperatures to surge back into the mid to upper 90s with heat index values up and over the 100 degree mark east of the Blue Ridge Wednesday afternoon. Some uncertainty remains in regards to temperatures due to the progression of the next shortwave trough and incumbent cold front from the Ohio River Valley set to approach the region. 12z synoptic/ensemble guidance suggest fairly spotty convection Wednesday afternoon and evening with more widespread thunderstorm activity developing across the Ohio River Valley and advancing east toward the region Wednesday night. This is partially due in part to the modeling trying to resolve what looks to be a complex of thunderstorms diving south and east from the Ohio River Valley ahead of the cold front late Tuesday night into Wednesday morning. In the event this occurs the atmosphere may be turned over reducing the potential threat of widespread severe weather or pushing it later into Wednesday and perhaps Thursday. Current CSU learning machine probabilities and the SPC discussion in the Day 5 timeframe also illustrate this potential threat/uncertainty for severe weather during the midweek timeframe. Additional shower and thunderstorm chances are possible especially east of the Blue Ridge Thursday as the front and upper level trough slowly push south and east of the area. With that said, extra cloud cover and a front overhead will lead to cooler temperatures in the mid to upper 80s. Broad high high pressure will return from the north Friday delivering mostly sunny skies, seasonable temperatures, lower humidity, and light onshore flow. The high slides off the New England coast Saturday allowing south to southwesterly flow to return along with the terrain based showers and thunderstorms. Temperatures on both days will sit in the mid to upper 80s and low 90s with upper 70s to low 80s expected in the mountains. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... VFR conditions can be expected through Sunday morning with mainly southerly winds. By Sunday afternoon into the evening, there is an increasing threat for showers and thunderstorms as a cold front approaches from the Ohio Valley. Winds shift to southwesterly on Sunday with gusts up to 20 knots from the late morning until around dark. The threat for storms will also lead to some restrictions at times. Showers remain in the picture through Sunday night as winds gradually shift to westerly. Prevailing VFR conditions are expected Monday outside of a few thunderstorms along and east of the corridor terminals Monday morning into early Monday afternoon. Convection will mainly be tied to the cold frontal boundary as it sweeps through. Any convection that we do see will cause brief MVFR or lower restrictions. Outside of thunderstorm chances some morning river/valley fog and ground fog could create restrictions especially west of corridor Monday morning in the wake of the departing frontal boundary. High pressure returns to the area Monday evening into Tuesday bringing continued VFR conditions. Additional showers and thunderstorms are likely Wednesday into Thursday as another cold front passes through the area. && .MARINE... Southerly channeling effects persist through tonight and into Sunday morning. Expect a gradual shift to southwesterly flow during the day on Sunday. Winds stay up through the day which warranted additional Small Craft Advisories through early Sunday evening. There is also an increased risk for showers and thunderstorms, particularly from the late afternoon through the early overnight hours. Special Marine Warnings may be required for some of Sunday`s convective activity. The cold front responsible for all of this action pushes across the waters Monday morning. Small Craft Advisories may be needed for portions of the waters Monday into Monday night as a cold front passes through. A few thunderstorms may develop along the front Monday morning into Monday afternoon mainly over the middle and lower waters. Winds will switch to the west and northwest with gusts up to 20 kts. The primary threat with thunderstorms will be strong winds. Sub-SCA level west to northwest winds return Tuesday as high pressure builds back over the area. Winds turn back to the south to southwest Wednesday as high pressure pushes offshore. Some southerly channeling could occur over the lower waters Wednesday ahead of an approaching cold front from the Ohio River Valley. SCA level winds look to return to portions of the waters Wednesday night into Thursday as a cold front passes through. && .CLIMATE... Very hot temperatures are expected through Sunday, and again on Wednesday next week. Several records could be in jeopardy, as seen below. Below is a list of record high temperatures for Jun 23rd, and 26th, the year the record was set, and the current forecast high temperatures for those days. A plus sign after the date signifies the record was set multiple times, with the most recent year indicated below. RERs are only issued for DCA, IAD, BWI, and MRB, but other sites are shown for reference. Sunday Jun 23nd Climate Site Record High Forecast High Washington-National (DCA) 98F (1988) 98F Washington-Dulles (IAD) 96F (1988) 98F Baltimore (BWI) 97F (2010) 99F Martinsburg (MRB) 100F (1934) 95F Charlottesville (CHO) 100F (1894) 96F Annapolis (NAK) 98F (1988) 96F Hagerstown (HGR) 98F (1988) 95F Wednesday Jun 26th Climate Site Record High Forecast High Washington-National (DCA) 101F (1952) 98F Washington-Dulles (IAD) 95F (1998) 98F Baltimore (BWI) 99F (1954+) 97F Martinsburg (MRB) 102F (1943) 94F Charlottesville (CHO) 99F (1998) 98F Annapolis (NAK) 98F (1952) 93F Hagerstown (HGR) 98F (1954+) 96F && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Heat Advisory from 11 AM to 7 PM EDT Sunday for DCZ001. MD...Heat Advisory from 11 AM to 7 PM EDT Sunday for MDZ003>006-008- 011-013-014-016>018-503>508. VA...Heat Advisory from 11 AM to 7 PM EDT Sunday for VAZ037>040-050- 051-053>057-501-502-505-506-526-527. WV...None. MARINE...Small Craft Advisory from 6 AM to 6 PM EDT Sunday for ANZ530. Small Craft Advisory until 6 PM EDT Sunday for ANZ531>534- 537>543. Small Craft Advisory from 11 AM to 6 PM EDT Sunday for ANZ535- 536. && $$ SYNOPSIS...EST NEAR TERM...LFR SHORT TERM...BRO LONG TERM...EST AVIATION...LFR/EST MARINE...LFR/EST CLIMATE...LFR