Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
723 FXUS61 KLWX 091426 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1026 AM EDT Tue Jul 9 2024 .SYNOPSIS... Excessive heat and humidity along with daily thunderstorm chances look to continue through midweek as a stalled frontal boundary wavers to the north and west. By late Wednesday into Thursday morning, a cold front will approach from the Ohio River Valley. The front will try to cross the area Friday before washing out along the coast as broad high pressure builds for the upcoming weekend. && .NEAR TERM /THROUGH TONIGHT/... The current forecast remains on track with mid-morning temperatures already well into the 80s, accompanied by dew points in the low/mid 70s. Relative to yesterday, continued moistening is evident with the frontal boundary now arcing north to south along I-81. To the west of this boundary, dew points are lower with readings mainly in the 60s. A thinning mid/high level cloud deck continues to streak toward the east. However, its diffuse nature has generally not shown much signs of impeding ongoing morning heating. The atmosphere remains seasonably moist with very high freezing levels up to near 17,000 feet (per the 12Z KIAD sounding). Any downpours that do develop could be brief heavy rain producers. See below for additional details on the convective threats. Another hot and humid day ahead with diurnally driven isolated showers and thunderstorms expected this afternoon. Heat Advisories have been issued for a large chunk of the forecast area outside the mountains from noon to 8pm today. Heat indices will range between 100-104 degrees west of the Blue Ridge with heat index values as high as 105 to 108 degrees further east into the Baltimore/Washington DC metro areas. The humidity will be more notable today as we sit square within the warm sector. This is due largely in part to our stalled frontal boundary draped north of the PA/MD border and west of the Allegheny Front. WIth that said, this will be our only real trigger point for convection this afternoon outside of the terrain. Bufkit forecast indicate convective temperatures been reached around midday with fairly isolated coverage along and west of the Blue Ridge during the peak heating period this afternoon. Flow at the surface will be out of the south while flow aloft will be more westerly inhibiting the potential for widespread thunderstorms. Will maintain a low PoPs (20- 30 percent) through the early evening evening as the air mass slowly stabilizes. High temperatures today will range from 93 to 99 degrees east of the Alleghenies. Mountain temperatures will be quite hot as well with highs running 84 to 90 degrees. Highest heat index values will likely occur between 2-6pm with values around 100 in the mountains and 103-108 degrees east of the Blue Ridge. No relief is expected tonight with lows in the mid to upper 70s and low 80s. Skies will remain partly cloudy to mostly cloudy as a cold front encroaches from the Ohio River Valley. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... Heat Advisories have been issued once again for Wednesday with heat indices east of the bLue Ridge running anywhere between 105 to 108 degrees. Some model guidance has even the potential for Excessive Heat Warning criteria being met across areas south and east Washington DC Wednesday afternoon. This will be something that will need to be re-evaluated with upcoming model runs. The upper level ridge finally flattens allowing the upper level trough over central CONUS (which ultimately absorbs the remnants of Beryl) to move east into the Great Lakes and Ohio River Valley. Meanwhile, the stalled boundary over our region lifts further north as a warm front driving more moisture into the region. Flow aloft will switch back to the southwest allowing for the eventual progression of several shortwave disturbances and fronts to cross the region.As a result, expect a better shot for showers and thunderstorms with probabilities around 40 to 60 percent. Where these storms do occur would offer beneficial rains to drought- stricken areas as well as provide some relief from the heat. Highs temperatures Wednesday will range from the low to mid 90s east of the blue Ridge with 80s further west. Low temperatures stay fairly close to preceding nights. The exception would be the Alleghenies where clouds and showers should keep lows in the 60s. On Thursday, the remnant energy of Beryl is expected to be passing to our northwest with a broader trough behind it, moving into the Great Lakes and Ohio Valley. Meanwhile at the surface, a cold front associated with a surface low over the Northeast will be pressing into the area. With the high pressure over the Atlantic remaining strong, the front likely stalls across the area into Friday. PoPs are persistently elevated to 50-60% or higher from Thursday afternoon through Friday evening as a result. Additionally, while Thursday will be a bit cooler than Wednesday, dewpoints in the mid to upper 70s and highs in the low 90s still spells out heat indices near and above 100 degrees. && .LONG TERM /FRIDAY THROUGH MONDAY/... The threat for showers and thunderstorms exist Friday into Friday evening with a stalled front and increasing humidity with high pressure offshore of the East Coast. There could be enough cloud cover from these showers and storms that our high temperatures may be closer to average, if not a few degrees below average. The chance for showers and a few thunderstorms linger into Saturday and Saturday night with high temperatures reaching the 90 degree mark again with predominantly temperatures in the upper 80s. Brief high pressure moves into the region Sunday and persists into Monday. Although we can`t rule out a few showers and thunderstorms either day, should each day remain dry, then temperatures will reach the middle 90s each afternoon. Monday could result in heat indices values approaching the triple digits. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... Prevailing VFR conditions are expected through Wednesday midday. A stalled frontal boundary remains north and west of the terminals this morning and will continue to waver along the Mason-Dixon line into this afternoon before lifting further north tonight. The front will eventually come back as a cold front late Wednesday into THursday before finally clearing the area later this week. SHower and thunderstorm chances will increase each afternoon and evening as a result of these boundaries passing through. Coverage today will be fairly isolated with light southerly flow at the surface and westerly flow aloft. By Wednesday and Thursday thunderstorms coverage becomes a bit more scattered ti numerous amongst the terminals given increasing moisture as the remnants Beryl passes to the northwest of the region. Expect intermittent MVFR to IFR conditions in and around thunderstorms during this time. Southerly winds on Wednesday pick up ahead of a slow moving cold front to the west. Afternoon gusts may push up to around 15 to 20 knots before decreasing some overnight. The cold front crosses the region THursday before stalling out Friday. MVFR conditions possible Friday into Friday evening due to showers and a couple of thunderstorms. This activity should form along the stalled front. As for Saturday and Saturday night, a few showers or thunderstorms may still be around but coverage should be less than Friday. && .MARINE... Southerly winds speeds start to funnel this afternoon and Small Craft Advisory conditions are anticipated this afternoon. Timing based on the HREF shows the chances of 20kt winds substantially increasing after 5pm as the flow becomes funneled especially along the western shores. Isolated thunderstorms will be possible this afternoon due to the head and humidity but will need some boundary interactions to trigger. For Wednesday, southerly winds pick up with channeling effects likely requiring Small Craft Advisories from Wednesday afternoon through the night, particularly over the wider waters of the Chesapeake Bay. Gusts up to 20 to 25 knots are possible during this period of enhanced flow. Additionally, ahead of a cold front, showers and thunderstorms become more likely on Wednesday afternoon/evening. Thus, Special Marine Warnings may be needed for some of the more robust convective development. Southerly flow is expected both Thursday and Friday with a front likely stalled to the west of the waters. Winds could approach SCA criteria by Thursday afternoon. Winds likely diminish overnight, but could remain around the threshold in our far southern waters. No marine hazards expected Friday through Saturday night. Any heavy thunderstorms that form Friday afternoon and evening or Saturday afternoon could bring brief Special Marine Warnings. && .TIDES/COASTAL FLOODING... Tides should stay below action stage at all locations, except for sensitive ones like Annapolis and SW Waterfront. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Heat Advisory until 8 PM EDT this evening for DCZ001. Heat Advisory from noon to 8 PM EDT Wednesday for DCZ001. MD...Heat Advisory until 8 PM EDT this evening for MDZ003>006-008- 011-013-014-016>018-503>508. Heat Advisory from noon to 8 PM EDT Wednesday for MDZ003>006- 008-011-013-014-016>018-503>508. VA...Heat Advisory until 8 PM EDT this evening for VAZ026>031- 036>040-050-051-053>057-501-502-505-506-526-527. Heat Advisory from noon to 8 PM EDT Wednesday for VAZ026>031- 037>040-050-051-053>057-501-502-505-506-526-527. WV...Heat Advisory until 8 PM EDT this evening for WVZ051>053. Heat Advisory from noon to 8 PM EDT Wednesday for WVZ052-053. MARINE...Heat Advisory until 8 PM EDT this evening for ANZ530. Heat Advisory from noon to 8 PM EDT Wednesday for ANZ530. Small Craft Advisory from 4 PM this afternoon to 2 AM EDT Wednesday for ANZ531>533-537-539>542. Small Craft Advisory from 4 PM this afternoon to 6 AM EDT Wednesday for ANZ534-543. && $$ SYNOPSIS...BRO NEAR TERM...BRO SHORT TERM...BRO LONG TERM...ADM AVIATION...BRO/ADM MARINE...BRO/ADM TIDES/COASTAL FLOODING...LWX