Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
450 FXUS61 KLWX 151407 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1007 AM EDT Mon Jul 15 2024 .SYNOPSIS... A surface trough will linger east of I-95 through midweek while high pressure remains offshore. The surface trough will be overtaken by a cold front late Wednesday into Thursday. This front will then stall to the south through the end of the week and into the weekend. && .NEAR TERM /THROUGH TONIGHT/... Previous forecast remains largely on track. Did tweak dew points down a degree or two, but increased temperatures as well given latest obs. 12Z RAOB from IAD has notably more moisture in the mid-levels than the 00Z sounding, and upstream 12Z RAOB from PIT shows moisture around the periphery of the surface ridge. Latest 12Z guidance has convection initiating by 16-18Z in the vicinity of the Blue Ridge and slowly moving northeast through the day towards the metros (especially western). Potential for downbursts exists today, especially in the larger cores. Previous discussion follows... The further breakdown of the Bermuda high off to the east will allow for increasing moisture and humidity across the Mid- Atlantic. Main story for today will be the continued well above normal airmass overhead. Excessive Heat Warnings and Heat Advisories remain in place for most areas aside from the highest terrain zones. Highs will flirt with 100 degrees in some areas, especially east of the Blue Ridge. This, coupled with dewpoints near 70 will allow heat index values to soar near 110 F in localized areas, with low 100s more common elsewhere in the lower elevations. Latest convective model guidance suggests another round of showers and thunderstorms this afternoon and into the early evening hours. Nonetheless, a lee surface trough situated just east of the mountains will likely be enough to spawn at least a few showers and thunderstorms further east later today. Some of these storms may become strong to severe given the available convective parameters. Most likely hazards will be damaging winds and maybe some hail. Most convection should depart to the east a little after sunset, with some residual showers sticking around into the overnight hours. Overnight lows will drop down into the upper 60s to low 70s for most with mid to upper 70s closer to the waters. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... By Tuesday, continued excess heat will linger across the area. Excessive Heat Watches remain in effect for the climo areas outside of the mountains for the potential for heat index values well into the triple digits. Many models have backed off on dewpoint values on Tuesday compared to previous days by a few degrees which may limit the overall coverage of potential Excessive Heat Warnings. Nonetheless, well above average temperatures and heat danger will persist on Tuesday. Additionally, showers and thunderstorms return thanks in part to remnant MCS activity and a local surface trough. Still more uncertainty as to where coverage may be greatest but have tried to highlight the northern two-thirds of the CWA as the best chance for convective initiation. Better forcing exists further north of the area but should this change, strong to severe thunderstorms may become more common across our northern half of the forecast area. Some solutions have the decaying MCS right on the doorstep of the Allegheny Front by the early evening hours. Will be worth monitoring this potential. Precipitation wanes by the mid to late evening hours with lows dropping down into the 70s for most areas aside from upper 60s in the mountains. Another hot day is expected on Wednesday, although heat index values may be a few degrees cooler compared to previous days. Heat Advisories are still possible, especially east of the Blue Ridge Mountains. A cold front will approach the area from the Ohio Valley, leading to an increase in shower and thunderstorm potential across the area. There are some timing discrepancies with the front that may inhibit strong to severe storms with post-peak heating initiation. The front is expected to slowly move south where it will eventually stall past Wednesday night. Lows are expected to be in the 60s to low 70s for most areas with increasing northwest flow. && .LONG TERM /THURSDAY THROUGH SUNDAY/... The cold front will likely be bisecting Virginia by Thursday morning. The exact position of the front will be important for focusing any lingering showers as well as convective initiation Thursday afternoon. The highest chances will be across central Virginia to southern Maryland, but it`s possible most activity will be south of the CWA. The front will bring relief from the heat areawide though, with most locations topping out in the mid 80s. The upper level pattern will be blocky for the end of the week, with strong ridges over Bermuda and the Intermountain West and a closed low near Hudson Bay. The front will stall southeast of the area Friday. We will be on the cool side of the boundary, meaning temperatures will remain closer to normal. There is more uncertainty in regards to the frontal position and any subsequent waves of low pressure thereafter. Friday appears to have the minimum in rain chances as high pressure builds to the north and the front reaches its southern extent. Moisture will work back northward over the weekend as the high to the north weakens. Expect more clouds along with increasing chances of showers and thunderstorms, but the more intense heat will not be returning through the weekend. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... VFR conditions are expected to persist through much of the period. Main exceptions are for shower and thunderstorm development by the afternoon to early evening hours at the terminals today and Tuesday. Some of these storms may be strong to severe with damaging winds as the main hazard potential. Winds will continue to be fairly light out of the south to southwest leading into Tuesday before becoming more westerly to northwesterly on Wednesday as a cold front approaches the area sometime later in the day on Wednesday. Some sub-VFR clouds may be present Thursday morning as a cold front passes through the area. A chance of showers and thunderstorms may linger into Thursday afternoon depending on the frontal position, with the highest chance at CHO. The front should be far enough to the south Friday to result in VFR conditions. && .MARINE... Southerly channeling is continuing to produce locally 20 knot gusts across the central Chesapeake Bay and lower tidal Potomac River this morning. Winds should diminish heading into the late morning hours. SMWs are possible today and Tuesday with any strong thunderstorms that cross the waters. SCAs will be possible Wednesday after a cold front crosses the waters later in the day and into the overnight hours. Winds will turn northerly as a cold front passes Thursday and eventually more easterly by late Friday. At this time, the pressure rises across the front appear gradual enough that winds would generally remain below advisory criteria, but this will be worth monitoring for channeling effects. Some thunderstorms remain possible Thursday as the front pushes through, but the strongest activity may be south of the Maryland waters. && .TIDES/COASTAL FLOODING... Anomalies will be slightly elevated over the next several days with some more sensitive tidal locations reaching action stage. No minor flooding is expected over the next several tide cycles locally. && .CLIMATE... Here are some daily high temperature records during the July 15-17 timeframe next week. Records (RERs) are only issued for DCA, IAD, BWI, and MRB, but other sites are shown for reference. A `+` sign indicates multiple years currently hold that record. ***MONDAY, JULY 15TH, 2024*** LOCATION RECORD (YEAR) FORECAST Washington-National (DCA) 100F (1988) 100F Washington-Dulles (IAD) 98F (1995) 101F Baltimore (BWI) 102F (1995) 101F Martinsburg (MRB) 107F (1936) 99F Charlottesville (CHO) 102F (1954) 100F Annapolis (NAK) 101F (1995) 99F Hagerstown (HGR) 102F (1954) 98F ***TUESDAY, JULY 16TH, 2024*** LOCATION RECORD (YEAR) FORECAST Washington-National (DCA) 104F (1988) 100F Washington-Dulles (IAD) 104F (1988) 102F Baltimore (BWI) 104F (1988) 102F Martinsburg (MRB) 107F (1988) 100F Charlottesville (CHO) 102F (1988) 100F Annapolis (NAK) 98F (1997)+ 98F Hagerstown (HGR) 104F (1988) 100F ***WEDNESDAY, JULY 17TH, 2024*** LOCATION RECORD (YEAR) FORECAST Washington-National (DCA) 102F (1980) 97F Washington-Dulles (IAD) 100F (1997)+ 96F Baltimore (BWI) 101F (1988) 97F Martinsburg (MRB) 102F (1988)+ 93F Charlottesville (CHO) 100F (1988)+ 96F Annapolis (NAK) 100F (1900) 94F Hagerstown (HGR) 100F (1953)+ 93F && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Excessive Heat Warning until 8 PM EDT this evening for DCZ001. Excessive Heat Watch from Tuesday morning through Tuesday evening for DCZ001. MD...Excessive Heat Warning until 8 PM EDT this evening for MDZ003- 006-008-011-013-014-016>018-504-506>508. Excessive Heat Watch from Tuesday morning through Tuesday evening for MDZ003>006-008-011-013-014-016>018-502>508. Heat Advisory until 8 PM EDT this evening for MDZ004-005-502- 503-505. VA...Excessive Heat Warning until 8 PM EDT this evening for VAZ027>031-053>055-057-527. Excessive Heat Watch from Tuesday morning through Tuesday evening for VAZ026>031-037>040-050-051-053>057-501-502- 505-506-526-527. Heat Advisory until 8 PM EDT this evening for VAZ025-026- 036>040-050-051-056-501-502-504>506-526. WV...Excessive Heat Warning until 8 PM EDT this evening for WVZ051>053. Excessive Heat Watch from Tuesday morning through Tuesday evening for WVZ050>053-055-502-504. Heat Advisory until 8 PM EDT this evening for WVZ050-055-502- 504-506. && $$ SYNOPSIS...DHOF/ADM NEAR TERM...ADM/CPB SHORT TERM...ADM LONG TERM...ADS AVIATION...ADS/ADM MARINE...ADS/ADM TIDES/COASTAL FLOODING...LWX CLIMATE...LWX