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Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
276 FXUS61 KLWX 300800 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 400 AM EDT Sun Jun 30 2024 .SYNOPSIS... Low pressure will move across the Great Lakes region early this morning. A cold front will then push through this afternoon and evening. A strong area of high pressure settles over the area Monday and Tuesday before drifting offshore the second half of the week. A warm front nears the region by mid-week yielding a warming trend. && .NEAR TERM /THROUGH TONIGHT/... A residual pool of elevated instability continues to spark off isolated to scattered showers and thunderstorms early this morning. What has developed has not been terribly organized, but has been stout enough to produce locally heavy rainfall and frequent lightning strikes. The 0720Z radar imagery shows a loosely organized line tracking east of the Baltimore area toward the Chesapeake Bay. Farther upstream, a shield of decaying thunderstorms have begun to march toward the I-81 corridor. With the atmosphere downstream largely worked over per ample inhibition (100-150 J/kg) on the 06Z RAP objective analysis. Based on how much shower activity is occurring back over central West Virginia, expect some threat of showers during the morning hours. It will be a warm and muggy start to the day given current temperatures in the 70s to low 80s and dew points in the low/mid 70s. The latest radar trends and hourly update high-resolution models support showers during portions of the morning. This would introduce a hefty amount of cloud cover which will influence how afternoon convection unfolds. The 00Z HREF mean shows plenty of clouds through the lunch hour before some breaks become evident west of the Blue Ridge. If this is the way things play out, the forcing from a formidable mid-level trough should help ignite some convection by the early afternoon. 500-mb wind fields are fairly healthy this afternoon, generally running around 40 to 45 knots. The forecast surface-based CAPE values along and east of U.S. 15 run between 1,500-2,500 J/kg. Thus, expect convection to further intensify when pushing from U.S. 15 and points eastward. Thunderstorms are expected to coagulate into an eastward surging squall line. A Slight Risk continues across from I-81 eastward with damaging winds and large hail being the primary threats. However, cannot rule out a brief tornado from I-95 eastward given some interactions with local bay/river breezes. All of this activity exits into the lower Chesapeake Bay by the mid/late evening hours as a cold front ushers in drier air in the wake. Regarding the threat of daytime heat and humidity, there is a lot of question marks in whether heat indices are able to push to advisory thresholds (105 east of the Blue Ridge and 100 to the west). There has been a subtle cooling trend in the guidance which caps high temperatures to around 93 to 95 degrees. This is in response to the extensive cloud cover which may hinder some of the afternoon heating. Based on the air mass in place, dew points in the low/mid 70s should stick around much of the day. Some vertical mixing could lower dew points by a couple degrees. The net combination of heat and humidity carries heat indices into the 100 to 104 degree range. Despite falling short of a Heat Advisory, the public should ensure to stay hydrated, find shade or the indoors to escape the heat, and wear light clothing. For the night, expect cooler temperatures than the past several nights. Lows will be in the mid 50s to low 60s, locally falling into the mid/upper 40s along the Alleghenies. This comes with northerly winds that gusts up to 10 to 20 mph at times. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... A seasonably strong area of high pressure will advance from the Upper Midwest toward the northeastern U.S. on Monday and Tuesday. This ushers in an air mass characterized by below average temperatures and lower humidity levels. Ample sunshine is likely on Monday, accompanied by high temperatures in the upper 70s to low 80s. 60s to low 70s will be more commonplace for those in mountain locations. Along the eastern extent of the ridge of high pressure, a steady northerly wind is expected through the day with afternoon gusts up to 20 to 25 mph. By Monday night, the ridge settles over interior New England down into the Mid-Atlantic region. This helps lower overnight temperatures into the 50s to low 60s. A few mid 60s are possible along and east of the I-95 corridor. As the ridge slowly nears the New England coast, the surface winds will respond to become more east-southeasterly in nature. Tuesday`s high temperatures will be a tad warmer as they rise into the low/mid 80s. This comes with a few more clouds, but sky conditions should still be mostly sunny across the area. Humidity levels remain on the low side for early July standards. Wind fields become southerly overnight yielding a milder night than the previous two. Forecast lows will be in the low/mid 60s, with mid/upper 50s across mountain locales. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... Return flow from surface high pressure offshore will usher in warm and moist air on Wednesday. High temperatures will be in the upper 80s to low 90s for most with overnight low temperatures staying in the upper 60s to low 70s. With high pressure in charge, dry weather is expected throughout the day. As an area of low pressure north of the Great Lakes tracks eastward, the associated cold front will approach the area. This will bring a slight chance to a chance of showers and thunderstorms to the area beginning Wednesday night. Shower and thunderstorm chances will remain confined to along and west of the Blue Ridge overnight Wednesday into Thursday, before becoming areawide Thursday afternoon. With upper level ridging over the east coast on Independence day, temperatures will warm to the mid to upper 90s for those east of the Blue Ridge. With high relative humidities, heat indices are expected to rise into the low 100s in the afternoon. Similar pattern continues Friday and Saturday as the cold front looks to stall to our northwest. This will allow for daily chances of showers and thunderstorms, with highest chances in the northwestern portions of the forecast area. High temperatures each day will rise into the upper 80s to mid 90s with higher elevations staying in the upper 70s to low 80s. && .AVIATION /07Z SUNDAY THROUGH THURSDAY/... Ongoing convection activity across northeastern Maryland has maintained some restrictions across the Baltimore terminals. The reduced visibility should improve with any lightning activity pushing toward northern/central Delaware. Isolated showers and thunderstorms also persist near KMRB which should exit to the east in the next hour. Strong to severe thunderstorms may erupt this afternoon and evening in response to an approaching cold front. While much of the day will feature VFR conditions, a 2 to 4 hour window of restrictions are likely sometime in the early afternoon to early evening timeframe. Gusty and erratic winds, frequent lightning, and reduced visibility/ceilings are possible in such thunderstorms. Any threat wanes by the mid-evening as the cold front pushes off to the east. Winds shift to northwesterly with gusts up to 15 to 20 knots tonight. VFR conditions are expected on Monday and Tuesday as high pressure takes control of the weather. Northerly winds may gust up to 20 knots during the afternoon to early evening. As the ridge of high pressure pushes off toward the New England coast, winds shift to east-southeasterly on Tuesday, before becoming southerly at night. Prevailing VFR conditions are expected Wednesday and Thursday at all terminals. Shower and thunderstorm chances increase Thursday morning, mainly for western terminals, with precipitation possible at all terminals in the afternoon. && .MARINE... Small Craft Advisories remain in place until 6 AM across wider portions of the Chesapeake Bay down into the lower tidal Potomac River. Southerly winds persist through the day which could near Small Craft Advisory thresholds. However, these should fall short and be handled by Marine Weather Statements. Eventually, hazardous weather could impact the waterways late this afternoon into the evening. Strong to severe thunderstorms are possible as a cold front migrates east toward the waters. Thus, Special Marine Warnings may be needed at times, mainly between 3-10 PM (southern waters would be on the later side of this range). In the wake, a gusty northwesterly wind eventually shifts to northerly on Monday. Small Craft Advisories are likely needed late tonight through Monday during period of cold advection. Winds turn more east-southeasterly on Tuesday, largely staying below advisory thresholds. Southerly winds on Wednesday shift to westerly on Thursday. Small Craft Advisories are likely across the Chesapeake Bay on Wednesday with winds gusting 15-20 knots. Winds decrease to below SCA criteria for Thursday. && .TIDES/COASTAL FLOODING... Tidal anomalies begin decreasing this morning as winds become more southwesterly. No tidal sites are expected to reach minor flood stage, but DC Waterfront, Straits Point, and Annapolis may reach action stage in the new couple high tide cycles. As winds shift to northwesterly Sunday night, tidal anomalies continue to fall with all tidal sites expected to stay below action stage. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 AM EDT early this morning for ANZ530>534-537-539>541-543. && $$ SYNOPSIS...BRO NEAR TERM...BRO SHORT TERM...BRO LONG TERM...AVS AVIATION...AVS/BRO MARINE...AVS/BRO TIDES/COASTAL FLOODING...AVS