Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
903 FXUS61 KLWX 121412 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1012 AM EDT Wed Jun 12 2024 .SYNOPSIS... A weak area of low pressure passes off to the southeast while high pressure returns through Thursday leading to mainly dry conditions. A cold front tracks through the area on Friday leading to renewed shower and thunderstorm chances. High pressure settles over the area this weekend with lower humidity. Next week looks to become hot as a strong upper ridge builds towards the region. && .NEAR TERM /THROUGH TONIGHT/... MORNING UPDATE: Still seeing some mid-level clouds traverse the region from west to east in response to the upper trough that is gradually moving offshore. Another area of low pressure is currently located over the southeastern CONUS, with the northern periphery of its cloud shield starting to move into southwestern portions of the forecast area. For the most part there is more sun than clouds out there this morning outside of those areas. PREVIOUS DISCUSSION: For the remainder of the day, the aforementioned upper low is forecast to continue to pull away from the New England coast. A weak shortwave ridge pushes through this morning before eroding toward the Delmarva Peninsula. Some diffuse lift from additional perturbations in the flow aloft may spark isolated afternoon rain showers across the Potomac Highlands eastward toward central Virginia. However, updrafts are not expected to drive tall enough convection to produce any lightning activity. Any instances of showers should decay by dark given the loss of heating. Otherwise, the rest of the region stays dry underneath a mix of fair weather cumulus and high cirrus. Forecast highs rise a bit from previous days owing to a wind shift to southwesterly. Today`s high temperatures likely range from the upper 70s to low 80s, locally in the low 70s across mountain locales. Residual surface high pressure holds on into the overnight hours. This will make for another cool night for mid-June standards. Upper 50s to low 60s are expected across most areas, accompanied by some mid 60s in the usual warmer pockets. Some patchy fog may materialize overnight for locations west of I-95. However, its development could be hindered by any cloud cover that lingers into the night. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... Thursday will mark the start of a brief period of above average temperatures as highs begin to near the 90 degree mark. The flow aloft turns quasi-zonal in nature with 24-hour height rises on the order of 4 to 6 dm. At the same time, the prevailing surface high exits off the coast on Thursday. In response, the lower/middle atmosphere will further warm with 850-mb temperatures rising into the 14-16C range. Typical deep afternoon mixing should allow for dry adiabatic profiles down to the surface. This would yield spotty 90 degree temperatures across the area. The persistence of low-level warm advection also aids in moistening the boundary layer. This favors an increase of dew points into the mid 60s. Some spotty showers are possible during the peak in diurnal heating. Any such activity should be more pulse/instability driven and decay pretty quickly after genesis. Expect dry weather through the later evening and overnight hours. Conditions turn milder at night with lows around 4 to 8 degrees above preceding nights. By Friday morning, a cold front tracking across the Lower Great Lakes and Ohio Valley will set the stages for a possible round of showers and thunderstorms. Before this occurs, Friday will mark the hottest day of the week and perhaps the first crack at a 95 degree day in 2024. Relative to preceding model runs, forecast highs have dropped down from the upper 90s back to the low/mid 90s. Heat indices should be in the mid/upper 90s based on the latest dew point forecast. While falling short of typical heat headlines, it is the first real bout of summertime heat this season. Model guidance have begun to show an increasing signal for showers and thunderstorms Friday afternoon into the evening. This is all in response to a cold front set to slide through the region during the near peak in the diurnal heating cycle. While just outside the realm of the convective-allowing model world, coarser-scale models do show an envelope of ample buoyancy in the pre-frontal environment. Forecast vertical shear values between 35-45 knots would be more than enough to support organized convection. Damaging winds would be the primary threat for any more potent storm or along an eastward propagating squall line. This activity should all exit into the Eastern Shore by late Friday night. In the wake, prevailing northwesterly flow will gradually usher in some drier air from central Canada. However, temperatures do stay slightly above average with widespread 60s expected (50s over the mountains). && .LONG TERM /SATURDAY THROUGH TUESDAY/... In the wake of the cold frontal passage, a ridge of high pressure settle over the Great Lakes to northeastern U.S. this weekend. This allows for a dry forecast along with less humidity than previous days. Each day should bring mostly sunny skies with high temperatures that increase through the weekend. Sunday will certainly be the warmer day of the two as surface winds shift back to southerly. This eventually sets the stages for a hot work week ahead. A building subtropical ridge aloft gradually parks over the eastern U.S. during the early to middle portions of the week. Depending on the global ensemble, some show mid-level heights around 2 standard deviations above average. This sprawling 594-dm ridge will really begin to crank up the heat with widespread mid to upper 90s expected. Some of the more upper echelon solutions carry temperatures to just over 100 degrees. Given dew points ranging from the mid 60s to low 70s, heat indices should easily reach and exceed the century mark most afternoons. If this all holds, heat-related products will likely be necessary ahead of this expected heat wave. While not explicitly shown in the forecast package, there should be some instability forced convection. However, this will be largely dependent on the position of the upper ridge as well as any capping that becomes evident in thermodynamic profiles. This hot and steamy air mass could persist through the entire work week if the ensemble means are taken at face value. The Climate Prediction Center agrees with this notion with a moderate risk for excessive heat in the June 19-21 period. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... VFR conditions are expected today with dry weather likely. Also a few spotty showers are possible near KCHO, there is not enough confidence to introduce this into the TAF. Some patchy fog may develop tonight which would lead to sub-VFR conditions at times at KCHO and KMRB. Otherwise, winds remain on the light side with a shift from mainly northerlies to south/southwesterlies. Prevailing southerlies are expected on Thursday as high pressure retreats off the coast. Although isolated showers are possible, it is difficult to say whether this would impact any of the local terminals. The period heading into Friday afternoon into the evening will likely lead to some restrictions given the threat for showers and thunderstorms. Some of these could become severe given the degree of warmth and instability in the atmosphere. Winds quickly shift over to west-northwesterly in the wake. VFR conditions are likely for the weekend under the influence of high pressure. North-northwesterlies given way to a warm advection pattern to finish out the weekend. && .MARINE... Winds should stay below advisory threshold through Thursday morning given the influence of surface high pressure over the waters. Some model soundings do have around 15-20 knots of wind up just above the mixed layer this afternoon over the lower Chesapeake Bay zones, so will have to watch those areas for some sporadic higher wind gusts this afternoon. As this ridge slides offshore, southerly channeling effects may require Small Craft Advisories across wider portions of the Chesapeake Bay. The period of interest mainly covers Thursday afternoon through the overnight hours before the heftier flow diminishes. A cold front tracking across the area Friday afternoon/evening will lead to the threat of strong to severe convection. This could require some Special Marine Warnings for the area waterways. As the convection and frontal zone exit off to the east, expect an uptick in the post-frontal northwesterlies. Small Craft Advisories may be needed late Friday into the first half of Saturday. Otherwise, winds decrease in strength for the rest of the weekend under the influence of high pressure. && .TIDES/COASTAL FLOODING... As winds turn southerly late tonight into Thursday, tidal anomalies will rise as a result. This could result in some minor tidal flooding towards the end of the week. No flooding is forecast at this time, but the current forecast does gradually rise some of the more sensitive sites well into action stage, so it will certainly be close. && .CLIMATE... High temperatures could approach records on Friday afternoon, and again early next week. Below is a list of record high temperatures for June 14, 17th, and 18th, the year the record was set, and the current forecast high temperatures for those days. Daily temperature records are currently only maintained at DCA, IAD, BWI, and MRB. Others are shown for reference. Friday Jun 14th Climate Site Record High Forecast High Washington-National (DCA) 98F (1994) 93F Washington-Dulles (IAD) 98F (1994) 92F Baltimore (BWI) 98F (1994) 92F Martinsburg (MRB) 101F (1943) 89F Charlottesville (CHO) 96F (1954+) 93F Annapolis (NAK) 95F (1994+) 88F Hagerstown (HGR) 95F (1994+) 89F Monday Jun 17th Climate Site Record High Forecast High Washington-National (DCA) 99F (2022) 94F Washington-Dulles (IAD) 96F (2022) 94F Baltimore (BWI) 96F (2022+) 93F Martinsburg (MRB) 98F (1939+) 92F Charlottesville (CHO) 97F (2022) 94F Annapolis (NAK) 96F (1939) 88F Hagerstown (HGR) 96F (1952) 94F Tuesday Jun 18th Climate Site Record High Forecast High Washington-National (DCA) 97F (1944) 96F Washington-Dulles (IAD) 94F (2018+) 96F Baltimore (BWI) 97F (1957+) 94F Martinsburg (MRB) 99F (1943) 94F Charlottesville (CHO) 96F (2014+) 95F Annapolis (NAK) 96F (1957) 90F Hagerstown (HGR) 95F (1957) 96F + indicates that value has been reached on multiple years, with the year displayed being the most recent. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BRO NEAR TERM...BRO/CJL SHORT TERM...BRO LONG TERM...BRO AVIATION...BRO MARINE...BRO/CJL TIDES/COASTAL FLOODING...BRO CLIMATE...BRO