511 FXUS61 KRLX 061717 AFDRLX AREA FORECAST DISCUSSION National Weather Service Charleston WV 117 PM EDT Tue Jul 6 2021 .SYNOPSIS... Heat and humidity continue across the region with isolated popup showers and/or storms. Coverage increases midweek as a cold front approaches which will moderate temperatures some. && .NEAR TERM /THROUGH TONIGHT/... As of 1053 AM Tuesday... The river valley fog that formed overnight has dissipated resulting in milky sunshine. Everything appears to be on track today with some isolated showers/storms and some localized areas reaching heat advisory criteria. Have tweaked the temperatures down a little in the Point Pleasant area as the thermometer at that location may read a little high in sunshine. As of 621 AM Tuesday... Fog has expanded since the previous update and is most concentrated across southern portions of the forecast area based on latest satellite trends. This should mainly lift within the next hour or so. Otherwise, just made some minor tweaks to hourly temperatures this morning based on recent trends and observations. As of 329 AM Tuesday... Recent GOES-16 Night Fog satellite imagery shows valley fog is once again developing across the area early this morning amid the light to calm winds, clear skies, and low dewpoint depressions. The expectation is for fog to continue to increase in coverage through sunrise, but then quickly dissipate shortly after. Meanwhile, both ridging aloft and surface high pressure remain in control across the area and this will yield another warm and humid day. In fact, highs this afternoon should be a degree or two warmer than yesterday in many locations with low/mid 90s across the lowlands and mid 70s to 80s in the mountains. With dewpoints in the upper 60s and low 70s, heat indices in some locations should reach the upper 90s today and possibly even reach 100 in some isolated spots, but thinking we won't reach Heat Advisory criteria as any instances of reaching the triple digits should be for a short duration and only in a few isolated sites at most. The warm and humid conditions will also lead to rather strong destabilization later today with the latest NAM showing MLCAPE values reaching the 2500-3000 J/kg range. However, despite the potential for strong instability, upper support is expected to be weak and with high pressure aloft and at the surface, subsidence should act to generally suppress convective activity. That said, will still include Slight PoPs in the forecast across the area today during peak heating given the anticipated instability values amid this warm and humid air mass, but overall storm coverage should be low if anything is able to pop. If any showers and storms are able to develop today, this activity should mainly taper off shortly after sunset with the loss of heating. Attention will then turn to the potential of yet another night of valley fog across the region. However, there may be more cloud cover tonight than what has occurred in previous nights as an upper trough drops into the Great Lakes region and the flow aloft becomes more southwesterly, which is expected to bring an increase of moisture into the area. As a result, have kept patchy fog wording in the forecast rather than greater coverage at this time. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/... As of 425 AM Tuesday... The period begins with a broad mid-level ridge across the western CONUS, while across the northern CONUS, a progressive trough is shifting S/E. At the surface, a cold front located across the central midwest will be sliding towards the region, while Elsa, located in the vicinity of Northern Florida, is progged to move up the eastern seaboard. Wednesday will generally feature much of the same weather that Tuesday did, with heat and humidity continuing. Temperatures should be a bit cooler, with highs generally in the upper 80s to low 90s for lower elevations, with 70s across the higher terrain. Heat indices at lower elevations could once again approach the mid 90s in spots. Isolated diurnal showers/storms will once again be possible given the environment, but the activity should be fairly isolated/scattered given the lack of forcing and dry air aloft. Thursday will provide the greatest chance for showers/storms across the area as the cold front approaches during the afternoon/evening. Some guidance is showing the front's progression slowing, possibly stalling, as it moves across the area, with it possibly taking until midday Friday to clear the mountains. At this point any severe threat associated with it is quite low. A brief and minor reprieve from the recent heat will occur across the area Thursday/Friday, with highs back to near seasonable levels, possibly a few degrees below. && .LONG TERM /SATURDAY THROUGH MONDAY/... As of 105 PM Tuesday... Starting Saturday, a system to the west approaches the area with rising chances of showers and/or storms. I limited coverage to just chance category (high end) since long range models are inconsistent with timing and location of the system. A passing wave to the north may add to the POP coverage a bit through the rest of Saturday and likely POPs from guidance may just become justified in future shifts. As aforementioned surface low moves toward us into Sunday the frontal boundary will lift north. The system will become quasi- stationary as its parent upper low rotates in place overhead due to weak steering flow and will finally decide to move north early Tuesday according to long range models. This slow movement will keeps POPs and thunderstorm probability capped out at just chance until outside this extended period where slight chances come into play later on Tuesday. Temperatures will continue a warm path trending consistently above average for this time of year. Monday should likely be the warmest. Being that the system sticks around near the area will likely result in the influx of moist air with daily chances for diurnal thunderstorms to occur. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... As of 621 AM Tuesday... Any fog from overnight will lift at the beginning of this TAF period and VFR conditions should then prevail area-wide through much of the day as high pressure will be in control. However, isolated showers and thunderstorms could develop in the afternoon and evening hours, but did not include mention of VCTS in the TAFs at this time as shower/storm coverage is expected to be low. In addition, surface winds will be light throughout the day, mainly from the WSW at around 5 kts. If any storms are able to develop today, they are expected to taper off after sunset with the loss of daytime heating. Since winds will remain light overnight with at lest partial clearning, patchy valley fog will also be possible towards the end of the TAF period, which could bring a deterioration of conditions overnight. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 18Z WEDNESDAY... FORECAST CONFIDENCE: High. ALTERNATE SCENARIOS: Brief MVFR or IFR restrictions are possible Tuesday afternoon if a shower/storm directly impacts a terminals. The development of valley fog tonight could vary from forecast. EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY OF WFO FORECAST TO AVAILABLE MODEL INFORMATION: H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS. L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. UTC 1HRLY 17 18 19 20 21 22 23 00 01 02 03 04 EDT 1HRLY 13 14 15 16 17 18 19 20 21 22 23 00 CRW CONSISTENCY H H H H H H H H H H H H HTS CONSISTENCY H H H H H H H H H H H H BKW CONSISTENCY H H H H H H H H H H H H EKN CONSISTENCY H H H H H H H H H H H M PKB CONSISTENCY H H H H H H H H H H H H CKB CONSISTENCY H H H H H H H H H H H H AFTER 18Z WEDNESDAY... IFR conditions will be possible in showers and thunderstorms Wednesday and Thursday as a cold front approaches the area. && .RLX WATCHES/WARNINGS/ADVISORIES... WV...None. OH...None. KY...None. VA...None. && $$ SYNOPSIS...JSH/JZ NEAR TERM...JSH/RG SHORT TERM...04 LONG TERM...JZ AVIATION...RG