Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/20/19

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
846 PM PDT Wed Jun 19 2019 .SYNOPSIS...19/818 PM. Clouds will increase at the coast and valleys Thursday as onshore winds strengthen. Through the rest of the week, expect clear skies in interior areas with clouds persisting at the coast. Patchy morning fog and drizzle are possible at the coast and valleys. Temperatures will cool through Friday and warm slightly into the weekend as clouds dimish. && .SHORT TERM (WED-SAT)...19/846 PM. Upper level ridge of high pressure will weaken and shift eastward as a fast moving upper level trough moves into northern and central California on Thursday. This will lead to strengthening of the onshore pressure gradients and a deepening of the marine layer, resulting in a cooling trend across the district. Already seeing stronger onshore pressure gradients this evening, with LAX-Daggett currently at +8.6 mb this evening (as compared to +7.4 mb this time yesterday). By tomorrow afternoon/evening, expecting LAX-Daggett gradient to peak over +10 mb onshore. 00Z Vandenberg sounding and ACARS data over LAX basin indicating a rather uniform marine layer depth this evening around 2500 feet. The upstream upper level trough combined with the strengthening onshore gradients is expected to deepen the marine layer to between 3000 and 3500 feet on Thursday morning, and most likely even deeper by Friday morning. In evening update, will expand the low clouds and fog into the lower coastal slopes. This deepening marine layer pattern will likely result in widespread drizzle across the region overnight into Thursday morning, and again Thursday night into Friday morning. In fact, there is a chance of some measurable light rain across LA county, mainly in the foothills and coastal slopes, especially on Friday when we are carrying 20-30 percent Pops. As we would expect with a deep marine layer and strong onshore flow pattern, look for low clouds to linger all day across the coastal plain, and possibly some of the valleys. Onshore winds picking up this evening across the Antelope Valley, and will continue to strengthen into Thursday, with little change into Friday. Wind gusts between 40 and 50 mph will be common across the Antelope Valley both days, mainly during the afternoon and evening hours, with isolated gusts as high as 60 mph in the foothills (near Lake Palmdale). A wind advisory has already been posted for these strong onshore winds tomorrow afternoon/evening across the Antelope Valley. Elevated fire weather conditions are expected across the Antelope Valley and adjacent foothills due to these strong onshore winds, fairly low humidities, and abundant grass crop. Valley temperatures expected to remain in the 70s on Thursday, with Friday likely being the coolest day of the week (when some interior areas being 12 to 15 degrees below normal). *** From previous discussion *** Very weak ridging is expected Saturday and the winds will trend offshore helping the marine layer clouds clear earlier and allowing afternoon high temperatures to rise a few degrees. .LONG TERM (SUN-WED)...19/208 PM. By Sunday, temperatures will be near normal across the interior but will still be 5 to 10 degrees below normal across the coasts and valleys. Another trof will arrive Monday, this time from the northwest. We`ll have westerly zonal flow aloft on Monday as we`re just south of the trof, then the lower heights work their way south through Wednesday. The low will bring back the strong onshore flow, less clearing and cooler coastal temperatures. && .AVIATION...20/0019Z. At 2034Z, the marine layer depth was around 2400 feet deep at KLAX. The top of the inversion was near 3400 feet with a temperature around 21 degrees Celsius. Moderate confidence in the current forecast. The latest visible sattelite imagery trends show considerable marine layer coverage over the coastal sections of Ventura and Santa Barbara counties with clear skies over the LA county coastal areas. The latest MOS guidance and mesoscale models are supportive of marine layer moving onshore to the LA county coastal areas by 03z-04z...and by 04z-05z over the inland valleys. As an upper level trough deepens across the region, deeper marine layer will set up across much of the coastal and inland valleys through the 00z TAF period with limited clearing tomorrow afternoon. Terminals over the Antelope valleys should see continued gusty W/WSW winds overnight into tomorrow with tightening onshore pressure gradient. KLAX...Expect MVFR ceilings to develop by around 03z-04z...with limited clearing tomorrow afternoon due to the deeper marine layer. KBUR...Expect MVFR ceilings to develop by around 04z-05z...with IFR cigs and MVFR visby in light FG by early tomorrow morning. MVFR ceilings will persist tomorrow though a brief period of parital clearing can be seen 20z-00z. && .MARINE...19/814 PM. Winds and seas will likely remain below Small Craft Advisory levels through at least Thursday. There is a 50 percent chance for advisory level seas and winds across the northern most outer waters Friday afternoon and evening, and a 30 percent chance of advisory level winds each afternoon and evening through the weekend. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...Wind Advisory in effect from 2 PM to 10 PM PDT Thursday for zone 59. (See LAXNPWLOX). PZ...NONE. && .HAZARD POTENTIAL OUTLOOK (SAT-WED). No significant hazards expected. && $$ PUBLIC...Gomberg/jld AVIATION...OH/Gomberg MARINE...Sweet SYNOPSIS...Phillips
Area Forecast Discussion
National Weather Service Blacksburg VA
912 PM EDT Wed Jun 19 2019 .SYNOPSIS... A stationary front will remain draped over the Mid Atlantic through tonight into Thursday. By Thursday afternoon, a cold front will shove this stalled frontal boundary offshore. High pressure should return to provide drier weather for Friday. && .NEAR TERM /THROUGH THURSDAY/... As of 911 PM EDT Wednesday... A few decaying showers in the region will continue to weaken with loss of heating. The focus then turns to the complex of thunderstorms across central KY into northern TN at 01Z (9 PM EDT). Most of the CAMs agree this complex will weaken as it approaches our area after 06Z (2 AM EDT) tonight, as instability continues to drop and low level winds veer to the southwest/west reducing the inflow into this complex. With SBCAPE values still a couple of hundred j/kg, still would expect this complex to produce some rain, especially west of I-77, so kept chance POPS in place during the pre-dawn hours in this area. Little changes were made to temps, winds, but cloud cover was lowered early this evening before low clouds/stratus return late tonight. For Thursday, a cold front will push eastward from the Ohio River Valley and arrive over the Mid Atlantic during the day. Some prefrontal convection could arrive by daybreak but eventually decay over the mountains. However, the cold front will produce another round of showers and thunderstorms by midday that persists until sunset. The threat of severe weather and flash flooding seems a little greater on Thursday as compared to this afternoon, but confidence is too low to pinpoint exactly where these threats will materialize. For now, all these weather threats have been mentioned in the HWO. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... As of 131 PM EDT Wednesday... A broad upper trough will initially be responsible for sensible weather conditions Thursday night into Friday, in the wake of Thursday`s cold frontal passage. This trough will bring with it a noticeable drop in humidity levels from present elevated levels, and a period of breezy northwest winds Thursday night into part of Friday. While this upper feature will be to our northeast through late week/early weekend, at the same time an anomalous upper ridge associated with summerlike heat and increasing humidity will be building over the lower-mid Mississippi Valley. This will set up a period of enhanced mid-level northwest flow later Friday into Saturday from the upper Midwest across the Ohio Valley and into the southern/central Appalachians. Majority of guidance over the last 24 hours suggests will likely be a convectively-active storm track on the periphery of the warm and conditionally unstable air mass brewing over the lower Ohio/TN Valleys. Decreasing PoPs for Thursday night will be the general trend, though still some stratus/light showers to linger in the WV mountains into the Blue Ridge. Also in the post-frontal regime will be seasonally strong 6-hourly pressure rises between 3 and 7 mb, coinciding with 850 mb jetstreak perpendicular to the Blue Ridge of around 45 kts, most of which lie locked above a subsidence inversion. MAV-based wind speeds are around 20-22 kts between 00z-06z Friday however, with lighter speeds moving into the daytime hrs Friday. Will show wind gusts overnight into early Friday in the mountains nearing 35 mph, with about 20-25 mph east of the Blue Ridge. It`s possible these winds may be strong enough to bring some weakened trees down along the southern Blue Ridge where considerable rains have fallen of late for overnight into early Friday. On the whole, Friday should see decreasing wind gusts and an overall pretty pleasant day with plentiful sun. As mentioned, for late Friday into Saturday we`ll likely be needing to keep a close eye toward the northwest for the potential for convective storm complex(es) moving southeastward either close to or over the Blacksburg area of responsibility. While models have shown or at least hinted at the convective potential for a few model cycles, remainder of the period regarding PoP chances, especially on timing when and where they are the greatest, is pretty low- confidence. Details on location, timing and to an extent the scope of any severe or hydro threat will hinge on any leftover boundaries or leftover embedded convectively-enhanced vort maxima. GFS-based 0- 6 km bulk shear is around 35-50 kts Friday night into Saturday, and while summerlike humidity levels boost CAPE values during the daytime hours, a plume of steep mid-level lapse rates shown by the GFS in the northwest flow may keep thunder chances going into the evening/overnight. That`s certainly a background environment that would foster strong to severe storms, but again is conditional on aforementioned mesoscale details which are unresolvable at this time range in model-world. Current thinking is areas southwest of a Lewisburg to Roanoke to Reidsville line, where the GFS shows the periphery of the instability axis lying. Given stated uncertainties, will show 20-30% PoP across this area Friday night, with a dry forecast elsewhere. Generally will keep highest PoPs in the 40-50% range south/west of that Roanoke-Reidsville line Saturday, with 20- 30% elsewhere. Will hold off on any HWO mention regarding late week/early weekend severe/hydro at this point; but the severe/hydro threat is something that we`ll have to be carefully monitoring and refining. Temperatures on the whole are near to close to late-June climatology in the 70s to mid 80s. Will start to increase the humidity level late Friday night and into Saturday. Forecast confidence is moderate to high for Thursday night into Friday; uncertainty regarding placement and location of convective complexes renders confidence at low to moderate levels for Friday night into Saturday. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 133 PM EDT Wednesday... Amplified ridge axis initially over the OH/TN Valleys begins to shift eastward over the Blacksburg forecast area by Sunday. Increasing heat and humidity is likely to be the rule for Sunday and most of Monday. GFS has advertised 850 mb temperatures in the low +20s C by Monday, which will likely push temperatures east of the Blue Ridge into the low 90s, with heat indices in the mid to upper 90s. Potential for scattered showers and thunderstorms should exist as well on Sunday in the heat of the day but coverage may be limited by absence of larger-scale forcing mechanisms. Later Monday a rather strong shortwave trough aloft looks to topple the ridge and will drag a weakening cold front across the Appalachians and mid-Atlantic region. This should bring with it a greater chance for thunderstorms areawide; while a few strong storms possible, too much uncertainty to place in the HWO or in the zone forecast. A bit cooler, although temperatures likely still to run close to or just above late-June climatology for Tuesday. Forecast confidence is overall moderate for this period. && .AVIATION /01Z THURSDAY THROUGH MONDAY/... As of 740 PM EDT Wednesday... Isolated to widely scattered showers and thunderstorms along a weak surface trof may move over BCB, ROA and LYH between now and 02Z (10 PM EDT) before waning with loss of heating. Later tonight, lingering low level moisture and light winds will likely produce another round for MVFR to IFR vsbys and ceilings, especially at the mountain TAF sites and LYH. Confidence is lower regarding the timing of showers and thunderstorms for Thursday, as a complex of storms across the Ohio Valley this evening march east. With limited instability, and a turn to southwest low level winds, this complex will weaken and may completely dissipate before reaching our area. For now, kept VCSH in during the early morning hours for the mountain TAF sites. Re-development of scattered thunderstorms is expected Thursday afternoon ahead of a cold front, and again included VCTS at all TAF sites to account for this. Winds may be issue, especially for small aircraft tomorrow with gusts winds 20-25 kts expected during the afternoon. Extended Aviation Discussion... The cold front should head offshore by Thursday night with breezy winds expected. Dry weather and VFR conditions with lighter winds will follow for Friday into early Saturday as high pressure builds overhead. Scattered showers and thunderstorms could return during late Saturday through Monday with MVFR conditions possible in the strongest storms. MVFR may also be possible due to any low clouds or fog during the early morning hours, especially in the mountains. && .HYDROLOGY... As of 225 PM EDT Wednesday... The probability of flash flooding is above average if there is training of storms this afternoon, especially across the NC mountains/foothills where 1 hour flash flood guidance of 1-2 inches exists. Given precipitable water values over 1.5 inches with deep convection, rainfall rates of 3 to 4 inches may cause some issues. The storm motion is expected to be in the 20-30 MPH range, but training may set up along the Blue Ridge. No flash flood watch has been issued at this time so that trends can be observed on how the storms evolve first. If a watch is needed, it may be for the Blue Ridge south of Roanoke into the North Carolina mountains and eastward to the foothills. Another threat of flooding exists ahead of the cold front on Thursday. As far as the rivers go, there is just localized runoff, and only South Boston is expected to reach action stage by Thursday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PW NEAR TERM...PW/PH SHORT TERM...AL LONG TERM...AL AVIATION...PH/PW HYDROLOGY...WP