Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/26/17

Area Forecast Discussion
National Weather Service Charleston SC
1029 PM EDT Tue Jul 25 2017 .SYNOPSIS... Broad low pressure will remain across the Carolinas and Georgia through tonight. A weak cold front will then stall over or near southeast South Carolina through Thursday. Another cold front will move into the area this weekend and stall into early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... As of 1020 PM: IR detected rapidly warming cloud tops and radar indicated largely stratiform rainfall across SE GA. It appears that the remaining rainfall will generally dissipate before midnight. I will update the forecast to increase sky cover and decrease PoPs. Latest runs of the HRRR have indicated that the rest of the night will remain quiet. However, near range guidance shows that the core of the mid level low will reach the Altamaha River by day break. As the low approaches, convection is expected to develop near the coast and drift inland. Based on the guidance, I will maintain CHC PoPs beginning around dawn. Otherwise, temperatures across most of the forecast area is expected to remain steady at the latest readings in the mid to upper 70s. As of 725 pm: At the top of the hour, an automated raingauge at Midville, GA indicated that 3.11 inches of rain fall in one hour. At this time, a multi-cell thunderstorm over McIntosh was producing torrential rainfall rates that ranged close to what was observed at Midville. In addition, a line of thunderstorms should drift north across the Altamaha River Valley, likely raining out and becoming stratiform rain by 10 pm. Elsewhere, light stratiform rain should continue or areas that are dry will remain dry overnight. However, there is a chance that convection may approach Berkeley County form the north. I will update the forecast to reflect the latest radar trends and thinking. Previous Discussion: To start, ahead of an upper low advancing east across southern GA, thunderstorm coverage will range from numerous/widespread across SE GA to isolated/scattered across SE SC into early evening. Primary concerns focus on the threat for locally excessive rainfall within an environment featuring PWATs exceeding 2 inches and weak steering flow, especially where coverage is maximized across SE GA. MLCapes exceeding 2000 j/kg could translate to an isolated/brief pulse severe event with damaging wind gusts, but the probability for severe weather will remain low. Thunderstorms should undergo diurnal weakening/dissipation later this evening. Then, as the upper low continues to roll toward the region, isolated/scattered showers/thunderstorms could redevelop later tonight. Locally heavy rain could again occur, especially along the coast. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... Troughing will linger through the period, although it will be strongest through Thursday. The deepest moisture is also likely through Thursday so through this time is when we expect the highest rain chances, especially Wednesday. Although cannot rule out isolated severe storms, the bigger risk will be heavy rainfall/flooding given weak wind fields and very deep moisture. This wetter than normal pattern will lead to lower than normal high temperatures and generally above normal low temperatures. By Friday temperatures could reach above normal in the mid 90s with heat index values peaking in the lower 100s. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Deep moisture will advect to the Southeast United States ahead of a cold front that is expected to move into the area Saturday. PWATs between 2.25 to 2.5 inches and forcing associated with the front support numerous showers and thunderstorms Saturday into Sunday while the front slowly progresses south and eventually stalls over or near southern areas of Southeast Georgia. A few thunderstorms could become more organized than previous days given greater wind fields aloft, but the overall threat of stronger thunderstorms could be limited due to the timing of fropa during earlier hours on Saturday. At least chances of showers and thunderstorms could linger into early next week while moisture continues to lift over or near the stationary front. Temps will generally be a few degrees below normal this weekend and early next week given extensive cloud cover and precip activity. In general, temps should peak in the mid/upper 80s. Overnight lows will range in the low/mid 70s. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... Thunderstorms are expected this afternoon at both terminals, with most significant impacts at KSAV. Then, VFR conditions are forecast at both terminals through the 18Z TAF cycle. However, low-level moisture could support MVFR/IFR ceilings later tonight. Then, as an upper level low advances east and deep- layered moisture spreads north across the region, showers could redevelop late tonight, and thunderstorms could develop before the end of the 18Z TAF period. Any showers/ thunderstorms could produce flight restrictions. Extended Aviation Outlook: Brief flight restrictions are possible with showers and thunderstorms, especially Wednesday into Thursday as weak low pressure approaches the region. VFR conditions should prevail late Thursday and Friday before flight restrictions return with showers and thunderstorms along/near another cold front Saturday. && .MARINE... Seas of 2-3 feet will persist through tonight. The sea breeze and synoptic winds will combine to produce S/SW winds 10-15 knots into early evening, then synoptic SW winds mainly 15 kt or less will prevail for the remainder of tonight. Thunderstorms could produce locally hazardous conditions over GA waters this afternoon/evening and anywhere across the coastal waters later tonight. Wednesday through Sunday: A cold front looks to stall near the SC waters through Thursday before dissipating before another cold front moves into the area this weekend. Conditions are expected to remain below Small Craft Advisory levels through the period. However, a southwest/south flow could gust around 20 knots Friday night into early Saturday until cold fropa occurs. Seas will gradually build from 2-3 ft up to 4 ft at times later this week as the pressure gradient tightens a bit ahead of the front. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...NED/SPR SHORT TERM...RJB LONG TERM...DPB AVIATION...RJB/SPR MARINE...RJB/SPR
Area Forecast Discussion
National Weather Service State College PA
1200 AM EDT Wed Jul 26 2017 .SYNOPSIS... A large area of high pressure will slide southeast from the Great Lakes to blanket most of the Middle Atlantic Region with an airmass consisting of slightly below normal temperatures, comfortably low humidity, and abundant sunshine for most places on Wednesday. Low pressure and an attendant cold front will approach from the Ohio Valley for later Thursday into Friday bringing a few periods of showers and scattered thunderstorms. Another refreshingly drier and cooler airmass will overspread the commonwealth this coming weekend. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 00Z observed soundings support trapping thin layer of moisture below the inversion. Clouds are breaking up, but slow to do so. Also some mid and high clds from central Lake Erie to western PA. Will adjust grids some more for this. Earlier discussion below. Some sunshine at times, but still a lot of clds. Even a hint of perhaps some drizzle across the far northeast. Adjusted cloud grids some. Low level thermal trough was situated from northcentral PA into the New England states, while warmer air was advecting into the region in the mid levels. This increasingly stable vertical thermal profile will help to maintain plenty of mainly shallow strato cu with sprinkles scattered across the central and nrn mtns. A few brief showers could drop a quick 0.01 or 0.02 of an inch, but that will be about the extent of it in the QPF dept until Thursday afternoon or night. The clouds should slowly break from west to east (but temporarily in some places) late this afternoon. High pressure will gradually build in from the Great Lakes Region late today and tonight, as the coolest air aloft shifts east of the CWA with llvl downsloping helping to dry out the boundary layer SE of the I-99/RT 220 corridor. Across the east, an inverted sfc trough/marine layer boundary will be located mainly to the east of the Susq Valley through early tonight, bringing with it a slight enhancement to llvl theta-e convergence and the chc for a brief/light shower in some spots. Skies should become mostly clear across the western mtns for most or all of the overnight, and clear out temporarily across the Central Mtns through around midnight. Afterward, the HRRR looks quite realistic is pushing a layer of 1-2kft agl stratus/stratocu wwd across the Susq Valley between 05-08Z Wed and reaching a KELZ to KUNV and KMRB line around or shortly before sunrise. Prior to the arrival of the low clouds, a 20-25F air/stream delta T will lead to patchy valley fog (mainly across nrn PA) where min temps will dip into the 50-55F range. Elsewhere, mins early Wednesday will upper 50s to lower 60s. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... High pressure will build over the region Wednesday, bringing clear to partly cloudy skies and dry conditions across the NW mtns and Laurel Highlands. There is some concern that whatever lower clouds spread wwd into the Susq Valley and Central Mtns may have a difficult time eroding through the morning hours under very light NE to SE breeze, and a stable llvl profile with subsidence aloft placing a lid on any appreciable vertical mixing. Something to watch closely, but not to jump into with both feet just yet. For now, we`ll play the middle road and have the morning clouds across the east transition into a mix of sun and sct-bkn flat strato cu for the afternoon across the Susq Valley and points east. Highs Wednesday will be slightly below normal across the eastern half of the CWA, and near normal across the Western Mtns. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... Increasing dual to multi-layer clouds advect east into the state later Wednesday night through Thursday morning with little more than some scattered and brief showers moving East to NE. Deep layer warm advection and a return to a notable higher PWAT airmass will occur in advance of a cold front and another upper trough headed our way from the Great Lakes region. Anomalous PWATs on a SW to NE axis will top out between 1.5-1.75 inches over the state Thursday afternoon and night before likely settling just south of the state on Friday. It appears that a highly anomalous North-Northeast flow in the sfc-850 mb layer may be sufficiently strong to push much of the precip (forming beneath the left exit region of a potent upper level speed max) to the southern half of PA. Precip chcs and QPF display a distinct north-south gradient for Friday from under 40 percent just NW of KBFD to over 70s percent in the far SE near or just north of the path of a 1002-1005 mb sfc low. Some 12Z model solutions linger the precip accompanying this wave of low pressure into the first part of Saturday as weak high pressure building over Lake Michigan (and the surge of drier air) may be too far west to nudge the baroclinic zone to our east. Conditions eventually dry out later Saturday and Saturday night as high pressure builds in. Sunday and Monday appear dry at this time. && .AVIATION /04Z WEDNESDAY THROUGH SUNDAY/... Lower clouds beginning to develop over norther tier airfields (KBFD and KIPT). As high pressure builds in from the west, shallow marine layer under lowering inversion will try and sneak lower stratus deck back to the west overnight. This lower stratus deck will likely bring MVFR to IFR conditions overnight into early Wednesday morning. Secondly, in central areas, scattered to clear skies exist at 04z...but radiational cooling, combined with light winds, will promote valley fog formation, with it`s own associated restrictions in visibility and low ceilings. Overall, certainty is increasing that low clouds and fog will manifest themselves overnight. Have bolstered low clouds and fog in the TAFs with this 04z issuance. Models rather insistent in these conditions developing as well. Morning clouds and fog will erode Wednesday morning, with VFR conditions expected by mid day Wednesday across the region. Numerous showers and scattered thunderstorms return for Thursday afternoon and night with the approach of another cold front. .OUTLOOK... Thu...VFR, but with restrictions developing in SHRA/TSRA. Fri...Scattered SHRA north with more numerous and heavier SHRA/TSRA across the south. Sat-Sun...No sig wx. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert/Martin SHORT TERM...Lambert LONG TERM...DeVoir/Lambert AVIATION...Jung
Area Forecast Discussion
National Weather Service Cheyenne WY
848 PM MDT Tue Jul 25 2017 .UPDATE... Issued at 848 PM MDT Tue Jul 25 2017 Evening GOES-R water vapor animation showed the center of the upper ridge over the south-central CONUS and upper low near the northern CA coast. Abundant mid/upper level subtropical moisture was streaming north-northeast across WY/CO/NE. A cold front was located from south-central WY to northwest NE and eastern SD. Regional radars indicated mostly light to moderate showers with isolated t-storms. Convection allowing models maintain this precipitation trend through most of the nighttime period. Also, moistening low level upslope flow north of the front will promote patchy fog and low ceilings later tonight into Wednesday morning, especially along and east of the Laramie Range. Zones were updated earlier this evening to lower t-storm coverage to isolated and tweak PoPs. && .SHORT TERM...(This evening through Wednesday) Issued at 147 PM MDT Tue Jul 25 2017 Thunderstorms will likely become more numerous across southeast WY and the western NE Panhandle over the next few hours w/the passage of a strong mid-level short wave tracking across southwest WY late this afternoon. GOES-16 Water Vapor satellite imagery shows plenty of monsoonal moisture spreading northeast from Utah and western CO on the back side of upper-level ridging anchored over the southern high plains. The GFS and NAM have been somewhat meager w/ coverage of storms this evening, but the HRRR has shown very strong run-to- run consistency with widespread showers/thunderstorms mainly after 21z. We lean toward the HRRR given the amount of available mid and high level moisture and dynamic support. Main hazards through this evening will be locally heavy rain w/ tall and skinny CAPEs, but a risk for strong/gusty winds is also there with stronger flow aloft and an inverted-V signature on forecast soundings. It appears that the overall threat for severe weather is low, but will need to pay close attention to the northern Panhandle w/ a surface low lifting northeast early this evening. This will likely enhance directional shear and lead to a ribbon of stronger instability with CAPES over 1500 J/kg courtesy of dew points in the mid 60s. If LCLs were just a bit lower, this would be a concern for a tornadic threat but the main concern appears to be hail if a discrete storm can form. Mode of storms will likely be too messy and disorganized to support any kind of substantial severe threat. Widespread precipitation in the next few hours will contribute to enhanced boundary layer moisture early Wednesday morning, so anticipate low stratus over the plains along with the possibility of some fog. Forecast soundings suggest this burning off by mid morning. For Wednesday, expect to see less storm coverage outside of the mountains with the upper-level ridge axis building into the CWA through the day. .LONG TERM...(Wednesday night through Tuesday) Issued at 230 PM MDT Tue Jul 25 2017 We maintain a fairly active pattern for afternoon and evening showers and thunderstorms Thursday and Friday as we remain under southwesterly monsoonal flow aloft. Friday would appear the most active for sheer coverage of storms east of the Laramie Range as a shortwave moves across the region. By Saturday, it would appear that upper ridging will be extending northward and pushes the deeper moisture to our southeast, so we will advertise a little less coverage of showers and thunderstorms over the weekend into next week. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 520 PM MDT Tue Jul 25 2017 Area of mostly showers should move northeast across much of the area this evening with some MVFR cigs and vsbys possible in the heavier ones. Surface front will move across the area this evening with a more moist upslope flow behind it likely producing widespread MVFR/IFR cigs and some fog east of the mtns late tonight into Weds morning before lifting. && .FIRE WEATHER... Issued at 147 PM MDT Tue Jul 25 2017 No fire weather concerns with widespread showers and thunderstorms likely this evening and overnight. Thunderstorms may produce gusty and erratic surface winds. Afternoon RH values should remain above 30 percent for most areas over the next several days. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ UPDATE...MAJ SHORT TERM...CLH LONG TERM...JG AVIATION...RE FIRE WEATHER...CLH
Area Forecast Discussion
National Weather Service Goodland KS
926 PM MDT Tue Jul 25 2017 .UPDATE... Issued at 922 PM MDT Tue Jul 25 2017 Just completed an update. Raised mins in the east. Guidance has been consistent in having the lows in those locations a few degrees warmer than currently forecast. Also adjusted winds to match the recent trend of a gust front moving across the area in advance of the incoming cold front. Hrrr caught this nicely and used that. Thunderstorm coverage and intensity has been decreasing. Model guidance has been poor and inconsistent with this, even the high resolution and rapidly updating output is not doing well. So will leave alone for now, and continue to watch trends. Still may trend down later. UPDATE Issued at 632 PM MDT Tue Jul 25 2017 Just completed an update to adjust pops. All scale of model output having difficulty as to where to pinpoint locations of thunderstorms. Majority of output emphasizes the west and especially northwest portion of the area. Current activity does support that. However, where the models are lacking and where the update had to be made through the rest of the night was for the convection over the south and west central portion and activity approaching from the southwest. The model catching the details the best right now, especially over and near our southern areas is the Nam. Using it and latest trends expanded pops further east faster and also farther east. Based on that also adjusted the qpf. && .SHORT TERM...(This afternoon through Wednesday) Issued at 1126 AM MDT Tue Jul 25 2017 17Z Water vapor imagery indicated large anticyclonic circulation centered over south central Colorado. Morning soundings indicated a large change in airmass qualities between KDDC and KDEN. KDEN sounding was primarily dry with steep (greater than 8 C/km) lapse rates off of the surface. KDDC was much more humid with PW values of 1.29 inch and a fairly deep moist layer, but with overall poor lapse rates between H7 and H5. At the surface, trough axis was draped across eastern Colorado with dewpoints in the mid and upper 60s to its east and dewpoints in the 50s to the west. Thunderstorm chances will be primary forecast concerns tonight and tomorrow, followed by magnitude of cool down behind cold front Wednesday. Various short range models show a lot of variance with respect to how afternoon and evening thunderstorms develop. Solutions vary from storms remaining near sfc trough to forming into large cluster and advancing across whole CWA. Starting to see cumulus development along trough which may shed some light on how storms will evolve. As cold front advances south tonight and short wave trough flattens ridge somewhat, expect storms to advance to the east and south with best coverage mainly along and north of Interstate 70 where large scale forcing and available instability most in line. Expect storms to diminish in the morning hours with the bulk of the morning and afternoon being dry across the area. Thunderstorm development will be heavily influenced by how much clearing and heating can occur. Should a low stratus deck maintain itself this will greatly diminish potential for any post frontal storms. Overall confidence high that temps will be around 15 degrees cooler than today in northwestern CWA, but confidence in frontal position lower to the south so not ready to dial down temps a lot in this area. .LONG TERM...(Wednesday night through Tuesday) Issued at 141 PM MDT Tue Jul 25 2017 Wednesday night-Thursday: As front pushes through the area, there will continue to be a a chance of storms and showers across our southern CWA. Model soundings are not that impressive on shear and CAPE, therefore, widespread severe weather is not expected at this time. Thursday should be dry with ridging aloft. Temps will be below normal Thursday with highs in the low to mid 80s and overnight lows in the upper 50s and low 60s. Friday-Tuesday: Upper level ridge amplifies over the Rockies placing us in strong NW flow aloft. Monsoonal moisture plume builds back into the area. A series of shortwaves should traverse the periphery of the ridging through the period. Will have chance of showers and thunderstorms each afternoon and evening. Saturday night into Sunday looks to have the best chance of precipitation. Models also hinting at a good amount of fog Sunday morning, but chose to leave out of the forecast at this time, since it was in the Day 5/6 period. Temperatures will be near normal for the time frame. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 544 PM MDT Tue Jul 25 2017 For Kgld, vfr conditions and south southeast winds are expected through mid evening. From 04z to 07z thunderstorms are expected to be near or affect the site. At this time chose to just have vcts because high resolution models are showing a variety of scenarios. There are currently storms to the west and north of the area. Will amend if storms become move certain. However, mvfr conditions will be possible with the stronger storms. Because of surface boundaries and outflow from storms the winds will be variable in direction from mid evening until mid morning tomorrow. A cold front will start moving through the area around 15z with sustained winds near 18 knots with gusts to near 26 knots. This and mvfr ceilings are expected until 20z. At that time vfr conditions and north winds near 15 knots are expected. For Kmck, at this time vfr conditions are expected through the entire period. south southeast winds near 15 knots with gusts to near 22 knots will decrease to 12 knots near sunset and will continue until the middle of the night. At this time it looks like thunderstorms will be near or affect the site from 05z until 08z. As with Kgld uncertainty is above average due to model differences so will have vcts during this time. This will also be the time period where mvfr conditions could occur and high variable winds due to outflow. Around 15z a cold front will also move through this site as north winds increase to near 15 knots with gusts to near 22 knots. This will continue until the end of the period. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...NONE. CO...NONE. NE...NONE. && $$ UPDATE...BULLER SHORT TERM...JRM LONG TERM...SME AVIATION...BULLER
Area Forecast Discussion
National Weather Service Elko NV
238 PM PDT Tue Jul 25 2017 .SYNOPSIS...The weather will remain active through the evening tonight. Some storms may be strong and could produce brief moderate to heavy rain. Drier air will start to move in tomorrow, bringing with it lessening storm chances. && .SHORT TERM...Tonight through Friday. Convective activity is getting a slow start this afternoon as high temperatures are cooler today than what they were yesterday. Many readings were about 7-10 degrees cooler and thus have delayed the convection. Storms are not moving too fast with 700-500mb speeds progged at around 5 knots or so. The showers and storms will continue to form through the afternoon and evening hours per the latest HRRR runs. In addition, we have seen some training storms in northern Nye county, and the possibility does exist further north. Still concerned about heavy rain on recently created burn scars. Based on these factors, will keep the flash flood watch going at this time. Overnight lows will be in the 50s for the most part. All model solutions are showing the closed upper level trough off the California coast slowly shifting to the northeast. There will continue to be a jet max over the northern parts of the forecast area. It looks like another active day across the region. Storm motions will be a little quicker at 10-15 knots. But precipitable water values are expected to be down slightly, with many locales coming in around 0.75 inches or so. The highest readings will be in the eastern spots along the border with Utah. High temperatures will be in the low to mid 90s. Winds will be light. Wednesday night into Thursday. The upper trough energy will shift east. Southwest flow will bring some drier air into the area, with precipitable water values decreasing to 0.66 to 0.75 inches. Will need to see how much drier air will be over the area. Have kept isolated showers and thunderstorms in the forecast as model solutions typically are too quick with removing the moisture. Highs will be in the low to mid 90s with light winds. Thursday night into Friday. Drier air continues to move into the area. Have limited thunderstorm coverage to isolated only. Afternoon highs will be in the low to mid 90s again. .LONG TERM...Friday night through next Tuesday. Upper ridge will gradually rebuild over the Great Basin this weekend into early next week. Lingering moisture and weak instability under this feature will result in a chance of isolated thunderstorms across portions of central and eastern NV each day. ECMWF is more aggressive and quicker to build a closed upper high right on top of Nevada by early next week which would lead to an overall hotter and drier solution. GFS has slowly rising heights through the weekend while bringing some monsoonal moisture back into southern and central parts of the state later Sunday into Monday. Eventually, the GFS does build a closed high back over southern California during the later half of next week while keeping some moisture in place over Nevada. Overall, will lean toward the GFS solution with above normal temperatures likely for the balance of next week. && .AVIATION...Scattered showers and thunderstorms will redevelop this afternoon around and en route of all TAF sites given available monsoonal moisture and instability. Scattered storms will persist through mid-evening before diminishing to pockets of light rain later this evening/overnight. Outflow winds over 30 knots, locally heavy heavy downpours and small hail along with reduced visibilities to at least MVFR are likely in the vicinity of stronger convective cells this afternoon and early evening. Cannot rule out the possibility of an isolated severe gust/wet microburst to 50 knots associated with a more intense descending storm core. AMD NOT SKED will continue for KWMC until further notice due to comms line issue. && .FIRE WEATHER...Scattered to numerous showers and thunderstorms will continue this evening across all zones. Some of these storms can produce brief heavy rain and strong gusty outflow winds. Localized flash flooding and strong to severe storms are still possible and remain the main threats. Additionally, awareness of recent burn scars for the potential of flash flooding and/or debris flows in and around recent burn scars is critical and will be monitored closely. This active pattern will diminish towards the end of the week. && .LKN WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch until 11 PM PDT this evening for Humboldt County-Northeastern Nye County-Northern Elko County-Northern Lander County and Northern Eureka County-Northwestern Nye County- Ruby Mountains/East Humboldt Range-South Central Elko County- Southeastern Elko County-Southern Lander County and Southern Eureka County-Southwestern Elko County-White Pine County. && $$ 86/95/95/86
Area Forecast Discussion...UPDATED
National Weather Service Reno NV
820 PM PDT Tue Jul 25 2017 .UPDATE... Storm coverage has diminished considerably as drier air aloft works into the Sierra and western NV. Storms were becoming lower topped with more rain than hail being reported. Thus some minor flooding is still possible with stronger isolated cells. We will be allowing the flash flood watch to expire on time as the threat for flash flooding is diminishing. Coverage is expected to remain isolated overnight across western NV and northeast CA with a new round firing Wednesday afternoon as afternoon heating gets going. The best chances will be across the Basin and Range and from northeast CA into northwest NV. Hohmann && .SYNOPSIS... Drier air will intrude Wednesday resulting in reduced coverage of thunderstorms, with dry weather expected Thursday through Saturday. Near average high temperatures rise to above average late in the week. && .PREVIOUS DISCUSSION... /Issued 115 PM PDT Tue Jul 25 2017/ SYNOPSIS... Thunderstorms have formed again today for northeast California and western Nevada. Stronger storms could bring strong winds, as well as heavy rain with localized flash flooding. Drier air intrudes Wednesday resulting in reduced coverage of thunderstorms, with dry weather expected Thursday through Saturday. Near average high temperatures rise to above average late in the week. SHORT TERM... Another day of thunderstorms is on tap with the greatest coverage this afternoon and evening expected to be from a Mono Lake-Pyramid Lake eastward and north of I-80 toward the Oregon border. Isolated coverage is possible in the eastern Sierra and western Nevada Sierra Front, but this is expected to move eastward through the afternoon. The greatest risks from storms today will once again be localized heavy rainfall and plentiful small hail, with strong outflow winds looking more likely than they did yesterday due to some drier air moving in aloft. With decent shear aloft, storms are likely to be organized which lends itself to stronger storm development. Heavy rainfall may cause flash flooding and debris flows, especially over recent burn scars and steeper terrain and a Flash Flood Watch remains in effect for portions of western Nevada. Despite the localized heavy rain, new fire starts due to lightning are always a possibility and the gusty/erratic outflow winds could cause rapid spread. Nocturnal convection is looking probable overnight, and coverage has been expanded in the forecast to include areas mainly east of a Susanville-Reno-White Mtn line. Instability remains elevated aloft and there is a passing upper wave to help add some forcing to the equation. The HRRR and NCAR ensembles are hinting at this scenario as well. PWATs remain high, which lessens the risk of a dry lightning outbreak (as is common with nocturnal events), however once again new fire starts could occur. The upper level low sitting off the California coast moves inland Wednesday into Thursday, bringing a drier airmass with it. This will lessen thunderstorm coverage, but isolated storms are still likely for Wednesday, with lessening chances heading into Thursday. -Dawn LONG TERM...Friday through Tuesday... High pressure begins to strengthen across the region going into the weekend bringing warming temperatures, with triple digit highs expected for valleys of western Nevada and upper 80s-low 90s for Sierra valleys. A few weak shortwaves approach the California coast Saturday and Sunday, with latest forecast models indicating one possibly strengthening by the end of the weekend. Typically this would bring drier southwest flow across the Sierra and extreme western Nevada while southerly flow across central and eastern Nevada advects modified monsoonal moisture northward. This would lead to greater thunderstorm chances from approximately Highway 395/Interstate 580 eastward for the weekend. Additional thunderstorms remain possible going into next week with temperatures continuing to be near to slightly above normal. -Dawn AVIATION... Concerns today include thunderstorms across the region in addition to smoke and haze from wildfires creating pockets of reduced visibility and terrain obscuration. The greatest thunderstorm coverage this afternoon and evening is expected to be from a Mono Lake-Pyramid Lake eastward and north of I- 80 toward the Oregon border. Isolated coverage is possible in the eastern Sierra and western Nevada Sierra Front, but this is expected to move eastward through the afternoon. Storms will bring localized heavy rainfall, creating short-lived periods of IFR CIGS/VIS and obscuring terrain. Abundant lightning, small hail, gusty and erratic winds, blowing dust, and turbulence are also concerns. Chances for a storm to affect a terminal site: KRNO/KCXP/KMMH: 20 percent KTRK/KTVL: 10 percent KNFL/KLOL/KSPZ/N58: 40 percent As far as the smoke and haze...the majority of it is from the Preacher Fire just east of Gardnerville, NV and the Detwiler fire in Mariposa County, CA. Smoke may be blown in erratic directions through the evening due to thunderstorm activity. -Dawn && .REV Watches/Warnings/Advisories... NV...None. CA...None. && $$ For more information from the National Weather Service visit...
Area Forecast Discussion
National Weather Service Blacksburg VA
703 PM EDT Tue Jul 25 2017 .SYNOPSIS... A weak front across northern North Carolina will shift south of the area tonight into Wednesday before dissipating. High pressure north of the region should continue to ridge south across the area through Wednesday night keeping overall dry weather in place. Another cold front approaches from the northwest Thursday into Friday exiting to our southeast by Saturday morning. && .NEAR TERM /THROUGH WEDNESDAY/... As of 702 PM EDT Tuesday...No major changes needed to the going forecast. Did make a few minor adjustments though. First was to remove isolated/slight chance PoPs for northern NC tonight as it appears that in surface METARs that the inverted trough axis has shifted southward. Visible satellite imagery trends imply that deeper cumulus development has been few and far between in this area where residual instability is the greatest (though is not significant). Also increased sky cover some for the after- midnight period east of the Blue Ridge into the foothills in VA/NC. Recent RAP and 18Z NAM/GFS guidance continue to show increased low-level RH/stratus as 2-m AGL to 850 mb flow becomes light easterly with passage of backdoor front to our northeast. Coverage may be somewhat greater in the southern Blue Ridge versus along the southern Shenandoah Valley. Outside of that though, forecast appears to be in good shape with counties west of the Blue Ridge likely to see sharply falling temps with sunset and areas of patchy fog in the New, Holston and Greenbrier River Valleys. Lows in the upper 50s to middle 60s appear on track, though if stratus comes in sooner than presently anticipated, possible that lows may need to be adjusted up some in late-evening update. Previous near-term discussion issued at 215 PM follows... Surface front has drifted farther south this afternoon with dry advection having pushed into northern North Carolina per latest dewpoints. This has basically shifted instability to the south of the CWA with only the far southwest currently holding onto a bit more of a cumulus field. Appears best chance at seeing any isolated showers will be across the North Carolina mountains where a weak inverted trough lingers and expect a little more convergence as winds start to turn more easterly by early evening. However not more than a 20 pop at best with clear skies elsewhere this evening. High pressure to the north shifts east overnight allowing a little deeper easterly trajectory to develop by morning. Some guidance again trying to bring low level moisture back into the Blue Ridge espcly far south where dewpoints should be a little higher. Think too dry elsewhere as models remain too moist, so running with mostly clear to partly cloudy overnight with patchy fog/stratus around. Should be quite comfortable overnight with low dewpoints and better radiational cooling under the high allowing temps to fall well into the 60s most spots, with even some 50s possible in the valleys. Will start to see low level moisture start to slowly rebound on Wednesday as the high to the north shifts farther east resulting in a gradual veering of the flow to a more southerly component later in the afternoon. This seen via model jump in dewpoints and northward shift in progged PWATs from south to north during the day. However instability remains lacking as well as upper forcing with any convection likely due to weak southeasterly flow convergence and orographics. This again mainly over the southwest with ridging holding across the north and east so trimmed pops back to only isolated/low chances mainly southern Blue Ridge. Otherwise expect any low clouds to mix out to more sunshine by afternoon with highs cooler, mostly upper 70s to mid 80s, within a lingering east- southeast flow until late. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... As of 205 PM EDT Tuesday... Surface high pressure will weaken Wednesday night into Thursday as a cold front approaches from the west. This front is stuck in zone flow and will slowly move from the upper Midwest Wednesday night to the Ohio Valley Thursday. This front will pick up speed, moving over the mountains early Friday morning, then east of the Blue Ridge Friday afternoon as an upper level low tracks across the Great Lakes. Diurnal heating and orographical lift should generate isolated to scattered showers and thunderstorms across the mountains early Thursday afternoon. These storms may slowly drift over the foothills towards evening. As the front approaches the mountains early Friday morning, the chance for wide spread showers will increase. Despite these showers coming in during non-diurnal heating, linger instabilities and a 30-40 knot low level jet could allow some strong storms to pass over the area overnight. The chances for showers and thunderstorms will move east of the Blue Ridge Friday morning, exiting the piedmont by sunset. The best dynamics with this front will remain north over Pennsylvania and Maryland Thursday night then along the New England coast Friday. For the forecast area, the severe weather outlook for Friday is marginal with scattered strong storms to possibly a few severe cells across the foothills and piedmont counties. If the front is slower by 6 or more hours, the severe threat could increase to slight as this would place the frontal passage during peaking heating Friday afternoon. Even if the timing is slower, the best dynamics will remain to the north. Temperatures will be slightly warmer than normal Thursday with low to mid 80s west of the Blue Ridge and upper 80s to lower 90s east. Friday will be a lot cooler across the mountains with morning showers and a frontal passage. High temperatures will range from the mid 70s to near 80F across the mountains. Temperatures will warm to near normal east of the Blue Ridge with afternoon temperatures in the mid 80s. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 240 PM EDT Tuesday... An upper level low will track from the Great Lakes Friday, then south over Virginia Saturday. Heating under this cold pool will bring scattered showers to the region Saturday afternoon. Temperatures will actually be cooler than normal for the first time since late June. Surface high pressure will build over the region starting Sunday. This ridge of high pressure will keep the area cool and dry into early next week. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... As of 702 PM EDT Tuesday... VFR through at least 06z Wednesday. Thereafter, potential for some degraded flight categories in two general areas: (1) In developing easterly stratus along and east of the Blue Ridge, affecting Lynchburg and the southern Blue Ridge after 06z. (2) MVFR to LIFR patchy river valley fog in the New and Greenbrier Valleys, affecting Lewisburg and Blacksburg between 09-12z. Confidence is moderate at best on stratus ceilings; expect at least BKN/OVC VFR which at times may drop to MVFR category. Indicated potential for lower ceilings as a SCT025 group. Confidence is higher on fog development and end time. If stratus ceilings develop as anticipated, they may linger until mid-morning. Light north winds become northeast 3-6 kts in the Piedmont and foothills, though become light and variable west of the Blue Ridge. For Wednesday, again some question on timing stratus scattering out but by 15z most areas should be VFR. Should see renewed VFR fair weather cumulus for the afternoon; recent guidance continues to show spotty showers later in the TAF period but feel these are overdone with large mid-level dry air in place. Thus will not mention in the TAF at this point. Winds mainly light east to southeast through Wednesday. Aviation Extended Discussion... Should start to see a front approaching with better threat of showers/thunderstorms Thursday into Friday. Outside of storms expect VFR conditions, with possible late night fog by Friday morning. Saturday looks drier with northwest flow, but could see lingering low end VFR/high end MVFR ceilings in SE WV along with a few added shra/tsra mainly southern sections Saturday afternoon. Expect widespread VFR to return Sunday under high pressure following the front. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...AL/JH SHORT TERM...RCS LONG TERM...RCS AVIATION...AL/JH