Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/23/20

Area Forecast Discussion
National Weather Service Bismarck ND
946 PM CDT Sat Aug 22 2020 .UPDATE... Issued at 944 PM CDT Sat Aug 22 2020 For late evening update have removed precipitation chances over the north since the only activity from the boundary, one little shower, quickly dissipated a few hours ago with nothing since then. High-res models have also backed off on the potential for precipitation. Otherwise, going forecast remains in good shape. UPDATE Issued at 636 PM CDT Sat Aug 22 2020 For early evening update have adjusted winds a bit, particularly over the northwest, with the approaching boundary pushing through far northeastern Montana. Have also added some very low precipitation chances over the north while this boundary pushes through. Only other change was to put areas of smoke through the CWA as satellite shows smoke has pushed almost across all of western and central North Dakota. Still unsure how much will make it to the surface, but well worth mentioning. && .SHORT TERM...(This evening through Sunday) Issued at 215 PM CDT Sat Aug 22 2020 This afternoon, a stationary front extended across north central North Dakota and will remain nearly in this location tonight. A cold front in Montana will move into western North Dakota tonight. This front will be initially dry, but should pick up some low chances for showers and thunderstorms along the front late tonight and Sunday. Sunday afternoon the front and associated baroclinic zone will be across south central ND into Northwest SD. The RAP13 continues to show low to mid level frontogenetic forcing increasing along the boundary Sunday afternoon and evening. This will be the focus for lift across southwest into central North Dakota Sunday afternoon and evening. While the shear remains moderate at 50 kts, the GFS boundary layer CAPE is still marginal at 500-1000. Current thinking is this will be sufficient for some widely scattered strong to isolated severe thunderstorms late in the afternoon and evening Sunday. Areas of smoke from the Montana and Colorado fires will become more prevalent across the west and central this afternoon and tonight. Initially the smoke will be aloft. We used the HRRR smoke model as an initial input for this. Lows tonight will be in the mid 50s to lower 60s. It should be cooler across the north on Sunday, with highs there around 80, to the lower 90s south. .LONG TERM...(Sunday night through Saturday) Issued at 215 PM CDT Sat Aug 22 2020 The broad features in the h500 pattern continue to persist, with a strong h500 upper high across the southwest US, with a band of moderate westerly flow over the top of the ridge into the northern plains. This will bring a above average convective pattern for the region though the period. Warm temperature will persist through midweek, followed by a cooling trend into the weekend as a shortwave trough finally moves through the ridge and forces it down. Wednesday may see a potential for severe weather, as the shear and cape are sufficient, as depicted by the GFS. However, the capping may still present an obstacle, especially central and east. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 636 PM CDT Sat Aug 22 2020 A few showers or thunderstorms will be possible overnight over northwest and north central North Dakota, but coverage is expected to be sparse if storms even do develop, so have refrained from mentioning in TAFS. Low chances for storms spread over most locations on Sunday, but again coverage is expected to be quite low and timing remains questionable, so have refrained from mentioning in the TAFS at this point. Smoke from western wildfires has spread across the area. So far no visibility restrictions have been noticed over North Dakota. Will continue to monitor observations and will amend if smoke results in visibility restrictions. && .BIS WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JJS SHORT TERM...WAA LONG TERM...WAA AVIATION...JJS
Area Forecast Discussion
National Weather Service Columbia SC
755 PM EDT Sat Aug 22 2020 .SYNOPSIS... An upper trough axis to our west will continue to bring deep moist southwesterly flow over the region today. An upper ridge over the western Atlantic will build into the area late in the weekend into early next week. Tropical Storm Laura is forecast to move into the Gulf of Mexico early next week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Mesoanalysis as of 23z shows a stable airmass remains in place over the area with only some light showers over the CSRA. Generally expect showers to decrease into the overnight as the upper trough to the west begins to lift into the Tennessee Valley while upper ridging over the Atlantic begins to build over coastal SC. Even with lingering moisture, expect conditions to remain mostly dry tonight, outside of some isolated light shower activity mainly in the south and southeast forecast area along weaknesses in the ridge and where moisture is higher. High level clouds will persist over most of the region through tonight with some patchy low stratus developing late tonight. Overnight lows once again in the upper 60s and low 70s. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... Sunday and Sunday Night: A weakening upper level trough to the west will lift into the Ohio valley, allowing the subtropical ridge to extend farther west across the region. As the ridge extends westward, channeled vorticity along the western periphery of the ridge will shift inland from the coast, likely acting as a trigger for showers and thunderstorms. Even to start the day, there could be some isolated showers along a weak surface trough, but expect the showers and thunderstorms to increase in coverage, becoming scattered during the afternoon and early evening. Lingering showers could persist into the overnight hours. Temperatures will remain slightly below normal, with highs in the upper 80s. Nighttime lows should be in the lower 70s, with a good deal of cloud cover expected. Monday and Monday Night: Ridging will strengthen over the area, but an onshore low level flow off the Atlantic will ensure an ample amount of moisture advects into the area, with precipitable water values rising upwards of 2.3 inches in some areas. The moisture and an active seabreeze will result in scattered to numerous showers and thunderstorms in the afternoon/evening, with the greatest coverage across the lower CSRA and eastern Midlands. Highs will be around 90 most areas. && .LONG TERM /TUESDAY THROUGH SATURDAY/... An upper level ridge digging across New England and part of the Mid- Atlantic will flatten the ridge some on Tuesday, but the ridge will restrengthen Wednesday and Thursday. Increased uncertainty for late week into the weekend as much of the synoptic weather pattern will depend on the eventual track of TS Laura. Best chances of rainfall appear to be on Tuesday as the ridge flattens, but more of a typical summertime pattern with diurnal scattered convection expected Wednesday into Thursday. Have maintained a forecast favored by climatology for late week given the uncertainty with Laura. Temperatures appear to rise above normal levels mid-late week. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... VFR conditions expected through most of the TAF period, although some restrictions possible Sunday morning with stratus and patchy fog possible. Ridge extending inland from offshore. Relatively deep moisture across the area in southwest flow aloft. Satellite indicating mainly mid and high level ceilings at the moment but some scattered lower strato-cumulus possible this evening. Showers in east central Ga appears to be dissipating near the CSRA and any showers should be limited overnight. Low-level moisture appears higher tonight which may result in stratus toward morning. With some clearing possible at times, there may be fog although some mixing possible in the boundary layer through at least 09z. HRRR model does not hit stratus too hard but lamp and mos suggesting at least a limited threat so including restrictions in a tempo group toward morning with lower ceiling and visibility to IFR at AGS. Light mainly south and southeast winds Sunday with increasing low to mid level moisture. Scattered showers mainly in the afternoon in weakly to moderately unstable air mass. EXTENDED AVIATION OUTLOOK...Scattered mainly diurnal shower and thunderstorm activity through the period. Patchy late night/early morning fog/stratus possible. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. && $$
Area Forecast Discussion
National Weather Service Des Moines IA
630 PM CDT Sat Aug 22 2020 ...Aviation Update... .DISCUSSION.../Tonight through Saturday/ Issued at 250 PM CDT Sat Aug 22 2020 The focus for the near-term is lingering convection this afternoon into the evening hours. Otherwise, the primary story is the long- duration heat next week with little relief until possibly Friday. This afternoon into tonight...weakening convection across the northeast where there is a little more deep moisture convergence present and very weak mid-level theta-e advection. MUCAPE values range from 2000-3000 J/kg but effective shear and lapse rates remain weak and as mentioned with the lack of significant forcing, expecting these storms to gradually wan into the early evening. The latest HRRR run does suggest a couple of isolated storm to trickle south and even possibly impact the DSM Metro, but much of the storm threat should diminish by 04-06z at the latest. Sunday through Thursday...It`s gonna be HOT! The saving grace during this time frame is the lower dew points than what is typical for late August. Thus, the extreme heat index values are not anticipated. Still can`t rule out the afternoon hours each day in a few locations getting close to 100 for a heat index, especially Monday with less mixing. Tuesday and Wednesday are forecast to be the hottest days, wrt temperatures. Good mixing each afternoon should help push temperatures well into the middle and upper 90s both afternoons. Other than the Des Moines Metro, there should be some overnight relief as lows barely dip into the upper 60s. The heat island effect looks to keep low temperatures in the 70s Tuesday night and Wednesday night and there might need a headline for the long duration heat for just the metro area. By Friday, models are in agreement with the upper ridge breaking down and conditions cooling off into next weekend. Precipitation chances however look fairly bleak as any significant moisture is being pinched off by the tropical remnants of Laura moving up through the Ohio Valley. Thus, unfortunately the drought conditions are likely to worsen/expand with this hot and dry week ahead. && .AVIATION.../For the 00Z TAFS through 00Z Sunday evening/ Issued at 627 PM CDT Sat Aug 22 2020 Prevailing VFR conditions generally expected at all sites, but could see some brief MVFR conditions around KFOD/KALO/KMCW through around 03z this evening with showers/storms in their vicinities. Otherwise light, variable to southerly/southwesterly, winds will be seen throughout the period. && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ DISCUSSION...Podrazik AVIATION...Curtis
Area Forecast Discussion
National Weather Service El Paso TX/Santa Teresa NM
604 PM MDT Sat Aug 22 2020 ...Updated for 00Z TAF Discussion... .AVIATION...00Z TAF CYCLE A pretty quiet evening so far. There are a few thunderstorms near KLSB moving west, but the short term models are indicating that once those storms move into Arizona, we will be done for the night. We could still see some gusty outflow winds affecting KDMN as those storm exit the region, but generally our winds tonight will be variable at less than 10 knots. We will see some high ceilings of BKN250 west of the Rio Grande, but east of the river we will have unlimited ceilings tonight. The skies west of the river will clear later tonight. Our weather pattern won`t change much, so tomorrow will be much like today, with just a slight chance for rain and our winds from the southeast at less than 10 knots. && .PREV DISCUSSION...235 PM MDT Sat Aug 22 2020... .SYNOPSIS... Scattered mountain and isolated storms will remain possible through Monday. On Tuesday and Wednesday, most locations will be dry with only the Gila wilderness seeing a chance for rain. By next weekend, the Sacramento mountains may see storm chances return as well. Temperatures will remain much above normal throughout the period, and most lowland locations will see zero rain. && .DISCUSSION... .SHORT TERM... Tonight and Sunday... Very little movement of upper high currently located over the Four Corners region through Sunday. Moisture over the area is currently deepest over the far west where dew points remain in the 55-60 degree range but will be mixing out into the 50-55 range by late afternoon. Decent disturbance should allow for isolated to scattered storms to develop by mid to late afternoon over the Gila with some surface convergence allowing for a few storms on the lowlands west of the Continental Divide for this evening. Less moisture and instability over the east so think isolated coverage is the best that can be expected there. Convection should be done by 06Z or earlier. Overnight lows look close to last night, maybe just a few degrees cooler out west where lows remained in the upper 60s to lower 70s. For Sunday, with little change in the pattern and an easterly low level continental trajectory, do not see much increase in storm activity although there will be a disturbance affecting the eastern zones in the afternoon and may get a couple storms to move onto the lowlands toward far west Texas which is what the longer range HRRR is indicating. High temperatures will be around 100 degrees for the lowlands but should remain a few degrees short of records. && 26 .LONG TERM... On Monday the upper-level high/ridge axis centered over the Four Corners will take on more of a NE-SW orientation, and this will cause flow aloft to take on more of an easterly component over our area. Dry air is upstream on this trajectory, so moisture will begin to exit. Thus, Monday looks to be the last day for lowland storms, perhaps, through the remainder of the period. Even then for Monday, coverage looks scattered for mountains and isolated for lowlands, at best. On Tuesday, enough dry air moves in that PWAT values drop well below one inch and instability drops to near zero. Even the Sacramento Mountains may struggle to see any convection though at least Wednesday. Enough moisture will linger over the Gila/Black range for isolated storms. The pattern will bring a couple of possible bright-spots. The reorientation of upper-level flow will allow temperatures to come down below 100 for the lowlands, and it may also give us a break from the smoke or at least a reduction in it. Forecast guidance diverges some beginning later Thursday. The GFS moves the high just enough to the north and west, aided by a weak tropical low (which may at least be partially attributed to Marco) to allow some recycled low-caliber monsoonal moisture to move back in across NM and far W TX. The high then shifts back overhead, but the GFS keeps moisture trapped beneath it. This would allow scattered mountain and isolated lowland storms back into the picture as soon as Thursday. The Euro does not move the high as much as the GFS and is quicker to bring it overhead. Moisture is not allowed to be trapped beneath it. In the Euro`s solution we would be hotter and drier than the GFS. Given how this summer has gone and neither pattern are really conducive for much rain, I kept pops out of the forecast for much of the lowlands Tuesday onwards with lowland highs back within a couple degrees of 100. && 34 .FIRE WEATHER... Upper high over the Four Corners region will move little through Monday with hot and dry conditions generally the story with just some isolated lowland and widely scattered mountain storms expected with greatest coverage next couple days. As the high moves shifts east by midweek, high temperatures will fall into the lower to mid 90s, but still remain above normal. Relative humidities through much of the week will remain in the teens to lower 20s lowlands with 20s and 30s mountains. Winds will not be a big concern except near thunderstorms. && 26 && .PRELIMINARY POINT TEMPS/POPS... El Paso 75 100 74 97 / 0 10 10 0 Sierra Blanca 72 95 65 91 / 0 0 0 0 Las Cruces 70 98 69 95 / 0 20 20 0 Alamogordo 71 99 68 96 / 0 20 20 10 Cloudcroft 46 75 50 73 / 20 40 20 30 Truth or Consequences 72 98 70 96 / 20 20 20 10 Silver City 66 90 65 91 / 30 40 20 20 Deming 69 100 69 98 / 20 20 20 0 Lordsburg 72 99 70 98 / 20 20 20 0 West El Paso Metro 75 103 76 100 / 0 10 10 0 Dell City 69 100 67 96 / 0 10 10 0 Fort Hancock 72 102 71 98 / 0 0 0 0 Loma Linda 73 94 70 91 / 0 20 10 0 Fabens 74 100 74 97 / 0 0 0 0 Santa Teresa 71 100 71 97 / 0 10 10 0 White Sands HQ 72 100 71 96 / 0 20 20 0 Jornada Range 67 98 69 96 / 10 20 20 0 Hatch 71 100 69 97 / 10 20 20 0 Columbus 73 101 71 99 / 20 10 10 0 Orogrande 72 99 69 96 / 0 20 20 0 Mayhill 54 88 56 83 / 10 40 20 30 Mescalero 52 87 55 83 / 10 40 20 30 Timberon 52 85 54 81 / 10 30 20 20 Winston 57 91 57 89 / 20 40 20 30 Hillsboro 67 96 64 96 / 20 30 20 20 Spaceport 66 98 68 96 / 10 20 20 0 Lake Roberts 54 92 57 90 / 30 40 20 30 Hurley 66 93 64 93 / 20 30 20 10 Cliff 62 98 64 97 / 30 40 20 30 Mule Creek 58 94 66 93 / 30 40 20 30 Faywood 65 95 66 93 / 20 30 20 10 Animas 67 100 67 100 / 20 20 20 0 Hachita 68 99 66 97 / 20 20 20 0 Antelope Wells 67 98 66 96 / 20 20 10 0 Cloverdale 66 93 66 92 / 30 20 10 0 && .EPZ WATCHES/WARNINGS/ADVISORIES... NM...None. TX...None. && $$ 99/99/15
Area Forecast Discussion
National Weather Service Elko NV
237 PM PDT Sat Aug 22 2020 .SYNOPSIS...Haze and areas of smoke will continue into Sunday, especially in northern Nevada. Temperatures will remain much above normal this weekend and through next week. Tropical moisture will increase Sunday from the south and make its way northward on Monday and Tuesday, bringing the chance for Thunderstorms to the region. && .SHORT TERM...Today through Monday High pressure centered over the four corners region will lead to continued southwesterly flow aloft across northern and central NV through Sunday morning. This will mean ongoing hazy or smokey conditions in NV due to the wildfires burning in California. A Smoke Advisory remains in effect through Sunday morning for northwestern counties, with lowest visibility expected to continue there. There will start to be a wind shift more from the south on Sunday in central Nevada, which will cut off the transport of smoke to that area leaving the thicker haze to be more limited to northern Nevada by Sunday afternoon. There will also be a gradual push of mid-level moisture and weak instability spreading up into portions of central NV this afternoon and evening, then over most of central and portions of northern NV on Sunday. Any thunderstorms that may develop this afternoon and evening should be very limited, and centered over the southern portions of NE Nye County and in White Pine County in the Great Basin National Park region. Today being the initial push of moisture, not expecting much if any precipitation to reach the ground in any cells that may develop. Latest guidance continues to show the ongoing surge of moisture and instability to be gradual. By Sunday, mainly isolated thunderstorms will form in central Nevada and in southern sections of Northern Nevada, though there could be some pockets of a mix of wet and dry scattered thunderstorms around Hwy 50 and south. There looks to be enough instability to perhaps fire off a few strong storms there as well. Some showers may linger into the nighttime hours overnight on Sunday and lasting into Monday morning with perhaps a few lightning strikes. The moisture is expected to make its way northward into northern Nevada on Monday. There will be an area of isolated to scattered mix of wet and dry storms from around Elko County southwestward into Eureka and Lander counties. Outside of this area looks to mainly be isolated drier storms. As for temperatures, analysis indicates that the smoke is shielding the high temperatures just a little bit from reaching the NBM highs and therefore highs were dropped a degree or two for this afternoon and Sunday afternoon. Regardless, temperatures are still well above normal. .LONG TERM...Monday night through Saturday Upper ridging extends out to a good portion of the CONUS at the start of the long term period. Overnight Monday into Tuesday morning some nocturnal convection is possible once again. Isolated thunderstorms are expected once again on Tuesday afternoon and evening as tropical moisture persists, with the focus on eastern Nevada, with a few strong storms possible in northeastern Elko County. Troffing in the Pacific northwest on Wednesday looks to begin moving onshore and flattens the ridge some on Wednesday night through Thursday night as it quickly moves eastward across the northern CONUS. Thunderstorm coverage wanes on Wednesday and Thursday, though some isolated mainly dry thunderstorms will still be possible in eastern Nevada. On Friday and Saturday, the ridge could rebuild some, though likely only temporarily as a deeper and cooler Low looks poised to move into the West the following week. Isolated thunderstorms are once again possible for eastern nevada Friday, then all moisture may shift east of the area for Saturday. While cloud cover on Tuesday and Wednesday should damper high temperatures a little on Tuesday and Wednesday, much above normal temperatures persist, with highs mainly in the 90`s throughout the long term period. && .AVIATION... Smoke continues to stream across northern Nevada with the lowest visibility observed at KWMC at less than 2 miles earlier in the day. Trends offered by the vertically integrated smoke and visibility per HRRR model do not show any hints of improvement, particularly northwest Nevada and KWMC. Smoke will be thick enough with periods of IFR possible at KWMC. The smoke is less dense at KBAM and KEKO, but prevailing visibility is likely to stay in the 3-5 SM range. KTPH has better visibility but periods of MVFR Vis may still occur. KELY is the farthest from the smoke source and should stay VFR. By late Sunday afternoon, a few thunderstorms could be in the vicinity of KELY that generate erratic gusty winds. && .FIRE WEATHER... Dry and stable air mass today means no convection this afternoon. This changes Sunday as higher level moisture increases over central Nevada with the best chance for storms over the higher terrain surrounding Ely, or zone 425. Monday, moisture spreads over northern Nevada with an ejecting Pacific short wave to enhance convection. Possible that a few late afternoon convection may persist after sunset. Isolated cells may generate brief showers, but most storms will be dry or do not produce any significant rainfall. Tuesday, dew point values do rise into the 40s in the morning meaning higher humidity values, supporting an environment for mixed dry and wet storms. Will need to make another assessment on lightning potential for Monday and Tuesday and whether fire weather hazards exist, but confidence is lacking today on the areal extent of lightning potential. && .LKN WATCHES/WARNINGS/ADVISORIES... Dense Smoke Advisory until 9 AM PDT Sunday for Humboldt County- Northern Lander County and Northern Eureka County-Southern Lander County and Southern Eureka County. && $$ 90/90/88/88
Area Forecast Discussion
National Weather Service Marquette MI
633 PM EDT Sat Aug 22 2020 .SHORT TERM...(This evening through Sunday) Issued at 414 PM EDT SAT AUG 22 2020 Water vapor imagery and RAP analysis show a shortwave trof moving over the the western Great Lakes. This trof is largely made up of a well-defined MCV that spun up from convection in MN last night. Center of this MCV is currently located w of KGRB, and it is slowly moving ene toward far northern Lake MI. Plenty of cloud cover has kept instability from building much this aftn ahead of this feature. Latest SPC mesoanalysis has MLCAPE under 500j/kg underneath and directly downstream of the feature. In the last couple of hrs, shra have been developing/expanding near the center of the MCV, though no lightning has been detected yet. Farther upstream, greater instability w of Upper MI combined with subtle shortwave has been supporting sct tsra from near KDLH sse along the backside of the MCV. MCV will move ene toward the Straits/far eastern Upper MI tonight. Expect shra, and eventually some thunder, to continue increasing in coverage around the MCV over the next few hrs. Given the expected track of the feature, greatest coverage of shra/tsra will occur across the e half of the fcst area, especially Menominee County out to Luce County. Some breaks in the clouds are forming over western Upper MI. So, some increase in instability combined with weak upstream shortwave may support isold/sct shra/tsra development there into the evening. At the moment, not expecting any svr storms this evening given shear under 25kt and instability on the lower side. There is a pocket of shear up to 35kt noted over Menominee County toward Manistique. If for some reason clouds break for a time over the next couple of hrs (looks doubtful), there could be a svr risk in that area. During the night, pcpn will diminish/end from w to e. Conditions should be favorable for fog/stratus to develop overnight. Fog could become locally dense. Expect fog/stratus to lift during Sun morning. During the day, height rises in the wake of the shortwave trof should offer a drier day. However, weak pres gradient will allow lake breeze development. With low-level air mass not drying out, fcst soundings suggest there may be enough moisture for parcels to slip past a weak cap, if present, per some fcst soundings. Thus, fcst will reflect isold to sct aftn convection over the w half ahead of the Lake Superior lake breeze. Fcst soundings suggest less potential for convection over the e, but converging lake breezes over the interior could spark isold convection. Expect high temps mostly in the 75-80F range. Will be slightly cooler lakeside. .LONG TERM...(Sunday night through Saturday) Issued at 338 PM EDT SAT AUG 22 2020 The upper level pattern of persistent ridging over the western CONUS and the western Atlantic will continue this week, allowing for a period of more zonal flow to establish itself over the northern CONUS. A parade of shortwaves will move through the Upper Great Lakes within this flow as these large synoptic features vary in strength and position. By the end of the week, troughing looks to reestablish itself southward out of an upper level low over Hudson Bay. This overall pattern will give the region multiple opportunities of showers and thunderstorms this week as well as near normal to above normal temperatures most days. As the omega pattern develops early this weekend, expect cooler temperatures. Beginning Sunday night, a shortwave and warm front north of Lake Superior may bring some showers parts of Lake Superior late, but overall, Upper Michigan looks dry. Expect lows to be in the low and mid 60s. Some upper 50s could be seen in the traditional cooler spots of the interior. Monday into Monday night, a weak shortwave and surface cold front will move into the west early and continue east through the day and evening. Models vary on the evolution of precip and have dialed back on precip potential ahead of the front. Given the model`s pulling back some, limited PoPs to chance and slight chance. Guidance is still queuing in on 1000-2000 j/kg MLCAPE coupled with 30-40kts of deep layer sheer though, so if showers do develop, there is will be a chance for some organized thunderstorms, mainly across the south- central and east. Inverted V and steep mid-level lapse rates suggest both large hail and gusty winds could be possible if an organized updraft develops. Guidance also suggests PWATs above 1.5 inches, which coupled with favorable MBE velocities, could lead to some training and localized flooding in any organized thunderstorms. Some guidance is suggesting that as the front exits, its east-west elongation may allow for some additional showers early on Tuesday in the south, but confidence is low. High pressure will build in across Ontario behind the front as upper level ridging shifts eastward across the northern Plains. With the exception of any morning showers associated with the lingering front, Tuesday looks to be mostly dry for Upper Michigan under increasing heights. Expect highs in the 70s. Tuesday night, another shortwave looks to ride the top of the upper level ridge, bringing the region another shot for showers and thunderstorms early on. At the moment, the timing of the wave in the region looks like it could outrun its instability before reaching the forecast area, but will still be accompanied by a good amount of deep shear, suggesting that much of the impacts across the forecast area will largely depend on upstream development. Wednesday, warm front lifting through the region could again lead to the development of some strong to severe thunderstorms. Another shortwave could lead to more showers and storms Thursday. On Friday, as upper level troughing begins to establish itself over eastern North America, guidance is suggesting a deepening clipper moving through Ontario, with potential phasing resulting in cyclogenesis over the Upper Great Lakes. Details about this evolution are still uncertain, including phasing with another system to the south or any tropical system contributions into this development. Model consensus does highlight the CAA on the lee side of the low, allowing for a period of northerly flow and cooler temperatures for the weekend. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 633 PM EDT SAT AUG 22 2020 Combination of a stalled frontal boundary and a disturbance moving ene from WI will result in shra and some tsra developing this evening. Expect KSAW to be most directly impacted with KCMX least likely to see any shra. VFR conditions should generally prevail into this evening at all sites. At KIWD, MVFR cigs should largely be the rule. Fog and stratus are likely to develop tonight, leading to deteriorating conditions to IFR at all terminals. Slow improvement expected Sun morning. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 414 PM EDT SAT AUG 22 2020 With a weak pressure gradient over the area thru Sun, winds across Lake Superior will remain mostly under 15kt. Winds should then be mostly under 20kt Mon thru midweek. A humid air mass over the area combined with some showers moving across the lake will lead to some fog patches tonight and Sun. The fog could be locally dense. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...Rolfson LONG TERM...JP AVIATION...07 MARINE...Rolfson
National Weather Service Morristown TN
913 PM EDT Sat Aug 22 2020 .UPDATE... EVENING UPDATE. && .DISCUSSION... An upper trough axis will remain just west of the region through the next 24 hours. Weak waves will rotate around this trough enhancing areas of isentropic lift but overall activity will mainly be diurnal in nature as dynamics are limited. Scattered showers and isolated thunderstorms will slowly diminish overnight. Main question is how much cloud cover will remain. If enough breaks in the clouds occur, greater likeihood of low cloud/fog development. Will continue with patchy/areas of fog across the region given the recent rains, wet soils and calm winds. Made some minor changes to forecast lows and hourly temperatures. && .AVIATION... 00Z TAF DISCUSSION. Main concerns through the forecast period are mainly diurnal convection from now through 03Z and again mainly late morning through the afternoon Sunday. Also, potential of low cloud and fog development producing IFR and possibly LIFR conditions mainly at TRI and TYS between 08-13Z. An upper trough axis across Kentucky and Tennessee will remain producing periods of mainly diurnal showers and storms. Winds will decouple this evening but return of south to southwest winds of 5 to 10kts expected Sunday. && .PREV DISCUSSION... /ISSUED 319 PM EDT Sat Aug 22 2020/ SHORT TERM...(Tonight and Sunday)... The H70-H50 wave that has persisted across the Tennessee valley continues to slowly move north into the Ohio valley this afternoon. Most of the convection this morning and early afternoon has remained well to the north across the Ohio river where a weak theta-e axis developed. While synoptic scale lift should be maintained across the area today, the lack of SHRA/TSRA coverage across the local area can likely be explained by very poor lapse rates and slight mid- level warming. The boundary layer does continue to destabilize this afternoon with a couple thousand j/kg of CAPE. Differential heating should be enough to maintain isolated to scattered convection across the higher terrain. This activity will have a northerly forward motion. Strong to severe chances look very low today as the better shear exists to the east of the area associated with slightly stronger southerly mid level flow. Overnight, showers and thunderstorms will likely continue with some uncertainty regarding the coverage. The NAM and RAP continue to favor precipitation across the area just downstream of the H70-H50 shortwave an environment of mid-level PVA and weak isentropic ascent on the 310-315K surfaces. Hi-res CAMs also feature isolated SHRA overnight but coverage is much less impressive. Will continue to favor PoPs overnight with a decreasing trend. Some heavy rainfall and isolated flash flooding is a possibility given increasing 0-2km moisture flux convergence...although PW values are not overly impressive and some drier air aloft will exist. Will leave out the mention of heavy rainfall and isolated flash flooding as coverage is uncertain. Lows will drop into the mid 60s to near 70 degrees. Will not see many changes to the synoptic pattern on Sunday as the H70-H50 shortwave continues to slowly move through the Tennessee valley. Continued moisture advection in southwest flow aloft combined with synoptic scale ascent will bring another day of showers and thunderstorms to the area. Weak lapse rates and warming aloft should limit any strong or severe thunderstorm chances. Only hazard would be additional heavy rainfall and possibly flash flooding as PW values remain elevated. Highs on Sunday will rise into the upper 70s to mid 80s still several degrees below average. Again, the low probability of hazardous weather will preclude the mention of any hazards in the HWO. Diegan LONG TERM...(Sunday night through Saturday night)... The extended begins with weak troughing across the Tennessee and Ohio Valleys between two large anticyclones across the Mountain West and the western North Atlantic. TC Marco will be nearing landfall across the Gulf Coast on Monday before slowing and dissipating across the lower Mississippi Valley on Tuesday with very high PW values remaining near the remnant system. An old/remnant moisture boundary across SC/GA/AL will be a focus for low-level convergence and diurnal thunderstorm development. There is some uncertainty in the exact location of this boundary, but with it generally being near or south of the forecast area, PoPs will be highest across our southern zones with a diurnal trend in probs and coverage each day. With this general summer-like pattern, kept temperatures near or slightly above normal. Late in the extended, uncertainty is high. Much depends on the tracks of TC Marco and TC Laura. Landfalling tropical systems across the norther Gulf Coast occasionally impact the Tennessee Valley and Southern Appalachians with remnant heavy rainfall and breezy conditions. Current global model guidance is coming into better agreement with TC Laura approaching the northern Gulf Coast by Wednesday and then moving northward through the Mississippi Valley. The remnants of Laura would then merge with a shortwave trough and amplify troughing across the Eastern CONUS. This scenario would bring abundant moisture into our forecast area ahead of a surface cold front moving southeast on Friday and Saturday with the potential for locally heavy excessive rainfall. However, QPF and PoPs will be highly dependent on the remnant tracks of TC Laura and the TC Marco. Guidance is beginning to include likely PoPs on Friday and Saturday, but with the uncertainty of tropical system tracks 5 to 7 days out, did not include any higher than high chance PoPs at this time. If better run to run consistency develops over the next 24 hours, PoPs could be trended higher late week in future forecast issuances. JB && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 70 86 70 88 72 / 40 40 20 40 20 Knoxville McGhee Tyson Airport, TN 68 85 68 87 70 / 40 40 20 30 10 Oak Ridge, TN 68 85 68 88 69 / 40 40 20 30 10 Tri Cities Airport, TN 64 84 66 85 66 / 40 40 20 30 10 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$