Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/26/20

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
803 PM CDT Tue Aug 25 2020 .UPDATE... Issued at 802 PM CDT Tue Aug 25 2020 No major changes for the overnight period. HRRR continues to advertise isolated late night activity with LLJ, so will keep that going. Otherwise, temperatures/winds look fine. && .SHORT TERM...(This Evening through Wednesday Night) Issued at 304 PM CDT Tue Aug 25 2020 Forecast challenges include temperatures throughout the period, along with thunder chances early Wednesday morning through Wednesday night. Currently, under a sunny sky, temperatures are warming into the 90s to near 100 degrees south of a warm frontal boundary moving up through the forecast area. Once in the hot muggy air south of the boundary, winds are switching from an easterly component wind to more of a south-southeasterly component wind. With such warm air aloft over the CWA this afternoon through late tonight, the expectation is dry weather conditions will prevail. There is a cold front moving out of Montana/Wyoming this afternoon. It will overtake this warm front advancing northward overnight, while slowly making eastward progress across the Dakotas. Isolated/widely scattered thunderstorms late tonight across mainly north central South Dakota are still a rather low confidence and low probability of occurring prospect. But, there should be a fairly decent belt of mid/upper level westerlies just off to the north/west in the morning. And, models are hinting at the possibility of seeing 700hpa temps cool a degree or two down to around +12C to +13C across western/northern South Dakota heading towards 12Z Wednesday. Forcing/lift and a little bit of cooling aloft may be all that`s needed to set off a handful of elevated showers/storms by morning. Thermometers tonight reading close to 70F degrees puts the CWA at appx 15 degrees above normal for low temperatures. A warm/humid late August night for sure. The gradual cooling trend aloft continues throughout the day Wednesday and Wednesday night. Models do all agree on a few pockets of convective potential, mainly associated with forcing from this cold frontal passage that is progged to be ongoing on Wednesday, along with the lift associated with any subtle s/w`s rotating up out of the desert southwest in this latest rendition of monsoonal flow up into the northern plains. But, they don`t agree on placement or timing of those pockets of convection, so forecast confidence (and pops) remain on the low side during the day Wednesday and Wednesday night. At this point, models indicate there should be enough instability/shear around Wednesday afternoon/evening to support a few strong to possibly severe thunderstorms, should any storms actually develop. Low level thermal progs suggest there will be a portion of forecast zones over the eastern CWA that could warm back up to around 90F degrees or so, prior to fropa. Locations that end up warming up, post-frontal, on Wednesday should notice things becoming a bit cooler/drier by the end of the day. Overall though, high and low temperatures Wednesday and Wednesday night will probably end up being a good 5 to 10 degrees above climo normal. .LONG TERM...(Thursday through Tuesday) Issued at 304 PM CDT Tue Aug 25 2020 The main focus in this period will be on convective chances followed by a fairly noticeable cool down by the end of the term. Sfc high pressure will be sliding northeast of our area on Thursday as sfc low pressure organizes to our west. These features progress eastward during the day into Thursday night. Some ongoing convection will perhaps be moving across the region early Thursday in association with some mid lvl s/w energy. However, better chances for convection look to hold off until later in the day into the nighttime hours as shear and instability become more favorable(especially southern half of this CWA). These indices combined with a frontal boundary passage and mid lvl s/w trough could potentially lead to a round of strong to severe storms for portions of this forecast area Thursday night. This activity is progged to be clear of the area Friday morning as sfc high pressure begins to move in. This should deliver a more comfortable airmass to the region along with slightly cooler conditions. This respite from the active, hot weather will spill over into the first half of the weekend as the high drifts over the area and eastward. Southerly flow returns by Sunday as low lvl moisture works northward ahead of the next low pressure system that is forecast to be sliding into the western Dakotas. Storm chances will be on the increase by Sunday, but moreso by Sunday night into Monday. Model consensus remains up in the air with the timing and intensity of this system. The broadbrush of PoPs will remain in the forecast for this time, but enough agreement points to the latter half of Sunday through the first half of Monday being the best window for precip chances at this point. Once this system departs early next week, models do agree the region will see a much cooler airmass take hold. Temperatures will start off the period above normal with highs in the 80s to around 90 on Thursday. Slightly cooler conditions return behind the departing system Friday into Saturday with temperatures about normal for late August. Above normal readings return briefly on Sunday with highs back into the 80s to around 90 degrees. The more noticeable change arrives early next week as daytime highs look to remain in the low-mid 70s and overnight lows fall into the 50s, perhaps a few upper 40s by Tuesday morning. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening) Issued at 617 PM CDT Tue Aug 25 2020 Terminals KABR,KATY,KPIR,KMBG Mainly VFR skies/vsbys are expected through tonight at all terminals. ***Construction to improve taxiways at both KABR/KPIR terminals may cause an occasional temporary visibility reduction due to blowing dust (bldu), mainly during daytime hours UFN. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ UPDATE...TDK SHORT TERM...Dorn LONG TERM...Vipond AVIATION...TDK
Area Forecast Discussion
National Weather Service Denver/Boulder CO
851 PM MDT Tue Aug 25 2020 .UPDATE... Issued at 850 PM MDT Tue Aug 25 2020 Several outflow boundary interactions over the metro areas and plains ended up sparking scattered showers and thunderstorms this evening, with some strong outflow gusts of 35 to 50 mph. Extended the chance for showers and thunderstorms further east as the outflows have lined up just right to provide extra lift into eastern Adams, eastern Arapahoe and Washington counties. Most convective activity is decreasing now, with diminishment expected by midnight. Though wouldn`t be surprised to see a few weak showers last for a couple hours after that over the northern mountains and Cheyenne Ridge based on a slight disturbance seen in water vapor imagery moving across Wyoming, as well as model forecasted CAPEs. No other forecast updates needed at this time. && .SHORT TERM...(This evening through Wednesday) Issued at 141 PM MDT Tue Aug 25 2020 The upper level ridge is near the Four Corners region this afternoon with a weak westerly flow aloft. Weak flow coupled with a slight increase in precipitable water values over the mountains. One storm near Glen Haven in Larimer County produced 0.55 inch of rain in 30 minutes, so better rainfall potential with the storms that do develop. The HRRR still shows some weaker showers and storms developing along the urban corridor and adjacent plains through this evening, then tapering off by midnight. Late tonight into Wednesday morning, a shortwave trough will pass from the central Rockies into western South Dakota. This will nudge the ridge more to the southeast on Wednesday. This will allow for a slightly stronger westerly flow in the mid and upper levels. In addition, the models bring in a push of north to northeast winds Wednesday morning that stick around in the afternoon. Temperatures still hot on Wednesday, but there should be a gradual increase in dewpoints over the northeast plains in the afternoon. The models still show precipitable water values increase across the forecast area on Wednesday, 0.75 inch in the mountains, at or above 1.0 inch over the northeast plains. Best shower/thunderstorm coverage will be over the mountain areas in the afternoon, spreading across the urban corridor and northeast plains after 21z. ML CAPE/MU CAPES 500-1000 j/kg in the afternoon across the urban corridor/northeast plains from the NAM12 forecast soundings. In the mountains, values similar to this afternoon with drier air below 600 mb. Main issues will be gusty winds with the stronger storms but there will be a better potential for wetting rainfall. .LONG TERM...(Wednesday night through Tuesday) Issued at 141 PM MDT Tue Aug 25 2020 Models still show the ridge which has dominated the area recently weakening some on Wednesday and Thursday. Precipitable water values are showing slight drying of the high terrain on Thursday, which should limit convection. Highs should remain in the mid 90s in the foothills and on the plains. Friday, a front is expected to bring temperatures down to more seasonable levels across the area, with highs in the low or mid 80s in the metro area. While precipitable water and dew points don`t increase much, the decrease in temperature should significantly increase humidity, especially on the plains. A small, upper-level disturbance should also contribute to showers and storms in the afternoon and evening. Saturday, the flow aloft should turn to west-northwest with southerly surface flow and an increase in moisture. In the evening, MLCAPE may exceed 1500 J/kg on the eastern plains and scattered storms can be expected. Sunday should see drying and much less storm coverage. Monday and Tuesday, both the GFS and ECMWF show strong troughing across the area, with northwest flow aloft with an approaching jet late Tuesday into early Wednesday. MOS show highs in the mid or upper 70s in the foothills and plains. Along with an expected increase in moisture, this situation should bring some storms. The latest ECMWF shows a cutoff low developing all the way into the far southwest and the GFS shows a more relaxed trough through the plains, and the solution is expected somewhere between. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 850 PM MDT Tue Aug 25 2020 Areas of smoke/haze with poor slant visibilities will continue to be the primary aviation impact through the next 24 hours. Surface visibilities may drop to 6 miles at times, but VFR conditions will prevail. Most shower/storm activity is done for the terminals, however decaying showers just SSE of DEN is pushing strong outflow winds into DEN and APA. These should calm down over the next hour with surface winds shifting to drainage. Expect north/northeast winds to push into the terminals after 15z Wednesday and continue from that direction into the afternoon. Should see a better chance of showers/thunderstorms Wednesday afternoon. && .FIRE WEATHER... Issued at 141 PM MDT Tue Aug 25 2020 Slow moving showers and thunderstorms developing in the mountains and foothills this afternoon with the potential of producing gusty winds but also wetting rainfall. A site near Glen Haven picked up 0.55 inches in 30 minutes earlier this afternoon. More of the same type of weather is expected to occur on Wednesday afternoon, although the winds in the mid and upper level may be a little stronger from the west. Overall precipitable water values should remain high enough to produce wetting rainfall, but strong gusty outflow winds to 40 mph as well. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Kriederman SHORT TERM...Cooper LONG TERM...Direnzo AVIATION...Cooper/Kriederman FIRE WEATHER...Cooper
Area Forecast Discussion
National Weather Service Medford OR
737 PM PDT Tue Aug 25 2020 .DISCUSSION...Isolated showers and thunderstorms east of the Cascades earlier this evening are mostly dwindling over the past 30 minutes or so and will probably fizzle around or shortly after 8 pm. The most CG lightning occurred in Modoc County this evening with almost 30 flashes SE of Alturas. That was in addition to the 50 or so flashes that occurred across northern Klamath/Lake Counties earlier in the day. Have adjusted the grids to account for the diminishing trends on satellite/radar. Smoke/haze cover a large area from Siskiyou County northeastward, but conditions have noticeably improved here in the Rogue Valley this evening as north to northwest up-valley breezes helped scour out some of the lower- level smoke. We`ll maintain the haze though as high-level smoke continues to lift northeastward from the fires to the south and southwest. It`s clear along the coast currently, but we expect some stratus/fog to return to those areas overnight into Wednesday morning. Other than that and the isolated showers/storms this evening, tonight should be tranquil. Wednesday will be a repeat of today with isolated storms forming again east of the Cascades in the afternoon. That part of the forecast looks to be in good shape. -Spilde && .AVIATION...For the 26/00 TAFs...Over the coastal waters and along the coast...Areas of IFR cigs/vsbys in low clouds and fog will spread south into the waters around 03Z this evening, then soon after will move onshore into the Coquille Valley. These lower ceilings will dissipate after 16Z Wednesday morning. Inland areas west of the Cascades in Oregon...VFR conditions will prevail into Wednesday afternoon, but there will be areas of smoke and haze. Northern California and east of the Cascades...VFR conditions will prevail into Wednesday afternoon, except for areas of MVFR vsbys in wildfire smoke. There will be isolated thunderstorms this evening and again Wednesday afternoon into the evening. && .MARINE...Updated 730 PM PDT Tuesday 25 August 2020....A thermal trough will persist near the coast through the week. This will bring gusty north winds and steep to very steep seas with the strongest winds and highest seas south of Cape Blanco. Winds and seas will become more hazardous from Wednesday into the weekend with gale force winds likely south of Cape Blanco and strongest south of Ophir. All areas will remain hazardous for small craft through this time. && .PREV DISCUSSION... /Issued 223 PM PDT Tue Aug 25 2020/ DISCUSSION...As of 2 PM, a few showers are making their way northeast over northern Lake County, and a line of thunderstorms has developed over southeastern Modoc County. This activity is likely to continue through the afternoon and into the evening as a weak shortwave passes overhead, with additional convection likely across northern California and the East Side of Southern Oregon. Thunderstorms are expected to be more isolated, but several lightning strikes and light to moderate rainfall is possible should one of these cells move directly overhead. The upper level trough, currently offshore, will make a run through the region tomorrow, passing mostly to the north of us, but it should be enough to touch off additional thunderstorms tomorrow afternoon and evening, in the same general area as today. This will likely be the last significant chance for thunder and/or precipitation until a weak front makes its way into the area this weekend into early next week. The front will most likely pass as a dry one, but some model solutions, mainly the ECMWF, do suggest the possibility of convection. These more amplified solutions are in the minority, and seem more than a bit out of place for this time of year, thus confidence is much too low to include these in the forecast. Otherwise, the weather for our area will be characterized by smoke and warm but not overly hot temperatures. Once the trough exits tomorrow, ridging will slowly begin to build in from the west, and the thermal trough along the coast will strengthen. This will produce a broad offshore flow, drying the region out and potentially setting up the Chetco Effect in the Brookings area, with high temperatures in the 80s possible there through the weekend. The hottest day for the area (excluding the south coast) is likely Friday, with highs reaching about 5 degrees above normal for this time of year, but most days will hover right around seasonal normals. The shift in the pattern will help, but will not completely clear smoke from area skies. The prevailing winds and the day-to-night wind cycle will likely clear smoke from areas west of the Cascades in Oregon, but with fires still burning strong to the south, prevailing winds aloft, and daily mixing to the surface, smoke is expected to continue to impact the bulk of Siskiyou, Modoc, Lake, and Klamath Counties for the foreseeable future. -BPN AVIATION...For the 25/18 TAFs...Over the coastal waters and along the coast...Areas of IFR cigs/vsbys in low clouds and fog will burn back offshore by late morning, then move back onshore this evening. The lower ceilings will persist into Wednesday morning. Inland areas west of the Cascades in Oregon...VFR conditions will prevail into Wednesday morning, but there will be areas of smoke and haze, along with a few showers or thunderstorms Tuesday morning. Northern California and east of the Cascades...VFR conditions will prevail into Wednesday morning, except for areas of MVFR vsbys in wildfire smoke. There will be isolated thunderstorms through Tuesday evening. MARINE...Updated 200 PM PDT Monday 24 August 2020....A thermal trough will persist near the coast through the week. This will bring gusty north winds and steep to very steep seas with the strongest winds and highest seas south of Cape Blanco. Winds and seas will become more hazardous from Wednesday into the weekend with gale force winds likely south of Cape Blanco and strongest south of Ophir. All areas will remain hazardous for small crafts through this time. FIRE WEATHER...Updated 200 PM PDT Tuesday 25 August 2020...The main concern over the next couple of days will be thunderstorms, mainly east of the Cascades and northern California. The one thing that could put a cap on the amount of thunderstorms will be smoke. With that said, recent Geocolor satellite images are showing signs of smoke starting to thin out some in Fire Zone 285 and southeast portions of fire zone 625. At the same time were starting to see cumulus development in these areas. A few storms have developed in southeast fire zone 285 and we`ll continue to keep a close watch on further development as the afternoon progresses. The past several runs of the HRRR (high resolution rapid refresh) model has been rather consistent with where, when, and amount of storm development this afternoon into this evening. It looks like the best chance for isolated thunderstorms are expected to be between 2 and 8 pm pdt, but would not be surprised if they begin to fizzle out an hour earlier (7 pm pdt). At this time, were not expecting anything more then isolated, so we`ll continue to headline in the fire weather forecast. However, if something unforeseen happens, we will update everyone. Any storms will end this evening with dry conditions tonight with mostly moderate overnight recoveries (except for the coast and Fire zones 615 and northwest 616). Wednesday, the upper trough axis remains west of out area which will still put us in a favorable position for isolated thunderstorms from the Siskiyous south and Cascades east Wednesday afternoon and evening. Like today, smoke will be the main wild card and could limit surface heating and thus cap the amount of thunderstorms. After Wednesday, the threat for thunderstorms are almost or at zero through at least next Tuesday. However, our focus will go from thunderstorms to winds and low relative humidity starting as early as Thursday morning. Details follow below. A thermal trough will develop along the coast Thursday and could very well last into the early next week. This will bring gusty winds near and at the ridges in fire zones 618, 619, 620, and 280 with moderate to locally poor overnight recoveries. Meanwhile, an upper trough will slide northeast of our area Sunday and we could see gusty winds and low relative humidity for fire weather zones 624, 625 and 285 Sunday afternoon into Sunday evening as the pressure gradient tightens up. Afternoon temperatures are not expected to vary much from one day to the next through Thursday. They are expected to increase for most inland locations Friday and Saturday, followed by slight cooling Sunday. At the coast, mainly south of Cape Blanco, they are expected to increase (due to increasing offshore flow and Chetco effect) Thursday through the weekend. -Petrucelli && .MFR WATCHES/WARNINGS/ADVISORIES... OR... CA...None. Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT Thursday for PZZ356-370-376. Gale Warning from 11 AM Wednesday to 11 PM PDT Thursday for PZZ356-376. Small Craft Advisory from 11 AM Wednesday to 11 PM PDT Thursday for PZZ350. $$ MAS/DW
...Updated Aviation Forecast Discussion...

.DISCUSSION... Issued at 248 PM CDT Tue Aug 25 2020 Today and Tomorrow: A visual check of the sky and satellite imagery reveal there is a bit of a haze above the area today. The experimental HRRR vertically integrated smoke parameter shows values around 150 mg/m^2 (a high value) over the northern Plains. The source of the smoke is the wildfires over the western CONUS. The HRRR does show that this value should decrease over Nebraska and Iowa over the next couple of days due to a change in the upper level wind pattern. The smoke shouldn`t have a great effect in the area. The haze may linger for a couple of days and temperatures may be a degree or two lower due to the increased aerosols in the air. Temperatures this afternoon could reach 100 degrees in some spots. Winds this afternoon have been observed in the 15 to 20 mph range gusting up to 25 mph. They`ll begin to taper off this evening. Temperatures tomorrow will be similar to today, but a degree or two cooler. More of the forecast area should see increased wind speeds as a surface low moves in from the west. Expect winds tomorrow from the south at 15 to 20 mph gusting up to 30 mph. There is a slight chance for rain along the NE/SD border Wednesday after 7 pm. It is a small chance for rain and even if rain does materialize, the total amount would be less than a tenth of an inch. Thursday through Monday: By Thursday the ridge will have begun to flatten. The hottest temperatures should be confined to southeast Nebraska. The best chance for rain in the area is going to be late Thursday night into Friday morning. An upper level disturbance is expected to develop off the Rocky Mountains in Wyoming and move across South Dakota. The main mechanisms for lift will be the upper level disturbance and a cold front that is expected to stall out Thursday across South Dakota. Significant rain in Nebraska isn`t looking likely, but it is more than 48 hours yet. The SPC has issued a slight risk for severe weather for that period. With strong shear behind the front, the primary severe weather threats are strong gusty winds and hail. The weekend will be much cooler as the upper level disturbance will break down the ridge and bring in cooler temperatures. High temperatures Saturday and Sunday should be in the 80 to 85 degree range. Another upper level disturbance is expected to move south from the Canadian Plains on Monday and further reduce temperatures which should lead to a cool start to the week. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 624 PM CDT Tue Aug 25 2020 VFR conditions will prevail through the period. Threat for LLWS at all terminals though early Wednesday morning. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ DISCUSSION...Fajman AVIATION...DEE