Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/27/21

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
925 PM CDT Thu Aug 26 2021 .UPDATE... Issued at 918 PM CDT Thu Aug 26 2021 Severe Thunderstorm Watch has been issued for the southern part of the CWA near a stalled out frontal boundary and in association with a strengthening low level jet. Increased POPs in that area and included a mention of possible severe storms. No other changes made to the forecast at this time. && .SHORT TERM...(This Evening through Friday Night) Issued at 251 PM CDT Thu Aug 26 2021 We remain under a persistent and messy weather pattern with off and on showers and thunderstorms that remain a little difficult to time. Southwesterly flow remains at 500mb with several embedded waves. The main shortwave is over MT/WY this afternoon and will move into the western Dakotas tonight. Will continue to monitor rounds of showers and thunderstorms that are being enhanced by an area of high shear. We`re still looking at the chance for more storms over our southwestern counties this evening into the overnight hours. Just how the storms evolve is in question, mainly on how far north the storms will move. The HRRR continues to be on the more aggressive/farther north solution, with the potential of storms mainly near the Missouri River around 05-06Z (mainly south of Mobridge). HREF keep much of the more significant UH values over our southern counties, but can not rule out the HRRR. Expect whatever develops to shift east-northeast overnight and exit into northeastern SD/western MN by around 12Z. This will be while the surface low over NE pushes northeast into portions of southeastern SD. While that feature moves into southwestern MN Friday evening, yet another low will be moving into southwestern SD. At this point expect mainly dry weather for Friday afternoon, before storms near from the northwest Friday night and expand across the forecast area overnight. Any storm that does develop will have the potential to produce strong winds, hail, and heavy rain. PW values remain over 1in through the period. .LONG TERM...(Saturday through Thursday) Issued at 251 PM CDT Thu Aug 26 2021 A somewhat active pattern will continue across the northern CONUS through the extended time period. To start the period, an upper trof will be advecting across the Dakotas Saturday and Saturday night. The main low level boundary associated with the upper trof will stretch from ne-sw across eastern South Dakota by afternoon. Moderate instability is expected to develop along this feature with daytime heating, particularly over far eastern SD, and western Minnesota. So, expect most activity that develops over eastern SD to likely move into MN quickly in the evening. Moderate instability and strong deep layer shear suggests some severe weather is likely. Later Saturday night and Sunday should be mostly dry as sfc high wafts over the forecast area. Return southerly flow begins in earnest Monday through Tuesday, with convection chances returning to the forecast. Mid-level ridging builds across the region for midweek, but with a sfc boundary in the vicinity, pcpn chances will continue. The end of the week may bring a lesser chance of pcpn as a front settles out to the south of the forecast area. Temperatures, overall, will favor near to slightly below normal for the period, except for mid-week when the ridge aloft may allow for warmer than normal temperatures. && .AVIATION...(For the 00Z TAFS through 00Z Friday Evening) Issued at 628 PM CDT Thu Aug 26 2021 Terminals KABR,KATY,KPIR,KMBG Scattered showers and thunderstorms will affect the northeastern part of the area this evening, with additional showers and thunderstorms expected to develop during the overnight hours and spread eastward through early Friday morning. Cigs will fall to IFR/MVFR levels with the precipitation development, then will remain at those levels into early Friday afternoon before lifting to VFR levels. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ UPDATE...Parkin SHORT TERM...KF LONG TERM...TDK AVIATION...Parkin
Area Forecast Discussion
National Weather Service La Crosse WI
1100 PM CDT Thu Aug 26 2021 .SHORT TERM...(Tonight) Issued at 329 PM CDT Thu Aug 26 2021 ...An Active Night Of Weather Expected... A complex but potentially impactful weather scenario is shaping up across the region for tonight. Current storm and rain activity moving through is reinforcing the cool stable layer which extends across all of northern Iowa. There is still some MUCAPE available above the surface there /1500-2000J/Kg/. Surface-based CAPE pool is growing and impressive but still far southwest in SW IA. Using RAP guidance and surface observations, the front between the very unstable mT air and the "cooler" stable air to the north should be roughly NW>SE Iowa by early evening. This low-level thermal boundary orientation and isentropic lift zone extends from southern MN into eastern IA. After about 9 pm, the low-level jet amps up into the isentropic lift zone to erupt storms over southwest MN and nrn IA. These storms, quickly forming into a line, tracking southeast, would have the best chances of being severe with damaging winds as they shift in. It seems the trajectory and low-level front and CAPE pool should provide NERN IA with the highest probability of damaging winds...and closer to I-35 or southwest of the area. That would likely end the damaging wind threat. However, heavy rain and flash flooding is now the greatest concern overnight with moderate moisture transport convergence via low-level jet inflow /850 mb/ at 35 kts isentropically lifted over the entire thermal gradient - northeast of the surface front. The entrance region of the upper jet also provides a favorable larger mesoscale lift boost. This looks like it will cause cause widespread storm eruption by late evening across southern MN into northern IA with storms shifting east into WI and repeating over some of the same areas. There could 3 to 7 inches of rain with this rich air mass of 170-190% normal precipitable water, 3.5-4km warm cloud depth, and propagation vectors east-southeast along the front...suggesting some training. While it is concerning, soils can take some rain, but really the character of the waves of storms and if they can concentrate on one area is still a bit in question. So, have decided to wait a bit longer on a Flash Flood Watch, possibly until early evening. Right now, it appears NERN IA and SERN MN would be the target. But widespread rain/storms are expected with 1-3 inches by morning for many, higher in training storm regions. Any assistance from our TV/media partners in suggesting people stay weather aware overnight, keeping their phones on, is appreciated! Campers near streams/smaller rivers will want to be alert overnight as well - they likely wont sleep much with hours of storms. .LONG TERM...(Friday through Thursday) Issued at 330 PM CDT Thu Aug 26 2021 After any lingering Friday morning convection clears, the 850mb boundary should be on the move northward into central WI. The models have been hinting at this every day, but each day we see that the boundary does not actually move. Friday may be another day where that happens. If the boundary stays put, we could see more showers and thunderstorms develop right over us and increase our risk of flash flooding. The 850mb moisture transport will actually be pushing right into our area (or to our north) all day Friday. The more amplified upper trough will approach the Upper Midwest Friday night with an embedded shortwave crossing MN Saturday afternoon. Each wave will bring a renewed chance for storms and those storms will be focused along the 850mb frontal boundary and nose of the low level jet. The upper trough and associated surface cold front will finally swing through sometime on Sunday, although the upper wave will become removed from the surface front by the time it moves into southern WI. Therefore, models are showing a weakening trend in precip along the front. Quiet and less humid weather will finally return early next week as high pressure settles over the Upper Great Lakes. There will continue to be shower and isolated thunderstorm chances toward northeast IA on the edge of the surface high as weak ripples in the upper flow move overhead. && .AVIATION...(For the 06Z TAFS through 06Z Friday night) Issued at 1051 PM CDT Thu Aug 26 2021 Widespread showers and thunderstorms overspread the area tonight, which will taper off in coverage during the morning hours. Expect restrictions to IFR or even LIFR with the regions of heaviest rainfall overnight. MVFR to IFR fog is also likely in areas that clear out from the rain before sunrise. Winds will generally be from the east to southeast at 5-10 kts, with locally higher gusts around any thunderstorms. Ceilings during the day on Friday may be slow to lift above MVFR during the morning to early afternoon. Additional showers and storms will affect the area late in the afternoon and evening hours. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...Flood Watch until 7 AM CDT Friday for MNZ079-086>088-094>096. IA...Flood Watch until 7 AM CDT Friday for IAZ008>011-018-019-029-030. && $$ SHORT TERM...Baumgardt LONG TERM...MC AVIATION...Skow
Area Forecast Discussion
National Weather Service Bismarck ND
912 PM CDT Thu Aug 26 2021 .UPDATE... Issued at 850 PM CDT Thu Aug 26 2021 Slightly slowed the eastward progression of PoPs tonight based on model guidance and latest radar trends. Past couple runs of the HRRR make for a potentially more interesting night with more widespread stronger cells in the southwest and south central parts of the state. Plenty of shear is available, however, instability is limited. Thus while a severe storm or two cannot be completely ruled out this evening, still thinking severe weather is less likely than likely to occur. UPDATE Issued at 610 PM CDT Thu Aug 26 2021 Removed PoPs from the western forecast area and lowered them slightly over the eastern forecast area over the next few hours to reflect current radar and model trends. With fairly light winds tonight and a very low stratus deck expected at times after the fresh rainfall, added patchy fog to much of the forecast area. Locations most likely to see fog for an extended period are primarily those in more elevated terrain. && .SHORT TERM...(This evening through Friday night) Issued at 247 PM CDT Thu Aug 26 2021 Widespread scattered showers and thunderstorms are possible through the short term forecast, with some strong to severe thunderstorms possible on Friday. This afternoon, flow aloft was turning southwesterly across the Northern Plains as a shallow trough was based over the western CONUS. Broad high pressure was centered to the northeast of the forecast area, with a moderate pressure gradient between the high and relative low pressure over northeast Wyoming. A surface trough extended northeast-southwest across central Minnesota, with a few isolated thunderstorms ongoing in the wake of it across the southern James River Valley. We are expecting some widely scattered shower and non-severe thunderstorm activity across the area through the afternoon from elevated warm advection. Chances for showers and thunderstorms will increase late this evening and through the overnight hours as another shortwave moves through the southwesterly flow, ahead of the approaching trough base. At this point, we are not expecting any of these storms to be severe, with marginal instability during the overnight hours. The highest chance for a strong to severe storm would be in the southwest, where there is the best overlap of shear and instability. Lows tonight will be in the upper 40s to mid 50s. The main concern in the short term is the potential for severe thunderstorms on Friday. Precip chances from tonight`s shortwave taper off from west to east through Friday morning, but PoPs quickly increase again in the afternoon and evening as the trough base moves over central Montana. Development is expected in south central Montana during the afternoon on the nose of an upper jet, with storms then moving east into the western Dakotas. Instability around 1000-1500 J/kg and 0-6 km shear on the order of 35-45 knots will be enough to support discrete cells forming along a frontal boundary moving through Friday evening. Main hazards will be ping pong ball sized hail and 60 mph wind gusts, as well as locally heavy rainfall with PWATs still around the 90th percentile. Expect the threat to start in the evening, with the storms moving east through the late evening and overnight. .LONG TERM...(Saturday through Thursday) Issued at 247 PM CDT Thu Aug 26 2021 A slow warming trend and various chances for showers and thunderstorms highlights the extended forecast. Precipitation chances linger through the day on Saturday, especially central and east, as the base of the upper trough moves overhead and eventually off to the northeast by Saturday night. It will be another pleasant day, with clearing skies from west to east and highs generally in the 70s, although winds will be breezy in the west. Sunday will finally be a dry day, with zonal flow aloft and broad high pressure at the surface. Temperatures will slowly be warming as upstream troughing deepens over the western CONUS and ridging develops over the Northern Plains in response. Highs will warm to the mid 70s to mid 80s by Tuesday, when low but relatively persistent chances for showers and thunderstorms begin in the evening. Multiple shortwaves look to move through southwest flow aloft through much of the work week, with uncertainty then emerging in how long the trough persists out west before it breaks down. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 610 PM CDT Thu Aug 26 2021 IFR and MVFR ceilings are expected at all locations at times throughout the TAF period. Patchy fog is also possible at most TAF sites at some point, although KDIK is the site most likely to see longer lasting fog that will reduce visibilities to IFR levels. Finally, showers with the occasional rumble of thunder are expected to work into the area from the west tonight and linger into Friday morning. These could further reduce visibility, lower ceilings, and/or create erratic wind gusts while showers and thunderstorms are ongoing. && .BIS WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Telken SHORT TERM...MJ LONG TERM...MJ AVIATION...Telken
Area Forecast Discussion
National Weather Service Birmingham AL
705 PM CDT Thu Aug 26 2021 .UPDATE... Evening Update and 00Z Aviation. && .SHORT TERM... /Updated at 0648 PM CDT Thu Aug 26 2021/ Central Alabama is positioned between two subtle easterly waves early this evening. Precipitable Water values are near 1.5 inches per the latest RAP analysis. This is a relative minimum with 2+ in southern Mississippi and southern Georgia. Therefore, a limited cumulus field this afternoon with mixing and little vertical growth. A few small scale boundaries were here and there plus another outflow in west central Georgia. Left a token 15 pop for a few hours this evening but a majority of the locations will be high and dry. Some low clouds may try and inch into or develop over southeast areas just after sunrise and will monitor this potential development before mixing begins. Due to lack of rain today and no particular boundary or convergence, fog should not be a widespread problem overnight. The big news is that Tropical Storm Ida has formed in the northwest Caribbean Sea. The initial path and intensity forecast from NHC has Ida moving into the central gulf coast as a hurricane Sunday afternoon. Parts of west central Alabama are in the error cone as the storm moves inland. Much more on the tropics in later forecast. If you have interest along the gulf coast, pay particular attention to the latest forecast and updates for the NHC. 75 Previous short-term discussion: /Updated at 1247 PM CDT Thu Aug 26 2021/ Today through Friday. Features of Interest. Broad ridging remains over much of the Southeast while lower- level ridging remains to our east and northeast. Surface east to southeasterly flow was continuing to support humid conditions. The 26/12z BMX sounding contains a subtle subsidence inversion around 900 mb with saturated low-level conditions. This has allowed persistent low-level clouds to remain across much of our northern and central counties through late morning. Hazard Assessment. The wet microburst risk is moderate today, which is similar to yesterday`s outlook. We will monitor the potential for some of the heavier thunderstorms to produce strong winds. Today. The lower clouds are mixing out and expect partly cloudy skies this afternoon with isolated showers and thunderstorms developing over the next few hours. The better chances will be northern and northwest counties today with the lowest chance across our far southeast counties. Highs will range from the upper 80s in the higher elevations east to the lower 90s elsewhere. Winds will remain from the east to southeast 6-12 mph. Tonight. Partly to mostly cloudy skies are forecast overnight with some lower clouds expected toward daybreak. Chances for lingering showers will be widely isolated at best with the best potential north and west. Lows range from around 70 north and east to readings in the lower 70s south and west. Winds will be light from the east 3-6 mph. Friday. Morning clouds look to begin the day Friday with scattered showers and thunderstorms developing from late morning through the afternoon hours. The best chances will be across the eastern and southern portions of the forecast area in association with a mid level disturbance that is progged to move into the area from the east during the daytime hours. Highs will range from the upper 80s in the higher elevations east to readings in the lower 90s elsewhere. Winds will be out of the southeast 6-12 mph. 05 .LONG TERM... /Updated at 400 PM CDT Thu Aug 26 2021/ The main tweaks in the extended are based on the latest guidance for TD 9. While official tracks may vary some over the next couple of days, we will likely have some affects from being on the right side of the storm as it moves northward across the Gulf of Mexico onshore late Sunday into the beginning of next week as the tropical system moves around the SE US upper ridge. It will encounter the main upper flow causing it to turn NE Monday into Tuesday some. To what extent as to how much remains to be seen. With that said, there will be a threat for tornadic activity in the right front quadrant across C AL on Monday as of now. The W half of the area will likely have the better chance. Heavy rain at times and some flash flooding will be possible in any training feeder bands. Will add a low confidence 1 in the HWO for Monday to account for this. Other changes include tweaking down highs for Monday and Tuesday due to more cloud cover and tropical rain bands. 08 Previous long-term discussion: /Updated at 300 AM CDT Thu Aug 26 2021/ Friday night through Wednesday. Friday`s diurnal convection will weaken and lingering into the evening hours. Overall, coverage should not be that great with most of the activity gone by midnight. An upper ridge off the Carolina Coast will produce a moist southeast flow across Alabama over the weekend. On Saturday, sea-breeze initiated storms will likely be main focus for storms across south Alabama, and carried likely rain chances for areas south of I-85. By Sunday a low level convergence zone will likely set-up along the MS/AL state line between the ridge over the Carolinas and the approaching tropical system in the Gulf of Mexico, so better rain chances west of I-65. Beyond Sunday, the models are in fairly good agreement in moving the tropical system northward along the MS river. Based on model consensus, feel fairly confident in raising rain chances across west and northwest Alabama Monday and Tuesday. This track would also place Central Alabama in the favored region for the potential for tornadoes. 58/rose && .AVIATION... 00Z TAF Discussion. VFR conditions will be forecast outside of convection through the period. Much drier conditions through the atmospheric column today than yesterday. Expect light and variable winds overnight with little cloud cover for most. Some MVFR clouds may approach or develop near TOI around daybreak and will have to monitor for possible inclusion on later forecast. Due to lack of rainfall and convergence, fog has not been mentioned at the terminals overnight. Although there may be a few locations where vis drops some, not expecting anything widespread. On Friday, another easterly wave and increased mean moisture move over Central Alabama. Therefore, there should be more convection than there was today. Started with PROB30 in the afternoon at all terminals. Winds maintain an easterly component at 5-7kts. 75 && .FIRE WEATHER... An increase in rainfall coverage is expected Friday and Saturday. An additional increase in shower coverage can be expected by next week, but will be dependent on activity in the Gulf of Mexico and direction during the first of next week. Weak low level winds remain out of the east to southeast through the end of the week, with elevated humidity values keeping min RH values above 50 percent range. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 70 91 71 91 71 / 20 40 20 30 10 Anniston 71 90 73 90 73 / 20 50 20 30 10 Birmingham 73 92 73 91 73 / 20 40 30 40 10 Tuscaloosa 74 92 73 91 74 / 20 40 30 40 10 Calera 72 89 73 89 74 / 20 50 30 40 10 Auburn 72 89 73 88 73 / 20 60 20 50 10 Montgomery 73 91 73 92 74 / 20 60 30 50 20 Troy 72 91 73 90 73 / 20 60 30 60 20 && .BMX WATCHES/WARNINGS/ADVISORIES/... None. && $$
Area Forecast Discussion
National Weather Service Cheyenne WY
525 PM MDT Thu Aug 26 2021 .SHORT TERM...(This evening through Friday night) Issued at 151 PM MDT Thu Aug 26 2021 Current radar imagery indicates some cells developing in northern Carbon County and to the south across Colorado. Fairly slow start to the Convection today, with some model inconsistencies with the later runs. NAM-NEST and the HRRR models have picked up on a line of convection developing just off to the west traveling eastwards across the CWA. However, it seems the HRRR is a bit more bullish as this line of convection travels downstream towards the Panhandle. Main concerns today exist with severe potentials. Low level winds are expected to turn near zero just east of state line between Wyoming and Nebraska. NAM-NEST has picked up on this feature, shearing the convective cells and effectively decreasing their intensity. Already seeing signs of this occurring with a cell developing over Morrill County. In addition, the SREF CAPE probabilities indicate a near zero percent chance for greater than 1000 J/kg of CAPE for southeastern Wyoming and around a 30 percent chance across the Nebraska Panhandle. Most of the better energy appears to be northward, with a good bullseye close to our northern region of the Panhandle. Could see some outflows develop from the north that could cut southwards towards Dawes County. Nevertheless, main threats today include strong damaging winds from any storms able to develop in the Panhandle with a good inverted V signature and will likely be similar to yesterday. Due to the model inconsistencies, confidence for tonight severe potentials is low. Looking ahead into tomorrow, a series of shortwave disturbances is expected to dig to the east/southeast across the region, kicking up the wind speeds along the way. Overall, dry and windy conditions expected from these features, with most of the moisture advection to the east of the CWA, raising fire weather concerns. Went ahead and upgraded the current Fire Weather Watches to Red Flag Warnings. .LONG TERM...(Saturday through Thursday) Issued at 151 PM MDT Thu Aug 26 2021 An upper level trough will begin to dig east/southeastward from the Pacific Northwest towards the Rockie Mountains through late Saturday night. Could see some showers and thunderstorms develop late Saturday night into early Sunday morning. However, the likelihood of any convection during that period is decreasing. Current model runs are picking up on the moisture advection into the region that now seems poor with Tropical Depression Nine coming on board towards the Gulf of Mexico, effectively cutting off the flow from the Gulf and tilting the moisture advection eastward. Looking into next week, mostly quieter weather ahead with near zonal flow developing overhead and bringing drier conditions across southeastern Wyoming and the Nebraska Panhandle beginning on Monday. Daytime highs are expected to increase, relative to the cooler weekend, with highs in the mid-90s east of I-25 and in the mid to low 90s to the west on Monday, and climbing on Tuesday. With the increase in daytime highs across the Great Plains and the drier conditions will inevitably raise fire weather concerns as the afternoon RH values drop to the mid-teens. However, winds are expected to remain below warning criteria level at this time. Next round of precipitation is expected to return by mid-week, as the next system comes on board. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 523 PM MDT Thu Aug 26 2021 VFR. Thunderstorms in the vicinity at all terminals except Rawlins until 03Z. Wind gusts to 25 knots at Laramie, Cheyenne and Sidney until 02Z, then to 35 knots at Rawlins, Laramie and Cheyenne after 15Z Friday. && .FIRE WEATHER... Issued at 151 PM MDT Thu Aug 26 2021 A series of shortwave disturbances is expected to dig to the east/southeast across the region, kicking up the wind speeds along the way. Overall, dry and windy conditions expected from these features, with most of the moisture advection to the east of the CWA, raising fire weather concerns. As a result, went ahead and upgraded Converse, Niobrara from a Fire Weather Watch to a Red Flag Warning, in addition to including Carbon County for the warning. Fire weather concerns will remain elevated through the weekend with low humidity values and gusty winds. Will need to evaluate later model runs for any headlines needed on Saturday, Monday, and Tuesday where wind speeds inch closer to critical thresholds. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...Red Flag Warning from noon to 8 PM MDT Friday for WYZ301>304. NE...None. && $$ SHORT TERM...MD LONG TERM...MD AVIATION...RUBIN FIRE WEATHER...MD
Area Forecast Discussion
National Weather Service Quad Cities IA IL
643 PM CDT Thu Aug 26 2021 ...AVIATION UPDATE... .UPDATE... Issued at 606 PM CDT Thu Aug 26 2021 Have issued a flash flood watch for the northern third of the area. Satellite trends show new convection developing further south than expected. The concern is that this is the effective boundary that the expected MCS will develop and move along. This first round of storms may prime the ground for when the very heavy rain occurs overnight. The potential for storms to repeat over the same area may be increasing given trends in more recent RAP runs. Regardless, an extremely heavy band of rain looks very possible and it will be mesoscale in nature; potentially 1-2 counties wide and 4-6 counties long. If storms repeat over the same areas then amounts over 4 inches are very possible. && .SYNOPSIS... Issued at 327 PM CDT Thu Aug 26 2021 18Z surface data has in inferred low in southwest Wisconsin. A warm front ran east from the low across southern Wisconsin while an outflow boundary moved toward the Mississippi river in eastern Iowa. Dew points were in the 70s from the Ohio Valley west into the central Plains. Dew points in the 40s and 60s were across the northern Plains and upper Midwest. && .SHORT TERM...(This Evening through Friday) ISSUED AT 327 PM CDT Thu Aug 26 2021 The situation through sunrise Friday is a continuous nowcast where surface, satellite and radar data along with conceptual models are the inputs to the forecast. The boundary from the overnight storm complex is providing the focus for new storms in southeast Iowa. Satellite also shows an implied air mass boundary so additional storms are expected to develop across the southern third of the area through sunset. Outside of some light rain and a possible thunderstorm north and west of Cedar Rapids through sunset, the rest of the area looks to remain dry. The question is what happens during the late evening and overnight hours. Here the situation is not entirely clear. Satellite data shows another upper level disturbance moving through Nebraska. Given the agitated cumulus cloud field in the area surrounding KFSD, the next organized storm complex will likely develop in this area late this afternoon and evening. Conceptually this storm complex should move east along the elevated boundary seen in satellite along the IA/MN border toward Wisconsin. A gradual southward sag to the storm complex is expected with it reaching the northern parts of the area after midnight. Given the high moisture levels in the atmosphere heavy rainfall is likely. However the ground may soak up much of the rain given the moderate to severe drought conditions across the northern parts of the area. If storms repeat over the same areas late tonight then excessive rainfall is possible that `could` result in flash flooding. Right now we will not be issuing a flash flood watch but that could change later this evening depending upon on how the storm complex develops and evolves. On Friday lingering nocturnal convection will dissipate during the morning hours followed by new diurnal convection in the afternoon. Again locally heavy rainfall will be possible from the stronger storms. Cloud cover and precipitation will dictate how warm it gets on Friday. The potential does exist for another heat advisory with areas south of I-80 being favored. Again this will depend upon cloud cover during the day. .LONG TERM...(Friday Night through Thursday) ISSUED AT 327 PM CDT Thu Aug 26 2021 Continued hot and humid through the weekend with some relief next week. Potentially active weather will continue. Heat headlines will be assessed on a day by day basis. Friday night Assessment...low to medium confidence Storms that develop Friday afternoon will continue into the evening hours followed by dissipation. Boundaries from these storms will then dictate where the next round of nocturnal storms will develop. Right now the area north of I-80 is favored for the nocturnal storms. Saturday Assessment...medium confidence Right now the model consensus has hot and humid conditions with no rain expected during the daylight hours. Based on forecast high temperatures and dew points, heat index readings of 100+ are expected which would necessitate another heat advisory. Saturday night/Sunday Assessment...medium confidence The models have slowed down the arrival of the next cold front. Several model solutions keep Saturday night dry with the front moving through on Sunday. Other solutions bring the front in very late Saturday night and slowly move it through the area on Sunday. Right now the model consensus has slight chance to chance pops across the northwest half of the area Saturday night with chance pops across the entire area on Sunday. Monday through Thursday Assessment...low to medium confidence The cold front pushes through the area and then stalls/dissipates. The models are, for the most part, in a cycle of daily diurnal convection occurring with the highest pops in the afternoon and evening. However the models also have several upper level disturbances moving through in the flow aloft that may cause convection to persist through the night and into the morning hours. Right now the model consensus has slight chance to chance pops Monday and Monday night, chance pops Tuesday and slight chance pops Tuesday night and Wednesday. Wednesday night the model consensus has mainly dry conditions followed by slight chance pops on Thursday. && .AVIATION...(For the 00Z TAFS through 00Z Friday Evening) ISSUED AT 640 PM CDT Thu Aug 26 2021 Satellite/radar trends shows new convection has developed further south than what the models indicated. This suggests that this is where the nocturnal TSRA complex will develop and track east. Through 06z/27 VFR conditions are expected outside of SHRA/TSRA. After 06z/27 KDBQ has a high probability of IFR conditions with TSRA. The rest of eastern Iowa and northern Illinois south of Interstate 80 can expect mainly VFR conditions with patchy MVFR conditions around sunrise Friday. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...Flash Flood Watch from 10 PM CDT this evening through Friday morning for Benton-Buchanan-Delaware-Dubuque-Jackson-Jones- Linn. Heat Advisory until 8 PM CDT this evening for Des Moines-Henry IA-Jefferson-Lee-Van Buren. IL...Flash Flood Watch from 10 PM CDT this evening through Friday morning for Carroll-Jo Daviess. Heat Advisory until 8 PM CDT this evening for Hancock-Henderson- McDonough-Warren. MO...Heat Advisory until 8 PM CDT this evening for Clark-Scotland. && $$ UPDATE...08 SYNOPSIS...08 SHORT TERM...08 LONG TERM...08 AVIATION...08
Area Forecast Discussion
National Weather Service Grand Forks ND
1036 PM CDT Thu Aug 26 2021 .UPDATE... Issued at 1036 PM CDT Thu Aug 26 2021 Showers have ended in our CWA, and main impact into the overnight hours is related to smoke advecting in from fires in the MN arrowhead from the east. HRRR smoke model indications this may linger until the next cluster of showers/thunderstorms arrives Friday morning. There is increasing consensus with this cluster and timing favors southwest to northeast progression after 6AM through midday and eastward through the afternoon (additional development still possible after this cluster). I adjusted timing of PoPs/thunder tonight into Friday including increasing coverage to reflect numerous showers/embedded thunderstorms Friday. There is enough instability advertised to support thunderstorm mention, but not enough to message strong/severe convection. Higher moisture content and embedded storms do raise the possibility for localized heavy rain amounts. So far the consensus would favor 0.1 to 0.25" amounts with pockets of 0.5-0.75" possible where thunderstorms occur (outliers in guidance and very low probs in NBM 24hr QPF). UPDATE Issued at 707 PM CDT Thu Aug 26 2021 Cluster of showers and embedded thunderstorms is lingering in our south with isolated showers further north. Current consensus of CAMs supports trends for this activity to shift east-southeast through the evening hours with a lull overnight before next round of showers/embedded thunderstorms arrive (southwest to northeast) Friday morning. Adjustments were made to reflect current radar/satellite trends and to tweak timing overnight. Impacts will be lighting and brief heavy rain where thunderstorms track. Elevated instability 500 J/KG or less and stabilizing low levels with sunset lower chances for any stronger storms the rest of the night. && .SHORT TERM...(This evening through Friday night) Issued at 256 PM CDT Thu Aug 26 2021 Near term impacts through the remainder of the day are expected to be minimal, with scattered showers and thunderstorms generally south of Interstate 94. A few of these storms could produce brief wind gusts and small hail. The late evening period into the early overnight hours will remain quiet, with a slight chance for an isolated thunderstorm, mainly along the SD border. For Friday, additional showers and thunderstorms are in the forecast along a pre-frontal trough and associated theta-e gradient boundary. This will move through the area during the mid-morning through mid- afternoon period. Periods of heavier rain are possible during the overnight hours as PW values continue increasing ahead of the main cold front. .LONG TERM...(Saturday through Thursday) Issued at 256 PM CDT Thu Aug 26 2021 Scattered strong to severe thunderstorms should move out of the area late Saturday evening with cold frontal passage. Behind the front expect a dryer, cooler, and more stable pattern for the early week period. A warmer and more unstable pattern then develops for the mid to lake week period. Saturday night into Sunday... An unstable pattern with southwest flow aloft looks to move eastward and out of the northern plains region from Saturday night into Sunday morning. Consensus guidance now depicts a lead cold front and deep convection moving well east of the FA by early evening, with a lower risk of a secondary cold front and isolated showers impacting mainly far northern portions of the FA during the overnight into early morning hours. On Sunday, a building H5 ridge aloft and drier west-northwesterly blayer flow should overspread the area bringing generally fair skies and temperatures just a bit cooler than long term averages, ranging from the upper 60s north to mid 70s south. Monday through Tuesday... A transitory H5 shortwave ridge continues to build in aloft from Monday into Tuesday, while a southerly return flow develops near the surface. With that, temperatures should edge back back to near seasonal normals and daytime highs range through the middle to upper 70s. While morning low temperatures ramp up from the lower 50s on Monday into the upper 50s by Tuesday. The increasing low level flow and warming blayer temperatures will likely struggle with the capping affect of warming temperatures aloft, thus isolated to scattered showers and thunderstorms are possible each day. Wednesday through Thursday... By midweek, ensembles favor an amplifying trof/ridge pattern over the western and central NOAM with a strengthening southerly blayer flow. From mid to late week a return to a more unstable southwest flow aloft pattern looks quite probable, with an increased risk for more widespread string to severe thunderstorms and wetting to soaking rains. Temperatures through this period look to remain near long term averages, with highs 70s and lows in the 50s. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 707 PM CDT Thu Aug 26 2021 MVFR ceilings have improved, however low stratus eventually overspreads all of eastern ND and northwest MN after 09-11Z tonight/early Friday and IFR appears likely through the daytime period Friday. Most showers and isolated thunderstorms have transitioned to southeast ND and west central MN and should end this evening, however another round of showers/embedded thunderstorms is likely to spread southwest to northeast Friday morning. Coverage may remain scattered and thunderstorms isolated, so I held off on introducing thunderstorm mention during this update. Winds should generally remain from the east-southeast 8-13kt through Friday based on current trends and expected surface pattern. Erratic winds are still possible due to shower/thunderstorm activity. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. $$ UPDATE...DJR SHORT TERM...Lynch LONG TERM...Gust/Lynch AVIATION...DJR
Area Forecast Discussion
National Weather Service Grand Rapids MI
1148 PM EDT Thu Aug 26 2021 LATEST UPDATE... Update .SYNOPSIS... Issued at 330 PM EDT Thu Aug 26 2021 -Heat/humidity with storm potential through Sunday -Dry with more comfortable conditions starting Monday && .UPDATE... Issued at 1148 PM EDT Thu Aug 26 2021 I have updated our forecast grids for showing the highest pops overnight to be mostly on the east side of US-131. We have a stationary front (overnight) from near MKG to near GRR to near LAN. It is not forecast to move much until after 10 am Friday. It now seems a low level jet (weak but there) develops just east of US-131 early this morning and where it crosses the front generates showers. This is were the RAP model shows the 80 to 95 percent 850 to 700 rh to be between now and 10 am. Just about every run of the HRRR since 18z has shown nearly no precipitation west of US-131 overnight. East of US-131 it has pockets of 1 to 2 inches of rain between now and noon. Locally heavy rainfall is possible east of US-131 during the early to mid morning hours. So I have updated the forecast to show this largely. && .DISCUSSION...(This evening through next Thursday) Issued at 330 PM EDT Thu Aug 26 2021 --Heat/humidity with storm potential through Sunday-- Heat indices will continue to peak in the mid 90s to around 100 in the absence of any clouds/convection through Sunday with dew pts remaining in the lower 70s and H8 temps holding near 20C. We expect isolated showers and storms through early evening, particularly along the lake breeze front near and north of GRR. Some of these could produce localized higher wind gusts and torrential downpours. ML Capes are around 2000 J/KG with mid level lapse rates around 7 C/KM and DCAPES around 1200 J/KG, although really no shear to speak of. Diurnally driven activity should fade with sunset, then attention turns to the upstream convection currently in ern MN and IA. Based on extrapolation of the upstream convective clusters (which are associated with a shortwave and also contain a couple MCVs), the shower and storm risk should ramp up again after midnight into early Friday morning. In addition to the shortwave approaching from the west we also have a warm front lifting north toward the area tonight, supporting a period of higher pops. Then it looks like a diminishing trend in convective coverage should develop by Friday afternoon with the warm front lifting farther north and subsidence/NVA moving in behind the aforementioned shortwave. However our capes will soar again on Friday to at or above 3000, and can`t rule out a few additional storm clusters riding our way from the SPC SLGT risk area over WI. Several of the CAMS support this notion, showing decent coverage of convection across our area on Friday evening. Saturday and Saturday night appear to be fairly quiet at this point as we`ll be fully in the warm sector with lack of trigger. Cant rule out some isolated diurnal convection though on Saturday afternoon/early evening inland from Lake Michigan. Coverage of storms expected to ramp up on Sunday afternoon/evening as a sfc cold front approaches from the west. Some of these could be strong/severe since deep layer shear should increase due to the shortwave passing east across the nrn GrtLks Rgn. --Dry with more comfortable conditions starting Monday-- Cooler temperatures and drier air/lower dew pts pour in behind the cold front Sunday night, ushering in a stretch of dry weather with more tolerable dew pts in the 50s and highs near 80. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 739 PM EDT Thu Aug 26 2021 The short story is largely VFR through Friday. Now there are a few lake breeze generated thunderstorms near US-131 this evening, one storm came over GRR and dissipate over GRR around 23z. A few more storms will develop and dissipate early this evening before the sun sets but other than than expect partly cloudy skies overnight. It would not be out of the question that the storms currently near the Mississippi River in MN and IA (23z) could make it into our western TAF sites in the 09z to 11z time frame. However, there is little low level jet support for this. The RAP model (22z) has the feeble low level jet axis that is forecast in this area at that time. It is centered near TVC (at 09z) and moving northward at that time. Also the moisture transport is aimed at northern lower Michigan at that time too. This sort of set-up is typically not good for thunderstorms to do well over Southwest Michigan. I am thinking whatever is coming this way will die before reaching here. Since there is a low level jet and some moisture convergence north of our CWA early Friday morning, maybe the storms will cross our northern CWA at that time but I do not see them impacting our TAF sites. As a result I took the mention of it out of the TAFs. During the day light hours of Friday I do not seem much happening either. It is true the stationary front will still be near I-96 in the morning and it wills start lifting north later in the day. Even so, most of the push for the warm front is near and west of the Mississippi River over MN. It would seem to me any storms would largely stay north of our TAF sites even then. So at this point I feature no VCTS in any of our TAFs for the next 24 hours. If it becomes more clear that storms will impact our TAF sites, we will update those impacted TAFs. && .MARINE... Issued at 330 PM EDT Thu Aug 26 2021 Increasing southerly flow over the weekend may lead to hazardous winds and waves developing, especially north of Holland from Saturday night into Sunday. A brief period of stronger northwest flow may also occur on Monday behind a cold front which comes through on Sunday night. Scattered thunderstorms will impact Lk MI on and off through the weekend and may occasionally pose a threat to mariners. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...None. && $$ UPDATE...WDM SYNOPSIS...Meade DISCUSSION...Meade AVIATION...WDM MARINE...Meade
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
959 PM CDT Thu Aug 26 2021 .UPDATE... 947 PM CDT Evening updates include lowering pops overnight across parts of the cwa. Convective evolution overnight continues to be unclear, though it appears the best focus for much of the night will be west and northwest of the forecast area across parts of IA and MN. Have eased pops to generally slight chance across our far east and southeastern counties and kept chances in the west, mostly after midnight for the majority of the area. Had a few isolated weak thunderstorms develop along the lake breeze this afternoon, and along outflow boundaries across our southeastern cwa. These have faded with the loss of diurnal heating. Currently, local air mass is generally capped with respect to near-surface based parcels. South-southwesterly low level jet back to our west across central/western IA and MN will likely be the driving feature for renewed convective development overnight, with RAP mesoanalysis depicting the best organized deep moist convergence from far northern NE across northwest IA and southern MN. Some recent convective development noted across northwest IA in fact within the low level jet axis. While CAM guidance has not been very helpful of late, latest 00Z 3km NAM and recent HRRR runs do focus on the IA/MN border region overnight for best thunderstorm coverage. The LOT cwa will be on the far eastern periphery of the low level jet, thus not expecting significant coverage for the most part. Elevated showers/embedded thunder with MCV across eastern IA will likely move into northwest/north central IL later this evening/overnight, though better potential for stronger convective development looks to remain off to the west. Some potential may exist for remnants of southern MN/northern IA MCS to push into the area Friday morning in a decaying form. Based on this have maintained going chance pops across north central IL from late evening into the overnight hours, while have decreased pops across the east/southeast to slight chances. Otherwise, no significant changes made to forecast through Friday morning. Ratzer && .SHORT TERM... 302 PM CDT Through Friday night... Main concerns are low confidence convective trends (especially tonight into Friday morning) and heat and humidity on Friday afternoon. In the near term, main areas of concern are near the lake breeze convergence and in the vicinity of the remnant MCV over the east and southeast CWA. Have seen pulse convection into our southernmost counties, with the somewhat more organized convection farther south over ILX and IND CWAs. Recent AMDAR soundings, visible satellite, day cloud phase RGB, and radar trends indicate the cap has eroded or is in the process of eroding near the lake breeze. Still think that coverage and organization will be less than yesterday but expect a few widely scattered storms until sunset. Lack of deep layer shear today vs the more supportive shear with MCV yesterday will make lightning, heavy downpours/localized flooding, and brief likely non-severe downbursts the main threats. Turning to the thunderstorm threat tonight, unfortunately confidence continues to be quite low. Thus far, the upstream convection from central IA to southern MN hasn`t really taken off this afternoon. There appears to be a weak short-wave near the southeast IA/southeast MN border assisting the ongoing convection, with the RAP initializing this and passing it north of us through Wisconsin this evening. If organization doesn`t increase with signs of MCS development and cold pool formation from this activity this evening, the chances of organized convection tonight drop off drastically given modest height falls focused north of the area. It`s possible thunderstorms to the northwest from one of the various waves over the Upper MS Valley and northern Plains congeals and pushes in later overnight, but confidence is too low to put stock in this scenario. Due to the low predictability nature of convection evolution tonight, lowered PoPs a bit from previous and show them increasing to mid to high chance overnight. If any organized/semi-organized convection moves in tonight, main threat would be wind gusts strong enough to down tree limbs. High PWAT air mass and large MUCAPE reservoir would also be supportive of at least localized flooding in the presence of deep moist convection. Trends *should* become more clear with time by this evening. Held onto chance PoPs Friday morning for the possibility of showers and thunderstorms lingering from overnight activity to the extent that it occurs. Thereafter, Friday afternoon will be hot and humid but otherwise could turn out more quiet as low level winds will increase and likely keep lake breeze development at bay, with unidirectional south-southwest winds also limiting low- level convergence across the area. In addition, modest mid-level height rises are forecast and a majority of the models advect in some pretty dry air in the 700-500 mb layer. Forecast low level thermal progs from 925 to 850 mb support highs near low to the lower 90s, with some upside potential if the afternoon ends up mostly sunny. With dew points back up in the lower to mid 70s this yields forecast maximum heat indices of the upper 90s to lower 100s (with overperforming temps bringing values closer to 105F advisory criteria). Friday night, the support for thunderstorms will primarily be across the Upper MS Valley and central and northern Wisconsin closer to the stalled frontal boundary and where short-wave forcing will be focused. Most locations have a dry forecast, except the Wisconsin state line counties where some slight chances are indicated to account for wiggle room if storms form a bit farther south than expected. Any thunderstorms that form later tomorrow-tomorrow night would have a lower end threat to become strong to severe (mainly wind threat) over far north central Illinois with up to 20-25 kt of deep layer shear forecast. Castro && .LONG TERM... 305 PM CDT Saturday through Thursday... Forecast thinking for the long term period has not changed. Hot and humid conditions will persist through the weekend then trending "cooler" next week with periodic shower and thunderstorm chances through at least Monday. The upper ridge continues to amplify in advance of an approaching upper shortwave trough. In response to this, 850 temperatures around 20C move overhead again, and this will support surface temps into the lower 90s areawide. This combined with yet another day of dewpoints in the lower to mid 70s will result in heat indices around 100 degrees. There will be some breezes out there which should help some with the heat. A few isolated to widely scattered thunderstorms are possible on Saturday afternoon. Details for Sunday into Monday are a little less certain and will depend greatly on the timing of the arrival of the upper wave and associated surface cold front. At this time, this looks to move through late Sunday night into Monday. Thus have another warm day forecast with highs in the upper 80s. Model guidance has development out ahead of the main cold front Monday afternoon and early evening with additional storms moving through with the cold front overnight. Once the cold front moves through, temperatures through at least the first half of next week will be closer to normal in the lower 80s with east northeast winds off the lake keeping lakeside areas in the upper 70s. The front does look to stall out somewhere across central IL/IN on Monday with showers and thunderstorms possible mainly south of I-80. We then trend cooler with generally low chances for thunderstorms. Will note that uncertainty in the upper pattern and precip chances increases by midweek with potential influences from a tropical system in the Gulf. Petr/KJB KJB && .AVIATION... For the 03Z TAFs... Update at 03Z: Observational and forecast model trends have backed away from convection overnight, favoring expansive thunderstorms along the IA/MN border. Accordingly, we removed the TEMPO groups for thunder at all terminals. Depending on how organized convection becomes upstream overnight, some form of remnants may try to sneak in late Friday morning or early afternoon, but will withhold on any mention in favor of watching trends overnight. Borchardt Previous Discussion issued at 00Z: The primary forecast concerns through the next 24 to 30 hours are as follows: * Isolated thunder chances through the next few hours * Chances for additional thunderstorms overnight * Potential for an easterly wind shift Friday afternoon Isolated showers and a few storms continue to percolate along a lake breeze stretching from near DPA/ORD/MDW to IGQ. With waning instability (e.g. setting sun), coverage should continue to wane over the next few hours, but opted to hold onto VCTS at the Chicago terminals through 01Z just to be safe. Attention then turns toward Iowa where thunderstorms are developing along the intersection of the nose of a 30+ kt 850mb low-level jet and a residual outflow boundary. Forecast model guidance continues to perform poorly with convective evolution tonight, though with continued low-level forcing (aided by the approach of a subtle upper-level wave over the central Plains), convection will likely continue to develop if not "grow upscale" with time with eastward motion into at least southern Wisconsin. The greatest uncertainty lies with how far south the convection will develop, so for now opted to maintain the inherited TEMPO for thunder at all terminals, but slide the timing back toward the predawn hours of Friday. Should a more organized system develop tonight, strong northwesterly winds would become an increasing concern, especially at RFD. Finally, depending on convective coverage tonight and whether the brunt passes to the north into Wisconsin, a northeasterly wind shift off Lake Michigan cannot be ruled out particularity during the early afternoon hours of Friday at ORD/MDW/GYY/DPA. After collaboration with CWSU ZAU, opted to withhold formal mention for now in place of watching convective trends over the next few hours. Otherwise, light winds will prevail tonight, with a southerly to southwesterly direction preferred tomorrow during daylight hours. Borchardt/Doom && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion
National Weather Service San Francisco Bay Area
435 PM PDT Thu Aug 26 2021 .SYNOPSIS...An interior warming trend will continue into Friday and Saturday under strong high pressure as dry northerly winds pass over the region. A few degrees of cooling by Sunday afternoon as onshore winds return then a West Coast trough brings temperatures back closer to seasonal values early next week. The forecast remains dry through the end of the month and likely into Labor Day weekend. && of 01:50 PM PDT Thursday...The region-wide warming trend is well underway this afternoon as high pressure builds over the region and temperatures aloft warm. This has compressed the marine layer to between 1,200- 1,500 feet in depth with morning fog and stratus having quickly dissipated except for along the immediate coastline. Temperatures at this hour are running a few to as much as 15 deg F warmer compared to 24 hours ago. Overnight, look for a shallow marine layer to persist with low clouds to develop near the coast and potentially over the Monterey Bay and locally into the Salinas Valley. Elsewhere, stratus will be less widespread with the HRRR forecast model indicating very little to no clouds over much of the greater San Francisco Bay Area (including the North Bay). Warm and very dry conditions will also prevail in the region`s hills, ridges and peaks given the warming air mass aloft not only tonight but also through the upcoming weekend. Smoky/hazy conditions are also forecast to be transported across the region on Friday and potentially into the upcoming weekend as winds aloft remain northerly. Will have to monitor the amount of smoke and any impacts it may have on forecast maximum daytime temperatures. Speaking of temperatures, the warming trend will continue on Friday and into Saturday as 850mb temperatures reach to around 25 deg C. This will translate to more widespread mid/upper 90s to around 105 deg F across the interior. The interior East Bay Valleys and region`s typical hot spots are the most likely to approach or exceed the 100 deg F mark in the coming days. Elsewhere, light onshore winds are likely to hold temperatures in the 60s/70s near the coast, 70s to 80s around the San Francisco Bay Shoreline and 80s/90s for other inland areas both Friday and Saturday afternoons. This said, Heat Risk analysis keeps most populated areas across the interior in a Moderate Risk with some sparsely populated higher elevation locations reaching into the High Risk. While heat products are not anticipated at this time, any added smoke may exacerbate health concerns for sensitive populations during the peak heating during the coming days. The mid/upper level ridge is forecast to begin to weaken by Sunday along with a slight increase in onshore flow. Thus, look for temperatures to cool by a few degrees across the interior albeit remaining well above seasonal averages. Forecast ensembles are in decent agreement with another mid/upper level trough to develop along the West Coast early next week. This will bring a region-wide cooling trend early next week and likely return of a deeper marine layer. Longer range outlook leans toward continued warm and dry conditions into the Labor Day weekend. && of 04:35 PM PDT Thursday...For the 00z TAFs. The marine layer continues to compress this afternoon, with the latest coastal profilers reporting a depth that is running at around 1000ft. Onshore winds (15-20kt) are also peaking this afternoon along the coastal gaps and passes. These winds will gradually subside this evening, but given the shallow nature of this marine layer, and in accordance with the latest surface smoke values on the HRRR-smoke, are on track for winds aloft to loft smoke into portions of the inland North and East Bay terminals (e.g. STS/LVK/CCR) through tonight and into tomorrow. As such, have added HZ to the terminals, while using FU for LVK to account for greater concentrations expected over the East Bay. The compressed marine layer will also result in cig reductions at the coastal terminals (e.g. MRY/SNS/WVI) where IFR/LIFR conditions are on track to develop in the overnight. Moderate confidence (TEMPOs OAK/APC) in patchy marine stratus developing along the Bay Shoreline, with higher likelihood of stratification developing along the East Bay Hills and coastal portions of the Napa Valley. Cigs that do develop will lift and clear by 16-18Z tomorrow morning. Will then see a return of onshore flow along the coast and bays by Friday afternoon. Vicinity of KSFO...VFR through the period. 20-25kt gusts will be possible at times this afternoon as onshore flow streams in from the gaps and passes. These winds will gradually subside by early evening. While stratification is possible tonight within the OAK vicinity, the chances for patchy stratus reaching SFO tonight and into Friday morning are rapidly decreasing due to a shallow marine boundary layer. Are expecting a relatively quiet night with light onshore winds (5-10kt). Winds will then pick up once again tomorrow afternoon as onshore flow streams back in to the vicinity from the gaps and passes. KSFO Bridge Approach...Similar to KSFO. Monterey Bay...VFR cigs this afternoon with breezy onshore winds, and slightly stronger winds in the Salinas Valley. IFR/LIFR ceilings with patchy FG will return late Thursday night and lasting through Friday morning due to a shallow marine layer.Cigs will then lift by 17-19Z. && .FIRE of 3:30 AM PDT Thursday...Nighttime drying event is currently underway above the marine inversion layer. Were seeing humidity values as low as 3% at Ben Lomond and 4-8% at Rose Peak in the Diablo range and even down to 12% Mallory Ridge over in the East Bay hills just below 2000 feet. Elevations above 1500 feet showing significant warming trend with readings already in the lower 70s or about 15 degrees warmer than yesterday at this time. Marine layer is compressing as forecast. Fuels are climbing back to the 97th percentile across the North Bay with values 90 percent Bay Area hills and near normal below 1000 feet due to the recent persistent marine layer influence. However given the long term drought and late summer conditions the fine fuels will dry rapidly as the next warming and drying trend starts. Expect to see that by this afternoon for inland areas. Expect little or no humidity recovery in the hills the next several nights and perhaps even night time drying like were seeing early this morning. Minimal smoke today but increasing from north to south Friday and likely into Saturday as smoke from the NorCal fires drifts south. The incoming smoke will literally be a smoke signal that the dry north winds are working down the Sac Valley and arriving. Expect this to occur overnight into Friday for the North and East Bay. Widespread 90s and lower 100s Friday afternoon and then Saturday looks to be the hottest day for inland areas. The coast will remain mild. Expect light offshore winds at night peaking early Saturday morning for the Napa hills. Criteria will be near critical but at this time we look to fall short of Red Flag criteria as no moderate/strong offshore winds are forecast. On Weds afternoon we saw heavy initial attack fires erupt across the state as well as continued activity for the large ongoing wildfires. The hot/dry conditions will now be over the Bay Area the next several days so any new starts will likely exhibit rapid growth. Essentially the marine layer has been our safety shield for much of August. The ridge will minimize its impacts and we are rapidly approaching September which signals the start of our climatological offshore wind season and peak fire season for the Bay Area. && of 02:44 PM PDT Thursday...Winds out of the northwest increase over the waters this afternoon growing strong and becoming more widespread over the waters by Friday. These winds will have the potential to generate steep waves and produce hazardous seas conditions, particularly for smaller vessels. Seas remain wind drive at a period around 8 to 10 seconds with a lighter, longer period southerly swell embedded it. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tngt...GLA...Pt Arena to Pigeon Pt 10-60 nm from 3 AM SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 AM SCA...Pt Arena to Pigeon Pt 10-60 nm until 3 AM SCA...Pt Arena to Pt Reyes 0-10 nm SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm && $$ PUBLIC FORECAST: RGass AVIATION: Diaz MARINE: Diaz FIRE WEATHER: RWW Visit us at Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion
National Weather Service Shreveport LA
941 PM CDT Thu Aug 26 2021 .UPDATE... No wholesale changes are needed to this afternoon`s forecast package at this time. Updated the 00Z-03Z PoPs to reflect the diminished convective activity as of 02Z, and updated the QPF and Wx grids accordingly. RAP13 and HRRR are in agreement that no further convection is expected throughout the overnight hours, thus maintaining minimal PoPs through 12Z. Otherwise, ingested the last several hours worth of temperature and dewpoint observations and interpolated through to morning lows in the low to mid 70s areawide. /26/ && .PREV DISCUSSION... /issued 639 PM CDT Thu Aug 26 2021/ AVIATION... For the 26/00Z TAFs, a line of thunderstorms is tracking westward across our southern zones, primarily south of the I-20 corridor, thus TEMPO for TSRA at LFK. Carrying VCTS for GGG, SHV and TXK. Storms will dissipate after sunset, with VFR conditions prevailing through the nighttime hours. Some brief MVFR conditions resulting from patchy fog are possible near dawn at MLU, ELD, LFK and TYR. VFR conditions will then prevail at all terminals into the afternoon. Winds will be generally from the east/southeast with peak sustained speeds of 5-10kts. /26/ PREV DISCUSSION... /issued 240 PM CDT Thu Aug 26 2021/ SHORT TERM.../Tonight through Friday Night/ Temperatures this afternoon have climbed into the lower to mid 90s across the area with heat index values ranging from the lower to mid 100s. A Heat Advisory will remain in effect this afternoon through 6:00 PM CDT this evening. Starting to see some showers and thunderstorms develop this afternoon across deep east Texas and southwest Arkansas. Expecting this activity to increase and move into our Louisiana Parishes during the afternoon hours before coming to an end shortly after sunset. Overnight lows will range from the lower to mid 70s across the area with generally clearing skies. We could see some patchy fog overnight for a few locations, but definitely not widespread. As we move into Friday, the good news is that temperatures and dewpoints will be slightly lower than what we have seen over the past few days, which in turn means no need to issue another Heat Advisory. Afternoon highs will generally range from the lower 90s to near 95 degrees across most of the region. Showers and thunderstorms will once again be possible Friday afternoon, with the best chances coming for areas along and south of I-20. Overnight lows Friday night will generally range from the lower to mid 70s across the area. /33/ LONG TERM.../Saturday through Wednesday Night/ The first 24 hours of the long-term forecast, mainly Saturday through sunrise Sunday, will continue to be characterized by a deep southerly flow around a strong deep layer ridge centered over the Carolinas. This should continue to bring chances for diurnal showers and thunderstorms associated with the sea breeze northward into the forecast area. Low-level moisture will be rapidly surging northward into the area. Given the cloud cover and a relatively high amounts of convective coverage, this should help to hold daytime high temperatures in the lower 90s for Saturday. Now...onto the big story. Tropical Depression Nine has developed in the Western Caribbean Sea. Very early Saturday morning, TD #9 should move across Cuba and into the very warm waters of the Southeast Gulf of Mexico. There will be a very favorable environment in place for strengthening into an eventual hurricane. The flow around the ridge over the Carolinas will steer this storm northwestward towards the Louisiana coast, with an expected landfall either very late Sunday or very early Monday morning. Most of the operational model guidance continues to trend with a more eastward track, generally towards Southeast Louisiana, followed by a more northward turn either generally up the Ouachita or Mississippi Rivers, and eventually northeast into Northwest Mississippi by Tuesday morning. There is still enough uncertainty in the track that a shift eastward or westward will significantly change the impacts to our area, both in terms of wind and rainfall. At this time, the areas most likely to be impacted by this storm appear to be Louisiana...especially east of Interstate 49, and South Central Arkansas. The western side of a landfalling tropical system tends to be the "dry" side. Thus, there will be very tight gradient in the rainfall amounts. Potential rainfall amounts should range from 3 to 6 inches east of a line from El Dorado to Colfax, with totals increasing with eastward extent. Rainfall amounts decrease quickly to the west. While the main impacts appear to be focused on Louisiana and Arkansas, this storm still has a long way to travel. The remainder of the forecast area is still not out of the woods. Everyone is encouraged to continue to monitor the latest forecasts over the next few days. Beyond Tuesday, the forecast is very uncertain. The NBM continues to hint that a moisture plume trailing southwest from the remnants of this tropical system will continue to provide chances for mainly diurnal showers and thunderstorms through the midweek time frame. Therefore, chance PoPs were maintained, with the highest rain chances across the southeast half of the forecast area close to this tropical moisture plume. CN && .PRELIMINARY POINT TEMPS/POPS... SHV 75 95 75 91 / 10 30 0 40 MLU 73 94 74 91 / 10 30 10 50 DEQ 74 93 73 91 / 0 10 0 20 TXK 75 93 75 90 / 0 20 0 30 ELD 72 93 72 91 / 0 20 0 40 TYR 75 93 74 91 / 10 30 0 30 GGG 73 93 73 90 / 10 30 0 40 LFK 74 94 73 89 / 20 30 10 60 && .SHV WATCHES/WARNINGS/ADVISORIES... AR...None. LA...None. OK...None. TX...None. && $$ 26/33/CN
Area Forecast Discussion
National Weather Service Sacramento CA
238 PM PDT Thu Aug 26 2021 .SYNOPSIS... Winds shift to the north today, and will become locally breezy Friday and Saturday. This along with low humidity and dry fuels will bring critical fire weather, so a Red Flag Warning has been issued. Smoke and haze from the wildfires will continue to impact portions of the area.Temperatures will warm to above normal levels by late week, though the smoke may keep it from getting as hot as it otherwise could be. && .DISCUSSION... A building high pressure ridge will increase the north to south pressure gradient late tonight into Friday. The HRRR smoke model shows near surface smoke levels increasing across the Valley and Delta as northerly winds increase with this gradient. Air quality will likely worsen. For more details on this, go to or check with your local air quality district. There north winds over the northern and central Sacramento Valley will increase further early Friday morning and become gusty. Winds could gust to 35 mph during the strongest winds mid day and afternoon. Relative humidity recovery will be moderate to poor in the morning, with afternoon humidity dropping to single digits to teens from around Chico northward. The Fire Weather Watch in that area has been upgraded to a Red Flag Warning from 5 am Friday morning to 11 am Saturday morning. The earlier start is due to winds picking sooner than previously expected. The ridge strengthening offshore will also lead to warming over the next several days. Triple digit high temperatures are forecast for northern Sacramento Valley on Friday, with chances expanding south down the Valley for Saturday and continuing Sunday. Wildfire smoke may reduce solar heating, so have reduced forecast high temperatures by a few degrees, with highs projected to peak around 100-101, bringing moderate heat risk. Monday Valley highs cool down into the low to mid 90s as an upper trough approaches, bringing cooler onshore flow. This should act to shift the smoke eastward, bringing clearer air. Gusty southwest winds over Sierra ridges could enhance fire weather concerns there. EK && .EXTENDED DISCUSSION (Monday THROUGH Thursday)... Ensembles are in good agreement with dropping an upper level disturbance south along the British Columbia coast toward Oregon itno Tuesday. Locally, this would lower geopotential heights and allow temperatures to moderate closer to normal by around Tuesday. This would also bring gusty southwest winds, which could increase fire weather concerns over the Sierra. && .AVIATION... VFR with gusts generally under 12 kts. By 00 UTC Friday, conditions begin to degrade starting in the northern Sacramento Valley terminals due to area wildfires smoke. Widespread MVFR to locally IFR conditions develop southward overnight due to the area wildfire smoke. Northerly winds increasing after around 10 UTC with surface gusts 15-30 kts. && .STO WATCHES/WARNINGS/ADVISORIES... Red Flag Warning from 5 AM Friday to 11 AM PDT Saturday for Central Sacramento Valley in Glenn, Colusa, Yuba, Northern Sutter, and Butte County Below 1000 Ft-Eastern Mendocino NF- Eastern Portion of Shasta/Trinity NF-Northern Sacramento Valley to Southern Tehama County Line Below 1000 Ft-Northern Sierra Foothills from 1000 to 3000 Ft. Includes portions of Shasta- Trinity and Butte Units-Southeast Edge Shasta-Trinity NF and Western Portions of Tehama-Glenn Unit. && $$