Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/20/22

Area Forecast Discussion
National Weather Service La Crosse WI
1041 PM CDT Mon Sep 19 2022 .UPDATE... Issued at 638 PM CDT Mon Sep 19 2022 Latest radar trends are showing more of a shift southeast in their movement in the area of showers and scattered storms. It now looks like they are trying to follow the most unstable CAPE axis. If this trend continues may have to lower the PoPs north of Interstate 90 and raised them even more across northeast Iowa and southwest Wisconsin this evening. && .DISCUSSION...(This evening through Monday) Issued at 240 PM CDT Mon Sep 19 2022 Key Messages: - Shower and storm chances increase overnight - Very warm and muggy tomorrow SHOWERS AND STORMS LATE TONIGHT: As a warm front approaches the area overnight, shower and storm chances will be on the rise-especially in central Wisconsin. A surge of warm, very moist air helps saturate the lower levels late tonight. Once the low levels are saturated, warm air advection, moisture transport, and a low level jet will all work to provide plentiful lift and initiate showers and storms in western Wisconsin. With a nighttime inversion and an elevated mixed layer aloft, storms that form will likely stay elevated (1-2 km) across our forecast area. Even so, upwards of 2000 J/kg of CAPE could be realized with any storms and pose a localized large hail threat. Overall, the risk for organized severe weather remains low due to very marginal effective shear values. Precipitation is progged to push east of the local area by the start of the work day tomorrow. WARM AND MUGGY TOMORROW: Very warm temperatures will arrive in the wake of the warm front tomorrow with highs reaching 85-90 for most. The NAFES Standardized Anomaly shows two standard deviations above normal at 850mb for this time of year! While it will be cloudy in the morning, skies will become mostly sunny south of Interstate 94. Heat index values are currently forecast in the low to mid 90s tomorrow afternoon. COOLER WEATHER ON THE WAY...WITH ON AND OFF PRECIPITATION CHANCES: Tuesday night through Wednesday night, we`ll see the Canadian trough lower heights from the Great Lakes into New England. This trough will push a cold front through the ARX county warning forecast area. 850mb temperatures around 24 deg C. will plummet to 10 to 18 deg C by Wednesday morning and the 0 deg isotherm approaches Taylor County by 12Z Thursday. Spotty precipitation chances linger Tuesday night into Wednesday. The cold front will usher in brisk northwest flow and drier/cooler air later Wednesday and Thursday. Surface high pressure will be centered over the region with return flow setting up Thursday night. How cold it gets will depend on how quickly the clouds arrive from the west with the. The MDZ forecast sounding shows light winds through a depth of 3km with some increase in 400mb moisture. The current forecast has lows in the 30s for parts of the La Crosse River Basin, Black River Basin, and the Lemonweir River Basin. The trend has been colder over the last few days at BCK with lows in the lower 30s and a 10th/90th percentile spread of 30/40. The current soundings were a bit dry, but with clear skies, could see valley fog as well. We`ll continue to watch the cloud trends for Friday morning`s forecast. Highs in the 60s and lower 70s for Wednesday with 50s/60s for Thursday and Friday. The closed low over the West Coast lifts northeast into MT/Northern Plains and eventually the Upper Mississippi Valley through Friday night. Shower chances increase Friday and exit the area by Saturday with this system. Shortwave energy swings through the region Saturday night into Sunday. Shower chances may have to be increased per recent trends of stronger cyclonic flow for Sunday. Warmer temperatures are on tap for Saturday with closer to normal temperatures Sunday and Monday. && .AVIATION...(For the 06Z TAFS through 06Z Tuesday night) Issued at 1040 PM CDT Mon Sep 19 2022 The showers and storms that have been moving across the area this evening will be off to the east of both airports by 06Z. Attention then turns to the possibility of more convection developing overnight on the nose of the low level jet ahead of an incoming short wave trough. The CAMs all show this activity developing but with differences on how far north it will be. The HRRR has been continuously trending farther north through the evening and is now an outlier compared with other models. Thinking this should generally be north of both airports, in the Interstate 94 corridor, but could be close enough to KLSE to include a couple hours of VCTS. Once this activity moves off Tuesday morning, the clouds will scatter out with VFR conditions expected through the evening. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...NONE. MN...NONE. IA...NONE. && $$ UPDATE...Boyne DISCUSSION...KAA/Zapotocny AVIATION...04
Area Forecast Discussion...CORRECTED
National Weather Service Duluth MN
1018 PM CDT Mon Sep 19 2022 .MESOSCALE UPDATE... Issued at 925 PM CDT Mon Sep 19 2022 (Corrected for LLJ wind direction.) Relatively quiet evening so far may become more active over east- central Minnesota and northwest Wisconsin overnight. Several CAMs are developing thunderstorms well inland from Lake Superior on the nose of the southernmost branch of a southwesterly low-level jet. Taking a peek at RAP forecast soundings over Price and southern Sawyer counties reveals a noteworthy increase in instability in the 08-12Z time range. Thermal and moisture advection associated with the jet will create a favorable environment for storm development. MUCAPE generated from parcels either side of 850 mb (depending on location) will increase from a negligible amount currently to 2000-3000 J/kg. Effective shear also appears to increase as the LLJ arrives, increasing to 35-40 knots. Downdraft CAPE is also noteworthy in response to the low- level advection at around 1000 J/kg. There are a few elements which appear to mitigate the increase in instability. First would be pressure perturbations potentially affecting the trajectory and intensity of the LLJ as it develops over Minnesota in response to the existing band of storms as of 20.02Z over eastern MN and western WI. The storms are stronger than guidance indicates at this time, which may limit the northward extent of the LLJ overnight. The other factor is the considerable amount of dry air above 850 mb. Dry air entrainment will reduce the effective instability the storms are able to draw from. Confidence in storm development is higher than it was this afternoon, but only hovering in the 20-30 percent range. Should storms develop, a few may be strong with hail to penny-size, wind gusts of 40-50 mph, and frequent cloud-to-ground lightning possible. The storms should move out of the region in the 11-14Z timeframe. && .DISCUSSION...(This evening through Sunday) Issued at 407 PM CDT Mon Sep 19 2022 Summary...A passing low pressure system will bring precipitation chances tonight through Wednesday. After that, a surge of much colder air will move into the area, bringing the potential for frost to the area for Wednesday night/Thursday morning, and again Thursday night/Friday morning. Temperatures moderate into next weekend as yet another shortwave brings precipitation chances for the weekend. A low pressure system and shortwave is pushing a warm front across the area this afternoon and tonight, which should help generate precipitation, mainly along and north of the MN-Canada borderlands where the dynamics are strongest. There is enough instability for a few thunderstorms, but not enough for any severe storms. We will still be in the warm sector to start out tomorrow, but the trailing cold front will slowly advance through the area starting around mid morning, and should kick off yet more shower and storm chances. During the afternoon and early evening before the front sags south out of the area there may be some strong to severe storms nearby for a short time period. SPC has put a marginal risk over Wisconsin adjoining the forecast area, but may ooze into the CWA. Otherwise, showers should linger into Wednesday in the cyclonic flow, moisture and steep low level lapse rates behind the cold front. As the Tuesday system departs, it will bring a surge of cold air in behind it, with 850 mb temperatures dipping to around zero in most of the forecast area Wednesday night through Thursday afternoon. Assuming we can get clear skies, the surface ridge of high pressure that slides over the area Wednesday night through Thursday night should cause winds to become very light and set up good to excellent radiational cooling conditions. Temperatures should fall significantly below normal overnight, with a lot of ensemble probability products showing increasing probabilities of temperatures at or below 32 degrees, especially in the Wednesday night or Thursday morning time frame. Have included frost in the forecast both Wednesday night and Thursday night. We will have to keep an eye on this, as this early in the fall a bit of cloud cover or wind can keep temperatures from dropping far enough to make frost. High temperatures both Thursday and Friday will be mostly in the 50s with a few locations getting up into the low 60s. Another shortwave advances toward the area pushing showers and thunderstorms into the area starting Friday, lingering into at least Friday night as the initial warm air advection wing moves across the area, with additional precipitation chances Saturday night and Sunday along and behind the cold front. After the cool temperatures Thursday and Friday, we warm back towards normal for the weekend and early next week, but still will feel cool. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 646 PM CDT Mon Sep 19 2022 VFR conditions are expected this evening and into tonight. Patchy fog may be possible early Tuesday morning, particularly in BRD and HIB. Only reduced visibility to MVFR in BRD, where confidence is highest for fog development. Cloud cover will increase tomorrow ahead of an approaching cold front. Recent model runs have been increasing the potential for MVFR cigs in DLH and especially HYR, so made a reduction in category. Any MVFR cigs across the region will lift to VFR by the afternoon. Thunderstorms may be possible in the late afternoon on Tuesday. However, since this is conditional on the amount of daytime heating we can achieve, a VCTS mention was left out for now. && .MARINE... Issued at 407 PM CDT Mon Sep 19 2022 Generally quiet conditions are expected on the lake tonight through Tuesday. Southwest winds of 15 knots or less with waves under 3 feet. Winds become northwest Tuesday night and increase on Wednesday, with Small Craft Advisory conditions possible for Wednesday and Wednesday night. && .PRELIMINARY POINT TEMPS/POPS... DLH 58 77 52 59 / 10 20 10 10 INL 56 73 47 56 / 30 10 30 30 BRD 60 81 51 63 / 10 20 0 0 HYR 58 79 51 63 / 20 20 20 10 ASX 58 82 53 65 / 10 20 20 10 && .DLH WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. LS...None. && $$ MESOSCALE...Huyck DISCUSSION...LE AVIATION...Unruh MARINE...LE
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1024 PM EDT Mon Sep 19 2022 .SYNOPSIS... Dry weather continues into midweek as a dome of high pressure expands across the Southeast, allowing temps to warm well above normal. A cold front crosses the area from the north on Thursday and could have enough moisture to squeeze out a few showers across the forecast area. Canadian high pressure will bring cooler and drier weather to the region for the weekend. Another cold front will arrive early next week. && .NEAR TERM /THROUGH TUESDAY/... As of 1000 PM EDT Monday: Most sites have gone calm or retain very light NNW flow. RAP analysis indicates a measure of drying just upstream from the CWA, which appears to be limiting cloud cover over the mountains thus far. Tonight will be a mixed bag in terms of mountain fog; guidance has backed off still more on cloud cover, opting to largely clear out 500mb moisture soon after nightfall, and maintaining only a shallow mid/low-level moist layer near 700mb, the tenacity of which is questionable based on the latest satellite imagery. Still, this may be enough to halt radiative cooling for the first part of the night...setting us up for a situation with more isolated, patchy dense fog where intermittent clearing allows rapid deterioration of visibility. Otherwise, upper anticyclone will remain nearly stationary over the Southern Plains/Lower MS Valley through the period. Any weak surface trough associated with a diffuse remnant cold front is expected to shift east of the area before peak heating Tuesday and should keep any convection or PoPs in general at bay through the daytime period, notwithstanding some likely overdone convective initiation in the NAMnest. Overnight lows will be no more than a category above normal, while highs on Tuesday run up to 10 degrees above normal. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... As of 200 PM Monday: Upper ridging will hold on across the area Wednesday, as the large anticyclone will begin to flatten under a digging trough across the Great Lakes. Dry conditions will continue, and temps will be about 10 deg above normal, with low 90s across most of the Piedmont. A cold front will cross the forecast area from the NW on Thursday, thanks to a digging upper trough. The front will have a narrow band of some 1.5" or so PWATs, and the guidance seems to be converging on at least a narrow line of some frontal precip possibly pushing into the NC mountains. Have bumped up PoPs slightly above NBM to reflect that. East of the mountains will have a solid downslope flow, which will help bump temps up toward the mid 90s, while killing off any convection that tries to survive over the mountains. The front will have strong upper support, so cannot rule out a stray shower or two across mainly the NC Piedmont. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 230 PM Monday: The upper pattern will quickly evolve into more of a zonal regime by the weekend, as a series of short wave troughs/ upper lows migrating across the western half of the country causes the Texas anticyclone to break down. Friday will be noticeably cooler behind a strong fropa, with highs near to slightly below normal. Then temps rebound a few deg Saturday, and then a few deg more on Sunday, as high pressure slides east and brings a warm SWLY flow. A deep trough will dig into the eastern U.S. by Monday, bringing another cold front into the area from the west. This front will be slower-moving than the Thursday front and may have a little more moisture to work with. So PoPs ramp up into the chc range (in the mountains Sunday-Sun night, and across all but the lower Piedmont Monday). && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... At KCLT and elsewhere: Generally quiet conditions through the period as a weak upper disturbance enhances overnight cloud cover in the mountains. This should not in itself be significant, with no ceilings expected to form; however, it presents a difficult situation for fog/low stratus in the mountain valleys. Most guidance hints at IFR cigs developing at least across the Little Tennessee River Valley and perhaps also the French Broad River Valley, with far lower likelihood of restrictions farther north. That said, even in the favored valleys, cloud cover may initially limit fog development, with later periods of clearing allowing for a sudden drop in vis and/or cigs. For now, have only advertised IFR restrictions at KAVL, but have hinted at the possibility at KHKY as well with BR mention. Tuesday, conditions once again suppressed by the synoptic pattern. NNW winds pick back up after sunrise and another round of cu picks up. For now, don`t expect any showers to break containment and enter the Carolinas. Outlook: Relatively dry high pressure remains over the region and VFR conditions are expected to persist through much of the week. Low stratus and/or fog will remain a concern each morning, primarily in the mountain valleys. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...CAC/MPR SHORT TERM...ARK LONG TERM...ARK AVIATION...MPR
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
855 PM CDT Mon Sep 19 2022 .UPDATE... Issued at 855 PM CDT Mon Sep 19 2022 The main focus is convective trends through Tuesday morning. A narrow zone of sufficient moistening at around 700 mb paired with a mid-level speed max and some mid-level f-gen has resulted in elevated convection from southeast MN down to northeast Iowa. This is on the eastern periphery of a sharp MUCAPE gradient across the region as an impressive EML oozes east-southeast. The Iowa activity is farther south than most guidance has been depicting. Latest radar mosaic and lightning trends suggests weakening has commenced, though given proximity, added some slight chance PoPs in western 1/4 or 1/3 of CWA in the late evening and early overnight. With the broad warm advection near elevated frontal boundary continuing through the night, concern is that activity in the vicinity of the Twin Cities area increases in coverage and gradually intensifies as instability gradient slides eastward. The MUCAPE gradient is forecast to retain a sharp northwest to southeast edge, but position itself roughly across the Chicago metro into Tuesday morning. Conditional to sufficient moistening between 800 mb and 700 mb (which is currently quite dry) and aided by 850-700 mb fgen near the elevated warm frontal zone, cluster of elevated convection could track southeast from southern Wisconsin along the instability gradient. This is well south of the past several HRRR runs, but has support from some guidance including the 18z NAMs, 18z ECMWF, and 18z 2.5 km (Canadian) HRDPS. Potentially impacted areas would include areas within a zone roughly bounded by South Beloit IL in the northwest and Valparaiso IN to the southeast between about 7AM and 12PM. Thinking is threat would last up to 2-3 hours in any given location and then exit east/southeast. Very steep mid-level lapse rates sampled by 00z RAOBs are a concern for a hail threat if sufficient low-mid level moistening enables tapping into MUCAPE up to 1500-2200 J/kg amidst 30-40 kt of effective bulk shear. Main adjustment in the forecast grids Tuesday morning was to bring chance PoPs a bit farther south. Planning to highlight this potential in a graphic. Otherwise no changes to the message of late season heat and humidity Tuesday afternoon. Drying aloft will result in strong capping and prevent any additional activity (if scattered t-storms due occur in the AM). Castro && .SHORT TERM... Issued at 122PM CDT Mon Sep 19 2022 Through Tuesday night... We`re enjoying yet another beautiful September day thanks to a 1016mb surface high pressure system centered along the IA/IL/WI borders. Light east to northeasterly winds, lowering humidity levels, and mostly sunny skies are giving way to temperatures in the upper 70s to lower 80s. From a broader view, national satellite imagery bolstered by RAP-analyzed height fields depict an expansive summer-like ridge across much of the United States with the apex of mid-level heights over the central Plains. The pattern sure looks more like July than September! After midnight, a low-level jet will develop from central Iowa into west-central Wisconsin along the northwestern periphery of the surface high pressure system and ahead of a subtle upper- level trough approaching from the northwest. A narrow tongue of low- level moisture currently stretching across southern Iowa will "pivot" northeastward and engage a plume of steep mid-level lapse rates of 7-7.5 K/km extending across the Upper Mississippi River Valley to generate elevated instability. Taken altogether, a narrow axis of thunderstorms appears poised to develop overnight in central Wisconsin and track southeastward along the nose of the LLJ toward Lake Michigan by daybreak. Questions remain on just how far south the activity will build (e.g. into northeastern Illinois) given 1). the low-level jet supporting the convection will wane toward daybreak; 2). the low-level moisture plume will be rather narrow and may not survive into our relatively dry airmass. Available high resolution CAM guidance seems to be trending away from thunderstorms surviving into far northeastern Illinois, though steep mid-level lapse rates often "overperform." For this reason, we will maintain low-end chances (20-30%) for thunderstorms toward daybreak in northeastern Illinois with the better chances (>30%) remaining in Wisconsin and Lower Michigan. Chances for severe weather during the morning appear low (<5%) owing to what will probably be a messy cluster storm mode though a few spits of pea to dime size hail cannot be ruled out. Outside the chances for thunderstorms toward daybreak, tonight looks quite across our area with clear skies, light winds, and overnight lows in the upper 50s to lower 60s. Areas of shallow ground fog cannot be ruled out in river valleys and low-lying fields, though increasing low-level winds atop the stable layer should provide enough dry-air entrainment to prevent any fog from becoming dense. Tomorrow, the ridge axis is expected to drift eastward over the Great Lakes leading to an unseasonably warm and summer-like day. Forecast 925/850mb temperatures near +27C/+22C with nearly complete sunshine will support afternoon high temperatures climbing into the upper 80s to lower 90s areawide. Gusty southwest winds will bring the warmth all the way to the Lake Michigan shore. Increasing low- level moisture advection most easily tracked by rising dew points into the lower 70s will make it feel like the mid to upper 90s by early afternoon. Wet bulb globe temperatures - which takes into account the sun angle, cloud cover, and wind speed in addition to the humidity levels and temperature - peak in the 85-87 degree range tomorrow afternoon, which is an entry point for heat-related illness for those engaging in prolonged outdoor activity without adequate hydration. Accordingly, take frequent breaks in shade and hydrate often if planning to be outdoors tomorrow afternoon such as during after-school activities. (Also, and this is almost reckless to ask, but will tomorrow be our last 90 degree day of 2022? Daily record highs at or above 90 stretch into early October but the long-range forecast certainly looks more fall-like than summer). We`ll also have to keep an eye on attempts for an isolated thunderstorm or two to develop tomorrow afternoon within the increasingly humid and unstable airmass. Forecast soundings depict stout low-level capping (anchored by the aforementioned unseasonably warm 925/850mb temperatures). However, an approaching upper-level speed max from the northern Plains may encourage a few updrafts to fight against the cap particularly across Wisconsin and Michigan and perhaps as far south as the Illinois border. If a thunderstorm were to become established, a localized severe weather threat with all hazards would materialize given the available instability and speed/directional shear. Again, such a threat appears highest across Wisconsin and Michigan. Tomorrow night will be breezy and humid ahead of an approaching cold front from the northwest. Overnight lows will range from the upper 60s to lower 70s. Borchardt && .LONG TERM... Issued at 247 PM CDT Mon Sep 19 2022 Wednesday through Monday... The forecast messages for this period are: * Next chance of showers and possible storms comes with a strong cold frontal passage on Wednesday. * Our first true taste of fall weather arrives in the wake of this front for the second half of the week. Daytime highs expected to be in the 60s, with lows in the 40s and 50s. * Brief moderation in temperatures for Saturday, then turning cooler with another chance of rain with another cold frontal passage later in the weekend. An upper trough currently over southwestern Canada is expected to dig over the Upper Midwest and Great Lakes Regions during the second half of the work week. As it does so, a strong surface cold front will drop southward across the region during the day Wednesday. A strong baroclinic zone is expected to accompany the front, so we actually experience or daytime high temperatures on Wednesday in the morning, with steady or even slowing falling temperatures during the afternoon, especially across northern sections of the area as winds turn breezy from the north. Depending on the actual timing of the frontal passage, we will need to keep an eye on the potential for some thunderstorms, particularly over southern sections of the area into the afternoon. It appears that the area may largely remain capped to near surface based convection by a lingering Elevated Mixed Layer (EML) inversion ahead of the front. So, shower and thunderstorm activity may be favored more along and in the wake of the surface front (Anafrontal structure). The lasted NBM guidance offered up chance pops during this period, which seems reasonable at this early stage. Dry and unseasonably cool weather will be the story in the wake of this front Wednesday night through Friday as the main upper trough digs in over the Great Lakes. Conditions looks to remain breezy on Thursday as high temperatures on climb in the low to mid 60s. Wind speeds should tail off quickly into Thursday night, however, as an area of surface high pressure moves into the area. Light winds, and mainly clear skies under this high Thursday night should set the stage for a rather chilly night across the area. Currently temperatures are forecast to bottom out in the low to mid 40s away from the city early Friday morning, but would not be surprised to see a few upper 30 degree readings in the usual cold spots. Cloud cover looks to increase on Friday in association with the next impulse expected to shift over the Northern High Plains. Cool weather continues Friday, with highs once again expected to only be in the low to mid 60s. A surface warm front looks to shift northeastward across the area sometime late Friday night into Saturday morning. While this could result in a brief period of showers Friday night, it should lead to an uptick in temperatures back into the 70s for Saturday. Thereafter, however, model and ensemble guidance are in general agreement that sometime later in the weekend into early next week another digging trough will send another decent cold front our way. Another period of inclement weather is possible with the front, followed by another cool down. KJB && .AVIATION... For the 00Z TAFs... Aviation Forecast Concerns: * Some potential for scattered thunderstorms in far northeast IL Tuesday morning. * Breezy south winds Tuesday afternoon with gusts around 20 kts Quiet aviation weather is on tap this evening with surface high pressure centered over Lake Michigan. Light east-southeast winds and clear skies will be the rule through midnight or so. Later tonight, a warm front currently stretching from eastern South Dakota to central Illinois will begin to shift to the northeast, with an axis of mid-level warm/moist advection developing from northern Iowa/Minnesota into southern Wisconsin. Model guidance is in generally good agreement in depicting thunderstorms developing across the upper Mississippi Valley before sunrise, then propagating southeast across southeast WI and southern Lake Michigan Tuesday morning. While there is some uncertainty about the southwestward extent of this activity in to northeast IL, some high-res CAM guidance does clip the region (and notably KORD/KMDW). Current convection along/south of the IA/MN border has not been handled well by CAMs and is generally occurring farther south then forecast. Therefore feel it prudent to have a prob30 TSRA mention for northeast IL airports. Surface winds will become light southeast early this evening as the high drifts slowly east and the weak lake breeze circulation decays. The surface warm front will move through the area midday Tuesday, with winds becoming breezy from the south (180-210 deg) with gusts around 20 kt during the afternoon. Will likely lose gusts with sunset, though maintain southwest winds around 10 kt into the evening. Some potential for LLWS conditions later in the evening as low a 35-40 kt level jet develops, though not included in current TAFs with plenty of time to assess that further. Ratzer && .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 Sacramento CA
320 PM PDT Mon Sep 19 2022 .Synopsis... Showers and thunderstorms over interior NorCal through Wednesday. High temperatures well below normal through mid-week, returning to near normal by next weekend. && .Discussion... Water vapor satellite imagery shows an upper level low sitting just off the CA coast this afternoon. Latest radar returns indicates showers and some thunderstorms moving across portions of the northern Sacramento Valley and adjacent terrain this afternoon. Additional showers and thunderstorms are spreading across the northern San Joaquin Valley and into portions of the Sierra Nevada. CAMs suggest additional thunderstorm development through this evening into early Tuesday. HREF probabilities of reflectivities greater than 40 dBZ are highest in the Delta, central/southern Sacramento Valley and the northern San Joaquin Valley this afternoon and evening, then over the Sierra this evening. Cannot rule out the potential for small accumulating hail, heavy rain or even weak tornadoes with any thunderstorms that develop through this evening. In addition, moderate to heavy rainfall rates are expected to near burn scars including the August Complex, Mosquito Fire and LNU Complex burn scars today. HREF Probability of rainfall exceeding 0.5" in 1 hour is 20-45% for the LNU Complex. Current expected rain rates are 0.50-0.75"+ per hour based on the latest the HRRR Post-Fire Debris Flow tool. Therefore, a Flash Flood Watch remains in effect for the LNU Complex through this evening. The northern Sierra, including the Mosquito Fire, will continue to see additional heavier precipitation and possible thunderstorms through this evening, with more precipitation expected on Tuesday. Probability of exceeding 0.5" in 1 hour is around 20-30% for the Mosquito Fire through this evening. A Flash Flood Watch remains in effect for the Mosquito Fire through Tuesday evening given the threat for afternoon thunderstorms and the potential for some ash flows. Shower and thunderstorm threat will continue into mid-week as the low meanders in the vicinity. Best thunderstorm potential appears to be over portions of the Coastal Range, Shasta County and the Sierra north of I-80 on Tuesday. Much cooler than normal temperatures will stay around through the middle of the week. && .EXTENDED DISCUSSION (Friday THROUGH Monday)... Main upper low progged to progress east as NorCal comes under upper ridging, which amplifies and progresses through the area over the weekend into early next week. As a result, dry weather expected with a warming trend. Below normal high temperatures Thursday into Friday, warm to near to slightly above normal through the weekend into Monday. && .AVIATION... Rain showers and isolated thunderstorms possible in the Valley through 10z Tuesday with showers continuing over the foothills and mountains through Tuesday. Areas of MVFR/IFR and localized LIFR possible in showers and thunderstorms, otherwise VFR conditions next 24 hours. Surface winds mainly below 12 kts in the Valley with local gusts up to 25-30 kts possible in thunderstorms. Over the mountains, local southwest surface wind gusts up to 30-45 mph. && .STO WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch until midnight PDT tonight for Motherlode- Southern Sacramento Valley-West Slope Northern Sierra Nevada. && $$