Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/13/23


Area Forecast Discussion
National Weather Service Grand Rapids MI
1039 PM EDT Sun Mar 12 2023 LATEST UPDATE... Update .UPDATE... Issued at 1039 PM EDT Sun Mar 12 2023 No change at this time to the Winter Weather Advisory. Latest guidance continues to put down a swath of around one third of an inch of QPF from MKG to JXN overnight into Monday morning. This zone/corridor represents the area of best mid level FGEN forcing and deformation on the northeast side of the upper low drifting southeast from WI. Even some trowal characteristics are noted within this band, with pronounced thermal/theta-e ridge at 850 mb curling around the east and nrn side of the upper low. Respectable omega in the DGZ is shown in this zone as well and supports snow ratios on the order of roughly 15:1. The main challenge with the fcst continues to be the exact placement of the relatively narrow heavier band of snow which sets up within the current advisory area. This is a typical conundrum when dealing with an upper low-related band such as this. Some amounts of 4-6" are certainly possible in spots, with latest guidance still suggesting that the MKG to GRR area has the best shot at that. Time of day and the cooler boundary layer conditions under the upper low also supports the notion of locally higher amounts near 6 inches. Otherwise a broad 1-4" fcst is still the way to go within the advisory and there`s even a possibility for a sharp nrn gradient/cutoff leading to the nrn portions of Montcalm and Newaygo counties not really seeing much at all from this. Another thing to keep a close eye on is the possibility of a separate burst of heavier snow around South Haven Monday morning. This is an area of enhanced low level convergence in the vicinity of the sfc trough which also has some help from lake effect via a core of -12C air at H8 and westerly flow on the south side of the upper low. RAP Fcst sounding at LWA during this time shows deeply moist/unstable conditions cutting through the DGZ and extending way up beyond 10K ft. If confidence grows in this scenario coming to fruition, we may need to add the southwest corner counties into the advisory. && .DISCUSSION...(This evening through next Sunday) Issued at 344 PM EDT Sun Mar 12 2023 -- Synoptic Snow Tonight into Monday -- First order of business is the light to moderate snow that will pivot through Southwest Lower Michigan tonight and Monday. Bottom line up front is we will be issuing a Winter Weather Advisory for a swath of counties extending from the lakeshore southeast towards Lansing and Jackson. The following counties are in the Advisory...Oceana...Newaygo...Muskegon...Montcalm...Ottawa... Kent...Ionia...Clinton...Allegan...Barry...Eaton...Ingham... Calhoun and Jackson. A period of light to moderate snow will begin this evening and continue through tonight and into the afternoon on Monday. The snow is associated with a compact vorticity maximum near the Twin Cities in MN at the present time. Snow arcs out to the east of the vort and its associated surface low into Eastern Wisconsin. The vort in the mid levels and the surface low are forecast to pivot through our area laying down a swath of heavier snow. Many areas will at least see an inch of snow, but there is a zone in the aforementioned counties that will likely see 2-4 inches. Would not be surprised to see this system overperform a bit at least on a local scale. Lift in BUFKIT overviews, like at MKG, is significant and deep stretching through the DGZ especially in the NAMnest. The models have been consistent in showing an axis of heavier snow from MKG to LAN/JXN. Snowfall rates and time of day of heavier snow (around daybreak) and air temperatures dipping into the 20s tonight will likely bring about some impacts. Specifically we are concerned that the morning commute to work and school on Monday will be impacted. Extra time will need to be allowed to reach destinations and roads will not be in ideal condition given snow ongoing. Highest amounts may be in a zone across Muskegon...Ottawa and Kent Counties given what we are seeing in BUFKIT overviews and plan views of lift within the DGZ. -- Period of Lake Effect Snow Monday Aft. into Monday Night -- A period of lake effect snow is expected on the backside of this system Monday afternoon, potentially lasting into Tuesday morning. 850mb temperatures dip to around -15C, so when combined with lake T`s around +2C, upper teens C delta T`s are in play. Plenty of instability in place. Wind direction during this time frame will be from the north-northwest (around 340 degrees). This places Mason...Oceana and Van Buren Counties most in line for accumulating snow. The most significant lake effect should occur Monday evening between 00z and 06z when upper troughing is still hanging on. We could see several more inches of new snow out of the lake effect at places like Ludington, Pentwater and South Haven/Covert. No headline at this point for the lake effect, but later shifts will be monitoring. -- Stronger system for end of the week with rain then snow -- A stronger system is still forecast by the medium range models to affect the Great Lakes region. Initially a warm system with rain Thursday into Thursday night. Precipitation begins to mix with snow on Friday changing to all snow as we head into Saturday. The GFS has +8C at 850mb Thursday night, plunging to -14C by Saturday. Looks like the heavier snow with this system will occur north and west of the low track which would place it in Wisconsin. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 756 PM EDT Sun Mar 12 2023 Snow will impact the terminals tonight and Monday. Generally MVFR conditions this evening will trend to mostly IFR toward/after midnight as the snow increases in intensity. Most of Monday morning should feature IFR vsbys in snow as well before a diminishing trend moves in after 18Z from northwest to southeast. Gradual improvement in vsbys into at least MVFR category anticipated as that occurs, with northerly winds increasing to 10 to 20 knots. && .MARINE... Issued at 344 PM EDT Sun Mar 12 2023 Small Craft Advisory looks good from this evening into the Tuesday evening. An increasing north to north-northwest flow will set up behind a departing low. The winds really ramp up Monday morning after daybreak when winds increase to around 30 knots. Solid 20-30 knot winds will continue into Tuesday morning. Waves will likely approach or exceed 10 feet in much of the nearshore zones, especially south of Holland. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Winter Weather Advisory until 1 PM EDT Monday for MIZ043-044-050- 051-056>059-064>067-073-074. LM...Small Craft Advisory from 11 AM Monday to 10 PM EDT Tuesday for LMZ844>849. && $$ UPDATE...Meade DISCUSSION...Duke AVIATION...Meade MARINE...Duke
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1045 PM CDT Sun Mar 12 2023 .SHORT TERM... (Through Late Monday Night) Issued at 158 PM CDT Sun Mar 12 2023 A rather deep upper low across the upper MS Valley will continue to deepen and dig southeastward tonight leading to both weak large scale height falls and the subtle passage of a secondary cold surge late this afternoon and evening. Attendant with this cold surge is a narrow band of decent low-level frontogenetic forcing. This forcing along with a shallow zone of steeper low level lapse rates could result in a band of light showers later this afternoon and this evening, progressing from NW-SE and impacting parts of eastern MO and southwest IL. A few of the CAMS and especially the HRRR have been consistent depicting these showers. I have added isolated showers into the forecast with this in mind with the precipitation at any point short-lived and light. Otherwise in addition to the current cloud cover another big surge of stratus will spread into the area from the north tonight as colder air spreads into the region. The upper low/trof will continue to deepen as it moves into the eastern Great Lakes/Ohio Valley on Monday and resulting in deep cyclonic flow and CAA across the area. Monday looks will be the coldest day of the period with well below normal highs owing to cloud cover and the colder air mass. We could see a few flurries or sprinkles across parts of the area, namely east of the MS River in IL where the moisture is a bit deeper and magnitude of the cold air is greater. High pressure will then build into the region on Monday night as the aforementioned upper low/trof continues to move east into the mid-Atlantic/northeast U.S.. How cold we get will be dependent on the clearing of cloud cover, but it certainly will be the coldest night in this stretch of the week. Glass .LONG TERM... (Tuesday through Next Sunday) Issued at 158 PM CDT Sun Mar 12 2023 There will be a lot of changeable weather during this period with several significant pattern changes. We pretty much remain locked under the influence of surface high pressure on Tuesday with northwest flow aloft and confluence in the the base of the upper trof progressing eastward. Clouds should have departed and the low-level thermal trof will have shifted eastward. As a result, temperatures overall will remain below normal but won`t be as chilly as Monday. By Wednesday the first pattern shift will be well underway as upper ridging builds into the area and the surface high retreats. The return to low-level south-southwest flow along with rising heights aloft will bring warmer temperatures with most of the area near to slightly above normal. From late Wednesday night through Thursday into Thursday night into early Friday morning we will see a return of active weather as separate northern and southern stream upper trofs evolve into a progressive more deeply meridional trof. There are some model differences in how all this will come to fruition, as well as the upper trof structure and timing. However at least into Thursday evening those differences are negligible to the sensible weather. Moisture transport will commence late Wednesday night/early Thursday morning via a robust southwesterly LLJ and this could produce showers across mainly parts of central and northeast MO. Rain chances will ramp-up Thursday afternoon and night with the progression of the upper trof and associated cold front and attendant lift. Continue moisture transport and low level WAA will bring even warmer temperatures, above normal, but how far above will ultimately be dictated by the amount of cloud cover and precipitation coverage. The lower and middle quartile of the NBM temperature spread is entirely above normal. The resultant advections will also bring a slight chance of thunderstorms into the region associated with weak elevated instability. Whether we see any post-frontal precipitation within the CAA is still in question. This will be dependent on the upper trof structure and the ensemble cluster analysis shows enough variance that there remains uncertainly. A more progressive structure of the upper trof aka the latest deterministic ECMWF would not support any post-frontal precipitation. Alternatively a bit deeper and lagging short wave aka the latest deterministic GFS would result in weak large scale ascent, moisture, and frontogenetic forcing such that there could be a short-period of post-frontal/anafront precipitation distribution where rain changes to snow and results in minor accumulations. As we move Friday into Saturday the development of an expansive upper low and trof over the upper Midwest and slow movement to the east signals a cold period. The ensemble height cluster analysis has good agreement on this pattern and the cluster analysis of 850 mb temperatures has over 90% of the population well below normal. At this time the above pattern would favor below normal temperatures Friday-Sunday and as much as 20 degrees below normal on Saturday. Glass && .AVIATION... (For the 06z TAFs through 06z Monday Night) Issued at 1035 PM CDT Sun Mar 12 2023 A deck of largely-MVFR stratus continues to drop slowly south through the Mid-Mississippi Valley at this hour, now impinging on the St. Louis metropolitan area. Gusty northwest flow is reinforcing colder air moving into the region, which will keep stratus in place overnight. Guidance continues to drop CIGs too much, so this TAF issuance stays on the higher side. Some terminals may remain out of fuel-alternate conditions for most (if not all) of the night due to their elevation (particularly KJEF and KSUS, which are a few hundred feet AGL below their surrounding terminals). The MVFR CIGs remain in place through the morning, though high pressure will slowly move in from the west and erode the lower stratus during the afternoon from west to east. I`m not confident we`ll lose the clouds completely, but improvements to VFR conditions are expected by the early afternoon at most sites. The one exception is at and around KUIN, where low-level moisture will be stubborn to exit. As such, the forecast is for MVFR to continue through the TAF period in far northeast Missouri and west-central Illinois. MRB && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX
Area Forecast Discussion
National Weather Service Mobile AL
658 PM CDT Sun Mar 12 2023 ...New AVIATION... .AVIATION... (00Z TAFS) Issued at 640 PM CDT Sun Mar 12 2023 Showers and storms will continue to move east across the area through the evening hours. MVFR ceilings persist this evening before IFR ceilings develop at the TAF sites overnight as light to moderate rain persists near the coast. Ceilings eventually erode after sunrise on Monday with VFR conditions expected by 12z. Northerly winds will redevelop tonight as the cold front drops into the area. Gusts up to 20kts are possible during the day on Monday in the wake of the front. 07/mb && .PREV DISCUSSION... /issued 502 PM CDT Sun Mar 12 2023/ ..New MESOSCALE UPDATE... MESOSCALE UPDATE... Issued at 453 PM CDT Sun Mar 12 2023 Strong to severe thunderstorms remain possible across southeastern MS into southwestern AL and the FL panhandle this evening. Several supercell thunderstorms have developed over the past hour across south-central MS with large hail being the primary hazard. KMOB and KDGX VWP`s continue to exhibit long, straight hodographs above 1km AGL with muted low level curvature. As mentioned earlier, this hodograph shape with strong mid-level shear supports hail growth and hail production in splitting supercells. This is particularly the case considering these thunderstorms remain elevated with around 1,000 to 1,500j/kg of MUCAPE. There does appear to be a MUCAPE gradient oriented northwest to southeast over southwestern AL, which is evident from radar imagery of a recent storm weakening after moving into Clarke and Monroe Counties. Unless some airmass modification occurs over the next couple hours, this would suggest the better severe threat will remain to the west across southern Choctaw County southward into Mobile/Baldwin Counties, and points west into our southeastern MS Counties. As the shortwave and associated surface cold front continues to push east into the early to mid evening hours, expect coverage of discrete to semi-discrete supercells and multi-cell clusters to continue to increase and for storm intensity to increase as well until MUCAPE values diminish in the hours following sunset. In summary, strong to severe thunderstorms with the threat for large hail upwards of golf ball size remains possible across portions of southeastern MS into southwestern AL, and perhaps the FL panhandle through early to mid evening. MM/25 PREV DISCUSSION... /issued 357 PM CDT Sun Mar 12 2023/ .New NEAR TERM, SHORT TERM, LONG TERM, MARINE... NEAR TERM... (Now through Monday) Issued at 244 PM CDT Sun Mar 12 2023 Showers and storms will continue to slide east across the area through the mid evening hours for inland communities. Further to the south (closer to the coast), showers and storms will continue to develop and progress east through much of the evening. The HRRR has the best handle on this afternoon`s convection and continues to show redevelopment across the coastal counties and Gulf waters well into the pre-dawn hours on Monday. As we head into the overnight and early morning hours, the main concern will switch from hail to nuisance flooding as showers and storms repeatedly moves over the same locations along the coastline. Only expecting another inch or so of rain overnight along the coast, but this may be problematic given the heavy rainfall that has already fallen today and the saturated soils (especially for locations south of I-10). A surface high begins to build into the region in the wake of the cold front tonight and Monday. Subsequently, northerly winds will usher in much drier air to inland communities overnight with PWATs falling below a half inch. Cold air advection sets up after midnight and temperatures steadily fall into the 40s across inland communities while remaining in the 50s along the coast/beaches. Temperatures will struggle on Monday in this pattern with highs only rebounding into the low 60s inland with upper 60s at the beaches. Spring Break Note: The HIGH RISK OF RIP CURRENTS remains in effect through tonight for coastal Alabama and northwest Florida beaches with surf remaining around 3-4 feet. The risk subsides to MODERATE on Monday as northerly winds persist at the beaches. 07/mb SHORT TERM... (Monday night through Wednesday night) Issued at 244 PM CDT Sun Mar 12 2023 An upper level northwest flow will dominate through the period with surface high pressure building into the area. This will maintain dry and cool conditions with precipitable water values of 0.5 inches or less as northerly winds advect cooler and drier air into the region. This pattern will keep temperatures below seasonal norms for this time of year. Lows Monday night will range from the mid and upper 30s inland to mid 40s near the coast. Tuesday night will feature the coldest temps with lows in the low to mid 30s inland to mid 40s near the coast. Temps will be very close to freezing over far northern areas which we will continue to monitor for a possible freeze watch due to the warm conditions we have experienced recently. Highs on Tuesday will only be in the upper 50s and low 60s inland to low 60s near the coast. Wednesday will be slightly warmer, in the low to mid 60s across the area. /13 LONG TERM... (Thursday through Sunday) Issued at 244 PM CDT Sun Mar 12 2023 Surface high pressure will move east of the area on Thursday with a southerly flow developing. Meanwhile upper ridging will build over the area as an upper trough digs across the southwestern states. This will allow moisture to increase ahead of an approaching cold front. This front is expected to bring the next chance of showers and storms to the area on Friday into Saturday. Highs on Thursday and Friday will warm into the low to mid 70s with another shot of cooler and drier air moving into the region behind the front. /13 MARINE... Issued at 244 PM CDT Sun Mar 12 2022 A moderate to strong onshore flow persists over the nearshore and offshore coastal waters this afternoon as an outflow boundary sits along the coast. Offshore flow will set-up later this afternoon into this evening as a cold front dives south into the marine area. Moderate to strong offshore flow will continue through the early part of the week before subsiding by midweek. A light to moderate onshore flow is expected to redevelop late in the week with a gradual increase in winds by Friday. SCA conditions persist over most of the marine area through Monday morning. 07/mb && .PRELIMINARY POINT TEMPS/POPS... Mobile 49 66 42 62 42 66 45 73 / 70 0 0 0 0 0 0 0 Pensacola 53 66 45 62 44 65 49 70 / 80 0 0 0 0 0 0 0 Destin 56 68 46 61 45 63 50 69 / 80 0 0 0 0 0 0 0 Evergreen 46 64 37 59 36 64 37 73 / 70 0 0 0 0 0 0 0 Waynesboro 44 63 37 58 36 64 38 73 / 40 0 0 0 0 0 0 0 Camden 44 61 35 57 34 62 36 72 / 50 0 0 0 0 0 0 0 Crestview 52 68 40 62 38 66 39 72 / 80 0 0 0 0 0 0 0 && .MOB WATCHES/WARNINGS/ADVISORIES... AL...High Rip Current Risk through Monday morning for ALZ265-266. FL...High Rip Current Risk through Monday morning for FLZ202-204-206. MS...None. GM...Small Craft Advisory until 10 AM CDT Monday for GMZ630>632-650- 655-670-675. && $$ This product is also available on the web at: www.weather.gov/mob
Area Forecast Discussion
National Weather Service Reno NV
252 PM PDT Sun Mar 12 2023 .SYNOPSIS... Bands of rain and snow showers continue through Monday, mainly for the Sierra and northeast California, with isolated thunder also possible through this evening. Heavier precipitation with increased winter and hydrologic impacts arrives with a stronger storm late Monday night through Tuesday. Unsettled and showery conditions remain possible later this week through next weekend. && .SHORT TERM...through Tuesday Night... The Pacific moisture continues to stream into northern and central CA, with higher elevation (7500+ feet) snow totals adding up to between 2 and 3.5 feet since Thursday night. The next shortwave within the moist flow will bring increased convective activity across central CA this afternoon-evening with bands of heavier rain and snow showers spreading over the Sierra and western NV. While snow levels will generally range from 6000-7000 feet during this activity, they could dip to near 5500 feet at times from Tahoe northward during heavier shower bands. A few lightning strikes may occur near the Sierra crest and also in west central NV near and east of US-95. For late tonight through Monday, the overall shower coverage is expected to decrease with orographic effects limiting most activity to areas near the Sierra northward to western Lassen County. Western NV will remain dry on Monday with milder temperatures ranging from the 50s to near 60 degrees. Monday night will feature the early stages of the more significant storm with another atmospheric river connection. Precipitation will increase across northern CA and push into the Sierra with increasing intensity, but the consensus of the guidance holds off on spreading precip across lower elevations of eastern CA-western NV until near daybreak on Tuesday. This period of shadowing could allow for a period of stronger winds during the overnight/early morning hours. The main effects and impacts of this storm continue to target the region during the day Tuesday, producing the following highlights: * WINDS: We will issue a High Wind Watch for all of western NV and the Surprise Valley as a period of 60+ mph gusts is possible in these areas, but confidence levels aren`t high enough for a definite major wind event. The eventual position of the upper level jet will affect the location and magnitude of the peak winds. When the main precip pushes through western NV (most likely Tuesday morning-midday) the wind speeds could be dampened a bit, but the afternoon-evening still holds a window of opportunity for stronger gusts to mix down into lower elevations when precip rates show a decrease but stronger winds aloft remain overhead. Sierra ridges can expect gusts surpassing 100 mph all day Tuesday. Plan on wind-related travel impacts, especially for aviation interests and high-profile vehicles. * SNOWFALL/SNOW LEVELS: A short period of higher snow levels is on tap from Tuesday morning through early afternoon as the main surge of subtropical moisture arrives. However, the heavier precip intensity along with a slight intrusion of cooler air with the advancing low pressure center should prevent an excessive rise, with projections relatively consistent to near 6500 feet for northeast CA/northwest NV, 7000-7500 feet for the Lake Tahoe Basin eastward across western Nevada along I-80 and US-50, and near 8000 feet for Mono County and western Nevada south of US-50. These snow levels will then start dropping by late Tuesday, eventually bottoming out below 4000 feet well north of I-80, between 4000-4500 feet from I-80 to US-50, and near 5000 feet south of US-50 by early Wednesday morning. However, most of the precipitation is expected to diminish before the coldest air arrives. If any low elevation snow occurs, the best chances are north of Susanville-Gerlach closer to the upper low`s inland track, with potential for 1-3" prior to daybreak. Around the main urban areas, spotty amounts up to 1" are possible if a stray snow band manages to hold together in the pre-dawn hours. Higher elevation snow potential is detailed in the Winter Storm Warning message, with heavy wet snowfall adding at least a couple more feet of snowpack depth mainly above 7000 feet. but amounts drop off quite a bit below 7000 feet. Prepare for significant travel impacts and delays over Sierra passes starting Monday evening, which could last through early Wednesday morning. As always, check road conditions with Caltrans and Nevada DOT before traveling. We have seen several structural issues from snow loading in the Sierra communities from recent storms. Snow loading concerns on structures will likely increase with the added heavy rain and snow especially on Tuesday. There will also be a higher risk of roofalanches in these areas. Follow guidance from local officials and building inspectors for ways to monitor and mitigate the risk of increased snow loads on roofs. * LOWER ELEVATION RAINFALL: A new Flood Watch has been issued for lower elevations due to the expected period of heavier rainfall on Tuesday combined with more saturated ground conditions. This could aggravate flooding concerns in areas already impacted during the recent rain, even though the faster movement and shorter duration of Tuesday`s heavier rain spreading into western NV has trended the rainfall potential a bit lower compared to previous projections. The latest precipitation forecast for Tuesday shows 0.30-0.70" for far western Nevada communities of Reno, Carson City, and Minden, with around 1" possible for foothill areas including Virginia City. Amounts taper off to 0.10-0.30" into the Basin and Range of western Nevada. While areas south of US-50 in west central NV currently are less likely to have the spillover moisture compared to last Friday, their rain totals could increase if a deeper subtropical moisture feed sets up longer over Mono County. MJD .LONG TERM...Wednesday onward... Wednesday will start with weather related impacts winding down as the strong AR driven storm begins to exit the region. Flooding concerns could still remain even though precipitation will start to wind down. Temperatures will be the first sign that things are changing as lows Wednesday night slide down 5 to 10 degrees below seasonal averages. These lower temps will also decrease snowmelt across lower elevation areas across the Sierra. Temperatures through the remainder of the week, however, will make a gradual comeback to more seasonal averages. We’ll finally get a much needed rest from the relentless days of heavy mountain snows and lower elevation rain on Thursday into much of Friday. This period will be brief as this current progressive pattern will continue through the weekend. The next weather system is looking to bring another round of precipitation later next weekend with guidance trending slightly higher with amounts, although well below the magnitude of Tuesday`s storm. That being said, anticipate another quick shot of higher elevation snow and valley rain later Saturday into Sunday. Ensemble guidance is presenting the notion that less snow will fall around the Lake Tahoe Basin with this upcoming weekend storm, but there is a good chance that travel impacts will continue for higher Sierra passes. However, these periods of higher elevation snow and lower valley showers are looking to bring fewer impacts going into next week as the systems moving onto the west coast are projected by the ensemble guidance to be on the weaker side. -Amanda && .AVIATION... Unstable airmass over CA continues to generate scattered thunderstorms upstream over the Central Valley. Latest HRRR projects these cells to spill over into the TVL/TRK and eventually RNO/CXP/MEV areas this afternoon and evening. A 50/50 chance for LIFR snow squalls at TVL/TRK with brief runway accumulations, and even some lightning in the vicinity. For MMH there is a chance for IFR snow showers if convective cells can spill into the higher terrain. For Western NV including RNO mainly looking at on/off MVFR rain showers between 22z this afternoon and 06z this evening. Winds have remained elevated on the ridges with gusts above 40 MPH, so we could see some brief gusts of stronger wind this afternoon and early evening. Flow aloft remains breezy so that could set up some wind shear overnight into early Mon AM. For Monday, airmass remains unstable so continued risk of rain/snow showers remains, though latest HRRR shows more isolated precip coverage -Chris && .AVALANCHE WEATHER... Waves of Pacific moisture will continue to produce additional rounds of snowfall through Tuesday. Several inches of new snowfall will continue to accumulate on top of the deep existing snow pack creating varying snow densities. Another atmospheric river (AR) will bring increased winds, heavy snowfall rates along with high snow levels. These conditions will result in low snow-to-liquid ratios Monday night through Tuesday. * 24-hr Snow Water Equivalent (SWE): 1-3" through tonight for the Lake Tahoe Basin/Alpine County, with heaviest totals north of US- 50, then decreasing to about 0.75-1.50" from tonight through Monday. Lesser SWE rates of 0.50-1.00" for Mono County through Monday. SWE rates increase again late Monday night through Tuesday with the next incoming AR. * Snow-to-Liquid Ratios (SLR): Medium to high snow-to-liquid ratios about 11-15:1 through tonight, then trending lower late Monday through Tuesday with SLR’s dropping 4-8:1 between 6500-8000 feet and 8-12:1 above 8000 ft. * Winds: Southwest winds continue with gusts generally 55 to 65 mph across the ridges through tonight, with an increasing trend late Monday through Tuesday where ridge top gusts could exceed 100 mph. -Johnston/Amanda && .HYDROLOGY... Heavy rain and snowmelt associated with the atmospheric river Monday night through Wednesday will renew flooding potential mostly in areas below approximately 7000 feet. Areas of primary concern are small creeks and streams, and areas with poor or obstructed drainage, especially if impacted by flooding recently. Renewed river flooding is also a concern especially in the Carson Valley, along the Carson Mainstem, and along the East Fork and mainstem of the Walker River. Areas of concern for potential new river flooding include the Pit River into Big Valley, the Susan River near Susanville, and the Middle Fork of the Feather near Portola. Flooding is not currently forecast at these points, but they should be closely monitored as minor flooding can not be ruled out. The combination of wet soils, primed low-mid elevation snowpack and currently high streamflows will lead to a more rapid response to rainfall, even if we have less rain and lower rain-snow elevations then our previous atmospheric river event. Expect new and renewed flooding problems Tuesday morning through Wednesday. Ongoing high flows on the Walker River and along the Carson River (both above and below Lahontan Reservoir) could lead to new impacts with any additional inflows or debris issues. -Bardsley && .REV Watches/Warnings/Advisories... NV...High Wind Watch from late Monday night through Tuesday evening NVZ001-003>005. Flood Watch from late Monday night through Wednesday evening NVZ001>004. Winter Storm Warning until 5 PM PDT Wednesday NVZ002. CA...High Wind Watch from late Monday night through Tuesday evening CAZ070. Winter Storm Warning until 5 PM PDT Wednesday CAZ071. Flood Watch from late Monday night through Wednesday evening CAZ071>073. Winter Storm Warning until 5 PM PDT Wednesday CAZ072. Winter Storm Warning until 5 PM PDT Wednesday CAZ073. && $$
Area Forecast Discussion
National Weather Service Sacramento CA
228 PM PDT Sun Mar 12 2023 .SYNOPSIS... Periods of rain with high elevation snow today, along with scattered thunderstorms in the Valley. Another wet, warmer system early week bringing moderate to heavy rain, high elevation snow, and renewed flooding concerns. && .Discussion... Upper level trough is pushing east over the far part of the state. This short wave has been bringing widespread showers to the area with some locally moderate to heavier rain in the northern San Joaquin Valley. It has also kept skies mainly cloudy across the region. This has had a major impact on instability and our thunderstorm chances and was always the wild card for today. Meso- Analysis is estimating 100-250 j/kg of ML-CAPE from about Sacramento north to Chico. HRRR runs are still favoring the northern San Joaquin Valley to about Sacramento for scattered thunderstorms this afternoon which doesn`t seem reasonable at this point and the HRRR has been under doing these showers all morning. The better thunderstorm chances today will likely be south of our area into Hanford`s area. We still could see some isolated thunderstorms mainly over the central and southern Sacramento Valley. Model soundings are still showing good hodographs, sufficient 0-1 km shear, high PWATs, and CAPE in the hail growth zone. This would indicate that we could see some stronger storms but cloud cover has likely modified these sounds some. Still will have to keep an eye on any thunderstorms that develop but heavy rain at this point looks to be the biggest threat. Overall we will see showers diminish overnight with them lingering over the mountains. A deeper trough and cold front will then approach the area later Monday into Tuesday. This will bring the return of periods of heavy rain and heavy mountain snow. Models are in slightly better agreement but still seeing a wider range in the 500 mb pattern than what you would like to see this close to the event. The GEFS continues to be slower and a bit further south with the southern part of the trough. Overall there is good agreement with QPF though, it`s looking like 1.50-3" in the Valley and 3-7" over the foothills and mountains. Snow levels will be 5500-6500 feet into Monday rising to pass level Tuesday as the burnt of the storm hits us. Snow levels fall Wednesday falling back down to 3500-5000 feet. Several more feet of snow is expected over the Sierra with this storm. This will bring travel issues at times mainly as you get to the passes. We will also see gusty southerly winds with this system. 850 mb wind increase to 45-70 knots Tuesday morning into the afternoon. This will result in winds gusting 45-60 mph across much of the area and up to 70+ mph over the higher Sierra. With another warmer and wetter storm in the forecast for Monday- Tuesday flooding is a concern. Streams, creeks, and rivers will continue to rise as we see additional rain and snow melt. Some urban and street flooding will also be possible mainly Monday night through Tuesday. Streams, creeks, and rivers of most concern will be those coming out of the Sierra. A few showers will linger on Wednesday mainly over the mountains. Upper level ridge will build in later in the day bringing the return of dry weather. -CJM && .EXTENDED DISCUSSION (Thursday THROUGH Sunday)... Dry weather forecast for Thursday into early Friday as short wave upper ridging moves through. Short wave trough progged to follow Friday afternoon into night. This system looks weak and QPF limited. First part of Saturday appears dry except for some possible lingering mountains showers. Another storm is progged later Saturday into Sunday. Model differences exist with timing and associated precip amounts resulting in some forecast uncertainties at this time. && .AVIATION... Widespread MVFR cigs with areas IFR and isolated LIFR conditions over interior NorCal next 24 hrs. Snow lvls 5500-6500 ft. Isolated tstms possible through 03z again Monday 21-02z. In Central Vly, areas Sly sfc wind up to 20 kts possible aft 18z with lcl gusts to 30 kts over the northern Sacramento Valley through Monday afternoon. Over mtns, areas S-W sfc wind gusts up 40 to 50 kts possible. && .STO WATCHES/WARNINGS/ADVISORIES... Flood Watch through Wednesday morning for Burney Basin / Eastern Shasta County-Carquinez Strait and Delta-Central Sacramento Valley-Motherlode-Mountains Southwestern Shasta County to Western Colusa County-Northeast Foothills/Sacramento Valley- Northern Sacramento Valley-Northern San Joaquin Valley-Shasta Lake Area / Northern Shasta County-Southern Sacramento Valley- West Slope Northern Sierra Nevada. High Wind Watch from Monday evening through Tuesday evening for Carquinez Strait and Delta-Central Sacramento Valley-Motherlode- Mountains Southwestern Shasta County to Western Colusa County- Northeast Foothills/Sacramento Valley-Northern Sacramento Valley- Northern San Joaquin Valley-Shasta Lake Area / Northern Shasta County-Southern Sacramento Valley-West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park. Winter Storm Warning until 4 PM PST Wednesday for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park. && $$