Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/14/21

Area Forecast Discussion
National Weather Service Charleston SC
644 PM EST Mon Dec 13 2021 .SYNOPSIS... Dry high pressure will prevail through much of the week before a cold front arrives over the weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Water vapor images showed a well-defined shortwave tracking east across the Deep South early this evening. This feature was contributing to an area of developing showers over the Gulf Stream off the FL coast. HRRR indicates that additional showers will develop off the GA/SC coast late tonight, remaining over the Gulf Stream. However, cloud cover is expected to increase from the east, resulting in at least partly cloudy conditions over the coastal counties late tonight. Temperatures are on pace to range from the mid 30s over inland GA to the mid to upper 40s along the coast. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/... Deep high pressure will prevail across the region and then make an eastward shift on Thursday. A coastal trough will linger in the vicinity. While a dry forecast is in place over land, there could a few showers over the waters along the trough and where moisture is slightly higher. Although, any showers that do form, should generally be light and short-lived due to dry air aloft. In regards to temperatures, Tuesday will be in the 60s and by Thursday, temps will warm into the low to mid 70s across SE SC and upper 70s across SE GA. Low temperatures on Tuesday night will be in the upper 30s to mid 40s inland and upper 40s to low 50s just along the coast. Wednesday will be a few degrees warmer. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... High pressure will remain offshore through Saturday followed by a cold front. For Thursday and Friday, a dry forecast is in place, except for a slight chance over the waters. Then, as moisture increases ahead of the aforementioned cold front, showers will be possible starting Saturday. The cold front will move through the region overnight Saturday and into Sunday, before stalling just offshore. Decent moisture and shortwave energy will support isolated to scattered showers through early week. Heights will support warm temperatures on Fri/Sat then after the cold front, highs in the 60s will return. Lows will be in the 40s to 50s. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... VFR conditions expected across the terminals through the 0z TAF period. A ridge of high pressure will yield light northeast winds through the period. Extended Aviation Outlook: VFR is expected to prevail through late week. && .MARINE... Tonight: The local waters will be situated between high pressure to the north and a coastal trough located to the south. This will drive northeasterly flow across the local waters with wind speeds generally topping out in the 10-15 knot range. Seas will average 2-3 feet, except up to 4 feet in the outer Georgia waters. Tuesday through Saturday: Northeasterly winds at 5 to 10 knots will prevail through late week before becoming south-southwest. Seas will start out around 2 to 4 feet before building to 3 to 5 feet by the weekend. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...NED SHORT TERM... LONG TERM... AVIATION...NED MARINE...BSH
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
600 PM EST Mon Dec 13 2021 .AVIATION... A weak front will sag south into the area overnight and stall. This will bring nearly calm conditions late. The atmosphere is very dry, but slightly moisture pooling along the boundary coupled with decent cooling conditions may produce patchy MVFR to possible IFR fog a few hours either side of sunrise. Winds will become east/southeast north of along/north of this front on Tuesday. .DTW THRESHOLD PROBABILITIES... * None && .PREV DISCUSSION... Issued at 352 PM EST Mon Dec 13 2021 DISCUSSION... Southeast Michigan resides on the anticyclonic shear side to a broad +150 knot upper level jet streak that is in place across most of north central North America. Absolute anticyclonic vorticity advection across Southeast Michigan combined with very strong statically stable conditions between 1.5 and 7.0 kft supports surface high pressure influence extending out of the Carolinas back to the northwest into Lower Michigan. No significant weather to speak of throughout the next 36 hours with the persistent ridging influence and dry ambient air mass. The item to watch for tonight and Tuesday morning will be the potential for shallow ground based fog. NAM soundings look way overdone with a substantial low stratus signal while the RAP soundings strictly point to a ground/surface layer signal. There is uncertainty here for a couple of reasons, very high surface T to Td depressions running some 15-20C today, and possibly some better potential for frost formation over supercooled liquid droplets and fog. Do think there is some possibility for visibility restrictions but may be more of a haze at daybreak. Surface col region will push to the east already by Tuesday morning that will cause some subtle low column cold air advection. Biggest factor for Tuesday will be change in wind directions to the southeast. Limited mixing depths should keep moderation in check with afternoon highs in the middle to upper 40s. Surface warm front and plume of high thetae is forecasted to advect into all of Southeast Michigan between 12-18Z. 800mb moisture transport will be earlier, 06-12Z, which will provide low level saturation in the lowest 3.0 kft agl. A significant environmental wind profile through this cloud bearing layer points to a high end drizzle light rain shower setup. Went ahead and increased PoPs into the likely category for the latter half of Tuesday night. Tricky to pin down highs on Wednesday given amount of cloud and moisture but indications suggest a humid/damp middle 50s Wednesday. A strong absolute anticyclonic vorticity signal off of the upper Mississippi River Valley supports dry slotting by Wednesday evening and night. Wednesday night is an interesting forecast period as the potential exists for a well mixed layer from the surface to 2000 ft agl. The progged low level jet is very impressive at over 65 knots. Not expecting this to fully mix down to the surface but depending on how this unfolds, the potential exists for wind gusts to reach and exceed 40 knots during the Wednesday night period. Latest indications suggests a slightly quicker timing of the surface cold front through Southeast Michigan Thursday morning. The nam is a little later compared to the ECMWF but even then the NAM shows a veered wind profile just off of the deck with bulk of the cold air advection at 800 to the southeast of the forecast area by 15Z. Regardless, very windy conditions are expected as daytime heating causes fresh mixing and downward momentum transport around late morning. A wind headline may be needed for Wednesday and Thursday. The main baroclinic zone is expected to stall out over portions of the Ohio and Tennessee River Valleys Thursday/Friday before advancing northward for the weekend. Latest forecast data suggests a more winter like system for Southeast Michigan during the weekend. MARINE... Strong high pressure dropping out of northern Ontario builds over the central Great Lakes tonight bringing light winds back to the area. This high quickly moves into eastern Ontario Tuesday shifting flow to the SE. An uptick in strength accompanies this shift with gusts reaching 20-25kts by Tuesday night. Gradient tightens again Wednesday as a warm front lifts through the region tied to a strong developing low over the northern Plains. Warm front brings a chance of showers throughout the day Wednesday as well as strengthening southerly flow. This low looks to track into the upper Midwest/western Lake Superior late Wednesday into Thursday. Peak winds are expected during this timeframe with gales looking possible across portions of Lake Huron (particularly central LH). CLIMATE... Record highs for Wednesday Dec 15th: DTW 61 (1933) FNT 60 (1971) MBS 60 (1971) Thursday Dec 16th: DTW 65 (1984) FNT 62 (1984) MBS 60 (1984) && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....DG DISCUSSION...CB MARINE.......KDK CLIMATE......CB You can obtain your latest National Weather Service forecasts online at
Area Forecast Discussion
National Weather Service New Orleans LA
400 PM CST Mon Dec 13 2021 .SHORT TERM (This evening through Wednesday Night)... Nice and quiet evening to finish up a fresh start to the work week. GOES-16 Ch2 VIS shows ongoing patchy low-level stratus advecting east across the region. This was sampled well looking at RAP/HRRR analysis and trends indicating a fetch of low-level Gulf moisture riding north over a stationary frontal boundary currently situated in the northern Gulf. Some of this took its time getting too far north, which led to mostly sunny skies over northern parts of the CWA, but slightly cooler by a few degrees underneath thicker stratus south of I-10/12 including the southshore. As mentioned in the morning update, the current vertical thermal profile shows a distinct frontal inversion locked in place from the surface to around 925mb/3kft AGL supported by nearby high pressure anchored over the mid-Atlantic states helping to promote light easterly surface to low-level winds. Above this layer, winds transition from the southwest to eventual west which has continued to pump moisture north in the from of stratus clouds. There is some indication of towering Cu development underneath a deeper vertical moisture plume over coastal central LA pushing north. 18Z RAP illustrated this area well with the center of a H7 ridge just to our south, helping to pull this plume north. See a few isolated showers in this area of enhanced low- level moisture, but HRRR trends continue to keep things quiet and dry here tonight with no strong indication of Tamiko ascent at play, other than subtle isentropic lift nearby the low-level front but this should stay over southwestern parts of the CWA or around the Atchafalaya basin. Not going to get cute by mentioning PoPs in this region, as coverage potential looks too low. Staying partly to mostly cloud tonight, mainly as this same aforementioned H7 moisture plume pushes in along the northern periphery of the ridge axis in the northern gulf, spreading low- level moisture east. HRRR RICAPS keeps clouds in place tonight within a thick/moist surface to low/mid-level layer, but what degree of influence this might have in fog development daybreak Tuesday is in question. For now, deterministic and probabilistic guidance is not entirely confident on coverage and density, with NBM probabilities only in the 15-20% range over most of the CWA. While low cloud ceilings will definitely be possible tonight, just looks like this will entrap any longwave radiation attempting to escape reducing radiational cooling processes. However, checking the MS river temperatures and comparing to forecast temperatures/dewpoints, we may see some fog along the river or around/nearby any other water sources come daybreak (greater chances for northwestern areas where T/Td is closer to river temps). Left in the mention of patchy fog for a large portion of the area but refrained from mentioning thicker/denser coverage as confidence is just too low. Will closely monitor updated guidance this evening/early tonight and adjust where necessary. Going into Tuesday, the stationary front to the south slowly dissipates undergoing frontolysis with no distinguishable frontogenetic characteristics anymore. Deeper surface to low-level moisture takes over and spreads north, eroding the frontal inversion placing us back in a subtle veering profile and well- mixed PBL following daytime heating. We will see partly to mostly cloudy skies again, but with more convective cloud development as we build positive bouyancy from the LCL to mid-levels (eventually striking a subsidence inversion at H5). Can`t rule out an isolated shower, especially nearby coastal SE LA within deeper moisture but again, expecting a mostly dry day. Temperatures several degrees warmer, with a slight bias above deterministic NBM which gets many areas into the mid to upper 70`s. Nothing changes much going into Tuesday night with persistent moisture locked in place the low-levels, leading to partly to mostly cloudy skies. NBM VIS probabilities are again on the low side which makes sense, but hints at patchy fog potential moreso for northern and western areas. Letting the mention of patchy fog ride for early Wednesday and will fine tune better as we get closer. Overall, expect low clouds to persist, likely with low ceilings into daybreak on Wednesday. The warming trend persist as we climb into the daytime hours on Wednesday, this time with a bit more upper-level cloud cover. Otherwise, subsidence takes over by suppressing/warming the layer right above the LCL leading to a pretty strong subsidence inversion between 925 and 800mb. This is due to the same low-level ridge eventually weakening/stretching and becoming absorbed within strengthening southerly low-level flow. This presses a dry layer west with time so perhaps not as much low-level clouds, but upper-level cirrus will persistently continue spreading east as we reside along the northern periphery of a deep upper-level ridge parked over the central Gulf, helping to advect moisture in from the base of a deep longwave trough over the intermountan West. But generally speaking, another nice day with warm afternoon temperatures in the upper 70`s. Even when adjusting to a warmer bias, this produces some areas flirting with the 80`s which is nearing record highs. May be close, but if guidance comes in warmer we might not be too far off daily records. KLG .LONG TERM (Thursday through Monday)... The winter blowtorch continues late-week as deep Gulf ridging continues to dominate our area leading to very warm afternoon highs, likely reaching or surpassing daily records for a few areas. Keeping a warmer bias above deterministic NBM going which for now, hints at Thursday and Friday being the warmest days. Won`t take much for areas to surpass the 80 degree mark, with light onshore winds and patchy late morning/afternoon Cu or Cu streets. Still a lot of influence from this ridge noticeable in area model sounding guidance with persistent dry air in the middle to lower troposphere, compressed down to the LCL above a well mixed PBL meaning we will warm up fast while staying humid. NBM is coming in with the mention of isolated PoPs Friday afternoon for coastal SE LA and MS. Both the latest ECMWF and GFS illustrate this possibility, perhaps with greater coverage coming from the ECMWF. Investigating this closer, there appears to be a weak low to mid-level impulse riding north from the north-central Gulf into the northern Gulf coast states. The GFS shows some hint at this, but is not entirely distinguishable (maybe somewhat of a weak impulse at 850mb). Back-tracking the origin of this impulse shows this to be a lingering piece of energy from an earlier weak shortwave trough diving south of Florida around Wednesday. It goes without saying that resolving such a small-scale impulse will be hard to include in the forecast with confidence, especially so far in advance. However, with persistent WAA, can`t rule out some isolated showers but not overly excited about coverage just yet. Riding with the NBM, but will be interesting to see if or how this changes over the next few days. By the upcoming weekend, things get challenging. The same deep longwave trough mentioned earlier over the intermountan west splits, with a piece of energy breaking off over the southern Plains. With this shortwave closing off, we don`t really get much in the way of an eastward push, meanwhile at the surface, we have a slowing (yet strong) cold front ever so slowly pushing in from the east into the southern Plains/mid MS valley region. With the lead energy ejecting east off New England, the front becomes parallel to upper-level flow meaning the front will attempt to slow or completely stall to our north. Should this happen, we will see a warmer weekend - perhaps warmer than currently forecast as we continue underneath a warm/moist WAA flow regime. The model solution really splits going beyond into next week, as a second "kicker" shortwave trough dives into the northern US and helps to phase up and press the closed low east. If it phases, we eventually get surface cyclogenesis along the front with an eventual eastward kick pushing through here with time. If it doest not phase, and the upper-low is more south farther away from the northern trough`s influence, it`ll meander east. Either way, will have to watch for showers and storms again with this one, and deepening on either solution will determine the potential for some strong storms. Will favor/bias on the GFS due to recent months model performance, and if so, we should see this upper-low phase up a bit more helping to push east. Something to keep a close eye on. KLG && .AVIATION (18Z TAF DISCUSSION)... Low-level stratus deck continues spreading east over a large portion of southeastern LA and coastal MS late this morning, bringing intermittent MVFR CIG`s. Patchy to areas of stratus should continue generally over the same areas through the afternoon with CIGs lifting, but still could see periodic MVFR at times. Otherwise, will need to monitor for the potential of surface fog development after 06z tonight, primarily towards daybreak between 10 and 12z for terminals along/near I-10 and 12. Have included lowest VIS forecasts in TAF`s with higher confidence for now. Conditions will steadily improve thereafter around 15Z tomorrow with VFR/MVFR CIGs to follow. KLG && .MARINE... A weak frontal boundary will continue to dissipate going into Tuesday, with easterly winds eventually transitioning to onshore flow by mid-week. This will lead to a subtle increase in fetch with time, building wave heights to around 3 to 5 feet for outer Gulf zones. Some showers/storms possible Friday and into the weekend, with the next cold front expected through here early next week. && .PRELIMINARY POINT TEMPS/POPS... MCB 54 77 58 76 / 10 0 0 0 BTR 57 78 60 79 / 10 0 0 0 ASD 54 78 56 78 / 0 0 0 0 MSY 61 77 63 78 / 0 0 0 0 GPT 53 74 57 75 / 0 0 0 0 PQL 51 75 54 76 / 0 0 0 0 && .LIX WATCHES/WARNINGS/ADVISORIES... LA...None. GM...None. MS...None. GM...None. && $$
Area Forecast Discussion
National Weather Service Newport/Morehead City NC
1009 PM EST Mon Dec 13 2021 .SYNOPSIS... Strong high pressure will continue to build over the area today and remain in control through the upcoming week. A cold front will impact the area over the weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... As of 10 PM Mon...Forecast remains on track with no changes. Prev disc...High pressure will remain over NC tonight but the northern center will become the dominant circulation. This will cause the flow to become N/NE by Tuesday morning. Tonight skies will remain clear and winds will decouple early this evening resulting in strong radiational cooling and rapidly falling temps once again. Thus will undercut most MOS/NBM forecast lows by 2-4 degrees with min temps in the upper 20s to low 30s. The higher resolution models like the HRRR are indicating a stronger signal for radiational fog tonight beginning around midnight and becoming extensive especially over southern inland locations. Have included this in the forecast since localized dense fog did develop late last night. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... As of 215 PM Mon...High pressure will ridge into the area from the north on Tuesday, with light winds and clear skies continuing. Areas of morning fog should dissipate by 9 AM. Highs will climb into the low to mid 60s. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... As of 240 AM Mon...A stretch of very quiet weather is expected this week with temperatures initially around normal, increasing through the week to well above average. By Friday, a cold front will stall just north of the region, keeping the area dry, and then another, stronger front will push through the area Sunday. Wednesday and Thursday...By Wednesday strong high pressure will rebuild off the New England coast and ridge down the eastern seaboard. This will allow for southerly flow to develop (though a weak coastal trough may briefly develop Wednesday, keeping northerly flow present across the area), and low levels heights will build both days. Expect highs to reach the mid to upper 60s Wednesday, and low to mid 70s Thursday. Friday through Sunday...High pressure will remain offshore Friday, while a cold front moves eastward out of the Mid-South. As the front tries to push east of the Appalachians it will stall to the north and west of the area as high pressure holds steady overhead, and most of the associated upper level energy moves into New England. On Saturday this stalled front will lift north in response to cyclogenesis along the front farther to the west, and a developing low pressure system will move into the Mid-Atlantic through the day. To the south of this developing low, a stronger cold front will march into the Southeast states by Saturday night, and cross through Eastern NC Sunday morning. A period of wet weather is anticipated along this front, but much uncertainty regarding rainfall amounts. Low level heights will continue to build through Saturday leading to very warm conditions both Friday and Saturday, with highs reaching the low to mid 70s. Behind the cold front Sunday, strong CAA will limit warming, keeping temps mostly in the low to mid 50s for highs. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... SHORT TERM /through Tuesday/... As of 630 PM Mon...Strong subsidence from high pressure directly overhead tonight will keep skies clear and winds calm. As a result, VFR conditions likely this evening with the threat of fog early Tue AM. Hi res guidance is showing a stronger signal for fog development across southern terminals. Though airmass remains dry, strong radiational cooling will allow temps to drop quickly tonight and fog to potentially develop. Though fog will likely be predominantly shallow steam fog, some more substantial development is possible. Localized IFR/LIFR fog in the TAFs this morning for EWN/OAJ with MVFR fog elsewhere for the time being. Any fog burns off after sunrise, giving way to high confidence VFR conditions for the rest of Tuesday. LONG TERM /Tuesday night through Saturday/... As of 240 AM Mon...VFR conditions are expected to persist through the week with high pressure in control. && .MARINE... SHORT TERM /through Tuesday/... As of 215 PM Mon...Good boating conditions are expected through Tue as high pressure remains over the waters. Winds are expected to remain light through Tue morning mainly 10 kt or less with the direction veering from W this evening to NE by Tue morning. The NE flow could increase to 10-15 kt late Tue. Seas will be 2-3 ft through Tue though some 4 ft seas will be possible over the outer waters late Tue in response to the increased northerly flow. LONG TERM /Tuesday night through Saturday/... As of 240 AM Mon...NE winds will be strengthening to 10-15 kts Tuesday night. A weak coastal trough likely develops Wednesday with winds mostly out of the E/SE at 5-10 kts to the east of the trough, and out of the NE at 5-10 kts right along shore. Southerly flow then develops Thursday with winds 5-10 kts, increasing to 10-15 kts Thursday night, and then coming around to the west on Friday at 5-15 kts. Seas will be 2-3 ft Tuesday and then 3-4 ft Tuesday night through Thursday. Seas then build further Thursday night becoming 3-5 ft through Friday. && .MHX WATCHES/WARNINGS/ADVISORIES... NC...None. MARINE...None. && $$ SYNOPSIS...MHX NEAR TERM...JME/ML SHORT TERM...JME LONG TERM...SGK AVIATION...SGK/ML MARINE...JME/SGK
National Weather Service Raleigh NC
935 PM EST Mon Dec 13 2021 .SYNOPSIS... High pressure will persist over the Carolinas and Mid Atlantic through midweek. && .NEAR TERM /THROUGH TONIGHT/... As of 935 PM Monday... High pressure remains over southeastern North Carolina. The only meaningful change to the forecast is to remove the patchy fog that was possible across southeastern counties. Confidence in the fog earlier was low, and the most recent model guidance shows a very low chance of any visibility reductions occurring. Skies will remain clear, and although winds should be relatively light overnight, the fact that there should be a little bit of wind compared to widespread calm conditions last night should allow overnight temperatures to be slightly warmer than last night, ranging from the mid 20s to mid 30s. && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... As of 248 PM Monday... Broad ridging will be in place Tue into early Wed at mid-levels. At the surface, high pressure over southeastern Canada will move into New England early Wed. Northeasterly flow at the surface will commence during the daytime Tue as a result. Low-level thicknesses remain about the same over the northern Piedmont and Coastal Plain but warm slightly over the southern Piedmont and Sandhills. High temperatures then to be about a degree or so warmer area-wide, ranging from the upper 50s to 60 in the north to lower 60s in the southwest. While it is difficult to discern if the surface high over New England will bring the back door cold front all the way through central NC, either way thicknesses will drop by early Wed with a light northeast wind. In the low-levels, the east-northeast moist flow from the western Atlantic may lead to some morning fog or low stratus Wed morning, primarily over the eastern Piedmont and Coastal Plain. Forecast soundings have been indicating this moistening at low-levels, with the NAM the most aggressive. The HRRR has also been consistent on the pattern. As a result, overnight lows to be a tad warmer in the low to middle 30s under increasing clouds and slight stirring in the wind. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... As of 330 PM Monday... A subtropical ridge aloft will remain across the Southeast US through Friday, resulting in dry weather for central NC. However, this will gradually get pushed southeastward as a series of mid/upper disturbances moves across the Plains and Upper Midwest. At the surface, a backdoor front will move through at least part of the area Tuesday night and Wednesday morning. Behind this front, easterly flow may result in low-level cloudiness and cooler temperatures, particularly if the NAM were to verify, with the best chance of this in the east. Thus increased forecast cloud cover and cooled forecast highs a bit on Wednesday closer to the NAM, generally mid-50s to near 60. Otherwise, surface high pressure centered over the area on Wednesday will shift east and offshore, resulting in southerly flow and warmer temperatures from Thursday through Saturday. Forecast highs increase from mid-60s to lower-70s on Thursday (around 15 degrees above normal) to 70s areawide on Saturday (around 20 degrees above normal). Thus the record high of 72F at RDU on 12/17 (Friday) could be in jeopardy. Precipitation chances increase for the weekend into early next week. A strong cold front will cross the region late Saturday or early Sunday, though timing of the front has slowed down in the latest model runs. The front may be accompanied by some showers, and there is enough model support to increase POPs to high chance during this period. However, similar to recent frontal passages, there is no wave along the front and it does not look to have a ton of moisture associated with it, so rainfall amounts do not look impressive at this time. Confidence then greatly decreases for the rest of the period. There will at least be a lull in precipitation on Sunday as the front moves south of the area, but a shortwave trough will then move across Texas and the lower Mississippi Valley on Sunday night into Monday. The 12z ECMWF keeps the system suppressed well to the south with high pressure over our region, but the 12z GFS continues to be much wetter as it brings the system farther north. The Canadian is more in line with the wetter GFS solution, though it holds off precipitation until Monday night. Considering even a majority of 12z ECMWF ensembles have at least some precipitation over the area, the operational ECMWF appears to be an outlier, and have high chance POPs again on Monday. While the 12z GFS is warmer than the 06z run, it still has low-level thicknesses near 1300 m in the far northern Piedmont at the onset of precipitation Monday morning. The event if it occurs should be mainly liquid, but a bit of frozen precipitation at the onset can`t be entirely ruled out. Temperatures will be much cooler on Sunday and Monday, but exactly how much will depend on how the overall pattern plays out. For now forecast highs are near normal. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... As of 630 PM Monday... High confidence in VFR conditions for the next 24 hrs across central NC, as deep dry air sits atop the region, within surface high pressure stretching across the area. This high will weaken later tonight, while another high pressure area centered just north of Lake Ontario begins to ridge southward into NC. This will result in very light to calm winds tonight becoming mostly from the NE on Tuesday, under 10 kts. Few to no clouds are expected through Tue, with no vsby restrictions. Looking beyond 00z Tue, VFR conditions will dominate through Fri, although there is a risk of sub-VFR fog and low stratus late Tue night/early Wed morning, and again late Wed night/early Thu morning, with increasing easterly low level flow pulling moisture in from the Atlantic. A chance for showers with sub-VFR conditions is expected starting Sat. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Kren NEAR TERM...Green SHORT TERM...Kren LONG TERM...Danco AVIATION...Hartfield
Area Forecast Discussion
National Weather Service Reno NV
225 PM PST Mon Dec 13 2021 .SYNOPSIS... A major winter storm is bringing areas of strong winds and significant snow in the Sierra, with rain changing to snow for the lower elevations of western Nevada Monday night. Lengthy travel delays in the Sierra are expected with full road closures possible. Another colder winter storm is expected late Wednesday into Thursday with additional travel impacts expected. && .SHORT TERM... ...RAPID DETERIORATION OF TRAVEL CONDITIONS IN THE SIERRA AND FAR WESTERN NV BETWEEN 4 and 10 PM... Impact-wise, no major changes to thinking through Tuesday with the current storm system bringing heavy Sierra snow and gusty winds, notable snow (tonight-Tuesday morning) for western NV, and strong winds for portions of western NV. Precipitation, mostly of the lighter variety, has been affecting the Sierra/eastern CA today with moist upslope flow and some upper forcing with a potent upper low off the northern CA and Oregon coasts beginning to swing eastward. So far today, occasional periods of precipitation have been spilling over into western NV but nothing prolonged yet as that area waits for better forcing tonight. As for snow levels, they are currently stuck around 5200 to 6200 feet from Lassen down to Tahoe/Reno, respectively, with levels slower to 6500-7000 feet down in Mono County. Travel difficulties are already underway in northeast CA with slushy and snow-covered passes requiring chains and/or snow tires. As we get into the late afternoon and evening, conditions are expected to deteriorate substantially in the Sierra and across northeast CA as a strong cold front (currently over northern CA) approaches and ramps up snowfall rates and drives down snow levels. At least the HRRR is definitely hinting at an NCFR (Narrow Cold Frontal Rainband) advancing across the region through tonight; indeed, there are already hints of one near Interstate 5 stretching down towards Ukiah, CA so confidence is increasing in the HRRR solution. The HRRR has the NCFR pushing across the majority of western and west-central NV by daybreak Tuesday. Why is an NCFR significant? Well, intense snowfall rates of 2-3" per hour or even higher can be associated with an NCFR. Also, the NCFR typically drives the snow level down abruptly for a rapid increase in the area of travel difficulties. Therefore, while some areas even in the Sierra are currently just experiencing wet roads, don`t be caught off guard when conditions deteriorate rapidly (i.e. snow accumulating on roads quickly) later today. Also, near the Sierra crest, there is even a low chance for a brief thunderstorm tonight. For western NV, while notable rainfall has spilled into the immediate lee of the Sierra, most of the area is seeing more impact from strong winds at this time. However, by between 7-10 PM, expect rain to change to snow in far western NV (even lower valleys) with at least a few inches of snowfall possible by morning. Farther east into the Lovelock, Fallon, and Hawthorne areas, it looks to be well after midnight into Tuesday morning before snow levels fall off enough to begin to cause travel issues. Be prepared for travel slow downs and chain and/or snow tire requirements across western NV for the Tuesday morning would be wise not to wait until the last possible minute to start your morning commute! Late tomorrow morning into the afternoon, coverage and temporal nature of snow showers is expected to decrease substantially, although not end completely as a cold pool aloft settles overhead. Tuesday night could be quite cold as winds diminish with a surface high settling into the region (albeit, briefly), especially in areas that receive at least a few inches of snowfall with the current storm. However, models do show clouds already spreading overhead ahead of the next system early Wednesday morning so the current forecast lows are a bit moderated with that expectation. -Snyder .LONG TERM...Wednesday evening through early next week... The next Pacific low pressure system will sweep across the Sierra and western NV through Thursday afternoon. This quick moving shot of winter weather will spread a fresh layer of new snow across the region with considerable snowfall in the Sierra and Tahoe Basin overnight Wednesday through Thursday afternoon. Lesser snow accumulations are expected over western Nevada as the cold front quickly passes to the east and southeast into the Great Basin. Although ensemble model guidance is showing minor variances between model simulation runs, precipitation and wind forecast confidence still remains relatively moderate for this system. * Abundant Mountain Snow: Although there will always a certain amount of forecast uncertainty with snow forecasts, a moderate level of confidence remains that 1-2 feet of accumulating snow will fall across the Sierra. Areas above 7000 feet will be the most favored areas for these higher snowfall totals. In western Nevada, probabilistic snow guidance for lower valley areas will range from a dusting to less than an inch of new snow. But slightly higher areas above 5000 could see 3"- 6 of new accumulating snow on the ground. This same model guidance shows higher mountain communities receiving nearly a half to almost a foot of fresh snow on the ground by early Thursday morning. * Storm Impact Timing: From late Wednesday afternoon through early Thursday morning, the largest snow impacts will be centered over the Sierra. Lower valley locations of western Nevada could see accumulations gathering on the ground shortly after midnight Thursday and lasting through the early morning hours. Snow impacts over Mono County could continue to till midday Thursday. Anticipate travel impacts for both aviation (turbulence/LLWS/icing) and ground (especially over Sierra passes) during these noted time periods. * Increasing Winds: Thermal and pressure gradients in advance of this incoming cold front will begin to increase Wednesday afternoon and peak around midnight into Thursday morning with gradients gradually loosening through Thursday afternoon. Wind gusts in the lower valleys will range 30-40 mph with a moderate potential of seeing some gusts to 50 mph in the Sierra. Sierra ridges could still see gusts greater than 100 mph. Gusty periods could see localized wind impacts mainly confined to wind-prone areas. Impacts on aviation, recreation, and high-profile vehicles are likely especially along the US-395 and US-95 corridors. Friday and beyond, an upper level ridge axis will extend across the West Coast as high pressure strengthens over the Sierra into the Great Basin region. Friday will see gusty northeast winds possibly increasing along the Sierra crest with accompanying fair skies and slightly colder temperatures. Early next week and onward, the synoptic pattern continues to look a bit on the active side but increased uncertainty in this extended forecast period warrants a precautionary wait and see until model guidance shows less disparity. Nonetheless, above normal precipitation and slightly below normal temperatures are expected. -Amanda && .AVIATION... An ongoing major winter storm will continue through Tuesday. Significant impacts to aviation are expected: (1) Wind-LLWS- Turbulence; (2) Snowfall-obscurations-visibility; and (3) In- flight icing. (1) Wind-LLWS-Turbulence: * Mountain wave turbulence and LLWS are anticipated through at least Tuesday morning. Currently, there is a SIGMET in effect over the Sierra south of Lake Tahoe for turbulence due to strong up-drafts and LLWS. Surface gusts look to range between 30-40 kts for most area terminals, with some higher gusts possible in the northern Sierra (TRK-TVL) terminals. West-central Nevada terminals, especially HTH, could see a burst of strong wind gusts exceeding 50 kts into tonight. (2) Snow-flight Conditions: * Central northern Sierra terminals (TRK-TVL), snow will continue into Tuesday morning, with the heaviest rates and IFR/LIFR conditions expected 00Z-12Z Tuesday. Accumulations will likely exceed 2 feet in these areas. * Western Nevada terminals (RNO-CXP-MEV): A mix of light to moderate rain will give way to snow later this evening. Snow should accumulate later tonight as snow levels quickly drop to valley floors overnight. Accumulations will likely exceed 2 inches, with CXP-MEV having a moderate chance of exceeding 4 inches. RNO has a moderate chance of exceeding 4 inches. IFR/LIFR conditions are expected mainly between 03-06Z Tuesday in western Nevada. * Eastern Sierra terminals (MMH): Heavy snow and long duration IFR/LIFR conditions are expected through Tuesday morning. Accumulations will likely exceed 1 foot. (3) In-flight Icing: * Icing impacts to aviation will be elevated across the Sierra and into western Nevada through Tuesday morning. Be sure to check forecast icing conditions and PIREPs at before departing or arriving at area terminals. -Amanda && .REV Watches/Warnings/Advisories... NV...High Wind Warning until 10 PM PST this evening NVZ001. Lake Wind Advisory until 6 PM PST this evening for Pyramid Lake in NVZ004. Winter Weather Advisory from 10 PM this evening to 10 AM PST Tuesday NVZ001-004. Winter Weather Advisory from 4 PM this afternoon to 10 AM PST Tuesday NVZ005. Winter Storm Warning until 10 PM PST Tuesday NVZ002. Winter Storm Warning from 5 PM this afternoon to 10 AM PST Tuesday NVZ003. CA...Winter Storm Warning until 4 PM PST Tuesday CAZ071. Winter Weather Advisory from 4 PM this afternoon to 10 AM PST Tuesday CAZ070. Winter Storm Warning until 10 PM PST Tuesday CAZ073. Winter Storm Warning until 10 PM PST Tuesday CAZ072. && $$ For more information from the National Weather Service visit...