Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/12/22

Area Forecast Discussion
National Weather Service Boston/Norton MA
959 PM EST Sun Dec 11 2022 .SYNOPSIS... Periods of snow will continue at times tonight with the highest accumulations across western MA and northern CT. Mainly dry and chilly weather follows through the middle of the week. Confidence increasing in an impactful storm late Thursday into Friday, but odds favoring more rain that snow at least along the coastal plain. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... 955 PM update... Heavier snow bands impacting areas from RI into south central and western MA, with steady snow across CT. RAP shows area of enhanced omega in the snow growth region from western MA through CT and western RI, which lines up well with the heavier snow. Snow intensity really drops off to the east and NE of this band as best forcing will be aligned just ahead of the track of the mid level low which slides across SW New Eng tonight. The strongest omega will collapse toward south coast around midnight before moving to the south. An additional 2 inches of snow is possible across western and central MA through northern CT and RI, with less than an inch additional accum across eastern and NE MA. We expanded the advisory to SW RI where 2-4" accum likely. Given current accums, a few locations in the Berkshires will likely see locally up to 8-9 inches and 6-7 inches in portions of Hartford county before the snow tapers off after midnight. The snow will linger the longest across southern RI. Given the snow in western MA will be tapering off during the next few hours, there is not much gained by upgrading headlines at this point. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... * Very cold tomorrow night Tomorrow Any lingering snow flurries come to an end early tomorrow morning as an area of low-pressure departs over The Atlantic Waters. Northwest flow behind the departing low will usher a cooler and drier air mass over southern New England throughout the day tomorrow. As a result we should see skies gradually clearing by early afternoon. Cloud cover may linger a bit longer across southeastern MA, The Cape, and Islands. Chilly afternoon for those across interior MA north of I-90 with highs struggling to get above freezing. Further south and along the coastal plain temperatures will be relatively milder in the upper 30s to low 40s. Tomorrow Night High pressure builds in from the west tomorrow night. Clear skies and light winds are expected to support very efficient radiational cooling through Tuesday morning. As a result we`ll experience some rather frigid temperatures Tuesday morning across the interior with lows well below 20 degrees likely. Coastal areas will stay a bit more mild thanks to proximity to the relatively warmer ocean. Nonetheless most areas will see temps drop to the mid 20s by Tuesday morning. Mildest temperatures will be in the low to mid 30s across the outer Cape. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Highlights... * Mainly dry & cold Tue/Wed with highs in the 30s, but it will feel colder Wed with windy conditions expected. * Confidence increasing in a storm late Thu/Fri with odds favoring more rain vs snow at least near the coast, but uncertainty remains * Quieter weather probably returns in time for next weekend with seasonable temperatures Details... Tuesday and Wednesday... Mainly dry but cold weather will continue Tuesday and especially Wednesday. Vigorous amplifying shortwave in the vicinity of the Canadian Maritimes/Maine will drop south late Tue/Tue night and drag a strong cold front across the region. The inverted trough swinging through may allow for a few brief snow showers to clip the coast...mainly towards the Cape/Islands Tue night. However...the main story will be a reinforcing shot of cold weather along with rather windy conditions on Wed. High temps will mainly be in the 30s on both Tue & Wed. The big difference on Wed will be the windy conditions, so it will feel quite a bit colder. Overnight low temps will be mainly in the teens to lower 20s. Thursday and Friday... Confidence is increasing for a storm to impact the region late Thu into Fri. This is supported by most of the deterministic guidance along with their ensembles. That being said; there is still a large spread regarding potential strength and track of this system which is also depicted by the ensemble guidance. Much of this will be determined by the interaction of northern and southern stream energy...which is too early to determine at this time. Despite the uncertainty...there are ingredients in place that currently favor more rain as opposed to snow at least towards the coast. The surface high in eastern Canada appears too far north and east for what we would normally want to see for a significant snowstorm at least along the coastal plain. The surface track also is trending towards a coastal hugger or even a bit of an inland track. So again while nothing is set in stone...more rain is favored as opposed to snow along the coastal plain. The greater risk for significant snowfall will be further back into the interior...but ptype issues may exist across our entire region. Next Weekend... Appears the brunt of the storm will have departed by the start of next weekend. In the wake of that system...a blustery flow of seasonably chilly air is expected with dry weather likely dominating. && .AVIATION /03Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 00Z TAF update... Tonight...High Confidence in trends but moderate confidence in timing. IFR conditions continue for the first half of the evening in snow which was reducing vsbys to generally 1 or 2 miles. We should see improvement to MVFR conditions from northeast to southwest roughly in the 2z to 6z timeframe...but perhaps an hour or two later across portions of CT and areas near the south coast. This a result of drier air working in from the north allowing the steady snow to taper off to more scattered light snow showers/flurries. Ptype will be all snow pretty much northwest of the Cape Cod Canal. A general 1 to 4 inches of snow is expected on untreated runways with the higher amounts across our western terminals. N winds 5-15 knots. Tomorrow...High Confidence Lingering MVFR ceilings should improve to VFR by lunchtime...except for the far southeast New England coast where this process may take a bit longer. There may also be lingering ocean enhanced scattered light rain/snow showers in the morning. Otherwise...NNW winds 10 to 15 knots with a few gusts near 25 knots along the coast. Tomorrow Night...High Confidence VFR. Northwest winds 5 to 10 knots. KBOS Terminal...High Confidence in trends but moderate confidence in timing. KBDL Terminal...High Confidence in trends but moderate confidence in timing. Outlook /Tuesday through Friday/... Tuesday: VFR. Breezy. Tuesday Night: VFR. Windy with gusts up to 30 kt. Wednesday through Wednesday Night: VFR. Windy with gusts up to 35 kt. Thursday: VFR. Breezy. Thursday Night: MVFR/IFR conditions possible. Windy with local gusts up to 30 kt. Chance RA, chance SN. Friday: Mainly MVFR, with areas IFR possible. Strong winds with local gusts up to 40 kt. RA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Tonight Area of low-pressure moves over the coastal waters overnight with light to moderate rainfall. Winds continue to prevail out of the east/northeast from 15 to 20 knots with higher gusts. Seas stay elevated in the 6 to 8 foot range across the outer waters. Tomorrow and Tomorrow Night Moderate 15 to 20 knot winds become north/northwesterly tomorrow as low-pressure exits to the east. Winds begin to gradually diminish tomorrow night as high pressure builds in from the west. SCY conditions persist through mid-week with seas above 5 feet. Outlook /Tuesday through Friday/... Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Tuesday Night: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 10 ft. Local visibility 1 to 3 nm. Wednesday: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 12 ft. Wednesday Night: Low risk for gale force winds with gusts up to 40 kt. Rough seas up to 13 ft. Slight chance of rain showers. Thursday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 9 ft. Thursday Night: Moderate risk for Small Craft Advisory winds with areas of gusts up to 30 kt. Rough seas up to 8 ft. Chance of rain. Friday: Moderate risk for gale force winds with gusts up to 35 kt. Rough seas up to 12 ft. Rain likely. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Winter Weather Advisory until 7 AM EST Monday for CTZ002>004. MA...Winter Weather Advisory until 7 AM EST Monday for MAZ002-003- 008>012. RI...Winter Weather Advisory until 7 AM EST Monday for RIZ001>004- 006. MARINE...Small Craft Advisory until 7 AM EST Tuesday for ANZ231-232-250- 251-254>256. Small Craft Advisory until 4 AM EST Tuesday for ANZ233>235-237. && $$ SYNOPSIS...Frank/RM NEAR TERM...KJC SHORT TERM...RM LONG TERM...Frank AVIATION...Frank/RM MARINE...Frank/RM
Area Forecast Discussion
National Weather Service Des Moines IA
550 PM CST Sun Dec 11 2022 ...Updated for the 00z Aviation Discussion... .DISCUSSION.../Tonight through Sunday/ Issued at 404 PM CST Sun Dec 11 2022 Forecast Highlights: - Widespread patchy to dense fog tonight into Monday - Mainly Quiet Monday, then active late Monday through much of the work week with a variety of p-types mainly Tuesday - Winds continuing to look concerning Tuesday, especially north - Snow Wednesday and Thursday, lighter QPF amounts though Widespread stratus remained across the state into this afternoon, though some areas of clearing have been noted over southern and parts of western Iowa as seen from GOES Satellite Imagery. Despite a rather prominent low level temperature inversion and low level moisture, areas of dense fog lifted briefly but has since started to return mainly over portions of western Iowa this afternoon. Therefore after some coordination have included a Dense Fog Advisory for the rest of the today into Monday morning out over northwestern/western Iowa, though may have to expand further east depending on trends. Overall, widespread patchy fog is expected into the evening to Monday, though the HRRR as well as HREF guidance depicts very low visibilities mainly along and west of I-35. There is more uncertainty on the potential of dense widespread fog potential as increasing southeasterly winds as the NBM has indicated could limit this potential, though the GFS and RAP deterministic models hold off on increasing winds until later Monday. Unfortunately, low clouds will continue to filter in as winds shift more southeasterly with some increasing moisture over the region. Like yesterday, temperatures have struggled to increase today, thanks to the cloud cover, with values ranging in the mid 20s to low 30s. Upper level ridging with a surface high pressure system will continue to push southeast today, with light winds and temperatures remaining roughly in the upper 20s to mid 30s. Have trended down highs as a response, as heating potential for the rest of the afternoon will be very limited. Overnight lows are expected to fall into the 20s across the state. Low level flow is expected to become more southerly Monday, with increasing warm air advection and moisture flow as indicated by increasing theta-e advection across much of Iowa, especially into Monday evening. Temperatures will remain mild as highs make it into the mid to upper 30s north and in the low to mid 30s south, though with widespread clouds remaining overhead will need to potentially lower values a bit given recent trends over the past few days. Quiet weather is expected for much of the day as the upper level ridge departs and pressure height falls begin to move into the region ahead of the large weather system out west. Model guidance remains consistent on overall track as it arrives into the Central Plains. A large trough and mid level low pressure system strengthens as it moves out of the western CONUS, developing into a powerful surface low after experiencing strong lee cyclogenesis. Initial onset of precipitation looks to begin late Monday into Tuesday over western Iowa, before spreading east across the rest of the state bringing widespread precipitation. Precip types have remained to be one of the more challenging aspects with this system, as models continue to vary on the evolution of p- types late Monday through Tuesday morning. Though the NAM has let up slightly on the colder solution and high freezing rain and hence ice accumulations, it still is quite hot on totals over northern and into north central Iowa Tuesday morning. Other deterministic models like the GFS and Euro are warmer with overall little ice accumulations largely remaining over northern Iowa under a tenth of an inch while the rest of the state sees rain. Given the southeast flow and WAA regime over the state, have continued to favor the warmer p-types with rain for much of the state Tuesday while the north sees some wintery mix with some ice accumulations. Will continue to closely monitor these details over upcoming forecast packages. Rain accumulations overall look to range around a half inch to inch, especially west through the day. Winds continue to increasingly look concerning, especially over northern Iowa as NBM guidance shows 20 to 25 mph winds over the north while slower further south, and gusts in the 40 to 45 mph range. By Wednesday as the deformation zone of the low moves into southern Minnesota into the northern half of Iowa, snow will likely impact the area throughout the day. There is more consistency however with drying across central into southern Iowa as a dry slot moves through the state, so there may be a break in any precipitation concerns elsewhere. Expect to see lows in the 20s to low 30s and highs in the mid 30s west and into the 40s further east. Light snow by Thursday into Friday is looking more likely and more widespread across the state, though with limited moisture suggested from guidance would expect lighter accumulations, though further north could see a few inches. These details will largely depend on the track and evolution of the system over the week, as well as the blocking of another larger system rotating southward through the far northeastern CONUS slowing the movement of the low overall. By Friday, activity slows with dry conditions eventually ending for all, with cooler and mainly quiet weather for the weekend. && .AVIATION.../For the 00Z TAFS through 00Z Monday evening/ Issued at 545 PM CST Sun Dec 11 2022 Stratus and fog remain the primary aviation concerns through the period. Where stratus is, cigs should lower to IFR/LIFR overnight while fog development is possible in the clear areas. Cigs and vsbys should begin to improve during the day Monday but cigs likely will remain at MVFR at best for most sites. && .DMX WATCHES/WARNINGS/ADVISORIES... Dense Fog Advisory until 9 AM CST Monday for IAZ004-015-023-033- 034-044>046-057-058-070. && $$ DISCUSSION...Bury AVIATION...Donavon
Area Forecast Discussion
National Weather Service Quad Cities IA IL
511 PM CST Sun Dec 11 2022 ...00Z AVIATION UPDATE... .SYNOPSIS... Issued at 244 PM CST Sun Dec 11 2022 The latest sfc analysis was indicating a ridge of high pressure progressing eastward acrs the region with light and variable winds, while return flow and a warm front was organizing up the plains. Aloft, sharp lobe of short wave ridging was adjusting eastward acrs the MO RVR Valley and western MN. Inversion trapped stratocu has held on thick in many areas, but a few breaks noted on Vis satellite loop west of the MS RVR, and a bigger clearing hole has occurred acrs the southwestern DVN CWA. Further west/upstream, a large upper trof/low was seen on the current water vapor loop rolling into northern CA. && .SHORT TERM...(This evening through Monday) Issued at 244 PM CST Sun Dec 11 2022 Tonight...Main challenge tonight will be tricky cloud cover fcst and potential fog development. Sub-inversion east-southeast flow will look to undercut the west-northwesterlies further aloft and slosh the stratus off to the east back acrs the area where there has been some clearing or breaks. Plus re-enforce any deck still maintaining. But if some breaks or clearing can maintain under subsident upper ridge axis passing overhead, some areas or patchy fog may develop tonight as light winds become east-southeast with some convergent swaths. This combo of clear patches and convergent sfc flow more likely west of the MS RVR into west central IL and have added at least patchy fog wording into these areas, with some locally dense possible. Will bank on subsidence fields and shallow moisture depth to prevent any drizzle or freezing drizzle to occur, but the fog itself may deposit on elevated sfc`s if it can get established. More of a widespread fog occurrence looks more likley acrs portions of central into western IA in southeasterly BL moisture fetch. Low temps tonight could be quite variable depending on cloud cover and clear patches, ranging from down in the 20s to low to mid 30s where low level cloud blanket maintains. Monday...Large/deep inversion gets even more enhanced by backing flow aloft in the H85 to H6+ MB layer, and concern continues for this feature to keep trapping clouds and some fog acrs the area. But slow moving omega upper ridge and it`s associated subsidence fields will still be acrs the area most of the day, which could create some breaks in the cloud cover or expand ones already occurring. Mixing southeasterly sfc winds of 10-15 mph and some breaks could make the fcst highs in the upper 30s to low 40s a few degrees too cool, but have sided with the 50 percentile NBM blend as a happy medium. ..12.. .LONG TERM...(Monday night through Sunday) Issued at 244 PM CST Sun Dec 11 2022 Key Messages 1. Long term will be active as broad cyclonic flow and a series of waves will drive the weather. 2. Wintry mix changing to all rain with strong winds expected Tuesday into Wednesday. 3. Sporadic chances for rain/snow showers through the rest of the week as upper level low locks in place overhead. Discussion: Active upper level flow through the long term period. A long wave trof will slowly lumber east through the period as southwest flow aloft begins to impinge on the area early in the period. This trof soon closes off and fills in. Before this happens a warm front and precip will move into the area Tuesday into Wednesday. The rest of the week this low slowly moves east as a series of vort maxes rotate around it. This low is slow to move out of the area and will affect us into next weekend if not longer. Main forecast challenge is with the system Tuesday into Wednesday. Guidance has continued a slowing progression for pops. Most of the 12z guidance keeps our area mainly dry through 15z Tuesday. The 12z ECM came in a little faster. As a result, have cut pops back but kept schc pops a little further east than blended QPF would suggest to keep that chance going. Also went to 3hr pop windows to better time the arrival of the pops. While most of this will be rain the onset of precip could have some mixed precip. This should be a top down saturation event with the warm front moving into the area. Different models, with different timing of ice introduction and sfc temps continues to lead to a difficult onset ptype forecast. NBM has ra/sn as dominant but cant rule out pl and fzra. The RAP/NAM continue to have less ice so more FZRA, which is notable in longer range HRRR runs. While this is def a possibility, I think the longer onset is pushed off the more this becomes a sn/ra onset issue. FZRA would be an issue if we speed up onset of pops to before sunrise and before temps increase. At this time do not think this is the likely forecast. That said, it still remains in the plausible realm and as such have kept fzra probs but capped them at schc. Any impacts from fzra should be short lived as temps climb above freezing quickly. It does look like blended forecast has highs/low for Tues-Wed that are 5-6 degrees different from hourly temps. Did match the highs to be represent the hourly temps during this time. Wind will remain an issue Tuesday into Wednesday. While the earlier GEFS and ECMWFens kept sustained wind probs at 20kts or less, gusts could easily get into the 40-45 range. That said, I think the warmer we get, the better the mixing and better the chance for winds near wind adv criteria. This also looks to be a failure point for us getting strong wind gusts/adv level wind gusts. This will need to be looked at by later shifts. After this, it does seem we will see showers and some snow through the end of the week. Ensemble forecasts struggle to have much snow accum with many of the prob for 1 inch accum under 50%. This seems to be more nuisance stuff. That said, any change in vort max structure could make this change. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 505 PM CST Sun Dec 11 2022 GOES Nighttime Microphysics imagery shows more widespread clearing near KBRL and patchy clearing near KCID, with widespread stratus and MVFR ceilings elsewhere including at all the terminals. A loop shows the stratus actually working back westward, and so with nightfall and lack of strong subsidence I don`t foresee much improvement, and thus anticipate MVFR ceilings into Monday with some areas of IFR ceilings with BL cooling later tonight. Forecast soundings show stronger winds developing Monday with deeper mixing, and the hope is that this will foster more of the breaks and a return to VFR conditions. Light and variable winds will become E/SE at around 10 kts on Monday with some gusts to 20 kts possible Monday PM. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...NONE. IL...NONE. MO...NONE. && $$ SYNOPSIS...12 SHORT TERM...12 LONG TERM...Gibbs AVIATION...McClure
National Weather Service Hastings NE
536 PM CST Sun Dec 11 2022 ...Aviation Update... .DISCUSSION...(This evening through Sunday) Issued at 338 PM CST Sun Dec 11 2022 Key Messages: * Dense fog and patchy drizzle expected tonight into Monday morning. Temperatures may initially be near freezing, leading to isolated slick spots on roads. * Thunderstorms expected Monday night into Tuesday. Some of these may be severe. * Snow creeps into the area on the backside of the system late Tuesday through Wednesday. * A cold pattern is expected through the end of the year. Details: Skies are clear across the area with southeast surface winds gradually increasing as our next storm system deepens over the western CONUS. These winds will continue to advect low-level moisture into the area tonight, and it appears likely that dense fog will develop late tonight into Monday morning. The HRRR/RAP have been very consistently showing low visibility, and the SREF is actually showing 100 percent probabilities of visibility less than 1 mile. As such, we decided to go ahead and issue a dense fog advisory until noon Monday. In addition to the fog, model soundings and QPF output indicate the potential for light, patchy drizzle as well Monday morning. Temperatures will be on an increasing trend in the early morning, but may initially be near freezing as this fog and drizzle develops. Therefore, some slick spots on roads are possible for the Monday morning commute...mainly north of I-80. The main story on Monday is the threat for thunderstorms. Clouds will stick around through the daytime, and a few showers cannot be ruled out through the afternoon. But the main chance for thunderstorms arrives late in the evening (mainly after 9pm) as stronger forcing from the upper low pushes into the area. At first glance, the timing (and time of year) may lead one to believe that the severe threat is negligible, but the strong dynamic lift coupled with abundant shear will be sufficient for at least a few strong updrafts through the late overnight hours. In fact, the 18Z HRRR is indicating the potential for supercell structures developing over northwest Kansas and approaching our forecast area after midnight. The stacked surface/upper low pushes into Nebraska on Tuesday, with continued chances for rain and thunderstorms. Rainfall totals will be spotty, but could be quite beneficial, with some areas receiving over 1.00" through midday Tuesday. Colder air rushes in on the backside of the system late Tuesday. The heaviest of the precipitation should be exit the area to the east at this point, but some light snow may wrap in from the northwest and continue off and on through Tuesday night and Wednesday. Snow amounts are forecast to be light for most of the area, with only our far western/northern zones possibly receiving 1 to 3 inches of snowfall. That said, any snow that does fall will be accompanied by strong northwest winds with gusts of 40 to 50 MPH at times. Some light snow may linger in our east/northeast on Thursday, but the system finally moves out of the area Thursday night into Friday. Dry conditions are expected to prevail Friday and Saturday, with only low chances for light snow next Sunday. But it will be cold! Highs in the 20s and single digit lows will be common. Ensembles indicate that this cold pattern will continue through Christmas and possibly even through the end of the year. The EPS ensemble has -15 to -20 degree temperature anomalies for December 20-24. Specifics on exactly how cold we get remain uncertain, but that is an impressively cold signal for a 5 day average at this lead time. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Tuesday) Issued at 526 PM CST Sun Dec 11 2022 Will have VFR conditions continue for a few more hours this evening, then things look to deteriorate as lower level moisture and the potential for fog and drizzle increases with time. Models are in fairly good agreement with lowering ceilings and visibility, though the timing of the onset differs a bit. Once those lowered conditions set in later this evening, expecting little/if any change through the rest of the overnight hours and into at least mid-late morning on Monday. May see some improvement closer to midday-afternoon Monday, mainly with visibility...the low sub-1000ft ceilings may stick around through the duration of this TAF period. As far as winds go, direction remains southeasterly through this period. Sustained speeds through the overnight hours look to be around 15 MPH. From late morning through the afternoon, speeds increase and gusts near 30 MPH will be possible. && .GID WATCHES/WARNINGS/ADVISORIES... NE...Dense Fog Advisory from 9 PM this evening to noon CST Monday for NEZ039>041-046>049-060>064-072>077-082>087. KS...Dense Fog Advisory from 9 PM this evening to noon CST Monday for KSZ005>007-017>019. && $$ DISCUSSION...Mangels AVIATION...ADP
Area Forecast Discussion
National Weather Service Grand Rapids MI
934 PM EST Sun Dec 11 2022 LATEST UPDATE... Update .UPDATE... Issued at 915 PM EST Sun Dec 11 2022 One challenge for the night is whether we will see some patchy flurries or drizzle/freezing drizzle. Overall this risk is low at this time. A shallow cooler and moist airmass was filtering down from the northeast. Cloud bases have mostly risen this evening. But models are forecasting the low level convergence to increase slightly late tonight. The DGZ remains unsaturated tonight. Currently where several high res models suggest there is precipitation upstream...observations indicate none reaching the ground. Trends in the last couple of runs of the HRRR suggest the precipitation potential is decreasing. Based on this we will maintain a mostly dry night for the region...but will need to monitor it closely. Currently the surface temperatures were mostly above freezing. We did raise the overnight lows slightly given the lack of falling temperatures at this time. && .DISCUSSION...(This evening through next Sunday) Issued at 311 PM EST Sun Dec 11 2022 ...Rain/Mix Mid-week then turning Colder with Snow Showers... Upper low pulling off to the east tonight with cyclonic flow on the back side being replaced by shortwave ridging and dry weather for early this week. Light showers in northwest flow off Lake Michigan this afternoon will diminish this evening and move off to the west as drier easterly flow develops with surface ridge axis building over Lower Michigan. Longwave trough across the West CONUS will result in lee cyclogenesis that translates east and brings the chance for rain and mixed precip on Wednesday changing to snow on Thursday. The forecast problem is for timing of the precip onset on Wednesday as dry easterly flow persists and moisture transport from the Gulf may be interrupted by deep convection across the SE CONUS. There could be virga rather than precip Wednesday morning but eventually the column moistens and the hydrometeors reach the ground. The next question is what form of precip can be expected Wednesday into Thursday. Thermal profiles suggest a mix at the onset across at least the northeast half of the forecast area as wet bulb zero contours indicate snow, sleet and freezing rain potential there. We will have to fine tune p-type as we get closer to the event but for now we will have mixed precip persisting northeast of a line from Mount Pleasant to Cadillac for Wednesday into Wednesday night. Looks like the dry slot moves in Thursday morning with precip tapering off to drizzle then colder air moving in Thursday night and Friday. Lake effect snow showers develop Friday with westerly flow allowing snow showers to reach well inland through Saturday. Inversion heights are between 5 to 8 kft much of this time which should allow for some snow accumulation as sfc air temps remain below freezing over the weekend. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 615 PM EST Sun Dec 11 2022 Low level moisture will remain abundant into Monday leading to MVFR and IFR conditions at times. The main impact was currently coming from lower ceilings...however fog should start to develop and increase as well. The flow will become light easterly and that may allow for slight drying Monday afternoon. This would support conditions potentially improving to VFR. Any showers should be confined to the area southwest of a KMKG to KAZO line this evening. && .MARINE... Issued at 311 PM EST Sun Dec 11 2022 Offshore winds will increase early this week with gusts over 25 knots on Tuesday and potential for southeast gales to 35 knots by Wednesday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...None. && $$ UPDATE...MJS DISCUSSION...Ostuno AVIATION...MJS MARINE...Ostuno
Area Forecast Discussion
National Weather Service North Platte NE
812 PM CST Sun Dec 11 2022 ...Update for Dense Fog Tonight... .SYNOPSIS... Issued at 335 PM CST Sun Dec 11 2022 -High confidence, high impact winter storm expected late Monday through Wednesday with dangerous travel expected for portions of western Nebraska due to heavy snow and strong winds. -Blizzard conditions are likely for portions of northwest Nebraska into the Sandhills with a sharp gradient in forecast snow amounts expected. -Ice accumulations prior to snowfall will further hamper travel and lead to dangerous conditions across much of the area. -Strong northwest winds with widespread gusts exceeding 45 mph and potentially as high as 60 mph will lead to blowing snow concerns regardless of accumulation amounts. -Temperatures trend colder for mid-week and beyond with wind chill values falling into the negative teens each morning Wednesday through Saturday. && .UPDATE... Issued at 812 PM CST Sun Dec 11 2022 The HREF, RAP, HRRR and a few other models show visibility falling to near zero across much of wrn and ncntl Nebraska overnight and Monday morning. The result of dry air aloft and rapid low level moisture advection. The RAP and HRRR also show light QPF in some areas suggesting at least the potential for freezing fog. This could be freezing drizzle. A forecast update is in place for dense fog and freezing fog from midnight tonight to noon Monday. && .SHORT TERM...(This evening through Monday night) Issued at 335 PM CST Sun Dec 11 2022 Fairly quiet weather is expected over the next 18 to 24 hours. Shortwave ridging ahead of the next upper-level disturbance will limit sensible weather for the remainder of Sunday before abrupt changes arrive early Monday morning. Constricting west to east pressure gradient across the area will keep winds elevated as the early stages of lee-cyclogenesis begin across the central High Plains. The belt of stronger flow off the surface will be quick to advect increasing low-level moisture into the area. This will come in a couple waves, the first of which looks to be in the predawn hours Monday. Widespread low-level stratus will filter in from the south, leading to a dreary start to the day Monday. This increased cloud cover and low-level moisture streaming in will help leading to warming temperatures just prior to sunrise. Isentropic upglide in the low-levels, particularly on the 280k surface for areas east of Highway 83. Cannot rule out some patchy drizzle for these areas and with surface temperatures near the freezing mark, will have to watch for some frizzle. Thinking this threat is fairly limited and may behave more as advection fog. Will keep little to no QPF for the morning hours given little signal from the HREF outside the operational NAM then tends to overdo QPF in these setups. As WAA increases, however, expect deepening saturation and lift adequate to lead to some afternoon rain chances. As dew points continue to rise, LI values begin to turn negative by late evening across central Kansas into portions of southern Nebraska. This will be sufficient for some modest MUCAPE values to develop in the evening leading to some threat for embedded thunderstorms. Will maintain the thunder mention for this period and some pockets of heavier QPF given expected convection. Overall trend has been to slow the arrival of these convective elements which may support this threat lingering into early Tuesday. This notion is supported by SREF probabilities and extended CAMs, notably the NAM Nest. No severe is expected but some moderate downpours are possible in the stronger cores with HREF max ensemble values showing a few pockets of quarter inch per hour rates. Further west, sharp baroclinic zone will develop along an inverted surface trough. This feature will drop south quickly through the morning hours on Tuesday with precipitation in the form of snow from onset across our far northwest zones but a mix of rain and freezing rain invof this zone. Will keep a mention of ice for areas generally between Highway 61 and Highway 183 as a result with some appreciable ice accumulations nearing a tenth of an inch across the northern half of the area. Convective rain overtop sub-freezing temperatures at the surface would be the greatest concern given a strong low- level warm nose. Will have to watch for increased icing amounts based on this potential but thinking this would be the extreme case given higher NBM Percentile groups show limited accumulations. .LONG TERM...(Tuesday through Sunday) Issued at 335 PM CST Sun Dec 11 2022 A very dynamic storm system will unfold across the area beginning Monday night into Tuesday morning. This slow storm system will meander east through the middle of the week, with wintry impacts lingering into Thursday. Winter Storm Watches have been expanded further south and east with new Blizzard Warnings in effect for the northwest Sandhills and northern Panhandle. Upper-level pattern continues to showcase deepening h5 low as longwave trough traverses the central Rockies. Height falls ahead of this feature will overspread the area by early Tuesday morning. Temperatures for the day will start off mild but begin falling across much of the region by midday suggesting a non-diurnal temperature trend and raw afternoon. Increasing upper-level divergence within largely diffluent flow will support strong forcing for ascent with lee-cyclogenesis taking place across eastern Colorado. Strengthening low-level flow with constricting surface pressure gradient will draw anomalous moisture into the area. EFI table highlights multiple highly anomalous parameters through the Tuesday and Wednesday timeframe, lending credence to the potential for a significant storm system for the time of year. Surface low will take shape and track east to northeast through Tuesday morning. NAEFS output shows mean MSLP at climatological minimums with low 990s hPa central pressure. This low will track east-northeast into south central Nebraska, putting much of the forecast area in the northwest quadrant. Aforementioned upper-level dynamics will lead to strong, vertically stacked system with h7 and h5 lows tracking into central Nebraska. This puts the greatest backside convergence across the Sandhills into southern South Dakota and it`s here that we`ll see the greatest QPF amounts and resultant snowfall amounts. Greatest fgen will occur through the day on Tuesday with decreasing intensity by late in the day as the TROWAL looks to spread over the area. Given strong forcing and anomalous moisture in the area, opted to go heavy on the forecast liquid equivalent. NBM 4.1 50th percentile for event liquid generally exceeds one inch across the entirety of western and north central Nebraska with values approaching 2" near the Nebraska/South Dakota border. Of course, some of this may fall in the form of rain, snow, and/or ice. Even so, with expect SLR ratios early on expected to be around 7-9:1 but increasing to 13-15:1 by late in the event, expect a fairly efficient snowfall though strong winds may lead to some dendrite fracturing which could limit final SLRs somewhat. Even so, high QPF and expected snow ptypes support heavy snow accumulations. Given a small overlap and negative surface wet bulb temperatures and positive h85 temperatures, expecting a fairly progressive buffer zone of freezing rain between the rain and snow. Am not expecting significant ice accumulations but with ice followed by snow...some heavy...expecting very dangerous travel conditions. In total, expecting 3 to 5 inches of snow near a Imperial to North Platte to Butte line. Northwest of this line, expect 5 to 10 inches, with 10 to 18 inches and locally higher amounts for the northern half of Sheridan and northwestern Cherry Counties. Ice accumulations will likely remain at or below a tenth of an inch mainly between the Highway 61 and Highway 183 corridors. With expected snow and strong winds gusting 50 to 55 mph, whiteout conditions are likely within the Blizzard Warning and are possible within much of the Winter Storm Watch. Will need to monitor potential for expansion of Blizzard Warning with later forecasts. Lift will gradually weaken heading through the day Wednesday as the surface low departs to the east and main h7 and h5 lows fill in. Even so, wrap around precipitation will still work into the area from the north. Have slowly decreasing PoPs from south to north through the latter half of the day. Believe this has the potential to see a quicker exit than currently forecast. For now, thinking any additional precipitation on Wednesday will be fairly light with the NBM 50th percentile showing only a few hundredths south of Highway 2 but closer to a quarter inch near the South Dakota border. Strong winds persisting through the day will only continue the blowing snow concerns though so expecting continued hazardous travel conditions especially in areas that saw significant snowfall accumulations. EFI values for winds are actually maximized for Wednesday versus Tuesday which suggests the going forecast may not be aggressive enough but winds exceeding 40 to 50 mph will be enough to prolong issues. Accumulating precipitation will largely be done by late Thursday into early Friday. Strong winds will continue with bufkit soundings showing potential for gusts in the 25 to 30 mph range which may continue some blowing snow concerns into the late week. Temperatures Wednesday through Friday will remain cold with values only reaching the 20s to low 30s and morning lows in the low teens and single digits. Factoring in the winds, prolonged periods of sub-zero wind chills are likely and some minimum values will fall into the negative teens Thursday and Friday but look to remain short of Wind Chill Advisory criteria for now. Though upper-level low will depart to the east-northeast and keep the area within northwesterly flow aloft, multiple embedded PV anomalies will dive south across the northern and central High Plains heading into the weekend. The strongest of these features looks to affect the area sometime in the late Friday to early Saturday timeframe, though model discrepancies limit confidence in this. Will keep the low-end PoPs from the model blend in the forecast but look for these to potentially be removed with later forecasts. Overall the extended period looks to favor colder than normal temperatures as northwesterly flow remains prevalent. Some signals that an encroaching high pressure prior to Christmas may bring a significant cold spell to much of the area. Ensemble guidance hints at high temperatures falling into the single digits with lows well below zero. Confidence regarding this is medium at best but given support from multiple ensemble suites, will need to be monitored. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 535 PM CST Sun Dec 11 2022 Low stratus and fog will move into the area overnight, leading to widespread IFR/LIFR CIGs and visibilities for all area terminals. The low stratus looks to persist through the entirety of the day tomorrow, though visibilities are expected to somewhat improve in the afternoon. This is ahead of an approaching storm system, which could lead to increasing SHRA near the end of the valid period. Winds remain out of the southeast through tomorrow evening, at around 10 to 20kts. && .LBF WATCHES/WARNINGS/ADVISORIES... Blizzard Warning from midnight CST /11 PM MST/ Monday night to 6 AM CST /5 AM MST/ Thursday for NEZ004-094. Dense Fog Advisory from midnight CST /11 PM MST/ tonight to noon CST /11 AM MST/ Monday for NEZ005-023-024-035-036-057-058-069- 094. Winter Storm Watch from late Monday night through late Wednesday night for NEZ005>009-022>026-035>037-056>059-069. Freezing Fog Advisory from midnight tonight to noon CST Monday for NEZ008>010-025>029-037-038-059-070-071. && $$ UPDATE...CDC SYNOPSIS...NMJ SHORT TERM...NMJ LONG TERM...NMJ AVIATION...Brown
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
535 PM CST Sun Dec 11 2022 .SHORT TERM... Issued at 214 PM CST Sun Dec 11 2022 Through Monday night... Key Message in the short term: 1. Areas of drizzle possible overnight into Monday AM near the lake (temps to remain above freezing in those locales) Expansive cloud cover and light northwesterly flow have held down temperatures below 40 so far today making for another cloudy and cool day across Chicagoland. Other than some patchy drizzle into far northeastern Porter County, the rest of the area should stay precip free through the rest of the afternoon and evening. Widespread cloud cover continuing overnight will again limit our cooling with temperatures remaining in the mid 30s in the Chicago metro and near the lake with lower 30s expected further inland. As winds begin to trend more north northeasterly this evening there is the potential for more drizzle to push inland off the lake after midnight tonight into portions of the Chicago metro, especially for areas nearest the lake. The drizzle may persist through the morning hours on Monday as well. Lake induced equilibrium levels are fairly shallow suggesting the majority of this is expected to be drizzle, but a few spotty showers cannot be ruled out. Will also note that the HRRR is the most bullish with QPF up to 0.05-0.10" with this activity. Temperatures near the lake and where any precipitation falls are expected to remain above freezing. Accordingly the concern for any icing remains low. Further inland should remain mainly dry through the period, though some patchy drizzle cannot be ruled out Monday morning. Overall, tomorrow looks like a repeat of today with cool and cloudy conditions and highs in the upper 30s to around 40 degrees. Petr && .LONG TERM... Issued at 214 PM CST Sun Dec 11 2022 Tuesday through Sunday... The key weather messages through the end of the week are: * Blustery conditions developing on Tuesday, with a potential for stronger winds Tuesday night. * Cold, soaking rainfall mainly Tuesday evening into Wednesday * Some snow (showers) possible, mainly Thursday night into Friday. * Colder into the upcoming weekend. The potent upper trough currently digging across the Great Basin will head eastward on Monday, with subsequent intense divergence on the nose of a robust upper jet inducing lee cyclogenesis across the central Great Plains. Model guidance remains in very good agreement on the progression of salient large scale features, with the deepening surface low slated to rapidly occlude by later Tuesday and Tuesday night well to our west. As this occurs, it`ll slingshot an appreciable low-level jet eastward across the region, yielding an increase in gusty winds by Tuesday afternoon, but moreso overnight into Wednesday. Forecast soundings suggest vertical mixing will be greatly limited by a pre-existing inversion and rapidly-saturating column. This suggests gusts should stay just under Wind Advisory levels, with sporadic gusts into the 35-40 mph range. Guidance continues to indicate that much of Tuesday (if not all of the daytime hours) will remain dry. Deeper saturation finally moves in very late in the day and into the evening hours. Widespread cold rain looks like a good bet through Tuesday night into Wednesday as robust upper jet forcing arrives. Temperatures will likely remain steady or slowly rise through the night, and while they may be in the mid 30s across northern Illinois as precipitation starts, no wintry precip types are expected with full melting of hydrometeors due to a notable warm nose aloft. Still unclear how much (if any) impact on rain totals we`ll see from upstream convection, but the presence of some instability aloft and decent large scale forcing suggests localized swaths of amounts near 1"+ are possible through Wednesday afternoon. Current indications are that the system`s dryslot will blast overhead Wednesday morning and afternoon before the deeper cold airmass arrives. Suppose a few elevated thunderstorms can`t be discounted immediately ahead of the dryslot arrival, but this would be brief as deeper saturation and any MUCAPE will be lost very quickly. The ECMWF continues to show quite a bit more in the way of elevated instability/steepened lapse rates and moisture than other guidance which results in a second round of heavier convectively-driven precipitation through Thursday morning. This remains a bit of an outlier solution, with it mostly looking like we`ll transition to either dry conditions or lingering patchy drizzle through the night. The colder airmass finally pushes into the region on Thursday. Precipitation looks pretty inconsequential at this point through the end of the week, although as we`ll likely eventually get into a regime supportive of isolated to scattered snow showers, possibly lingering into Saturday. Colder conditions will prevail through the weekend, with highs only in the 20s to near 30 degrees. Carlaw && .AVIATION... For the 00Z TAFs... MVFR ceilings are expected to persist through the forecast period as moisture remains trapped under a 4kft inversion amid weak flow. A weak boundary over Lake Michigan is expected to shift westward across the Chicago metro late tonight into Monday morning. Low-end MVFR ceilings and patchy -DZ are likely during this time, with perhaps a brief period or two of IFR ceilings around daybreak Monday. Light winds around 5 knots will favor just east of north this evening, though some variability between NNW and NE is expected. winds will veer E late tonight and ESE by Monday afternoon, remaining 10 knots or less through the period. Kluber && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
942 PM EST Sun Dec 11 2022 ...New UPDATE... .UPDATE... Issued at 938 PM EST Sun Dec 11 2022 No major changes are needed to the forecast. Rain has exited the area as a front appears to have pushed south. We are starting to see some clearing in SW VA and NE TN, and western portions of the TN Valley, likely due to the N-NW downslope flow off the Plateau, and some dry advection aloft behind the front. The models are doing a pretty good job of picking up on this, especially the HRRR and HREF. The forecast captures this clearing as well. Forecast temps and dewpoints are all staying close to obs. && .SHORT TERM... (This evening through Tuesday) Issued at 313 PM EST Sun Dec 11 2022 Key Messages: 1. Hope for sunlight on Monday and early Tuesday, then clouds increase Tuesday afternoon. 2. Regardless of clouds, dry conditions expected Monday and Tuesday. Discussion: Visible satellite imagery paints the picture. Much of the eastern and southeastern United States are beneath grey, overcast skies again today. Models soundings show that the lowest 5,000 to 6,000 ft of the atmosphere are saturated, and will remain that way until later tonight. Visible and water vapor satellite imagery confirm the location of an east-west H3 jet streak that will be shifting eastward away from the Carolinas this evening. Some spotty drizzle or even light rain will still be possible across the east TN mountains and areas near the GA border, including our NC counties, through late this evening. By 00z or shortly after, influence from this jet streak should have waned enough that any drizzle or light rain should come to an end for the remainder of the night. For the overnight hours into Monday, a strong and very deep western upper low will be digging south across Nevada and the four corners region. Downstream, upper ridging will build over the Mississippi river valley, with some cyclonic flow aloft lingering over the southern Appalachian region into Monday afternoon. Models show low level moisture thinning substantially overnight and on Monday morning as surface high pressure builds in from the north and heights begin to rise. Given the thinning seen on visible imagery well to our north, the addition of rising heights aloft should allow for plenty of sun to break out across the CWA tomorrow. It may be midday or early afternoon before that occurs - a little slower than perhaps previous runs would have suggested. However I do think that sunny/clear skies are very likely tomorrow. A welcome change by many I am sure. Upper ridge moves overhead on Tuesday in advance of the western low ejecting eastward from the southern Rockies into the plains. Likely see additional sun early Tuesday, but high clouds should increase as the day wears on, with low clouds moving back in during the afternoon as southerly low level flow ramps up. Do not have any rain chances in the forecast late Tuesday; the consensus is that precip associated with that western low will hold off until the early parts of the long term period. && .LONG TERM... (Monday night through next Sunday) Issued at 313 PM EST Sun Dec 11 2022 Key Messages: 1. Numerous showers are expected Wednesday into Wednesday night ahead of an approaching cold front. Rainfall totals of near or above 2" are possible in most areas. 2. Gusty winds are likely in the Tennessee mountains and adjacent foothills Wednesday as well. 3. A transition to snow showers is expected in the mountains of Tennessee and southwest North Carolina by late in the week with flurries possible elsewhere. Temperatures will also be well-below normal through the weekend with some places staying below freezing. Tuesday Night through Thursday At the start of the period, upper ridging will be in place ahead of a deep trough and developing surface low just east of the Rockies. This will be of focus heading into Wednesday morning as increased upper jet dynamics and moisture advection move into the region ahead of its associated frontal boundary. The latest deterministic and ensemble guidance have suggested an overall increase in potential rainfall totals due to better moisture and longer duration. The slower trend for onset of precipitation has also continued as well with only a minor change from the overnight shift. With PWAT values of near 1.2" area-wide, this illustrates the extent of available moisture as these values are above the 90th percentile and near the daily max for this time of year. When combined with the strong dynamics and ~50kt 850mb jet, there is definitely support for totals of near or above 2" in many places as the latest GEFS and deterministic guidance predicts. These values still don`t exceed 6- hour flash flood guidance in most places, but the trend definitely emphasizes the importance of keeping an eye on the forecast as higher resolution models can view into this timeframe. This is also considering the potential for repeated heavy rainfall in southern portions of the area closer to the warm sector. With the strong 850mb jet and MSLP gradient magnitude of 80+ micrometers/km over the mountains, potential for mountain wave enhanced continues to be of focus, in addition to the locally heavy rainfall. The main inhibiting factor for warning vs advisory-level winds will be the strength of the 850mb jet as the surface low itself will be stacked and far into the Great Plains. Overall, messaging will be kept largely the same with a focus on these two potential impacts. Some elevated instability is still suggested in southern areas, but severe potential remains very low as the warm sector/instability get cut off. With exiting of dynamics and forcing, drier conditions will return by Thursday. Friday through Sunday By the end of the week, CAA behind the front will lead to a notable cooling trend with temperatures going from above normal to far below normal for the rest of the period. This will also come with deep upper troughing and a strong (150+ kt) jet streak setting up overhead. Wrap around moisture behind the front will keep chances for precipitation in the forecast with a transition over to snow showers as the layer cools into Friday. The more notable coverage will be in the mountains as westerly flow of 25+ kts will help to increase orographic lift. Right now, the latest GEFS mean suggests 60% or more probability for 1" of snowfall in the mountains, using the dynamic ratio developed by WFO MPX. Through the rest of the weekend, embedded shortwaves will move through with 850mb temperatures persistently below -5 Celsius via ensemble means. The nature of any additional systems, indicated with the GFS for example and some GEFS members for example, remains uncertain. However, the main message will be multiple days of well-below normal temperatures. && .AVIATION... (00Z TAFS) Issued at 614 PM EST Sun Dec 11 2022 Low cigs, mainly in the IFR/MVFR range, will persist at all sites through the night. Not much change is expected to the current conditions until after daybreak, when drier air is expected to build into the area and help cigs rise and scatter through the morning at TRI and TYS, and into the early afternoon at CHA. Lower visibilities will be mainly associated with patchy drizzle, which is expected mainly at TYS and CHA through the first few hours of the TAF period. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 48 57 42 55 / 10 0 0 10 Knoxville McGhee Tyson Airport, TN 43 55 36 57 / 10 0 0 0 Oak Ridge, TN 40 54 35 56 / 10 0 0 0 Tri Cities Airport, TN 37 50 31 54 / 10 0 0 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...DGS LONG TERM....BW AVIATION...DGS