Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/18/20

National Weather Service Sioux Falls SD
601 PM CST Thu Dec 17 2020 .UPDATE... Issued at 550 PM CST Thu Dec 17 2020 Issued a Dense Fog Advisory for Buena Vista and Ida counties in northwest Iowa. Surface observations, satellite, and local reports indicate that dense fog has spread westward back into this region. The HRRR is doing a decent job picking up on the current extent of fog and indicates potential for dense fog, although more patchy in nature, to spread another county or two north and west of the current advisory area. Increasing winds late tonight should curtail the westward spread and longevity of the dense fog. && .SHORT TERM...(This Evening through Friday Night) Issued at 240 PM CST Thu Dec 17 2020 As an upper level ridge builds across the area, the stubborn stratus deck has stuck around a bit longer than expected as the downward vertical motion kept the clouds from mixing out. Sunshine was finally able to break through, and began mixing out the clouds and improve visibility conditions across the area. Heading into the evening hours, not looking at any significant weather concerns but do expect winds to turn southwesterly and breezy which will last into the overnight hours. Would not be surprised to see another round of fog and/or low stratus for areas in NW IA and SW MN, as low- level moisture remains trapped in the boundary layer. After midnight, the ridge begins to flatten as an upper level trough moves into the area. The associated cold front will be traveling through central SD, and will likely be reaching locations near the Missouri and James River Valleys by daybreak. Ahead of the front, there is a slight chance for some light precipitation as a mid-level vorticity maximum moves through, most likely falling as snow but there is potential for it to fall as light freezing drizzle. Behind the front, expect winds to turn northwesterly fairly quickly, and also increasing in strength with gusts up to 30 mph possible into the early afternoon hours. Large-scale ensemble guidance suggests a couple areas have a chance of seeing more than a trace of precipitation, but probabilities quickly drop off to a zero percent chance of seeing more than a tenth of an inch of liquid. On the other hand, the HREF shows the vast majority of its members don`t even produce a trace of precipitation. Because of this, have kept vast majority of locations getting zero QPF, with scattered chances for receiving barely measurable precipitation along the Highway 14 corridor in SE SD and SW MN. Otherwise, cooler air is brought into the area overnight, leaving early Saturday morning lows in the lower teens. .LONG TERM...(Saturday through Thursday) Issued at 240 PM CST Thu Dec 17 2020 The upper level trough axis continues to move through the area throughout the day, leaving temperatures on the cooler side (but still above normal) with mid 40s in central SD and lower 30s across SW MN and NW IA. Another cold front and associated upper level wave looks to move over the area overnight into Sunday morning, but with no available moisture to work with, will likely only notice a shift in wind direction. Northwesterly flow aloft sets up leaving Monday rather uneventful with continued above normal temperatures. Global models continue to indicate that a digging trough will move in from the northwest CONUS, sending a low pressure system towards the high plains. Global models are handling this system slightly different, so there is little confidence in impacts from this system. However, there is good agreement that temperatures will fall to below average with this system, keeping high temperatures in the 20s on both Wednesday and Thursday. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 531 PM CST Thu Dec 17 2020 VFR conditions and broken to overcast mid level clouds will prevail at TAF sites through the period. However fog and IFR stratus have regressed back westward into western MN and IA are expected to prevail for much of MN and IA this evening and overnight. Will be closely monitoring to see how far west fog and stratus extend. Could reach as far west as the I-29 corridor near SUX, but there is little model guidance to support this so left it out of the TAF at this time. Light southeast winds will increase overnight with gusts up to 30 kts developing. Expect winds to become more southerly early Friday morning, turning northwest behind a weak cold front during the daylight hours Friday. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...Dense Fog Advisory until 3 AM CST Friday for IAZ022-032. NE...NONE. && $$ UPDATE...BP SHORT TERM...APT LONG TERM...APT AVIATION...BP
National Weather Service Wilmington OH
851 PM EST Thu Dec 17 2020 .SYNOPSIS... Low pressure exits the region today, leaving cold and cloudy conditions with a few leftover snow flurries. High pressure will dry out the region Friday before another system brings back chances for precipitation Saturday into Sunday. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... It is interesting to note that the location of a trough axis moving across the ILN forecast area is more readily apparent this evening on mosaic radar imagery than on satellite imagery. A notable swirl can be detected in the reflectivity field, about to pass north of Wilmington as it moves gradually eastward. Behind this axis, for roughly the western half of the ILN CWA, precipitation should be on a downward trend. East of the axis, light snow will likely continue for another few hours. This has been more than just flurries at times, with <3SM visibilities indicating the potential for very minor accumulations, verified by a 0.3" measurement at the NWS office at 7PM. Adjusting for these snow trends (and delaying the light snow > flurries > dry transition by several hours) has been the only change to the forecast this evening, with temperatures and winds and other fields generally on track. It is interesting to note that both the HRRR and the RAP are indicating a small pocket of very cold temperatures over the next few hours over northeast Indiana and west-central Ohio, with surface observations showing no signs of this actually occurring. Previous discussion > Mean trough axis will position itself across the fa today with a s/wv traversing through the upper Ohio Valley. Low-level moisture, weak instability and colder air remain locked in place today. The 12z ILN sounding reinforces the potential for some lingering pcpn - which generally started out as a freezing drizzle in the morning, but transitioned to light snow/flurries by the afternoon. This trend of light snow/flurries is likely to continue through the evening as bufkit suggests additional saturation occurring just above the -10C layer - aiding in the development of more ice crystals aloft. However, don`t expect much in the way of accumulation as overall forcing remains weak. Thicker cloud coverage and a cold air mass in place only allowed temperatures to rise a few degrees into the lower to middle 30s this afternoon. Have snow flurries dissipating overnight from southwest to northeast as high pressure from the south builds across the Ohio Valley. Skies will generally remain overcast, but a few more breaks in the clouds will occur across the northern KY counties early Friday morning. Low temps will dip into the middle 20s across the fa tonight. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... A short-lived H5 ridge will traverse the Midwest on Friday, allowing conditions to dry out. However, the mid-level flow regime is still predominately from the northwest, so expect moisture advection from the Great Lakes to keep skies mostly cloudy throughout the period. High temperatures will continue to trend below seasonal norms in the middle to upper 30s. Surface high pressure begins to shift eastward towards the Atlantic coast Friday night as another s/wv trough approaches. No notable changes in the overall pattern expected until Saturday afternoon with an approaching low pressure system. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Short wave emerging out of the Plains will move across the area Saturday night. There is some timing uncertainty given faster/weaker solution of the 12Z operational GFS. But most guidance is continuing a slower trend which this forecast follows. It should be warm enough for most precipitation to be rain, but some mix with snow is probable in at least northern counties, although any accumulations would be minimal at best. Slower solution would result in some precipitation lingering into Sunday. Next short wave will move out of the Canadian Rockies Sunday night and drop southeast across the region late Monday into Monday night. This has been trending a bit stronger and so there is a chance of some precipitation with it, once again mainly rain. In the wake of this system, high pressure will build in and then move off to the east on Wednesday. A stronger short wave will move southeast and start to carve out a long wave trough at the end of the period. There have been differences in the details of how that evolves. Following an ensemble mean, it appears that an initial front may move into the area on Wednesday night with a secondary Arctic front late Thursday. Expect a pretty good chance of precipitation. Uncertainties extend to thermal profiles, so chance of rain will be higher southeast and earlier in the event and chance of snow higher northwest and later in the event. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... Flurries / light snow will continue for the next few hours, perhaps a bit longer at KCMH/KLCK. At worst, this snow may briefly bring visibilities into the IFR category. Otherwise, IFR to MVFR ceilings will continue overnight, though with gradual improvements expected with time. Winds will remain out of the west at under 10 knots. Dry conditions are expected tomorrow, with MVFR ceilings breaking to VFR -- though this will occur quicker at KCVG/KLUK/KDAY/KILN than at KCMH/KLCK. Winds will begin a shift from the west to the south as the day progresses. OUTLOOK...MVFR conditions are possible from Saturday night through Monday morning. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Clark NEAR TERM...Clark/Hatzos SHORT TERM...Clark LONG TERM... AVIATION...Hatzos
Area Forecast Discussion
National Weather Service Lincoln IL
904 PM CST Thu Dec 17 2020 .SYNOPSIS... Issued at 320 PM CST Thu Dec 17 2020 Temperatures will return to above normal Friday with breezy south winds and highs back into the lower to mid 40s. A front will move across the region Saturday bringing a chance of rain through the day. Even more mild temperatures are expected next week with highs into the upper 40s to lower 50s Monday and Tuesday. && .UPDATE... Issued at 903 PM CST Thu Dec 17 2020 A nearly stagnant area of clouds across our northwest counties has been eroding on the leading edge instead of progressing toward PIA and BMI. The 01z HRRR and RAP output indicate that band of clouds will continue to erode from both sides as it eventually shifts over Peoria by 3-4 am. Overall impact to sensible weather will be slightly warmer lows in our NW counties, with the cold spots being east of I-55 toward the Indiana border where clear skies are expected the rest of the night. Light winds will allow for efficient radiational cooling, as lows drop toward 20F in a large portion of our CWA by sunrise on Friday. Have adjusted the low temps down in clear areas, and increased lows a bit where clouds will linger the longest. Updated forecast info is already available. && .SHORT TERM...(This evening through Friday) ISSUED AT 320 PM CST Thu Dec 17 2020 High pressure is centered over the lower Mississippi Valley this afternoon with ridge axis extending north across central Illinois. This has helped provide some extensive breaks in the cloud cover for much of the area today, but additional clouds are spreading east on the back side of the ridge. South flow will also overspread the area behind the ridge axis overnight, becoming breezy through the day Friday. Winds are expected to peak Friday afternoon out of the south with gusts into the 20 to 25 mph range. Stronger south flow and mid level warm air advection will give a boost to temps Friday and highs are expected to return to above normal with afternoon temps in the lower to mid 40s. .LONG TERM...(Friday night through Thursday) ISSUED AT 320 PM CST Thu Dec 17 2020 An elongated trough will dig across the Desert SW and central Great Plains Friday night and is expected to shift east across the Mississippi Valley Saturday. Meanwhile, a northern stream system will track east across the Canadian Prairies Saturday with a trailing cold front extending south across Illinois. This front will pass across Illinois bringing a chance of showers, but with the better upper level support displaced well south and north of Illinois, there could be some sizable breaks in precip coverage across Illinois. For the areas that do see precipitation, leading air mass is warm and will support all rain at the onset of the event. As some colder air filters into the region and temps cool overnight, some locations may begin to mix with or briefly change to snow before precip ends, but at this time any wintry mix looks to be short lived if at all. Despite passage of a cold front over the weekend, very little cold air overspreads the Midwest with the upper pattern overall fairly zonal. Flat ridging will begin to build from the west coast and slowly amplify over the Great Lakes by Tuesday. This will result in a couple days of dry weather and very mild temperatures with some southern portions of the CWA topping out above 50F. The pattern continues to amplify with a strong shortwave digging from the PacNW Tuesday to the southern Great Plains Wednesday night and carving out a deep upper trough over the mid section of the country. A very cold air mass is progged behind this front to arrive on Christmas Eve with h85 temps plunging to around -20C. This should translate to high temps below freezing and overnight lows in the teens and possibly single digits for the more northern and typically colder spots in the area. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 608 PM CST Thu Dec 17 2020 Main concern with the early portion of the TAFs will be the advance on an MVFR cloud deck from west to east. An upper level shortwave on the back side of the trough. The MVFR ceilings are projected to remain in place overnight. Dry air mixing coupled with breezy S/SSE winds on Friday should prompt a return to VFR conditions during the morning. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Shimon SYNOPSIS...Deubelbeiss SHORT TERM...Deubelbeiss LONG TERM...Deubelbeiss AVIATION...Shimon
National Weather Service Jackson KY
1041 PM EST Thu Dec 17 2020 .UPDATE... Issued at 1041 PM EST THU DEC 17 2020 A few updates were made to the ongoing forecast. First, loaded in the latest observations for temps and winds to make sure the current forecast was on track with the ongoing conditions. Second, some enhancements started to show up on the radar as light snow developed across portions of northern and eastern Kentucky, likely in response to the energy of the passing shortwave. Several reports of light snow coatings across portions of the northern CWA have also been made, and snow has increased from flurries here at the NWS office. As a result, went ahead and added light snow into the grids based off of the current radar trends, shifting eastward and exiting to our east with the short wave just after 6Z. In accordance with the increased snow, also added in a small amount of QPF and snow accumulation. This could result in 0.1 to 0.3 inches of snow across portions of eastern KY it exits. Finally, while snow has increased across some portions of the CWA, the sky cover is actually decreasing a bit quicker than originally forecast across south-central KY, and will likely affect the SW portion of the CWA sooner as well. As clearing occurs here overnight, and high pressure moves into the state from the SW, there is some concern that this could trap the lingering moisture in place near the surface and result in fog development across portions of the Cumberland Valley. The day shift had already lowered temps in this location with the expectation of some clearing throughout the overnight, which cooler temps would also lend themselves to better likelihood of fog development as well. Just went with patchy fog for now, which in the case of sub- freezing temps will be freezing fog. However, if fog is more dense in nature in places, this could actually work against the temperatures and cause them to be a bit warmer than forecast. There is a lot of unknowns with this at the moment, so will need to continue to monitor temps and coverage into the overnight/early morning hours. All updates have been published and sent to NDFD/web. A new set of zones/SAFs was also sent to reflect any changes to the forecast. In addition, we have received a couple reports of slick road conditions as temperatures fall below freezing and wet roads begin to develop some black ice. To account for this, went ahead and issued an SPS throughout the overnight to account for potentially hazardous road conditions due to the falling temps, wet pavement, and contribution of the light snow in some locations. UPDATE Issued at 702 PM EST THU DEC 17 2020 Didn`t make too many changes to the ongoing forecast. A shortwave is currently passing over, which is keeping cloud cover intact across much of eastern Kentucky and providing enough energy that a some pockets of light precip may still be ongoing across eastern Kentucky. Given the current temperatures across the region, any precip that is falling is on the threshold of freezing. So can`t rule out some drizzle, but the general likelihood is that most locations are receiving snow flurries. Temperatures are not expected to fall rapidly given the abundant clouds in place, but any nudge cooler will solidify flurries being the main weather type. As such, kept with the ongoing forecast for snow flurries throughout the first half of the overnight, slowly exiting to our east after midnight as the shortwave exits the state. All updates have been published and sent to NDFD/web. && .SHORT TERM...(This evening through Friday night) Issued at 340 PM EST THU DEC 17 2020 20z sfc analysis shows deep low pressure pulling further away from eastern Kentucky. Before it goes and takes its low level cyclonic flow with it, partially upslope west winds and ample low level moisture are combining to keep flurries and some light snow showers around in the forecast. With temperatures most places just above freezing and road temps in the mid to upper 30s expect the impacts from the snow to be minimal. One concern going forward would be the potential for icing later tonight on any untreated wet road that cools below freezing - particularly in the southwest this evening. Otherwise, under a low overcast temperatures are in the low to mid 30s. Meanwhile, dewpoints are in the upper 20s to low 30s - dropping as drier air advects into the region on westerly winds of 5 to 10 mph. The models are in very good agreement aloft through the short term portion of the forecast. They all depict a sharpening of the 5h trough over Kentucky as it starts to pull out tonight. This is in response to a strengthening shortwave dipping through Kentucky this evening - spreading east quickly. Heights will climb smartly in this wave`s wake with a large area of ridging working in from the west on Friday - though it moderates over the area by Saturday morning in the face of more general troughing from the Plains. Given the small spread among the models and ensembles will favor the blended NBM for the end of the week forecast, though leaned toward the HRRR for PoP details tonight. Sensible weather will see temperatures cool off fairly steady, though the clouds hold on for most of the area. The southwest will have best shot at some thinning and clearing skies later tonight and so have placed cooler temps there. Under the lower clouds snow showers and flurries will continue with the HRRR appearing to capture the ongoing PoPs best. Accordingly have kept them up for most of the night in the east and to a lesser extent elsewhere. Look for better clearing on Friday between systems but temperatures will be slow to rebound into the upper 30s and lower 40s by mid afternoon. Some high clouds return Friday night, but we should still see a decent ridge to valley temp split set up. Made the most changes to NBM temps for terrain differences tonight in the southwest and for the entire area on Friday night. As for PoPs, again kept them much higher this evening and overnight - more in line with the HRRR - due to upslope and any enhancement from the arriving mid level wave. .LONG TERM...(Saturday through Thursday) Issued at 458 PM EST THU DEC 17 2020 A shortwave trough will cross into the region from the plains late Saturday. We should see southerly flow ahead of this system producing milder temperatures for Saturday. However, as the trough moves in Saturday night positive vorticity advection ramps up quickly across east Kentucky. This will provide ample support for precipitation development. Going to be a close call between snow or rain for our area, but it does look like there could be quite a bit of mild air in the low levels through the night, potentially limiting the snowfall potential. However, it will be a close call. For now, going to stick with a mix of rain and snow and hopefully sort out the details after a few more model runs and we get closer to the event. It is more likely some of the ridgetops see a bit more snow as they should have less warm air present. Clouds may hang tough on Sunday and Monday as a southern stream shortwave trough passes by to our south. Another quick hitting system will push across the Ohio river valley Monday night and could provide another quick shot of precipitation to the area. Given the amount of low clouds around Sunday into Monday and looking at the depth of the cloud layer at times, it feels prudent to keep a low chance of precipitation in the east and southeast from Sunday through Monday night. This is especially true given how precipitation materialized today. It does appear we should see heights quickly build by Tuesday and Wednesday ahead of our next shortwave trough. These building heights should allow for a nice warmup for Tuesday and Wednesday. In fact, some guidance suggests, highs could reach the lower 60s by Wednesday. Precipitation chances will increase again Wednesday night as a strong cold front gets pushed across the region. This front will bring a blast of arctic air into the area for Christmas Eve and Christmas. It does appear likely that some light snow showers or flurries will accompany this airmass change, but there is still quite a bit of spread in the models to jump on any outcome as of right now. In fact, the Canadian develops a much more ramped up low pressure system, and brings a good amount of rain to the area during the same period, that other models have the arctic airmass entrenched over the area. Thus, too much spread to have any kind of confidence at this point. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) ISSUED AT 712 PM EST THU DEC 17 2020 A shortwave is currently passing over eastern Kentucky, keeping the MVFR cloud cover intact. This added energy, along with temperatures at or just below freezing, is allowing for some continuing light drizzle or snow flurries across eastern Kentucky. These should remain light enough as to not have any impact on VIS, but may continue through 6Z until the shortwave exits the state. Even after it exits, the strong inversion that will set up could keep MVFR to low end VFR cloud cover in place well into the morning hours Friday. Dry air will then finally filter into the low levels and skies will slowly clear from west to east throughout the daytime hours as high pressure moves in overhead. SJS may be the last to see clouds break and VFR conditions, by around 20Z, according to the latest models. Winds will remain light and variable throughout the entirety of the period as well. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JMW SHORT TERM...GREIF LONG TERM...KAS AVIATION...JMW
Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
922 PM CST Thu Dec 17 2020 .UPDATE... Issued at 919 PM CST Thu Dec 17 2020 A forecast update is in place for slightly warmer temperatures overnight using the RAP model plus bias correction. Cloud cover, a low level jet and warm air aloft should hold up temperatures overnight. && .SHORT TERM...(This evening through Friday night) Issued at 236 PM CST Thu Dec 17 2020 Concerns in the short-term forecast revolve around temperatures the next 36 to 48 hours as well as the potential for light wintry precipitation across the far northwest Friday morning and the far southwest Friday afternoon. Quiet weather will round out the day Thursday with increasing cloud cover expected as the next potential weather producer moves in from the west. Surface trough will enter the area late tonight with winds switching to the west-northwest by early Friday morning. With strong northwesterly winds, modest upslope flow main lead to some light snow showers along the Pine Ridge. While moisture will be limited, cannot rule out some light snow showers. Went ahead and introduced some -DZ/-FZDZ to the forecast as well for Friday morning as dry air in the mid-levels will limit ice introduction in the column. Forecast soundings, particularly the NAM and NAM Nest, show low- level saturation from approximately h7 to the surface with ample dry air overtop. Thinking any ice accumulations will be isolated in nature across the western Sandhills and limited to just a light glaze. Areas that see snow, generally in closer proximity to the Pine Ridge, will likely see a dusting to potentially a half inch in spots. Went ahead and introduced some slight chance PoPs (~15-18%) across far southwest Nebraska during the afternoon Friday. This is tied to the mid-level vort lobe moving through the area. Moisture will once again be limited, especially with northeastward extent, therefore have the PoPs confined to primarily Chase County with little to no measurable precipitation expected as a result. Trends have been to bring this activity further north and east and thus decided to add to the forecast. Temperatures Friday morning will generally be limited to the 20s with some upper teens seen where snowpack remains the greatest. For highs during the day, opted for the 40s with some locations managing to hold onto the upper 30s across the far northwest zones. Winds will be strong during the afternoon out of the northwest. This is in part due to a fairly sharp pressure gradient across the area and further aided by cold air advection and strong h85 flow of around 30 to 40 mph. The forecast calls for sustained winds in the 15 to 20 mph range with gusts as high as 35 mph. Wind gusts should peak around midday to the early afternoon, diminishing quickly after 3pm CST. Skies clear in the evening with overnight lows falling into the teens. .LONG TERM...(Saturday through Thursday) Issued at 236 PM CST Thu Dec 17 2020 Beginning 12z Saturday. Ridging remains anchored across the western CONUS with the departing trough moving into the Mississippi Valley by late afternoon. Overtop the aforementioned ridge, a shortwave trough will quickly approach from the northwest by the latter half of Saturday. This feature will be in tandem with a deep surface low crossing the Canadian Prairies. Trough axis will traverse the area Saturday evening with strong post-frontal gusty winds expected to develop Saturday night into Sunday. At this time, fropa appears to be dry given the fairly dry airmass in place characterized by PWAT values AOA 0.25-0.35". The GFS is the lone exception, which has a small pocket of QPF in the Pine Ridge vicinity. Will maintain the dry forecast. Surface high pressure will build into the central Rockies by early next week as mid-level ridging translates east. This should yield a warmup for Sunday and Monday as downsloping flow and generally clear skies should allow temperatures to climb quickly. Will see highs reach the 50s each day with some locations potentially approaching 60 on Monday. Similar temperatures are possible on Tuesday, however, changes in the weather pattern will begin across the area therefore forecaster confidence begins to decrease this day and beyond. Ridging across the west will begin to become squashed as large troughing moving ashore the Pacific Northwest and takes aim for the Central and Northern Plains by late Tuesday. While both the GFS and ECMWF maintain a positively-tilted open wave, a coupled jet will lead to the development of a rapidly deepening surface low across western South Dakota...potentially as far south as the Nebraska/South Dakota border. While it appears the area will remain on the warm side of the system...both GFS and ECMWF advertise a track generally paralleling I-90 and clustering by GEFS members ranging from as far south of Valentine to as far north as Mobridge, SD...confidence is relatively high considering how far out we remain. The majority of any winter weather impacts look to remain to the north, however, the trailing cold front bolstered by a nearly 1040 hPa surface high pressure system will bring back winter temperatures in force with strong cold air advection and h85 temperatures of at least 5-10C below normal. Will keep an eye on that and the prospects for precipitation out of the cold air stratus that is sure to follow. At this time, a dry forecast remains. Cold air remains in place Wednesday and Thursday with highs in the 20s and 30s expected, but temperatures should begin to moderate toward the weekend as westerly flow return and modest ridging redevelops across the Southwest CONUS. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 536 PM CST Thu Dec 17 2020 A storm system moving thorugh the srn Rockies may be capable of setting off isolated snow showers across wrn Nebraska late tonight and early Friday morning. The area of concern is west of highway 61 and local MVFR ceilings may accompany the snow showers. Otherwise, VFR will prevail across wrn and ncntl Nebraska tonight and Friday. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...CDC SHORT TERM...NMJ LONG TERM...NMJ AVIATION...CDC
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1004 PM CST Thu Dec 17 2020 .UPDATE... 1000 PM CST Only change to the forecast this evening was to add a mention of patchy fog across the area after midnight tonight, omitting our far northeastern zones where dew points are still rather low. Northern Illinois currently resides in a wide gap in the low stratus which combined with the light surface winds has helped temperatures drop quickly this evening into the 20s outside of downtown. As a result, we are already seeing signs of lowering visibilities in the 5-7 mi range at a few sites where dewpoint depressions are the lowest. There is still rather low confidence on fog development tonight given that guidance continues to suggest fog potential is low. Any fog that does develop, however, should be quite shallow. Model soundings indicate low level winds will begin to increase toward daybreak which should help create enough turbulent mixing to erode any lingering fog. Petr && .SHORT TERM... 227 PM CST Through Friday... Quiescent weather is ahead tonight and into the day Friday. A couple items we will have to be a little watchful for are 1.) continued snow showers along the immediate Indiana shore area, including the I-80/90/94 corridors through early this evening, and 2.) the potential for patchy fog tonight. Northwest winds over the cloud-bearing layer atop southern Lake Michigan continue to usher lake effect flurries and some embedded snow showers into far northwest Indiana. Using the sparse observations (with buoys no longer deployed this time of year) and high-resolution diagnostic streamlines, there is actually a low- level circulation indicated over far southern Lake Michigan. Flow into this though is generally light, but the convergence within has been responsible for occasional snow showers that had brought visibility sharply down earlier along the immediate Cook County shore. These flurries/snow showers should gradually work eastward into early evening before dissipating. Overall little impact anticipated besides very temporary but sharp visibility drops under any showers. Confidence on sky cover for tonight into Friday morning is quite low. The current clouds across the CWA are on primarily residual moisture that now is trapped within a low-level ridge and gradually building inversion overhead. Gradually increasing cloud- bearing flow up from the west should keep ushering the back-side of these clouds from north central Illinois into northeast Illinois this evening, and model guidance is in fairly good agreement with this. More clouds are upstream however, namely over Iowa but also far western Illinois. How these evolve is of especially low confidence, and with some 275K isentropic ascent noted (near/within cloud layer) in RAP and NAM solutions, cannot entirely rule out spotty light flurries or freezing drizzle mainly west of the area. Between the aforementioned cloud areas, there does look to be a period of clearing tonight for most of the CWA. After a cloudy day today with little flow, such clearing might result in patchy fog. Despite low confidence in this, will have to keep an eye on it as if any patchy dense were to develop it could result in some slick spots underneath. With cloud cover trends uncertain as noted above, Friday`s temperature specificity is also lower. Southerly winds will be increasing into the afternoon, with gusts of 20-25 mph anticipated. That should help temperatures into the mid 30s, but how many degrees above will hinge upon duration of cloud cover. MTF && .LONG TERM... 315 PM CST Friday night through Thursday... At the start of the period Friday night, attention will focus on the next approaching mid-level disturbance. This feature is likely to drive a weak surface frontal trough of low pressure northeastward across northern IL and WI on Saturday. Prior to its arrival, expect breezy south winds across the area Friday night. This will keep temperatures nearly steady, with overnight lows likely only a couple of degrees off of Fridays highs. Forecast guidance has backed off on the strength of this mid- level disturbance as it moves over our area Saturday. In fact, model and ensemble guidance suggests that the upper trough will maintain a positive tilt (northeast to southwest orientation) as it shifts across the area Saturday. Overall, this looks to less or overall chances for precipitation, and any precipitation that we do get looks to remain light. Also given the area looks to remain above freezing, it appears precipitation type will primarily be in the form of drizzle and/or light rain, so impacts should be minimal. The small threat of precipitation with this system will end by Saturday evening. The forecast period from Sunday into the Holiday week looks to be semi-active across the central part of the country. Initially it appears that a northwesterly upper pattern will steer a couple of upper level impulses southeastward towards our area. The first looks to shift over southern WI and far northern IL on Sunday. While this could result in a few flurries over northern IL Sunday afternoon, we have left the forecast dry at this time. A second, and potentially more substantial clipper type system then looks to track southeastward across WI for Monday. We will have to keep an eye on the evolution of this disturbance as it could track close enough to us to result in some light precipitation. However, with it its track expected to be to our north, we likely would not be looking at much in the way of snow. Following the clipper system attention then will turn to the next north Pacific upper impulse, which is likely to dig in over the the central CONUS by late Tuesday. While this is still rather far out, there continues to be strong signs that it will drive a decent storm system somewhere from the northern Plains, eastward across the Upper Midwest and Upper Greats Lakes region into mid- week. This track would support a period of breezy southerly winds and warmer weather for our area, especially late Tuesday into early Wednesday as it approaches. However, as it shifts into the Upper Great Lakes sometime late Wednesday a strong attendant cold front should shift eastward across the area. In its wake, windy west-northwesterly winds and a turn to much colder weather then looks to set up for Christmas Eve as a strong Cold Canadian surface high builds into the Midwestern region. The projected track of this midweek system looks unfavorable for much in the way of snow for our area at this time. However, it is possible that some post cold frontal precipitation could develop over the area, with even the possibility for light snow into Christmas Eve as the main upper trough and cold airmass shift overhead. Lake effect snow would also be likely to ramp up substantially over Lake Michigan with this cold airmass. However, with what looks to be primarily northwesterly boundary layer flow, it appears the main lake effect snow threat may remain over the eastern shores of the lake. KJB && .AVIATION... For the 00Z TAFs... Aviation forecast concerns: * Chance of patchy fog overnight. * Potential for redevelopment of MVFR ceilings later tonight and Friday. * Gusty south winds develop by late morning Friday. * LLWS possible Friday evening as winds increase to 40-45 kt above the surface. Weak surface high pressure ridge will drift east across the forecast area tonight, with winds becoming very light southwest. Some clearing has occurred in the low level stratocu field across parts of northwest and central IL, and this will likely bring a period of at least partial clearing to the TAF sites overnight. Clearing skies may allow for some patchy fog development as temperatures fall quickly in the light wind regime, though confidence is fairly low as to just where/when and how impactful this would be. Farther west, another area of MVFR stratus across IA and parts of west central IL will also be drifting east, and may move back into KRFD before morning before continuing east into the Chicago areas terminals by mid-late morning. Most model guidance is not handling the low cloud trends very well at this point, lending lower confidence to the cloud forecast, and have continued a somewhat pessimistic trend based on upstream observed trends. The surface ridge will move east of the area by Friday morning, with south winds increasing in response to an area of low pressure which will pass north of the region later Friday and Friday night. Though boundary layer mixing is expected to be fairly shallow, surface gusts into the 20-25 kt range are likely from late morning on. Winds will likely remain gusty into Friday evening, while veering slightly more south-southwest. Even with the gusty surface winds Friday evening, it appears that low level wind shear (LLWS) may become an issue as winds increase to 40-45 kt in the 1500-2000 foot AGL layer by mid evening or so. This would likely persist most of Friday night before easing. Model forecast soundings also depict lowering ceiling conditions Friday evening as well. MVFR would be likely, with IFR possible overnight, just beyond the end of this TAF period. Ratzer && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742...noon Friday to 6 AM Saturday. Small Craft Advisory...LMZ743-LMZ744-LMZ745...noon Friday to 9 AM Saturday. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion
National Weather Service Paducah KY
604 PM CST Thu Dec 17 2020 .SHORT TERM...(Tonight through Saturday night) Issued at 130 PM CST Thu Dec 17 2020 Scattered to broken pancake cumulus clouds formed during the midday hours. With loss of daytime warmth, these clouds should quickly melt away by sunset. The small area of overcast sky over parts of se Missouri looks more stratiform, and it could linger well into the night. Much like last night, lows will fall into the lower 20s where skies are clear. Light fog may again be widespread around sunrise, but it should not be impactful. Clouds will begin to increase late Friday ahead of a sharp mid- level trough entering the western high Plains. However, plenty of sun and south winds will be enough to boost high temps into the mid and upper 40s. Friday night and Saturday, the upper trough will swing eastward and then east-northeast across the Mississippi Valley. A weak surface cold front will cross the forecast area Saturday night. A decent (30 knot) southerly flow around 850 mb, along with strong upper support, will produce a band of rain ahead of the front. Rainfall will not be heavy, but a widespread quarter to half inch seems likely. Despite the rain, highs Saturday will still reach the mid to upper 40s under moderate southerly flow. .LONG TERM...(Sunday through Thursday) Issued at 130 PM CST Thu Dec 17 2020 The main targeted forecast opportunity is days 6-7, specifically late Wednesday night into early Thursday morning, when boundary layer temperatures might cool enough for a light precipitation event to include some mention of change-over hydrometers. With pops still in the low chance range, and qpf light, we`re talking trace to one tenth of an inch possibilities here, as the pcpn chances end upon cold fropa. The primary impact will be the cool off in temps, where we see seasonally mild 50s earlier in the week, drop into the upper 30s to lower 40s for Christmas Eve high temperatures. && .AVIATION... Issued at 603 PM CST Thu Dec 17 2020 The consensus guidance presented for the 00z Friday WFO PAH TAF issuance was not handling the evolution of the VFR/MVFR cloud deck stretching from northeast Missouri into southwest Illinois. For the 00z friday issuance, added a TEMPO group to handle the transition of this cloud deck through the KMVN, KEVV, KOWB TAF locations this evening. The RAP CAM guidance appears to have the best handle on this movement of this cloud deck at this time. May have to revisit the cloud forecast for the aforementioned locations after 06z to reflect a more pessimistic low VFR - upper MVFR forecast through 13z-14z Friday. && .PAH WATCHES/WARNINGS/ADVISORIES... IL...None. MO...None. IN...None. KY...None. && $$ SHORT TERM...MY LONG TERM...DH AVIATION...Smith