Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/12/25


Area Forecast Discussion
National Weather Service Grand Forks ND
730 PM CST Sat Jan 11 2025 .KEY MESSAGES... - Accumulating snow is expected to continue through the overnight hours. Generally between 2 and 5 inches are expected with the highest totals between US Highway 2 and I-94. - Winds increase overnight into Sunday morning, with blowing snow bringing visibility as low as a 1/4 mile at times in rural areas. - Hazardous wind chills are likely Monday and Tuesday morning. && .UPDATE... Issued at 730 PM CST Sat Jan 11 2025 Warm layer/dry lso ahead of the main mid level circulation has correlated with reports of light freezing rain/drizzle and this area extends from the far southern Red River Valley and over parts of west central MN. As the mid level low circulation moves in deeper saturation and colder air aloft both are helping contribute to a transition back to all snow. In the mean-time, light icing will contribute to slick travel conditions in those areas (included in advisory). Light to moderate snow rates continue where all snow is in place, with a narrow lull behind this current wave in accumulating snow. Additional light to moderate snow is moving into the Devils Lake bAsin ahead of the next wave, which features a strong PV height anomaly/region of subsidence. How long/organized this next period of light to moderate snow is and if it holds together through the night will influence whether accumulating snow will be falling as winds increase after 06Z tonight (still large variation in current CAMs with NAM/NAMnest the most aggressive on lingering snow). Falling accumulating snow at the time of stronger winds would be required for BLizzard impacts based on wind forecast (which hasn`t changed). Upstream the stronger CAA and surface pressure rises match well with the PV anomaly/region of downward motion and this is shown to slide to the west overnight towards the James River Valley and west. Still, as with previous discussion there is a signal for CAA and increasing pressure gradient as N-NW winds develop in our area (peak based on HRRR after 08Z through 15Z north to south). Gusts to around 35 mph appear likely, but sustained winds are more likely to fall in the 20-25kt range as still favored by current guidance. Freshly fallen snow (reports around 2"), should be capable of being lofted, however for blizzard impacts sustained winds (not gusts) would need to be closer to 30kt based on surface temps in the 8-13F range during the period of strongest winds. Confidence is low in that occurring still and it is more likely that advisory impacts (isolated periodic drops to near 1/4sm) occur. && .DISCUSSION... Issued at 128 PM CST Sat Jan 11 2025 ...Synopsis... 18z surface analysis indicates the center of a surface low over southeast North Dakota. Isentropic ascent from an attached warm front and warm air advection has created broad swaths of snow across much of the region. Embedded within this snow is very weak frontogenesis that has contributed to unorganized heavier snowfall rates. Webcams thus far indicate very limited impacts, with the primary impacts observed tied to earlier freezing drizzle in the Sheyenne River Valley. Snow is expected to continue through the overnight hours, with winds increasing after midnight. This will contribute to increasing blowing snow impacts, however the probability of warning impacts is 50% due to limited wind speeds and duration of high enough winds. Following this system, strong cold air advection will bring a much colder first half of the week. Hazardous wind chills are expected to develop for the overnight hours of Sunday into Monday and Monday into Tuesday. Shortwave ridging will develop midweek, bringing temperatures above freezing for most and crusting over any snowpack we have left. There is a fairly strong signal for an arctic airmass with the potential for dangerous wind chills by next weekend as well, although the strength of the cold blast right now has a low predictability. ...ACCUMULATING SNOW THROUGH SUNDAY... Accumulating snow will continue through the day today and last into the morning. Snowfall rates will continue to be fairly light with rates generally between 0.1 and 0.25 inches per hour. This should keep impacts generally to advisory level, as stronger forcing does not appear expected to develop. Frontogenesis is fairly weak, but nonetheless has collocated with warm air advection to create bursts of heavier snowfall. These have been fairly transient so significant snowfall accumulations have not been observed. Generally speaking, snow amounts are roughly on track. Given the delayed start of snow, it seems like we should be fairly close to the 50th percentile when all is said and done. The heaviest snowfall amounts are likely to develop between I-94 and US Highway 2. It is possible for these regions to experience 6 inches of snow, however given the lower average snowfall rates, these areas should remain fairly isolated. Snowfall ratios will greatly increase overnight, but forcing will diminish in intensity at the same time. This means an additional 1-2 inches may push locations to 6 inches, but warning impacts resulting from this are unlikely given the space between snow. Expect snow to leave the region by tomorrow afternoon. ...BLOWING SNOW THROUGH SUNDAY... Blowing snow remains a concern as cold air advection and pressure rises push through after midnight. Given the timing of this, the timeframe for the greatest blowing snow impacts is between 12am and 6am. With the potential for light snow to continue and for sustained winds to push towards 25-30mph, there is the potential for 1/4SM visibilities, particularly in rural areas. This hinges solely on occurring at the same time as falling snow. It is unclear how long falling snow will continue, so we are choosing to hang onto the advisory and will wait and see if an upgrade to a Winter Storm Warning is necessary. Right now the probability for warning impacts from blowing snow is 30%. Winds will remain elevated after 6AM, but the intensity of sustained winds will diminish enough that the primary impacts will be in open country and in the Red River Valley. ...HAZARDOUS WIND CHILLS MONDAY AND TUESDAY MORNING... A decently strengthen arctic airmass will settle in over the area after this system exits. This will allow for temperatures to fall into single digits for afternoon highs and below zero for overnight lows. It is likely that a Cold Weather Advisory will be necessary after this system exits the area, as apparent temperatures are expected to get below -30 during the overnight hours of Monday and Tuesday morning. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 618 PM CST Sat Jan 11 2025 Snow continues across all TAF sites, with a mixture of MVFR to IFR ceilings and visibilities. North northwest winds will increase overnight, resulting in blowing snow. Blowing snow will cause reduced visibilities through Sunday morning, before slow improvement Sunday afternoon and evening. Therefore, current set of TAFs maintains 1 statue mile through much of the day on Sunday. There remains uncertainty with how low visibilities could drop. If light snow persists a little longer or winds are a little stronger, it is possible visibilities drop to a half mile at times Sunday morning. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...Winter Weather Advisory until 3 PM CST Sunday for NDZ026-027- 029-030-039-053. Winter Weather Advisory from midnight tonight to 3 PM CST Sunday for NDZ008-016. MN...Winter Weather Advisory until 3 PM CST Sunday for MNZ001>003- 014>017-022>024-027>032-040. Winter Weather Advisory from midnight tonight to 3 PM CST Sunday for MNZ004-007. && $$ UPDATE...DJR DISCUSSION...Perroux AVIATION...Rafferty
Area Forecast Discussion
National Weather Service Hastings NE
533 PM CST Sat Jan 11 2025 .KEY MESSAGES... - Strong cold front will push through tonight and lead to colder temperatures for Sunday and Monday. Some flurries can`t be ruled out Sunday AM with the initial push of cold air. - Temperatures will be coldest Sunday night through Tuesday AM, but it appears minimum wind chill values will remain high enough to avoid Cold Weather headlines. - A nice warmup with dry conditions is still on tap for the middle to later portions of next week. Some areas may top 50 degrees, esp. on Thursday. - The next shot of Arctic air arrives next weekend along with a chance for at least light wintry precipitation. && .DISCUSSION... Issued at 355 PM CST Sat Jan 11 2025 As expected, it`s been a fairly quiet, but cloudy, day today with only small pockets of the forecast area actually receiving any sprinkles and/or light rain. Most likely areas for a few hundredths was over portions of north central Kansas. Some recent HRRR runs suggest some spotty/brief sprinkles could develop this eve, mainly N/W of the Tri-Cities, but this also looks minor. Late tonight, an Arctic cold front arrives from the N and brings much colder/blustery conditions for Sunday. Various hi-res guidance, along with 12Z EC, show very light QPF/reflectivity returns consistent with transient, narrow bands of flurries associated with the cold air advection. Temps within the stratus deck are favorable for flurries, and lapse rates are steep. Areas particularly N/NE are most likely (relatively speaking) to get in on some of this. No impacts are expected due to very very light, brief nature of any light snow. Main sensible weather impact on Sunday will be breezy NW winds gusting up to around 30 MPH that will make the daytime hrs feel quite blustery. Combination of strong cold air advection and likely at least some continued stratus will make it tough for temps to go much of anywhere, so aftn highs in the 20s to around 30F are only about 5-7 deg warmer than morning lows. Fortunately, winds back off pretty quickly Sun eve, such that wind chill temps should only be slightly lower than air temps. Unfortunately, this just allows the air temps to cool more efficiently, likely into the single digits above zero area wide. Deep troughing persists over the Great Lakes Mon into Mon night, but this will be close enough to keep the cold locked in through Tue AM. Coordinated with neighboring offices to introduce some low end (20%) chances for snow on Mon night for NE half of the CWA, associated with a clipper system in fast NW upper flow. Not expecting this to amount to anything impactful. Highs could start to rebound back into the 40s far SW zones Tue aftn, but most areas will be chilly again in the upper 20s to 30s. More notable warm up arrives for the second half of the work week. Thursday, in particular, looks decently warm with highs at least in the 40s...and temps have trended even warmer into the low 50s for areas SW of the Tri-Cities. Fri should be mild, though not as warm as Thu. Ensembles and 12Z EC remain consistent in bringing the next shot of Arctic air into the region in about a week. While the signal for anything major in terms of precip remains weak for our area (stronger signal S/SE of here...again), these sudden, significant pattern changes almost always come with something at least light. So if nothing else, some cold air advection snow showers/flurries appear quite possible. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 527 PM CST Sat Jan 11 2025 For KGRI/KEAR Airports: Potential for MVFR ceilings will be around this evening into the overnights...somewhat spotty in nature at first. Have MVFR ceilings continuing through roughly midday Sunday, some uncertainty with that exact return to VFR conditions. Winds remain generally northwesterly around 10 MPH. As we get into the early morning hours Sunday, an upper level disturbance will push a surface cold front south through the region, ushering in a more solid put of NW winds. Gusts near 30 MPH will be possible through the early-mid afternoon hours. Can`t totally rule out at least some flurries being around with the passage of that front...so did keep a PROB30 group for some light snow from 11-14Z. && .GID WATCHES/WARNINGS/ADVISORIES... NE...None. KS...None. && $$ DISCUSSION...Thies AVIATION...ADP
Area Forecast Discussion
National Weather Service Green Bay WI
526 PM CST Sat Jan 11 2025 Updated aviation portion for 00Z TAF issuance .KEY MESSAGES... - Hazardous travel is likely late this evening through Sunday afternoon due to a light to moderate snowfall. Most places are looking at total accumulations of 2 to 4 inches, though locally higher amounts of 3 to 5 inches are possible over Door County. - Wind chills are forecast to fall from 15 below to 25 below zero away from Lake Michigan Monday and Tuesday mornings. && .DISCUSSION... Issued at 234 PM CST Sat Jan 11 2025 Snowfall Tonight through Sunday... 20Z RAP analysis shows a low pressure center moving into western MN. As the low continues east this evening an area of isentropic lift/WAA will spread over central and north-central WI. Snow may initially struggle to reach the ground as RAP soundings show a dry layer between 850-750mb. Expect light snowfall to start around midnight in central WI and spread east and north overnight. Snowfall rates should increase early Sunday morning as a short-wave/mid-level jet currently lifting across eastern NE phases with the isentropic lift to supply additional dynamic forcing. Periods of light to moderate snow should then continue through Sunday morning and into the early afternoon hours before a surge of dry low-level air brings an end to the snowfall Sunday afternoon. Overall snowfall amounts have come up slightly to 2-4" across central, north-central and northeast WI where a Winter Weather Advisory is in effect from midnight to 3PM Sunday. Locally higher snowfall amounts are expected in Door County with lake enhanced totals of 3-5" expected. Increased southeast winds over the Door Peninsula should bring periods of moderate to potentially heavy snow early Sunday morning through the early afternoon hours before winds veer around and become westerly. However, low-level shear will likely be to strong for one focused lake effect band to develop. Lingering Snowfall Monday and Tuesday... As the low stalls out and spins around over eastern Ontario periods of light snow may develop over northern WI Monday and Tuesday as spokes of moisture wrap around the low. Will cold temperatures during this time don`t expect much accumulating snow during this period. Wind Chills Monday, Tuesday, and Wednesday... Persistent CAA/northwesterly flow will usher in much colder temperatures to being the work week. 850mb temps are forecast to fall to -20 to -25C which will result in near 0 to single digit below zero low temps Monday, Tuesday, and Wednesday mornings. Breezy northwest Monday and Tuesday may create wind chills as cold as -15 to -20 degrees. Winds should weaken by Wednesday morning, but apparent temps will still range from -5 to -15 degrees during the early morning hours as skies clear over the new snowpack. Headline wise wind chills Monday and Tuesday mornings are forecast to be right around Cold Weather Advisory criteria, so will continue to monitor low temperatures trends. If Cold Weather Advisories are needed they would likely run from the overnight to mid-morning hours both Monday and Tuesday. Temperatures should moderate back above normal late in the week as wind turn to the southwest. Highs may break freezing Thursday and Friday at many locations. The warm up does look to be short-lived as long range ensembles show another shot of cold Canadian air arriving next weekend. Late Week Snow Chances... Details are still broad brush but LREF ensembles show the next chance (20-25%) for widespread accumulating snow coming late Wednesday into Thursday as a weak mid-level shortwave dives across the region. Does not look like a significant snowfall event, however, as LREF probs show less than a 10% for greater than 1" of snow at most locations. There is also another chance for light snow next weekend as another northern stream trough digs over the region. && .AVIATION...for 00Z TAF Issuance Issued at 520 PM CST Sat Jan 11 2025 Conditions will deteriorate later this evening into early Sunday morning as low clouds and snow overspread the entire region. CIGS at times will drop into the IFR category as the heavier band of snow moves across the area late tonight through mid to late morning on Sunday. Most locations will see between 2 and 4 inches which will result in snow plow operations at local airports. Conditions should gradually improve Sunday afternoon as the snow diminishes and end across much of the area. Gusty west winds of 10 to 20 knots with gusts around 25 knots are expected Sunday night and Monday. Along with the winds, it will be very cold. && .GRB WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from midnight tonight to 3 PM CST Sunday for WIZ005-010>013-018>021-030-031-073-074. Winter Weather Advisory from 3 AM to 3 PM CST Sunday for WIZ022. && $$ DISCUSSION.....GK AVIATION.......Eckberg
Area Forecast Discussion
National Weather Service Grand Rapids MI
956 PM EST Sat Jan 11 2025 .KEY MESSAGES... - Potential for localized snow related impacts Sunday - Arctic air arrives by Monday and persists into Wednesday && .UPDATE... Issued at 955 PM EST Sat Jan 11 2025 Mosaic radar is showing widespread echoes over WI and nrn IL but this is misleading as most if not all of the echoes are aloft and not reaching the ground. No sfc obs to the west have reported precip and individual radar loops from MKX/LOT have the classic donut look indicative of dry low levels. Therefore look for precip to be slow to develop overnight, possibly even holding off until closer to daybreak as lingering dry air wins out. The shoreline north of Grand Haven looks to be most favored after 09Z Sun due to potential southerly flow lake enhancement although the sfc winds at MKG and LDM are progged to have a bit of a southeast component so it`s possible that any lake snow will stay just offshore until the winds veer Sun afternoon. By then the deeper moisture is peeling away from that area though and temps are warming above freezing, so still not seeing the need for an advisory in the NW CWFA at this time. Our better risk for snow is from synoptic forcing after 15Z Sunday related to left front quad of the apchg upper level jet streak. That precip is currently coming together across KS and nrn MO and should impact a large portion of our area Sunday afternoon and early evening with a fairly widespread inch or two of accumulation. 00Z HRRR is currently favoring a corridor from AZO/BTL to LAN for the best lift from that feature. && .DISCUSSION... Issued at 250 PM EST Sat Jan 11 2025 - Potential for localized snow related impacts Sunday A wave of low pressure in the Upper Plains tracks into northern Michigan later Sunday. South to southwest flow ahead of this system will focus an area of snow to push into northwest parts of the CWA starting later tonight/daybreak Sunday. The snow then spreads eastward during the day and east of the CWA Sunday evening. Several inches of accumulation are possible from the passage of this system, especially along the lakeshore north of Muskegon. We did notice on BUFKIT from the various models that initially the low levels will be dry while the DGZ saturates. Then there is a period of deep moisture through the column for part of the day. Then the DGZ dries out in the mid afternoon to early evening hours while we maintain low level moisture. As a result of the limited hours of deeper saturation, snow amounts could be limited. Ensemble snow trends have been downward slightly. Another complicating factor with this system is that we will likely see surface temperatures rising above freezing mainly for northwest parts of the CWA. - Arctic air arrives by Monday and persists into Wednesday Arctic air flows in behind the departing storm for later Sunday night and then through Tuesday. A westerly flow sets up Monday and persists into Monday night. This commonly leads to enhanced low level convergence along I-96 to I-94. As a result we may see bands of snow extending well inland towards Lansing and Jackson. Inversion heights become very low, under 5k ft. However the DGZ is shown to be saturated at times so enough is there to warrant high POPs. The flow then becomes northwest by Tuesday and low level convergence is enhanced along the lakeshore and down into the Kalamazoo region. Thus the snow will likely be focused in those regions possibly into Wednesday. Any snow that falls during this period will be dry and easily blown around. This will likely periodically lower the visibility which would enhance the impacts, especially on highways. Wind gusts will likely top 20 knots for inland locations as indicated by ensemble values. Higher wind gusts are expected for the lakeshore. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 626 PM EST Sat Jan 11 2025 Low pressure will move toward the state tonight and clouds will decrease to MVFR after midnight as the column saturates. Snow will develop around 11z at MKG, 14z at GRR and 18z at LAN. Cigs/vsbys will correspondingly fall to IFR after the snow starts and remain there the rest of the period. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Small Craft Advisory from 4 AM to 7 PM EST Sunday for LMZ844>849. && $$ UPDATE...Meade DISCUSSION...MJS AVIATION...04
Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
522 PM CST Sat Jan 11 2025 .KEY MESSAGES... - There is a 40-50% chance for accumulating snow Sunday morning along the IL River Valley, with lower chances elsewhere. There is even a small chance (20-30%) for freezing drizzle during the afternoon, which could result in any untreated surfaces becoming slippery. - There is a 20-30% chance for light snow accumulations Monday night into Tuesday, which could once again result in any untreated surfaces becoming slick for the Tuesday morning commute. - Late Monday through early Wednesday, periods of sub 0 wind chills are expected with even a 30-50% chance wind chills fall below -10 either Monday night or Tuesday night. && .DISCUSSION... Issued at 232 PM CST Sat Jan 11 2025 Current satellite imagery shows scattered mid to high clouds atop an expansive area of snow cover across the nation`s midsection into the Great Lakes. After a dry and mostly sunny day today, conditions turn gloomier and more typical of mid winter late tonight into tomorrow as southerly flow brings potential for advection (freezing) fog across southeast IL, and a wintry mix across central IL. Thinking most of this will be snow, but we left a slight (20%) chance for (freezing) drizzle in the forecast for tomorrow afternoon/evening because the NAM and GFS each advertise a possible loss of cloud ice, continued reduced visibilities and low level saturation (0-1km RH >85%), and weak upward omega. Latest suite of guidance is honing in the IL River Valley for greatest chances of measurable snowfall. The 18z HRRR gives that area a half inch to an inch of snow, but fortunately 12z HREF probs for more than one inch of snowfall (assuming a 10:1 ratio, which is probably a little low) are only around 20% there. Next chance for precip comes Monday night into Tuesday in the warm advection wing of the compact trough that`ll bring bitterly cold wind chills Monday into Wednesday. NBM 10-90th percentile range for QPF is on the order of 0-0.03" of precip with this wave, so it doesn`t appear it`ll deliver a whole lot of snow but it could still result in some minor travel impacts during the Tuesday morning commute. It seems recent model iterations have backed off on the duration and intensity of the cold snap early to mid next week, with chances for hitting Cold Weather Advisory criteria now on the order of 15-30% (vs 25-40% yesterday). Thinking is the most uncomfortable conditions might actually be Monday evening-night when temps fall into the teens and northwest winds gust to 25 mph. However, Tuesday night is likely to bring the coldest actual air temps as the surface high builds in from the west, particularly if we have mostly clear skies as currently forecast. For Wednesday morning, NBM advertises a 30-60% chance for sub 0 lows east of a roughly Bloomington to Robinson line, but other locations will still likely be close. Ensemble mean guidance suggests westerly flow will advect a milder airmass into the region from the Great Plains as the expansive ridge across the western US simultaneously shifts east and breaks down Thursday into Friday. However, uncertainty surrounds how much of this warmer air will work its way this far east before another trough sinks south across the Midwest and Great Lakes early next weekend. NBM advertises 30-50% probabilities temperatures will exceed 40 degF on Friday west of a Peoria to Litchfield line and south of roughly I-70. Deterministic and ensemble guidance is in general agreement a very cold airmass will gradually sink southeast across the Northern/Central Plains and Upper Midwest as we head into the upcoming weekend, leaving us along or near the thermal (and geopotential height) gradient - a favored corridor for precip with any stronger southern stream waves that lift this far north, especially if phasing occurs. NBM paints broad PoPs across the Ohio Valley, Great Lakes, and even as far west as our area, which captures this precip potential. These PoPs ought to become more concentrated with time as ensemble guidance comes into better agreement on timing and placement of any weather makers. Once that cold airmass enters our area, whenever that is, precip chances should be on the decrease and we`ll have to deal with another arctic airmass. CPC 8-14 day hazards outlook depicts a slight risk for hazardous cold temps across the region from the 20th- 24th. Between the 80 members in the combined EPS and GEFS ensembles, 54 members bring surface temps to sub 0 in Lincoln (roughly the middle of the CWA) around/during this time period. Most of those members are coming from the EPS, which is not surprising given the GEFS mean depicts both the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) on an increasing trend towards above normal during this time period. For the unfamiliar, a negative AO implies high pressure over the arctic that tends to send cold air southward, while a negative NAO suggests a strong Icelandic low that fosters a more amplified pattern allowing that cold air to spill south across the central US (vs the Northeast); hence, arctic outbreaks are most favored in our area when both are negative. We`ll keep an eye on this potential moving forward and highlight the chances for excessive cold as it eventually comes into our forecast period. Bumgardner && .AVIATION... (For the 00z TAFs through 00z Sunday Evening) Issued at 522 PM CST Sat Jan 11 2025 VFR conditions will start the forecast period, but ceilings will gradually lower after 06Z as a weak storm system approaches the area. Light snow is most likely at KPIA/KBMI beginning between 07-10Z and persisting on and off into early afternoon. IFR ceilings will be more widespread beginning Sunday morning and persisting most of the day, though HREF guidance suggests probabilities of sub-1000 foot ceilings at KPIA drop to below 30% by late afternoon. South winds will average less than 10 knots tonight, but will pick up and begin swinging more west/southwest on Sunday as the cold front passes the area. Geelhart && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
915 PM CST Sat Jan 11 2025 .KEY MESSAGES... - Period light snow likely late tonight into Sunday morning. - Very cold Monday through Wednesday, with the lowest wind chills Tuesday morning (-10 to -15, locally to -20). - A low (20%) chance for light snow accums and associated travel impacts Tuesday morning, mainly south of the IL and Kankakee River Valleys. - Temperatures will thaw toward the end of the week, though below average temperatures will return during next weekend and beyond. && .UPDATE... Issued at 915 PM CST Sat Jan 11 2025 Expanding echoes on regional radar mosaics are all virga at this time, with cloud bases generally above 9 kft leading to sublimation/evaporation of snow before it reaches the ground. Incoming 00z hires guidance generally appears to be aligning with earlier global output, focusing a primary stripe of locally-enhanced precipitation amounts in the vicinity of the I-55 and particularly I-57 corridors Sunday morning. While any f-gen looks to remain fairly disorganized and ephemeral in this zone, a substantial 140+ kt upper jet streak and some degree of mid-level deformation, in tandem with some weak mid-level instability looks like it will help focus a relatively narrow band of "heavier" precipitation generally after daybreak Sunday. Have reorganized PoPs and QPF a bit to better reflect this latest trend, and it seems plausible some isolated snow amounts near or a smidge above an inch will be possible in this corridor. The main time window for any peak in snowfall rates looks to be about 6 AM to 11 AM in this zone. Outside of this potential region of more organized banding, snow accums will be limited to less than a half inch, and in many cases, less than a quarter. Straddling this zone to the northwest and southeast, saturation looks notably shallower. As a result, snow to liquid ratios will undoubtedly be lower, and precip will be on the cusp of transitioning to freezing drizzle. In fact, latest 00z NAMNest soundings across northwest Illinois suggest that precip could even just start out as drizzle late tonight as opposed to snow. Furthermore, through late Sunday morning, any pockets of deeper saturation will gradually be lost, leading to a transition to any lingering precip towards drizzle (or snizzle/very low quality snow). This was all handled well in the previous gridded forecast, but just made some tweaks to account for the latest guidance trends. Given the overall light nature to rates with this event and the degree of road treatments in place, travel impacts may be limited to untreated surfaces. Additionally, temperatures will warm to near and above freezing through early Sunday afternoon, curtailing the main slippery travel threat. Temperatures will then fall back below freezing through the evening with the arrival of a reinforcing front, with some slick spots re- developing where roads remain wet. Carlaw && .DISCUSSION... Issued at 200 PM CST Sat Jan 11 2025 Through Sunday Night: Clipper will dig southeast to around MPX tonight before pivoting slowly northeastward across the northwoods of Wisconsin to Lake Superior by Sunday evening. Rather strong isentropic ascent to the east of the north-south oriented warm front extending south from the low should result in a band of snow developing late this evening into the overnight hours over eastern IA or western IL. Given the dry low levels, a sizable amount of the ascent is going to be used on top-down saturation. There is pretty good model consensus that the top-down saturation will be sufficient to break through the dry layer and allow for a relatively narrow band of mostly light snow to move across the CWA overnight into Sunday morning. Model consensus would support QPF of about 0.05-0.10", especially across IL portion of the CWA, which would fluff up to half inch to around an inch of snow. Mid level dry intrusion pivoting around the south side of the trough looks to result in a loss of cloud condensation nuclei (Cc) by from west to east Sunday, which could result in a period of some freezing drizzle or drizzle on the back edge of the snow. There are a couple of potential negative factors toward drizzle potential: first, FZDZ/DZ potential will hinge on there being think stratus present, which would require sufficient snowfall to fully saturate the low levels. This is certainly possible, but HRRR has been consistently less impressive with QPF/snowfall with this band which could end up leaving CIGS fairly high and unfavorable for drizzle. Second, guidance generally suggests that the loss of CCN necessary for snow will occur close to or coincident with the loss of low level ascent which would limit the drizzle threat even if low stratus develops as expected. Also, as overnight shift alluded to, temperatures will be rising to and likely just above freezing during the day Sunday, which would result in mainly just plain drizzle most areas by afternoon, if anything is falling. Best chances for a period of freezing drizzle would likely be western CWA, toward Rockford, Dixon, and DeKalb areas where loss of CCN would likely occur early enough in the day for temps to be just a bit below freezing. Confidence in occurrence and impacts from any freezing drizzle is too low to consider a headline or SPS at this time. - Izzi Monday through Saturday: The western flank of a lobe of the tropospheric polar vortex over northeastern North America will pivot south Monday through Wednesday. Forecast ensemble median 850mb temperatures plunge toward -20C Monday night into early Tuesday. This will set the stage for highs in the teens (F) and lows in the single digits to locally below zero Monday through Wednesday morning. Wind chills look like they`ll be stuck near to below zero from Monday morning to Wednesday morning, bottoming out at -10 to -15F, locally colder, early Tuesday morning. The strongest winds of the cold shot will occur on Monday, when west-northwest winds gust to 25-30 mph. Precipitation wise, there`s not much to speak of, but low amplitude waves in Arctic air masses need to be monitored closely given that any snow accums with very cold temps cause at least some travel impacts. One of these waves will pass across the mid-MS Valley Tuesday morning. A blend of ensemble mean PoPs support 20% PoPs in our southern CWA Tuesday morning. If it does snow (ie. coating to 1" type amounts), air temps in the single digits during that time will render road treatments much less effective. Thankfully, the bout of cold air looks to be short-lived as short-wavelength upper-level ridging allows for thawing temperatures from the middle to the end of the week. Wednesday will see temps climb back toward or a bit above 20F north of I-80, followed by low-mid 30s (locally upper 30s) on Thursday. Highs on Friday may make a run toward the upper 30s if not into the 40s in spots, which will feel some 40 to 45 degrees warmer than earlier in the week. Upper-level ridging into the Gulf of Alaska will maintain a pattern favorable for Arctic intrusions into the northern US for the foreseeable future. It is hence no surprise that ensemble guidance advertises a return of mean upper-level troughing across the northern US next weekend and beyond. Just how cold readings get will depend on the eventual evolution of the upper-level troughing, though multi-run means from both the EPS and GEFS support highs dropping back toward the teens and lows toward the single digits by the end of the weekend. In terms of any snowfall, we`ll again have to watch any wave that tries to take advantage of what may end up a broad baroclinic zone draped across the central US (ensemble meteograms across the general region show opportunities for measurable snow, but with little consistency in time and location among individual members). The first opportunity would be Friday night into Saturday as the next surge of cold air arrives, with some potential for rain initially if precip starts early Friday evening. PoPs peak in the 20-40% range Friday night, highest south of I-80. Castro/Borchardt && .AVIATION /00Z TAFS THROUGH 06Z MONDAY/... Issued at 530 PM CST Sat Jan 11 2025 Key Aviation Messages for the current TAF period: - Snow expected at all sites Sunday morning with associated vsby reductions to IFR - A 30 percent chance for drizzle/freezing drizzle late Sunday morning and afternoon - IFR cigs during time of precipitation, but lifting to MVFR conditions in the afternoon VFR conditions with southerly winds less than 10 knots are expected through around 09Z As the next system approaches Sunday morning, winds will increase with gusts around 20 knots. Models have trended such that a period of snow is expected tomorrow morning, so the PROB30 group was converted to a TEMPO to try and hone in on the current timing expectation. There is a low chance for some light flurries ahead of the main system snow, but for now was kept out of the TAF as impacts are not expected. Accums with the main system are expected to be limited to around a quarter to a half an inch, but cigs and vis reduced to IFR levels are possible during the snowfall. If expansiveness in the system snow increases, there is a chance that the TEMPOs may be converted into a prevailing line. As the main band passes, precip has a chance (around 30 percent) to transition over to drizzle or freezing drizzle and linger through the early afternoon. For now, a PROB30 was added with -FZDZSN, but there is uncertainty in both ambient and runway surface temperatures. With enough warming on Sunday, it`s possible any -FZDZ changes to -DZ during the afternoon, but this will likely be handled tactically based on temperature trends. Precip eventually diminishes through the afternoon as the surface low in Wisconsin moves east. Post-frontal winds will turn to of the west in the late afternoon through the evening. Gusts in the TAFs were increased slightly during this package, but there is a chance for isolated gusts up to 25 knots. DK && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago
Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
1011 PM EST Sat Jan 11 2025 ...New UPDATE... .UPDATE... Issued at 1001 PM EST Sat Jan 11 2025 No real significant changes for the evening update. Clouds were eroding a bit slower than expected earlier in the shift but they have since begun to rapidly dissipate across the region. Touched up the cloud cover forecasts with a heavy dose of the latest HRRR run which seemed to be handling the cloud cover exceptionally well I think. The question remains, how much longer will the clouds take to fully dissipate and what effect, if any, will that have on overnight lows. The last several runs of the HRRR have been gradually raising overnight lows, dropping them down only into the low 20s verses the teens that we have advertised. With winds being calm as they are, if the clouds fully dissipate as expected, temperatures could still fall rapidly. For that reason, I didn`t make any changes to the overnight low forecast. The only other item of note is that patchy fog is still forecast to develop later tonight. I`m probably a little heavy handed here, but I did put in some big swaths of patchy freezing fog later tonight, expanding the coverage versus what the day shift had. This will really depend on the clouds, but there seems to be enough support to have it in there. && .SHORT TERM... (This evening through Sunday) Issued at 223 PM EST Sat Jan 11 2025 Key Messages: 1. Black ice development is possible tonight and early Sunday morning, as well as, continued snow and ice covered roadways especially secondary roads. 2. Patchy freezing fog possible overnight but confidence is low on extent. 3. Sunshine returns Sunday with temperatures warming into the 30s to near 40. Welcome return of the sunshine !!!! Discussion: Currently, light snow showers or flurries continue across southwest Virginia and northeast Tennessee. These showers are in response to low-level instability which will end by sunset. Additional light snow accumulations of 1/2 inch or less possible across the mountain areas before ending early this evening. Plenty of cloud cover across the region. Interesting that the melting of the snow across west Tennessee/west Kentucky, and southern Illinois is aiding in the production of cloud cover over Tennessee and Kentucky. As temperature drop this evening this moisture feed will cut off. For Tonight, a gradual decrease in cloud cover is expected this evening with sky becoming mostly clear/partly cloudy early Sunday morning. Low confidence in potential of patchy freezing fog tonight. Best chance is near area waterways. Main message of concern is the potential of black ice development tonight as melted ice/snow refreezes. Also any standing water will freeze. Most of the main roadways have cleared but snow/ice covered secondary roadways are possible. For Sunday, mostly sunny/partly cloudy day will allow for plenty of sunshine. Even though a cold start is expected temperatures will warm into the 30s to near 40. A welcome return of sunshine... && .LONG TERM... (Sunday night through next Saturday) Issued at 223 PM EST Sat Jan 11 2025 Key Messages: 1. Cold temperatures are expected into the middle of the week with snow showers or flurries possible. 2. A warming trend is expected by the end of the week with rain chances next weekend. Discussion: Quieter period of weather to start of next week with mid level zonal flow to slight ridging to go along with higher surface pressure. Biggest weather of note for the upcoming work week will be a cool down mid week. A weak moisture starved front will move through the eastern United States with the majority of the precipitation staying well off to our south near the Gulf of Mexico. Further north in our area there may be enough forcing along the higher terrain within the northwest flow to create some light snowfall, with light accumulation along the ridge lines and mountaintops of northeast TN and southwest VA Monday into Tuesday. The more widespread impact from this front will be the drop in temperatures Monday night into Tuesday. Temperatures will drop back into the teens with light northwest winds at the surface and lower levels of the atmosphere. Winds during the middle of the week will remain generally below 10 mph, keeping the wind chill values close to the ambient temperature, and sunnier skies will hopefully take the edge off this mini cold spell. The colder weather wont last for terribly long as a quick warm up is expected the second half of the work week and continues through the weekend. Quick ridging, winds turning more southerly and sunny skies ahead of our next system will let temperatures warm back up into the 40s for much of the area Friday/Saturday, and depending on the strength of the southerly flow we could even see a few places cross the 50 degree mark. This system will also be our next chance of widespread precipitation. At this time it looks like temperatures will remain warm enough that the precipitation falls as rain in all locations outside the very peaks of the mountains and ridgetops of northeast TN and southwest VA. && .AVIATION... (00Z TAFS) Issued at 627 PM EST Sat Jan 11 2025 VFR conditions should prevail through the period. The only caveat is that there is some concern for fog/freezing fog to develop in the KCHA vicinity tonight. It`s not highlighted too much in guidance, with most guidance only showing a 1-3 hour window of possibility. As such, confidence in it occurring is low and will just keep the mention of VCFG and a SCT003 base in there for now. Otherwise, expect the VFR BKN-OVC035 deck across the region to break up by 04z, leading to SKC with light winds at all terminals through the remainder of the period. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 36 19 41 26 / 10 0 0 10 Knoxville McGhee Tyson Airport, TN 34 17 40 24 / 20 0 0 0 Oak Ridge, TN 35 17 39 24 / 10 0 0 0 Tri Cities Airport, TN 30 14 38 21 / 30 0 0 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...CD AVIATION...CD
Area Forecast Discussion
National Weather Service Topeka KS
549 PM CST Sat Jan 11 2025 .KEY MESSAGES... -There is a chance (20-40%) for light mixed precipitation this afternoon and evening. -A glaze of ice could develop where temperatures are below freezing this evening. -The rest of the forecast is dry with temperature fluctuations through next week. && .DISCUSSION... Issued at 245 PM CST Sat Jan 11 2025 This afternoon, a mid-level trough axis extended from central North Dakota southward toward the Four Corners regions. At the surface, a weak frontal boundary was noted from low pressure near the North Dakota/South Dakota border into central KS. Some radar returns were showing up across northern and north-central KS. Forecast soundings from the RAP and HRRR show saturated mid-levels with slightly drier air underneath. Thus, most of what was showing up on radar was not reaching the ground initially. Where returns are higher and more persistent, there have been a few reports of mixed precip. With time this afternoon and evening, the front and upper trough will continue to move eastward. CAMs agree on a small batch of light precip accompanying the surface front where there will be a bit of lift along the boundary. Forecast soundings struggle to saturate the low levels, so any precip that makes it to the surface should be fairly light. Temps and wet bulb temps look to hover close to freezing this evening, with a layer of warmer air just above the surface. So precipitation types are expected to primarily be a mix of light rain and freezing rain. The HREF grand ensemble only has a 20 to 30 percent chance for greater than 0.01" of ice accumulating, while WPC shows slightly higher probabilities. Where temps are below freezing, a few slick spots could develop on untreated or elevated surfaces where precip falls. Tonight, some patchy fog could develop in eastern KS. The extent of any fog is somewhat uncertain given that winds will stay a little elevated just off the surface. Temperatures will be slightly cooler tomorrow with breezy north winds. High pressure expands over the area on Monday, which will bring in a cooler/drier air mass for early in the workweek. Early morning temperatures are expected to be in the single digits with highs only in the 20s. Monday night, another mid-level trough axis passes just to our northeast. Most models keep conditions dry across northeast KS at that time, with the GFS the main outlier with bringing light snow into far northeast KS. Have kept POPs less than 15 percent for now. The rest of the week should remain dry with temperatures starting to moderate a bit into late week when highs will be near 40 degrees. A stronger front could move through the forecast area late in the week with models in good agreement on a Friday afternoon timeframe. Right now, moisture looks limited and confined to areas to our southeast. The main impact from that front currently appears to be another drop in temperatures early next weekend. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 530 PM CST Sat Jan 11 2025 Over the next few hours KTOP/KFOE likely maintain -SHRA through 02Z before the chances become higher for a mix of either -FZRA or PL. KMHK appears to be mostly done with precipitation chances with higher cloud bases and precipitation chances on the general decline. Expecting cigs to remain around or above marginal VFR conditions through the overnight period. Chances for fog remain low with cloud cover not likely to clear until mid to late morning tomorrow. Could still see a few hours of brief ground fog on top of the snowpack if winds go calm. && .TOP WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Teefey AVIATION...Drake