Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/09/18

Area Forecast Discussion
National Weather Service Charleston SC
954 PM EDT Sun Apr 8 2018 .SYNOPSIS... High pressure will push offshore tonight as a frontal system approaches from the south to impact the area Monday into Tuesday. Dry high pressure will then prevail into Saturday. A cold front could approach on Sunday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Short term guidance has come into better agreeement in placing the strongest isentropic assent along the Savannah River into the Beaufort area overnight. Adjusted pops slightly to reflect this, but 70-80% pops still look on track. KJAX radar already showing isolated showers beginning to develop just north of the Florida/Georgia border as expected. GOES-E imagery shows clouds are rapidly expanding north and skies should go cloudy all areas soon. Overnight lows have likely occurred or will soon occur for most areas. Adjusted hourly temperatures to match going trends. Isentropic lift is progged to steadily intensify overnight as a coastal trough sharpens offshore and a 40 kt LLJ strengthens across the Southeast States. As is typical in these return flow patterns, it is proving difficult to determine the spatial and temporal distribution of rainfall that is likely to breakout across the forecast area with the initial onset of 290-300K isentropic ascent. It does appear that many areas could see measurable rainfall prior to daybreak, albeit quite light, so 70-80 percent pops look reasonable for now. The initial burst of light rain could be quite spotty at first and possibly even fall as virga, but do anticipate measurable rains to occur by 6 AM for many area as the Troposphere steadily moistens. Made some minor adjustments to hourly pops based on the latest RAP and H3R, but the general flavor of the rain forecast was maintained. Overnight lows will be highly dependent on how quickly clouds thicken from south to north. Latest high resolution guidance suggests temperatures may end up being a few degrees warmer than what the current forecast depicts. Will trend overnight lows up a few degrees, but not quite as warm as some of the guidance would suggest. It is very possible temperatures may fall this evening then hold steady or even slowly rise as the cloud canopy thickens and lowers. Further adjustments may be needed with the late evening forecast cycle. && .SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/... Overview: A very unsettled and cooler than normal period expected through Tuesday. Models continue to show a series of low pressure systems moving well south of the area Monday and Tuesday with widespread light rain, then clearing and more mild by Tuesday night and Wednesday. Monday and Monday Night: The day will start off with widespread light rain across the area as a surface low moves just southeast of the region over the Atlantic waters. Isentropic lift/overrunning will produce likely to categorical chances for light rain through early afternoon, especially for the eastern half of the area. Rain chances will gradually decrease later in the day. Expect a short break in rain chances during the evening, then increasing again later at night as the next surface low moves south of the region. Have gone slight chance to chance pops after midnight. High temperatures will be very cool again, around 60 north, to the mid to upper 60s extreme south with low level northeast winds of 10-15 mph on the back/west side of the low pressure center. Lows Monday night in the upper 40s to lower 50s, coolest north. Tuesday: Models differ on placement of low center, deepest moisture and rain chances. NAM and Euro are drier, keeping the best moisture confined to the southeast and Atlantic waters, while the GFS holds better moisture/rain chances back further west over much of the region. Have nudged up pops higher to give some credit to the GFS forecast, with high end/marginal likely pops over the southeast, and then generally chance further inland and north. Depending on exact strength and track of low center, highs could once again be quite cool, in the low to mid 60s, as the area will be on the west side of the low with north- northeast low level winds. Tuesday night and Wednesday: The surface low center will continue to move east-northeast away from the region, with clearing and drying conditions. Expect low temperatures Tuesday night in the mid to upper 40s under clearing skies. Mostly sunny/sunny on Wednesday as high pressure builds over the area with light low level winds and high temperatures rebounding into the lower to mid 70s, closer to normal. Rainfall: Although light rain will be quite widespread on Monday, overall rainfall totals are expected to be generally between 0.25 to 0.5 inches Monday through Tuesday. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... Deep layered ridge will prevail Wednesday night into Saturday before a highly amplified upper trough approaches late in the weekend. A strong cold front is currently forecast to move into the area next Sunday. Above normal temps expected most days. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... VFR conditions will steadily deteriorate overnight as strong isentropic lift develops across the area. Cigs will steadily lower from south to north with prevailing IFR conditions expected after 10z at both KCHS and KSAV. Spotty light rain will begin to breakout along the Georgia coast by late evening, then blossom over the terminals Monday morning. Widespread vsbys of 3-5SM are likely in mainly light rain. Vsbys should improve by late morning as the bulk of the light rain pushes offshore as low pressure pulls away, but low clouds will linger through the day. Opted to show improving conditions to low-end MVFR by early-mid afternoon, but is very possible that IFR cigs could linger through the remainder of the 00z TAF period. Extended Aviation Outlook: Monday and into Tuesday: Models continue to indicate the potential for MVFR/IFR conditions as a series of low pressure centers move southeast of both sites, producing periods of low ceilings and widespread light rain. The best rain chances will be Monday, then again late Monday night and the first part of Tuesday. Tuesday night through Friday: High pressure will dominate with generally VFR conditions. && .MARINE... Tonight: Northeast winds will prevail in the 10-15 knot range through the evening. The flow could turn a bit more easterly for a few hours, before the coastal trough sharpens late and the flow closer to shore becomes more northeasterly. Closer to sunrise, localized pinching of the pressure gradient will help push wind speeds into the 15-20 knot range in the Charleston County waters and perhaps further south. Seas should average 2-4 feet. Monday and Tuesday: A series of weak low pressure systems will track just south and east of the waters, producing moderate northeast winds and periods of light rain/showers. Current model strengths of the low centers look too weak to produce any highlights, but winds could still be up to 15 to 20 knots at times, with seas 3 to 5 feet, highest offshore. Tuesday Night through Wednesday Night: High pressure builds back over the area with northeast winds 15 knots or less and seas 3 to 4 feet. Thursday and Friday: Still no highlights as high pressure pushes northeast of the waters, with winds veering to southeast 15 knots or less. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$
Area Forecast Discussion
National Weather Service Quad Cities IA IL
725 PM CDT Sun Apr 8 2018 ...AVIATION UPDATE... .UPDATE... Issued at 633 PM CDT Sun Apr 8 2018 Radar, reports, and HRRR data all support the mesoscale band of moderate to heavy snow persisting another few hours in southeast Iowa and west central Illinois. Under that band, 1 to 2 inches has already fallen in the past 2 hours, and likely another 1 to 3 will fall. I have extended the winter weather advisory through west central Illinois to cover this band of higher accumulation. Temperatures have already crashed to the upper 20s to lower 30s, so slushy roads are already being reported in that area. Otherwise, though not cancelling during snow, the amounts in the northeastern portion of the advisory appear too high, and that may result in only 1 to 2 inches in Cedar/Jones/Delaware counties for this event. && .SYNOPSIS... Issued at 330 PM CDT Sun Apr 8 2018 Shortwave is shifting across the Northern Plains this afternoon. Strengthening warm advection/isentropic ascent has resulted in a broad band of snow extending from around Independence through Iowa City to near Burlington moving east. Various webcams show accumulation is occurring on grassy and elevated surfaces within this band, mainly along and north of I-80 where intensity has been moderate and decent dendritic flakes. Roads appear to be just wet as pavement temps are running well above freezing this afternoon. The aforementioned shortwave will traverse east-southeast over the next 24 hours and continue to bring likelihood for some snow, and potentially drizzle/freezing drizzle Monday as the column dries out aloft. && .SHORT TERM...(This Evening through Monday) ISSUED AT 330 PM CDT Sun Apr 8 2018 Tonight...Assessing several of latest model runs and comparing to what`s occurring upstream, seems incoming warm air advection wing of snow(with some rain mix on the southwest flank) may be mainly east of the area by 03z-04z. Incoming convergent axis of LLVL jet and enhanced upward omega strip, suggests an enhanced band of snow accums of 1-2" possible by mid evening from just north of Sigourney IA, southeastward to Burlington and Macomb IL. Most other areas to get a half inch to and inch through midnight mainly on elevated and grassy surfaces, except northwestern IL which is being impacted by dry east-southeast boundary layer fetch any may not even get any snow until 8-9 gradient drop off in precip to the northeast. A lull of flurries or drizzle acrs much of the area generally from 9-10 PM through at least Midnight, before weakening upper wave/trof progresses toward the CWA from the west. After Midnight...expect an uptick in snows again as the upper wave moves in from the west, like mentioned above. This wave may produce up to another inch or two generally along and north of the I80 corridor, and west of the MS RVR by 12z Monday...areas east of the river 0.5 to 1 inch by sunrise. Loss of ice crystals, lower liquid- to-snow ratios may foster more rounds of drizzle/freezing drizzle mixing in with less intensity wet snow or flurries acrs the southern third of the CWA late tonight, making for lower snow accums of a half inch or less in these areas. But additional shifts will have to watch out for another southward pull of the upper low and it`s associated main lift/forcing axis...which could actually place a higher snow amount band during the 06z-12z window from southwest of Iowa City, to east of Burlington again. The latest available run of the ESRL HRRR suggests this. Lows tonight mainly in the upper 20s acrs most of the CWA...around 30 in portions of the south. Monday...Additional light snow accums generally of a tenth or two acrs the northern 2/3`s of the CWA through mid morning...before low to mid layer drying may support more of a drizzle or freezing drizzle regime where lift persists. Expect mainly marginal sfc temps diurnally for much of any freezing drizzle impacts on traveling surfaces Monday morning. Any lingering light precip should become mainly regular drizzle or spotty light rain in steepening low level lapse rates and sfc temps increasing into the upper 30s to low 40s by afternoon. All in all, with dry air to overcome/much of initially lift going into saturation, and marginal sfc temps...storm total snow amounts acrs most of the CWA to range from 1-3 inches, lower in northwest IL. Will expand the ongoing advisory a tier of counties south, with the southward trend in forcing/lift regime of both the WAA wing this afternoon/evening, and the overnight upper wave. Will continue to advertise the Advisory areas getting a total range of 2- 4 inches, but lowered confidence in these locations getting toward the higher end of that range. ..12.. .LONG TERM...(Monday Night through next Sunday) ISSUED AT 330 PM CDT Sun Apr 8 2018 The main story or emphasis is the transition to a warmer pattern with at least a couple days of potential to be above to much above normal. Monday night-Tuesday will remain seasonably cool and dry with high pressure in control. Tuesday night into Wednesday... This is the first transition toward much warmer conditions, as high pressure shifts east and southerly flow strengthens. Temps will likely level off in the evening and then rise overnight right on through the afternoon Wednesday. Will have to watch the Wednesday afternoon time for fire weather concerns with the gusty south winds and lowering RH. An upper level disturbance is shown to move across the area mainly to our north Wednesday night and will bring an attendant chance of showers and possibly a few storms with strengthening nocturnal low level jet and moisture transport. Resultant cold front from the upper level disturbance will settle in/near the area on Thursday, and from here leads to considerable uncertainty and challenges with high temps both Thursday/Friday dependent on the location/movement of the boundary. Potential for well above normal warmth with 70s to near 80 in the warm surge south of boundary. Meanwhile, north of this boundary will be much cooler in the 40s/50s. Location of the front will hinge some on whether any easterly fetch and lake enhancement off Lake MI occurs. This time period of late week also offers potential for strong convection in/near the area with right now seemingly more of a consensus on this being to our south/east. Nonetheless will be a period to watch. Then next weekend it appears to be cooler and more seasonal in wake of departing low and cold front. && .AVIATION...(For the 00Z TAFS through 00Z Monday Evening) ISSUED AT 647 PM CDT Sun Apr 8 2018 Ongoing snow across the area this evening will continue into the overnight hours. KDBQ was observing MVFR conditions, but conditions have been deteriorating as the snow has caused visibilities and ceilings to drop. More snow and IFR to LIFR conditions will be seen through the evening, especially in areas south and west of KDBQ, impacting KCID, KMLI, & KBRL. A fairly narrow band of heavy snow is expected to continue through at least mid evening, however may not hit any of the terminals. By 04Z, snow should be becoming light in all areas, but visibilities will stay low with fog setting in. Precipitation may change to drizzle on Monday morning, and if temperatures haven`t risen above freezing could get some patches of light freezing drizzle. Amounts should be very light though so don`t expect a large impact from this. After 18Z on Monday visibilities and ceilings will be improving, but likely to stay at least MVFR with through the majority of this forecast cycle. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...Winter Weather Advisory until 10 AM CDT Monday for Benton- Buchanan-Cedar-Delaware-Des Moines-Henry IA-Iowa-Jefferson- Johnson-Jones-Keokuk-Linn-Louisa-Muscatine-Washington. IL...Winter Weather Advisory until 10 AM CDT Monday for Henderson- Mercer-Warren. MO...NONE. && $$ UPDATE...Ervin SYNOPSIS...McClure SHORT TERM...12 LONG TERM...McClure AVIATION...Brooks
Area Forecast Discussion
National Weather Service Sioux Falls SD
652 PM CDT Sun Apr 8 2018 .SHORT TERM...(This evening through Monday) Issued at 407 PM CDT Sun Apr 8 2018 Vigorous storm system continues to move eastward. Surface low pressure is currently located in central NE, with a strengthening upper short wave moving into northeast SD. The mid and upper level QG forcing is rapidly exiting our eastern zones early this evening in front of this wave. However PV forcing in the 700-600mb layer remains strong behind the QG forcing across the northeast half of our forecast area all evening long. This helps to keep deep layer saturation going for those locations, with much drier mid levels heading toward the Nebraska border which currently are causing a light wintry mix. The 850mb low off of the RAP13 is projected to head toward Yankton SD by 01Z and 02Z this evening, from its current location near Chamberlain. Therefore a constant low level feed of moisture is supplied ahead of this low using the 850mb streamlines, and water vapor imagery also showing a feed in the upper reaches of the atmosphere from the southwest. The radar mosaic is filling in nicely across east central and northeast SD as the 850mb low tracks southeast. Therefore expecting another two to three inches of snow over the headlined area this evening. Thought about changing some of the winter weather advisory to a winter storm warning but there are some concerns. First, the frontogenetic part and instability of the event is largely gone. Therefore not sure if rates will be sufficient enough to produce a widespread 8 inches of snow or so. In the headlined area, we already have a lot of 5 to 7 inches of snow forecast, so not sure if the message radically changes between these amounts and 8 inches of snow, especially noting that half of the snow depth will be gone by Monday due to melting and compaction. The HRRR and HRRRx continue to show a small heavier band of snow very late this afternoon and early this evening in extreme southeast SD and extreme northwest IA. So there may be some enhanced amounts just south of KFSD if those solutions pan out. At any rate, that will be the main challenge in the next few hours is worrying about headline changes. As the next round of snowfall moves southeastward, the freezing drizzle/light sleet threat should recede through the early evening hours. Although the threat for a light wintry mix overall will not totally end in our southern zones. The wave will slowly exit our eastern zones overnight. Light snow and a light wintry mix remains a threat in our eastern zones well into the overnight and late night hours. RH time sections keep the area pretty cloudy with stratus. Therefore despite the new snow cover over many locations, opted to not tank lows too much. Mainly used raw model consensus values. On Monday, lowered highs a few degrees over many of the snow covered areas which will produce another way below normal day. .LONG TERM...(Monday night through Sunday) Issued at 407 PM CDT Sun Apr 8 2018 The upper flow becomes more quasi-zonal for the mid week which ushers in more of a Pacific air mass. On Tuesday, continued to lower highs a couple/three degrees across the northeast half of the forecast area. However with a southwest wind, raised highs over consensus values in our southwest zones to give readings in the 60s across our south central SD zones. The temperature range could be very large from southwest to northeast across our CWA on Tuesday. A quick moving short wave should pass harmlessly by on Wednesday. But this wave will help to produce very mild conditions south of it across our southern zones. With 850mb temperatures projected to be +10C to +12C on the ECMWF in our far south, raised maximum temperatures on Wednesday to 65 to 70 degrees in our zones from south central SD to near Highway 20 in northwest IA. All eyes are then trained to the very strong system exiting into the plains late this week in the Thursday night through Friday night/ Saturday time frame. Obvious timing differences exist in the deterministic solutions with the GFS being much quicker then the ECMWF. But latitude placement wise, the models continue to trend on the cool side overall in this forecast area. The one exception may be late Thursday night and early Friday in our eastern zones who are temporarily in the warm sector - but are also largely dry slotted to the south of an occlusion at that point, at least on the ECMWF. Taken literally, another snow event is the offing on the backside of the low but will continue to monitor. It appears next weekend will be very much below normal again in terms of temperatures. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 651 PM CDT Sun Apr 8 2018 Snow will continue north and east of KFSD during this evening, with an additional inch or two of accumulation. The best forcing has passed KHON, so they are likely done with accumulating snow. But KFSD and KSUX will likely both have several more hours of freezing drizzle mixed with light snow. An additional light glaze should be expected for these terminals. By 09/0400z, any drizzle looks to become very light, perhaps more of a mist. By the early morning, fog may develop during the morning hours as high pressure builds in behind this system. Expect areas of fog through the morning, perhaps even into the afternoon as moist, relatively stagnant air remains over the region. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...Winter Weather Advisory until 1 AM CDT Monday for SDZ038>040- 053>056-061-062-066-067-071. MN...Winter Weather Advisory until 7 AM CDT Monday for MNZ071-072-080- 081-089-090-097-098. IA...Winter Weather Advisory until 7 AM CDT Monday for IAZ001>003- 012>014-020>022. NE...None. && $$ SHORT TERM...MJ LONG TERM...MJ AVIATION...VandenBoogart
Area Forecast Discussion
National Weather Service Wilmington NC
1103 PM EDT Sun Apr 8 2018 .SYNOPSIS... Low pressure will develop along the Gulf Coast along a stalled front tonight, then will move near the Carolina coast Monday. Widespread rain on Monday could linger into Tuesday, along with continued chilly temperatures. The low will move out to sea Tuesday night and Wednesday as high pressure builds in from the west. This high will move offshore Thursday, with much warmer temperatures expected through the weekend. Wet weather may return Sunday ahead of the next cold front. && .NEAR TERM /THROUGH MONDAY/... As of 1030 PM Sunday...Minor changes to account for temperature curve and cloud cover, and also to slow precip onset overnight. Zonal flow aloft is south of a subtropical jet moving through the Mid-Atlantic. Beneath this jet, high level moisture from the Pacific is streaming overhead as high level cloud cover, and this is "saving" the area from frost/freeze conditions tonight. Despite rapid cooling earlier, temperature curves are leveling off as the clouds thermally insulate the ground from longwave cooling. This will keep mins from falling much below 40 except in the coldest sheltered locations of Bladen and Pender counties, with low 40s expected across most of the area. The other concern tonight is onset of precip as well as areal coverage before daybreak. Weak impulses within primarily zonal flow will spawn a low pressure off the GA coast late tonight which will then lift NE into Monday. Isentropic lift atop the surface high combined with forcing in the vicinity of the low and onshore flow will cause the column to saturate, and showers will develop from south to north towards dawn. Latest RAP soundings and HRRR output suggest a much slower development of precip than previously forecast, so have slowed the timing, but still expect widespread light rain beginning well after midnight, and increasing into Monday. Relevant portion of previous discussion below: As of 300 PM Sunday...A quick moving shortwave moving through the Tennessee VAlley will crank up isentropic lift around the 290k surface early Monday morning. This will first increase clouds late tonight with light rain shortly thereafter. We are advertising categorical pops through most of the day Monday but overall rainfall amounts should be light. Highs Monday will be in the middle 50s. && .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... As of 300 PM Sunday...Low pressure off the coast not to make much progress through most of the period. As such it will be hard to get rain completely out of the forecast for much of the time, though expected amounts will be negligible. The final wave of energy aloft finally swings through Tuesday night and the surface low finally accelerates off to the northeast. This will mark the beginning of dry weather. Temperature-wise both nights will be seasonably cool thanks to cloud cover whereas these same clouds will keep Tuesday highs below climatology. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 300 PM Saturday...The upper trough responsible for the chilly weather the first half of this week should finally push offshore late Wednesday. Moisture trapped beneath a growing subsidence inversion between 8-10kft should keep skies at least partly cloudy Wednesday, maybe even mostly cloudy at times as shown on the GFS. Highs should only make it into the mid-upper 60s. Surface high pressure across North Carolina on Wednesday should push offshore Thursday. The 12z GFS is the fastest of all model guidance with the departure of the high, and I`m delaying the onset of southerly return flow until Thursday, in line with the bulk of model guidance. With lingering marine influence along the coast I`m also trending toward the cooler side of high temperature guidance on Thursday along the coast with upper 60s/lower 70s contrasting with upper 70s farther inland. A flat upper ridge will build across the Southeast Thursday and Friday, building more strongly as it pushes offshore Saturday and Sunday. Southwesterly winds should bring much warmer air into the Carolinas late in the week with inland highs expected to reach the lower 80s Friday and Saturday. Healthy seabreeze circulations should develop each afternoon Thursday through Saturday with onshore winds increasing by 5-8 mph above the background synoptic wind. The GFS is again the fastest of all available guidance with the eastward progression of a strong trough over the lower Mississippi Valley region Saturday night into Sunday. A deep plume of tropical moisture lifted northward ahead of this feature will move across the Southeast states, probably reaching the Carolinas on Sunday. I`ll put Sunday`s PoPs at 50 percent for now. Model ensembles show this could be a significant rain- maker for the Carolinas early next week with continued slow movement of the upper level system beyond our extended forecast period. && .AVIATION /03Z MONDAY THROUGH FRIDAY/... As of 00Z...A low pressure area will move northeast along a frontal boundary located offshore this TAF valid period. VFR through 12Z with lowering cigs and light winds becoming northeast by daybreak. Light rain will gradually overspread the terminals as cigs lower to MVFR shortly after daybreak. IFR cigs appear most likely around 15Z KCRE/KMYR, and around 17Z at the remaining terminals. Vsbys should remain VFR as rain should remain light. Rain tapers off west to east by the end of the TAF valid period, but cigs remain IFR. Extended outlook...Mon night-Tue, IFR/rain. Wed-Fri VFR. && .MARINE... NEAR TERM /THROUGH MONDAY/... As of 1030 PM Sunday...No significant changes with the evening updates other than to drop the SCEC early. Very light winds will persist across the waters overnight, with direction slowly becoming easterly and then increasing to 10-15 kts towards morning as weak low pressure develops. Seas of 1-2 ft will build late to 2-3 ft, and then further on Monday. Relevant portion of previous discussion below: As of 300 PM Sunday...Northeast winds veer to east overnight and increase as low pressure develops to the west and moves rapidly east. Speeds increase to 15-20 back from the northeast Monday afternoon. Seas will increase possibly into small craft criteria late Monday. SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... As of 300 PM Sunday...A nearly stalled area of low pressure will be off the coast Monday night into Tuesday. The gradient may become sufficiently pinched to necessitate Small Craft Advisory. If so then these flags may be lowered Tuesday as the low weakens and/or starts moving to the NE, though a period of SCEC is tough to rule out. Conditions continue to abate Tuesday night as high pressure builds in from the NW. LONG TERM /WEDNESDAY THROUGH FRIDAY/... As of 300 PM Sunday...High pressure across North Carolina on Wednesday will slowly move off the coast late Wednesday night and Thursday. The GFS model is the fastest of our available model guidance with the movement of the high; virtually all other models are 6-12 hours slower. Northeast winds should veer around to the south during the day Thursday, and veer to south- southwest on Friday as the high moves farther away from the coast. Also by Friday look for the reappearance of our typical afternoon seabreeze, with nearshore wind speeds becoming 5-8 knots higher than 10-20 miles out. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...TRA NEAR TERM...JDW/SHK SHORT TERM...MBB LONG TERM...TRA AVIATION...MRR MARINE...
Area Forecast Discussion...UPDATED
National Weather Service Chicago/Romeoville, IL
732 PM CDT Sun Apr 8 2018 .UPDATE... 730 PM CDT No major changes are planned to the forecast tonight. We are monitoring moderate to even heavy snow across eastern Iowa across western Illinois, but a gradual weakening with eastward movement is expected with this. While some of these rates could clip Dixon to Pontiac to Watseka before weakening, the potential accumulations of 1" to possibly 2" in that area from 9pm-4am still are on track and look to have minimal impacts. Less snow remains forecast further north and east. Water vapor imagery early this evening indicates the primary closed wave across central/southern MN with a couple attendant waves to its south. One of these is enhancing the 850-700mb warm advection and ascent across eastern IA and western IL and is responsible for the modest snow. Multiple locations have gone down to 1/2SM visibility within the first hour of snow, including Galesburg, Peoria, Lincoln, and Springfield. While strong mid- level frontogenesis is moving over the forecast area, lower very dry air with temperature/dew point depressions of 15 to 30 degrees and lack of a low-level jet per the 00Z DVN sounding are keeping this only virga over the CWA as of 730 pm. Snow will gradually inch its way eastward with warm advection aloft, reaching near the I-39 corridor by 9 pm and to the western and southern Chicago suburbs by midnight. Again while rates may be occasionally moderate, especially in the far western and southwestern CWA, much of the snow is expected to be light with any accumulation mainly on grassy or cooler surfaces. The primary wave presently across MN will begin to dampen as it loses jet support and reaching eastern Wisconsin by daybreak. Light snow gradually diminishing in coverage is anticipated between 6-10 am in the morning. Impacts to the morning commute, especially in Chicago, are expected to be minimal with mainly occasionally reduced visibility and wet possibly some minor slushy side roads. MTF && .SHORT TERM... 259 PM CDT Through Monday... Main concern for the short term forecast period will remain the unseasonably low temperatures and the snow amounts for tonight into tomorrow. While the models are in relatively decent agreement on the larger scale pattern and potential for snow tonight and into tomorrow, there remains a bit of uncertainty as to the timing and strength of individual shortwaves, which could, ultimately, impact the timing of the periods of more impactful snowfall. The first complicating factor is the very dry air mass across the CWA. Sfc dewpoints range from single digits to middle teens this afternoon as temperatures top out in the upper 30s to lower 40s. A lake breeze that pushed inland earlier this afternoon has kept the immediate lakefront a bit cooler. Also, the day started out with ample sunshine which would allow road surface to warm up some, though increasing cloud cover through the afternoon will limit the full potential for road surface warming. So, combining these factors, expect that the onset time of precipitation will be a little later than previously anticipated to give time for top-down saturation to occur and for pcpn to reach the ground. Temperatures should still be well above freezing at the time that pcpn starts, so a short period of rain is likely before changing over to a rain/snow mix and then a change to all snow for the late night and early morning hours. The latest RAP moisture/temp/UVV profiles indicate that strongest forcing will be in the the -10 to -15C range, on the lower end of the most favored DGZ, so snowfall rates may not be quite as high as could be expected with a more favorable DGZ. Also, low level thermal profiles will be somewhat marginal as well. So, in general, expect a period of wet snow, with highest amounts generally over the swrn portions of the CWA, including the Greater Pontiac Metro area, which could see an inch or so of wet snow. The northeastern portions of the CWA, including the Chicago Metro Area should see around a half inch. Given the relatively warm road surfaces, much of the accumulation will likely be on raised or grassy surfaces. Temperatures tomorrow will remain much below normal, with highs only in the upper 30s along the lake, where flow will remain onshore, to the lower 40s inland. && .LONG TERM... 156 PM CDT Monday night through Sunday... The main weather story during the period will be the likely shift towards at least a couple days of above normal temperatures mid through late week. Surface high pressure is forecast to shift over the area for Tuesday, which should result in a dry but continued cool day across the area. However, things begin to change Tuesday night into Wednesday as a mild spring airmass begins to shift into the area. This will occur as the lower-level flow turns southwest on the back side of the surface high and as upper level heights begin to rise in response to a western U.S. upper ridge shifting eastward over the central CONUS. Breezy southwest flow over the area on Wednesday looks to result in a quick response to temperatures, with 925 mb temperatures expected to warm to around +10C, which local climo for this time of year suggests would support highs around 60. A fast moving upper level disturbance is progged to shift eastward late Wednesday and Wednesday night atop the broad upper ridge over the central CONUS. This is expected to induce an uptick in the low-level jet over the region Wednesday night. As this occurs, it may induce a period of showers and perhaps some thunderstorms across northern portions of the area Wednesday night. Otherwise, gusty southwest winds will continue Wednesday night, so overnight lows are likely to be quit mild. The real warmth for the area looks to be late in the week. During this period a large upper trough will shift eastward into the plains, essentially inducing the development of a potent surface low over the plains and into the Upper Midwest by Friday. This surface low is likely to send a warm front northward over the area late Thursday. A good surge of warmer air in the wake of this front may support temperatures well into the 70s (~80 ???), especially on Friday. Thursday also looks to be a mild day, however, there are some questions as to if the winds will try to shift easterly off the lake across northern Illinois in advance of the northward moving warm front. If this occurs, areas near the lake will likely be significantly cooler than areas farther inland. Will also be some low end chances for showers and storms within the vicinity of the warm front later in the week, but at this time it appears the main threat of showers and storms may set up north of the area by Friday. Depending on the actual timing of the storm system entering the Upper Midwest on Friday, it will shift a cold front across the area sometime Friday night into Saturday morning. This would likely be or best chance to get a few showers and storms before colder air begins to return to the area in the wake of this frontal passage next weekend. KJB && .AVIATION... For the 00Z TAFs... A band of snow has crossed the Mississippi River, but in between the snow and terminals is a lot of dry air. Dew points are slowly climbing indicating moistening air, but the arrival of snow will be slow thanks to the dry air. In addition, models are showing that the snow will be weakening as it moves over the region, so I have low confidence in how long snow will occur. East winds diminish this evening and light snow should start falling at the terminals between late this evening and midnight. MVFR cigs should accompany the snow, and I have low confidence in IFR or lower cigs. Models show a few stronger snow showers early Monday morning, so I left 2SM visibilities in the window of stronger snow showers. Steady snow itself may come to an end quicker than currently forecast, but we may have snow showers through Monday morning. Some models indicate additional light rain showers may form Monday afternoon, but I have very low confidence in occurrence and coverage. Therefore, I put a VCSH in the TAFs to account for the possibility of additional precipitation. Cigs should become VFR Monday afternoon, and light northeast winds will back to north and perhaps north-northwest late Monday evening. JEE && .MARINE... 203 PM CDT Surface high pressure is currently in place across the Great Lakes Region, and this is producing fairly light and variable winds across the lake. Overall, expect fairly quiet conditions on the lake for the next couple of days before the winds begin to increase out of the southwest late Tuesday and Wednesday. A quick moving area of low pressure is forecast to shift eastward over the lakes region Wednesday night into early Thursday, so a period of southerly winds of 15 to 25 kt looks likely for Wednesday, followed by at least a short period of winds approaching 30 KT Wednesday night. This will likely result in the need for a small craft advisory for the IL and IN near shore waters. A stronger low will take shape in lee of the Rockies late in the week (Thursday night time frame) and then slowly move east as strong high pressure holds across central Canada. This will allow a sharp frontal zone to setup across the lake with ENE winds north and southerly winds south. Depending on the strength and path of the low, gales are a possibility even though the low should be weakening as it shifts eastward. KJB/KMD && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO