Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/31/17

Area Forecast Discussion...UPDATED
National Weather Service Albuquerque NM
442 PM MST Sat Dec 30 2017 .AVIATION... 00Z TAF CYCLE Dry northwest flow aloft with occasional high clouds. A modified arctic airmass along the NM/TX border at 23Z will continue to ooze westward thru 31/15Z with the western extent eroding somewhat thereafter before pushing to the east slopes of the central mt chain by 01/01Z. Attendant MVFR to IFR cigs/vsbys in br or fzfg will be more widespread along and east of the Pecos Valley before 31/15Z, but will eventually reach the east slopes of the central mt chain. && .PREV DISCUSSION...327 PM MST Sat Dec 30 2017... .SYNOPSIS... An arctic airmass will dive into the eastern plains tonight reinforcing a shallow and cold airmass already in place. Temperatures will not rise above freezing again across parts of the far eastern plains until Tuesday. Areas of dense freezing fog, light freezing drizzle and snow flurries will impact much of the eastern plains tonight through Sunday morning, and may linger across the southeast plains through Sunday afternoon. Sunday night the focus for freezing fog will probably shift to the east slopes of the central and south central mountains. A ridge of high pressure will cross the Rocky Mountain states during the middle to latter half of the work week spreading fair and warmer weather from western areas eastward over the plains as well. && .DISCUSSION... The shallow and cold airmass lingering over the eastern border from the Canadian River northward should allow areas of freezing fog to return there this evening. A persistent and moist low level south and southeast flow over the southeast plains will probably also allow freezing fog to develop there this evening. The area of freezing fog is expected to become more widespread late tonight into Sunday morning across the eastern plains as an arctic airmass arrives with a stronger back door cold front. Areas of light freezing drizzle will combine with the dense freezing fog and snow flurries to make travel hazardous. The NAM and RAP models suggest patchy fog and drizzle could linger across the southeast plains into Sunday afternoon. Will issue a Special Weather Statement to caution travelers about these hazards across the east tonight into Sunday. The night shift will monitor and issue a Dense Fog Advisory when and where needed. After some freezing fog along the east slopes of the central and south central mountains Sunday night (and possibly on parts of the plains), the airmass will finally begin a slow retreat on Monday; but, much of the far eastern plains will probably remain below freezing until Tuesday. Freezing fog may again return to parts of the east Monday night into Tuesday morning. Meanwhile, locations west of the central mountain chain will continue to experience unseasonably warm and dry weather for the remainder of the weekend as a ridge of high pressure builds over the west coast, then through the coming work week as the ridge moves inland. Eastern areas will join in the warmer weather during the mid to latter half of the week, as temperatures gradually rise above normal there as well. 44 && .FIRE WEATHER... West winds and very low humidity are generating spotty critical fire weather conditions this afternoon from the central mountains across the eastern slopes. Critical fire weather will be alleviated as winds taper off early this evening. The focus the next 5 to 7 days will be widespread poor ventilation across NM, and the timing and placement of cold frontal passages and associated higher humidities across the east. A reinforcing shot of cold air will slide into eastern NM tonight and lead to more areas of freezing fog. Well below normal temperatures will continue into Sunday behind this airmass in the east. Another reinforcing blast of arctic air will arrive over eastern NM on New Year`s Eve. This will bring another round of freezing fog and frigid temperatures. A gap wind will attempt to trickle into the Rio Grande Valley through New Year`s morning, and result in decent improvements to humidity values through New Year`s Day. This will also trend temperatures several degrees colder, but still above normal. Guidance keeps cold temperatures in place across eastern NM through Wednesday morning, while central and western NM remain above normal and very dry. A ridge is then expected to crest eastward over NM Wednesday through Friday and trend temperatures much warmer across the east. Light winds will favor strong midslope inversions each night for the central and west with very weak daytime mixing. Guidance was starting to come into better agreement on increasing chances for rain/snow around Sunday of next weekend, but there are now significant differences, which does not bode well for precip. Guyer && .ABQ WATCHES/WARNINGS/ADVISORIES... None. && $$
Area Forecast Discussion
National Weather Service Amarillo TX
924 PM CST Sat Dec 30 2017 .UPDATE... Backed off on the expiration time of the Freezing Fog Advisory until 12Z Sunday now. HRRR and 00Z NAM indicating that the lower visibilities in the freezing fog should begin to improve around 09Z to 12Z Sunday. The original 16Z Sunday expiration time was likely too long considering the rapidly improving conditions expected by sunrise Sunday. Conditions may even improve prior to 12Z Sunday, however later shifts can cancel earlier if necessary. Schneider && .PREV DISCUSSION... /Issued 746 PM CST Sat Dec 30 2017/ UPDATE... The HRRR has been consistent over the past few to several runs about developing low visibilities in freezing fog mainly across the far western Panhandles and then extending south southeast across Dumas, Amarillo and Canyon areas into Carson and Armstrong counties beginning around 02Z to 03Z Sunday and then lifting around 16Z Sunday or so. The HRRR has been doing a great job of handling the timing and coverage of the freezing fog over the past couple of nights or so. Updated all public forecast products but otherwise, no other changes to previous forecast. Schneider PREV DISCUSSION... /Issued 531 PM CST Sat Dec 30 2017/ AVIATION... 00Z TAF Cycle VLIFR to IFR conditions will prevail at the Dalhart and Amarillo TAF sites through about 15Z to 17Z Sunday and should become VFR after 17Z Sunday. MVFR conditions will prevail at the Guymon TAF site until around 14Z to 15Z Sunday and then becoming VFR after 15Z Sunday. Winds at the Guymon TAF site will be southeast 5 to 10 knots and then become northeast 5 to 15 knots after 07Z to 09Z Sunday. Winds at the Dalhart and Amarillo TAF sites will remain southeast 5 to 10 knots and then shift to the northeast 10 to 20 knots after 08Z to 14Z Sunday. Schneider PREV DISCUSSION... /Issued 418 PM CST Sat Dec 30 2017/ DISCUSSION... Theme for this forecast package is basically cold. A cold stretch will last for several days through the beginning of next week. We will slide towards "warmer" temps middle of next week. A wind chill advisory will be needed for the next couple days during the overnight and morning hours. Monday morning we may need a wind chill warning but winds will be the limiting factor, but for now we will advertise just an advisory as we are borderline warning criteria across northern areas of the forecast area. At the surface, high pressure will continue to build in from the north across the region through the next couple days...peaking Monday and pushing eastward by Tuesday. Monday will be the overall coldest day for wind chill values in the morning hours with some locations flirting with warning criteria near 15 below zero. Wind speeds are borderline for the needed 10 mph criteria, but the main things is we will be bitterly cold and its also a holiday. Also noteworthy is the chance for freezing drizzle tonight. Forecast soundings show a very shallow moist layer near the surface. There will be low clouds and fog around tonight into tomorrow morning. Given the moist layer its certainly not out of the question for some light precipitation. However, there is little to no lift in this timeframe. Confidence is not that high for a winter weather advisory for freezing drizzle, but will mention the freezing drizzle chances in the weather element. We will see a warming trend towards the middle of next week to the end of next week. Looks like next weekend we could possibly get above normal with highs in the 50s across the local area. Guerrero && .AMA Watches/Warnings/Advisories... TX...Wind Chill Advisory until 10 AM CST Sunday for the following zones: Armstrong...Carson...Collingsworth...Dallam...Deaf Smith...Donley...Gray...Hansford...Hartley...Hemphill... Hutchinson...Lipscomb...Moore...Ochiltree...Oldham... Potter...Randall...Roberts...Sherman...Wheeler. Wind Chill Advisory from 6 PM Sunday to noon CST Monday for the following zones: Armstrong...Carson...Collingsworth... Dallam...Deaf Smith...Donley...Gray...Hansford...Hartley... Hemphill...Hutchinson...Lipscomb...Moore...Ochiltree... Oldham...Potter...Randall...Roberts...Sherman...Wheeler. Freezing Fog Advisory until 6 AM CST Sunday for the following zones: Armstrong...Carson...Dallam...Deaf Smith...Hartley... Moore...Oldham...Potter...Randall...Sherman. OK...Wind Chill Advisory until 10 AM CST Sunday for the following zones: Beaver...Cimarron...Texas. Wind Chill Advisory from 6 PM Sunday to noon CST Monday for the following zones: Beaver...Cimarron...Texas. Freezing Fog Advisory until 6 AM CST Sunday for the following zones: Cimarron. && $$ 11/99
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
925 PM EST Sat Dec 30 2017 .UPDATE... Clear and cold conditions will take hold over SE Michigan tonight as lake effect diminishes near the Lake Huron shoreline. Since the afternoon burst of activity, additional snow bands have only brushed Huron and northern Sanilac counties while gradually settling offshore. The offshore drift is expected to hold as low level gradient flow weakens slightly and nocturnal cooling over land areas further favors the normal lake aggregate trough positioning. In addition, larger scale subsidence under confluent flow aloft will force shallower convective depth for any bands or clusters of snow showers that manage to waver westward during the night through Sunday morning. For these reasons, a late evening update will be good timing to cancel the winter weather advisory in favor of scattered snow showers. Elsewhere, the wind chill advisory will remain in effect through Sunday morning. && .PREV DISCUSSION... Issued at 638 PM EST Sat Dec 30 2017 AVIATION... The terminal corridor will be on the edge of a stratocu field originating from Lake Huron and Saginaw Bay during the evening. Ceiling is VFR while some light snow is reported farther east through the interior Thumb region. Expect the clouds to brush through FNT, PTK, and DET while struggling to reach DTW during the evening. Otherwise, northwest wind will be around 10 knots at the surface and a bit more due north above the surface, which is a dry combination and is expected to maintain mostly clear conditions overnight followed by thickening high clouds Sunday morning. Backing low level flow then has a chance to carry some stratocu eastward from Lake Michigan Sunday afternoon and evening. //DTW THRESHOLD PROBABILITIES... * None. PREV DISCUSSION... Issued at 237 PM EST Sat Dec 30 2017 DISCUSSION... Surface convergence zone over Lake Huron associated with surface trough/cold front clipped the eastern Thumb region this afternoon with short lived heavy thunder snow (up to 3 inches reported at Harbor Beach). Northwest-North (340 degrees) winds to follow for this evening, and majority of guidance (NAM/RAP) keeps bulk of the 925 MB convergence/lift offshore tonight, which seems reasonable considering the ICE cover extends past the nearshore waters of Lake Huron. None-the-less, will maintain the advisory in case of a wobble, or if we end up with more multi-bands as indicated by the HRRR/ARW, which will lead to snow rates not as intense as inversion heights lower, but at least impacting the Eastern Huron shoreline with additional light accumulations (few inches) this evening- tonight. Frigid airmass working through the Great Lakes Region today as deep upper level low center (505 DAM height at 500 MB with a temp of -46 C) resides along the Ontario/Quebec border. 12z GRB raob indicated an 850 mb temp of -25 C and this slightly modified cold core is over southern Lower Michigan early this evening, setting us up for very cold night as gradient slackens and low clouds dissipate/retreat closer to the Lake Michigan/Huron shorelines. Planning on carrying mins of zero to -10 F, coldest readings probably along U.S. 23, in line with Euro ensemble temps, as 12z Regional Gem and latest RAP raw temps are even a bit colder. Wind chills will be flirting with -15 F, as falling temps are offset by decreasing winds, and elected to issue a marginal wind chill advisory overnight into tomorrow morning. More solid wind chill advisory potential over the upcoming week. Re-enforcing shot of arctic air descending from Hudson Bay on Sunday, swinging through the Central Great Lakes on Monday. 850 MB temps bottoming out close to -24 C during Monday morning, supportive of highs stuck around 10F degrees during the day. Exact timing and extent of Lake Michigan clouds/modification early Monday will determine our mins, but good chance for temps to sneak below zero, with a potential wind chill advisory needed for the morning hours of New Years day. Even with "warm" advection pattern attempting to kick in Monday night, min temps do not look to be too far from zero Monday evening/night. Elevated winds 10+ MPH probably enough for wind chills to touch -15 F once again. Extended Period - Temperatures Little change to the extended forecast regarding temperature. A high- amplitude longwave troughing pattern will remain in place across the eastern-third of the U.S., bringing temperatures that will run 15 - 25 degrees below the seasonal normal. For reference, highs are typically in the lower 30s across SE MI. Tuesday temperatures will peak in the upper teens across Flint to Saginaw and up through the Thumb, but will remain capped in the low to mid-teens across the Metro region. The pressure gradient will also strengthen across the Great Lakes throughout Tuesday due to a strong high pressure system moving east across the Plains, producing breezy conditions for most of the day. As a result, wind chill temperatures will start off ranging between -20 to -10F for the morning hours, and will struggle to peak above the 0F mark for the afternoon. After sunset, expect wind chills to return back down to morning values. Temperatures again will peak into the mid-teens Wednesday, but with the wind, wind chills will reside again between the -20 to 0 F degree mark, peaking in the afternoon. There were some thoughts yesterday that Wednesday would have a chance to peak at or above the 20F mark, however, confidence is increasing that we will reside in the mid- teens for a high. The upper-level trough will continued to amplify across the Great Lakes and will bring even colder air to the region for both Thursday and Friday, highlighted nicely in the 850mb thermal temperature maps. Temperatures averaging -17 to -20C by Wednesday afternoon will drop down to -22 to -24C by Thursday afternoon. Taking a peak at sounding climatology for DTX, these temperatures approach record values (~ -27C) for 12Z soundings. In any case, confidence has increased regarding single digit temperatures highs for both Thursday and Friday, with overnight lows dipping down into the negative single digits to negative teens. Saturday will see temperatures back in the teens, and while outside our official forecast period, long-range models are showing early signs that we will potential rebound back to seasonal temperatures by next Sunday/Monday. Last thing to note -- With increased confidence regarding sub-20 degree temperatures on Wednesday, Detroit will have a shot at breaking the record for number of consecutive days where max temperature < 20. The current record is 11 days in a row, once achieved on 02/02/1936 and again on 02/18/1979. Extended Period - Precipitation The first chance for snow will move in across SE MI throughout Wednesday afternoon as a clipper system pushes southeast across Lake Huron and southern Ontario. As the trough deepens across the Great Lakes and winds shift from the west to the northwest, persistent lake effect chances will then be possible across the Thumb, mainly for communities bordering Lake Huron. Low confidence regarding where the band of lake effect will set up, with various models keeping the band just onshore, while other solutions keep it just offshore across western Lake Huron. The set-up will be something to keep an eye on heading into next week. Lake effect chances across the eastern portion of the thumb will be possible late Wednesday through early Saturday. MARINE... The forecast period will be characterized by episodic northerly or northwesterly gusts to near-gales as waves of strong Arctic high pressure descend south along the Front Range of the Rockies. The first such episode will be over the southern Lake Huron basin this evening and will be accompanied by intense snow squalls. After winds diminish for the latter half of the weekend, gusty northerly flow will return Monday and Tuesday. Expanding ice cover may result in some forecast fluctuations in wind gust intensity as affected areas experience reduced mixing depth. Climate... The deep freeze continues, with no let up in site during the next 7 days. Yesterday`s high at DTW was 19, which sets us up to break the longest stretch of days where the high temperature fails to reach 20 degrees. The current longest streak is 11 days, set in 1979 and 1936, with the end dates occuring Feb 18 and Feb 02 respectively. For reference tonight, The record low temperatures for DEC 31: FNT -11 (1976) MBS -7 (1976) DTW -5 (1976) && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Wind Chill Advisory until 10 AM EST Sunday for MIZ047>049-053>055- 060>063-068>070-075-076-082-083. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ UPDATE.......BT AVIATION.....BT DISCUSSION...SF/AM MARINE.......MR CLIMATE......SF You can obtain your latest National Weather Service forecasts online at
Area Forecast Discussion
National Weather Service Wichita KS
500 PM CST Sat Dec 30 2017 .SYNOPSIS... Issued at 354 PM CST Sat Dec 30 2017 The Arctic air officially has its hold on the Plains. Temperatures were in the single digits to lower 20s across Kansas which is definitely a stark contrast from the upper 30s to lower 40s of yesterday. It is downright frigid further north with temperatures not wind chills of -10 to -25 in Minnesota and the Dakotas. There is a low pressure system over the Great Lakes. && .SHORT TERM...(This evening through Monday night) Issued at 354 PM CST Sat Dec 30 2017 Forecast highlights: Dangerous wind chills tonight and Sunday night into the morning of New Year`s Day Wind chills or the feels like temperatures are the most significant part of the entire forecast with values plummeting tonight and Sunday night into Monday. The Wind Chill Advisory is on target, and no modifications were needed. Previously there was a question if the criteria of -25 degrees would be met for a Wind Chill Warning on New Year`s Day. This does not appear to be the case thus the advisory should suffice at this time. Given the holiday and respective travel or many people heading out to celebrate, it is very important to: bundle up, cover your extremities, avoid extended periods of time outdoors, stay indoors if possible, have a winter disaster kit in your car and protect your pets by either bringing them indoors or providing them a warm shelter. High pressure is over the area at the lower levels. A weak trough in the mid and upper levels will move through on Sunday. This does beg the question of flurry chances tonight as mentioned in the previous discussion. The NAM and RAP are showing some forcing across central Kansas, so flurries were added for tonight from 3-6AM. Record cool high temperatures are still expected on Sunday or New Year`s Eve for Russell and Salina. Please see the climate section for a complete breakdown of the potential records. .LONG TERM...(Tuesday through Saturday) Issued at 354 PM CST Sat Dec 30 2017 In the discussion from the last forecast issuance, the wind chills on Tuesday morning were brought into question for meeting advisory criteria of -15 degrees for a few hours. This forecast shows a hint of meeting this criteria in central Kansas. It is possible that an advisory could be issued, but the decision was made to hold off at this time given the expected coverage and day in the forecast. Wind chills are going to be from -5 to -15 degrees which is concerning especially with many children returning to school following their winter breaks. Please make sure to add extra layers to them and yourself before you head out the door. A ridge is in place for the rest of the week. The return to above the freezing mark for the entire area will not be until the end of the week. Saturday is going to be refreshing comparatively with forecast high temperatures back into the 40s. Unfortunately precipitation does not show up in the forecast; however, there is a hint of trough coming down from Canada next weekend with moisture transport in advance of this system. Thus there could be some precipitation to start the following week. It is too early to tell though. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 457 PM CST Sat Dec 30 2017 Cold arctic air continues to move into the region this afternoon and overnight. VFR conditions dominate the region as a result and this is expected to continue through the night and into New Year`s Eve. Some mid level clouds are expected to move into the region and affect all terminals tonight and tomorrow. This cloud cover is not expected to bring conditions below VFR tonight or tomorrow. && .CLIMATE... Issued at 332 PM CST Sat Dec 30 2017 This cold spell is challenging the current record books. New Year`s Eve or Sunday is expected to be record breaking in terms of cool highs for Russell and Salina. Below is a summary of the record values and their respective forecast. Cool high on Sunday for Russell Record: 8 degrees in 1978 Forecast: 4 degrees Cool high on Sunday for Salina Record: 8 degrees in 1927 Forecast: 5 degrees New Years Eve in Wichita and Chanute could have their coolest high temperatures since 1973 given the current forecast. As mentioned in the previous discussion, New Years Day could be the coldest since 1979. This month has been dry. In fact, Wichita will tie for the second driest December on record with only 0.03 of an inch of moisture. The last time that it was this dry for this month was in 1996. Russell is anticipated to tie their record for the driest December with only a trace for the month so far. This last occurred in 1976. Our monthly climate narrative will be issued on January 1st. Check it out if you want to read more on a summary of this month. && .PRELIMINARY POINT TEMPS/POPS... Wichita-KICT 6 11 -2 12 / 0 0 0 0 Hutchinson 3 8 -5 11 / 0 0 0 0 Newton 2 7 -6 10 / 0 0 0 0 ElDorado 5 9 -4 11 / 0 0 0 0 Winfield-KWLD 8 12 -2 13 / 0 0 0 0 Russell 0 5 -7 10 / 10 0 0 0 Great Bend 1 7 -6 12 / 10 0 0 0 Salina 2 5 -7 9 / 10 0 0 0 McPherson 1 7 -7 11 / 0 0 0 0 Coffeyville 9 15 0 13 / 10 0 0 0 Chanute 6 11 -3 11 / 0 0 0 0 Iola 5 10 -4 11 / 0 0 0 0 Parsons-KPPF 8 13 -2 12 / 10 0 0 0 && .ICT WATCHES/WARNINGS/ADVISORIES... Wind Chill Advisory from 6 PM Sunday to noon CST Monday for KSZ067>072-082-083-091>096-098>100. Wind Chill Advisory from midnight tonight to noon CST Monday for KSZ032-033-047>053. && $$ SYNOPSIS...VJP SHORT TERM...VJP LONG TERM...VJP AVIATION...ELM CLIMATE...VJP
Area Forecast Discussion
National Weather Service North Platte NE
609 PM CST Sat Dec 30 2017 .SHORT TERM...(This evening through Sunday) Issued at 331 PM CST Sat Dec 30 2017 The primary forecast challenges through Sunday afternoon are temperatures and snow. Near record cold continues as the next (and coldest thus far) polar plunge swings around the Hudson Bay low. Meanwhile, a shortwave is currently dropping through the northern Plains and will traverse the forecast area this evening. Precip... The first round of flurries/light snow showers has moved across the northern tier of the state late morning, and the next is just north of the Neb/SoDak border as of 21z. Mid level moisture has been present for much of today, but fgen really increases early this evening as the wave nears. Forecast soundings suggest decent lift sub H7, while isentropic analysis (mainly at 270-275K) also shows upglide in a nearly saturated layer. Sfc obs and RAP mesoanalysis suggest two layers of the temp profile in the DGZ... one from the sfc to about H85 and another H7 to H6, with colder air in between and the elevated warm layer (pushing -5C). In short, relatively little of the saturation and forcing occur in the DGZ. However, with fairly high SLR`s (20:1) and plenty of upper level support (130kt+ H3 jet overhead), kept minor accumulations (1-2") along/north of Hwy 20. Subsidence quickly takes over after 06z, essentially shutting off precip potential. Dry air gradually entrains through the day on Sunday, helping to clear out the stratus, mainly north. Farther south, low level moisture and lift support brief snow showers and/or flurries through tonight. Continued scattered flurries into Sunday afternoon across the far southwest (mainly Perkins and Chase counties) to account for upslope flow. Temps... Continued the trend of using the coldest guidance for tonight lows and Sunday highs. The 30/12z model suite is in agreement regarding H85 temps approaching -25C across the Sandhills (around 1%ile of climo) and a 1050mb+ sfc high pushing into the state. Made no change to current Wind Chill headlines as air temps alone drop below -15F tonight across the north and -5 to -10F south. Clouds and northerly winds will do little to help temps recover Sunday, as highs stay below zero north and struggle to reach 5 above south. .LONG TERM...(Sunday night through Saturday) Issued at 331 PM CST Sat Dec 30 2017 The models, which are in very good agreement, suggest the 1045+mb arctic high will move very slowly through the Missouri Basin Monday. This will support subzero lows and wind chill advisories or warnings both Monday and Tuesday morning. A blend of guidance plus bias correction was the basis for lows of 10 below to 20 below zero Monday morning and 5 below to 10 below zero Tuesday. Wind speeds will be fairly light, generally 5 to 10 mph both mornings and near calm at times in some locations. Both the NAM and GFS indicate precipitable water between 0.10 and 0.15 inches which should support good radiational cooling. These models show a swath of low clouds persisting Monday morning but clear skies are indicated Tuesday morning. Once this arctic high moves off south and east Tuesday afternoon, high temperatures should warm into the 20s. Arctic high pressure will move south through the Midwest Wednesday and back into western Neb. This high will ridge slowly south Thursday and Friday. We should see a prolonged period of south winds recycling cold air north. The model consensus would suggest a relatively brief period of low clouds on the wrn flank of the high pressure system affecting ncntl Neb. The high temperature forecast Wednesday through Friday is for 20s and 30s. The high pressure system ridging through the Midwest should be across the Southeast U.S. by Saturday, well south and east of Nebraska, and the models signal a chinook with west and southwest winds developing next Saturday for highs in the 30s and 40s. The forecast is dry and the temperature forecast is a blend of model guidance data, plus biased correction. Bias correction had little impact on the high and low temperatures but did suggest the warm up late next week could commence as early as Friday and high temperatures Saturday could be about 5 degrees warmer than currently forecast. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 609 PM CST Sat Dec 30 2017 Snow will be the main focus for the next day with KVTN being the most likely to see any snowfall. Visibilities at KVTN could be reduced to near 1 SM at times Saturday night. Snow will slowly taper off shortly after midnight. Cloudy skies with ceilings under 5000 ft will stick around through Sunday morning. Ceilings rise back into VFR conditions late Sunday morning. At KLBF, snow will mainly stay north of the terminal. However, ceilings are still expected to fall to near 3000 feet for the overnight and Sunday morning period. Ceilings rise back into VFR conditions by Sunday afternoon. && .LBF WATCHES/WARNINGS/ADVISORIES... Wind Chill Advisory from midnight CST /11 PM MST/ tonight to noon CST /11 AM MST/ Monday for NEZ022>025-035>038-056>059- 069>071. Wind Chill Warning from midnight CST /11 PM MST/ tonight to noon CST /11 AM MST/ Monday for NEZ004>010-026>029-094. && $$ SHORT TERM...Snively LONG TERM...CDC AVIATION...Kulik
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
855 PM CST Sat Dec 30 2017 .UPDATE... 855 PM CST Main concern is lake effect snow/mesolow trends on Sunday. Had earlier issued a Wind Chill Advisory for portions of the CWA as multiple sites fell below criteria due to a quick temperature drop early this evening. Clouds from the next approaching clipper type wave have overspread the area and resulted in rising temperatures in some locations. Not planning any changes to the Wind Chill Advisory at this time. Regarding the clipper type wave, light snow or flurries remains possible with it overnight into tomorrow morning, with a low but better chance for anything more than a dusting (up to a few tenths or so) appearing to be mainly south of I-80. Turning to the primary concern, lake effect snow associated with the prominent mesolow evident on regional radar mosaic along and off the northern lower MI shore. Have been closely monitoring radar and guidance trends with the mesolow. Overall trend, including on latest HRRR runs and on 00z 12km and 3km NAM has been a westward shift of the mesolow into Sunday morning and an increasing chance for a period of snow clipping northeast Illinois. The position of the mesolow is also important with respect to snow potential and associated impacts into northwest Indiana into the afternoon hours. Have become more concerned for at least a few hours of snow and some accumulation, particularly in northern/northeastern Porter County, though north central/northeast Lake County IN could get clipped as well. Thermodynamics will needless to say be excellent, so more than an hour or two of snow band residence time will increase potential for more significant accums and impacts and midnight shift possibly needing to issue a headline. This forecast remains lower confidence and fraught with uncertainty. However, for now, given what can be gleaned from trends, will be bumping up PoPs and QPF/accums and issuing a SPS and graphic for the web and social media to ramp up the message of possible travel impacts on Sunday. Castro && .SHORT TERM... 224 PM CST Through Sunday... Cold and snow chances continue to be the focus through Sunday.Afternoon water vapor imagery shows the large upper low continuing to spin over eastern Canada with a secondary upper low moving southeast out from Alberta and British Columbia. Upper ridging continues off the west coast. Of note is a wave moving southeast across South Dakota/northern Nebraska which is generating some snow. This wave will move across the local area overnight. On the snow side, there is not much moisture to work with but most guidance shows sufficient forcing to generate some snow. However, saturation may be an issue and the forcing is mainly above the favored snow growth zone. In addition, guidance differs on where the best forcing sets up over the forecast area. Radar and satellite trends support the most organized forcing tracking over the far southern parts of the area. Have seen some periodic expansion of radar returns across western/central South Dakota over the last few hours suggesting that a somewhat broad area of light snow may be what plays out locally. Will increase pops to lower end chance category for far southern areas mainly Livingston, Ford, Iroquois and Benton Counties overnight and carry lower pops across the rest of the area. Most areas, especially those south of I-88/I-290 could see some light snow but the focus is favored south. A dusting is possible just about anywhere and southern areas could see even a few tenths accumulation if some persistent, though weak, banding can continue into the area. On the temp side, the overnight system will bring an influx of cloud cover. Visible Satellite shows mid level clouds advancing eastward across Iowa and these will work into areas along/south of I-80 late this afternoon closer to sunset and into the Rockford and Chicago areas early this evening. Have lowest temps this evening as they will likely fall steadily for a time but may be a little quick with the drop off given the above cloud arrival times. Temps will then level off and probably even come up a few degrees with the increasing cloud cover tonight. Winds will decrease this evening and given the expected temperature trends, expect wind chills to remain just outside of advisory criteria. For Sunday, the system will be departing to the southeast in the morning and some flurries may linger far southeast. Lake effect snow potential becomes the focus as winds will have diminished enough for a more concentrated lake influence to develop. With winds having turned more northerly into early Sunday a convergent band of lake effect snow will have set up over the lake. A meso low, which may stem from the one currently moving onshore over the central UP of Michigan off Lake Superior, is expected to be moving southward down Lake Michigan tonight and Sunday. The big question will be how far west the meso low will meander. Trends continue to favor it staying offshore of Wisconsin/Illinois but will have to watch this carefully as this is something not easily forecast. Will continue with the thought that the lake snow band/meso low will remain offshore of the forecast area and then possibly move onshore across far northeast Porter County or even east of there later Sunday afternoon. Otherwise, clouds will scatter through the day, especially northwest and it will continue to be cold with highs in the single digits. MDB && .LONG TERM... 224 PM CST Sunday night through Saturday... The initial concern will be bitterly cold air Sunday night through Tuesday as high pressure dips into the Mississippi River Valley and eventually moves eastward across the Ohio Valley. The area will be within the pressure gradient on the eastern flank of the high keeping a steady breeze in place as overnight lows fall into the mid teens below zero away from the lake and Chicago metro and into the minus single digits in the metro. This will result in wind chills in the -20 to -30 range Sunday night for the Chicago metro, and immediate surrounding areas with -30 to -35 at least west and south of there. Will go ahead and upgrade to a Wind Chill Warning for Sunday night and Monday morning west and south and continue with the Wind Chill Advisory all other areas. An advisory will be in place for all areas Monday afternoon through Tuesday morning. Monday highs will struggle to go above zero. Lows Monday night will be similar to Sunday night but winds will be weaker as the high will be closer to the area so expect wind chills to remain within advisory thresholds. Temps briefly moderate into the teens Wednesday ahead of a low pressure system which will need to be watched for some light snow potential. This system will bring a push of colder air with it so will likely return to single digit highs for a day or two. Otherwise it appears that mainly dry weather will be in place into early next weekend. Beyond that, models show that upper ridging off the west coast will move eastward across North America late next weekend and could lead to another active weather period but also a milder temperature regime. MDB && .AVIATION... For the 00Z TAFs... Quiet aviation weather this evening across the region, with the only real concern coming late tonight into Sunday morning with the potential for a period of some light snow or flurries, mainly south of the terminals. Strong arctic high pressure was centered across the northern plains early this evening, with surface ridging extending into central IL. Very dry air mass is largely cloud free at this time, with northwest winds around 10 kts expected to slowly diminish a little this evening. Turning attention to the west however, another quick-moving clipper system was emerging from the northern Rockies onto the plains, with an area of associated light snow developing from South Dakota into the mid-Missouri Valley. Various model forecasts continue to develop this light snow east-southeast overnight, with precipitation expected mainly along/south of a DBQ to LAF line by pre-dawn Sunday. Northern IL/IN terminals along the northern fringe of the forecast position of the light snow, which may eventually impact the terminals. Expectation is that impacts would be fairly minimal, with perhaps a brief MVFR vis/cig combo Sunday morning. Have maintained going prob30 at this time, monitoring evolution of northeast edge of precip shield to the west this evening. In addition, area of lake effect snow is expected to develop over Lake Michigan into Sunday, which may not be too far off to the east of the IL shore. Once the mid- level wave with the clipper moves through during the afternoon, VFR/SKC conditions are expected. Winds expected to remain 300-320 deg near 10 kts for the duration, perhaps increasing a bit late Sunday/Sunday evening. Ratzer && .MARINE... 254 PM CST Lake Michigan is positioned between low pressure over eastern Canada and high pressure ridging extending from Alberta to the lower Ohio River Valley. Steady northwest winds will ease this evening allowing conditions to fall below small craft advisory through the evening. A weak system will pass late tonight and lake effect influences will take over the wind field tonight through Sunday. Expect a meso/small scale low pressure circulation to work southward down the lake tonight into Sunday morning creating a challenge with the wind direction forecast. North to northwest winds are expected across the western sections of the lake tonight and Sunday while northeast to east winds will likely occur to the east thanks to the meso low with south and east winds to the southeast of the circulation. The low should meander southward to the southern half of the lake late tonight and eventually move eastward across the southeast part of the lake during the day Sunday. From there gusty northwest winds will set up Sunday night and persist through Monday before turning westerly and easing somewhat into early Tuesday. High pressure will pass to the south Tuesday night with a low passing to the north which will bring increasing southwesterly winds into early Wednesday. May see a period of gale force winds Tuesday night with a lull Wednesday and another period of gales later Wednesday as winds shift north- northwest. Steady northwest winds then continue through late week with a shift to southwest winds later next weekend. Freezing spray will be likely with each period of stronger winds as bitterly cold air remains in place over the next few days and then again behind the system Wednesday and Thursday. MDB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Wind Chill Advisory...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011- ILZ012-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039 until 8 AM Sunday. Wind Chill Warning...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019- ILZ032-ILZ033-ILZ039...9 PM Sunday to noon Monday. Wind Chill Advisory...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019- ILZ032-ILZ033-ILZ039...noon Monday to noon Tuesday. Wind Chill Advisory...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ020- ILZ021-ILZ022-ILZ023...9 PM Sunday to noon Tuesday. IN...Wind Chill Advisory...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM Sunday to noon Tuesday. Wind Chill Advisory...INZ010-INZ011-INZ019 until 8 AM Sunday. LM...Small Craft Advisory...Winthrop Harbor to Gary IN until 9 PM Saturday. Small Craft Advisory...Gary to Michigan City IN until 3 AM Sunday. && $$ 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