SchaumburgStormer Posted December 31, 2020 Share Posted December 31, 2020 Looks like an ice storm warning coming for extreme southern LOT Link to comment Share on other sites More sharing options...
Hoosier Posted December 31, 2020 Share Posted December 31, 2020 We got a FRAM reference in the LOT afd. Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 254 PM CST Thu Dec 31 2020 .SHORT TERM... 254 PM CST Through Friday night... Near term through tonight... Quiet conditions are expected through tonight we close out 2020 and welcome in 2021. For details on Friday`s winter weather event, see the following paragraph. Large scale subsidence over the area this afternoon appears to be suppressing what was a fairly shallow stratus deck under a 2kft inversion. Some stratocumulus has filled in where snow cover is less common south of I-80, but should erode with the loss of daytime heating. Confidence is low on whether stratus will redevelop under the inversion tonight or remain confined to pockets. A narrow window of a few hours exists this evening where temps may quickly drop over the snow cover north of I-80 before thickening high clouds moderate conditions by later in the evening. WAA will ensure overnight with increasing cloud cover, allowing temps to likely rise a couple degrees. Friday... From a "big picture" view, our thinking with the upcoming storm system is unchanged. As a Gulf of Mexico low pressure system tracks northeastward and along a line from just south of Springfield, IL, to Indianapolis, IN, a broad area of precipitation will spread across northern Illinois. With the low-level thermal profile becoming progressively cooler and deeper with northward extent, precipitation types will range from all snow on the northern fringe of the shield to freezing rain on the southern edge, with a sloppy wintry mix in-between (and right over the Chicago metropolitan area). As the freezing line inches northward Friday afternoon, freezing rain and the wintry mix should convert to "plain" rain for areas generally along and south of I-88 (though the exact location may not be known until, well, it happens). All areas should convert back to snow as the low pulls away Friday evening. Total snow accumulations should range from 1 to 4 inches generally along and northwest of a line from Mendota to Bolingbrook to Evanston (highest as one goes northwest). It`s worth noting the city of Chicago and immediate shoreline may remain above freezing for much of this event thanks to wind off the relatively warm lake, and hence only see liquid rain. Explicit output from the Freezing Rain Accumulation Model (FRAM) with the outgoing forecast package topped 1/2 to even 2/3 an inch of ice across central Illinois, including in Livingston and Ford counties. At face value, those values seem too high, considering: * A deep warm nose with max wet-bulb temperatures pushing +7 to +9 C (that`s rather extreme and should heat raindrops enough to prevent freezing upon falling into the near-surface sub-freezing layer) * Precipitation rates pushing 0.1 to 0.2"/hr when freezing rain would be occurring, which would encourage run-off rather than freezing * Relatively short period of time when trees, power lines, and elevated surfaces would be weighted down by ice given rising temperatures and switch-over to liquid rain. As such, we manually lowered ice totals to max out in the range from a quarter to third of an inch. While those values along would not normally lead to widespread downed tree limbs and power outages, breezy northeast winds of 25-35 mph could be the straw that breaks the camel`s back. As such, we felt there was enough justification to issue an Ice Storm Warning for Livingston and Ford counties (ending at 6 PM CST, though actual freezing rain should end after the noon hour). North and east of the Ice Storm Warning, total ice up to a quarter inch is expected which may yet lead to pockets of power outages and downed tree limbs when combined with the wind. Borchardt/Kluber 4 Link to comment Share on other sites More sharing options...
Kitchener poster Posted December 31, 2020 Share Posted December 31, 2020 The 18Z NAM onboard with a 3-5 inch band of snow along the entire 401. 1 Link to comment Share on other sites More sharing options...
A-L-E-K Posted December 31, 2020 Share Posted December 31, 2020 I'll take what the hrrr is selling 1 Link to comment Share on other sites More sharing options...
Natester Posted December 31, 2020 Share Posted December 31, 2020 ILX going for an Ice Storm warning for their NW CWA according to the point forecast matrix. 1 Link to comment Share on other sites More sharing options...
fluoronium Posted December 31, 2020 Share Posted December 31, 2020 20 minutes ago, Hoosier said: * A deep warm nose with max wet-bulb temperatures pushing +7 to +9 C (that`s rather extreme and should heat raindrops enough to prevent freezing upon falling into the near-surface sub-freezing layer) * Precipitation rates pushing 0.1 to 0.2"/hr when freezing rain would be occurring, which would encourage run-off rather than freezing I'm confused by the statement on the warm layer here in regards to hindered ice accumulations as it seems that this would favor more freezing rain over sleet. I have trouble believing that warm raindrops at the surface make that much of a difference regarding ice accretion, but I'm also just an arm chair . It's just that the amount of energy released by turning liquid water to ice is just SO much higher than cooling the liquid by a few degrees. Even if the rain drops are a toasty 9°C, the energy that's released by cooling the rain drops to 0°C is only ~10% of the energy released from freezing the liquid at 0°C to solid at 0°C. I've definitely seen the high precip rates hinder accumulations though. I remember witnessing nearly an inch of rain fall in 3 hours with surface temps of 28°F~29°F and only receiving a light glaze. 1 Link to comment Share on other sites More sharing options...
Hoosier Posted December 31, 2020 Share Posted December 31, 2020 Regarding what LOT said about the max temps in the warm layer aloft... If you look at the model progs of where the heavier band of ice is depicted, I wonder if the northern part of it would have a chance to accrete a little better/not waste as much precip. The warm layer in that area maxes out more like 4-6C instead of 7-9C. So in the LOT cwa, that would be a line from Pontiac-Kankakee-Valparaiso and maybe 10-20 miles north of there. 4 Link to comment Share on other sites More sharing options...
WeatherMonger Posted December 31, 2020 Share Posted December 31, 2020 Been too long, it was coming at some point. 1 Link to comment Share on other sites More sharing options...
fluoronium Posted December 31, 2020 Share Posted December 31, 2020 That's the first ice storm warning in likely over a decade for many of those ILX counties, mine included. I'm going to try getting some time lapses of the accumulating ice. I know the NAM seems to be the outlier with the northward extent of the warm air, but every recent shot at ice IMBY has always been killed by warmer than modeled temps. Even so, at least a few hours of freezing rain looks to be nearly certain here, so it should be enough to make the trees sparkly. 3 Link to comment Share on other sites More sharing options...
WeatherMonger Posted December 31, 2020 Share Posted December 31, 2020 ILX with a rather detailed AFD for a change Quote .SYNOPSIS... Issued at 417 PM CST Thu Dec 31 2020 Clouds will continue building overnight, as the next weather system moves into the Midwest. This system will build from the south and progress northward through Illinois overnight through Friday. Freezing rain is expected on the leading edge, with Ice Storm Warnings in effect for portions of central Illinois, while Winter Weather Advisories are in effect for much of the remainder of Illinois. Hazardous, and dangerous conditions, will persist through Friday, with the possibility of power outages around the area. As the system tracks through southern portion of Illinois, rainfall should begin taking over across southeast Illinois, while a mixed precipitation continues northwest of the I-55 corridor. This system exits Friday night, however with another system tracking through the southeast US Saturday, this could bring light precipitation to the Midwest as excessive moisture remains. && .SHORT TERM...(This evening through Friday night) ISSUED AT 417 PM CST Thu Dec 31 2020 Lots to discuss, therefore the late products: A deep upper level trof is carrying a large Low pressure system across the far southern Plains, near the Gulf of Mexico off the se Texas coastline. This is the system that will track northeast through the overnight, impacting central Illinois and the Midwest to ring in the new year. Currently looking at sfc observations and seeing most locations throughout central and southern Illinois sitting below freezing. This is the key component to precip type for the overnight moisture. As the Low pressure system lifts through the Mississippi River Valley, the excessive moisture content will continue to lift with the core. With some precip already edging out ahead of the system, this will work through moistening up the lower atmosphere and continue leading precipitation northward. Forecast soundings indicate that although the sfc temperatures will be below freezing at the onset of precip, the mid level will be much warmer. This will melt all frozen precip in the mid levels, however as this falls, the level near the sfc will be below freezing. This depth appears to only be in excess of maybe 2kft, which would not typically be enough to provide a full refreeze of water droplets. As these still liquid droplets reach the below freezing ground (as indicated by frost depth readings from this morning), they will freeze on contact. Frost depth readings this morning, in areas where Ice Storm Warning is in effect were from 1-6 inches deep. Here at the ILX office, we reported a 4 inch depth this morning. This is sufficient enough for freezing rain development. The leading edge of this system is expected to fall as all freezing rain overnight into Friday morning. With heaviest precipitation arriving towards morning north of the I-72 corridor, this is highlighted as the best chance for ice accumulations up to 0.40 inches of ice accumulation possible. This will create dangerous and hazardous conditions throughout the region, as travel would be nearly impossible and damage to trees and power lines could create widespread power outages. As the system tracks northward, warmer air will begin to filter into the area Friday morning into the afternoon, changing freezing rainfall to rainfall...however this is only expected to occur se of the I-55 corridor. Mixed precip is expected from the I-55 corridor through the Illinois River Valley. Nw of the Illinois River Valley is forecast to remain cold enough that freezing rain will likely prevail, before a change to snowfall as the backside of the Low pressure system begins shifting to the lower Great Lakes late Friday night. This could bring up to two inches of snowfall around GBG, while decreasing to near 1 inch along a line extending from Rushville to Peoria. This system is forecast to be out of the area by 06-09z Saturday (late Friday night). 1 Link to comment Share on other sites More sharing options...
WeatherMonger Posted December 31, 2020 Share Posted December 31, 2020 1 minute ago, fluoronium said: That's the first ice storm warning in likely over a decade for many of those ILX counties, mine included. I'm going to try getting some time lapses of the accumulating ice. I know the NAM seems to be the outlier with the northward extent of the warm air, but every recent shot at ice IMBY has always been killed by warmer than modeled temps. Even so, at least a few hours of freezing rain looks to be nearly certain here, so it should be enough to make the trees sparkly. Yeah, I can't remember the exact year of the last one but it was definitely over 10 years ago. I'm thinking 2007 for some reason. Think we ended up with around .3" here and can't remember if that was the one that hit Jacksonville pretty hard with closer to .6" or if it was another system. We've definitely been overdue though. 1 Link to comment Share on other sites More sharing options...
Radtechwxman Posted December 31, 2020 Share Posted December 31, 2020 35 minutes ago, WeatherMonger said: Yeah, I can't remember the exact year of the last one but it was definitely over 10 years ago. I'm thinking 2007 for some reason. Think we ended up with around .3" here and can't remember if that was the one that hit Jacksonville pretty hard with closer to .6" or if it was another system. We've definitely been overdue though. Nice to see you back man! It's been too long. Last significant ice I remember here in my county was like 2009 I think. Have had icing events since but they didn't pan out well or weren't excessive. Definitely nervous that temps could surge above freezing. Daytime ice events can be tricky. But I like we maintain northerly sfc flow which should help. 1 Link to comment Share on other sites More sharing options...
Jim Martin Posted December 31, 2020 Share Posted December 31, 2020 Link to comment Share on other sites More sharing options...
WeatherMonger Posted December 31, 2020 Share Posted December 31, 2020 6 minutes ago, StormChaser4Life said: Nice to see you back man! It's been too long. Last significant ice I remember here in my county was like 2009 I think. Have had icing events since but they didn't pan out well or weren't excessive. Definitely nervous that temps could surge above freezing. Daytime ice events can be tricky. But I like we maintain northerly sfc flow which should help. I can't root this one on, not this year lol. I'm just glad there is something to follow for a change, been a very boring year of weather here. Add in everything else going on and I just need an escape 2 Link to comment Share on other sites More sharing options...
Hoosier Posted December 31, 2020 Share Posted December 31, 2020 It looks like the HRRR started drinking early on this New Year's Eve. Not sure what it is doing in northern Indiana. At first I thought maybe it is using heavier precip as a reason to warm temps above 32, but that doesn't explain why the area south of there is still freezing rain. In reality, it should be a more uniform look without plain rain embedded in the freezing rain shield. Link to comment Share on other sites More sharing options...
sbnwx85 Posted January 1, 2021 Share Posted January 1, 2021 Just now, Hoosier said: It looks like the HRRR started drinking early on this New Year's Eve. Not sure what it is doing in northern Indiana. At first I thought maybe it is using heavier precip as a reason to warm temps above 32, but that doesn't explain why the area south of there is still freezing rain. In reality, it should be a more uniform look without plain rain embedded in the freezing rain shield. If nothing else it has been consistent in showing a donut of plain rain in Northern Indiana. Not saying it's right, but it is interesting. Link to comment Share on other sites More sharing options...
cyclone77 Posted January 1, 2021 Share Posted January 1, 2021 Nice little stat padding event here it looks like. Looking like 2-3" of snow after a mix of sleet/frz rain for several hours. Glazing shouldn't get too out of hand. 2 Link to comment Share on other sites More sharing options...
Hoosier Posted January 1, 2021 Share Posted January 1, 2021 Shame that we can't get a wide snow band given these surface conditions. But oh, that's not how it works. Probably gonna stay in as much as possible tomorrow. Even as temps rise to/just above freezing, the paved surfaces will likely lag and be a lingering disaster (especially untreated ones). 1 Link to comment Share on other sites More sharing options...
RCNYILWX Posted January 1, 2021 Share Posted January 1, 2021 If the 21z RAP is right, the only areas getting above freezing through the event are basically southeast of I-55 and along the Lake Michigan shore. I noticed that in our AFD, mentioned all areas along and south of I-88 warming to above freezing. I think that's probably too optimistic except along the Lake Michigan shore and a bit inland of there, and obviously if something like the RAP is right, ice accumulations could end up higher than forecast. [mention=14]Hoosier[/mention] made a good point earlier about accretion rates potentially being higher farther north where the warm nose is not as warm. That's something to watch and another reason to be concerned about some locations overperforming ice wise. Another thing we'll have to watch observation wise is how cold the low level cold wedge remains. The December 28 2015 event that's been discussed verified colder at that level than model forecasts, and if something like that happens tomorrow, also could have a zone that stays sleet for a while until flipping back to snow. Finally, was a bit surprised my office and DVN didn't extend the advisories to the northern tier counties staying snow, since it seems they have solid potential to come in at near typical advisory criteria for snow anyway. Will be an interesting event to watch unfold. 3 Link to comment Share on other sites More sharing options...
Hoosier Posted January 1, 2021 Share Posted January 1, 2021 22 minutes ago, RCNYILWX said: If the 21z RAP is right, the only areas getting above freezing through the event are basically southeast of I-55 and along the Lake Michigan shore. I noticed that in our AFD, mentioned all areas along and south of I-88 warming to above freezing. I think that's probably too optimistic except along the Lake Michigan shore and a bit inland of there, and obviously if something like the RAP is right, ice accumulations could end up higher than forecast. [mention=14]Hoosier[/mention] made a good point earlier about accretion rates potentially being higher farther north where the warm nose is not as warm. That's something to watch and another reason to be concerned about some locations overperforming ice wise. Another thing we'll have to watch observation wise is how cold the low level cold wedge remains. The December 28 2015 event that's been discussed verified colder at that level than model forecasts, and if something like that happens tomorrow, also could have a zone that stays sleet for a while until flipping back to snow. Finally, was a bit surprised my office and DVN didn't extend the advisories to the northern tier counties staying snow, since it seems they have solid potential to come in at near typical advisory criteria for snow anyway. Will be an interesting event to watch unfold. Yeah, 12/28/15 ended up with more sleet here than what it had been looking like. It reminded me a bit of what I experienced with GHD in LAF, just not as intense. Been looking back at previous setups and comparing them to this one. As far as 12/28/15, that had a stronger surface high and also had a stronger surface low than what we have this time. 2 Link to comment Share on other sites More sharing options...
Baum Posted January 1, 2021 Share Posted January 1, 2021 we need a solid over performer to change karma going back several years. Let's do it. 2 Link to comment Share on other sites More sharing options...
Hoosier Posted January 1, 2021 Share Posted January 1, 2021 Temp has dipped to 23 here. Not that this means that temps won't rise above freezing tomorrow, but the longer it takes to climb back through the 20s does have some ramifications on the paved surface response. 1 Link to comment Share on other sites More sharing options...
Cary67 Posted January 1, 2021 Share Posted January 1, 2021 45 minutes ago, RCNYILWX said: If the 21z RAP is right, the only areas getting above freezing through the event are basically southeast of I-55 and along the Lake Michigan shore. I noticed that in our AFD, mentioned all areas along and south of I-88 warming to above freezing. I think that's probably too optimistic except along the Lake Michigan shore and a bit inland of there, and obviously if something like the RAP is right, ice accumulations could end up higher than forecast. [mention=14]Hoosier[/mention] made a good point earlier about accretion rates potentially being higher farther north where the warm nose is not as warm. That's something to watch and another reason to be concerned about some locations overperforming ice wise. Another thing we'll have to watch observation wise is how cold the low level cold wedge remains. The December 28 2015 event that's been discussed verified colder at that level than model forecasts, and if something like that happens tomorrow, also could have a zone that stays sleet for a while until flipping back to snow. Finally, was a bit surprised my office and DVN didn't extend the advisories to the northern tier counties staying snow, since it seems they have solid potential to come in at near typical advisory criteria for snow anyway. Will be an interesting event to watch unfold. Are there concerns ice accretion will be significant in the northern tier counties or just snow mostly? Link to comment Share on other sites More sharing options...
WeatherMonger Posted January 1, 2021 Share Posted January 1, 2021 Hope HRRR is off it's rocker. Would be devastating for SW to East Central MO and wouldn't want that here either. Link to comment Share on other sites More sharing options...
RCNYILWX Posted January 1, 2021 Share Posted January 1, 2021 Are there concerns ice accretion will be significant in the northern tier counties or just snow mostly?I think that it looks like mostly snow and maybe some sleet up there and I guess that's why no advisory, though since there will be some travel impacts, thought they might have erred on the side of caution. Sent from my SM-G965U using Tapatalk 1 Link to comment Share on other sites More sharing options...
McHenrySnow Posted January 1, 2021 Share Posted January 1, 2021 1 hour ago, RCNYILWX said: If the 21z RAP is right, the only areas getting above freezing through the event are basically southeast of I-55 and along the Lake Michigan shore. I noticed that in our AFD, mentioned all areas along and south of I-88 warming to above freezing. I think that's probably too optimistic except along the Lake Michigan shore and a bit inland of there, and obviously if something like the RAP is right, ice accumulations could end up higher than forecast. [mention=14]Hoosier[/mention] made a good point earlier about accretion rates potentially being higher farther north where the warm nose is not as warm. That's something to watch and another reason to be concerned about some locations overperforming ice wise. Another thing we'll have to watch observation wise is how cold the low level cold wedge remains. The December 28 2015 event that's been discussed verified colder at that level than model forecasts, and if something like that happens tomorrow, also could have a zone that stays sleet for a while until flipping back to snow. Finally, was a bit surprised my office and DVN didn't extend the advisories to the northern tier counties staying snow, since it seems they have solid potential to come in at near typical advisory criteria for snow anyway. Will be an interesting event to watch unfold. As someone who lives in the northern tier of LOT counties, I agree. 1 Link to comment Share on other sites More sharing options...
WeatherMonger Posted January 1, 2021 Share Posted January 1, 2021 34 minutes ago, WeatherMonger said: Hope HRRR is off it's rocker. Would be devastating for SW to East Central MO and wouldn't want that here either. NAM comes in less bullish yet still alarming. I'll take all the ice they can give if the power stays on. Link to comment Share on other sites More sharing options...
Natester Posted January 1, 2021 Share Posted January 1, 2021 7 minutes ago, WeatherMonger said: NAM comes in less bullish yet still alarming. I'll take all the ice they can give if the power stays on. Yikes! Significant shift north. Wouldn't be surprised if the edge of the precip shield clips us. At least winds won't be strong here. EDIT: Nevermind. Previous NAM run has the precip shield clip us too. Link to comment Share on other sites More sharing options...
McHenrySnow Posted January 1, 2021 Share Posted January 1, 2021 Only managed 24º today and down to 17º. I just want snow, please, weather gods, just some straight up snow. 1 1 Link to comment Share on other sites More sharing options...
sbnwx85 Posted January 1, 2021 Share Posted January 1, 2021 Already down to 20 at KSBN thanks to some local clearing overhead. Link to comment Share on other sites More sharing options...
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