(10:00PM - 11/25/18) A short term/quick update on the blizzard that is currently affecting portions of the state...
The rain/snow line currently sits from downtown Chicago, down towards Central Illinois. This is steadily pushing east, with a transition to snow occurring. Heavy snows are likely overnight across a good portion of Northern and Central Illinois. Winds gusts of 30-50mph will also continue to be likely, leading to blizzard conditions. Additionally, the heavy/wet nature of the snow combined with the high winds will likely lead to widespread tree damage and power outages.
Our earlier snowfall TAM is still on track, with a large swath of snowfall totals of 9-12" being still likely, with localized totals of 12-15" possible as well.
The NWS has upgraded Cook County (which includes the Chicago metro area) along with Dupage, Grundy and Will counties all in Northeast Illinois. Rain is expected to transition to heavy, wet snow this evening.
Additionally, and the main reason for the blizzard warning, will be strengthening winds that will gust to around 50mph. This will make for extremely dangerous white out conditions. Travel is strongly discouraged.
Here is the warning text from the NWS.
Grundy-Will- Including the cities of Morris and Joliet 332 PM CST Sun Nov 25 2018 ...BLIZZARD WARNING IN EFFECT UNTIL 9 AM CST MONDAY...
* WHAT...Blizzard conditions expected. Winds gusting as high as 45 mph will cause whiteout conditions in blowing snow. Significant drifting of the snow is likely. Total snow accumulations of 4 to 8 inches, with localized amounts up to 10 inches, are expected. * WHERE...Grundy and Will Counties.
* WHEN...Until 9 AM CST Monday. Conditions will likely ramp up mid evening and overnight.
...BLIZZARD WARNING IN EFFECT UNTIL 9 AM CST MONDAY...
* WHAT...Blizzard conditions expected. Winds gusting as high as 45 mph will cause whiteout conditions in blowing snow. Significant drifting of the snow is likely. Total snow accumulations of 7 to 11 inches, with localized amounts up to 13 inches, are expected. * WHERE...DuPage and Cook Counties.
* WHEN...Until 9 AM CST Monday. Conditions ramping up between 6 PM and 9 PM this evening, first across northwest areas. * ADDITIONAL DETAILS...Travel could be very difficult. Snow covered roads and significantly reduced visibility are expected. Snowfall rates in excess of 2 inches per hour are possible. This snow is expected to be very heavy and will be difficult to shovel. The strong winds and heavy snow may cause falling tree limbs and possible power outages.
(1:15PM - 11/25/18) The expected major storm system is now pushing into the region, with precipitation ongoing across portions of Northern and Central Illinois this morning and early afternoon. The only real change this update is to tighten snowfall gradients on our likely final TAM snowfall map and the increased likelihood of blizzard conditions.
Most of the precip this morning has been in the form of rain. As colder air filters in and cooling occurs from heavy precip rates, precip is now slowly transitioning to snow across portions of Northern Illinois. Snow will continue across portions of Northern Illinois through this afternoon, before becoming more widespread to encompass just about all of Northern Illinois and portions of Central Illinois this evening and into Monday morning. During the height of the storm, snowfall rates will likely reach 1-3" per hour across portions of Northern and Central Illinois. Thundersnow will also be possible during the height of the storm as well for some areas.
Another major concern is windy conditions, with wind gusts of 30-50mph likely across portions of Northern and Central Illinois this afternoon into Monday morning. The combination of heavy snow and high winds will create blizzard conditions across a large area this afternoon into Monday morning. Additionally, given snow with this system will be of high water content, some tree and powerline damage may occur.
The main swath of snow will be across much of Northern and portions of Central Illinois. Within this main axis, a large corridor of 9-12" of snow is likely. It is also likely that there will be pockets of 12-15" within that corridor.
Good morning everyone. It is Sunday, November 25th and our approaching winter storm is taking shape and slowly moving our way. Latest model trends continue so slow the system down ever so slightly, which may actually help boost snowfall totals.
The system will not be an all snow maker and will start out as rain. Using some of the latest high resolution (HRRR) model guidance we will try and lay out the changeover to snow and break it down for you all so we know what to expect, where and when. Keep in mind the times won't be EXACT.
Currently (9am at the time of this writing) we see a band of light rain moving slowly north across N IL.
This is well sampled by the model, an indication it (hopefully) has a good handle on the situation and goes in line with our general thinking.
As the system begins to strengthen and continue east, colder air will wrap around the backside - which is common evolution - and rain will change over to snow. First across parts of northwest Illinois.
The changeover will slowly move to the east, while at the same time dipping south as the cold air continues to wrap around. By early evening as the sun is getting to set, parts of northeast Illinois will begin to see a changeover. The Immediate Chicago area will continue to see rain longer due to a combination of on-shore flow from the lake, and synoptic placement of the weather system.
Later in the evening the change continues east. Timing the change for the Chicago area is one of the more difficult aspects of this forecast. Various contributing factors such as flow off the lake, urban heat island and system placement could delay the onset even later. Model runs go back and forth about the exact time which is impossible to pin down, but we are fairly confident it won't be until 8pm or later. Its worth noting that the precipitation will be quite heavy at this time. Thunder and lightning may also be possible.
Just a couple hours later, our system has fully strengthened and is now raging across the state. Chicago is potentially changed over to snow and the heaviest snowfall rates - possible blizzard conditions - are now occurring. Snowfall rates could exceed 1 inch per hour. The heavy rate of precip could make up for the later start time across parts of northeast and north central Illinois. Snow is beginning to wind down across West Central and northwest Illinois.
As we move into Monday morning the storm rages on, battering north central and parts of northeast Illinois with heavy, wet snow. Areas further south of Chicago area, along the I-55 and I-57 corridors, will changeover from rain to snow around this time. The snow will come down fast, but the late changeover will reduce accumulations in these areas (see TAM below)
As the system continues east throughout the morning, it will take the heaviest rates with it and snow will begin to slowly wind down across northeast and central Illinois. Current indications are the system should exit the state by Noon on Monday, probably earlier. We are still continuing to monitor progress, and if the system continues to slow down these times may be delayed so stay tuned for further updates!
Below is a look at our current TAM. This map may be refined as the day progresses. We are still anticipating upgrades to blizzard warnings as well. Regardless if that occurs, conditions will be dangerous and travel is not advised. Hunker down, and stay safe today!
Text ISC to 900900 to receive alerts from ISC via the in-telligent app
(12:30PM - 11/24/18) Evening model data that has come in the past few hours is in fairly good agreement on track and intensity of the upcoming snowstorm, and with heavy snowfall totals likely. Most models are on the northern side of the envelope, but short term analysis would suggest the southern solutions is the way to go. For now will side with a southern-middle solution.
With that said, a swath of accumulating snow is still expected across much of Northern and portions of Central Illinois Sunday morning through Monday morning. Within this general axis of snow, a narrow corridor of 9-15" will be likely. This axis will likely be across Northern Illinois, from in the vicinity of the Quad Cities to around DeKalb to around Waukegan.
One thing you might notice by reading this update is Monday morning is now being mentioned. One of the changes that has been increasing each cycle of model guidance is the storm lasting longer, on into Monday morning for some areas. This slowing trend may continue, which could lead to falling snow still occurring for some areas during the Monday morning rush period, including the Chicago area.
In addition to the expected snowfall, winds will be an issue as well. As the storm passes through the area, winds will increase on the north and northwest side of the storm system. Wind gusts of 30-45mph will be likely across portions of Northern and Central Illinois Sunday afternoon into Monday morning. Wind gusts may reach around 50mph in Chicago near Lake Michigan as well. This will likely lead to blizzard conditions at times for some areas.
It's only late November but Mother Nature never likes to care what time of year it is and she's getting ready to throw a major winter storm together and impact all of northern Illinois during the day tomorrow and into the evening as well. It is very rare to get significant winter storms across this area during this time of year but tomorrow will be the exception with possible blizzard conditions along with 6-9" of snow, locally close to a foot in places across northern Illinois by late tomorrow night. I dig into the details below....
As usual, I like to get a first look at a CONUS water vapor loop and we can see that our system of interest, which looks fairly impressive on satellite, is slowly spinning its way across Wyoming with associated jet streak across portions of Utah and Colorado late this afternoon. This upper level low is forecast to continue southeast, crossing the Rockies tonight and emerging into the plains early tomorrow morning, before turning more easterly and it moves through the central plains.
As we go through the overnight and early morning hours tomorrow, low pressure will develop on the lee side of the Rockies across eastern/southeast Colorado before turning and moving east along the KS/OK border. As this is occurring, low level winds will be responding to the pressure falls occurring across the plains to the east of the developing cyclone along with strengthening as well. The strengthening will increase warm air advection and moisture transport northward up into the heart of the central plains (Nebraska/northern Kansas) and this in conjunction with large scale lift from the wave/upper level low itself, a large precipitation shield (including snow) will develop overnight tonight and into tomorrow morning. Also as you'll see in the loop below, cold air advection will also get going on the north side across the northern plains as colder air advects southward.
By late tomorrow morning and afternoon, the strong surface low and associated precipitation shield on the northwest side will be turning more to the ENE as the system moves through the state of Missouri. Right now, there is fairly good agreement on the surface low tracking from extreme southeast Kansas to just north of the St. Louis area from mid-morning to late afternoon tomorrow. With a storm moving ENE along this path, it is usually a favorable track for heavy snow across northern Illinois.
As the upper low and cyclone strengthen into tomorrow afternoon, low wind winds will really increase across most of Illinois, especially across the southern half of the state in the warm sector. This will lead to very favorable and continued moisture advection/transport up and over into the cold conveyor belt across portions of Iowa, Missouri and into northern Illinois.
Another favorable aspect of this event is the very impressive mid-level frontogenesis signal that will develop over portions of northern Illinois and this will act to lead to and enhance snowfall with a SW-NE or WSW-ENE heavy band of snow to setup somewhere across the area. Models are good in a lot of ways but they are not that good in being able to pin down the exact location, at least yet of where this potentially narrow band of extremely heavy snow will be. Even so, the signal is there for it to develop. This frontogenesis in tandem with very steep mid-level lapse rates and very strong large scale forcing could lead to some intense snowfall rates greater than 2"/hr and also the possibility of some thundersnow as well.
All these above ingredients mentioned will lead to period of potentially very heavy snow across northern Illinois tomorrow favoring the late afternoon into the late evening hours as rain changes over to heavy snow from west to east, as the surface low moves through central Illinois and into Indiana. As mentioned, there could be a several hour to 6 hour period over the Chicago metro area, at least way from the immediate downtown Chicago proper, where snow is falling at rates of 1"/hr or more and this could lead to rapid accumulations. There is also going to be chances for thundersnow as well in the deformation band tomorrow evening, also leading to impressive snowfall rates.
Surface temperatures will be marginal at first for accumulations but as the surface low passes to our south and southeast, cold air advection will continue to advect colder temperatures at the surface more southeast into more of northern Illinois. This will lead to snow ratios slowly becoming more favorable by evening along with snow being able to stick and accumulate easier.
Another big factor in all of this will be the strengthening northeast winds as the surface low approaches northern Illinois from the south and southwest. Numerical model guidance is forecasting winds just off the surface tomorrow night to be as high as 50kts, which is reminiscent of some of the more recent blizzards we've seen across this area, most notably the GHD I blizzard of 2011 and the GHD II blizzard of 2015 where both those events had winds as strong and even a little stronger than what is forecast for tomorrow night. As the pressure gradient tightens, winds at the surface will strengthen to 30-40mph by late afternoon and more so into the evening hours with gusts potentially as high as 45mph.
Snow will end from west to east early Monday morning, especially across northeast Illinois with cold air advection continuing on Monday, and with a fresh snowpack down, expect well below normal temperatures and frankly downright cold air the start the work week.
All in all this is going to be a major winter storm for northern Illinois and the Chicago metro area with a large swath of expected snow totals in the 6-9" range and a narrower swath of 9-12" expected, given all the favorable ingredients mentioned leading to the potential for some seriously impressive snowfall rates in both the frontogenesis band tomorrow afternoon and the deformation band tomorrow night. Below is our latest thinking from ISC on expected snowfall totals. We will have a full update after model guidance comes in this evening.
(11:30AM - 11/24/18) A morning update regarding the expected snowstorm across portions of Northern and Central Illinois, from very late tonight/very early Sunday morning on into late Sunday night...
Morning model guidance coming in is trending towards a better consensus on track and the potential for higher snowfall totals with this system. With that said, there will be a swath of accumulating snows across much of Northern and portions of Central Illinois. Within this main axis, a corridor of high snowfall amounts upwards of 9-15" are likely.
Temperatures will likely be falling from the mid-30's down into the upper 20's during this event, meaning this will be a heavy/wet snow, with high water content. Due to this, snow rations will be lower that what's often seen during winter. Even with that, high snowfall totals are expected given the high amount of precipitation expected, which will be 1.50-2.00"+ liquid equivalent in the main swath.
Wind will also be a concern from Sunday afternoon into Sunday night. Winds on the north and northwest side of the storm system will increase, with gusts of 30-45mph likely across portions of Northern and Central Illinois. Winds gusts around 50mph could be possible near Lake Michigan. The combination of the expected high winds and heavy snowfall will likely lead to near blizzard conditions for some areas.
Below is our updated TAM depicting expected snowfall amounts. Further updates on this system are likely through the day and into tonight. *It should be noted that due to mild lake waters, snowfall totals will be lower than depicted for downtown Chicago and areas near Lake Michigan. Map scale prevents this from being shown visually.
A brief update tonight regarding the potential snowstorm that will affect portions of Northern, and Central Illinois very late Saturday night/very early Sunday morning on into Sunday evening.
Evening model data has come in with an overall slight shift south from previous runs, but still a decent spread among guidance. While the exact location of the main axis is snow is unknown, it is fairly likely that within the main snow band there will be a corridor of 6"+ snow.
As mentioned above there is still a spread in model guidance. At this time we are favoring towards the south group of model guidance, which does have more support at this time. With that forecast, the main axis of snow would run from far N. Missouri and C. Iowa, up into much of Northern and portions of Central Illinois. Within that swath, a corridor of 6-9"+ of snow will be likely. Below is a visual representation of our current thinking on snowfall amounts, with our TAM map. Note that given the spread in model guidance, adjustments to snowfall amounts are possible. We will have further updates on this system on Saturday.
Over the last 24-48 hours, numerical model guidance has continued to both show a significant storm moving into the Midwest, including portions of Illinois along with coming into better agreement, at least to an extent on the overall evolution of this system as it moves into and through our area.
A fairly potent shortwave still out over the Pacific Ocean this morning is forecast to come ashore the Pacific Northwest tomorrow night and early Saturday morning and then dive southeast across the Rockies and emerge into the plains during the day on Saturday. It is after this where models start to diverge on exact solutions with regard to the exact track and strength of this system after crossing the Rockies, along the the potential for phasing with a northern stream wave that will be digging south and southeast into the northern Midwest from southern Canada. Even with these differences still at play, model guidance is consistent on a strong surface low moving east across the southern/central plains (the Kansas/Oklahoma border) later Saturday before turning it more northeast on Sunday.
As the strong upper wave dives southeast into the plains Saturday night, the strong surface low will continue east and northeast across the plains and into the western Midwest. As this is occurring, low level winds will be responding to pressure falls and this will mean stronger warm air advection and isentropic lift up and over the cold air, leading to a fairly widespread area of precipitation, some of it in the form of snow.
The surface low seen in the image above will then track into Missouri and eventually Illinois by during the day on Sunday, with a swath of accumulating snow from the central plains into portions of Iowa and Missouri, before moving into Illinois. As mentioned earlier, there still remains differences regarding the track and strength of this system and this has big implications on both snow amounts and the placement of the heaviest snow swath.
Timing wise for places in Illinois that look to see accumulating snow at this time would be during the afternoon and evening hours and possibly extending into the overnight hours as well depending on the exact speed of the system. Below is one models take showing rain changing over to moderate to heavy snow from west to east across western and northern Illinois by the late afternoon and evening hours and this is where several inches
Below is just one models take on forecast snowfall accumulations and is by no way a set in stone for sure forecast, so DO NOT TAKE IT VERBATIM at this range....
Good evening everyone. In my last article here - I talked about the potential for a bigger storm system to develop and affect Illinois on Sunday. We're still seeing this system appear on the models, and others have taken notice too.
In fact, I've already noticed a couple social media posts calling for a big snowstorm. While the system certainly carries the potential, there are a couple noteworthy things to point out at this time.
1 - Models still disagree on the placement and timing. Ill show below, but models still aren't in agreement on when this potential system will arrive. Some show Sunday, others Monday.
2 - The track could change drastically. One thing thats so hard about forecasting winter storms is even a 10 mile shift in the storm center can change the amount of snow someone receives by a great deal, or even mean the difference between seeing any snow at all VS just rain.
3 - It could still be too warm to snow. Ahead of the system, rapid warm air advection will take place. In fact, if certain forecasts pan out, much of IL could see temperatures in the 50s and 60s the day before. Cold air will filter around the backside, but will it be cold enough to snow? Some models say yes, others say barely.
So at thit, we continue to closely monitor the evolving forecast to get a better idea of what may happen. All we need for you to know is that something still appears to be brewing in the Sunday/Monday timeframe.
A first guess by me? Illinois will see mostly a rain event from this one, but these systems have a history of appearing too far to the north and west on the models when we are 5-7 days away, and a southward shift in the forecast track - which would put us at a bigger risk for snow - would not surprise me at all.
So lets take a look at some models and what we are seeing. First the GFS which has been pretty consistent in showing Sunday development. This seems like a good bet at this time.
But then we have the GDPS which shows a Monday system. At least they are both consistent in the strength and location, so there is that.
Here is a look at what we call an ensemble plot. Basically the model, in this case the GEFS is ran multiple times to see what the outcomes are. Here we can see many of them develop a storm, but with varying intensity and location. At this range this is pretty good agreement actually and confidence begins to increase.
And last but not least, everyone's favorite. A snowfall map. Given the current expected track it would seem most of the heavy snow targets Iowa and Wisconsin, but it is pretty close to our border. This is why we'll be watching the storm track closely. Shift it south or east by 25 miles and at least northwest Illinois could be in for a heavy snow. Unfortunately given the warm, wet nature of this system it could be that slushy heart attack type snow. This will not be a particularly cold system.
So like we always say everyone, stay tuned for the ever changing updates to the forecast! Especially as the days draw near.
We put out more frequent updates via the in-telligent app. To subscribe to those simply text ISC to 900900 to receive a download link!
Once again a Happy Thanksgiving and safe travels to all!