(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.
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Once again a Happy Thanksgiving and safe travels to all!
Thanksgiving week will start out featuring mostly quiet weather for Illinois. A couple weak weather disturbances will move through the state Monday and Tuesday morning. The first will breeze through southern Illinois early Monday, bringing some light mixed precipitation. Another will drop south Monday night and early Tuesday morning bringing a shot at some light snow across mostly northeastern Illinois. Right now any snow accumulation looks to be minor at best - 1" or less.
Temperatures will quickly moderate in the middle of the week as southerly flow returns. By Thanksgiving we should see temperatures at a comfortable seasonal level. Mid 40s north and 50s south. With the sun coming out if should feel nice - especially when compared to our recent cold snap.
Medium range models hint at things switching to the more active side Friday and beyond - but with typical track and timing differences. One potential weather maker arrives Friday bringing mostly a light rain threat due to temperatures returning to the mild side.
Afterwards, a stronger low pressure system may develop bringing a chance for a heavier, wind driven rain. If enough cold air wraps around the back side we could be talking about our next snow maker by the weeks end. That system is still 7+ days out though, so we will see how things continue to evolve.
Here are the highlights mentioned above as seen on some of the models.
Potential for light snow on Tuesday - not looking like too big a deal right now.
Approximate highs for Thanksgiving - with mixed sun and clouds!
Friday weather maker - right now temperature profiles support mainly a light rain threat.
Models hinting at a stronger low pressure system to develop around Sunday. We will see if this becomes anything.
So right now there isn't too much to be concerned about - but we do have a couple systems to monitor, especially towards the later part of the week.
From all of us here at ISC we hope you have a wonderful Thanksgiving and safe travels to all your families!
Good afternoon, Illinois residents. Our first significant winter storm of the upcoming winter season is about to get underway. Watches have been upgraded to Advisories and Warnings (see graphic below) in advance of the wintry precipitation.
'Overall, not much has changed from yesterdays forecast. Trends have shown a slight shift west with the storm center track, and much of the model guidance has shifted the snow potential a little further north and west than compared to yesterday.
Forecast amounts haven't changed much, with 4-6" expected across areas that are in a winter storm WARNING. Locally higher amounts are possible in these areas depending on the strength of any convective snow bands.
The below model plot, taken from the hi-res NAM shows the precip potentially reaching further north and west than we saw yesterday, and trends seem to support this. This will not occur until Thursday morning however, when the storm is in a weakening phase. We are not expecting any serious accumulations across northern Illinois but some areas could see an ill-timed inch of snow during the morning commute, just enough to create some road hazards, so be prepared for that.
Our latest TAM has been adjusted to reflect these new developments. We should see a healthy 3-6" swath of snow across much of central and southern Illinois. The areas that should see the most snow will Southwest Illinois, near the St Louis area. These are the areas that are currently under winter storm warnings.
While far from the worst snowstorm we've dealt with across this region. The early timing and location makes it somewhat unusual given the strength and amounts forecast. Safe travels everyone!
Winter is making an early presence across our state this fall (yes technically it is still fall.) We've been dealt abnormally cold temperatures and a couple early season snows. These snows were relatively minor - as early season snows tend to be. That will change Wednesday night as the first real winter storm potential targets parts of southern Illinois. Early indications are some areas could pick up as much as 4-6 inches of snow with locally potential higher amounts.
The National Weather Service has issued winter storm watches for the areas where the heaviest snow may fall. Mainly across Southern Illinois. We expect most of these areas to be upgraded to advisories as warnings as early as Wednesday morning.
Wintry precip, perhaps mixed with sleet and rain at first, should begin entering southern Illinois late Wednesday evening
As temperatures fall during the night and the associated surface low strengthens, any mixed precip should change to all snow, and come down in moderate rates overnight Wednesday into Thursday morning. The Thursday morning commute could be heavily impacted.
The entire system will move northeast, with lighter snow and accumulations spreading as far north as Chicago and Peoria. In those places, much less snow is expected, perhaps a dusting to an inch. The areas downstate will experience heavier snow for a much longer duration and that is why we anticipate the heaviest snow there. The entire system should exit Illinois by Thursday evening, say around 8pm.
SNOWFALL TAM: First Look
Below is our first TAM outlook for the upcoming event. An area of heavier snowfall will likely be added as trends continue to be monitored. Stay tuned for more updates as the event gets underway