Sun-Mon, Jan. 27-28th Winter Storm Threat Increasing Update #7

​(10:45AM - 1/27/19) Our storm system that we've been watching out over the northern Pacific Ocean over the last several days finally came ashore British Columbia in western Canada yesterday evening and continues to quickly come southeast across southern Canada in our direction this morning. This is the system that will end up becoming a fairly strong and impressive winter storm across portions of the Midwest, including for some here in Illinois. There have also been some important trends in the model guidance since last night as well, suggesting higher snowfall totals in Illinois.

​Lets dig into some details and what we can expect from this system across Illinois...

As we have mentioned over the last several posts, this system is still expected to move southeast across the northern plains through the day today and eventually enter the Midwest later tonight. There will be a fairly widespread area of snow with this system and we can expect by the late evening hours tonight that it will be moving into portions of northern Illinois. Looking at both the latest high resolution model guidance and radar right now, we can see that our area of low pressure is still located well to our northwest along with the snow that is now organizing across the northern plains.

Snow is slowly increasing in coverage across the Dakotas at this time in the circled area below and will eventually begin to make its way further southeast over the next 12 hours or so.

As stated above, snow will quickly overspread all of northern Illinois and portions of central Illinois late tonight and continue all through the overnight hours, especially across the northern portion of the state. Given strong forcing, very strong warm air advection and some steep mid-level lapse rates, snow could father rather heavily at times from about 9pm to 5am across northern Illinois, moving from west to east. The above mentioned atmospheric ingredients could lead to heavy snow snowfall rates of 1-2"/hr in spots but these rates would most likely only last for a few hours at most. Even so, there is the potential for significant snow accumulations in a fairly short amount of time (6-9 hour window).

As the strong area of low pressure approaches Illinois from the northwest tonight, winds will quickly strengthen and the strong gusty southwest winds will not only blow around the falling snow tomorrow night, we could see a period of blowing snow across northern and central Illinois tomorrow evening. This would be due to the last two evenings of accumulating snow and the light, fluffy nature of it. So when you throw in light, easy to blow around snow already on the ground, new snow falling, and winds potentially over 30mph early Monday morning, you could spell trouble for the Monday morning rush hour across the area.

​Depending on the exact track of the surface low, some model guidance is suggesting that temperature briefly warm into the low to mid 30's after the snow ends Monday morning and before the arrival of the arctic front later in the day on Monday. After a fairly brief warm up tomorrow afternoon, temperatures will crash quickly tomorrow night with temperatures below zero by Tuesday morning across much of northern Illinois.  

Even though it looks like the heaviest swath of snow is going to end up just north of us across southern Wisconsin, Illinois will not be escaping this one as several inches to possibly 6"+ of snow out of this system. We have added an area of 6-9" of snow further south into a greater area of Illinois, while extending the 3-6" further southward. South of the 3-6" corridor, amounts will taper off to 1-3" down south of the I-80 corridor.

MP

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