Temperatures warm just in time for spring's first weekend

Heat Alerts Out West:

Unseasonably and dangerous heat currently has a firm grip on the southwest United States. Cities from Los Angeles to Phoenix and Las Vegas are under Extreme Heat alerts as a strong high-pressure ridge, or "heat dome" has locked itself over the western U.S. 

  

Ridge Pushes East:

How is this relevant to our forecast?  The same dome of high pressure is expected to weaken and even push eastward over the coming days. This will help drive a noticeable warm up here at home, arriving just in time for the first weekend of spring. 

  

Temperature Trend:

Friday will be warm with highs in the upper 50s. We still have a minor uncertainty with Friday's warm up as we'll have to see how things trend with the timing of the first of two cold fronts. Behind said front, we then see surface flow turn to the south and southwest ahead of an even stronger frontal boundary. 

This, along with a decent amount of sun will allow temperatures to surge into the upper 60s Saturday afternoon. Sunday's warm up also depends on the timing of the cold front as one model (the European model) was quicker with the frontal passage. This displaced the milder air to our south, leaving afternoon temperatures in the 40s. However, the American model left some room for highs to briefly reach the 50s before cooling overnight into Monday. Next week starts off cooler with afternoon highs in the low to mid 40s.    

Why does snow melt so quickly in March?

 Recent snowfall has been quick to begin melting away especially with Wednesday's sunshine and afternoon highs pushing the upper 30s. But sunshine is not the only way to decrease the snow depth on the ground! Three main ways to melt away snow is through sunshine, sublimation, or latent heat release through higher humidity.

Heat from the sun is the most commonly thought of way to melt away snow, but this is especially true for later spring months. In December and January, the angle of the afternoon sun is much lower in the sky. While March and April feature a much higher sun angle, focusing more of the sun's radiation directly to the surface, which melts the snow faster even if the temperature were the same in March compared to January.

That was certainly evident Wednesday afternoon in the Stateline, with sunshine promoting rapid snow melt in Rochelle. Another way snow can disappear even when temperatures are not above freezing is through sublimation. That is when water molecules go straight from a solid state (snow and ice) into gaseous state (water vapor). This process is most common with ice cubes that you leave in the freezer for a long time. Even though the temperature in the freezer is never above freezing, the ice cubes can get smaller as individual water molecules turn straight into vapor and dissipate into the air.

Another way to melt snow is through latent heat release. That is when moisture from the air condenses onto snow, similar to how a cup of ice water "sweats" in the summertime. That process of condensation onto the icy surface leads to a release of latent heat, which cools the air around the snow but works to heat up the snowpack itself, only further melting it away. This is the main reason why snow can melt effectively even at night! When dew point temperatures are above freezing, the moisture in the air condenses onto the snow, melting it further!

We will have both the sunshine's radiation and a moist air mass over the next few days, so expect that recent snowpack to melt away rather quickly through the course of the weekend

Temperatures continue to climb following brief period of winter cold

 

We are beginning our climb out of the brief, but potent, chill we had the last couple of days which means spring-like warmth will soon return. For the rest of Wednesday evening, we'll hold on to the mainly clear sky before cloud cover moves back in later tonight. The increase in cloud cover is the result of an incoming upper-level disturbance from the northwest. We can see those clouds across the Upper Midwest and Plains, and few radar returns moving into northern Wisconsin.

While we may see a brief period of some light precipitation late tonight, it likely won't amount to much thanks to drier air we have down near the surface. Moisture increases aloft, which is why we'll see the increase in cloud cover tonight. But that moisture will be lacking the closer you are to the surface. This dry air will likely limit just how much precipitation, if any, reaches the ground. If we do end up seeing some light rainfall, we will have to keep a close eye on temperatures at the surface because they'll be very close to the freezing mark. However, I don't anticipate many impacts to the morning commute.

Temperatures will continue their climb through the rest of the week as a strong ridge of high pressure builds out west. This will bring several days of 90- and 100-degree heat to the Southwest. Closer to home we won't experience warmth quite that significant, but temperatures warming into the 60s - possibly back near 70 degrees - by the start of the weekend appear likely. The only 'fly in the ointment' would be any lingering fog or cloud cover due to the added low-level moisture from the recent snowmelt.

 

When does spring officially begin across northern Illinois

First Day of Spring:

We are progressing through what Tom calls the "belly of the beast" as winter is in it's final days, though it has been putting up quite a tough fight. The first day of spring is Friday. It officially begins at 10:46AM and that is the moment when the Earth's tilt allows the sun to shine directly over the equator.  

Amount of Daylight:

This is also the moment when daylight and nighttime are almost perfect balanced, marking the transition towards longer, warmer days across the Northern Hemisphere. After the equinox, our next astronomical milestone is the summer-solstice, also know as the longest day of the calendar year.  

  

Temperature Trend:

Milder air spills into the Stateline for the few days of spring, leaving us with 50s Friday, then closer to the 70-degree mark Saturday afternoon. Precipitation chances over this three day stretch will be highest on Sunday as that is when forecast models show a strong cold front pushing through.   

Light snow chances across northern Illinois taper off early

Scattered Snow Early:

Snow is still falling this morning as a weak storm system moves across the western Great Lakes. While totals have been minor, the snow that has fallen so far has been enough to leave roads in some counties partially covered. Those heading out early will need to give themself extra travel time. 

 

Snow chances should taper off before mid-morning, giving way to dry but partly cloudy conditions for the afternoon hours. The sunshine will give temperatures more of a boost than Tuesday, leaving afternoon highs just short of the 40-degree mark. 

 

  

Another Weak System:

Northwest flow continues to dominate the upper-level pattern, steering another weak disturbance in the direction of northern Illinois. Forecast models remain quite scattered with how much precipitation this system will produce, leaving us with just a chance for a few showers into Thursday morning. 

Light snow Tuesday night could create slippery travel for some

 

Clouds have filled back in Tuesday afternoon and evening ahead of our next clipper system that'll pull a warm front through the area later tonight. As it does, a period of light snow is expected to develop moving in from west to east overnight.

Dry air initially at the surface - surface dew points are in the single digits - will limit any snow from reaching the surface during the evening. But as more moisture eventually begins to saturate the atmosphere, we should start to see the light snow fall. Totals won't be much and most will remain under two inches. Look for the snow to move sometime after 9pm, although a few flurries could arrive a little before that.

The snow will be wrapping up before sunrise Wednesday but there could be a brief period of some freezing drizzle that mixes in before it comes to an end. Even though snowfall amounts will remain minor, when combined with the cold temperatures overnight, and ice/slush already on the roads from Sunday/Monday, we are going to see those slick and icy conditions continue into Wednesday morning. There was quite a bit of black ice Tuesday morning, and I anticipate there to be similar issues for tomorrow morning.

Bitterly cold St. Patrick's Day with additional snow on the way

Hazardous Travel Lingers:

Travel impacts from the latest blizzard continue into our Tuesday morning. As of 4:00AM , roads in a few Stateline counties including Stephenson, Carroll, and DeKalb County remain completely covered in snow and ice, especially in open areas. If you're heading out, be sure to use extra caution. 

  

St. Patrick's Day:

If you plan to celebrate St. Patrick's Day even further, make sure to bundle up. The bitter cold settling in behind Monday's blizzard will make for a harsh start to the day, with wind chills hovering around 10°  below zero. Even by this afternoon, wind chills will only "improve" to about 10°, and high temperatures will struggle to reach the 20° mark. Cloud cover will gradually increase into the evening as our next storm system approaches from the northwest.

Snow Chances Return: 

Forecast models show this weaker system sliding in overnight tonight, bringing the chance for scattered snow showers ahead of Wednesday's morning commute. While this won't be a major storm or compare to Monday's blizzard, it will be enough to lay down widespread 1"-3" totals. Expect slick and potentially slow travel early Wednesday. Overnight lows will briefly drop into the upper teens, then climb back into the 20s by Wednesday morning.