Today marks the first day of spring, and the new season officially arrives at 10:46AM. As we cross the vernal equinox, daylight and nighttime become nearly identical, and from here on out, we'll see the amount of daylight continue to grow.
Warmth Continues:
Spring begins where winter left off, partly sunny with afternoon highs in the low 60s. Forecast models show a cold front slipping through late in the morning in to the early afternoon. We're not expecting precipitation with today's frontal passage, but it will shift our winds around. By the afternoon, winds turn to the north, and then to the northeast overnight. This could bring the possibility for fog by Saturday morning.
This warm-up fortunately will carry on into the first weekend of spring. South to southwesterly winds on Saturday will give temperatures a huge boost, landing them in the upper 60s, close to 70°. By Sunday, a cold front moves in and shakes things up a bit, knocking temperatures back into the 50s and bringing a chance for a few showers throughout the day. Temperatures trend backwards briefly for the start of next week, landing in the upper 40s Monday.
Who remembers the heat wave much of the region experienced during the month of March in 2012? I know I do. The heat began early in the season during the month of March which sent many farmers into their fields to begin planting. But the jumpstart on the spring and summer warmth didn't come with much rainfall. March ended up just below the monthly average for precipitation at 2.09 inches (average 2.40 inches), and below average for snowfall. We were able to gain some moisture back during the month of April, but it was all downhill from there with several months in a row that ended up below their monthly average. This eventually led to extreme drought conditions over much of northern Illinois and southern Wisconsin that lasted well into the Fall season.
During the month of March many high temperature records were broken in a stretch of nearly 8 consecutive days of record heat: March 15th-18th, and 20th-22nd. The only day that didn't achieve a record was on the 19th when the high temperature reached 77 degrees, one degree away from the record of 78 set back in 1921.
We won't end up with any record heat this upcoming weekend, but temperatures will feel more like early to mid-May, rather than late March. Highs on Friday will warm into the low 60s but we'll likely see a little more cloud cover during the afternoon, which could limit the overall temperature - especially to the north in Wisconsin. Winds will turn back to the southwest Saturday which will push highs close to 70 degrees for the afternoon.
The recent warmth has aided significantly in melting the snow from the ground, with snow depth at the Rockford airport dropping to 1" as of Thursday afternoon. But unfortunately, that snow melt will be the primary source of soil moisture over the next week or so, with very little in the way of precipitation chances on the horizon.
The primary chance for any rain we have will come along a cold front Sunday afternoon, but even that does not come with much abundant moisture. Any rain showers we see will be relatively spotty in nature, with a good chance that parts or most of the area see no measurable rain at all.
This is not just the case locally but also across much of the country as well. The Weather Prediction Center highlights this well, showing zero precipitation across nearly the entire Central and Southwestern parts of the country. We only have that slim chance Sunday, but otherwise remain dry into the middle of next week.
That isn't great news for the Stateline which has already seen several dry months dating back to last fall. As of Thursday afternoon, soil moisture was quite dry across a large part of the Midwest, with nearly all in the Stateline under the 10th percentile of the moisture we should have. The dry spots also correlate with the latest drought monitor released today. Some moisture will soak in from recent snowmelt, but we will not see much precipitation add to those totals in the near term.
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.
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
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.
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 daysof 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.
