Thursday weather analysis

I thought I’d discuss our upcoming weathermaker a little differently. Don’t be scared off by the image to the left – it describes the complexity of the situation excellently.

That image is called a Skew-T diagram (since the temperature lines are skewed to the right). We’re basically taking a vertical look through the atmosphere at 7 p.m. Thursday using our friendly GFS weather model. I’ve highlighted a few important features.

First, the red line is the temperature, and the green line is the dew point. The two lines are right next to each other, which means a good chunk of the atmosphere is saturated at the time we’re looking at. So, the precipitation won’t be evaporating as it falls – it’ll be making it to the ground without a problem. The blue line is the freezing line. If the temperature goes to the right of it, then it’s above freezing at that point… to the left, below freezing. Now that we’ve got those introductory bits out of the way, let’s explore the numbered parts.

#1: In the lower-levels, a wind out of the northeast is occurring. This will be pulling in air from the northeast, where there will still be some snowcover (it takes a while to melt a foot of snow, as we all know) as well as the cool waters of Lake Michigan.

#2: The temperature at the surface is barely above freezing. If we can stay above that critical temperature, we won’t have to deal with ice. However, any change in the surface temperature will have a significant impact on the forecast… especially if it drops only one or two degrees. If we get below freezing at the surface but keep a warm layer aloft (which I’ll discuss next), then we’ll be facing a more icy situation.

#3: A nose of warm air aloft will try to work its way in here. That would cause precipitation to be in a liquid state, then freeze as it descends. So snow wouldn’t be a big issue – it’d become more of a sleet/ice scenario at that timeframe.

This is just a snapshot that one model is showing. The GFS has performed fairly well this winter, so we’re not straying too far from what it’s been showing. Through the day Thursday, we’re still expecting to be very close to that oh-so-important rain/snow/mix area. As explained above, the precipitation type hinges on what our temperatures are doing at the surface and aloft. I really am not exaggerating when I say that a one-degree change will affect what we see falling to the ground and if it sticks.

Let’s hope that things become more clear in the next 24 hours!

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This post was written by qni_it on March 25, 2008

Tonight’s system: Moisture starved

Low pressure will skirt across the Upper Great Lakes tonight and early Tuesday bringing some rain and snow to the Midwest. Accumulating snow will occur from Minneapolis/St. Paul over to Green Bay with some wet snowflakes or light rain showers from Rockford, northward. There won’t be huge amounts of moisture with this system because an area of high pressure over Dixie will keep the Gulf of Mexico shut off.

The next system that works down the pike won’t have the same fate. A high-precip event is possible for Thursday/Friday of either variety, rain or snow. We’ll blog more about this in coming hours/days. -ERIC
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This post was written by qni_it on March 24, 2008

Weather & Wildlife

RabbitThe Easter Bunny’s big day is over for another year, but did you know the original “bunny” was actually a hare? Hares are a close relative of rabbits but have a few key differences:

  • There are many species of rabbits and hares, but generally, hares tend to have longer legs and larger ears and are generally bigger than rabbits.The snowshoe hare is an exception with its small ears that help prevent heat loss. Large ears have more surface area and lose more heat.
  • Hares are incredibly swift and run from predators, while rabbits typically hide first, relying on camouflage, and only run as a last resort.
  • Hares give birth to precocial young which means their babies are born covered in fur, have open eyes, and are ready to run shortly after birth. Rabbit babies are furless, blind and helpless at birth.

Find out more amazing Easter Bunny trivia and rabbit facts at enature.com.

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This post was written by qni_it on March 24, 2008

Northwest flow is no friend of mine

Before heading off to work this afternoon, I was sitting in my living room eating lunch and had some mealtime entertainment in the form of sparrows and robins hopping around my deck and the tree outside the window. I think the robin was just poking around for a little food, but the sparrows looked like they were collecting any small twig, pine needle, or other scrap that could be used to build a nest. It’s so nice seeing and hearing the birds, even if it isn’t warm out yet.

I was also surprised to see so much sunshine today! It was “self-destructive” just not too far from Rockford, though, as it led to instability and pockets of small snow showers. When I went to the grocery store, I saw the bank of puffy cumulus to the west and got nervous, worried that some heavy-duty snow was going to come in and doubly bust my forecast. My meteorologist buddy in Cedar Rapids, Iowa calmed my fears and said that even when the snow came down pretty good, it wasn’t sticking.

I suppose I should say something about the image I posted above. We’re in northwest flow, which means our upper-level winds are coming from – you guessed it – the northwest. When we’re in such patterns, we tend to experience below normal temperatures. Disturbances also ride along the flow and impact us fairly frequently … to the tune of once every few days. This week, we’re under northwest flow, which explains the cool highs and two rain chances in the forecast. The Monday night/Tuesday system will have trouble scooping up Gulf of Mexico moisture and precipitation should be pretty minimal, but the system at the end of the week bears some watching. We’ll once again be riding on a sharp temperature gradient on Thursday and Friday. For right now, I’m sticking with the warmer side of things, but I’m seeing a few indications that our highs will have to have several degrees shaved off.

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This post was written by qni_it on March 23, 2008

Chilly Easter

I’m sure many of you have gotten that email forward that says that the last time Easter was this early was 1915 and the next time it’ll fall on March 23 will be in 220 years. Regardless of when it is that it happens next or when it last was, you can easily imagine that there’s always that chance that the latter part of March will still be cool with some snowflakes flying. That will be the case tomorrow.

A weak disturbance will push across the Upper Midwest tonight. It already has been producing a bit of snow in Minnesota and Iowa, but the air in that area is pretty saturated. Out our direction, the dewpoint is still about ten degrees away from the temperature, so evaporation will be an issue. Once we can close that temperature-dewpoint gap, some light snow will become possible. I don’t expect any accumulations other than a dusting at most, and the chance of seeing snow in one particular location is fairly low. So, I don’t expect this Clipper to provide any reason to change your plans – it’ll just add insult to injury of clouds, northwest winds, and highs in the upper 30s. The upcoming week is looking better, at least in the temperature department… highs getting back to more seasonable levels. That, along with the rain in the forecast, will get rid of the snow that hasn’t already melted.

I also have to point out that today is the 150th birthday of Iowa State University, the school from which Adam Painter and I both received our meteorology degrees. In celebration, and as a jab at Eric who gave me a hard time at spotter training this morning for being an Iowa Stater… Go Cyclones!

-Justin

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This post was written by qni_it on March 23, 2008

Snowfall Totals as of 5pm Friday

The image to the left is the forecast we gave on 13News 10@10 Thursday night. On the right is a plot of the official reports from the National Weather Service for this storm. Rockford officially received 4.5 inches of snow while areas around Beloit, Wisconsin had a half-foot. The Milwaukee metro got buried with this event with over 12 inches reported in the south suburbs! For more information on Milwaukee area snowfall totals, click here.

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This post was written by qni_it on March 21, 2008

No Good Weather for Good Friday

(12:34:48 PM) iembot: Lake Geneva [Walworth Co, WI] trained spotter reports SNOW of M6.0 INCH at 12:04 PM

Update 12:30pm:
The worst of this snow storm is behind us, but the roads are going to remain pretty poor throughout this afternoon. Drier air is moving in, as witnessed by the clear radar scan over Jo Daviess, Stephenson, Carroll, & Whiteside County. The heaviest snow this afternoon will be in southern Wisconsin and in portions of Illinois east of I-39. The entire region should dry out by 9pm tonight. The wind won’t quit anytime soon. These gusty east winds will continue to roar into the overnight hours. The guest that we had in for our interview segment on the noon show said, “the roads are horrible”. Needless to say, if you don’t have to venture out into this mess this afternoon, you might just want to get cozy on the couch! Adam Painter here signing out for this Friday and passing the baton onto the main man Eric Sorensen.

(12:21:09 PM)
iembot: 4 Nw Rockford [Winnebago Co, IL] trained spotter reports SNOW of M4.0 INCH at 12:15 PM CDT — storm total…2.5 since 7am.

(12:19:01 PM)
iembot: De Kalb [De Kalb Co, IL] trained spotter reports SNOW of M1.0 INCH at 12:15 PM CDT — sleet…freezing rain…and snow

(11:44:54 AM)
iembot: Clinton [Rock Co, WI] trained spotter reports SNOW of M2.5 INCH at 11:41 AM

(11:44:53 AM)
iembot: Monticello [Green Co, WI] trained spotter reports SNOW of M4.5 INCH at 11:36 AM

(11:28:24 AM)
iembot: Evansville [Rock Co, WI] trained spotter reports SNOW of M3.0 INCH at 10:55 AM

Update 11am:
I just measured 3.5″ of snow outside of the WREX studios in western Winnebago County. Snow still falling at a steady clip with visibilities less than a mile in some spots. Any measurements that you have in your backyard that you would like to pass along email me at apainter@wrex.com or Eric after 1pm at esorensen@wrex.com.

Update 9:55am: National Weather Service in the Quad Cities has canceled the Winter Storm Warning for the counties of Jo Daviess, Stephenson, and Carroll. They have also canceled the Winter Weather Advisory for Whiteside County. Windy conditions with some snow is expected in these parts, but the heaviest snow will stay to the north. My thinking is that with that 4 to 9 inch forecast range Rockford will be on the low end, while Monroe, Janesville, and Lake Geneva approach the high end.

Update 9:45am: Model data is conflicting itself. It is still cranking out heavy precipitation this afternoon even though drier air will be moving in higher up in the atmosphere (700mb). This tends to shut off snow high up in the clouds.

Update
9:30am: Intense band of precipitation moving through right now stretching from Rockford to Polo to Sterling. Snowing hard right now with wind gusts in many areas around 30 mph. Roads are certainly slick, with already a few reports of cars in the ditch.

Original post: A WINTER STORM WARNING continues through midnight tonight for all counties in the Stateline viewing area except for Whiteside County.

Last night, Eric upped the snow totals slightly and I can’t find enough strong reasons to downgrade those amounts this morning. The snow began around 3am this morning, and as of 7am I measured 2.1″ of snow west of Rockford at the WREX-TV studios. The snow likely will pick up in intensity again late this morning and continue at that pace into the afternoon hours. This storm should still be kicking out snow around dinnertime, but the accumulating snow should be done shortly after 9pm.

This forecast is incredibly tricky, because the distance between the haves and the have nots is going to be minuscule in the spectrum of the atmosphere. Beloit is separated from Rochelle by 45 miles. Beloit could end up with between 8-12 inches of snow, while Rochelle receives a mere inch or two.

Despite the sun being up, keep your headlights on all day today. Blustery east winds at 15-25 mph are going to whip those snowflakes around and cause low visibilities on area highways. For those with travel plans: the driving conditions are going to be the worst in southern Wisconsin. I’ve spoke with a few meteorologists who are forecasting around a foot of snow in Madison and Milwaukee. -ADAM

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This post was written by qni_it on March 21, 2008

New data: All over the place!

10:30pm – For what its worth, the new GFS computer model is mixing quite of rain into the storm during the midday hours of Friday. This would significantly cut down on snowfall amounts…perhaps back to our 3-6 inch range. I am throwing my hands up in the air for tonight. Adam’s got the duty beginning at 5:30 in the morning. Updates right here as we get the data! -ERIC

10:00pm – Here’s the updated snowfall forecast for the surrounding areas. Because this storm is a straight west-east storm, developing overhead I am not going to buy into the 12″+ scenario areawide. The highest threat of significant snow will exist in SE Wisconsin and far northern Illinois. Snow will begin tomorrow morning and continue through Friday night. Updates here first! -ERIC

Here are a few raw pieces of model data indicating snowfall potential. (Third image from the pro-site at accuweather.com) Now, these should NOT be taken as God’s Word, but can’t be discounted. It seems to me that there is now a potential for some areas to exceed one foot of snow, particularly in Southern Wisconsin from Janesville/Beloit eastward to Lake Michigan.

One more disclaimer, precipitation type, ground temperature, and convective (thunder) potential should be weighed in here. I have a model that is giving RFD 5 inches of snow in ONE HOUR. That’s highly unlikely so this should be taken with a huge grain of salt.

Either this storm will be very mixy with snow/rain or this snow will be a record-breaker. Unfortunately, I have no idea which one is the correct scenario. Bottom line: all travel interests should closely monitor forecasts tonight/tomorrow. -ERIC

This is accumulated snowfall from accuweather.com

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This post was written by qni_it on March 21, 2008

Major snowfall on the way

Update 3:30pm: I am going to keep the 3-6 inch swath going for the Rockford metro, but hike up McHenry and Lake Cos. into the 6″+ range. Should thunder be heard, we will go above 6 inches here in Rockford. Should we be mixed with rain for a time, totals will be lower. Areas south of I-88 may see a slushy inch with a higher threat of heavy rain/thunderstorms. -ERIC

Update 3:00pm: We’re pretty much staying on target with this system. It appears the snow will begin shortly after midnight and ramp up during the 2-6am timeframe. Thunder appears quite possible as upward forcing reaches its peak during the predawn hours. With the convective nature of this system, extremely heavy snow is possible…perhaps in the 2-3 inch per hour range. As mentioned earlier, we have a few things to consider this time of year: our ground is above freezing to a depth of three inches. Falling snow will have to overcome melting from ground. Another thing is the fact that this may not all be snow. Should we transition over to rain at any given time, snowfall totals will be significantly impacted. Of all of the snow systems thus far this winter (and early spring) this one is the trickiest! Will hold onto a solid 3-6 inch forecast for North-Central Illinois, but will be highlighting the higher end of that range. A few areas in McHenry and Lake County may see a 8-9 inch total…and if we can maintain the snow during times of thunder, a few 6″+ totals will be seen north of US20 in Boone, Winnebago, and Stephenson County. Snow-water ratios will be around 9:1 range meaning this is prime heart attack snow. Please do not shovel this snow if you have a health condition! More to come. -ERIC

Update 12:30pm: The latest model guidance continues to show a pretty potent storm impacting us on Friday. It is still cranking out a lot of precipitation, but it appears the end of the storm is being bumped up a bit. I’m looking at the precipitation (mostly snow) to start around 3am. As depicted by the graphic to the left, it will be the heaviest during the morning hours as the low spins just to our south. It will lighten up a bit during the afternoon, and taper off during the evening hours. The axis of heaviest snow appears to be on a line from Monroe, WI to Rockford and on through Chicago. Even though wind speeds tomorrow will range between 15-25 mph out of the east, blowing and drifting snow won’t be a big deal because of how heavy and wet the snow will be.

Update 11:05am: The National Weather Service in Chicago will be upgrading the watch to a warning shortly for all of northern Illinois.

Update 5am
: The WINTER STORM WATCH (light blue) has been extended to include Whiteside & Lee Counties. Also, the National Weather Service office in the Quad Cities has taken the liberty to upgrade the watch to a WINTER STORM WARNING (red) for Jo Daviess, Stephenson, and Carroll County. The rest of the region will probably be upgraded to a warning this afternoon. No doubt the entire viewing area is going to run into poor travel conditions on Friday.

Original Post: A WINTER STORM WATCH is in place for the majority of the viewing area. The only counties not included in this watch are Whiteside and Lee Counties. Simply put, if you have holiday travel plans on Friday… you might want to move them up to Thursday night.

This storm system will start kicking out precipitation shortly after midnight Friday morning. If you live along Interstate 88 you are going to encounter a mix of rain and snow, but if you live north of Highway 20 it appears as though the majority of the precipitation will come in the frozen form. There is a lot of moisture to work with in this storm system, so some fairly hefty snowfall totals by March standards are quite possible. At this point, the highest totals appear to be along the Wisconsin/Illinois border. The snow that does fall is going to be the heavy and wet variety. Temperatures during the storm are set to be sitting in the low to mid-30s. Because of this, some of the snow will be melting as Friday progresses, which could limit some of the higher snowfall totals. This is going to be an all day event with the precipitation finally winding down early Saturday morning. -ADAM

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This post was written by qni_it on March 19, 2008

Capron & Friday’s weathermaker

I just found out I was mispronouncing the town of Capron for this morning’s Weather Kid! My apologies to those of you who may have been a bit bugged by that. I’ll be saying it correctly in the future! 🙂

Adam blogged about the Thursday night/Friday weather system yesterday and, since it’s pretty much the only upcoming weather of note in our area, I’ll discuss it too. He discussed the surface features and the complications with them. I’m going to put my head in the clouds and take a look at the temperatures aloft and why they matter for Thursday night and Friday.

The two images are basically where the two main computer forecast models are showing the freezing line location at 850 millibars, or about 5000 feet up, for Friday morning. The reason I’m looking at the temperature almost a mile up in the atmosphere is that there’s a simple rule that we were taught in meteorology classes that relates to it: if the temperature at this height is above freezing, we will not get snow. However, if the temperature is below freezing at this height, any type of precip can fall, depending on the surface and near-surface temperature. Now, your first thought may be that this rule doesn’t really help us out that much, but in this springtime scenarios, they’re one of the few things that can really help us try to narrow things down.

The left image is what the GFS model is showing. It keeps Rockford below freezing aloft for the entire duration of the event (although a 50 mile shift northward puts us very near or just above freezing aloft). The consequence is that any type of precipitation may fall and that the temperatures at the very lowest levels of the atmosphere will determine what actually hits the ground. Now, the image on the right is what the NAM model is showing, and it keeps the freezing line aloft well north of Rockford until Friday night. If the NAM were to verify, snowfall would be basically nil (especially considering the winter we had).

So where does that leave us? Well, it leaves us in a very tough-to-forecast situation. The GFS has been doing considerably better than the NAM (and its biases easier to figure out) so we’ve been strongly leaning in its direction on many systems that have come our way. The best prediction we can really make right now is for a wintry mix and try to iron out the details over the next day as the low develops and can actually be “seen” by the observation networks.

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This post was written by qni_it on March 19, 2008