The featured chart is a timeseries from the Cantril RWIS site showing air, pavement, and sub surface temperatures since last Thursday. The impact of having sunny days on temperatures can clearly be seen with the textbook delayed response as you go deeper into the ground. The black dashed line is the temperature at 60 inches which was warming this past weekend while everything else was cooling off. While the impacts of sunshine near the surface have a daily signal, the deeper you go the slower things vary. You can even notice the difference between 8 and 16 inches.

Voting:
Good = 17
Bad = 9

Tags:   rwis  

This past weekend's blizzard brought traffic to a near halt across the state as blowing snow reduced visibilities to near zero at times. The featured chart looks at the combination of NEXRAD radar reflectivity, near surface wind speed, and observed traffic speeds from the RWIS site near Adair along Interstate 80 west of Des Moines. The chart clearly shows the impact of precipitation on traffic speeds as the arrival of snow caused traffic to slow around noon on Saturday. The situation deteriorated throughout the afternoon as more snow fell and thanks to 40 mph winds that blew around enough, eventually leading to road closure later that evening. Winds died down by Sunday morning and road crews were able to get I-80 open once again.

Voting:
Good = 37
Bad = 3

Tags:   rwis   winter1011  

If did not take much rain on Saturday evening to turn Iowa's roads to a sheet of ice. The featured time series is from the RWIS site on US Highway 20 near Waterloo. The green line (dew point) tells the story of what happened to cause an icing event. Moist air was surging into the state on Saturday with air temperatures hovering just below freezing. Since the cold air was shallow and near saturation, rain was able to fall to the ground without much evaporation nor phase change and then immediately freeze as pavement temperatures were below freezing. The timing of this event late in the afternoon followed by a cold front passage both conspired to prevent most any melting over night. Cold temperatures on Sunday kept nearly all of this ice around on untreated surfaces.

Voting:
Good = 17
Bad = 10

Tags:   ice   rwis  

The featured chart is from the Marshalltown RWIS on Sunday into Monday morning showing air temperature and 3 pavement temperatures. The plot shows pavement temperatures warming nicely during the day with air and dew point temperatures creeping above freezing (implying a lot of liquid water on the road way). By later in the afternoon, colder air moved in and you can see the rapid drop off of temperatures and also notice the little bump in pavement temperatures near freezing when some heat is released by the water freezing around 4 PM. Roads remain slick this Monday morning.

Voting:
Good = 16
Bad = 8

Tags:   ice   rwis  

The featured graph is from the Ames RWIS site for the past 24 hours. While air temperatures (red) only reached 25 degrees, pavement temperatures reached 45 degrees at a rather rapid rate. The pavement then cooled off to the air temperature late in the evening with the loss of solar heating. Then around 2 AM, there is a change in the cooling rate. This is a result of the sky clearing allowing rapid cooling. You can generate plots like these here.

Voting:
Good = 20
Bad = 6

Tags:   rwis  

A surge of very moist air made it into the state on Sunday with dew points (green line) rising into the mid 50s in Ames (RWIS site shown). If you get up before noon on Sunday, you should have noticed most surfaces being wet. The reason was that the dew point temperature was warmer than surfaces such as pavement, so air right next to the surface will cool to its dew point and water will be condensed out. The featured plot shows this as the 3 pavement temperatures become nearly equal during the morning hours before temperatures warm well above the dew point. You can also see the effects of the cold front that sweep out the moisture late Sunday night.

Voting:
Good = 17
Bad = 7

Tags:   rwis  

Our recent New Year's Eve snowstorm made driving home difficult Sunday night. The first day of 2007 brought bright sunshine and the pavement surface responded nicely as shown in the plot. While air temperatures were barely above freezing, pavement temperatures reached 45 degrees helping to melt all of the snow and ice off.

Voting:
Good = 16
Bad = 3

Tags:   rwis  

The featured plot gives you an indication of how effective the sun is these days. The plot shows RWIS pavement temperatures and air temperature (red line) for Tuesday. After the snow storm ended mid morning, the clouds started to thin and more of the sun's energy reached the pavement surface and quickly warmed it up to around 60 degrees. The positive outcome is that road conditions quickly improve during winter weather this time of year.

Voting:
Good = 20
Bad = 8

Tags:   rwis  

The featured plot was taken from the RWIS time series plotter for the Ames site. You may want to click the image to get a better view. You can see how the pavement temperatures warm more than the air temperatures during the day. The implication is that the increasing solar angle is becoming more direct on the pavement surface and thus able to more efficiently warm it. So the next time winter precipitation falls, it won't take much sunshine to quickly melt the mess away.

Voting:
Good = 33
Bad = 19

Tags:   rwis  

One of the most interesting plots the IEM produces are the RWIS pavement temperature traces. The recent warm up of our air temperatures (red line) has produced a response from the pavement temperatures (blue, pink, grey lines) as they have warmed too, even in the middle of the night! The sub surface temperature (black line) has also responded and is slowly creaping back to just below freezing. Great stuff.

Voting:
Good = 10
Bad = 3

Tags:   rwis  

One of the most interesting applications on the IEM website is the RWIS time traces. This application allows you to plot current or historical traces of air and pavement temperatures for a site and time period of your choice. The past few days have produced very interesting data traces as the mixed precipitation and cold temperatures have produced slick driving conditions.

Tags:   rwis