The featured chart plots the number of days per year that experienced a high or low temperature exceeding two standard deviations from average for Ames. For example, some of last week's cool high temperatures in the 40s were two sigma below average. This chart is an attempt to quantify how "extreme" a given year was. In general, the highest values were prior to 1940 which is probably a reflection of the data quality for that period, although the very hot years in the 1930s show up nicely in this chart.

Voting:
Good = 14
Bad = 5

Tags:   high   low  

The featured chart displays the yearly net total of days above average for low temperature (negative values would mean that more days were below average than above). So far in 2009, Ames has seen 50 more days below average for low temperature. This is roughly the largest negative value we have seen in the last 40 years, granted there are 2.5 months left to this year yet.

Voting:
Good = 34
Bad = 15

Tags:   lows  

The past week or so has seen high temperatures not vary much for Ames with the range being a mere 3 degrees (78-81). The featured chart looks at the minimum 7 day temperature range for all days of the year. In general, the lowest values are in the summer time when strong temperature fronts are not common. The spikes during the spring and fall months are when we often experience air mass changes via strong fronts.

Voting:
Good = 8
Bad = 12

Tags:   persistence   highs   lows  

Sometimes the winds experienced on the backside of a storm complex can be stronger than what occurs with the precipitation. The featured chart is a 1 minute interval timeseries from the United Community SchoolNet8 station east of Boone Iowa. The rapid pressure drop shown was associated with the backside of a thunderstorm complex to the south comprising a surface "wake low" structure. Wind speeds increased until when the pressure stopped dropping.

Voting:
Good = 27
Bad = 10

Tags:   wakelow  

The featured chart is the percentage of days per month that experience either high or low temperatures at least 1 degree warmer than the previous day. April has the largest value for high temperature, but is just a mere few percentage points larger than October which only equates to approximately 1 more day per month. This chart would imply that climatology does not have a strong influence on actually seeing our day to day temperatures warm. Day to day temperatures are more strongly influenced by the passage of air masses.

Voting:
Good = 22
Bad = 18

Tags:   climate   high   low  

Last Friday, we were experiencing low temperatures around our average high for the date. Today, we are on the opposite end with high temperatures near our average lows. The featured chart looks at frequency of having the high temperature below the average low. As with Friday's chart, there is a period in the summertime where this has never occured for Ames. Our actual weather is expected to warm up this weekend!

Voting:
Good = 22
Bad = 3

Tags:   highs   lows  

In some locations, low temperatures on Thursday were warmer than the average high temperature for the date. The featured chart looks into the frequency of this occurance with the bars representing the number of years that this has occurred for Ames. The red line is the record daily maximum low temperature and the black line is the daily average high temperature. Notice that during the summer season, the black line is always higher. In fact, the period of 9 May to 29 Sep has never seen a low temperature greater than the average high for Ames!

Voting:
Good = 35
Bad = 19

Tags:   highs   lows  

The featured graph shows the daily frequency of observed sub freezing high and low temperatures for Ames based on data since 1893. For this time of year, roughly a 45% chance exists that the high temperature will be below freezing. On the other hand, low temperatures are almost always below freezing this time of year. Our high temperature today may creep above freezing to help balance out our day yesterday below freezing.

Voting:
Good = 20
Bad = 10

Tags:   climate   below-freezing  

Keeping with the recent features, today's feature is a chart of the hour during which the low temperature occurs. Low temperatures tend to occur just after sunrise when net radiation finally becomes positive (downward). This chart shows this trend with lows happening earlier in the morning during the summer. You can also see a secondary maximum around 11 PM, which is often the case when clear skies at night follow a cloudy day allowing temperatures to drop rapidly below levels during the cloudy morning.

Voting:
Good = 23
Bad = 12

Tags:   climate   lows  

Some of you may be curious about the odd jump and then dip on many of the 1 minute pressure traces recently. The featured plot shows a 2 hour period from yesterday afternoon at the Brooklyn SNET site. These plots are showing the meso-high and then wake low structures that often pass during severe convection. Here are some other examples from Colo, Montezuma, Charles City (10mb!), and Newton. If you look at those plots you can see the two distinct pressure patterns. A quick pressure jump (meso high), a return to the pressure before the jump (wave node), and then a rapid drop (wake low). Great stuff!

Voting:
Good = 9
Bad = 5

Tags:   wakelow  

A strong wake low appears to have been detected by a number of IEM sites early afternoon on Wednesday. Eventhough the storms were to south of this feature, brief gusty winds were experienced. This phenemona was caused by rapid evaporation of cloud water from a decaying area of precipitation to the north and northwest of the squall line in southcentral Iowa. The evaporatively cooled air rushes to the ground and causes the large horizonal differences in pressure and thus wind! The plot shown indicates the rapid swing in pressure and the other plots show the increase in wind speed. Great stuff!

Voting:
Good = 14
Bad = 7

Tags:   wakelow  

LaCrosse, WI NEXRAD imagery indicates a strong line of thunderstorms that is putting out a nice outflow boundary (blue line). Surface observations agree nicely with the location of the boundary, notice the southerly wind to the south of the boundary.

Tags:   outflow