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Preview: Iowa Environmental Mesonet Daily Feature

Iowa Environmental Mesonet Daily Feature



Iowa Environmental Mesonet Daily Feature



Last Build Date: Sun, 17 Dec 2017 01:56:20 -0600

 



Continued Drought
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The weekly US Drought Monitor was released yesterday and depicts a worsening drought situation in the state. While heavy rains frequented the state in October, we have turned very dry again. The featured chart presents the combination of trailing day precipitation departures expressed in terms of standard deviations from long term averages for Osceola (just south of Des Moines). The shaded areas represent the US Drought Monitor conditions analyzed for the location. This area was particularly hard hit this year and while the heavy rains in October did remove the D3 category, the area has remained in D2 since. There is no one magic metric that determines the drought category, but a number of metrics are considered and local reported impacts.

Generate This Chart on IEM Website




Wind Advisories per Year
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The wind was howling again yesterday in Iowa prompting the NWS to issue a Wind Advisory for much of the state. The featured map looks at how common these advisories are by plotting the average number of advisories per year by county based on IEM archives. The general northwest to southeast pattern is rather clear with about three times as many issued between the extremes. Why does this difference exist? Local topography and land cover has some impact as western Iowa is flatter along with fewer trees. It is also closer to the "High Plains", which tends to be an area experiencing rapidly developing low pressure systems that help drive strong winds and drier landscapes which help mix deeper depths of the atmosphere (helps to bring stronger winds to the surface).

Generate This Chart on IEM Website




Waiting for first inch
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While places like Ames have seen flurries this season, any snow of consequence has been elusive. The featured chart displays the date of the first winter season one plus inch snowfall, the amount of that snowfall and the number of days until no snow cover was reported. By mid-December, about 75% of years have seen an inch plus of snowfall by now. So our current snowfall drought this season is not too exceptional.

Generate This Chart on IEM Website




'17-'18 Winter Storm #1
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The IEM generates snowfall analysis maps based on NWS COOP observations, Local Storm Reports, and CoCoRaHS reports. The arbitrary requirement for classifying these events as storms is for somewhere in Iowa to receive 2+ inches of snow or to have significant impacts from ice and/or blowing snow. So far NE Iowa has some isolated totals of two inches, so we have our first "winter storm" of the season. There have been other light snow producers in the state this season, but only have seen an inch or less reported. Look for more maps like these as the season progresses and the "Winter Storms of 2017- 2018" link on the homepage will bring you to a page showing all these maps.




Days since last Winter Storm Warning
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Significant snowfall events continue to be elusive this season for Iowa. The featured map displays the number of days since the last issuance of a Winter Storm Warning by NWS Forecast Office. All of the Iowa shown forecast offices have yet to issue such an alert this season and Davenport has gone a full year without issuance. Of course, the highlight of the map is the comparison with the deep south offices that just wrapped up a significant winter storm for their area. Snow was experienced from Houston to DC. Amazing to think that a place like Mobile, AL experienced a significant winter snow before Iowa did.

Generate This Chart on IEM Website




Dry Month and a Half
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The featured chart displays precipitation totals for Des Moines between 22 October and 7 December each year. The 21rst of October was the last significant rainfall for the site. This year's total between the given days is about the lowest on record behind 1904. Of course, with the growing season long over, the impacts of the dry weather are minimal and it was a major help to dry out area fields to allow crop harvest to proceed. But one starts to wonder if we are going to have a minimal amount of snowfall like last year again, and go into the next year's growing season needing moisture.

Generate This Chart on IEM Website




Consecutive Day Stats
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The featured chart presents consecutive day statistics for Ames based on long term daily high temperatures. The chart shows the maximum and minimum values of high temperature over a given number of consecutive days. For example, over a fifteen day period, the high temperature has averaged over 100 degrees and been over 100 degrees each day for the warmest period on record. Again for fifteen days, the coldest average high has been zero degrees with the high each day below about five degrees. Of course, we are nearer to the colder end of this range and even attempting such a cold period would require snow cover.

Generate This Chart on IEM Website




Tied December Max
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The quick turn of our weather to winter on Tuesday made Monday seem like a distant memory. The highs on Monday were some of the warmest possible during December and Des Moines was able to tie its all time record high temperature for the month. The featured chart displays the monthly maximum temperature records for the site. One can use the values in comparison to other months, so the 69 on Monday is comparable to seeing 110 in July!

Generate This Chart on IEM Website




Warm December Temperatures
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Warm and muggy air streamed into Iowa on Monday before being swept out by a cold front passage Monday evening. A harsh reminder of the current winter season impacted the state over night. But before then, Des Moines was able to tie its all-time warmest December temperature of 69 degrees. The featured table looks at the hourly temperature reports from Sunday into Monday for Des Moines and the previous hour for December with as warm of a temperature. For 8 AM and Noon yesterday, the hourly temperature was the warmest on record based on IEM archives for the site.




Fall Highs Above Average
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The fall season encompassing the full months of Sep, Oct, and Nov wrapped up last week. The featured chart looks at the percentage of days for the period that had a high temperature above average. The overall average is plotted as well and is slightly different than an even 50% due to asymmetries of the high temperature distribution. Anyway, years above this value are shown in red and below in blue. This fall was near 50% whereas the previous two where much higher for Ames. It has been about 20 years since the last fall season with substantially lower than 50% of the days above average for the fall season.

Generate This Chart on IEM Website




November Highs and Lows
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The calendar has turned to December, so it is a good time to look back on November. The featured chart displays a heatmap of daily high and low temperatures for November for Ames. Actual observations for this past November are overlaid. Temperatures were generally within the higher frequencies based on long term data, even though the actual time series of data for the month featured a chilly start and warm end to the month. The heatmap also shows the combination with the highest frequencies, which is a high between 47 and 50 along with a low between 29 and 32.

Generate This Chart on IEM Website




Frost Free Days
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With the period between the last spring and first fall freeze (frost free days) complete this year, it is a good time to look at the trend of this metric for Ames since 1893. The featured chart displays the yearly totals and a simple linear trend is fitted to the data. For the various climate change metrics for Iowa, this is one of the strongest signals going. This year is shown slightly above trend line and inline with the past 20 years or so of longer than average number of frost free days.

Generate This Chart on IEM Website




Great Sunsets
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The sunsets this week have been nothing sort of spectacular over much of Iowa. The IEM collected webcams have captured some awesome time lapses recently. The featured image is from the KCRG-TV webcam in Independence Tuesday afternoon. You can find recent lapses on this website and when exceptional lapses are found, they are uploaded to YouTube.

Generate This Chart on IEM Website




Tale of Two Novembers
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While the first half of November was cold, the second half has been rather warm. The featured chart looks at the combination of Des Moines average high temperature for the 1- 13 Nov period against the 15-27 Nov period. The 2017 value is highlighted and would indicate that such dichotomies are not that uncommon. The chart also contains some diagnostics looking at quadrant frequencies with the quadrants delineated by the means. While there is some correlation between the periods, a cold start to November did not doom us for a cold end of November.

Generate This Chart on IEM Website




3 inch Daily Snowfall Drought
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With a hat tip to Jim Lee at NWS Des Moines, the official daily snowfall total for Des Moines has not exceeded three inches over the past 697 days. This is the longest such streak on record. The featured table highlights consecutive day stretches over 600 days for the site. For the current streak, one has to go all the way back to December 2015 to find a 3+ inch snowfall. The current prospects for snowfall are near nil over the coming week with highs well above average for today.




Warmest Day of November
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High temperatures on Friday are expected to be the warmest so far this November. The featured chart looks at the frequency of a given day of the month of November being either the warmest high or warmest low. So having the warmest high this late in the month is a bit uncommon, but has happened in the past. The warm highs look to continue into next week.

Generate This Chart on IEM Website




Drab Thanksgiving
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Skies on Tuesday were mostly clear over Iowa, so it is a good time to check in on how we look from space. The featured map is of Aqua MODIS true color imagery and the colors over the state are rather drab. The map is rather interesting though as it shows the various land forms over the state, with forested river valleys and the dominant / intensive agricultural land use over northcentral Iowa. The darker brown areas are mostly fields that have had fall tillage done.




November Flight Categories
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The primary purpose of the airport weather sensors is to help the aviation industry. The stations provide information that guides what type of aviation can take place. The featured chart shows four main flight categories from the Des Moines airport for this month. VFR (Visual Flight Rules, ceilings above 3k ft and visibility more than five miles) conditions have dominated this month. These conditions look to continue for the rest of this week, making for good Thanksgiving travel for those taking to the skies.

Generate This Chart on IEM Website




60+ in November
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It took until the 20th day of November to breach 60 degrees for places like Des Moines. Strong south/southwesterly winds helped to push temperatures finally well above normal. The featured chart is a wind rose and looks at wind speeds and directions during November when the air temperature is at or above 60 degrees for Des Moines. The wind rose is a wonderful way to see direction and speed frequencies. The longest bars coincide with what we experienced yesterday, which were winds from the SSW. Of course, not many occurrences of NW winds are shown as that is typically a source of cold air.

Generate This Chart on IEM Website




Been cold since first freeze
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Since the first freeze of the season finally happened for places like Ames in late October, the temperatures have been rather chilly since. The featured chart looks at what we would expect to see after the first fall sub 32 degree temperature. The top panel shows the maximum high temperature following said date. The middle panel shows the combination of first fall sub 32 date and the subsequent max high. The bottom panel shows the number of 60+ degree high temperature days following said date each year. This year's max high is near the lowest on record and we have seen zero days 60+ so far. There are a few warm days in the forecast for this week, so we'll likely see the warmest temperatures since the freeze and maybe even a high above 60 degrees.

Generate This Chart on IEM Website