Past Features

This page lists out the IEM Daily Features for a month at a time. Features have been posted on most days since February 2002. List all feature titles.

Features for Jun 2023

Thu Jun 01, 2023
May Max VPD Averages
01 Jun 2023 05:30 AM
Vapor Pressure Deficit (VPD) is a weather variable that isn't as commonly used to express humidity like dew point and relative humidity are. The values also have units of pressure, which makes them even a bit more obtuse. So what use are they? They represent an absolute measure of potential demand from the air of water vapor from various surfaces that may contain water. For green house operators and horticulture folks, knowing VPD can inform plant health and development. The featured chart presents the average May daily max VPD values for Des Moines. Rewording, the maximum VPD is calculated each day of each May and then averaged by year. The 2023 value is higher than a simple average and higher than the past four years. Higher values indicate increased demand for water vapor or perhaps you could consider it as a suction force. It is interesting to see 1988 show up as the highest value since 1973, which of course, was a very bad drought year.
Voting: Good - 8 Bad - 0

Tags:   vpd  
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Fri Jun 02, 2023
Contrasts of May
02 Jun 2023 05:30 AM
The featured map presents IEM estimated climate district precipitation ranks for May. A value of 1 would indicate the wettest May since 1893 and 131 would be the driest. There is some remarkable variability shown, namely the east to west difference over Nebraska with southwestern Nebraska shown as the wettest and east central near the driest. Iowa had plenty of dryness for the month, but southwestern Minnesota was had above average wetness. Of course, these are spatially aggregated estimates, so there's variability to be found even inside the climate districts shown.
Voting: Good - 14 Bad - 2

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Mon Jun 05, 2023
Meager Shear
05 Jun 2023 05:30 AM
The weather to start off June has more resembled August with slow moving afternoon thunderstorms driven by a humid air mass and strong heating. The slow storm movement has even been in uncommon directions to the west and southwest. The reason is that the flow of air aloft is rather stagnant from the east and without much directional nor speed shear to support more robust thunderstorm activity. The featured chart presents a measure of speed sheer between the surface and 3km aloft based on an archive of soundings from Davenport. The units and concept here maybe a bit too meteorological, but generally higher shear values support more robust thunderstorms by allowing the updraft and downdraft of the storms to be separated. Otherwise you get pulsey behavior as the downdraft interferes with the updraft. Anyway, you can see how recent sounding values this year have been at the very low end of a climatological range.
Voting: Good - 13 Bad - 0

Tags:   sounding   shear  
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Tue Jun 06, 2023
Oelwein Precipitation Departures
06 Jun 2023 05:30 AM
This week's update to the US Drought Monitor is released on Thursday and assesses the seven day precipitation ending Tuesday morning. Degradation seems to be a given with much of the state continuing to be mostly dry and warm temperatures increasing water demand. Over the past month or so, one of the driest areas of the state is found in northeastern Iowa at Oelwein. The featured chart presents a number of metrics evaluating precipitation totals or departures over a trailing number of days ending yesterday. The values on each chart represent the given date until June 5th, so they should somewhat be evaluated from right to left. The bottom left panel denotes the Standardized Precipitation Index (SPI) values within the drought monitor assessment. You can see that over different time scales, different drought threshold indicators are to be found. The present drought monitor value for the location is "D1", which is well supported by this plot dating back into late 2022. The short term is certainly much drier and the weighting of this year's growing season totals continue to increase in the drought monitor assessment as impacts (brown lawns, degraded crops, low streamflows, etc) increase.
Voting: Good - 5 Bad - 0

Tags:   precip  
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Wed Jun 07, 2023
Weird Storm Motions
07 Jun 2023 05:30 AM
Those of you that monitor RADAR reflectivity loops every day have likely noticed the weird storm motions this month. Typically storms travel from the southwest toward the northeast, but the past days have seen storms travel west, northwest, south, and about every other direction. The featured chart attempts to illustrate these odd storm motions by plotting a histogram of Des Moines NEXRAD storm motion tracks. The top panel shows the combined May and June climatology and the dominance of storms travelling from the southwest is obvious. The bottom panel shows the histogram for storms this month and it is about the antithesis of climatology. The reason for these weird storm motions is the very blocked up upper level flow pattern that currently has weak westerly moving flow over the state. The hope is that this pattern will break next week and we can start getting into more typical June storm patterns with stronger flow aloft.
Voting: Good - 16 Bad - 2

Tags:   stormmotion  
Thu Jun 08, 2023
No GDD Problems So Far
08 Jun 2023 05:30 AM
While precipitation has been fickle, there's been no issue accumulating needed growing degree days so far. The featured chart presents the accumulated GDDs since 1 May for Ames with the blue area representing the envelope of period of record observations. This year is plotted along with last year and the drought year of 1988. This year's total is well above average and last year's total. Such is often the case with dry weather leading to warmer temperatures as the sun is able to more efficiently heat drier soil than wetter. The near term and longer term forecasts continue to advertise warmer than average temperatures, so it seems very likely that GDDs will not be of concern this growing season.
Voting: Good - 10 Bad - 1

Tags:   gdd  
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Fri Jun 09, 2023
Change in 60 Day SPI
09 Jun 2023 05:30 AM
The weekly release of the US Drought Monitor yesterday degraded much of the state with only small areas left analyzed without drought. The featured map and charts attempt to show how one metric that goes into drought monitoring, the Standardized Precipitation Index (SPI), has changed over approximately the last month. A trailing 60 day SPI is computed on 2 May and then compared with the same metric computed on 6 June. The top right panel shows arrows indicating how each of the long term climate sites in the state changed over this period. Colored arrows indicate at least a one category change. The bottom right panel shows the station count changing between the various SPI based drought categories. The map plots some of the current SPI based drought categories and is also colored by if it changed over this period. The filled in area on the map is the most recent drought monitor. So the main point here is found in the top right panel showing many of the points that started off in no or D0 drought category have degraded one to two categories. Areas east of Waterloo and southeastern Iowa have seem the worst of the degrading conditions since early May.
Voting: Good - 9 Bad - 0

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Features for Jun 2023