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Preview: Iowa Environmental Mesonet Daily Feature

Iowa Environmental Mesonet Daily Feature



Iowa Environmental Mesonet Daily Feature



Last Build Date: Fri, 21 Jul 2017 01:15:02 -0500

 



Missing Driest Areas
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Our rainfall patterns this summer have been quite interesting. Overall, the state has seen plenty of days with rain falling somewhere in the state, but these rains have been avoiding the driest areas. For example, the featured map displays the combination of rainfall estimates for 19 July and the current US Drought Monitor analysis valid on 18 July. It is remarkable to see how the heaviest totals in southwestern and northeastern Iowa avoided the dry areas of the state. More rain is in the forecast, but it would appear that the wet areas of northeastern Iowa will have the best chances again.




30, 60, and 90 Day Arridity
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Some of the driest conditions in the state currently can be found over southeastern Iowa. The featured chart looks at the arridity index calculated over 30, 60, and 90 trailing day periods for this year for an areal averaged value representing southeastern Iowa climate district. This index combines temperature and precipitation departures to access water stress. Since early June, the chart shows the increasing stress for this area. There are more chances of rain in the forecast, but the best chances are over northern Iowa.

Generate This Chart on IEM Website




Isolated Shower
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A lone thunderstorm was somehow able to fire over southern Iowa late Monday afternoon and dumped much needed rainfall over a very limited area. The featured map displays NOAA MRMS precipitation estimates based on RADAR and shows a very small area just to the northwest of Chariton and southeast of Indianola picking up an inch or more. This is a critical time of year to receive precipitation for a corn crop that is currently tasseling. These types of rainfalls can go a long ways to explaining differences in final crop yield between neighboring farmers and fields. Hopefully expected rainfall on Tuesday can be a bit more widespread, but some dry areas of the state will almost certainly miss out again.




Lots of Goose Eggs
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Since the end of May, rainfall has been difficult to come by for Ames. The featured chart displays daily precipitation reports from the Ames Airport since May 28th. Plenty of goose eggs (zeros) appear on the chart with only one significant rain shown of 1.65 inches back on the 14th of June. There are some chances of rain in the forecast this week, but it remains to be seen how much places like Ames will see. Certainly the driest areas of southern Iowa do not look to fare well this week with the best rain chances confined to northern Iowa.

Generate This Chart on IEM Website




Increasing D1 Drought
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While yesterday's IEM Daily Feature discussed flooding rains in one part of the state, today's feature discusses the worsening drought situation for other parts of the state. The featured chart displays the weekly coverage of analyzed US Drought Monitor condition in the state since June 2016. The D1 (Moderate Drought) category was expanded over the state this week. The current near term forecast is not very optimistic for needed rains over the dry areas of the state.

Generate This Chart on IEM Website




Clayton County Flooding
(image)

It is currently an interesting dichotomy in Iowa currently with some parts of the state experiencing drought and others flooding. One such area experiencing flooding is Clayton County up in far northeastern Iowa. The featured map shows 12 hour estimated precipitation from MRMS between Tuesday evening and Wednesday morning. The RADAR-only based estimates peg amounts over eight inches and one need not travel far to the south and west to find values of zero! This is the time of year for such extreme and highly localized precipitation events to occur as storms tend not to move very fast and can train over the same locations given a feed of moist air into the thunderstorm complex.




Where did 11 July rains fall?
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The featured chart is an attempt to access where the rain fell in Iowa on Tuesday. The blue bars represent the areal coverage of precipitation departures for the previous 31 days prior to Tuesday. The orange bars represent the areal coverage of 0.20+ inch rainfalls over the state that coincided with the given categorical departure value. So the combination allows an assessment of where yesterday's rain fell. Overall, about 25% of the state received 0.20+ inches of rain on Tuesday, but some areas with current deficits did receive some rain along with other areas that did not need it (already at large positive departures). A majority of the rain did fall over areas that needed it! This plot is a first attempt at illustrating this metric, so your feedback on usefulness is certainly welcome!

Generate This Chart on IEM Website




3 inches over 30 days
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The featured chart displays IEM estimated areal coverage of Iowa that received at least 3 inches of precipitation over a 30 day trailing window of days. The present value of about 50% is an improvement over late June. Of course, this time of year having three inches over 30 days is a below average total with average monthly precip between April and September all being over three inches. The continues to be more chances of rain in the forecast, but it remains to be seen if the areas with the deficits can be filled in.

Generate This Chart on IEM Website




Past 24 Days
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The dry conditions have have developed this summer remain the main story this growing season. The entire state has not been dry though. The featured map displays NOAA MRMS estimates since 16 June. The analysis indicates the driest areas over this period being south of Ames and north of Sioux City. One need not travel very far north and east to find substantial totals over this same period. The heaviest rainfalls over Sunday night and into Monday morning were over northeastern Iowa.

Generate This Chart on IEM Website




90 Degree Day Departures
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The high temperature on Thursday reached the 90s for most of the state. We have seen our fair share of days with a high of 90+ this year. The featured map is an analysis of the number of days at or above 90 this year for the year to date period against a simple average of the same period of days for the years 1981 to 2016. Positive departures, like in Iowa, mean that we have had more 90+ degree days this year than on average. This data is based on the Oregon State PRISM gridded dataset. It is interesting to see the large negative departures over the deep south where they have seen plenty of rain this summer season.




Sioux City YTD Precipitation
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The US Drought Monitor continues to analyze much of northwestern and southeastern Iowa in "D0" (abnormally dry) condition. The featured chart looks at year to date precipitation for Sioux City. It is kind of interesting to see how this year compares with 1976, which was the driest year on record for the site. Even more interesting is to note that just a month ago, the wettest, driest, and this year were all at about the same value! The best precipitation chances today look to be for the eastern half of the state.

Generate This Chart on IEM Website




Northwest Moving Storms
(image)

Our current stretch of weather with daily scattered thunderstorms continued on Tuesday. These storms were a bit unique with a storm motion to the northwest. The featured chart displays a histogram of RADAR derived storm motion from the Des Moines NEXRAD. RADAR algorithms attempt to track storm cells and derive a storm motion (direction and speed). The top panel displays frequencies for period of record data archived by the IEM. The bottom panel displays this information just for storms on the 4th. So yesterday's storm motion was somewhat rare, but not as rare as a pure east to west motion.




July Temps and Dew Points
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The muggy conditions that most Iowans equate with July was present on Monday for most of the state. Dew point temperatures reached the lower 70s for about the southern 2/3rd s of the state. The featured chart looks at the combination of average dew point at a given temperature along with the resulting dew point. The relative humidity plot shows a rather smooth relationship as once temperatures start reaching the mid 70s, our relative humidities start to drop. We should be thankful for this relationship was it allows some level of suitability to our weather as temperatures warm mostly independently of dew point. The general flat portion of the relative humidity curve below the mid 70s are indicative of the common near saturated condition that supports warm over night temperatures.

Generate This Chart on IEM Website




June Sigma Departures
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With the calendar now saying July, it is a good time to look back on June in Iowa. The featured chart compares June growing degree day and precipitation departures for a statewide Iowa average value. These departures are expressed in terms of standard deviations (sigma) from the mean. This allows for a comparison between variables that have different units of measure, but have similar statistical distributions. The value for 2017 came in just above average for GDDs and below average for precipitation. Years that are on the fringes of the plot are labelled as well.

Generate This Chart on IEM Website




Missed Ames to the North
(image)

Ames missed out on the big rainfalls this week. The featured map displays three day precipitation estimates from the MRMS project. The map is zoomed in on the Ames and surrounding counties area. One need not travel very far north to find estimated totals over four inches. The heavy rainfall band Wednesday evening was just a few miles south of the heavy rainfall band on Thursday evening, both of which are partially shown on this map. It remains to be seen how much rain we'll see next week with the next rounds of storms forecasted.




Early Fireworks
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The severe weather threat on Wednesday materialized over the state during the late afternoon hours with many tornadoes reported over state. The featured map displays NWS Local Storm Reports for the event. Tornadoes were reported from just southwest of Dubuque in far eastern Iowa to near Shenandoah in far southwestern Iowa. At this point it appears most of the tornadoes were brief and weak, but others did more significant damage. The NWS will be out and about on Thursday to survey damage and assign strength ratings to the tornadoes. You can generate this map on this website and interactively look at the storm reports.

Generate This Chart on IEM Website




Peak Thunder
(image)

The featured chart displays the average number of calendar days each month during which at least one automated thunder report was reported at the Des Moines Airport. Based on the averages, the month of June represents peak thunder for the year. So far, this year's total is a bit below average but a number of forecasted stormy days remain. Of course, there are caveats with a plot like this as automated reporting methods have changed over the years. So a value of eight days in June represents about one out of every four days.

Generate This Chart on IEM Website




Wet end to June
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The featured map presents a precipitation forecast from the Weather Prediction Center for the next five days. This forecast is optimistic for a heavy rainfall event to occur over southern Iowa with amounts over four inches depicted over portions of the area. This particular part of the state could certainly use the rain, but the dry portions of northwestern Iowa may miss out. As with storms this time of year, the day to day details can be tricky as small scale details of one round of storms will impact the subsequent round. The storms will get going Tuesday night as increased humidity levels return to the state.




Comparable January Low
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Sioux City set a record low temperature on Saturday of 44 degrees! Such chilly weather was a far cry from the June we had experienced prior to this past weekend. To place the 44 within some context, the featured chart compares quantiles for low temperature between June and January for Sioux City. Such a comparison is more simply equating frequencies, so having a 44 degree low in June is as common as a low of -20 in January. Warmer weather arrives on Tuesday, but mild for this time of year.

Generate This Chart on IEM Website




Severe Warning Duration
(image)

A cold front helped to fire late afternoon thunderstorms over the state on Thursday with some of these storms reaching severe limits. The NWS issued a few warnings valid for Polk County (Des Moines) last night and the featured chart looks at the frequency of Severe Thunderstorm Warning duration for the county. An individual warning is issued for a prescribed amount of time. This warning can be cancelled early if the conditions warrant. The two lines on the chart thus represent the frequency of warning duration at issuance and then the final duration based on any cancellation that was done. From the chart, about 50% of warnings are issued for a duration of 45 minutes or longer.

Generate This Chart on IEM Website