Last Build Date: Mon, 24 Oct 2016 14:42:51 -0500
After an extremely wet September, Iowa has mostly avoided any followup significant rains in October. The featured map is forecasted precipitation from the Weather Prediction Center showing a bullseye over two inches depicted over northeastern Iowa up until Wednesday evening. This is the same area that experienced big rains in September. Thankfully, it has been a number of weeks since the most recent big rainfall, so the impacts of this should be limited. It certainly will not help the crop harvest that was already delayed in the area.
The featured chart presents an analysis of duration and strength of the first fall periods at or below freezing for Des Moines based on one minute interval temperature observations since fall 2000. Each event represents a sequential fall date during which the low temperature reached 32 degrees or colder. For example, event three would be the third day during the fall season at or below 32. The time duration is the period between when the temperature hit 32 degrees and rose back above 32. The maximum duration period for each date was used in cases of multiple periods on a given date. The box and whisker plots represent the spread of duration. A strength metric is also calculated and is simply the temperature difference from 32 multiplied by time. So what is the moral of the story here? The initial dips below freezing are brief (1.5 hours on average) and shallow. Both the duration and "depth" increase with sequential event with more noise than signal appearing after the fourth or fifth event.
Getting Iowa's soybean crop harvested this fall has been a bit of a challenge. A very wet fall in places, high humidity levels and lack of killing frost have left some soybean fields unharvested to date. The featured chart displays yearly soybean harvest progress as reported by USDA NASS. The 'X' in each year's progress bar indicates the 62% level that would be comparable to this year's report valid on Monday. Mostly dry and less humid conditions have settled into the state, which will help soybean progress continue.
The record warm temperatures on Monday were way above average. The featured chart displays the daily high temperature departures for Des Moines this year. The 20+ departure was the largest since early April. Of course, it is more difficult to get such large departures in the summer season as average highs are quite warm already. While not extremely warm, very pleasant temperatures are in the forecast for the next week.
Not only were record high temperatures observed in the state on Monday, but extreme levels of humidity were reported as well for October. The featured chart displays hourly records of reported dew point for Ames. While the site only has 20 some years of data on record, the values reported yesterday morning were record setting. Thankfully the heat and humidity have been pushed off to the east with more pleasant fall weather arriving today.
Temperatures are expected to be very warm today. The featured map displays NWS predicted high temperatures for Monday. 80s are very common over the state! On Sunday, a few locations to our south and west set all time record highs for the month of October! These warm temperatures also included muggy dew points in the upper 60s. Cooler, but still nice for October, temperatures arrive tomorrow.
Freezing temperatures finally arrived in Iowa on Thursday with some locations, like Ames, even reaching sub 29 degrees. Cloudy conditions on Wednesday gave way to clear skies overnight, which greatly helped the atmosphere cool off. Do skies always need to be clear on the first fall occurrence of sub 29 degree temperatures? The feature chart looks at the hourly sky coverage as reported by the Ames Airport for the 24 hour period before and after the first sub 29 degree temperature event. All but two years since 1996 are indicated to be clear skies at the time of sub 29 (denoted as 0 hour on x axis).
The coldest air, by far, of the season arrived in Iowa on Wednesday with very chilly temperatures observed throughout the state by the afternoon. This was the coldest air since early April and even March as computed by an hour by hour basis shown in the featured table. The graphic presents the hourly air temperatures reported by the Des Moines Airport and the most recent date with a colder temperature at that given hour. Warmer weather will soon arrive and is expected to stick around through next week.
Much cooler air pushed into the state late Tuesday afternoon with high temperatures on Wednesday expected to be over 20 degrees cooler than Tuesday. How extreme is such a drop in day to day high temperature? The featured chart presents the largest day to day change in high temperature for Ames partitioned by week of the year. The largest negative values shown for this time of the year are around 35 degrees.
The featured chart displays the combination of MOS forecasts of morning low temperature and afternoon high temperature for Des Moines this month. Model Output Statistics (MOS) forecasts take raw weather forecast model output and using past forecasts with actual observations, attempt to provide a more accurate forecast. These forecasts are made four times per day, so the bars represent the range of values forecasted as the forecast is updated with time. It is interesting to note the cold weather forecasted for tomorrow, with the highs only in the mid 50s!
The featured map presents 30 day precipitation departures over the midwestern US based on NWS COOP reports and RADAR based precipitation estimates. The wettest departures are analyzed from eastern Kansas up into southwestern Minnesota. Even with such high departures, on only needs to travel a bit further south to southeastern Iowa to find drier than average conditions. Precipitation totals over the next seven days look rather meager, which will be helpful for the crop harvest progression.
The saga of Hurricane Matthew continues this morning with the center of Hurricane just off the eastern Florida coastline. The featured map displays NEXRAD composite reflectivity this Friday morning with the classic presentation of a hurricane shown. The forecasted track of this storm continues to be tantalizingly close to the coastline with even a 10 mile difference in track making a tremendous difference in impact. Hopefully the track goes further offshore and folks are spared the worst of the storm.
The Storm Prediction Center has portions of Iowa under an enhanced risk of severe weather today. Strong storms are expected to enter southwestern Iowa late this afternoon with all forms of severe weather possible. Hopefully this severe threat does not surprise folks as Hurricane Matthew is, rightly so, dominating the weather headlines today.
Is it too soon to think about the possibility of measurable snowfall in October? The featured chart displays the combination of October snowfall totals and melted precipitation totals for the month for Des Moines. While most Octobers have seen zero or near zero snowfall totals, there are a few handful of years that have seen measurable snowfall this month. The forecast has some of the coldest air of the season arriving later this week, but snow appears extremely unlikely for the near term.
High temperatures today are expected to approach 80 degrees for some portions of the state. How rare is it to reach 80+ degrees in October? The featured chart displays the number of days each October that the daily high temperature was 80+ for Des Moines. This is not uncommon at all with the average being around 3 days each year.
This past weekend was rather calm from a wind perspective. The featured chart depicts daily averaged wind speeds for Des Moines in a calendar layout. The lowest value of just three MPH was yesterday and only four MPH on Saturday. The calm weekend also had very pleasant temperatures for early fall.
The Des Moines Airport has yet to reach a sub freezing temperature, let alone a sub 50 degree temperature! If this holds for a few more days (thru 1 October), it would break the previous record for latest sub 50 degree temp set back in 1905. The featured chart displays the combination of first day below 50 and then the subsequent number of days until the first sub 32 temperature was recorded. The slanted lines are simply a convenience to bring the second date down to the timeline axis.
So far this fall, we have avoided any really cold weather. The featured chart displays the minimum to date low temperature for Des Moines after 1 July. The coldest low temperature thus far has only been 50 degrees. This value is one of the warmest to date minimum temperatures on record for the site. The featured chart displays the accumulated value for this year and the long term climatology of this value.
The featured chart displays the daily average wind speed and direction for Des Moines this month. The cooler and less humid conditions this week have been thanks to winds which are no longer coming from the south as they were last week. The arrows on the top of the chart display the vector averaged wind direction each day. Prior to this week, the periods without southerly winds were rather limited.
The big story in the state is the ongoing flooding of the Cedar River in Cedar Rapids. This flooding water is from rainfall last week over northeastern Iowa. The featured chart displays sequential river stage forecasts for the CIDI4 (Cedar River at Cedar Rapids) site. Forecasts are made out a number of days and updated a few times per day during active flow situations. The plot presents each of these forecasts and the observed data for the site. Thankfully the forecasted crests have slowly crept lower with time as the event has gotten closer to town.