While the calendar now says October, the summer like temperatures look to continue through at least this upcoming weekend. The dry weather looks to continue as well. With the start of a new month, it is a good time to check in on September precipitation totals. The featured map presents a heavily smoothed analysis of available NWS long term climate site precipitation totals for September. Some rather paltry totals below an inch are found over far eastern and northwestern Iowa. The worsening drought this fall season continues to be of concern as the dry August for parts of Iowa was followed by even drier weather during September for most of the state. Not everybody missed out during the month with a number of locations plotted shown above 3.5 inches, which is about average for Iowa during September.
The very warm early fall season weather continued on the first day of October with highs reaching 80°F degrees for much of the state. The featured chart presents the daily frequency of such a warm high temperature by day of October for Ames. It is quite interesting to see the increased frequencies during the first few days and then the rapid drop off with a settling around 15% on October 5th. A climate explanation for this is not apparent! Of course, the overall trend is downward for the month with such days becoming more fleeting as we progress. Interestingly and coincidentally, the present forecast has temperatures dropping back near 70°F for highs on the 6th!
The National Weather Service produces a number of weather forecast products. One of those is called Model Output Statistics (MOS), which attempts to provide a bias-corrected and point specific forecast based on raw model output. The IEM processes the MOS text bulletins and offers some tooling for this data along with a download option. The featured chart is another tool in this space and plots the combination of morning low and afternoon high observations (dots) along with the time-lagged ensemble range of forecast values for the Ames Airport. In this case, the "GFS Extended" MOS product is plotted. The forecast trend is rather clear with cooler weather arriving to start off next week and lows even perhaps dipping into the 30s by later in the week. Could we perhaps finally be done with summer like heat?
The first five days of October were exceptionally warm with highs mostly in the 80s and lows in the 60s for Iowa. The featured chart presents the average temperature for the first five days of October for each year on record for Des Moines. The 2025 average near 75°F is almost 2 degrees warmer than the previous warmest value way back during 1900! A bit of fall reality has settled over Iowa for Monday, but far southeastern Iowa will have another day of very warm October temperatures. Even after this early week drop in temperatures, moderation will happen for the remainder of the weekend with forecast highs expected again to be near 80°F next weekend!
The featured map presents the combination of NOAA MRMS precipitation estimates from Sunday through early Tuesday morning and the current US Drought Monitor analysis. This needed precipitation event was thanks to a slow moving front that has swept the state clean of the very warm air that started off October. The map shows that much of the heaviest totals missed the parts of the state presently within a "D0" drought analysis, but the entire state needed rain. Once the showers clear southeastern Iowa later this morning, there are a few chances of light rainfall over the coming days along with warming temperatures.
The featured chart presents daily high and low temperature climatology for Ames along with 2025 observations. A lot of information is packed into one chart here with the range between the average high and low temperature shaded in green and then the area between those averages and the daily record maximum and minimum values shaded in red and blue respectively. The brown bars are the range between the 2025 daily high and low temperatures. Qualitatively, you can see we have spent very little time this warm season with low temperatures within the blue area (below average). The two cool periods of late August and early September are about all to speak of for such periods since early April.
For the month of September, the Storm Lake (NW Iowa) NWS COOP station reported just two daily rainfalls with 0.04" on the 10th and 0.42" on the 19th. So roughly 90% of the monthly total fell on just one day. The featured chart looks into the frequency of that happening with the most recent yearly occurrence shown above each bar. While generally rare, these events are most frequent during the colder half of the year when precipitation totals are lower and more easily comprised of just one big event. This situation is much more difficult during the summer months as rainfall events are more frequent and heavy rainfall events less isolated.
Daily high temperatures have steadily warmed this week with even warmer temperatures expected for the weekend. There's an outside chance that Ames could hit 80°F on Sunday, which would be the sixth such day this October. The featured chart looks into the monthly frequencies and percentiles of a daily high temperature of at least 80°F for Ames. The long term average number of such days during October is around three, so this year has already bested that average by two days. If you like such weather, you should certainly savor it as meaningful frequencies of such days does not return until next April!
Our warm October continued this past weekend with highs reaching 80+°F over much of western Iowa on Sunday. A daily feature last week denoted the first five days of October were the warmest on record for many sites in Iowa. Today's featured chart looks into if this October could be the warmest October on record for Ames. The month to date accumulated average temperature is plotted along with each previous year providing a possible scenario for this year to potentially bet the warmest October during 1963. Interestingly, only that 1963 scenario repeating would lead to this year being the warmest on record. The actual forecast for this week continues the mild temperatures without much in the way of significant cold.
For a decent portion of the state, the chilliest temperatures this fall season happened over a month ago back around the 7th of September! Practically the entire state has yet to see a sub freezing temperature this fall. The featured map presents a smoothed analysis of mostly NWS COOP reporting stations for the minimum temperature since the first of September. A couple of 31°F temperatures are shown, but the vast majority of stations have reported values safely above freezing. The near term forecast has not much in the way of chilly weather, so the wait for the first freeze will continue.
Tuesday was a dreary day for most of Iowa with drizzle and occasional rain showers. The featured chart presents a time series this month of hourly cloudiness and near surface horizontal visibility reports from the Des Moines airport weather station. The top panel attempts to illustrate cloudiness by shading reported cloud level and amount reports by extending those values vertically away from the surface. For ASOS, once an overcast condition is reported, there are no subsequent cloudiness reports above that level. The bottom panel is more straight forward with the horizontal visibility reports shaded by the reported distance value. So the lowest cloud decks this month occurred back on the 6th, with the 10th joining yesterday for second lowest for the month.
The forecast has a good portion of Iowa reaching 80°F degrees today and some seeing such warm temperatures again tomorrow. It is certainly getting a bit late in the year for such warm temperatures to be observed. The featured chart presents the accumulated frequency of a given date having seen its last daily high temperature threshold of the year for Ames. The table at the side presents the percentile values. The combination of the 80°F threshold and 16 October comes in above the 70th percentile or rewording, seven out of ten years had seen their last 80+ degree temperature of the year by today's day of the year. Three other temperature thresholds are plotted for comparison with frequencies at 70°F and today's date being much lower, so such temperatures are more likely than not for at least one more week!
Temperatures warmed nicely again on Thursday with about half of the state reaching 80+°F for high temperatures. Sometimes it is difficult to contextualize how anomalously warm a temperature is during a month that should feel more like fall than summer. So the featured chart makes an attempt at this by comparing daily high temperatures during July and October for Ames. The left panel is a q-q (quantile) plot which matches temperatures by their observed frequencies. So a 80°F high temperature during October is comparable in occurrence frequency to a high of 95°F during July. The right hand plot presents histograms of each month's temperature distribution. There is a surprising amount of overlap between the two, but obviously October has most of its distribution below the July minimum value. The right hand table lists out the percentile values for each month and the difference between the two.
Sunday started off chilly with Des Moines setting a new fall minimum low temperature of the season at 42°F. It has been a rather mild fall season so far with not much in the way of chilly weather and very little limited coverage of sub-freezing temperatures across Iowa. The featured chart looks into the first fall season date with a low temperature below 43°F for Des Moines. This year's value is third latest on record, behind 1914 and 1963. Cooler temperatures are expected this week with lows down into the 30s for much of the state and even the first wide spread freeze mid week.
From the "Life mimics Art" department, the high temperature on Monday was 67°F for both the Ames and Des Moines airports. This was much to the delight of many school-aged weather / meme enthusiasts, including those within the IEM's developer's household. So today's featured map takes a look at the observed frequency of this high temperature value over the contiguous US using long term climate sites with at least 50 years of data. The highest frequencies are found over California and the lowest over the southern tip of Texas and the Florida Peninsula. Iowa is situated within the large continental frequency blob in the four to five day range. Within the IEM database, the highest frequency was found for the Hawaii National Park (25.0 days per year), which is an elevation of about 4,000 ft. If you are still reading this and wondering when this last happened for Ames + Des Moines, it was only last year on 24 April 2024!
The National Centers for Environmental Information (NCEI, formally NCDC) is the official US government source of climate information. Unfortunately, the current government shutdown has shuttered much of NCEI's product production, including their climate at a glance. This product provides monthly climate information for geographic areas ranging in size from the globe to cities. The IEM continues to attempt to independently replicate much of this dataset via expansive raw data processing and aggregation. The featured chart presents a comparison of yearly precipitation totals between the IEM and NCEI products for Iowa with positive values indicating the IEM estimate is higher than NCEI. While the overall bias is quite small, there are certainly periods of degraded performance and some systematic biases that likely could use some more work. A benefit of the IEM product is that it is available at a daily interval and updates in near real-time.
After sub-freezing temperatures were observed over northern Iowa on Wednesday morning, it is much of the rest of Iowa's turn this Thursday morning to terminate the growing season. The featured map presents counties under a Freeze Warning by the NWS at the time of this feature posting Thursday morning. Many counties to the south of the shown warning are under a Frost Advisory, which covers more marginal freezing temperature conditions. The Freeze/Frost NWS headlines can be a bit confusing this time of year as they are one-time products and can have local office variances on when they will be issued after assessments are made of previous freezing temperature events. For example, you don't see a Freeze Warning over the areas of northern Iowa that had such temperatures on Wednesday morning. Once the growing season is believed to be done for a county, there are no subsequent headlines issued for future events during the fall season.
