And yet another mostly dry month is in the books this year, but some lucky areas of the state did pick up close to average rainfall. The featured map presents an analysis of NWS COOP rainfall reports for the month and some parts of the state are shown under an inch. The forecast does not hold much hope with only limited and brief chances of rain this upcoming week.

For the first nine months of the year and based on preliminary estimates by the IEM, 2012 comes in as the third driest on record since 1893 for Iowa. The featured chart displays the yearly totals of precipitation for the first nine months of the year. Only 1988 and 1894 come in with lower totals than this year. We really need a wet fall and winter season to recover the soil moisture in time for the planting season next year.

Applying trend analysis techniques often used for stock price forecasting to weather data is an interesting venture. The featured chart looks at "golden and death crosses". The "cross" is a reference to the intersection of two moving average lines within a time series plot. One line represents a short term window average and the other is a longer term window average. The theory is that when the short term moving average moves above or below the longer term average, the immediate term direction of the trend continues (aka momentum). A "golden cross" is when the short term average surpasses the longer term average (upward momentum) and a "death cross" is the opposite situation (downward momentum). So applying this to a time series of daily average temperatures, we can find these cross events occurring between a 50 day and 200 day moving average (typical periods used for stock price analysis). The top chart shows an example of this analysis for the recent few years. These events happen once per year and their date of occurrence is included in the bottom two charts. When the actual data has a preference to be on one side of the trend line, this is called either support from going lower or resistance to going higher. The cross events are said to denote a regime switch between resistance and support. So within the past week we had a "death cross" which would indicate that the near term 50 day trend will now act as resistance and our temperatures are going lower! Of course, we live in a physical world and statistical behaviors of temperature are more a result of cyclical processes that play nicely with trend analysis techniques.

Our warm and dry weather this year has not felt like recent years in Iowa. The featured image presents an academic exercise of matching our weather to another place's climatology. On a two week basis, which site in the country has the closest climatology to the temperatures in Des Moines. Or more simply, where does our weather most feel like? As the graphic shows, we have had quite the journey this year with trips to Hawaii, the west coast, Texas, and others! The two sites in blue were the only matches for locations to the east of Iowa. While not shown, this analysis was run for the previous wetter years of 2010 and 2008. Those years had many more matches for locations to our east. Our climate this year has been more like a semi-arid one, than a humid continental.

Iowa remains in the firm grasp of a drought, but when did it start? It is hard to define when a drought starts as the term "drought" is ambiguous and it takes some amount of time of dry weather before the term can apply. The featured chart looks at the running departure of statewide precipitation over three different windows of time for a period around 1988 and our current drought period of 2012. For this year, this analysis would clearly indicate that significant deficits started showing up in May. Although, a closer look shows somewhat drier conditions existing since September of 2011. Let us compare 2012 with 1988 shown in the top chart. Significant deficits started appearing in March of 1988. If the 2012 drought started in May and 1988 in March, this may provide some insight into why agricultural crops were not a complete failure in the state this year. The reason being there was some soil moisture available to start off the growing season and some precipitation came in late August/September to help out. Notice how the 365 day departure degraded in Aug/Sep for 1988 and flattened out for 2012.

After spending most of the year comparing this year to the 1930s for hot temperatures, we now have a comparison for cold temperatures as well! At least two locations in Western Iowa reported a low temperature of 12 degrees on Sunday morning. This is the coldest temperature reported this early since 6 October 1935 when 12 degrees was reported as well. The featured chart presents the yearly minimum fall temperature reported prior to 8 October and the first date that a sub 13 degree temperature was reported for the fall for anywhere in the state. Typically, this cold of weather arrives in November.

Based on preliminary statewide data, this year is the third driest on record since 1893. Over various this year, it has been wetter or drier than that. The featured chart looks at precipitation ranks when computed from a period to today or from the first of the year to a given date. For a period from 1 May to 8 Oct, this year is the driest on record for the period. While the rains of August helped short term deficits (top chart), they did not change the year to date ranks (bottom chart). There are actually some chances of rain in the forecast! Hopefully they start a process on making up these deficits.

As with most of the year, rainfall has been difficult to come by in the past four weeks. When smeared over the entire state, the estimated rainfall on Tuesday added up to a mere 8 hundredths of an inch and matches the highest total we have seen since the 17th of September. The highest total so far for September and October is just 26 hundredths of an inch. Since 1893, the smallest maximum daily total for these months was 34 hundredths back in 1952 and 1953. Our fortunes may be about to change with thunderstorm chances arriving this weekend and expectations for heavier rainfall totals than what we have previously seen from passing storm systems.

The featured image presents an update on the chances that this year will be the warmest on average for Des Moines. The chances are computed by taking this year's observations and appending all previous years observations to represent scenarios. The result of this operation shows that over 86% of the previous years would result in this year beating out 1931 (current warmest year). The forecast for the next week has overnight low temperatures on the warm side, which should help keep 2012 with a comfortable lead!

The big weather story this week is the predicted severe weather outbreak arriving this weekend. The featured image is forecasted severe weather threat categories from the Storm Prediction Center for Saturday. Much of Iowa is in the slight risk category. Typically, these fall severe events are conditional on heating of the lower atmosphere, so seeing the sun shine on Saturday would be a bad omen as it would help to fuel thunderstorms later in the afternoon.

Most of Iowa picked up much needed rainfall this past weekend and avoided the severe weather as well. The featured map is of estimated precipitation for the event. The highest totals were near five inches with much of the state over an inch. This was easily the heaviest rainfall in Iowa since April! Some more rain is in the forecast for mid week with comfortable temperatures.

This past weekend experienced Iowa's heaviest rainfall since April of this year. This was thanks to an increase in moisture and efficient rainfall producers. The dew point temperature rose significantly into the weekend from 14 degrees on Friday morning to 64 by Saturday evening for Waterloo, which makes for a 50 degree jump in just under two days. Checking back on the archives of data for Waterloo, the largest two day change in dew point on record occurred on 17-19 January 1996 when the dew point went from 50 down to -21 degrees (71 degrees). When just considering rises in dew point over two days, 56 degrees was the maximum back on 1-3 July 1949.

Precipitation comes in various forms and at various rates for Iowa. For this year, precipitation has been difficult to come by. Have we missed out on heavy rainfall events or lots of smaller rainfall events? The featured graph attempts to address this question by showing the accumulated precipitation over increasing daily precipitation. For example during 2012, the total rainfall for daily events less than 0.5 inch has been 15 inches. Restating, 15 inches of rainfall this year has come from daily events of less than 0.5 inches. The flood year of 1993 certainly sticks out on the opposite end of the spectrum. So for 2012, the line would indicate we have missed out on both light and heavy rainfall events.

A strong fall storm system is currently providing Iowa with plenty of wind and severe weather over the southern plains. Our sea level pressure has dropped below 1000 mb for the first time since May. The featured chart looks at some climatological aspects to the mean sea level pressure (MSLP) reading for Des Moines. The top chart presents the range of observations for each day of the year since 1960. The range in pressure is much smaller during the summer time due to the strong storm system tracks being further north and the air mass dominance of warm air. The bottom chart is an attempt at showing the relative frequency of pressure readings and the variability of the fall, winter, and spring months can clearly be seen. These larger differences in pressure help to drive stronger winds as will be the case for today!

With a number of comparisons being made of this year to the years of the Dust Bowl Era (1930s), it only makes sense that a full blown dust storm visit the plains states now as well. A very large storm system generated a large area of strong winds on Thursday and kicked up a bunch of dust from Nebraska to Oklahoma. The featured image shows the combination of peak reported wind gust along with a true color image from the Aqua MODIS satellite. You can see the streak of brown just outside of the cloud shield from the storm complex. Peak winds were well above 50 mph and even reached 75 mph in some select locations.

After some blustery and chilly days this October, very warm weather returned on Sunday with the high temperature, once again, exceeding 80 degrees for Des Moines. Des Moines has already recorded the most number of days over 80 in any year for the site. The featured chart looks at the local day temperature departure for days this year that have been over 80. The very anomalously warm days in March were certainly the most exceptional of the year. The bottom chart shows the percentage of days over 80 that were also 10+ degrees warmer than long term average. 2012 shows up again with its contemporaries of 1934 and 1936.

Very muggy air for this time of year visited Iowa on Monday. The dew point temperature reached 65 degrees Fahrenheit for Des Moines. It is very late in the year to have such a high dew point temperature as shown by the featured chart. Only two other years (1934, 2004) have experienced 65+ dewpoint after 22 October. Two more very warm days are expected before much colder air arrives and highs will only be in the 40s!

The featured chart presents the number of days this year that Des Moines high temperature has been at or above a given threshold. For thresholds between 63 and 83, this year has seen the most number of days at or above those levels. Today will be yet another very warm day with highs expected to near 80 degrees. Big changes arrive on Thursday with highs back into the 40s for the weekend.

The very muggy air that has visited Iowa for the past fews days is almost swept clean from the state with the passage of a strong front this morning. It took a bit for showers and thunderstorms to get going Wednesday evening, but the rains did come after sunset. The featured chart looks at the frequency of getting measurable precip for a 24 hour period after a given dew point observation by week of the year. The general pattern is with increased dew points for a given week, the chances of precip increase as well. The highest frequencies are for the spring and fall periods at relatively high dew points for that time of year. These higher dew points are often associated with storm systems that draw moist air from the gulf region northwarn and eventually lead to precipitation, like what is happening today.

This year has seen many very warm days. When compared with the same day for 2011 for Des Moines, this year has had 117 net more warmer days for high temperature! This total dwarfs all previous years on record and interestingly makes for the fourth straight year for more net warmer days than the previous year. Even if you compare this year with previous years for the same period up until 26 October, it is still well ahead of any previous year. This total does look to go down slightly in the coming days as much colder air has arrived and even some snow over northwestern Iowa on Thursday afternoon!

While living in the here and now, it is sometimes difficult to grasp the historic event that is unfolding with Hurricane Sandy. Sandy will be associated with infamous names like Andrew, Camille, Hugo, and Katrina. The featured image displays a visual comparison of forecasts from the National Hurricane Center and the track of Sandy up until this morning. The track does not tell the whole story of the size and impacts from this storm system that are being felt from Maine to Florida and to the west even to Chicago!

Hurricane / Hybrid storm Sandy came ashore Monday evening and brought lots of wind, rain, and storm surge along with it. The featured map is a simple analysis of peak wind speeds reported on Monday. The big caveat with maps like this during big storms is that stations are often knocked offline during the highest impact weather and will miss reporting the highest wind speeds. The highest reported wind speeds were in the 60 to 100 mph range for most of the eastern coast from Virginia to Maine.

For Des Moines, October looks to be the first month with a below normal daily average temperature since September of last year. Statewide, August of this year was slightly cooler than average as well as October. The monthly departures are shown in the featured image and the departures have been rather large to the warm side in the past two years. November looks to start off on the warm side of average and mostly dry conditions.