Past IEM Features tagged: fog
January Fog Days
24 Jan 2023 04:49 AMBesides death and taxes, it appears dense fog is another certainty of life. Fog is again present over Iowa this Tuesday morning. The featured chart presents the number of days each month that the automated weather station in Marshalltown reported at least one hourly report of Fog. There are caveats with automated fog reports as equipment has changed over the years, but this year's total is certainly well above a simple climatology average. For this site and analysis, it would appear January is the peak for fog days, so that is something to look forward to as we creep closer to spring!
Voting:
Good: 11
Bad: 0
Tags: fog
Dense Fog Advisory Timing
04 Jan 2021 05:34 AMThe new year has seen plenty of dense fog, which has prompted the NWS to issue a number of Dense Fog Advisories to alert the public to its impacts. The featured chart presents the time of day frequency for advisories issued for Story County (Ames). Please note that this plot does not imply overall frequency in time, but only for time when the advisories are active. For example, for the 146 such advisories issued for Story County, about 70% of them were active during 6 AM. The chart shows a clear diurnal signal with sunshine often helping to "burn off" the fog and prompt the end to the advisory. Such will hopefully be the case today with sunny conditions expected after the fog dissipates.
Voting:
Good: 10
Bad: 1
Tags: fog
Best Time for Fog
22 May 2018 05:35 AMDense fog is present over much of Iowa this Tuesday morning. The featured chart looks at the frequency of reported fog based on hourly observations from the Ames Airport. This analysis would place late May as one of the least frequent times of year for fog for the site. The side and bottom panels show the hourly and weekly histograms. Of course, fog is most common during the early morning and pre-dawn hours as the atmosphere cools and the air becomes saturated.
Voting:
Good: 11
Bad: 0
Tags: fog
Dense Fog Advisory Counts
20 Jan 2017 05:40 AMA Dense Fog Advisory is in effect for the entire state this Friday morning. The featured chart presents some frequency metrics for how often this weather alert is issued for somewhere in the state of Iowa. The top panel shows the weekly frequency of having at least one event for that week per year. The bottom panel shows the overall total number of events. The winter months are certainly the most common time of year for this product with summer having the least. Fog is easier to maintain during the winter thanks to moist air masses over top a colder ground surface which helps to keep air temperatures near water vapor saturation.
Voting:
Good: 8
Bad: 0
Tags: fog
Fog Frequency
17 Aug 2016 04:55 AMSeeing fog this time of the year during the early morning hours is certainly not uncommon. The featured chart looks at the frequency of fog reports by the automated weather station in Des Moines. The chart is a 2-D histogram showing the observation frequencies by hour of the day and week of the year. The highest frequencies are in the early morning hours, when the best conditions for fog exist (longest duration of overnight cooling, highest humidities, calmest winds and least vertical mixing). The summer months show a clear minimum in the mid afternoon and overnight periods. These are periods influenced by heating, which lowers humidities and well mixes the lower atmosphere.
Voting:
Good: 9
Bad: 0
Tags: fog
Dense Fog Advisory
31 Aug 2015 05:34 AMThe past two mornings have seen Dense Fog Advisories issued by the National Weather Service. How common is this advisory issued? Are there favored places in the state for these conditions to warrant issuance of the product? The featured map attempts to answer both of those questions by displaying the average number of dense fog advisories issued each year. A clear east to west gradient is shown with averages ranging from 5 to 10 per year.
Voting:
Good: 14
Bad: 6
Abstain: 3
Tags: fog
Dense Fog Advisories
24 Oct 2014 05:44 AMAfter the rain yesterday, skies cleared off and temperatures cooled creating dense fog this morning. The National Weather Service has much of the state under a Dense Fog Advisory this morning. The featured map displays the yearly average number of Dense Fog Advisories issued by forecast zone. The lines on the map are the edges of NWS forecast office zones. For Iowa, most of the state is in the 7-10 advisories per year range. The highest frequencies are near the Gulf of Mexico as the warm and humid air comes onshore and cools, creating fog. There is an interesting white patch over West Virginia. This is the Charleston, WV forecast office, which according to IEM databases has not issued a Dense Fog Advisory since at least 1 Jan 2006.
Voting:
Good: 28
Bad: 12
Abstain: 9
Tags: nws fog
Fog and afternoon temps
04 Dec 2013 05:46 AMFog was common yesterday over Iowa and continues this morning as a major winter storm organizes. The featured chart presents the frequency of having the maximum afternoon temperature above the average daily high temperature when fog was reported at the 6 AM observation that day for Des Moines. The general signal is for fog in the winter time to be associated with warmer than average afternoon temperatures. Correlation is not causation and foggy conditions in the winter time are typically a sign of being on the warm side of a passing storm system. The cold side of the storm system will arrive today and take the fog with it. So enjoy the fog and slightly warmer temperatures while they last!
Voting:
Good: 19
Bad: 8
Abstain: 3
Tags: fog
Careful of the Fog
20 Dec 2007 07:17 AMDense fog has developed most every day this week as warmer air from the south keeps encountering all of this cold ice and snowpack covering Iowa. On Wednesday, the webcams caught some neat lapses of the fog lifting and then settling in again. The Nevada webcam lapse is from 150 feet above the ground, so it was above the shallow layer of fog that crept along Wednesday morning. The Newton webcam lapse shows thick forming, lifting, settling back in, and then lifting once more. We will see more dense fog today in some locations.
Voting:
Good: 13
Bad: 4
Tags: fog webcam