Last Build Date: Mon, 05 Dec 2016 16:15:55 -0600
The first snow storm to impact most of Iowa arrived over the past weekend with the highest totals appraching 8-10 inches found near Davenport. Air temperatures did not dip much below freezing and are above freezing over some locations that received snow yet this morning making for less significant travel impacts. Temperatures are expected to warm today, which should melt the snow for most Iowans.
For the September through November period, the Des Moines Airport reported its warmest fall season on record this year as shown by the featured chart. It beat out 1931 and 2015 by a rather wide margin of a full degree. The chart depicts years that are above long term average in red and below in blue. Most of the recent years have been above this long term average and the yellow highlighted line depicts a 30 year trailing average that has been trending upward as well.
Based on preliminary and unofficial data computed by the IEM, the featured map presents climate district precipitation total ranks for the September through November period this year. A remarkable contrast is shown in Iowa with northwestern Iowa analyzed to have its third wettest fall and southeastern Iowa having its eighteenth driest. Similar differences exist elsewhere in the Midwestern US.
Waterloo picked up 0.8 inches of precipitation on Sunday and 1.40 inches total for the month. So for this November, Waterloo received more than 50% of the monthly total of precipitation within one 24 hour period. How common is this situation? The featured chart presents the monthly frequency of having such an occurrence for Waterloo. About one in three years see this happen during November, so not uncommon at all. The climatologically wettest month of June has the lowest frequency as having a single intense rain event for month is very unlikely (other rain events are more likely to add up).
An ideal setup for tornadoes in Iowa during November materialized on Monday prompting the NWS Des Moines to issue seven tornado warnings. This makes for the second year in a row that November received the most number of warnings by the office. The featured chart displays the monthly warnings count for NWS Des Moines since 1986. Previous to last year, one has to go back to the famous tornadoes back in 2005 for issued warnings in November.
It was a windy trip back from Grandma's house for Thanksgiving on Sunday. We are well into the fall season and strong passing low pressure systems help to drive strong winds as was the case on Sunday. The featured chart displays a time series of sea level pressure observations from the Ames Airport for the past year. The plot nicely shows the change in variability of this atmospheric variable between the cold and warm half of the year. The increased variability during the cold season are due to the stronger storm systems and air masses. The absence of these during the summer months lead to the less variable pressure readings.
Snowfall has been difficult to come by in Iowa so far this late fall season. The featured chart looks at the total number of distinct days per month that light snow was reported at least once by the Des Moines Airport weather station. Only the 18th had -SN (light snow) reported by the station so far this November. On average, we should see about five days for November.
High temperatures for your Thanksgiving will continue the recent few days of chilly weather. The featured chart displays high temperatures for each Thanksgiving for Des Moines. The actual high today will be close to the long term average of 42. The chart shows lots of spread with some days in the 60s and some in the 20s!
A needed rainfall fell over Iowa on Tuesday with much of the state receiving totals unseen in the past two months. The featured chart displays a calendar of daily precipitation reports from the Ames Airport. The 0.62 inches yesterday is the largest total since 22 September.
On Friday morning, the first major cold front of the season plowed through Iowa. At the Des Moines Airport, the temperature dropped about 20 degrees between 6 AM and noon. The featured chart looks at the largest six hour temperature drops reported at the site during November. The largest drop of 35 degrees happened during the same 6 AM to noon period back in 1940! Temperatures will continue to be chilly with a cold rain on Tuesday.
It took a while for winter like weather to arrive in Iowa this fall, but our first snow producing storm of the season is in the books. The IEM Daily Feature attempts to document the snowfall totals from these events and sequentially numbers them over the season. Having about two inches of snow and/or significant impacts are an informal rule before numbering a storm event. These analyses combine available NWS COOP, CoCoRaHS, and NWS Local Storm Reports. Upwards of six inches are shown on this map over portions of extreme northwestern Iowa.
Very mild air returned again to much of Iowa on Thursday with record highs for Des Moines and Lamoni. The 76 degrees for Des Moines was just a few days shy of the latest in the year 76 degree reading on record. The featured chart presents the latest dates for a given high temperature for Des Moines. The chances of seeing 70 degrees again this year are very small, but the first major blow of the winter season will miss us to the north and west. While we won't see the snow, the cold and wind will be making a visit!
Temperatures are expected to again warm to very enjoyable levels today with the featured map depicting the NWS forecasted highs. Reaching the lower 70s for mid November is rather exceptional, so get outside and enjoy this weather before temperatures crash on Friday and the snow starts flying to our north over Minnesota and the Dakotas.
The featured map displays MRMS estimated precipitation totals for the past 31 days. Most of the western half of the state is analyzed to have received less than one inch of rain and there are a flew blotches in west-central Iowa near zero! With the growing season well over, the dry and warm weather has certainly been welcome to help with the fall harvest progress. The US Drought Monitor only has a small concern of abnormally dry conditions over southeastern Iowa. This dry fall weather followed a very wet end of summer, so impacts are nill thus far.
The primary purpose of the weather stations (ASOS + AWOS networks) located at airports is to support aviation! Besides measuring wind speed and direction, these stations also make important observations of horizontal visibility and an estimate of cloud coverage at altitude. The combination of these later two observations are lumped into four categories that generalize the flying condition. The featured chart displays the hourly flight category as computed by the hourly observations from the Des Moines Airport. VFR (Visual Flight Rules) are the best conditions for flying and for allowing many variants of pilots and flight. This category has dominated for the month with only a few hours on the 2nd in a less favorable category.
The temperature finally breached 32 degrees at the Des Moines Airport on Saturday, making for only the second latest freeze on record (behind just last year of 2015 and only a day later on the 13th). The featured chart displays the to date minimum temperature climatology for the site. After a quick dip back near average in mid October, the minimum was not breached until recently.
Thursday was yet another warm fall day in the state with some places, like Des Moines, reaching 70 degrees. The featured chart displays the period each year between the first and last 70+ degree high temperature. Reaching this warm of a temperature in November is not necessarily uncommon and the average last date is about 11 days earlier on 30 October. We shall see if this was our last 70 degree temperature of the year as the near term forecast has highs much closer to average for this time of the year, back in the 50s.
The featured map displays the number of days since last reported precipitation for the primary climate sites tracked by the NWS. While much of Iowa is in the 1-2 week range, there are parts of the southeastern US over 50 days without rain! In fact, Birmingham, AL has established a new record for longest period without rain (52 days).
Yesterday was yet another pleasant day this November with highs reaching into the 60s for much of the state. This was with mostly sunny skies overhead. The featured chart looks at the observed frequencies of overcast clouds at a given temperature in November for Des Moines. It is interesting to note the three regimes depicted in the chart. For really warm or cool temperatures, it is clear that less cloudiness needs to be present. This makes physical sense as the presence of clouds at night traps heat and during the day, limits heating by the sun.
The featured chart displays the number of year to date Severe Thunderstorm and Tornado Watches issued by the Storm Prediction Center since 1997. The top panel displays the number issued nationwide, the middle panel shows the number that had any part of the initial watch outline overlap Iowa, and the bottom panel shows the percentage of watches that overlapped Iowa for that year. This year's total is a mere 52, which is the lowest found within the modern database. It is interesting to see each of the past five years show up in the least number of watches for the period.