January 2015 Central Iowa Climate Summary

Temperatures

January 2015 was an interesting month with active winter storms and well below normal temperature during the first two weeks of the month, then spring-like conditions during the middle to late part of January before a big winter storm on the 31st. The statewide average temperature for Iowa was 21.3°F or 1.9°F above normal for January (See Figure 1). January 2015 becomes the 51st warmest January on record out of 143 years of records. The first three days of January were just above normal, before cold temperatures settled into the region on the 4th and lasted through the 14th. From the 15th through the end of the month, temperatures were above normal, making it 17 days in a row when the statewide average temperature was above normal.

A large Arctic high pressure dominated the weather pattern and brought the coldest stretch of the month from the 4th through the 8th (See Figure 2). In fact, the high pressure was so strong, that a new record all-time high pressure was set at Des Moines on the 7th with a barometer reading of 31.07” of Mercury. This broke the previous record of 31.06” set back on February 1, 1959 at that station. Low temperatures bottomed out well below zero and resulted in some very cold wind chill values during this time frame. The coldest mornings occurred on January 6 and 7, 2015 when 20 to 35 below zero wind chills were recorded (See Figure 3). Mason City and Clarion recorded -35°F wind chill values on the 7th.  Waterloo recorded low temperatures of -10°F or lower from the 5th to the 9th with the lowest temperature of -18°F on the morning of the 6th. In fact, Waterloo had 10 days in a row with minimum temperatures below 0°F from the 4th to the 13th (See Figure 4). Multiple other stations had similar temperature trends during the aforementioned time frame (See Figure 5).

The second half of the month was well above normal as there were several days with temperatures reaching the 50s and even 60s in a few spots. The warmest temperature of the month was 67°F on the 28th at Shenandoah, Iowa while the coldest temperature was -25°F at Cherokee on the 13th. Des Moines reached at least 50°F on 6 occasions from the 16th to the 28th, with the warmest temperature of the month on the 16th with a high of 57°F. Des Moines’ coldest temperature of the month was -8°F on the 7th. Waterloo’s highest temperature in January was 47°F on the 24th while the station’s coldest temperature was -18°F on the 6th. The warmest two days in January, on average, were the 16th and the 28th (See Figure 6).

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Figure 1: Average Temperature Departure from Mean for January 2015.

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Figure 2: Average Minimum Temperature, Departure from Mean from January 4 to 8, 2015.

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Figure 3: Wind chill values on the morning of January 7, 2015. Image is courtesy IEM.

Figure 4: Waterloo, Iowa temperature trend for January 2015 compared to normal. Notice the complete difference in cold temperatures in the first part of the month versus the warm temperatures in the last half of January.

Figure 4: Waterloo, Iowa temperature trend for January 2015 compared to normal. Notice the complete difference in cold temperatures in the first part of the month versus the warm temperatures in the last half of January.

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Figure 5: Average Temperature Departure from Mean from January 4 to 13, 2015.

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Figure 6: Average Maximum Temperature on January 28, 2015.

Precipitation

The statewide average precipitation totaled 0.56 inches or 0.36 inches below normal, which ranks 33rd driest January among 143 years of records. The statewide average snowfall was 6.3 inches which was 1.4 inches below normal. January 2015 became the 53rd lowest January snowfall total among 128 years of records. It was a fairly active first week of the year across Iowa with two separate blizzards and another light to moderate snow event sandwiched in between the two blizzards. The first storm of the year brought roughly a half inch to nearly 4 inches across central Iowa on the evening of the 3rd to the morning of the 4th, with the higher totals accumulating over northern Iowa. With the light snow and strong wind gusts in excess of 40 mph, visibility was reduced to less than a mile in several locations during the overnight hours from the 3rd to 4th (See Figure 7). A couple days later on the 5th, a clipper system brought a sharp band of snow that set up over northwest to southeast Iowa. Snowfall totals ranged from a trace in southwest Iowa to 4 to 7 inches from Fort Dodge to Ames to Newton (See Figure 8).  By Thursday, January 8, 2015, a very potent clipper brought blizzard conditions to central and northern Iowa as northwest winds gusted over 50 mph.  These strong winds, in conjunction with intermittent snow squalls and the fresh snow that fell on Monday earlier in the week resulted in significant visibility restrictions and even whiteout conditions (See Figure 9).  Travel was nearly impossible and the Iowa DOT even had to pull plows and shut down Interstate 35 Thursday evening (See Figure 10).

After the blizzard on the 8th, temperatures warmed up and allowed for the snow pack to melt during the middle of the month. By the end of the month, a long duration snow storm began on the 31st and finally tapered off on February 1, 2015 dropping a substantial amount snow over the state. Much of the precipitation started out as rain on Saturday the 31st and slowly transitioned to all snow by the evening. The statewide average snowfall from this storm, January 31st to February 1st, was 8.3 inches and was the largest snow average since December 23-27, 2009 snow storm. The totals from this year’s storm ranged from 5 to 15 inches over the state, with the heaviest band setting up along the Interstate 80 corridor from Stuart to Des Moines to as far east as the Quad Cities (See Figure 11).

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Figure 7: Visibility readings on the morning of Sunday January 4, 2015. Significant visibility restrictions resulted from the falling snow and strong winds.

Figure 9: Peak Wind Gusts on January 8, 2015.
Figure 9: Peak Wind Gusts on January 8, 2015.

Figure 10: The Iowa DOT Road Conditions on the evening of January 8, 2015 shows Interstate 35 closed north of Ames, Iowa.
Figure 10: The Iowa DOT Road Conditions on the evening of January 8, 2015 shows Interstate 35 closed north of Ames, Iowa.

Figure 8: Snowfall totals from the snow storm on January 5, 2015 across central Iowa.
Figure 8: Snowfall totals from the snow storm on January 5, 2015 across central Iowa.

Figure 11: Snowfall totals from the long duration snow storm on January 31 to February 1, 2015.
Figure 11: Snowfall totals from the long duration snow storm on January 31 to February 1, 2015.

Statewide statistics courtesy of State Climatologist Harry Hillaker:
http://www.iowaagriculture.gov/climatology/weatherSummaries/2015/pms201501.pdf

Blog Post by Kenny Podrazik – NWS Des Moines