Winter is approaching and Kansans are interested in what they should expect this winter. The NOAA Climate Prediction Center has released outlooks for temperature and precipitation during the winter season -- December through February.
The temperature outlook calls for a slight increase in the chance for warmer-than-normal temperatures statewide (Figure 1). That tendency increases as you move further north and west in the Plains. It is important to remember that this is the 3-month average. There could be significant cold periods and still have an overall warmer-than-normal winter. One difficulty with that pattern is that crops and livestock are not able to develop strong winter hardiness. This makes them more susceptible to severe conditions during the occasional extreme cold snap.
Figure 1. 2018-2019 Winter outlook map for temperature. Source: www.NOAA.gov
The precipitation outlook is neutral, meaning there is an equal chance to have above-, near-, or below-average precipitation this winter (Figure 2). Winter is normally the driest time of the year for most of the Plains. Southeast Kansas is an exception, with a more even distribution of precipitation across the year.
Figure 2. 2017-2018 Winter outlook map for precipitation. Source: www.NOAA.gov
It is worth noting that neither the temperature nor the precipitation outlook predicts the degree to which conditions will vary. Instead, these outlooks provide confidence that warmer- or wetter-than-normal conditions may occur as a percent. A tenth of a degree (0.1) warmer-than-normal average temperature would validate the outlook to a similar extent as an increase of 10 degrees. A hundredth of an inch (0.01) greater-than-normal average would have a similar result in the precipitation outlook. Significant wetter-than-normal conditions would be needed to improve the drought conditions in the Northern Plains. In Kansas, only 1% of the state is in moderate drought with approximately 7% of the state abnormally dry. With the equal opportunity for a wetter/drier than normal winter, anything is possible. More information about the outlooks and how to interpret them can be in found in the KSRE publication “Climate Outlooks Serving Agriculture” (MF3432, https://www.bookstore.ksre.ksu.edu/pubs/MF3432.pdf)
What factors are considered to produce winter outlooks?
The major force responsible for the current winter weather outlook is the ENSO (El Niño-Southern Oscillation) signal. At this time, a weak El Niño pattern (warmer-than-normal waters in the Pacific along the Equator) is expected through the majority of winter. Storm tracks during El Niño winters typically have a southern track across the continental U.S.
Given the uncertainty of the El Niño, other factors may have a stronger influence. Two patterns that deserve attention are the North Atlantic Oscillation (NAO) and the Madden-Julian Oscillation (MJO). The NAO is a comparison of high and low pressure in the Atlantic basins. When the NAO is negative (with a weak gradient between high pressure in the subtropics and low pressure over Iceland), the east coast of the United States tends to have stronger cold outbreaks with more snow (Figure 3). Some of that can clip the eastern Plains region. However, it most often positions the Central Plains in the transition area between a warmer/drier air mass to the west/north and a cooler/wetter in south/east. Often this means quick surges of moisture with storm systems and a prolonged period of drier, slightly warmer, and windier conditions afterwards. A positive Pacific/North American Oscillation that further emphasizes the increase in windy periods and dry spells is also reinforcing this NAO pattern.
Figure 3. Negative NAO. Source: www.NOAA.gov
The MJO is an eastward moving 'pulse' of cloud and rainfall near the equator that typically recurs every 30 to 60 days (Figure 4). The position or state of the MJO influences storm generation across the United States. Unfortunately, both the NAO and MJO conditions can change rapidly, and forecasts for these patterns are not as well developed as for the ENSO. That makes it difficult to gauge their impacts on an extended basis.
Figure 4. Madden Julian Oscillation. Source: www.NOAA.gov
For Kansas, average winter temperatures range from 28 degrees F in the northern regions to 37 degrees F in the southeast (Figure 5). Average total precipitation (Figure 6) ranges from less than an inch in the west to over six inches in the southeast.
Figure 5. Normal winter mean temperatures for Kansas. Source: Weather Data Library.
Figure 6. Normal winter precipitation for Kansas. Source: Weather Data Library.
Aside from the impact on fall-planted crops, such as wheat and canola, a big concern is how the winter conditions set the stage for the spring fire season. Widespread killing frost occurred in mid-October, brought the end to the growing season, and introduced fine fuel availability. Large, above-average fuel loads were reported in southwest Kansas this growing season along with "surprisingly" high, but were actually around average, fuel loads in east despite a long period of drought.
With gradually increasing El Nino and coinciding negative North Atlantic Oscillation and positive Pacific/North American Oscillation, a favored storm track would take a majority of moisture south of Kansas. This would develop warmer-than-normal temperatures with slightly above-normal episodes of dry/windy conditions the next 30-60 days. Climate models trend persistence of this pattern into mid-late winter - through portions of February. With coinciding high fuel loads in southwest Kansas, this would begin to increase concerns for earlier than normal short duration large fire concerns in this region by mid-winter. This would especially be a concern should preceding dry conditions combine with lack of snow and result in the drying of heavier fuels and standing fine fuels.
Mary Knapp, Assistant Climatologist
Christopher “Chip” Redmond, Kansas Mesonet Manager
Eric Ward, Assistant Fire Management Officer, Kansas Forest Service