An opening round of moisture has set the stage for an extremely wet weekend. The 24hr rainfall totals ending on October 4 show the heaviest amounts in south central and east central Kansas (Figure 1)
Figure 1. 24-hour measured precipitation totals for October as of October 4, 2018 (WDL).
Much of the state saw less than a tenth of an inch, although parts of south central, southeast and east central Kansas saw over an inch, with isolated areas reporting over two inches.
So how much moisture might be on tap with the storms expected through next week?
The National Weather Service Weather Prediction Center (WPC) uses a product known as the quantitative precipitation forecast (QPF) to indicate the amount of liquid precipitation that might be received. The QPF is available in a range of time scales from 1-day accumulation to 7-day accumulations. The most recent 7-day accumulation (Figure 2) shows isolated parts of Kansas receiving 7 to 10 inches in the week ending on October 12. Most of central and eastern Kansas could receive 4 inches or more.
Figure 2. Seven day forecasted rain amounts (NWS WPC)
Meteorological factors contributing to the heavy rain
A very unseasonal weather pattern and atmospheric blocking are to blame for the forecasted heavy rain amounts. This active pattern situated across the western United States, more attuned to spring, brings strong southerly surface flow into the Great Plains. This air mass consists of very warm/moist Gulf of Mexico air. Warm/moist air is unstable and is easily lifted up and over a very cold air mass across the High and Northern Plains. This is normal for these strong cold fronts… but the event duration is quite abnormal.
With a very strong ridge of high pressure stationed over the eastern United States, more typical of summer, it prevents the cold front (and associated upper level trough pictured in Figure 3 across the western U.S.) from pushing east out of the Plains. Instead, it wavers eastward with each push of the trough (and associated wind maximum) and brings a round of very heavy thunderstorms with abundant rain (similar to that observed October 3). The front stalls again and begins to push back west and north after the wind maximum passes (similar to the weather observed on October 4). That allows the warm air/moisture to pool up once again before the next system repeats the process. This “ebb and flow” pattern is forecasted to continue until mid-to-late next week (October 11-13).
Figure 3. Upper level winds forecasted for Sunday, October 7 with added descriptions of influences developing heavy rain in central Kansas (Tropicaltidbits.com)
The good: it is bringing much needed moisture to areas that need it for drought mitigation and storage ponds in advance of the driest time of the year.
The bad: very heavy rain is likely where thunderstorms persist. Areas of 3 inches or more will likely not be quite as widespread as forecasted. However, it only takes a few thunderstorms over a short time to likely see some very localized totals in excess of 8 inches. Any moisture, however, has unfortunate timing for those in the process of harvest/plant operations underway across the state. Delaying the drying down (before maturity) could increase the probability of potential impacts, primarily for soybeans and sorghum, related to freeze damage.
Implications for Wheat Planting
The two major implications of the potential excessive moisture for wheat planting are 1) the development of detrimental conditions to fields already planted, and 2) delayed wheat sowing in the fields yet to be planted due to mechanical and biological challenges.
Wet soils provides many operational challenges, often precluding a good sowing operation; thus, producers should not hurry and sow wheat into extremely moist soils. Planting wheat under wet conditions can present either mechanical or biological challenges.
Biological challenges include:
Implications for Harvest
Overall, late-season wet conditions can slow down harvesting progress in summer row crops. In general, harvest continues to advance but these weather conditions will slow its progress. Corn has been reported to be close to 50% harvested across the state with much progress needed for north central and western parts of the state; soybean and sorghum harvest has just started with close to 10% harvested across the state. For corn, late-season precipitation increased fungal colonization of corn ears (e.g. Diplodia issues), and reduced final test weight and grain quality. For soybeans, delay in harvest time could represent losses related to quality and potential issues on shattering. For both soybeans and sorghum crops, wet conditions are affecting the drydown grain rate and final maturity.
You can track rainfall data from the Kansas Mesonet is available at: http://mesonet.k-state.edu
Additional precipitation maps for Kansas can be found on the Kansas Climate website at: http://climate.k-state.edu/
Mary Knapp, Weather Data Library/Mesonet
Chip Redmond, Weather Data Library/Mesonet
Romulo Lollato, Wheat and Forages Specialist
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist