17 June 2020 Weather Update

Departure from Normal Precipitation
Departure from Normal Precipitation

Departure from Normal Precipitation

Departure from Normal Temperature
Departure from Normal Temperature

Departure from Normal Temperature

Drought Monitor
Drought Monitor

Drought Monitor

General Observations

During this past week, a wide range of conditions were observed, including severe weather, a brief cool down, then heat and wind. An upper air trough moved through the northern Plains June 8-9 bringing widespread severe weather to the region. Temperatures cooled briefly statewide from June 10th before the upper air ridge built back into the central United States. Hot, dry, and windy weather prevailed from June 11-14th.

The Storm Prediction Center’s (SPC) preliminary storm totals for June 8-9th indicated that 5 tornado, 25 hail, and 25 wind reports were submitted. Most of the reported severe weather occurred in a northwest to southeast direction from the western Sandhills through southeastern Nebraska. Rainfall was most prevalent in this region and accounts for most of the area where precipitation totals the past week were above normal.

Well above normal temperatures from June 11th to the 14th resulted in weekly average temperature departures ranging from 6 – 10°F above normal across the eastern half of the state, with departures running near normal to 6°F above normal, depending on location. Much of the difference in temperatures can be related to the slow progress of the upper air trough early in the period that kept western Nebraska in the cooler air an additional 2 days.

Crop specific water use calculations indicate that evapotranspiration rates were running 20% above normal with 5 straight days of highs in the 90s and winds averaging over 15 mph on several days, with gusts consistently in the 35 mph or greater range. According to Extension Educators, most of the corn was between the 4 and 8 leaf stage, with a few 10 leaf stage reports coming out of southeastern Nebraska. Growing Degree Day calculations indicate that corn emerged on May 5 should be at an average of 8 leaf statewide.

Based upon recent heat and dryness, along with significant precipitation departures accumulated since April 1, a significant portion of northeast, east central, south central, southwest and the Panhandle should be showing abnormally dry conditions on the U.S. Drought Monitor. It is expected that last week’s depiction (through 0700 CST, June 9) showing abnormally dry conditions across extreme southern Nebraska, as well as the northeaster and northwestern corners of the state will expand significantly with this week’s release.

Crop Progress

According the Nebraska Agricultural Statistics Service (NASS), corn ratings declined substantially during the past week. Corn in the good to excellent conditions dropped from 83% to 71% this week. Ratings are as of June 15. This represents a 12 percentage point drop and reflects concerns about recent heat, wind, and dryness impacts on young developing crops. Conditions appear to be most severe on light soils with low water holding capacity and conventional tilled soils.

University of Nebraska Beef Extension Educators reported on deteriorating pasture conditions last week during their monthly call, and the same issues were repeated on the University of Nebraska Extension crops call June 16th. It should also be noted that recent dryness is of concern for warm season crops, but it can be beneficial in June as is forces plants to develop deep roots to take advantage of deep subsoil moisture (below 2 feet).

If normal temperatures persist for the next two weeks, corn across the state should reach full evapotranspiration potential. At the same time, we will have passed the two wettest months of the year. Under normal climatic conditions, water use will exceed normal precipitation and be in a net deficit. Each year is different and the difference between poor and excellent yields often comes down to the amount of precipitation an area receives compared to normal during July and August.

Outlook

The GFS model is advertising a much wetter pattern during the second part of June than a week ago. As of the morning run on June 16, the GFS indicates that an upper air trough will work its way across the northern Plains early in the period. It then takes this upper air low into the western Great Lakes and pivots another upper air low into its wake across the northern Plains. This will place Nebraska on the southern periphery of an active storm track across the northern half of the High Plains region before briefly returning to a drier pattern to end the month.

As the upper air trough moves across the northern Plains from June 17th to the 20th, thunderstorm activity is expected to increase across the eastern half of the state, with June 18th likely to be the most active day of this period as the cold front associated with the upper air low moves through the state. Numerical models indicate 1 to 2 inches of moisture are possible across the eastern half of the state, with just scattered moisture across western Nebraska.

Relatively dry and normal temperatures are expected in the wake of the upper air trough moving into the Great Lakes region. As this low deepens, it is possible that energy will rotate around this low bringing a chance of a convective line sweeping through the northeast quarter of the state on June 22. As Great Lakes upper air low deepens, ridging will occur across the central Plains region, leading to temperatures in the mid to upper 80’s. Another potent upper air trough then slips into the northern Plains beginning June 23, according to the GFS.

The model aggressively hints at widespread convective activity statewide on the 24th and 26th, with more scattered storms on the 25th and 28th. Dry conditions are expected June 28th to July 1st, before another upper air low is now forecast to impact the central and northern Plains July 2nd to the 4th. This is a recent change from hot and dry conditions of recent runs, so confidence is extremely low in regards to the early July event.

Further out, the Climate Prediction Center (CPC) has updated its ENSO forecast for this summer and fall. There is over a 60% chance of neutral conditions through the remainder of the summer. CPC has lowered its ENSO neutral fall prediction from the 50-60% range to 45-50%. La Niña odds were increased slightly into the 40-45% range, while El Niño odds were decreased to less than 10%. Conditions are slowly cooling in the Equatorial Pacific and odds are increasing that La Niña conditions will be met by December.

Source: Al Dutcher at Nebraska State Climate Office

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