A Tale of Two Troughs

The big question in the next week is not whether we see precipitation across the state but how much as we move into an active period. Over the next several days, we will be visited by two different troughs coming in from the southwest.

The first trough will be making its way into the central Plains during the day on Friday, April 26, while the second trough will be coming in Saturday night, April 27 through Sunday, April 28. Both will be tapping into moisture and instability to produce widespread showers and storms across the state.

The SPC does have the eastern sixth of the state in a slight risk category on Friday. The risk on Friday afternoon and evening may be higher or lower depending on what happens in eastern Nebraska earlier in the day. If there is sufficient clearing, there may be an enhanced risk of severe storms in places like Pawnee City, Nebraska City, Omaha, and Macy.

Figure 1. Two troughs will bring rainfall to Nebraska from April 25-28.

Figure 2. SPC severe storm risk for Friday, April 26.

There will be ~24-hour break in precipitation, so Saturday currently looks dry and the state will be split by a near-stationary frontal boundary. On the warm side in eastern and south-central Nebraska, temperatures are likely to be well into the 70s, possibly climbing up to 82-85 along and south of I-80 in eastern Nebraska. On the cool side, expect temperatures to hold in the 50s and low 60s, with upper 40's more likely up around Harrison. If that boundary ends up being a bit further east or west, your Saturday high temperatures will look much different than what is currently projected.

By Saturday evening, the second trough will be making its way into our area, bringing additional showers and storms, with severe storms possible in southeast Nebraska. Heavy rainfall may be possible across the southeastern quadrant of the state on Saturday night into Sunday morning. So places that didn’t get as much Thursday night into Friday night have a shot at getting more — perhaps a lot more — on Saturday night into Sunday. Sunday also looks a good bit cooler than Saturday in the eastern half of the state as we will be on the cool side of the storm by mid-morning.

Figure 3. WPC projected precipitation April 25 to May 2.

Figure 4. ECMWF ensemble probability of two inches by Monday morning, April 29.

There is a slight chance precipitation could fall as snow in the Panhandle into the northern Sandhills on Sunday morning, but no major accumulations are expected at this time.

The start of the work week looks dry with seasonal temperatures in the east and a return to warmer temperatures in western Nebraska. Temperatures look to bounce back to the 70s statewide by Tuesday and possibly in the upper 70s to mid-80s by next Wednesday. Another potent storm system may be paying us a visit just in time for the following weekend bringing additional chances for rain. But that is a little ways out.

Figure 5. Projected temperature anomalies April 27 to May 2.

Figure 6. Eight- to 14-day temperature outlook.

Figure 7. Eight- to 14-day precipitation outlook.

Moisture and Temperature Update

Last Wednesday night, the southeastern corner of state saw showers and storms develop off a near-stationary boundary and some areas picked up beneficial rain. Amounts over an inch were reported in Richardson County. Around that same time, a shortwave brought moisture to north-central and northeastern Nebraska, mostly between 0.25-0.50-inch. Additional storms developed over far southeastern Nebraska on Monday evening, but amounts were generally under a quarter inch. In parts of the Panhandle and far southwestern Nebraska, light snow fell last Saturday but amounts were light.

Figure 8. Soil moisture percentiles.

Figure 9. Four-inch bare soil temperatures.

Figure 10. Streamflow percentiles from USGS.

A quick look at soil moisture percentiles shows that much of east-central, southeastern and southwestern Nebraska are at or below the 30th percentile for zero to 1-meter soil moisture, so rainfall in those areas over the weekend would be very welcomed.

With the strong frontal passages late last week, temperatures were below average the last third of last week and were well below average last Saturday in western Nebraska. A couple of sites in Kimball County (where the elevation is over 5,000 feet) didn't even manage to get above 30 last Saturday. Almost everyone in the state went below freezing at some point last weekend (congrats to Hebron for avoiding it) and much of north-central and western Nebraska saw temperatures dip into the mid 20s. For the southeastern quadrant of the state, it is possible — perhaps probable — that it was the last light freeze until next fall.

Crop Update

The latest Crop Progress Report shows corn and soybean planting were at 5% and 2%, respectively, at the end of last week, around average for the time of year. It's likely additional planting has occurred since the beginning of the week with the warmer, drier weather. It is also likely that farmers are going to be sidelined for a while starting later tomorrow. Winter wheat checks in at 68% good to excellent against 5% poor to very poor. Pasture ratings are not available yet (May 1 is often the first reporting date for that) but the VegDRI Rangeland specific map shows that most of the pasture in the state is in reasonable shape for this time of year. Exception being in Dundy and Chase counties where VegDRI indicates moderate levels of stress.

Figure 11. Minimum temperatures last weekend.

Figure 12. Latest VegDRI map.

Figure 13. Seven-day precipitation totals.

Temperature and Precipitation Roundup

Click here to view the average temperature, growing degree days and total precipitation for each station that had no missing days over the last week. Includes CoCoRaHS observer reports. Below are the temperature and precipitation extremes around the state over the past week

• Maximum High Temperature: 81°F, Tekamah Municipal Airport
• Minimum High Temperature: 28°F, Bushnell 15S
• Minimum Low Temperature: 11°F, Harrisburg 12WNW
• Maximum Low Temperature: 52°F, Falls City 4NE
• Max Precipitation: 1.59 inches, Shubert 2SW
• Max Snowfall: 2.4 inches, Bushnell 15S