A SUMMERTIME COLD FRONT APPROACHES

terryswails1
22 hours ago
2 min read

A rather potent cold front is forecast to move through the central US during the middle part of the week and will bring some (relatively) cooler temperatures and chances for thunderstorms. The Climate Prediction Center has below-normal temperatures forecast for the region July 18-22 as northwest flow takes over.

Model guidance has temperatures falling into the upper 70s/low 80s late this week following the cold front passage. This may come with some lower humidity as well so a pretty pleasant end to the week for the Quad Cities region, overall.

Notice the big warm up however before we get there - that will be the unstable air that may be the fuel for thunderstorms, some strong, on Wednesday along that cold frontal passage.

Upper air support will be sufficient for thunderstorms with a trough moving through the central US. This will provide adequate, but not necessarily strong, wind shear. The timing across Iowa and northern Illinois will be favorable based on the latest European ensemble.

EURO ENSEMBLE

GEFS ENSEMBLE

The main ensemble models are hinting at increased precipitation chances for the region along this cold front. As we are several days away this is lower confidence for now, but the signs are all there for rain and storms on both the European and American (GEFS) products.

Analog support is also there for this, including some increased severe weather probabilities. The analogs have an 80-90% chance of at least one severe weather report. For the time being the Storm Prediction Center does not have an official outlook for the area, likely due to limited confidence at this point in time. If these trends continue I would expect that to change.

Moisture levels ahead of this cold front will be on the higher-side of climatology with precipitable water values likely approaching 1.75" to 2.00". This is in the 90th percentile. This could be problematic for the region given recent heavy rains, especially around the Quad Cities which was placed under a Flash Flood Emergency Friday. The good news is that this cold front should be rather progressive, or quick moving, so ideally storms will not linger and keep training.

This July is off to a very wet start. For northwest Illinois its the wettest-start to a July on record (since 1893). For central Iowa it's in the top-five for wettest July 1-12 on record. The ground is starting to get saturated and cannot take another round of heavy rainfall.