Purpose:
This extended forecast (10-14 days out) is to help you see what we could expect to see on Friday (October 18th, 2019) to Tuesday (October 22nd, 2019). The area we will look at will be the Metro area which includes:
· Southern Illinois
· Southern and Southwest Indiana
· Western and Northern Kentucky
Always keep in mind to be flexible with the weather as it will likely change. This includes any upper air analysis. I hope this assists with planning, and be sure to check out the Metro Weather Watch (MWW) Facebook Page.
Technical:
The challenge of this forecast is time. Depending on how quickly the longwave develops over the west coast and progresses into the midwest will determine the type of weather in the metro area. The models used were GFS, GEFS Mean Spread, and NAEFS. All 3 show very different views on what may happen across each day. However, one thing to keep in mind is the Low-Level Jet becomes a major contribution for moisture transport.
The Friday of October 18th starts off with a high-pressure system over the metro area bringing mostly sunny skies. Temperatures are likely to be above the 50s or 60s and continue into Saturday and Sunday. Differences among the models are seen when Saturday, October 19th approaches. The GFS model has an aggressive outlook when the longwave moves into the midwest. On the other hand, GEFS and NAEFS show the longwave moving slowly into the midwest over time. This causes problems because it will affect how long the high-pressure system will be over the metro area. I would expect Saturday weather to be fairly similar to Friday, but with slightly warmer temperatures into the 60s or 70s across the area. Moisture approaching from the NNW will be enough for only a small chance of rain as it could hit the metro. GEFS shows that only 0.25 inch of rain could happen between the afternoon to evening.
The following Sunday of October 20th will begin with clouds increasing throughout the day. A 50% chance of rain showers and thunderstorms will begin in the evening to afternoon according to GEFS and NAEFS models. The GFS model shows precipitation occurring more into Monday rather than Sunday. Temperatures are expected to fall back to the 50s or 60s. The reason it could rain is from upper air analysis. The longwave trough from the GFS shows a deepening across the midwest. The reason thunderstorms could be possible is due to the GEFS model showing CAPE values around 400J/Kg.
Monday, October 21st will have an 80% chance of rain with 25% chance of thunderstorms according to the GEFS model. Temperatures will be in the 50s or 60s after looking at the GFS and GEFS. The GFS lines up with GEFS Mean, however, there is one major difference. The GEFS Mean extends the chance for any precipitation from Sunday into Tuesday. The GFS puts the rain event from Monday into Tuesday. Both of these models agree that any chance of precipitation will be on Monday, October 21st. Rain will occur in the evening to overnight hours. Severity is small because CAPE values decrease from 300 to 100 J/kg according to the GEFS Mean model.
Tuesday, October 22nd will have a 25% chance of rain. I did this because it’s the middle ground of the GFS, GEFS, and NAEFS models. Rain should not be totally ruled out because it is up for question on how fast the longwave trough moves. Temperatures will be above the 50s and 60s according to all the model outputs.
In conclusion, confidence for this forecast is below average. The Low-Level Jet will be the main contributor for moisture transport after the trough reaches the 4 corners (Utah, Colorado, New Mexico, Arizona). With moisture along the trough, low-pressure systems will appear over Kansas on Sunday and move into the metro area by Monday or Tuesday.
Meteorologist Sean Danaher
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