An active week of weather is ahead with multiple disturbances to note early in the week. A stationary front is currently stalled across the northern portions of our coverage area, extending roughly from Rock Valley to Charles City to Galena, IL. Pressure gradients also are tightening from west to east as a low pressure lurks west of the state. Already, early morning water vapor imagery has shown cloud cover with dew points up to the 50s already in some places. Bottom line: rain is on the way this morning. Light to moderate rain is expected to overcome the area by afternoon as southeast flow aloft brings ample moisture into the area. Temperatures today are expected to be moderated with upper 50s to low 60s the highlight numbers. There could be an isolated strong to severe thunderstorm late. These storms will be elevated and shouldn’t pose too much of a threat other than small hail. The SPC has outlined a marginal risk of severe thunderstorms in this area.
Tomorrow will be a similar story. Widespread showers and thunderstorms are expected (which will thankfully relieve some of the dry conditions that have set in the last couple of days) with the highest accumulations expected across northern Iowa. Nearly an inch of rain will be possible over the north with lighter amounts south. This will be the first of two big rain producers that we will see this week. Temperatures Tuesday will be chilly with upper 40s to mid 60s being the range. Some isolated strong to severe cells will again be possible across the south, however anything that does develop will be elevated and will just have small hail and gusty winds, similar to today. System should push east by evening, likely leaving some fog in it’s trail with a saturated air mass.
By Wednesday, a more powerful low pressure system will move into the area. Uncertainty still exists late into the cycle with different models pointing to different solutions. The American model, the GFS, is pointing to a single significant system Thursday afternoon. The European model (ECMWF) and the Canadian model (GEM) both point to two separate systems, one on Wednesday and another on Thursday.
We are still looking over a lot of model data and are waiting this event to get closer to be able to see the other American models that only go out mid-range. The Storm Prediction Center is expecting storms to begin firing across Kansas and Oklahoma in the afternoon on Wednesday afternoon and remain fairly isolated and scattered in nature (not linear). An elevated risk of severe weather has been posted for most of those south of Interstate 80 on Wednesday. As cells develop and continue moving into the area, large hail and damaging winds will be possible.
Wednesday’s activity should remain in the early morning hours on Thursday, which will present a variety of wild cards. The first one is if storms stall over the state too long. This could take away much of the instability available for the afternoon. The second, is where the boundaries are laid out – and how this would change things later in the afternoon. And the third, is Wednesday itself. The location and timing of everything that happens on Wednesday will create a strong dependency for Thursday. Clearly, there is a lot of issues, predictability-wise.
Currently, it’s expected that storms will redevelop in the mid-to-late afternoon hours on Thursday after clearing. If things work out with Wednesday’s storms clearing out allowing for re-development, anything that develops will have a lot of ingredients to tap into: from moderate instability to very good shear associated with the low pressure center moving into the area. This would lead to a widespread large hail, damaging wind, and tornado risk, primarily in the east. We won’t divulge too much into this too much at this time due to these uncertainties – we will likely know more in future outlooks.
Nonetheless, severe weather will be possible mid-week, and you should to pay attention to future forecasts as this is an evolving forecast. Stay tuned to the Iowa Weather Network for the latest information!
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