Midweek Thunderstorms & Their Severe Weather Risk

Before getting into the detail of thunderstorms for midweek, a quick recap on what was a sunshine-filled day with record setting high temperatures for the second straight day in November! Highs ranged from the lower 70s in extreme eastern Iowa to the lower 80s across extreme western Iowa. Record highs were officially set in Atlantic (77), Mason City (75), Dubuque (73) and the record was tied in Des Moines (76); not to mention several other records just outside the state of Iowa. Expect temperatures tonight to only fall into the lower and mid 50s, with a few upper 40s possible in northwest Iowa. Tomorrow's highs may be hampered some by scattered clouds, but near record highs in the lower to mid 70s throughout are still expected.

A low pressure forming off the Lee of the Rockies should push into the Dakotas Tuesday afternoon, and continue moving east overnight. This low will be aided by the development of a warm front that will likely drape across portions of northwest Iowa Tuesday night. This warm front may lead to some showers and thunderstorms across the western half of the state, but the chances are still fairly low. Overnight low temperatures should range from the lower 50s to upper 50s from east to west. As this warm front lifts north by the morning hours, expect strong southerly winds to bring in moisture and warmth ahead of a strengthening cold front to the west of the state.

Models are trying to come together on a solution for the surface low pressure, the frontal position, and overall severe weather threat for the plains states. The latest WRF model has came inline with what the GFS and other models have shown with the surface low lingering over southeast South Dakota by 00z (6 PM) Wednesday. A cold front and dryline will be the focus for thunderstorms along and south of the low through eastern SD/NE/KS and OK. With strong wind fields throughout the plains, the shear should be no problem, nothing unusual for either spring or fall systems. Moisture should be in the mid 50s to near 60 along and just ahead of the fronts from SD southward through OK. The combination of both moisture and warmth at the surface, and cold air aloft should allow for moderate instability over NE/KS/OK and points just east. Although the mode of severe weather is somewhat in question still, I do believe that all modes (damaging winds, large hail, and tornadoes) will be possible from southern South Dakota, through eastern NE/KS/OK, and then extending eastward during the early overnight hours into western IA/MO/AR.

Areas in southeast SD and northeast NE may be looking at some very strong low level shear values with their proximity to the low. Combined with the strong cold air advection aloft, the instability should be sufficient to warrant a low topped supercell event with tornadoes possible. Further south, isolated storms may develop during the late afternoon warranting the risk of hail/wind/tornadoes. Eventually, we may see the development of a large squall line from Iowa southward through Arkansas with the cold front/dryline surging eastward overnight. Continued risk of damaging winds and some large hail are going to be possible with these storms overnight... More updates on the severe weather risk are likely in Tuesday's blog update.

Beyond the potential for thunderstorms and severe weather, high temperatures on Wednesday in the mid 60s to lower 70s from northwest to southeast. Wednesday night lows from near 40 along the Missouri River to the mid 50s in eastern Iowa. Thursday highs in the mid 40s to lower 60s from west to east as the cold air continues to push into the state. By Thursday evening we'll see the transition to snow showers become possible over northwest Iowa. This potential for snow showers will continue to expand over the western half of the state Thursday night as lows range from the upper 20s to upper 30s from west to east. The potential for snow, and even some wintery conditions over the northwest quarter of the state will be discussed beyond the severe weather threat.