EXTREME HEAT WATCH

terryswails1
Jun 19
4 min read

I've been laying out the foundation of a weekend heat wave for days, and now confidence has increased to a point that the NWS has issued an excessive heat watch for much of the Midwest west of the Mississippi. Ironically, the heart of the searing weather arrives locally on the first "full" day of summer, June 21st.

Within the Watch area, highs in the mid 90s and dew points in the mid 70s are expected. That combination should allow heat index values to reach up to 105 degrees plus. East of the river in Illinois, the NWS has not included my Illinois counties in the extreme heat watch, despite the EURO showing similar values as what's expected in Iowa. It would not surprise me to see the watch extended further east into Illinois. Watch or not, if the EURO is right, you'll be suffering like the rest of us.

The upper ridge, with its expansive bubble of heat, is expected to only slowly drift across the United States into next week, departing the West and moving into the Central States this weekend. The heat wave will bring the highest temperatures of the year so far, and a few spots could get within a couple degrees of the century mark! Monday may be the day with the best chance, as dew points mix out in the south to the upper 60s. That would allow higher ambient temperatures, and the EURO does show that trend, with 101 in Mt. Pleasant and 100 in the Quad Cities. No matter what the thermometer says, it will still feel like 100-105+ in most areas.

The experimental NWS Heat Risk product continues to show the heat impacting all areas Sunday and Monday with a level 4 of 4 extreme heat outlook indicated, with only a slight shift southeast Tuesday that may provide some relief in my northwest counties. Here's the definition of the level 4 extreme heat risk. Extreme - This level of rare and/or long-duration extreme heat with little to no overnight relief affects anyone without effective cooling and/or adequate hydration. Impacts likely in most health systems, heat-sensitive industries and infrastructure.

Sunday

Monday

Tuesday

For what it's worth at this distance, the EURO keeps the blazing heat going in the Quad Cities much of next week. Beyond that, it does show the ridge breaking down enough to allow a significant cool-down next weekend, the 28th and 29th.

Shifting gears, the region had a relatively cool day Wednesday thanks to clouds and occasional showers and storms. Highs in the 70s were common, a far cry from where we'll be Saturday. The precious commodity known as rain was witnessed everywhere, with at least a 1/4 inch found in most locations. About 50 percent of the area did considerably better. Where you see yellow in the Doppler estimates, an inch or more of rain is indicated.

Thursday promises to be a quiet day with a weak high pressure in control. With some sunshine, highs will return to more seasonal levels in the low to mid 80s. Thursday night, the leading edge of this weekend's heat arrives with a strong low level jet. Well after midnight, this could fire some storms in my NW counties that would travel southeast along the baroclinic boundary. If they form (far from a sure bet) they would likely dissipate in the morning but could leave enough debris clouds to at least minimally impact temperatures in the northeast where readings may hold in the low to mid 80s. Otherwise, the southwest gets a taste of what's ahead, with highs near 90 and heat index values in the mid 90s.

After that the door is wide open to the heat, and it begins to sear the Midwest Saturday. With 850 temperatures at near record levels (+25-27 C.), a serious CAP develops that brings full sunshine and hot air. Despite impressive amounts of tropical moisture, the storm suppressing CAP should keep the region void of thunderstorms through at least the daytime hours of Monday.

Beyond that, the heat dome shifts far enough east to allow the ring of fire, situated to the north, to sink closer to the upper Midwest. That may allow thunderstorm clusters the opportunity to at least impact my counties NW of the Quad Cities. It's possible the boundary could remain quasi-stationary for 2–3 days, allowing multiple rounds of convection. Wherever this sets up, the potential is very much there for excessive rains and potentially strong storms. At this distance, the key detail of placement is impossible to determine. However, all the signs are there for more active weather someplace in the Midwest beyond Monday.

For now, the National Blend of Models (NBM), shows the core of the active weather from NW Iowa into SE Minnesota and beyond. However, with convective outflow boundaries or a slightly weaker ridge (or one that's a bit further southeast), a southward shift would be fairly easy to achieve. This is the zone to watch for rainfall and storms next week.