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Beautiful Spring weather (yes I said beautiful), ruled the central Midwest Thursday. Sunshine, dry air, and highs in the mid to upper 70s were common around my area. And when I say dry air, I mean it. Humidity values during the afternoon were in the 15-25 percent range. That dry air allowed the temperature in Lowden, Iowa to go from a low of 32 to a high of 79...a 47 degree rise! These are the highs reported across Iowa. Check out that 86 in Sioux City.

Back to the topic of dry air, dew points Thursday morning were in the single digits. Out near Ft. Dodge a dew point of 6 was measured. That's something you expect in January not May.

Around 2:00pm available water vapor on the HRRR was .shown at .27" just east of Cedar Rapids. That is bone dry air.

Of course, when the air is that dry you won't be seeing any precipitation of consequence and dry weather has become a concern. Since April 1st, Burlington has measured 1.21" of rain which is close to 3 inches below the norm for that 34 day period.

Going back a year to April of 2022, here are the rainfall deficits across Iowa. Many places, especially in the SW half of the state are showing 5-10" deficits. Some localized spots in the darker orange are looking at departures nearing a foot. In NW Iowa around Sioux City, the deficit has climbed to 17.25" over the past year.

Rain is needed, especially before the heat of summer settles in. To get it, we need to see moisture return to the pattern. As the animation below indicates, that is going to happen this weekend with water vapor going from 3/10s of an inch to 1.25+ Sunday night.



Along with the increased water vapor we will see a surge in temperatures Sunday that sends highs into the 80s. If all goes according to plan, Sunday should be the warmest day of 2023 so far. The EURO has this for highs.

The GFS is in good agreement.

Before we get there, a warm front comes into play that generates the warm advection necessary for some additional clouds on Friday. Some models even pop a few showers and storms, most notably the GFS which develops a thunderstorm complex in the afternoon. I have not seen support for that from any other model, especially with such concentrated development. Take a look.

The EURO has absolutely nothing at the same time.

I've been playing Friday's rain threat down all week and I see no reason to cave on that yet. Overall, I'm discounting the GFS with the idea Friday is a dry day in most spots with passing clouds allowing just enough sun for highs to get back in the low to mid 70s.

Saturday the warm front progresses northward into southern Iowa allowing temperatures south of I-80 to approach 80. Further north mid 70s look attainable. The EURO has this for highs Saturday.

Saturday night begins a period where thunderstorms could play a role in the forecast. With the warm front stretched across the region moisture will pool along it. As the low level jet increases amidst seep lapse rates strong storms are possible in the evening south of I-80. Further north, some elevated storms could also develop with a few hailers in the stronger updrafts along with some needed downpours. Models are struggling to resolve where (and even if) storms will develop. I would expect at least scattered storms, especially near and north of the slow moving warm front. We should know more later Friday on how this plays out. SPC has issued a slight risk outlook south of I-80.

Sunday the warm front is expected to make it into southern Wisconsin which creates the 80 degree day discussed earlier. With dew points shown inching into the low to mid 60s, it should be the first real muggy feeling day of the year. By evening instability is high with CAPE on the GFS reaching significant levels.

The question then is will a capping inversion (warm air aloft) break late Sunday or Sunday night to allow thunderstorms to erupt? With any sort of forcing, which could come from outflow boundaries or a front that approaches from the north, it would not take much to fire storms. If they do, strong to severe storms would certainly be a threat. Again, this is contingent on mesoscale features unknown at this distance. We'll need a bit more time to get all the pieces of the puzzle together. No matter what, Sunday is going to have a little sizzle with much of the day rain free. For now SPC has a slight risk outlook for severe storms in much of my area from about the Mississippi west.

I've seen a recent trend for enough ridging aloft to push a weak front south of the region keeping much of Monday and Tuesday drier and a bit cool than in previous model runs. Highs will drop back to the 70s before the next short wave arrives mid-week. More on those long range trends in my next post.

Some tricky weather ahead with the storm chances but at least you won't need the coat this weekend. Amen to that. Happy Friday and roll weather...TS


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