THAT SINKING FEELING...

I pulled into the driveway around 6:45 Friday evening and glanced at the car thermometer, which read 49 degrees. Even though I knew the chill was coming for several days, it was still a bit imposing and not well received. It felt like I should be at a football game in October. It was especially harsh considering Thursday's temperatures were in the upper 70s to low 80s. Here's the 24 drop of 28–30 degrees in my northern counties from Thursday to Friday. Nothing like changing seasons in less than a day!

Obviously, we've undergone a major air mass alteration, one that will bring us a chilly start to our Saturday. Notice the Canadian air mass driving cool, dry air into the Midwest.

A closer inspection reveals stable air rapidly entering NW Iowa. This will serve to clear skies, diminish winds, and drop temperatures into the upper 30s in the north by daybreak Saturday. Another cool feature of this hi-res satellite image is the frozen lakes in northern Minnesota, which I circled. The milky gray color depicts ice that remains on Red and Leech Lakes. Further south and east the lakes have opened up as shown by the blue colors. I don't think I could live in a place where the lakes are still frozen going into May.

Anyway, back to the cold. Just how chilly it gets depends on how fast the clouds clear. It happens sooner in my NW counties, and this will be the area to watch for some 30s. Elsewhere, clouds break later and the depth of the cold air is not as great, keeping lows in the low to mid 40s south of I-80. The 3K NAM shows this for temperatures around 7:00am.

Under the influence of a Great Lakes high, Saturday looks to be mostly sunny and bit on the cool side. After the cold start, the April sun should send highs into the upper 50s far north to the low to mid 60s south.

Sunday is a bit trickier as warm air advection begins to impact the region. The warm air will be first felt aloft where some elevated showers are shown, especially over the NE half of my area. The EURO is the most bullish on the potential. With dew points only in the upper 30s to low 40s, it is going to be tough for the atmosphere to saturate at the surface. Thus, the showers may remain elevated and little more than virga or sprinkles develops. Either way, it's worth adding a chance of some showers, mainly in the north. Currently, highs in the low 60s north to the upper 60s south look reasonable unless clouds are more extensive in the northeast, which could keep readings a bit cooler in that area.

Sunday night, the warm front dissects my area from NW to SE and with the addition of the low level jet provides a better chance of some showesr and storms, especially of the NE half of my area. If they get going, water vapor increases to more than an inch, indicating the potential for some locally heavy storms. A few of these could be hailers due to their elevated nature. The EURO shows this for rain potential Sunday through Sunday night.

The GFS is far less aggressive for the same period. Sunday night is a low confidence period regarding any showers or storms.

This leads us into Monday, a day with severe weather potential. As has been the case for several days, the synoptic set-up is still indicated that could easily promote strong thunderstorm development, especially Monday evening. Moisture is critical to any severe weather event, and water vapor is shown at 1.5 inches.

Dew points of 68 to 69 degrees are shown as far north as Cedar Rapids.

Another crucial ingredient is heating, and with highs in the upper 70s to low 80s Monday, that threshold is certainly met.

Thanks to the moisture and heat, instability, (shown as CAPE) is over 3,000 j/kg in that same area.

The Colorado State Machine Learning Probability model shows a 52 percent chance of severe weather in Iowa Monday.

Just in, the Storm Prediction Center has now upgraded my counties NW of a line from Iowa City to Dubuque to a level 4 of 5 moderate severe storm risk. The remainder of my area is in a level 3 of 5 enhanced risk.

At this point, small mesoscale details will eventually come into play to determine if the threat is realized. At least for now, there is enough evidence to think that all modes of severe weather would be possible if trends hold. There are still a couple of days to fine tune details, but considering the recent elevated risk, it's a good idea to stay abreast of the situation going forward. Have a fine weekend and roll weather...TS