The Roller Coaster of Weather

In Evening Brief, Winter Weatherby Henry LukerLeave a Comment

Happy Sunday. What a gorgeous weekend it was. Saturday saw highs ranging from 67 in Estherville to a whopping 78 in Perry. Somewhat cooler today, not like it really matters – 62 in Dubuque to 75 in Keokuk. Sitting 5-15 degrees above normal statewide.

1. Stormy Skies

Forecast for Tonight (4/7-4/8)

A very active weather situation this afternoon and evening. A strong line of showers and thunderstorms developed earlier along the Interstate 35 corridor and proceeded eastward; those have since fizzled off as of 10:00 p.m. A brief severe thunderstorm warning was in effect near the Birmingham area, but otherwise, hail from pea-to-dime size was common with the strongest of storms.

A weak area of high pressure will push any remaining activity out of the state within a few hours with clearing skies from west-to-east. Western Iowa should be clear most of the night with eastern Iowa still dealing with a few lingering clouds initially. Temperatures will be cooler in open-air areas, low-40s northwest to upper-50s southeast.

2. Warmth through Tuesday

Seven Day Forecast for Central Iowa

The good news in this forecast will be the very warm air that remains through Tuesday. Highs tomorrow will range from the low 70s north to almost 80 (!) south. A surface low moves from Canada into parts of Wisconsin with a cold front extending southwest; dryer air with somewhat-cooler and windier northwesterly flow will proceed the front. Clouds increase from west-to-east throughout the night; lows fall into the low 40s north to almost 50 south.

Some fire weather concerns for Monday, with warm temperatures, gusty winds, and RH values in the 30s. Be careful if you have any controlled burns planned; check out our Fire Weather page for more.

3. Significant System Impacting Area Later this Week

A significant weather system will impact the region beginning late Tuesday night and remain through Friday morning. The best chances for snowfall will be north of Highway 20, but specific details are still being worked out.

GOES-17 satellite imagery this evening (seen in the above right) shows an upper-level area of low pressure spinning close to 55.2° N, 145.9° W, about 450 miles off the coast of Anchorage, with a generalized trough extending over 1,000 miles off the coast. One other feature that’s interesting to note tonight is the “atmospheric river” affecting the Pacific Northwest, simply defined as a “narrow corridor or filament of concentrated moisture in the atmosphere” — well-observed in the left streamline image, with quite a stream of moist air (purple) being dug into parts of Washington, Oregon, and California.

The shortwave trough will be inland towards southern Oregon and northern California by early Tuesday morning. This will move over the Rockies early in the week, closing off at some point, before crossing (and deepening) into the Plains late Wednesday night. The cause of headache will be in regards to the surface low. The GFS shows this being a more linear evolution along the border of Nebraska and Kansas into the Great Lakes; whereas the ECMWF digs farther south into Kansas and Missouri, and in today’s 12z run’s case, sharply curve northward. A farther south track would bring snow farther south, and vice-versa with snow — hence why it matters so much.

The first wave of precipitation begins late Tuesday night in the form of showers and thunderstorms with the better chances expected to come later Wednesday alongside the arrival of the surface low. There is actually some limited threat for severe weather with the stronger storms on Wednesday, but a widespread threat is not anticipated, with small hail and gusty winds the primary concern. Widespread rain will be the primary story on Wednesday and Thursday, potentially with some snow very close to the Iowa-Minnesota border, but by Thursday night, cold air begins feeding the back-side of the low, bringing snow to southern Minnesota and parts of northern Iowa. It’s still too early to determine specific details as far as amounts, how far south, the exact time of the changeover, but confidence is increasing for northern Iowa to see some measurable snowfall by Thursday.

Here are some of the areas we’re working away on and their respective confidence factors:

  • Wind: HIGH CONFIDENCE. Regardless of the specific track, winds will be very strong around the low. Winds will be sustained at 25-30 MPH on the northern part of the low with much higher gusts possible. The 12z ECMWF from today was gusting 40-45 MPH sustained winds with gusts over 60 in parts of southwest Minnesota.
  • Overall Precipitation: HIGH CONFIDENCE. Models are suggesting 1-3″ of pure liquid precipitation with this system. This will fall in various types (see precipitation-type section below), but will be very concerning as the ground and rivers are already very saturated.
  • Timing/Precipitation-Type: MEDIUM CONFIDENCE. Late Tuesday night to Friday morning. Light rain beginning Tuesday night, becoming more widespread Wednesday and Thursday. Snow possible over far northern Iowa on Wednesday into Wednesday night, better chances north of Highway 20 on Thursday night into Friday morning.
  • Track: LOW CONFIDENCE, but increasing. Initial placement of the low in the Plains is still up-in-the air, as far as how north or south it goes. This matters for the changeover on Wednesday night. Nonetheless, likely will see it setup shop in southwest Iowa by Thursday morning, scooting off to Wisconsin on Friday. I will be much more confident once this storm moves inland and over the upper-air network.
  • Snow/Rain Amounts: LOW CONFIDENCE. Likely won’t see first numbers until late tomorrow or Tuesday. Bulk of the precipitation will be in Minnesota, but northern Iowa may be under the gun. It’s still too close to call.

Needless to say: make sure to check back into later forecasts. We should have a much better picture as the low comes onshore Tuesday morning.

4. Another Bout of Precipitation Sunday?

12z ECMWF Output for Sunday Night

One important thing to note beyond this weekend: Model solutions are going to be heavily-biased by whatever they’ve decided upon for the aforementioned storm. Basically: if there’s a snow pack, there will be a cold bias. This can be unrealistic if that snow doesn’t actually happen, so take it for what you will. The primary day we’ve been looking at is Sunday night. Models have been flashing about some form of rain, but with limited predictability, we can’t speak on much as far as certainty. But it’s something to keep an eye on, especially as we enter graduation season.

Temperatures will rebound back to the 60s by mid-week with 70s next week. Dry weather seems to prevail for the most part with no significant storms on the horizon beyond this week.

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