LESS OMINOUS LOOKING?
There will be showers and thunderstorms this weekend, but there has been a trend for less in the way of severe weather and more manageable rainfall amounts. In general, the timing and placement of forcing will be more favorable further west, which is interesting considering a front will be anchored across Iowa all weekend. Despite pooled moisture and dew points in the mid 60s, models are generally either off with timing, forcing, or instability. That could spare us from what otherwise would have been a promising weekend severe weather set-up with excessive rainfall potential. This is good news but a bit mystifying. There's still some overall doubt about how the weekend plays out. Let's take a deeper dive.
Currently, here are the weekend severe weather risk outlooks from the Storm Prediction Center. At this time, my region has no more than a marginal to slight risk assessment (level 1 to 2 out of 5). These outlooks are regularly updated, so keep in mind these could change later Friday or at any other time this weekend.
Friday.
Saturday
Sunday
As for rainfall, the area was highlighted for excessive rains yesterday. That has been downgraded recently. Even so, much of the region has a 40-60 percent chance of 2 inches of rain by the end of the weekend. Odds are greatest west of the Mississippi in Iowa.
I'll have the breakdown of individual days in the weather story below.
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DODGING STORMS AND RAINDROPS...
FRIDAY
Friday was a day when I saw little threat of severe weather the past couple days, and that idea holds today. With the system arriving slower, a warm front barely makes into SE Iowa, maybe as far north as HWY 34 by evening. That means rain and thunderstorms pushing across the south during the morning, while the north stays dry. During the afternoon, the forcing creeps northward, sending the rain into the rest of my counties north of I-80. Shower and storms are likely to diminishing in the south and end for a time by early to mid-afternoon. With clouds and rain cooled air, temperatures Friday look chilly with mid to upper 50s in many areas. The far south may attain the low 60s. Behind the warm front, much warmer air is shown from SW Iowa into NW Missouri. As this enters my region Friday night, steady or even rising temperatures are expected. Scattered showers and storms early should end in all areas by midnight. The EURO shows this for highs Friday.
SATURDAY
Saturday, with the first wave of energy departing, SW flow will send temperatures soaring with a stationary boundary setting up across the NW half of Iowa. The EURO has highs of 77-80, more than 20 degrees warmer than Friday.
Additionally, moisture increases as well, with dew points into the mid to upper 60s. That makes for a muggy spring day, with CAPE values soaring as high as 3,000 j/kg. on the 3k NAM.
The HRRR is every bit as impressive and further north with the highest CAPE.
With a front in the area, this is generally a very explosive situation in April. It certainly makes me nervous about any storms that fire. In fact, the supercell composite parameter late Saturday is roughly 8-14 in my area. That indicates shear and a good chance of rotating supercells known as mesocyclones, the type of updraft that can produce all modes of severe weather, including tornadoes.
Even with all that energy and shear in place, the 3K doesn't do much for storms due to a general lack of forcing and some capping, especially in the south. Hopefully that remains the case, as that's a concerning parameter. So far models such as the EURO and GFS remain less aggressive with severe storm potential
Whatever happens (if anything in the afternoon or early evening), the low level jet cranks up by midnight which may be enough to kick off some additional strong storms, perhaps and MCS, with heavy rain potential. Confidence on any of this is low owing to mesoscale details that are still unknown and likely to be influenced by storms from earlier in the day Saturday. It's kind of a wait and see situation right now.
SUNDAY
Sunday, storms should wane in the morning, and then it becomes a situation of heating. How much occurs is critical as once again that determines CAPE and instability. If we can get the sun out for a time, that increases the chances for additional storms late afternoon or evening when a speed max blitzes the region ahead of the ejecting trough out west. At this distance, confidence is low for the same reasons indicated Saturday. At least scattered showers and storms are expected, potentially stronger if we get into more instability. The southern half of my area seems to be more favored for strong storms at this juncture. It will be another warm muggy day but not as thick as Saturday. Highs should be down several degrees into the low to mid 70s.
Monday
Monday, the trough and associated cold front ejects to the east. Cooler and especially drier air sweeps in behind the front. That ends the storm and rain threat, with highs returning to the 65-70 range. Readings appear to warm quickly Tuesday as winds return to the south once again.
As for rainfall, that's a tough one to call, with it highly dependent in the location of stronger thunderstorms. To be determined is how I would qualify it right now. Here's what models are now suggesting.
The EURO
The GFS
The Weather Prediction Center
The National Blend of Models.
To summarize, there is a lot of uncertainty as to how the weekend plays out. Showers and storms are certainly expected at times Friday through Sunday. However, there will be plenty of dry hours between the wet periods. Along with warm muggy conditions Saturday and Sunday, severe weather is possible, but the extent of coverage and intensity is very much uncertain. If nothing else, most areas can expect rainfall of 1-2 inches, locally higher where multiple storms occur. More on the latest trends in my next post. Happy Friday and roll weather...TS.
