T/STORMS EXPECTED FRIDAY...
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One of the sure signs winter is fading is the emergence of weather systems like the one we'll see to end the week. It's got two big elements that we've not had to work with in a long time and that is warm, moist air. Not only does that give it the dimension of being a thunderstorm producer, it increases the chances of worthwhile precipitation.
Thursday the systems storm making dynamics will still be situated to the southwest. The warm sector will be inching northward through Missouri. That being the case, we've got another relatively cool day with southeast winds. Weak warm air advection should deliver quite a few clouds, perhaps a bit of morning fog and spotty showers early in the southeast. Temperatures will range from the upper 40s near HWY 20 to the low to mid 50s from I-80 south. Overall, another dreary day with little if any sunshine.
The the attention becomes focused on the springlike storm that ejects two pieces of energy, each with the potential to produce showers and thunderstorms. Friday morning the primary energy is situated over southern Colorado with the strong southwesterly flow at 500mb to the surface transporting moisture into the Midwest.
The animation below, depicting integrated water vapor shows two surges that impact the local area. One arrives early Friday moning and the other late in the day or evening. Watch as the waves of forcing and deep moisture in yellow surge across the area from the southwest.
The first volley arrives early Friday in the form of a 70kt. speed max zipping northeast through eastern Iowa. It's associated with strong warm air advection that produces warm and rather muggy conditions Friday afternoon. As that juicy air mass arrives, enhanced by the speed max, it ignites showers and what looks to be widespread thunderstorms.
Being north of the warm front early Friday, these are likey to be elevated, not surface based. Instability won't be as high as it will be later in the day but some of the updrafts have the potential to produce some gusty winds and hail as they charge northeast. If nothing else, there should be some good downpours in spots that get under the heavier cores. Below the simulated radar on the HRRR has a farily healthy cluster of rain with embedded convection pushing from SW to NE at 7:00am Friday.
As this round of rain moves out of the south in the morning, (early afternoon north), we enter the open warm sector of the storm. Clouds should thin and break allowing for rapid heating and moisture transport. One question regarding the heating will be the amount of debris clouds that linger after the morning rains. The sooner clouds break, the warmer. The northeast would be the area most likely to remain slightly cooler. No way to know for sure this far out. As it stands now, the EURO and GFS indicate this for highs Friday. With records ranging from 68 north to 73 south, we have strong chance of knocking a few off.
The GFS
The EURO
The next order of business is what happens with a second round of storms that is probable late in the afternoon or evening, out ahead of a cold front advancing east across Iowa. With temperatures in the 70s and dew points on the HRRR in the low 60s, there will be instability.
In fact, the hi-res convective HRRR shows CAPE over 1,000 j/kg. For March 6th that is healthy.
Due to the forcing from the front and the unstable air mass ahead of it, showers and storms should redevelop towards evening Friday. The HRRR at 7:00pm shows them approaching my western counties in Iowa.
If the timing is right and the paramters shown develop, there is enough shear for a few strong to severe thunderstorms. The Storm Prediction Center has my entire area in a slight risk of severe storms (level 2 of 5) Friday, with an enhanced risk reaching up to the Iowa border. Most likely storms locally will be more linear with gusty winds and hail the primary risks. Some of the stronger bowing segments could produce brief QLCS tornado spin ups. These are usually weak, brief tornadoes, EF1 or less. Something to watch as we get closer to the event.
By the way, the HRRR which only goes out to 6:00pm Friday shows concentrated lightning in its flash density product coming out of SC Iowa towards eastern Iowa.
Also note, the rainfall the HRRR depicts through Friday evening. Between what falls in the two periods early Friday and again towards evening, some very generous amounts are indicated, especially from the Quad Cities northwest. That would be big as we sorely need it.
After the front blazes by Saturday night colder air arrives. After early morning highs around 60, gusty NW winds and cold air advection will drop readings into the range of 45 north to 50 south where they will stay the balance of the day. The cooler air starts lifting out Sunday and with sunshine highs of 55 to 60 are back in the fold. Monday, another strong surge of warm air arrives sending highs into the upper 60s and low 70s, way above normal by 25-30 degrees.
Keep in mind this is a multi-faceted forecast with many elements. Some minor changes may need to be implemented as mesocale details become clearer the next 24 hours. However, I think I have the gist of it whatever comes our way. Roll weather...TS
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