A SPICY DOUBLE SHOT...

terryswails1
1 day ago
5 min read

Two weather systems will impact the region, one Thursday and the other Saturday, promising a very active period ahead. A wide variety of weather can be expected, including significant ups and downs in temperatures. Here's what's on the table the next 5 days!

Thursday: Rain, possible thunderstorms. Heavy rain, up to an inch. Mild temperatures, near 60 far southeast.
Saturday: Snow or rain changing to snow. Several inches of accumulation possible, especially in the northwest.
Saturday night and Sunday. Windy and sharply colder. Highs low mid 20s Sunday. WC 5–15 degrees

As you can see there is plenty to talk about, so let's get cracking, starting with one last quiet day Wednesday. While the amount of sunshine is still somewhat in question, the fact temperatures will be well above normal is not. Highs should range from 47 in the north, where clouds could be more prevalent, to as high as 57 in the far south. Southwest winds of 10-18 are expected.

THE ENERGETIC PATTERN AHEAD.

On the water vapor loop below, you can see two distinct branches of the jet. The southern branch is aimed at the California and the southwest, tapping subtropical moisture. The northern branch is slamming into the Pacific northwest, currently blocking a pathway for cold to enter the nation. System one, without the phasing of the two streams will have plenty of moisture Thursday, but without cold air, will be a rain producer.

The second system Saturday will see phasing take place directly over the Midwest. This time around, with colder air in place, the next round of precipitation falls as snow. It also opens the door for temperatures Sunday that should be 25–30 degrees colder than what we see Thursday with the initial storm. Again, you can see the dynamic pattern that is unfolding.

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A SPICY DOUBLE SHOT...

Thursday's storm is the result of an initial surge of energy ejecting out of the mean trough centered over the west. It's lifting out of New Mexico below, with the next surge of energy hot on its heels.

The wave has opened the door for Gulf of Mexico moisture to stream freely into the Midwest. Late Thursday, precipitable water vapor is shown reaching 1.26 inches in the Quad Cities. That is extremely robust by early January standards.

In fact, it's more than 400 percent higher than normal, which leads to the potential of a swath of heavy rain close to the storm track which cuts through eastern Iowa.

Recent trends have shown the system stronger which has drawn the track further west into Iowa, leading to the heaviest rains falling west of the Mississippi. This is what models are currently suggesting for potential totals.

The EURO

The GFS

The heavier rains on top of frozen rivers and stream poses the threat of some ice jams. River locations prone to that effect should keep the possibility in mind Thursday night, especially in eastern Iowa.

On the topic of thunderstorms, temperatures, while mild in the upper 50s to near 60 south, will limit the amount of CAPE (instability). Off-setting that somewhat is a high shear environment near the triple point of the surface low. The potential exists for some low CAPE, high shear thunderstorms over far southern Iowa later in the afternoon or early evening. Some of these could approach severe limits, but that is conditional on mesoscale details that won't be known until Thursday. Another factor to keep an eye on.

The K index is supportive of thunderstorm development towards evening on the 3k NAM.

Here is a simulated radar at 5:00pm Thursday evening with the surface low punching into SE Iowa.

After the mild temperatures of Thursday, readings Friday morning are around 40 north to 45 south and should hold pretty steady there the remainder of the day with cold air advection ongoing behind the front.

SYSTEM TWO BRINGS A WINTRY COMPONENT

We go from potential thunderstorms to the threat of snow Saturday as the southern and norther branch of the jet merge over the region. You can watch the process unfold in this animation, leading to a closed low digging into Iowa before sweeping into the Great Lakes Sunday morning.

The process spins up a new surface low that intensifies, moving from far southern Illinois into the eastern Great Lakes Saturday. The surface depiction on the EURO looks like this at noon Saturday. A swath of snow extends through eastern Iowa, northern Illinois, into Wisconsin.

Moisture is not nearly as rich as with Thursday's system, but there is enough for accumulating snow. The ensemble members still show some pretty good spread with regard to the surface low position Saturday. There is still a chance the storm could track further west or east, dependent on the degree of eventual phasing. That's kind of a wild card, but it would impact my area with changes in snow accumulations. One more thing to monitor the next 24–48 hours.

When all the ensemble member solutions shown above are averaged, they produce snowfall that looks like this at a 10:1 ratio.

Using the Kuchera method, which takes into account higher snow ratios, the operational EURO suggests this for snowfall totals.

The operational GFS produces amounts that look like this.

Clearly, there is still some wiggle room as to where the more significant snow falls. The common denominator is that wherever it does, a 1-3 inch band should fall somewhere Saturday into Saturday evening. I say this with low to moderate confidence due to the amount of phasing that's going to take place. Models can really struggle with the process, especially at this distance. I would think by Wednesday night, we should have a pretty good idea of how this all plays out and can dial in on amounts. In the end, I do not see anything that looks to cause major issues.

After daytime highs in the 30-35 degree range Saturday, much colder air swirls in behind the storm Saturday night and Sunday. Lows Saturday night should eventually fall into the upper teens to low 20s, with wind chills of 5-10 by morning. Readings will not go up much Sunday, with strong cold air advection and what should be fresh snow cover in many areas. Highs in the low to mid 20s look good, with wind chills all day of 5-15 north to south.

After some moderation Monday and Tuesday get highs back to near normal, another pop of cold air is possible midweek that drives highs back below freezing Wednesday. Pretty typical stuff of early January.

They say variety is the spice of life and things look pretty spicy the next 5 days! Roll weather...TS