Another Potent System Incoming

 Another Potent System Incoming this Week

By Aidan Cera 


Figure 1. GFS 18Z 04/02 output valid Monday night through Wednesday morning.

We are finding ourselves facing another powerful storm system that is expected to track across the upper Midwest Monday through Wednesday Night. Like the system last Friday, this storm is expected to bring a little bit of everything to the Midwest from blizzard like conditions in Dakotas and northwestern Minnesota to a tornado potential down in Iowa. This is still considerable uncertainty in what exactly this storm will do so this discussion is going to focus more on the wide scale pattern and the general idea of what is expected to take place and where. 

Upper-level Pattern


Figure 2. EPS Ensemble 12Z 04/02 run Sunday through Thursday 

A trough is expected to deepen as it traverses the Pacific Northwest and Rocky Mountain region Sunday night through Tuesday. The deepening trough is expected to lead to the development of a jet max ahead of the trough which will serve as a focus point for surface low development across the high Plains Monday Night into Tuesday morning. Unlike the trough last week, this trough is expected to propagate eastward at a considerable slower pace along with the surface low. This will allow more time for the trough to amplify and thus the surface low out ahead of it due to temperature advection processes. 

 Lower-level Processes

As a low pressure system develops over Colorado and begins tracking northeastward across Kansas and Nebraska Tuesday morning into Tuesday afternoon, a warm front is expected to develop across northern Kansas and track northeastward with the low as far north as Minnesota and Wisconsin by later Tuesday afternoon while the low itself will still likely be somewhere in Nebraska or South Dakota. We really don't see the cold front begin to intensify until later Tuesday afternoon across Nebraska and Kansas as the low tracks into South Dakota then Minnesota Tuesday Night as shown in Fig. 3. 


Figure 3. GFS 850 hPa temperature, temperature advection, frontogenesis and wind. Red contours represent temps above freezing, blue contours represent temps below freezing. Red shading represents warm air advection, blue shading represents cold air advection. Purple contours represent frontogenesis. Wind barbs are also plotted.

Due to the trough having more time to deepen, cold air advection behind the low will amplify the trough further while warmer and more moisture rich air will be able to make it further north than we saw with last Friday's system. Fig. 4 shows GFS 18Z run (04/02) output for dew points Monday Night into Wednesday ahead of the cold front. 




Figure 4. Dew point projects per 18Z GFS 04/02 run. Color scheme represents dew point temperature in F. 

Dew points well into the 50s and 60s are expected to be advected northward in Iowa, Wisconsin and southeastern Minnesota ahead of the cold front Tuesday.  Air temperatures will be relatively similar to the dew points in these locations. Precipitation onset appears to be Monday Night across the Dakotas across Minnesota and into Wisconsin. This initial precipitation is expected to be of the wintry variety (rain/snow/freezing rain/sleet) before the warm front passes through on Tuesday and advects warmer temperatures northward. By Tuesday afternoon, the warm front is expected to be draped across central Minnesota and northern Wisconsin. Areas north of I-94 in central Minnesota and western Wisconsin will have a greater risk of seeing mostly snow and sleet throughout the day on Tuesday. Area south of I-94 will likely see all rain if current model thinking is realized. 


Figure 5. Same as Figure 3, except focused on Tuesday night into Wednesday.

Tuesday night the low pressure tracks across northwestern Minnesota where very heavy snow is expected to be falling through Wednesday morning. Blizzard like conditions will be likely in the areas that receive snow due to the strong pressure gradient that will likely be associated with the low and thus, very high winds that will blow snow around and lead to drifting and very low visabilities. 

Across central, eastern and southern Minnesota, precipitation will likely be mostly rain and thunderstorms even into the overnight hours unlike the last system where all precip turned to snow. 

In fact, it's quite likely the Twin Cities metro doesn't receive much if any snowfall during this entire forecast period. There is still plenty of time for this storm track to shift however, so confidence is not the highest. 


Figure 6. NWS Twin Cities Mid-Week Storm summary issued 2 April 2023 around 4:15 PM CST.

Regardless, Minnesota and northern Wisconsin will likely be dealing with a wintry mix and snow Monday Night into Tuesday afternoon,changing to rain, then possibly changing back to snow Wednesday morning while far western and northwestern Minnesota sees a significant snowfall event. As a result, a Winter Storm Watch has been issued for parts of central Minnesota and all of northwestern Minnesota that will last through most of Wednesday. 

Snowfall totals are still a little unclear right now in terms of how far south the snowline will be, but 2-3 inches is a good bet for areas north and west of Saint Cloud, MN through Wilmar, MN down to Marshall, MN. Areas in northwestern Minnesota could easily receive over a foot of snow based on current model trends. 

The Severe Storm Threat



Figure 7. SPC Categorical Outlook for April 4th, 2023


Figure 8. SPC Probabilistic Outlook for April 4th, 2023.

Unfortunately, another high caliber severe weather outbreak appears possible across areas already heavily affected by last weeks severe thunderstorm outbreak. Higher probabilities for significant severe weather hazards including tornados, large hail and damaging winds have been issued. 

While a lot of the finer details are still quite grainy, an environment favorable for severe weather appears likely to set up across southeastern Iowa, northern Missouri, southern Wisconsin and northern and central Illinois. 

As shown in Figure 3-4, warm temperature and high dew points are expected to be advected northward across Iowa, Wisconsin and extreme southeastern Minnesota. These high dew points combined with warmer surface temperature will likely lead to ample destabilization potential. However, there are some limiting factors that may stunt this outbreak from realizing it's full potential. First off, some models are showing some sort of capping taking place across Iowa into the afternoon hours. This, coupled with moisture rich lower level profiles which may lead to more cloud cover may make it very difficult for thunderstorms to develop until the cold front tracks through the area early Wednesday morning, by which time the severe potential may be much lower. 
Most of the computer models, however, do show convective initiation around 4-5 PM CST across central and southeastern Iowa. The greatest tornado potential appears to be closer to sunset at this point but again, the details for this event are still a bit unclear. More will be known by this time tomorrow.

Until then, the bottom line is that another highly impactful storm system is expected to track across the upper Midwest Monday night through Wednesday. Whether the concern be blizzard like conditions in Minnesota to tornado potential in Iowa, it will be important to remain weather aware during this time. 

For more information, please consult your local NWS office, the Weather Prediction Center and the Storm Prediction Center for further details and the most up to date information.

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