Severe Weather Outbreak Possible Next Week

A severe weather outbreak looks possible on Tuesday and Wednesday across a wide portion of the Southern Plains.

A storm system looks to drop across the Rocky Mountains and sweep eastwards, forming a low pressure system in the southern Plains. This low pressure system will form a dry line in western Texas. As the storm system lifts northeast, the dry line will expand north and east in accordance with the motion of the storm. This will place Tuesday's severe weather risk in the vicinity of the center of the storm system. Storm initiation on Tuesday should occur overnight, as lower level winds ramp up and the jet stream inches further east as the storm system drags northeast. Storm formation should begin as individual cells that begin to cluster into multiple-cell storms. Tornadoes do not appear to be favorable- despite sufficient instability, lower level capping issues may hinder extreme supercell growth. Additionally, cloud bases are not as low as they could be to foster tornado development. Best chance for tornadoes is likely to be in central Oklahoma and into eastern Oklahoma in coordination with overnight strengthening of lower level wind speeds.

Andrew

April 16-19 Potential Winter Storm and Severe Weather

There is potential for a wintry side and a severe side to the next storm system in the US. We will start with the severe side.

The Storm Prediction Center has outlined two areas of interest in the Southern Plains- one on April 16th (purple) and another on April 17th (green). These outlines serve as long range indications that the SPC is monitoring the potential for a severe weather event on April 16th and 17th.

Model forecasts have been consistent with having a storm system sweeping through the Rocky Mountains before shifting east and provoking active weather in the outlined areas. The American GFS and European ECMWF models are in good agreement on this type of scenario happening. However, what happens when the system gets into the Plains is a different story. Precipitation forecasts from the European model show a very active event over the purple outlined area for April 16th, but sounding forecasts from the GFS are much less enthusiastic. Primary concern with the sounding data is what appears to be a strong capping inversion (thunderstorm suppressor) from the surface to about 4000 meters off the ground. This capping inversion is predicted to be stronger than the event we saw, making the event difficult to get going. Past the layer of stability, the instability higher off the ground is weaker than what we saw with the previous event. These two factors make for a hard time in getting thunderstorms to form. When moving forward in time, sounding forecasts become slightly better for thunderstorm development, with instability rapidly increasing throughout the day in eastern Oklahoma. Despite this, concern remains with the lack of instability from the surface to roughly 3200 meters above ground level.

Now, as for the wintry side, there is already a model battle setting up. The European model (top image) wants to take the storm on a track going through Chicago and the Lower Great Lakes to drop snow in the Upper Midwest. A severe weather event would then persist in the Ohio Valley and Southeast. The American model (bottom image) prefers to take the southern and faster route when compared to the European model. The American GFS model ends up dumping a significant amount of snow in the Midwest rather than the Upper Midwest, as the European model appears to show. The snowfall forecast from the European model below illustrates this potential:

A quick glance at other models and ensembles reveals that the American GFS model is on the losing side, with the Canadian and US Navy models agreeing with the European northward solution. The United Kingdom's forecast model agrees with the American solution, but the UK's model usually is not the best with forecasting storm systems. The American ensemble members agree with its parent GFS model, but that's to be expected. All in all, we are still a while away before we reach a solution on this event.

Andrew

Medium-Range Pattern: Cold West, Warm East

The overall pattern over the next 6 to 10 days is looking more and more like Old Man Winter isn't ready to let go, even though we're quickly pushing into mid-spring.

Shown above is the medium range height forecast across North America. In areas of cooler colors, low pressure is favored. In the same sense, warm colors indicate high pressure tendencies. Looking at the European model's forecast above, we see persistent low pressure pushing south from Canada into the Western US and Plains. In response to the low pressure in the West, high pressure is inclined to form in the Eastern US, and this trait is reflected nicely on the European model's above forecast. If the jet stream follows the low and high pressure waves, I would expect the jet stream to keep a relatively strong stance over the southern Rockies and southern Plains in response to the persistent low pressure anomalies in the area. When the jet stream approaches the high pressure area in the East US, it is expected the stream should make a quick move northeast through the Midwest and Great Lakes. This would put the last two regions in the temperature battle zones, and possibly in whatever severe weather risk may come along while this pattern is in place.

Lower level temperature anomalies for the same timeframe emphasize the cold weather deeply entrenched in the Rockies and Plains as a result of the low pressure pushing south from Canada. In the same sense, the high pressure anomalies in the East US result in above-average temperatures in the next 6-10 days. I expect the East US, mainly the Northeast and New England regions to get in on springlike temperatures, maybe even summerlike temperatures if the warm-up is strong enough. As for the Central Plains, that deep cold pocket from eastern Montana into the Dakotas, Nebraska and Kansas will return the Plains region into early springtime temperatures, possibly as chilly as late winter temperatures. The severity of both temperature anomalies is to be determined, but this pattern is certainly going to provide a chilly period for many people west of the Mississippi River.

Andrew

April 11th Severe Weather Event

I expect a severe weather event to unfold tomorrow, April 11th.

Short range model guidance suggests the cold front currently working its way east across the nation will fire off another day's worth of severe weather. Highest risk appears to be placed across Alabama and Georgia in the area of the highest instability. Overall instability is moderate at best, with highest values in the aforementioned areas. Helicity in the atmosphere will be decently high across all areas, but the lack of high instability makes for a rather low-moderate tornado risk. I can see a situation in which weak tornadoes evolve from this set-up, but I do not expect several big tornadoes across the Medium Risk area. High Wind index looks to be high for this event, as the typical cold front merging of severe thunderstorms occurs to form a squall line. New model forecasts indicate instability will be higher than previously thought, and that storm cells may be stronger than previously thought. I'm going to stay with my current thinking on the graphic above; I feel that the graphic best interprets my thinking right now.

Main concern for any tornadoes rests in the areas you see above with isolated storm cells. This image is valid for 8 PM Central Time, 9 PM Eastern Time on April 11th. Any tornadic activity is most likely to originate from isolated thunderstorms popping in Georgia, the Carolinas and Tennessee. These isolated storms would feed off of the instability and decent helicity to possibly provide a base for tornadic activity. The extent of this potential tornado activity is to be determined, and that determination should be made tomorrow morning.

Andrew

Massive Snowstorm Headed for Minnesota

A recent forecast image from the American GFS model shows portions of Wisconsin, South Dakota and Minnesota receiving snow totals above 2 feet in some spots, with Minnesota possibly getting in on 30 inches of pure snow!

Bear in mind this forecast is unlikely to verify exactly, as it is very rare to see extreme snow totals like this at any time in the year, much less in mid-spring. A more recent forecast has the same states getting anywhere from 10-16 inches of snow, and this range still seems pretty high. While it does seem pretty high, it technically is realistic- it isn't spring without a major storm system bringing a big winter storm and big severe weather event. While the most recent forecast shows only 10-16 inches, previous forecasts today have shown amounts still flirting with 2 feet of solid snow in many places.

Andrew