Quincy

The threat for severe thunderstorms, including tornadoes, continues for Tuesday. The area of focus is the lower Mississippi Valley into portions of the Tennessee Valley and lower Ohio Valley. Nothing significant has changed from the computer models, suggesting that a severe weather event is still probable Tuesday into Tuesday night with at least a few tornadoes possible. There are still details to nail down, but at least a few key ingredients are in place for tornadoes across the region. Thinking since Friday morning’s update has not really changed. The computer models have gotten into better agreement with timing, as the Euro stopped its westward/slower trend and both the GFS and NAM are similar with the overall timing. There still are big questions about instability, as greater instability than forecast would support a higher-end event. As usual, the GFS and to some extent the Euro show marginal to modest instability, while the NAM (as often is the case) is a bit more robust. Wind shear, both directional and speed, is very favorable for tornadoes and the overall upper level pattern is supportive as well. Backing of low-level winds to the south/south-southeast should be coupled with southwesterly winds in the mid and upper levels. The one notable trend on the models has been for more of an initially discrete mode for convection Tuesday afternoon and early evening. If initiation is delayed, that could allow for further daytime heating, juicing up the setup even more. Also, if the storm mode is more discrete versus a squall line, the tornado threat would be elevated. It appears that the storm mode will eventually trend to a squall line regardless, especially as the shear pattern becomes more unidirectional overnight. Current thoughts: Discrete and semi-discrete thunderstorms fire in far eastern Arkansas and northeastern Louisiana Tuesday afternoon. The storms moved northeast and have the greatest threat of producing tornadoes from near the Mississippi River, northeastward to southwestern Kentucky, western Tennessee, northern Mississippi and northwestern Alabama. Given the expected wind fields, strong, long-tracking tornadoes remain a possibility. Odds for at least one strong tornado are set at 60% with this update. A tornado threat exists outside the red shading above, mainly in two areas. One being near the triple point in eastern Missouri to southern Illinois, but meager instability suggests this threat is highly conditional. Also, a few discrete cells could fire in the warm sector farther south in Mississippi (possibly western Alabama), but weak height falls suggest that the best forcing will be farther northwest. Once more high resolution data can be reviewed Sunday night, hopefully more details on the magnitude of this threat can be given with higher confidence. When reviewing analogs of similar setups in the past, most have produced at least some severe weather, but when instability was moderate to strong, such a setup often produced a significant tornado outbreak. At this point, this appears to be a low to moderate tier winter tornado event, not too uncommon for early February. One recent trend that may support a higher-impact event is that surface temperatures on Saturday were much warmer than forecast across much of the Mississippi Valley and Ohio Valley. If this trend were to continue in the coming days, it could allow for more instability than currently forecast on Tuesday, enhancing the tornado threat. To give a rough idea of what this event might look like, below is a reasonable analog from the January 19th, 1988 event. That setup also had lower end instability, especially over western Tennessee. It's not uncommon for winter Dixie events with high shear/low CAPE to produce tornadoes, some strong and long-tracking.

A notable threat of severe thunderstorm activity in early February has been showing up in the models for several days now. As the event gets closer, confidence is increasing that a setup favorable for severe weather is likely to occur. However, there still are a lot of details left to be nailed down. The broad pattern involves a vigorous trough in the jet stream digging across the Four Corners region on Monday, February 1st and swinging east to northeast across the United States into Groundhog Day. The greatest severe weather threat will be focused on where energy around this trough ejects with the orientation (tilt) of the trough being a factor of important consideration. Lee-side cyclogenesis is likely on Monday across the southern High Plains with low pressure rotating from the Texas/Oklahoma vicinity into the Middle Mississippi Valley and eventually the Great Lakes. Given the low-level jet projected with this system, ample moisture return should bring 60+ degree dew-points northward into the Gulf Coast states. Instability forecasts have varied from weak to modest and the shear signal has been significant, with a sizable area of 50+ knots of 0-6km shear likely. Similar setups in the past (analogs) have mixed signals, with some showing significant severe outbreaks and others with little to no severe activity. My main focus at this point is the orientation of the trough. A more negatively tilted trough will yield an increasingly unidirectional wind field. If the trough is closer to a neutral tilt or slightly positive, that would maximize the amount of directional shear. The trends appeared to favor the trough becoming negatively tilted on Tuesday, February 2nd, meaning that the storm mode could get messy and trend toward a squall line. The new 00z ECMWF shows a trough closer to a neutral tilt as the upper level flow is southwesterly, not south-southwesterly. If this were to be a hiccup and the trough is more negatively tilted, then the severe threat will not be maximized. It is important to note that severe thunderstorms, including tornadoes, will still be possible in this scenario, but if the ECMWF is correct, we may have a more significant threat to monitor. Based on the latest data, I would expect an isolated, conditional severe threat to develop across the southern Plains late Monday into the overnight, mainly from parts of North Texas into the eastern half of Oklahoma. Given cold advection and steep mid-level lapse rates, the major threat would likely be large hail, although damaging winds and perhaps a couple of tornadoes would also be possible. Tuesday is the day of focus, as any discrete to semi-discrete thunderstorms that develop in the warm sector could become tornadic. It appears that this area will encompass northeastern Louisiana and eastern Arkansas into Mississippi, far southeastern Missouri, far southwestern Kentucky and western to middle Tennessee. Although the threat could punch north into southern Illinois, southern Indiana and more of Kentucky, meager instability amidst an increasingly pinched warm sector, there is lower confidence in this scenario. Also, the severe threat could reach Alabama later in the day, but the last several runs of the ECMWF have suggested a somewhat slower evolution, keeping the threat a bit farther west, perhaps only reaching northwestern Alabama. With all of this said, severe weather seems likely on Tuesday with at least a few tornadoes. The wind fields would support a strong tornado. If one or a combination of the following conditions are met, then this setup could turn into a higher-impact event with numerous tornadoes, some strong and long-tracking: More instability than currently forecast would support a more robust setup, particularly in terms of localized vs. larger scale. A near-neutral or even slightly positive tilted trough would increase the amount of directional shear. Discrete thunderstorm development in the warm sector, especially early in the day on Tuesday, would suggest an elevated tornado threat. First thoughts: -Conditional threat of a tornado or two late Monday night/early Tuesday. -At least a few tornadoes on Tuesday; better than 50/50 odds of a strong tornado. -Tornado threat is maximized on Tuesday from far northeastern Louisiana and eastern Arkansas into northern Mississippi, western to middle Tennessee, far southeastern Missouri, far southwestern Kentucky and northwestern Alabama.

Something is going to happen, but will it be significant and what area will be targeted? Climo seems to favor Gulf Coast/Dixie, but even with poor instability, this sort of setup would probably still produce at least some severe. It's been a very consistent signal, overall, on the models for quite some time:

Here is a snowfall map using reports from various sources. Many of the reports came from this forum and the National Weather Service. Only social media reports that passed through quality control were considered. All reports gathered were carefully considered and compared before being included. Snow reached southern Connecticut during the predawn hours on January 23rd. The snow gradually moved inland, dropping the most persistent bands of moderate to heavy snow on an axis from Fairfield County, northeastward into New Haven County and parts of eastern Connecticut. As low pressure slowly moved east to the south of Long Island, precipitation never reached the far northwest corner of the state. During the peak of the storm, winds consistently gusted to between 30 and 40 mph along the shoreline. No Connecticut stations officially reached blizzard criteria, but near-blizzard conditions affected southwestern Connecticut at times. Breaks in the precipitation shield across southeastern Connecticut resulted in locally lower amounts of snow, particularly across New London County. Snow quickly came to an end in all areas early on January 24th, ending from west to east across the state. The Blizzard of 2016 affected a large portion of the United States from the Arklatex region, eastward to the East Coast. The most intense snowfall fell from the Mid-Atlantic states into the New York City metropolitan area. Snowfall totals of 2 to 3 feet were common here, with a few locally higher amounts. All-time single event snowfall records were set at Allentown, Baltimore, Harrisburg and New York City’s JFK Airport. A record daily snow depth was also set at Washington Dulles International Airport. Both Harrisburg and JFK Airport reported 14 straight hours of snowfall rates of 1 to 3 inches per hour during the height of the storm. JFK Airport observed 30.2 inches of snow in one calendar day on January 23rd.

Two approaches with analogs... The GEFS long-range suite for 00/03 shows some severe risk across Dixie. When using the CPC d6-10 analogs and overlaying the events within 48 hours of the target, there are a few clusters over the Gulf Coast states:

Signal of a threat to start February has been fairly consistent. Certainly going to need to keep an eye on that.

For the fourth year in a row, overall severe thunderstorm activity, including tornadoes, finished below average across the Lower 48. This graphic shows the severe thunderstorm watch departure from the 13-year average. The vast majority of the U.S. saw at or below average numbers of severe thunderstorm watches. The greatest departures from average were across the central Plains into parts of the Midwest. The only state with more severe thunderstorm watches than average was Texas, with a higher instance of watches over parts of central to southern Texas. What was the cause for this, aside from the seemingly long-term lack of severe thunderstorm activity? The 2015 severe weather season actually got off to a relatively fast start from late March into early April, remaining active into much of May. Attention shifts toward June, which is usually the the peak of the season. June 2015 featured substantial ridging across the western U.S. While not the sole factor, that ridging was a big player in the relative lack of severe thunderstorm activity into June. The severe season climatologically focuses in to parts of the central and northern Plains in June, but the 500mb height pattern in June 2015 was not the most favorable for severe thunderstorms. Some troughing evident over the Great Lakes favored multiple severe weather events across the Midwest and Ohio Valley. However, even here, the season, overall (not in all cases), was on the quieter side. Above image shows 500mb heights and anomalies for June 2015. The overall tornado activity in 2015 was below average, but some parts of the country did see an increase in activity compared to recent years. Portions of Iowa and northern Illinois saw a very active tornado season. This included an early season outbreak on April 9th and a fall event on November 11th. Texas also saw an active season, particularly in North Texas. The High Plains saw a broad area of increased activity, particularly from the Texas panhandle into eastern Colorado and western Kansas. The other part of this graphic that stands out is the lack of tornado watches across the Deep South. Given recent trends and forecasts, it is conceivable that the severe season over the Gulf Coast states, including Florida, may remain on the active side over the next few weeks. Deeper into the year, it is a bit more unclear if March and April will see an uptick in activity across Dixie Alley. Only time will tell.

After a potential outbreak on the fringes of this subforum tomorrow, Sunday could bring another severe event. At the very least, have to expect some potentially heavy snow across portions of the southern High Plains into central Plains.

Another vigorous through is forecast to sweep through the south-central states over the next few days, bringing a threat of thunderstorms to the region. Although this threat looks substantially less impressive than the event in mid-November, there still exists the potential for at least a few severe thunderstorms, especially Saturday. The setup for Saturday has had a lot of question marks and red flags from the start, but now that the event is approaching, things are coming into better focus. The upper level pattern is split with a fairly complex setup forecast to develop. It looks like two pieces of energy will factor into the southern Plains severe threat. The first will be a strong daytime low-level jet across eastern Texas with vorticity maxima ejecting north-northeast toward the Ozarks Saturday afternoon. The second area of energy hangs back with a cold front and the more substantial height falls across the southern High Plains. The greatest severe threat, although still somewhat limited, should develop from eastern Texas into perhaps southeastern Oklahoma/far southwestern Arkansas during the afternoon hours on Saturday. Aided by a 40-50 knot low-level jet and modest instability, at least a few supercell thunderstorms could fire. Given the wind profiles, all severe hazards appear possible with perhaps a few tornadoes. The threat here shifts to damaging winds as storms merge and should tend to wind down after dark as daytime heating fades and the strongest forcing moves into the Ozarks and Middle Mississippi Valley. The secondary severe threat looks to be from central to North Texas, into central and western Oklahoma. This could extend into Kansas, but with northward extent, instability will become increasingly limited. There are three issues with this area, with the first being a continued messy look to the wind profile. Model soundings have shown a veer-back profile in the mid-levels, producing some jagged, criss-crossing hodographs. Also, some warmer temperatures in the mid-levels should keep the atmosphere capped in most areas until early in the evening. Finally, the trough has slowed down a bit on the models, which also keeps the best forcing farther west until after dark. The timing is analogous to 11/16/15, but instability is significantly less impressive and shear is not as robust. Although a tornado cannot be ruled out, the threat is fairly low. For this area, thunderstorms will try to develop around or shortly after sunset, but may have trouble organizing given the above-mentioned factors. Still, given cold advection aloft and moderate shear, a few briefly discrete/semi-discrete severe thunderstorms could develop. The most likely scenario is that thunderstorms form into a squall line and feature damaging winds as the main threat overnight. Speaking of mid-November, the Sunday threat has a lot of similarities to 11/17/15. Not only with timing and placement, but with the synoptic setup. Keep in mind that 11/17 had more instability and was an “elevated” 10% tornado threat, but the event struggled, mainly producing sporadic damaging wind gusts, although a few overnight tornadoes were reported in Mississippi. This Sunday, the initial squall line looks to be only marginally organized (unlike the robust 11/17 AM line) and the potential for warm sector supercells out in front, across the Lower Mississippi Valley, is fairly low. Still, a few damaging wind gusts and perhaps a tornado or two appear possible. With the warm sector becoming increasingly narrow (pinched) through the day, the aerial extent of severe threat should fade during the second half of the day, despite impressive wind fields aloft.

The focus has shifted earlier, but perhaps not enough for a big day on Monday. Although the evening looks interesting, the best environment seems to occur overnight across eastern Texas. It's the 06z-12z time-frame that instability is maximized, as the low-level jet really cranks and mid-level lapse rates steepen. Speed this up a bit and it could be really interesting. Tuesday looks messy, although I could see a potent squall line early in the day with embedded tornadoes.

12z model suite continues a strong signal for the lower Mississippi Valley and surrounding subforums to the east. Too soon for details, but this easily looks more impressive than what's going on today.

The GFS/Euro show another dynamic system in the Plains about a week from now. Not quite as impressive as this current system and a bit further south, but worth watching later forecasts and trends.

Based on the GFS/Euro (12z), certainly have to agree with this. The Euro actually shows the best instability in the east-central Plains at 12z on Wed, lessening with time with movement into Iowa and Missouri. Likewise, the GFS forecast soundings for eastern Missouri and southeastern Iowa are not as impressive as further west/earlier.