WunderBlog Archive » Category 6™
Category 6 has moved! See the latest from Dr. Jeff Masters and Bob Henson here.Busy Week of Severe Weather Ahead for Nation’s Midsection
In classic late-April fashion, the ingredients are coming into play for severe thunderstorms to prowl the central United States across several days over the coming week. The whole gamut of severe threats is likely to materialize before the week is out, from tornadoes to enormous hail, strong downburst winds, and torrential downpours. Residents of Texas and Louisiana hard-hit by flooding in recent weeks face another stretch with the potential for very heavy rain that would add to record amounts observed in the past 12 months. The storminess kicked off on Sunday with dozens of large-hail reports and at least 10 preliminary tornado reports from southern Minnesota to northern Kansas. Two storm chasers were injured, according to the Weather Channel.
Figure 1. Day 2 convective outlook issued early Monday, April 25, 2016, for Tuesday, April 26. The yellow and red colors indicate progressively higher risk for severe weather, with the red (moderate) the second-highest category.
The biggest immediate threat for tornadoes appears to be on Tuesday, when a strong upper-level storm will encounter very rich low-level moisture from Nebraska to Texas. In its early-Monday outlook for Day 2 (Tuesday), NOAA’s Storm Prediction Center placed a strip from southern Nebraska to central Oklahoma in a moderate risk of severe weather, the second highest of five risk categories. Tornadic supercells may cluster along a warm front expected to lie near the KS-NE border, and others may pop further south along a strong dryline that will advance through Kansas and Oklahoma through the afternoon and evening. A second pulse of energy rotating around the upper low will reach southern OK and north TX by late evening, possibly triggering a batch of supercells that could rage well after dark.
Figure 2. Jet-stream flow at the 250-mb level (about 34,000 feet) projected by the 06Z Monday run of the GFS model for 00Z Wednesday (7 pm CDT Tuesday). Winds at this level exceeding 90 knots (105 mph) will be nosing into southwest Oklahoma. Upward motion is enhanced where the contours separate (diffluence) and toward the front left area of highest jet-stream winds. Image credit: Levi Cowan, www.tropicaltidbits.com.
Figure 3. WunderMap depiction of CAPE (a measure of atmospheric instability) projected by the 06Z Monday run of the GFS model for 18Z (1 pm CDT) Tuesday. Just ahead of a dry line across central Kansas and Oklahoma, CAPE values of 3500-4500 J/kg (red and purple) are indicated, denoting extreme instability.
Plenty of atmospheric juice for big hail-makers
Summerlike dewpoints of 70-73°F (21-23°C) were streaming onto the Texas coast on Monday morning. This very humid low-level air mass has plenty of time to be pulled north into the moderate-risk area by Tuesday afternoon. With cold upper-level air overspreading the sultry surface air, lifted indices may get as low as -10 to -12; this would be close to the most extreme levels of instability seen in springtime tornado outbreaks across the Southern and Central Plains. The vertical wind shear (change in wind direction and/or speed with height) will also be more than adequate for tornadic storms, if not exceptionally strong. Wind speeds at 850 mb and 700 mb (about one to two miles aloft) will generally be in the 45 to 55 mph range, whereas they can sometimes top 60 mph in major tornado outbreaks. A strong “cap” (warm layer aloft) at these heights may keep storms from developing along the dry line till late afternoon or early evening. The cap will be weakest and the wind shear strongest near the warm front in northern Kansas and southern Nebraska, which is where I would expect the greatest tornado risk to evolve.
Figure 4. The National Weather Service office in Oklahoma City was warning residents Monday morning of the severe risk on Tuesday.
Given the adequate wind shear and extreme instability, there are likely to be extremely powerful updrafts in Tuesday’s storms that could produce giant hail, the size of baseballs or larger. Figure 4 shows the top-end hail risk expected in the Oklahoma City area. Large hail could extend into north Texas, where a massive hailstorm on March 16 damaged 50,000 cars and 25,000 homes, inflicting more than half a billion dollars in damage. As of April 11, the Dallas-Fort Worth NWS office had received 30 reports of severe hail for the year thus far, already the highest January-to-April total for any year in the last decade (see embedded tweet at bottom).
Looking ahead: more storms on the horizon
Tuesday’s severe weather will greatly affect the state of the atmosphere on Wednesday. As the upper-level storm and dry line push east, conditions should be generally favorable for more severe weather from eastern Missouri to east Texas, where SPC’s Day 3 outlook places a slight risk. The configuration of upper- and lower-winds suggests that the overall tornado risk may be somewhat less on Wednesday than on Tuesday.
Upper-level troughiness in the western U.S. will “reload” by late this week, as another potent upper low enters the Southwest. The Southern Plains will again be targeted for big storms around Friday, and severe weather may continue across parts of the area into the weekend, although it’s too soon to know exactly how the scenario will play out. It does appear that upper-level winds will become more meridional (flowing from south to north) toward the weekend, which would enhance the potential for storms “training” along boundaries and dumping excessive amounts of rain. NOAA’s Weather Prediction Center expects that rainfall amounts for the week starting Monday could hit 3-5” near Omaha, with a larger area of 3-7” rain projected for east Texas, southeast Oklahoma, northwest Louisiana, and much of Arkansas. Unfortunately, this coincides with some areas slammed by all-time record rainfall in March, including Little Rock, AR, and Shreveport, LA.
We’ll be back on Tuesday with an update on the severe weather threat. We are planning a liveblog as well, pending resolution of some technical difficulties that arose on Monday.
Bob Henson
Figure 5. 7-day precipitation outlook for the period from 12Z (7:00 am CDT) Monday, April 25, 2016, through 12Z May 2. Image credit: NOAA/NWS Weather Prediction Center.
Figure 1. Day 2 convective outlook issued early Monday, April 25, 2016, for Tuesday, April 26. The yellow and red colors indicate progressively higher risk for severe weather, with the red (moderate) the second-highest category.
The biggest immediate threat for tornadoes appears to be on Tuesday, when a strong upper-level storm will encounter very rich low-level moisture from Nebraska to Texas. In its early-Monday outlook for Day 2 (Tuesday), NOAA’s Storm Prediction Center placed a strip from southern Nebraska to central Oklahoma in a moderate risk of severe weather, the second highest of five risk categories. Tornadic supercells may cluster along a warm front expected to lie near the KS-NE border, and others may pop further south along a strong dryline that will advance through Kansas and Oklahoma through the afternoon and evening. A second pulse of energy rotating around the upper low will reach southern OK and north TX by late evening, possibly triggering a batch of supercells that could rage well after dark.
Figure 2. Jet-stream flow at the 250-mb level (about 34,000 feet) projected by the 06Z Monday run of the GFS model for 00Z Wednesday (7 pm CDT Tuesday). Winds at this level exceeding 90 knots (105 mph) will be nosing into southwest Oklahoma. Upward motion is enhanced where the contours separate (diffluence) and toward the front left area of highest jet-stream winds. Image credit: Levi Cowan, www.tropicaltidbits.com.
Figure 3. WunderMap depiction of CAPE (a measure of atmospheric instability) projected by the 06Z Monday run of the GFS model for 18Z (1 pm CDT) Tuesday. Just ahead of a dry line across central Kansas and Oklahoma, CAPE values of 3500-4500 J/kg (red and purple) are indicated, denoting extreme instability.
Plenty of atmospheric juice for big hail-makers
Summerlike dewpoints of 70-73°F (21-23°C) were streaming onto the Texas coast on Monday morning. This very humid low-level air mass has plenty of time to be pulled north into the moderate-risk area by Tuesday afternoon. With cold upper-level air overspreading the sultry surface air, lifted indices may get as low as -10 to -12; this would be close to the most extreme levels of instability seen in springtime tornado outbreaks across the Southern and Central Plains. The vertical wind shear (change in wind direction and/or speed with height) will also be more than adequate for tornadic storms, if not exceptionally strong. Wind speeds at 850 mb and 700 mb (about one to two miles aloft) will generally be in the 45 to 55 mph range, whereas they can sometimes top 60 mph in major tornado outbreaks. A strong “cap” (warm layer aloft) at these heights may keep storms from developing along the dry line till late afternoon or early evening. The cap will be weakest and the wind shear strongest near the warm front in northern Kansas and southern Nebraska, which is where I would expect the greatest tornado risk to evolve.
Figure 4. The National Weather Service office in Oklahoma City was warning residents Monday morning of the severe risk on Tuesday.
Given the adequate wind shear and extreme instability, there are likely to be extremely powerful updrafts in Tuesday’s storms that could produce giant hail, the size of baseballs or larger. Figure 4 shows the top-end hail risk expected in the Oklahoma City area. Large hail could extend into north Texas, where a massive hailstorm on March 16 damaged 50,000 cars and 25,000 homes, inflicting more than half a billion dollars in damage. As of April 11, the Dallas-Fort Worth NWS office had received 30 reports of severe hail for the year thus far, already the highest January-to-April total for any year in the last decade (see embedded tweet at bottom).
Looking ahead: more storms on the horizon
Tuesday’s severe weather will greatly affect the state of the atmosphere on Wednesday. As the upper-level storm and dry line push east, conditions should be generally favorable for more severe weather from eastern Missouri to east Texas, where SPC’s Day 3 outlook places a slight risk. The configuration of upper- and lower-winds suggests that the overall tornado risk may be somewhat less on Wednesday than on Tuesday.
Upper-level troughiness in the western U.S. will “reload” by late this week, as another potent upper low enters the Southwest. The Southern Plains will again be targeted for big storms around Friday, and severe weather may continue across parts of the area into the weekend, although it’s too soon to know exactly how the scenario will play out. It does appear that upper-level winds will become more meridional (flowing from south to north) toward the weekend, which would enhance the potential for storms “training” along boundaries and dumping excessive amounts of rain. NOAA’s Weather Prediction Center expects that rainfall amounts for the week starting Monday could hit 3-5” near Omaha, with a larger area of 3-7” rain projected for east Texas, southeast Oklahoma, northwest Louisiana, and much of Arkansas. Unfortunately, this coincides with some areas slammed by all-time record rainfall in March, including Little Rock, AR, and Shreveport, LA.
We’ll be back on Tuesday with an update on the severe weather threat. We are planning a liveblog as well, pending resolution of some technical difficulties that arose on Monday.
Bob Henson
Figure 5. 7-day precipitation outlook for the period from 12Z (7:00 am CDT) Monday, April 25, 2016, through 12Z May 2. Image credit: NOAA/NWS Weather Prediction Center.
Has there been more hail this year in North & Central Texas? Stats say yes. Especially bigger hail. #dfwwx #ctxwx pic.twitter.com/apkqaSEtni
— NWS Fort Worth (@NWSFortWorth) April 12, 2016
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.