We’re watching showers/storms as they pop up across the area. Poorly organized and weak currently. Moisture and instability lacking.
— NWS Northern Indiana (@NWSIWX) April 29, 2014
Best ingredients for any strong to severe storms lies east of Interstate 69. Threat remains isolated.
— NWS Northern Indiana (@NWSIWX) April 29, 2014
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| Photo from NWS website |
Meteorologists expressed a growing concern for cold-air funnel clouds this afternoon, in an area forecast discussion (AFD) the northern Indiana National Weather Service (NWS) office issued at 10:34 a.m. EDT. As always, the chances of any such funnels reaching the ground are very small, but they can cause concern among the untrained public. Read more about cold air funnels on the website of the Wilimington, Ohio NWS office.
Meanwhile, the AFD indicates that meteorologists continue to expect a short-lived severe weather threat from 5 p.m. and 9 p.m. EDT today, especially in the eastern half of the 37-county area covered by the northern Indiana NWS office (see map below). Straight-line winds will be the primary threat. Small hail is likely, but atmospheric instability is weak, so the threat of hail reaching severe criteria is very limited.
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| Light-colored area: Forecast area of northern Indiana NWS office. |
An isolated supercell thunderstorm is possible in the southeastern portion of the northern Indiana NWS office’s forecast area (e.g. Blackford, Jay and Adams Counties in Indiana and Van Wert and Allen Counties in Ohio). If such a storm forms, it would increase the risk of large hail and could create a brief threat of a tornado. But the threat of a supercell depends on sufficient atmospheric instability occurring.
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| Yellow area: Slight risk of severe weather between 9 a.m. EDT today and 8 a.m. EDT Wednesday. Red area: moderate risk of severe weather during same period. |
Almost all of Indiana, the southern half of Lower Michigan and all of Ohio have a slight risk for severe thunderstorms this afternoon and evening, according to the Day 1 Convective Outlook that the National Weather Service Storm (NWS) Prediction Center issued at 8:45 a.m. EDT. The main threats are large hail and damaging straight-line winds. The NWS might need to activate SKYWARN storm spotters this afternoon into this evening, according to the Hazardous Weather Outlook the northern Indiana NWS office issued at 4:47 a.m. EDT.
Risks
In the “slight risk” areas of Indiana, Michigan and Ohio (see map, above right), the convective outlook indicates a 15 percent probability of damaging thunderstorm winds of 50 knots (58 mph) or greater within 25 miles of a point. The outlook indicates the same probability of one-inch diameter or larger hail. The probability of a tornado in these areas is negligible at two percent or less. To understand these probabilities, remember how often 58 mph winds do damage or one-inch hail falls within 25 miles of your home. The normal probability of such phenomena is probably less than one percent, so today’s probability is at least 15 times greater than normal. Read more about the outlook probabilities.
Actions to take
Make sure your weather alert radio is plugged in and working and that you’ll hear it if the NWS issues a severe thunderstorm watch or warning today. During any times you won’t be near a weather alert radio, make sure you have other ways to receive such information, including keeping a broadcast radio or television on or signing up for text alerts from your favorite local TV station. Above all, don’t ignore a severe thunderstorm warning. Remember how much damage a severe thunderstorm did in the Fort Wayne area in June of 2012, when the now-famous “derecho” came through. Severe thunderstorms can do a lot of dangerous damage, even when they do not produce tornadoes!
If you’re a SKYWARN storm spotter, gas up your car, check your communications gear and review NWS reporting criteria, as you might need them this afternoon and evening.
Meteorological setup
Afternoon showers and thunderstorms are forecast to develop across the mid-Ohio Valley and northwestward into Lower Michigan, as the left exit region of a 120-plus knot jet stream rounds the southeast side of an upper low and spreads across the region. With 500 to 1000 joules per kilogram of relatively low-topped mixed-layer convective available potential energy forecast to develop, isolated severe storms are expected — with organization potential enhanced by strong flow through the mid and upper troposphere. Along with a risk for hail, locally damaging winds can be expected through early evening — after which a diminishing trend is expected in conjunction with the boundary-layer stabilization that happens every evening.
Mississippi, Alabama again targeted
Elsewhere, Mississippi and Alabama, which were clobbered by tornadoes yesterday, are again in the cross hairs today. Parts of both states have a 15 percent risk of tornadoes this afternoon and evening.
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| Risk of severe weather between 8 a.m. EDT Tuesday and 8 a.m. EDT Wednesday. Yellow area: Slight risk. Green area: Non-severe thunderstorms. |
Much of eastern Indiana and almost all of Ohio remains under a slight risk of severe weather from 8 a.m. EDT Tuesday to 8 a.m. EDT Wednesday, according to an updated Day 2 Convective Outlook the National Weather Service Storm Prediction Center (SPC) issued at 1:29 p.m. EDT.
Tomorrow afternoon, some surface heating in the wake of thunderstorms earlier in the day should provide sufficient buoyancy for isolated severe storms with damaging winds and severe hail. Some tornado risk might evolve from parts of middle Tennessee to the Ohio valley and possibly Lower Michigan, but this will be contingent on more appreciable daytime atmospheric destabilization, for which uncertainty remains.
Our next look at tomorrow’s serve weather risk will come at about 2 a.m. EDT tomorrow, when the SPC issues its first Day 1 Convective Outlook for the period.
The northern Indiana office of the National Weather Service issued a tweet this afternoon that indicates severe weather has ceased to be an issue today in any of the 37 counties in its county warning area (see map below). Here’s the tweet:
This morning’s rain has stabilized the atmosphere locally. Severe weather threat for remainder of day expected to remain S of the area
— NWS Northern Indiana (@NWSIWX) April 28, 2014
No part of Indiana has more than a 15 percent risk of one inch diameter or larger hail within 25 miles of a point, according to the updated Day 1 Convective Outlook that the National Weather Service Storm Prediction Center (SPC) issued at 12:46 p.m. EDT. An earlier version of the outlook indicated a 30 percent probability of severe hail in a few extreme west-central Indiana counties.
As of the latest outlook, approximately the southern two thirds of Indiana remained at slight risk of severe weather until 8 a.m. EDT Tuesday, with 15 percent probabilities of severe hail or damaging thunderstorm winds within 25 miles of a point. The probability of a tornado in Indiana during the same period is two percent or less.
Meanwhile, parts of Tennessee, Mississippi and Alabama remain at moderate risk of a tornado today, including a risk of a “significant” tornado (one capable of creating EF2 to EF5 damage).
The SPC will issue its next update to the convective outlook for today by 4 p.m. EDT.
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| Risks of severe weather between 8 a.m. EDT today and 8 a.m. EDT Tuesday. Yellow area: slight risk. Red area: moderate risk. |
Much of Indiana has a slight risk of severe storms between 8 a.m. EDT today and 8 a.m. EDT tomorrow, according to a Day 1 Convective Outlook the National Weather Service Storm Prediction Center (SPC) issued at 8:37 a.m. EDT. In addition, much of the eastern half of Indiana has a slight risk of severe weather during the subsequent 24-hour period, between 8 a.m. EDT Tuesday and 8 a.m. EDT Wednesday, according to this morning Day 2 Convective Outlook.
Area covered today
As you can see on the map graphic at right, The northern edge of today’s slight risk area includes all or parts (at least half) of the following Indiana counties: Jasper, White, Cass, Howard, Grant, Delaware and Randolph. Indiana counties to the north of these are either not included or only small parts are included. Today’s slight risk area includes all Indiana counties to the south of the counties listed above. In Ohio, today’s slight risk area includes Darke, Miami, Clark and Greene Counties and other counties to the south of those.
Today’s risks
The main severe weather risks in Indiana today and tonight are damaging thunderstorm winds or wind gusts of 50 knots (58 mph) or higher and one inch diameter or larger hail. The probability of either of those within 25 miles of a point is 15 percent, except for a few counties in west central Indiana, where the hail risk reaches 30 percent.
Timing
A band of showers and low-topped thunderstorms are forecast to develop during the afternoon today in the vicinity of eastern Iowa and western Illinois. Those storms will move east and are forecast to weaken at around sunset.
Tomorrow
This morning’s Day 2 Convective Outlook puts all but the easternmost counties of Ohio and much of eastern Indiana under slight risk of severe weather between 8 a.m. EDT Tuesday and 8 a.m. EDT Wednesday. Indiana Counties at last half of which are covered include: Steuben, DeKalb, Whitley, Allen, Huntington, Adams, Wells, Grant, Blackford, Jay and counties to the south of these, all the way to Louisville and Cincinnati. The probability of any kind of severe weather within 25 miles of a point is 15 percent. The greatest risk for severe weather during this period will be Tuesday afternoon through early evening.
Next looks
The SPC will issue an updated Day 1 Convective Outlook by 12:30 p.m. EDT. The next look at Tuesday’s severe weather risk comes in an updated Day 2 Convective Outlook by 1:30 p.m.
Elsewhere
If you have family in Tennessee, Mississippi or Alabama, you’ll want to know that there’s a moderate risk of tornadoes in parts of those states today, including tornadoes capable of producing up to EF5 damage. Its particularly important for people in those areas to remain aware of the weather situation today.
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| Example convective outlook map. Notice the new dark green “MRGL” (marginal) and orange “ENH” (enhanced) risk areas. |
The National Weather Service Storm Prediction Center (SPC) plans significant changes to its Convective Outlook product, from which many SKYWARN storm spotters and others get their first indications that severe weather could occur.
The SPC plans to expand the product’s risk categories from four to five, while clarifying the category previously labeled as “See Text.” Convective outlooks would instead have a new “marginal” category to denote areas with at least a five percent probability of severe weather. The upper end of the current “Slight Risk” category would be renamed “Enhanced” (short for “Enhanced Slight”) to denote a threshold 30 percent probability of severe wind or hail and/or a 10 percent chance of a tornado during the Day 1 period. For Days 2 and 3, the “Enhanced” risk category would denote a 30 percent total severe probability. The Moderate and High risk thresholds will remain essentially unchanged.
The SPC wants users of the Convective Outlook product, including storm spotters, to provide their opinions on the planned changes. Read details about the changes on the SPC website, where you can also follow a link to a survey.
The northern Indiana office of the National Weather Service (NWS) has a new way for SKYWARN storm spotters to send reports via the Internet. A new spotter report form on the office’s website succeeds the old eSpotter website. I wrote previously that the NWS plans to shut down the eSpotter site soon.
The new Web form allows you to report a number of weather phenomena, including:
Reports entered into the new form appear on an Advanced Weather Interactive Processing System (AWIPS) workstation at the weather forecast office, where a meteorologist will notice it immediately.
To get to the new form, visit the office’s home page at www.weather.gov/iwx and click on the “Submit Report” link in the left-hand menu (under “Current Hazards”). Or just click here and bookmark the page.
Meteorologists in Illinois documented the first radar hook echo on this date in 1953. This was a major turning point in monitoring severe weather, demonstrating that tornadoes could be identified by radar. This discovery helped lead to the first national weather radar network in the United States.
Read more on the blog of the Illinois State Climatologist »
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| First recorded radar hook echo of a tornado, April 9, 1953, near Champaign, IL (photo courtesy of the Illinois State Water Survey, INRS, University of Illinois). |