BLOG: One-Two Punch of Weekend Severe Weather?

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It's a beautiful Summer day today, but trouble may be on the horizon for the weekend. So lets get right to it. While we are enjoying unseasonably cool temperatures, high heat continues to bake the Plains: tempsnowThat dome of heat is going to start migrating east today. While it will not turn HOT here in eastern Ohio and western Pennsylvania, it will turn warmer and more humid tonight into Saturday. Here's Saturday morning's surface map, showing the leading edge of that warmer air: satsfcAs that warm air runs into the cooler air, it will be forced to rise over it, since warm air is less dense than cool air. That rising air will create spotty shower and thunderstorm activity during the day Saturday. Here's the midday simulated radar off of the NAM model: 11amsatNotice how "hit-or-miss" the activity will be.The threat for severe weather will ramp up toward evening. By that time, the atmosphere will have gotten quite unstable across our region (especially to the west of Youngstown), as shown on this map displaying CAPE (Convective Available Potential Energy) values: capesateveA complex of thunderstorms is likely to form somewhere in that zone of very high instability. Last night's NAM model placed it in Illinois and Indiana at 5pm: 5pmsaturdayThen, the model intensified the complex and took it into Ohio later in the evening: 11pmIf this model were to have EXACTLY the right idea (unlikely at this point), that would be a severe wind damage threat for southern Ohio particularly. That "bowing" shown on the simulated radar in SW Ohio is unsettling; that just screams "huge area of wind damage".The Storm Prediction Center outlook for Saturday and Saturday night has all of the region in the Elevated Risk (yellow): day2But, they also see that odds may favor the HIGHEST risk of severe weather being SW of Youngstown. This map shows the percent chance of severe weather within 25 mils of any location: day2catAll that said, let's not dismiss the chance for severe weather across the Mahoning and Shenango Valleys. It's still a period where the risk is elevated, even if the overall HIGHEST risk is to our southwest. The main threat from storms here will be damaging winds. Wind speeds aloft will be getting stronger and any hefty storm could pull some of that wind down to the surface. Winds at 5,000 feet will be up around 40-60 mph and tall thunderstorms can pull down winds from above that level easily: 850windsateveAdditionally, directional wind shear (the changing of wind direction with height) will be pretty significant: srhThis shear will help aid thunderstorm development and also means that an isolated tornado is something we cannot rule out. Here's a look at the threats Saturday evening: risksOk what about Sunday???On Sunday, a strong cold front will be pushing into the Ohio Valley and Great Lakes. sfcsunAhead of the front, the atmosphere will be warm and unstable. The big complex of storms that likely rolled through southern and eastern Ohio overnight will keep pushing to the east and the atmosphere will get a chance to "reload", especially if there is a long interval of sunshine.  Here's a look at Sunday afternoon's expected CAPE values: capesundayTHe Storm Prediction Center has us in the Elevated Risk again: day3So, we expect scattered strong storms to fire along and ahead of that cold front. Much like Saturday, the highest risk will be from damaging winds....but some hail is also possible.Meteorologist Mike Joyce will be in the Weather Center this weekend. Be sure to follow him on Twitter and Facebook. Have a good, safe weekend everyone.Eric

BLOG: Has it REALLY Been a Cool, Wet Summer?

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So, the Summer of 2014 has been unusually cool and wet, right?? Part of that statement is true, depending on where you live. In some parts of the Valley, it HAS been wetter than average since June 1. But temperatures? When we look at the average since June 1...it's really not much of a story at all.Let's take a closer look at the numbers. At the Youngstown-Warren Airport (the OFFICIAL reporting station for our area), the stats since June 1 look like this: junjulNotice that at the airport, rainfall has been almost EXACTLY average since the 1st of June. Also notice, temperatures have been slightly ABOVE average for the 52 days as a whole.On the subject of precipitation, amounts have been quite variable in the WFMJ viewing area...which is typical of Summer. Some places get a couple of soaking storms that drive up rain totals locally. In some communities is HAS been a wet Summer. A sampling of rain totals: raintotalsYou can also see what areas have been wettest since early June on this map, which shows satellite-estimated totals:   preipmapNotice the wet spots in Mercer and Columbiana counties.Temperature wise, the perception is certainly out there that this has been a "cool" Summer. I think this is mostly due to the lack of sustained hot periods and the lack of 90+ temperatures. AND, July has been a below average month: julyFor the Summer (June 1-now) this has been the 41st coolest Summer since 1930. Not a stat that jumps out!summerranksAnother cool shot on the way next week. Thanks for reading!Eric

BLOG: What Do Those Percentages on the Forecast Graphic Mean??

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One of the commonly misunderstood parts of a weather forecast is the "probability of precipitation", or PoP. It is so frequently misunderstood that some television meteorologists do not use them.At WFMJ, we DO use them and part of the purpose of this post is to show you WHY.First of all, what does a 40% chance of rain ACTUALLY mean? Let's start with what it does NOT mean:1) 40% of the area will get rain2) It will rain 40% of the timeWhat it actually means is that there is a 40% chance of measurable precipitation occurring at any point in the day at any location in the viewing area. The main reason we use PoPs at WFMJ is because it is a way to communicate graphically what a day will be like. Let's use this coming weekend as an example. Here is our current 7-day forecast WITHOUT PoPs included: nopopsOK, POP QUIZ. Based on that graphic, which weekend day is likely to be the wetter of the two???? Another way of putting it: which day are more backyards likely to get wet at some point in the day?Unless you are listening intently to what the forecaster is saying while this graphic is on the screen, there is virtually no way of knowing the answer. The icon looks pretty much identical both days. Some sun with a cloud over it and a lightning bolt coming out the bottom. Some television meteorologists include descriptive words to help describe the "flavor" of the day on the graphic. Common words used: scattered, widespread, isolated. Quick: what do those words mean? Which is the "wettest" sounding to you?? In my opinion, these words are too easy to misunderstand. So, we use PoPs. Here's the 7-day forecast WITH PoPs: 7day(Note: the icons are the same as the graphic above....my screen capture program just snapped this picture while the animated lightning bolts were not visible)So, you are busy and only half-listening (like my wife! heyooooo) and just have time to glance at this graphic. Very quickly, you should be able to determine that Saturday is likely to be the "wetter" of the two weekend days.This is not an exact science. There are situations when one part of the area is much more likely to get precipitation than another area. For example, a storm is just scooting by to our south. It will surely rain in Columbiana County for awhile, but northern Mercer County won't have a drop. What to do?? Of course we will explain the situation verbally but what about graphically? Often we just have to take an average. The PoP is 100% in Columbiana County but 10% in Mercer County. On the graphic we may just put 60%. Again, not an exact science.Some PoP guidelines, pulled straight from the PoP Gospel According to Eric:0%: The day will be dry throughout the viewing area.10%: We can't "completely rule out" a totally random rain/snow shower.20%: Anything that occurs will be very isolated. Often used on hot Summer days when some random thunderstorm might pop up.30%-40%: Used for hit-or-miss activity (think: thunderstorms or snow showers) in the short term (days 1-3) and as a "generic' chance in the long range (days 4-7). Rarely is a PoP higher than 40% used on days 6-7, since the confidence in any forecast is naturally lower that far out.50%: NEVER USED! There enough jokes out there about weather people just flipping a coin! We don't need to give other people a fat pitch down the middle to hit. (I use a dartboard instead of a coln anyway.)60%-80%: Measurable precipitation is likely (but not guaranteed) to occur at some point in the day.90%: Look, it's gonna rain/snow, but we have commitment issues. 100% is sooooo certain. We like wiggle room.100%:rainAnother misconception:A high PoP (say, 70% and up) means precipitation will be heavy and/or the day will be a washout. NOPE! Say a line of thunderstorms seems pretty likely to cross most of the viewing area from 10am-2pm. We go with a PoP of 80%. Most of the day will be dry though! This is the type of forecast that you would only likely see 1-2 days in advance since predicting a 4-hour window when it's likely to rain would be difficult 5 days out.I hope you found this post useful. I always welcome your feedback. Post questions or comments here or on my Facebook/Twitter pages.Eric