As of 6 a.m. Sunday, May 27, 2012, the National Weather Service has issued a heat advisory for parts of the area, including the counties of Lagrange, IN; DeKalb, IN; Defiance, OH; Paulding, OH; Putnam, OH; Allen, IN; Whitley, IN; Noble, IN; Van Wert, OH; Adams, IN; Wells, IN; and Huntington, IN (this is the area that I consider when I forecast the weather with a few exceptions.). The National Weather Service is expecting heat indices near 100 today in most areas except extreme Northern Indiana and extreme northeastern Indiana (mainly northeast parts of the forecast area). With dew points in the mid to upper 60's by this afternoon, combined with temperatures rapidly rising into the lower 90's by noon, I expect it will feel like one of the hottest days that Antwerp has seen since last July (which is true!). It is possible that by afternoon that mixing is so deep that it mixes extremely dry air to the surface from the 700 millibar level, which would drop dew point readings into the lower 60's, but causing hotter temperatures closer to one hundred. The main reason for this kind of record-breaking heat is because of the strong ridge of high pressure just above us. In the upper atmosphere, an area of high pressure is equivalent to a deep layer of warm air (due to equations such as the ideal gas law and the hypsometric equation). Therefore, a ridge of high pressure in the upper atmosphere could be used to define where a surface warm air mass is located. Strong subsidence within the high contribute to the warmth too, because air sinks it warms quickly if it is unsaturated (below 100% relative humidity). Not only that, but during the summer months, as warm air masses advect into a region and solar heating commences, strong mixing occurs within the boundary layer, which deepens the layer and mixes warm air to the surface. For example, 850 millibar (a height of about 1560 to 1590 meters today) temperatures will be close to 24 degrees Celsius by afternoon. As the winds increase today, strong mixing will occur, bringing that warm to the surface. The mixed air will increase its temperature at the rate of 10 degrees Celsius per 1000 meters. Since the height of the 850 millibar level this afternoon will be about 1590 meters, first divide the number by a thousand and then multiply it by 10 to get 15.9. Add this to 24 to get 39.9. Right now, I do not think temperatures will approach 104 this afternoon (mainly because 850 millibar temperatures probably will not make it past 22, which would yield highs near 98 or 99). Back to the forecast. Areas generally northeast of Route 6 will not see temperatures that hot, mainly because of the slow movement of the warm front and cold outflow boundaries from storms farther north last night, which will keep temperatures up there below 95. If we're talking about Fort Wayne's weather, it's a completely different story. If temperatures reach over 95 today, it will break the all-time record high for May. That's two all-time records broken in one year (a high of 87 back in March, broke the 100 year old record)! Since I am expecting Fort Wayne to be one of the hottest int the region due to its dryness, my forecast is calling for high temperatures from 97-99 by this afternoon, which is incredibly hot. In fact, of the last 12 years of the 21st century, in only one year (other than this year) has Fort Wayne seen temperatures higher than 95 and for more than one day in a row, and that was in 2011. The year before that saw 95 degrees was in June 2005, and that was for only one day. In 2011, we hit 95 or higher for 7 or 8 consecutive days (but that was in July). I nearly certain that temperatures will shatter May's all time record. Even tonight's low could shatter the record high minimum low (for those of you who are confused by this the warmest nighttime low). If we only get down to 73 by tomorrow morning, it will break the previous record for May which was 72. As for any rainfall today, there is a near 0% of rainfall anywhere south of Route 6. If you are north of the highway, the cap may be weak enough and instability strong enough to cause isolated showers and thunderstorms, which could also limit daytime highs. By tomorrow, temperatures will drop slightly but still be in the mid 90's, but with higher dew points, which could make it feel unbearable. Thunderstorms are also possible area wide, but in my opinion, the shortwave that will drop a cold front through the area will be too far north to cause widespread thunderstorm activity, even with the strong instability forecast by afternoon. By nightfall, though, I do expect a better chance of thunderstorms, but then again, given the dry pattern, it certainly isn't all that likely. After the cold front moves through temperatures will drop into the lower 80's by Tuesday, and then the lower 70's by Wednesday and Thursday, and yet another cold front will drop temperatures into the upper 60's by Friday. For all you warmth lovers, don't fret just yet, according to long-range guidance, after this Friday, yet another strong ridge will build into the Central Plains and East, bringing another heat wave that could be even worse than this one. Right now, this looks to happen around June 6-12. Enjoy the warm weather!
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