Significant Rainfall on the Way.

Our first significant and possibly heavy rainfall looks to be on the way by Thursday night and Friday.  This will really help the plants to shoot up after the long and hot dry spell we have been having.  Here's what's going on: currently a weak shortwave trough is located over the western portions of North and South Dakota.

This shortwave will amplify and strengthen rapidly during the overnight hours, as the jet streak, a region of stronger winds in the jet stream, enters and "digs" into the trough.  By tomorrow morning, widespread high and mid level clouds will enter into the region from the west, bringing the first signs of the storm system.  As it strengthens tonight, it will slow its quick pace due to several processes occurring within the storm's structure.  One of these processes is the latent heat release from the large area of convection currently located over South Dakota.  Latent heat release slows the system's pace, due to processes that occur near the tropopause, which are so complex, is it not entirely understood by most operational meteorologist.  In response, a low pressure system will begin to form and move along the frontal boundary that is currently located over the Ohio Valley region.  This will cause the front to strengthen rapidly, first strengthening the storm system, but also causing a low level jet to form, which will cause the front to move northward as a warm front into the region.  Increasing isentropic lift and frontogenetical forcing will foretell the coming of rain by late afternoon on Thursday.  This is where model differences come into play.  As the upper level wave strengthens, the low pressure system will deepen rapidly, drawing moisture northward above the warm front.  This, combined with strong upper level forcing and frontogenesis will cause the development of heavy rain bands over the area by 9-11 p.m. Thursday night.  Some of the models, such as the NAM, are too weak with the storm system, causing less rainfall, less moisture transport, and an obvious impact on the precipitation patterns.  The GFS on the otherhand (this is kind of surprising), is much stronger with the storm system, has much more intense moisture transport into the region, which positively impacts the storm system, making it stronger.  Usually, computer models do not have a good handle on rapidly developing storm systems in positive feedback processes.  Actually it is kind of surprising that the GFS is stronger with the entire storm system, due to the fact that it does not have a good handle on convective development (thunderstorms, heavy rain, etc.).  Therefore, my forecast will call for a stronger storm system, stronger moisture transport, and thus heavy rainbands, and much heavy rainfall.  In fact, if the forecast goes as predicted, I would expect rainfall amounts in excess of an inch, especially west of Defiance.  After the system moves out of the region by Friday afternoon, clouds will prevail, along with gusty winds and cool temperatures.  By Saturday, clouds will still persist, but will allow some sunshine through.  Temperatures will also moderate into the lower 70's.

Much Cooler Weather On the Way

After five days in a row of near or record breaking temperatures, daytime highs will finally begin to cool, with highs today only reaching the mid to upper 80's (still pretty warm).  This cooler weather will be brought on by a strong cold front moving through the region today, with a noticeable decrease in humidity also.  Temperatures will not be that cool today as strong cold air advection will not reach the area until later this evening, causing lows tonight to fall into the low to mid 50's.  By tomorrow, highs will be 25 degrees cooler than what they were on Sunday and Monday, with highs only approaching the lower 70's.  If upper level ridging were to build in behind this shortwave, temperatures would likely warm back up to the 80's and 90's, but not so this time, because the amplified jet stream is expected to break down this week into a more zonal flow pattern.  This will allow several disturbances to phase or "morph" into one stronger wave, which could cause more rain for Thursday night into Friday.  The bad side about this is that temperatures are likely to become very cool, with daytime highs well below normal by Friday, along with the rain.  In fact, I am only expecting highs to make it to the mid-60's on Friday, while Thursday, temperatures should still be near 70.  By Saturday and Sunday, the upper level wave moves away from the area, causing upper level height rises, and warmer temperatures.  Ridging will then build into the region for the foreseeable future, with highs back into the 80's and 90's by next Tuesday and Wednesday.

Season's First Heat Wave

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!