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May 02, 2011

More Heavy Rain Possible Again...

What a two weeks for rain. We ended April breaking numerous rainfall records for the month. On top of that, we broke the record for not only the most tornadoes in Kentucky in one month, but for the year with April's tornado total alone! What a year so far! Today, we are dealing with heavy rain again and that will be the topic of our discussion.


Heavy Rain Forecast Discussion


Probably the last thing you  want to hear is that a front got stuck along the river, but that is exactly what is happening right now. Notice the color contrast of temperatures along the river.




With a front stuck along the river, a Flash Flood Watch has been issued through late tomorrow. If anything, this will delay the fall of the Ohio, but it should not cause a significant rise in river stages as things look right now.




Unfortunately, much more rain is in our future. You can see the wave of rain now and another passing through Oklahoma as we speak.




Looking into the future and how much rain will fall, we are finding ourselves in a situation we are very familiar with. The NAM, GFS, and HPC are all showing significant rainfalls over the next 30 hours.


NAM Precipitation Totals Through Wednesday

Note the NAM is showing an additional 1" to 2" of rainfall in our area.


Nam precip totals 1 


GFS Precipitation Totals Through Wednesday

Note the GFS is showing an additional 1.5" to 2" of rainfall in our area.




HPC Precipitation Totals Through Wednesday

Note the HPC is showing an  2" of rainfall in our area with the highest values near 2.5" south of the river.



HPC 1 


My Heavy Rain Forecast


The bottom line is that we see very good agreement across the full spectrum this morning. I like the GFS overall rainfall totals as it has been performing well, but the t-storm bursts could still add 2" to any total you see. A widespread 1.5" to 2.5" additional rain is likely for much of the area with totals increasing if you get a thunderstorm. With saturated grounds, please use caution if you encounter a flooded roadway.




My Extended Forecast -- Including Derby/Oaks


The medium range forecast has some real complexities. The heavy rain will leave the area midday tomorrow, then we settle into a waiting game for two systems late week. This is very important outdoor forecast with Oaks and Derby approaching, so we need to look at both.


The storm system coming in late Thursday through Oaks, will arrive in a time frame that shouldn't bother too many people. The good news is that it is weak and coming out of Canada as a "clipper" style system. The timing is reliable on these storms normally within about 6 hours.


GFS Precipitation Forecast Friday at 7 AM

Notice the light showers early Friday Morning.




GFS Precipitation Forecast Friday at 7 PM

Notice the light showers are moving through Cincinnati late Friday as the Oaks posts at 5:45 pm.




The Kentucky Derby timeframe is proving more difficult to forecast as the timing on this storm has been shifting a bit. The last 3 runs of the GFS have shifted between rain and dry while the EURO/ECMWF has shifted the path of the low on almost every run. Here is an example from the GFS. Notice one run shows widespread rain late Saturday, while the other shows nothing at all.


GFS Precipitation Forecast Saturday 7 AM (Run 1 AM Today)

Notice an area of rain moving in late on Derby day in this run.




GFS Precipitation Forecast Saturday at 7 PM (Yesterday's Run)

Notice no rain in the area at all on Derby day from this run of the GFS.




This does indeed cause a dilemma. What I will do for now is place a 30% chance on Derby as we try to focus in on this event in the coming days. The EURO/ECMWF doesn't give any more focus, so we do need a little more time to dial in the Derby forecast.


The entire extended looks like this...




You will note a very nice Pegasus Parade forecast as I have moved the rain back a bit.


KDF 1 


With our slim chance of showers on Oaks 137, I will go with highs in the lower 70s with partly cloudy skies and just a 20%. The chance is going to sit at 30% for Kentucky Derby 137 do to some of the uncertainty. Again, as we get closer we will pin this forecast down for you.





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