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04/17/2017

THUNDER FORECAST: Rain Likely. Heavy Storms Possible!

While still several days away, confidence is growing on a wet forecast for Saturday.  Of course this is not good news for Thunder Over Louisville and the kick off to the 2017 Kentucky Derby Festival.  

The Storm in Question

Gfs jet

The storm is currently located over the North Pacific revolving over top of some high speed jet stream winds that are just now beginning to come onshore the West Coast.

By Friday the core of these upper level winds are expected to eject out of the Rockies and into the Southern Plains helping to develop a surface low over West Texas.  From there, the low is forecasted to deepen as it travels towards northeast and eventually into Kentuckiana by late Saturday and Saturday night.  

Let's time it out with the current run of the Euro...

The 12z run of the Euro shows an area of low pressure approaching out of Northern Arkansas with a large shield of rain extending into the Lower Ohio Valley Saturday morning.

Ecmwf_pr6_slp_T_ky_21

Widespread rain continues locally with thunderstorms developing near the low across the Middle Mississippi River Valley early Saturday afternoon.

Ecmwf_pr6_slp_T_ky_22

The low deepens arriving near Evansville by early evening with very heavy rain/storms approaching our area.

Ecmwf_pr6_slp_T_ky_23

The low travels right over our area Saturday night as widespread rain and storms continue.

Ecmwf_pr6_slp_T_ky_24

By morning on Sunday the bulk of the rain shifts east into Appalachia with wrap around showers locally.

Ecmwf_pr6_slp_T_ky_25

If the Euro is correct, then it rains all day Saturday and Saturday night potentially falling heavily at times with lightning and thunder.  This would mean that both the air show and the firework display would be negatively impacted.  In fact, it's possible that parts, if not all, of the air show could be cancelled due to low cloud "ceilings".  

What do I think?  

Unfortunately, I think the Euro might have the right idea.  This is a pretty classic set up for us this time of the year with a deepening Southern Plains low traveling northeast along an existing frontal boundary.  This would give it the ability to pull up abundant moisture over top of a strong "baroclinic zone" or tight temperature gradient presumably located over our area.  The latest run of the GFS supports this solution with the potential for heavy rain and storms especially late in the day.  

Is severe weather possible? 

The short answer to that is yes, it's possible.  However, a more likely scenario keeps surface temps too cool, likely in the 60's, for much of a severe threat in Louisville.  However, this doesn't reduce the potential for very heavy rainfall and thunderstorms.  

So how much rain?  

Data from both the Euro and GFS suggest that we could see widespread 1 to 2 inch rainfall amounts Saturday.

Ecmwf_precip_24_ky_24

Moral of the story... while I wouldn't cancel your Thunder Plans at this range, I would start preparing for what could turn out to be a very wet Saturday.  

Marc and Rick have your update on WDRB News this evening.

WDRB Meteorologist Jeremy Kappell

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