Monthly Archives: July 2016

Quiet night

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Monday, July 18, 2016  6 P.M.

Atmosphere has quieted over much of the region and should remain calm, but very warm and muggy tonight.  In spite of the Weather Service’s 40% chance for rain/t-storms tonight, the actual chance for rain is pretty close to zero.

Plenty of heat and humidity will be the primary story this week,  Don’t be surprised if we reach the upper 90’s.

What happened to that “Godzilla” El Nino

We did have a strong El Nino during the winter.  It actually turned out to be a little stronger than the one in 1998, but it was far less destructive for the U.S.  In fact, this El Nino  could probably be described as more beneficial than damaging for the western states.  Reservoir levels at at, or slightly above, normal for July from central California northward, but conditions remain far too dry over the south.  If this winter was “Godzilla”, California could use several more winters just like it.

Almost always, El Nino’s are followed by La Nina conditions.  It didn’t take long.  Ocean water temperatures have been falling for months.  Neutral conditions were reached during May.  Then last week entered weak La Nina conditions.  How strong the La Nina will become remains to be seen, but current forecasts predict it’ll remain in the mild to moderate range through the rest of the year.  As a result, global air temperatures  will probably drop below normal for a few months later this year.

 

Another tricky day

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Friday, July 15, 2016  3 P.M.

This has become an ongoing problem recently – wide model divergence on thunderstorm chances.  It’s back again today.  Both the GFS and NAM literally ignore the chances for thunderstorms later today while the short-term models develop storms in the area over the next few hours.

With a weak, slow-moving cold front lying over southern IN and plenty of low level moisture available, it should look like a no-brainer for storms.  However, there are some problems.  Even though the surface is moist, the upper air doesn’t appear to have much water to add.  And, there’s no readily available upper air energy to initiate convection.

Still, the surface-based instability is high along the Ohio River.  And we’re in the time of maximum daytime temperatures, so the surface conditions should suffice to create at least some small thunderstorms over the next few hours (until 7-8 P.M.)  The cold front should also be favorable to allowing a nearly solid line of storms to form and drift southeast.  So, it looks like most (if not all) of the Louisville Metro should experience a shower and/or thunderstorm later this afternoon

T-storm update

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Wednesday, July 13, 2016  4 P.M.

Looks like my earlier forecast is going to be a bust.  Radar showing nothing happening nearby.  So the heat and humidity rule.

My (former?) friends, the RAP/HRRR have backed off from the idea of afternoon thunderstorms, but still show high chances for a line of t-storms tonight – probably between 8 P.M. and Midnight.  So, at least part of my forecast may still happen.  Could be a good light show tonight.

8 P.M. update

Currently strong line of thunderstorms east of Evansville is racing eastward about 30-40 mph.  It should sweep across the metro area between 10 – 11 P.M.  It is weakening ( and will continue on that path) so no problems are expected.

Forecast models in conflict again

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Wednesday, July 13, 2016  11 A.M.

Once again, the short term models are at odds with the primary models.  Everyone agrees that it’ll be hot and humid today, but the chances for thunderstorms vary considerably.

First, the big models…the NAM doesn’t produce any  chance for t-storms anywhere over KY or southern IN.  The GFS hints at a small chance especially north of the Ohio River, but it’s numerical statistical output is less than 10% for this afternoon.

Meanwhile, the short-term regional models are much more enthusiastic with t-storm development.  The RAP predicts a large cluster of storms over our area late this afternoon.  The HRRR is even more aggressive with an afternoon and an evening storm cluster moving over us.

The Weather Service is sticking with the NAM/GFS, but with a slight nod toward the short term models.  They give us a 20% rain chance today and tonight.

But, the RAP/HRRR were developed for situations such as this.  They are designed to do the fine-tuning between the gaps in the larger models.  And, last week in a similar situation, they did a great job.  I expect the RAP/HRRR to continue doing their jobs well.  So, I’d expect a much higher chance we’ll see t-storms later today…60% chance or higher.

We’ll see how this battle works out in a few hours.

 

5 P.M. update

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Thursday, July 7, 2016

Storms fade…no threat to metro area.

Southeastward thrust to storms continues and any severe weather threat for the Louisville metro area has faded away.  Some heavy rain/gusty winds will hit southern Jefferson County and northern Bullitt County over next 30-45 minutes, but the storms will not be very strong.  Otherwise, rain is fading over southern Indiana.  So, it now appears that most of Jefferson County will get little, if any, rain.

Storm update – good news

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Thursday, July 7, 2016  4:45 P.M.

Decreasing threat to Jefferson County

Most active part of line of thunderstorms approaching us has shifted southward into parts of Meade and Hardin Counties.  Hardin County could still see strong winds of 50 mph or more for the next hour.

Meanwhile, northern part of the line is now entirely south of I-64 in southern Harrison County.  Gusty winds are still likely, but they should stay in the 40-45 mph range.  This line will bring similar winds to areas of Jefferson Co. south of the Watterson X Way between 5:15 and 6 P.M.  Northern Jefferson County and southern Indiana (north of I-64) will be much calmer – not much rain and little wind threat.

Late afternoon could get stormy

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Thursday, July 7, 2016  4 P.M.

After the wide model divergence this morning, it’s looking more and more likely as though the short-term models will win out over the big guys (GFS and NAM).  To their credit, the NAM and GFS are rapidly catching on.

Storm Prediction Center has a Severe Thunderstorm WATCH covering about the western half of KY, but it stops short of Louisville.  It doesn’t matter about the watch boundary, because we’re in just as much risk (low) for severe winds as the folks to our west are.  A line of thunderstorms covers southwestern IN and western KY and is rapidly moving eastward – pushing quite strong gusty winds our way.  Radar estimates suggest 60-70 mph winds, but surface results usually don’t match the estimates.  Nevertheless, extreme southern IN and the Louisville area can expect strong (perhaps severe) wind gusts as this line races  through the metro area between approximately 5:15 and 6:30 P.M.  Scattered minor damage and some power outages are likely during that time.

The threat of severe winds from this system drops to near zero very quickly north of I-64.  The above description and timing pertain mostly to the area of IN and KY along and south of I-64.

 

 

Interesting forecast problem today

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Thursday, July 7, 2016  11 A.M.

Looking at this morning’s forecast models and actual forecasts is almost a case of “What’s going on?”  Everything you look at has a different story to tell.  First, the NWS forecast includes a scant 20% chance for rain/t-storms today and another 20% chance tonight.  The backbone of our forecast system, the GFS produces a 1% chance today and about 40% tonight (LAMP) and a 4% chance today, 45% tonight (MOS).  Meanwhile, the NAM model output is also low…11% today and 53% tonight.  By the way, all of the “tonight” forecasts call for the rain after midnight.

On the other hand, the Storm Prediction Center gives us a 40% chance for thunderstorms today and just 10% tonight.   Then, the two primary short-term forecasts chime in with a slight different story.  Both the RAP and the HRRR predict a line of thunderstorms to reach the Louisville area between roughly 8 P.M. and Midnight.  Earlier today I saw WAVE TV’s in house model project a line of storms between 6 and 8 P.M..

What’s one to believe?  Good question!  First of all the GFS has been terrible lately as evidenced by a lot of forecasts we’ve heard recently.  Second, the short-term forecasts are better at picking up on the “outflow boundaries” created by previous storm systems, so they should be more reliable.  As a result, I’d lean toward the RAP/HRRR/WAVE forecast expecting a line of thunderstorms this evening.  We’ll see how it plays out.