Another attempt at a pattern change.

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Monday, November 20, 2016

Two weeks ago I wrote about the upper atmosphere’s attempting to evolve into a different, colder, weather pattern.  It tried, as several weak systems attempted to bring in colder air.  However, the upper air winds were unable to generate the anticipated west coast ridge- east coast trough.  As tv’s Colbert would say, we got some east coast “troughiness”, but not the real thing.

So, two weeks later we find a pattern that still contains a strong upper trough from the Gulf of Alaska southward.  New to the scene has been the development of weak troughing over the northeastern U.S.  The upper ridge over the southeast U.S. has moved westward and weakened quite a bit.  It’s now centered as a very flat ridge over the western Gulf and Texas.

So, what was expected has happened, but to a much smaller degree than anticipated.  Now the atmospheric jet stream over North America has been left in an unusual pattern – too little spacing between the two troughs.  That sets up an unstable situation  which will result in much more weather activity over the next two weeks.  We’ll see a big increase in storms and weather changes as energy pockets swing around the big west coast trough, rapidly swing across the U.S. and hook up with the weak east coast trough.

This situation looks to have two possible solutions – 1).  The increased atmospheric instability shifts enough energy from the western trough to the eastern trough to allow it to become the dominant system. That results in a colder than normal eastern U.S. for December (and probably most of the winter.  Or, 2).  The western trough remains dominant and the eastern one never really establishes much strength.  That would mean a wet, mild December.

So, which scenario is more likely?  Today, both the GFS and European models are favoring scenario number 1.  If it works out this way, we could have a very interesting December, weather-wise!

Stuff

Grey Poupon wasn’t given its name because of the color of the mustard. The moniker actually comes from the names of two 18th century mustard firms from Dijon, run by Maurice Grey and Antoine Poupon.

 

Pattern change ahead.

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Monday, November 7, 2016

Another weak cold front will pass through the area tomorrow evening.  And, the expected weather will be very similar to last week’s light rain.  The front and the upper energy will be arriving from the northwest and will not have much moisture with which to work.  So, same idea as last week – a pretty high probability for a little bit of rain.  For those who received some rain last week (unfortunately not my yard),  it’ll be about the same again – a trace up to about .10″ of water.  So, the dry conditions will continue.

Changes ahead

For most of this fall, our warm, dry weather pattern has been caused by a strong upper level ridging pattern (upper air high pressure) pushing the primary jet stream far to our north over Canada.  The ridging pattern has been dominate, but has weakened at times to allow some weak cold air masses to invade the eastern U.S.  But the ridge has always rebuilt quickly to bring back the above normal temperatures.  That’s been the basic upper air pattern since late August with the predictable result of a warm, dry autumn.

Last week, however, the global forecast models started pointing toward a breakdown of that system.  In general, the upper air ridge sitting over the central U.S. is expected to retrograde (shift westward) to the southwestern U.S./eastern north Pacific.  This will open the door for an upper level trough (upper low) to dig into the eastern half of North America.  This will not happen quickly.  It is starting now and will bring us some Canadian air by Wednesday, then a second burst of energy will bring us even colder air by the weekend.  Then, a third system will bring even colder air early next week.

How long this trend will continue is an open question.  Yesterday, the GFS brought a massive storm into the Ohio Valley (with snow!) on the Tuesday before Thanksgiving.  Today, it has forgotten all about that storm idea, at least for the Ohio Valley.  Meanwhile, the European model is generally a little colder than the GFS with the upcoming colder trend AND it still is hinting at a major pre-Thanksgiving storm over the Ohio Valley or the southeastern states.  It’s still far to early to do any serious speculation on any storms.  But, it does appear very likely that we’e going to drop into the “below normal” temperature category for the next 10 days to two weeks.

Election Day

Ever wonder why our Federal elections are held on a Tuesday?  If your answer is “no”, stop reading and be sure to VOTE tomorrow.

If, however, your answer is “yes”, continue reading.  Back in the early days (late 1700’s and early 1800’s) there were no national laws governing elections.  States could chose to hold them whenever they wanted…as long as they had their votes counted before an early December meeting of the members of the Electoral College in Washington.  That worked pretty well until the number of states starting growing larger.  In the 1810’s Congress tried to organize some of the randomness by mandating that the state elections had to be held within a 34-day period of the fall.  By the 1840’s, as communication methods improved, the varying dates of state’s elections started to play a role with the later-voting states’s voting patterns, or so it was believed.

So Congress agreed that everyone should vote on the same day.  But how to chose the day?  Back then, the country was mostly agrarian, so it should be a time after the crops were harvested.  But, the winter had frequent snow storms (remember, most of the U.S was in the northeast back then), so the winter months were too risky.  That left November as the logical choice.  But which day of the week?   Sunday was out because it was church day and a day of rest.  Monday was out because of Sunday.  Back in the horse and buggy days, many voters would have to travel the day before (Sunday) so they’d have the time to vote and get home on Monday.  So, Monday lost out due to possible Sunday travel (not a good idea in those times).  Wednesday was Market Day – when the farmers brought their goods to town to sell to the city-dwellers.  To Congress, the logical winner was Tuesday.  In 1845 the matter was settled by Federal Law – Election Day would be on  the Tuesday immediately following the first Monday in November.

That’s tomorrow…please VOTE.

Cutting back the rain forecast

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Wednesday, Nov. 2, 2016  6 P.M.

After a very dry October, forecasts had been indicating a possibly rainy start to this month.  Unfortunately, that outlook has been drying quickly.  The models stated playing down the rain last night and the trend has continued.  There’s still a pretty high chance for rain tomorrow morning (50%-60%) but even if we do get rain, it won’t be much.  It’s likely to stay below .10″, so not much help to our dry conditions.

One thing the models have strengthened, though, is the magnitude of the colder air to follow – models are now running up to 5 degrees colder (than yesterday) for the weekend.  That still keeps us in above normal temperatures, however.

Looks like we’ll see a period of colder-than-normal weather setting up after Election Day.  More on that later.

Who are the best mudders?

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Friday, Sept. 16, 2016

Although yesterday’s forecasts for tomorrow’s big game with FSU were generally upbeat…rain before and after the game, but not during…current forecasts show no such thing.  It now looks as though rain gear will be the best fashion statement during the game.

Both the NAM and GFS are still looking toward late night rains, but they are now showing an even higher chance for rain (and possible thunder) during most, maybe all, of the game.  I remember a big win over FSU during a heavy rain about 10-15 years ago, so maybe the now-likely rain is a good omen.

Contrary to the NAM/GFS, the very short term models are now downplaying the overnight rain expectations.  I hope that is wrong as we could certainly use a good, soaking rain.  However, the short term models have been outperforming the NAM/GFS all summer (by a big margin) , so wouldn’t be surprised if the predicted rains tonight are a no show.

Deja vu?

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Friday Sept. 9, 2016   4 P.M.

Back in August I wrote about an unusually bad string of forecasts the Louisville area has been subjected to this summer.  That week was the worst forecast performance (for a prolonged period) that I can remember.  Individual forecasts, yes, but not such a long string of them.  Well, it has started again.

We did have some isolated showers overnight and a good soaking rain south of Louisville this morning, so far three straight “high probability” showers and thunderstorm forecasts have come up largely dry for Louisville area.  That includes the current time forecasts for Thursday, Thursday night and today.  And, the current forecast for tonight, tomorrow and tomorrow looks to be just as bad (or worse.)

Without getting into specific details, let’s just say that if the most recent models are anywhere near correct, the current “official” forecast isn’t going to be.

Tonight, we’ll see a dying line of rain/storms approach us after midnight.  Like last night they don’t look like they’ll bring any widespread rains.

Tomorrow’s forecast for numerous showers and thunderstorms (60% chance) actually boils down to the possibility of a line of thunderstorms forming over us in the early afternoon… an hour of rain at most.  Both the NAM and GFS are tending have the formation either over us or to our east, so it would no be too surprising of they missed us entirely.  The NAM (and me) are leaning that way.

Then, the 50% chance for showers/thunderstorms tomorrow night is just plain “Crazy Talk.”

I don’t want to complain, but…

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Saturday, August 13, 2016  11:45 P.M.

What a miserable week of forecasting we’ve been victimized by all week and the worst is still happening.  Thursday and Friday the forecasts, aided by the ever-willing media hype made it sound like we were due for ark-building rains.  Only one thing was wrong – the models had already backed off of the extreme rain forecast by THURSDAY.  By Friday, the models had backed off the threat of heavy rain even more.  It was obvious that heavy, flooding rains were out of the picture for today and Sunday.  So, the NWS did the “obvious” thing – issued a Flash Flood Watch for Louisville area and southern Indiana.

Today worked out just the way the models predicted – a few very light showers in the metro area with heavier rain over central Indiana.  However, the Flash Flood Watch was expanded over a larger area Sat. morning…ever though the NWS forecast had reduced the chances for rain by about 20% or so for next 48 hours!

A few showers are possible overnight, but very little, if any, rain is likely for Sunday and heavy rain Monday will stay far to our west.  But, the Flash Flood Watch remains in effect through Monday.  My advice to the NWS is pretty simple:  Stop hyping a dead forecast…it died a long time ago.

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.