Category Archives: commentary

Forecast models still at odds

Thursday, Feb. 14, 2019  4:30 P.M.

Snow possible tomorrow night!

Happy Valentines Day!

First of all – tonight.  A weak cold front will cross the area.  It has little upper air support and slim moisture available.  Nevertheless, it could squeeze out a few, brief light showers tonight.  Only about a 30% chance for a measurable amount.  Temperatures tomorrow should stay near 40 during the day.

Snow situation

The northwest U.S. is being pounded by yet another winter storm.  A small piece of upper air energy is breaking away from the parent system and will move eastward across the country over the next two days.  Both the GFS and NAM portray this system a little stronger than yesterday.  They still differ on the storm path and consequences for us.

The GFS is gung ho on snow for us as the surface system slides south of us tomorrow night.  GFS snow totals are around 2″ for Louisville area with heavier totals (up to 4″) over  SW Indiana and western Kentucky.  Snow forecast is even higher along a path from near Evansville to south of St. Louis to Kansas City.

Then, there is the NAM.  Like yesterday, it isn’t taking the snow very seriously for the Louisville area.  It projects the storm track to be a little farther south.  That puts us on the northern edge of the snow threat.  Southern KY will see a mix of snow, sleet, freezing rain and rain creating major road problems tomorrow night and early Saturday.  It also has the heavy snow from far western KY back into Missouri.

So, which model is correct?

Good question.  Can you wait until Sunday morning for the answer?  Of course not!  We want to know beforehand.  So, I’ll give you my thoughts on the situation.

In general, most of the forecasting fraternity will go with the GFS.  Over the long haul, it seems to be the better of the two.  But, this winter the GFS has had snow lovers salivating over two big snow forecasts.  Both times local media and National Weather Service followed the GFS and went into hype mode only to have both forecasts fail.  Overall, the GFS has been in a slump but the NWS is going along with its 2″ forecast for tomorrow night.

But, what about the NAM?  It’s a good model, too.  But the wide differences between the two models for this forecast must mean something.  If tomorrow night’s weather solution were “settled science”, the two models would be very close.  The fact that they are not close tells us there is something about this atmospheric setup that they can’t quite resolve.  In essence, neither model can be ignored.

So, here’s my best shot.  I’m leaning toward the NAM ideas having the surface storm taking a more southerly track.  That means less snow for the Louisville area.  I’m expecting less than one inch for Louisville metro.  Snow totals will increase south of the city and could get an inch or two down to the E’town area.  South of the parkway they’ll see the wintry mix described above.

West of Louisville snow accumulate along and south of I-64.  The farther west in IN/KY, the more snow – as high as 4″ near Evansville.  North of Louisville, little or no snow will fall.

Again,  I believe the Louisville area will be on the northern edge of the snow system.  I expect less than 1″…probably closer to the lower end of the range.

Valentines Day

For hundreds of years BCE (B.C.), the Romans celebrated a Spring ritual known as Lupercalia.  It was a fertility rite to welcome back the growing season, among other things.  It was celebrated around February 14th.  About 500 CE (A.D.) the Catholic Church  decided that Lupercalia was a little too bawdy  for its flock, so it was banned.  It was replaced by a new Church holiday they named Valentines Day in honor of an Italian saint who had been decapitated (by the Romans).

Another weekend…another storm

Thursday, January 17, 2019…4 P.M.

Subtle changes

If you’re a snow-lover you’re not going to like the small changes to Saturday’s forecast.  Both the GFS and NAM have drifted in the same direction, so I’ve got pretty good confidence the solution they are pointing toward looks realistic.

We’ve been tracking a storm system blasting northern California and a large chunk of Arctic air moving south from Canada.  Original thought was these two systems would merge over the Ohio Valley/midwest on Saturday.  The result of the merged system would bring us plenty of rain (2″-3″) Saturday.  Then, as the cold air rushed in Saturday night, we’d see an inch or two of snow.  I’ve heard talk of heavier snow, a “flash freeze,”  and single-digit temperatures (even sub-zero).

That’s all nonsense if the current model trends are correct.  The new idea is that the west coast trough and the cold air system will not get “in phase” until the primary surface storm system passes east of the Louisville area.  That means the storm system will not get to its rapid development stage until it gets to Ohio or beyond.

Consequences of the recent changes

1).  Rain remains likely most of the day Saturday.  But it won’t be as much.  Totals will probably range in the 1″ to 1.5″ range.

2).  Rain should end by Saturday evening and we’ll probably see some snow flurries and/or snow showers overnight.  Accumulation, if any, should be less than 1″.

3).  The initial surge of colder air will be slower to arrive.  Temperatures will not fall rapidly enough to allow a flash freeze.  Icy spots, however, will form on roadways during Saturday evening.

4).  Sunday will be very cold…probably near 20-22 all day.  Because the primary storm system will intensify north/east of Louisville, the cold air transport southward will be weaker.  Thus, it appears the local temperatures won’t drop into the single digits in the Louisville area either Monday or Tuesday morning.  Rural areas especially in southern IN could see lows below 10 degrees.)

Note:

The cold upper trough expected over the eastern parts of North America due to the Sudden Stratospheric Warning of late December is now in place.  This system should provide us with frequent snow opportunities and plenty of cold air for the next 2-4 weeks.  Forecasting should be lots of fun.

If you’d like a little more detail on what a Sudden Stratospheric Warming is, see my post from a couple of weeks ago.

Stuff:

We are constantly bombarded by the things that the climate change “hawks” want us to hear, so you probably missed the news that the U.S. is one of the world leaders in carbon emissions REDUCTION.  Yes, compared to the 2005 baseline, total U.S. emissions have dropped 11%, even though we had a small increase last year.  As a whole, Europe has dropped a little (1-3%) as well.  But, the rest of the world continues their rapid increases.  Roughly 80-90% of the nations which signed the Paris Climate Accord continue to increase their emissions.  China and India are by far the biggest offenders.

Let’s not blame China too much.  After all, they have a signed agreement with the U.S.  to keep increasing emissions as much as they want until 2030.  The Climate Gang praised that agreement as just about the greatest thing since (the proverbial) sliced bread.  I’ve always felt that the agreement gave China all the bread and the slicer.  Maybe we’ll get some crumbs out of the deal.

Weekend Weather Prospects

6:30 P.M. Thursday, Jan. 10, 2019

Snow and rain likely.

Forecast models have changed little since yesterday, but that’s enough to bring our weekend forecast into better focus.  The primary change is that the NGM and GFS have both warmed a little.  My worry from yesterday about that prospect is looking like a realistic idea.  Consequences follow:

General situation remains the same…a weak system coming out of the southwest will drift ENE across the southern states.  It will start to regenerate Sunday, but that will be too late for us.  With the low center staying to our south, we’ll have a northerly component to our winds, so the colder air will hold in place with only a slight warming modification.

Heavy snow will break out over northern AR and southern Missouri tomorrow and march eastward into KY/IN tomorrow night.  Snow should begin in the I-65 region about midnight or later.  Temperatures should remain at or above 32 degrees overnight, so snow should accumulate ON GRASSY AREAS !”-2″ by morning.  Roads will have only a small accumulation of slushy/wet snow, but,as always, drivers will find the icy spots.  Luckily, since it’ll be Saturday traffic should be light.

Saturday most of the overnight snow will melt away and roads will improve rapidly.  It’s also looking like little or no precipitation will fall during the day.  If anything falls from the sky during the day, it’ll be light rain.

Part 2

Light rain/drizzle moves in Saturday night and continues off and on until early Sunday.  During Sunday, the surface storm system pulls eastward and drags colder air back into the Ohio Valley.  Some light snow/flurries are likely during the day, but little, if any, accumulation is expected.

We need babies!

Read an article today about the slowing birth rate in the U.S.  In general, the thought goes, our female population needs to produce  2.1  children during her lifetime in order to keep our population stable.  Our current rate has dropped to about 1.7.  So, in spite of what we’re being told, we need those immigrants!

Sudden Stratospheric Warming

January 2, 2019

New hope for some actual “winter weather”

Sudden Stratospheric Warming (SSW).  I first became familiar with that term in early 1977.  For those of you with good memories, you’ll remember January 1977 as the coldest month in Louisville’s recorded weather history.  And it featured a good bit of snow as well.  At the time, the reason was given as rapidly warming stratosphere temperatures over the Arctic. Some studies of the stratosphere began in the 1950’s, but it remained a rather esoteric field until 1977 when Mother Nature decided to put on a demonstration of the full effects of SSW.  January started normally, but by the second week we were covered with snow and extreme cold. The cold air just kept on coming.  The average temperature for the month was 18.6 degrees – far below the previous record.  In early February, warmer weather returned and dominated the rest of the month.  That was it.  Four weeks of the coldest weather we’ve ever seen!

Today, many people enjoy walking over the Ohio River on the Big Four bridge.  Back in 1977, however, many people walked  to Indiana across the frozen Ohio River.

What brings up this discussion about the SSW is that we’ve just experienced another one.  As far as I can tell this warming event is not nearly as strong as the 1977 event.  Even so, the general consequences of a SSW remain the same.  The sudden warming fouls up the circulation of the now commonly-called Polar Vortex.  In recent years, the media have blamed the Polar Vortex for just about every moderate to strong winter storm.  True, but somewhat misleading.  Usually the storms are created by a strong pocket of atmospheric energy which breaks off the Vortex and digs south into the U.S.  During  a SSW event, however, the warming actually breaks up the vortex into two (rarely three) major troughs which drop out of the Arctic into the middle latitudes.  Usually, the strongest cold weather hits Europe while the weaker one sets up over eastern North America.

Normally, the time between the appearance of the SSW until the consequences reach our surface weather is two weeks.  So, right about the middle of this month, our mild winter will vanish for about four weeks.  Cold, and probably snow, should be plentiful during that time.

Don’t give up on winter yet!

The little engine that could

Tuesday, January 16, 2018  3 P.M.

The relatively small weather system that moved ever so slowly over southern IN and KY yesterday was amazing to watch.  It just didn’t want to move in spite of the models efforts to move it away last evening.  Watching the snow pattern move across the radar screen last night was like watching the proverbial paint dry.  In spite of the prolonged period of snow, the system still couldn’t generate much snow, but it was an amazing effort.

The last very cold surge (for at least two weeks) of Arctic air has arrived and will dominate our weather for the next two days.  We’re seeing a good example of the power of the sun this afternoon.  The air temperature is only in the mid teens but yet we’re getting a lot of melting on asphalt roads.  Concrete roads don’t absorb as much heat, so they haven’t melted as much snow.

By all large scale features, we should be having temperatures at zero or below tonight.  The coldest part of the cold air mass will be over us tonight,  we have a snow cover, clear skies and light winds.  That normally would produce temperatures in the 0 to -10 range.  However, model and human forecasts are predicting a low range of 5 to 10 degrees. Why?  Lake Effect

We normally think of snow when Lake Effect is mentioned.  Not this time.  This is more subtle.  The model suite is in agreement that low level winds (3,000 to 8,000 feet) will develop a fetch (flow pattern) from Lake Michigan SSE across IN and into the eastern half of KY.  It’s too weak to produce snow, but it should be able to produce mostly cloudy skies after midnight.  The clouds trap what little heat we have so our temperatures stay higher.  (Skies should remain mostly clear 30-40 miles west of Louisville, so sub zero temperatures are likely there.)

The ability of today’s weather forecast models to pick up on such small details as a Lake Effect’s ability to alter our weather (hundreds of miles away)  is really amazing.  We’re light years ahead of the two primitive models I started using more than 50 years ago.

 

 

Potential storms update

Sat. Nov.18, 2017  3:10 P.M.

Severe Thunderstorm WATCH expanded  WHY?

The Storm Prediction Center has seen fit to expand the Tstorm Watch to cover most of Kentucky.  At least for northern half of KY and southern half of IN, watch seems pretty useless.  As mentioned earlier, the part of the storm line approaching our region has lost any severe weather characteristics.

So, risk of severe thunderstorms for Louisville area is extremely low.  Southern KY has a very slight risk.

Strong Storms likely early tonight.

Sunday, November 5, 2017  5 P.M.

A cold front will sweep across the area tonight bringing an end to the recent warm weather.  The warm air has brought an unusually large amount (for November) of moisture into the lower Ohio Valley, so the colder air looks as thought it’ll arrive along with rain, thunder and strong winds. just how strong the winds will be is the primary concern now.

This system has plenty of wind fields, convergence patterns and overall dynamics which provide an important side of the severe weather equation.  However, the thermodynamic part of the equation, while sufficient for severe storms now (from southern Missouri to central Indiana), is forecast to weaken quickly over the next few hours.

A similar system last spring stayed active all night creating probably our worst severe weather outbreak of this year. Chances for a repeat don’t look too high to me – storms along the front are not nearly as strong or widespread as the previous case.

Here’s what I expect to happen: A line of strong-to-severe thunderstorms to our west will move rapidly (30-40 mph) east this evening and be located from about western Ky to Evansville to Indy by 9 P.M.  This line of thunderstorms will cross the Louisville area from about 10 P.M. until 1 A.M.  After that, the frontal storms will race eastward across the rest of KY.

In terms of what is called “sensible” weather, the Louisville area can expect…

8 – 10 P.M. – Strong, gusty southerly winds will precede  the line of thunderstorms.  Winds should gust from 25-35 mph with some gusts reaching to around 40 mph.

10 P.M. – 1 A.M.  Line of strong storms sweeps rapidly through the area.  Winds should gust to 40-50 mph with a few higher gusts.  Gusts over 50 mph should occur mostly north of Louisville.  Brief periods of heavy rain are likely and some of the strongest storms may produce small hail.  Power outages and some tree/limb damage are likely.  However, such areas should be localized and not widespread.

AFTER 1 A.M. – Rain fades quickly but wind gusts remain in the 25 – 35 mph range for a couple of hours before fading  by morning.   One note of caution:  The area  roadways will probably be covered in leaves by morning.  Wet leaves on the roads can be almost as slippery as ice.  Be advised.

Hurricane Irma, part 6

3 P.M. Sunday, Sept 10, 2017

Irma Should hit land soon

“Ground truth” so far has been far below NHC predictions

Weakening Irma is now a low Cat 3 and could drop to a 2 in a few hours.  Cuba took out a lot of Irma’s punch yesterday and she did rebound a bit overnight.  Now, however, even with the eye still at sea, a large part of the eastern half of Irma is over Florida.  Plus, a pocket of drier air is invading the southwestern quadrant of the storm.  The result is a weakening Irma.  Her current path should put her over Marco Island within a hour.  Then move north to Naples, Sanibel Island and Cape Coral during the next 4-5 hours.  With the exception of some of the Keys, the above mentioned places will most likely see the worst that Irma has to offer.  While certainly significant, the current wind field contains only about 73% of the force compared to the wind field predicted yesterday.

So, Irma in her present condition poses much less of a threat than had been predicted for days.  A lot of the extreme conditions that had been hyped for days will not happen, but 110-120 mph winds can still cause a LOT of damage.

Note:  It still looks like the remnants of Irma will bring rain to Kentucky beginning Tuesday and ending Thursday.  So kudos to the GFS model which was the first model I know of that picked up on this idea. (2-3 days ahead of the other major models.)  A lot of forecasters deride the GFS and prefer to use the European Model.  But, in this case the GFS was the clear winner.

Hurricane Irma

Irma’s a Category 5

 

Irma is a long way from the U.S., but some islands like the U.S. and British Virgin Islands will get hit hard soon.  After that the various models seem to fall into two central ideas – both bring Irma WNW staying just north of Puerto Rico and Cuba (while wiping out the Turks and Caicos) until things change while she’s just south of Florida.  About half the models bring the storm north either over Florida or just off the east coast.  Then a move inland anywhere between Georgia and Myrtle Beach. (Hilton Head ?)
   Second set of models brings Irma along the west coast of Florida with landfall over the panhandle to as far west as Mobile.
   It’s anybody’s guess at this time – a few minor changes over the next few days could alter the forecast significantly.
As to intensity, Irma’s a Category 5 now.  The strongest hurricane ever observed purely over the Atlantic Ocean.  Stronger hurricanes have formed over the Atlantic Basin, but they were in either the Gulf of Mexico or the Caribbean Sea.
     While hurricane position forecasting has steadily improved, the same cannot be said for intensity forecasts.  They are notoriously poor!  Just yesterday the forecast for Irma was to remain a Cat 3 through tomorrow, then slowly weaken; today she’s a Cat 5. Today’s prediction is for Irma to slowly weaken over the next five days, but remain a major hurricane.
P.S. Just a final thought…The morning run of the U.S. workhorse forecast model, the GFS, brings Irma northward along the Florida Coast this weekend with landfall near the Georgia/South Carolina border.  The GFS then weakens the storm as it drifts northwest.  Finally, the GFS has Irma’s remnants fading away over Kentucky next Wed/Thu.  Just something to think about.
(I think you should NEVER believe  a weather forecast that far in advance – let’s see what happens.)

 

Hits and Misses

Thursday, August 3, 2017

Quote of the day.

Yesterday, as part of my waking-up ritual, I turned on NOAA Weather Radio to get my daily morning update.  Within seconds, I burst out laughing.  I thought I must have mis-understood what I heard.  But, a second time around I heard the same thing.  from the Hazardous Weather Outlook came this statement:  Some Thunderstorms may produce lightning.

Your tax dollars at work.

And, speaking of our tax dollars…is it just me, or do others believe that our “official” forecasts have been pretty bad this summer?  I know as well as anyone about the frustrations of forecasting convective systems.  But, we’ve been bombarded with forecasts of “rainageddon”, severe storms and chaos several times with nothing to show for it.  In fact, the biggest rain we’ve had recently (July 23) was barely given any attention.  That situation was fun to watch while it unfolded – the NWS changed/updated their forecast 4-5 times over about 8 hours AND the only one that was correct came out about 3 hours after the rain ended!    NOTE:  The NWS had another case of “the cat chasing its tail” a few days back when they issued a spurious heavy thunderstorm forecast about three hours after the threat had ended.

El Nino/La Nina outlook

Most of the first half of the year, NOAA’s long term climate forecast model, Cfsv2, was predicting a climb  back into mild El Nino conditions for late fall and winter.  Over the past couple of months, the model has done a flip.  Now, it’s forecasting a mild La Nina to develop.

The consequences/forecast for North America has also flipped -early forecasts indicated a below normal temperature for our winter.  Now, they are strongly indicating a very mild winter.

And, by the way… the current NWS forecast for tomorrow is just plain not going to happen.  No way.  We have about a 30% chance for showers around 8-10 A.M.  Nothing close to the “numerous showers and thunderstorms” in the forecast.