Author Archives: wx

Weekend Weather Prospects

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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!

We’re starting to feel the results of the SSW!

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Winter is mounting an offensive.

If you haven’t read last week’s post concerning the Sudden Stratospheric Warming, reading it now would be a good background for what comes next.

The shift toward a major cold trend for the eastern U.S. is now underway.  Today’s cold snap is the beginning and we’re likely to see several more cold surges over the next 7-10 days.  Then, it gets REALLY cold for the latter third of the month.  The primary focus of the cold trend looks like it’ll be over areas of eastern Canada, the Great Lakes and the Middle Atlantic/New England states.  But, there should be a sizable amount left for us, too.

What about snow?

Our first shot at snow will come this weekend.  A weak disturbance moving out of the southwest will stay south of us Fri/Sat.  That will hold the current cold air in place so that any precipitation is likely to be snow.  That should begin late Friday/early Saturday and continue on into Sunday morning.  Not much moisture should get this far north, snow potential is not very high.  BUT, even though all the major thickness indicators favor snow for this system, I still suspect a big problem- surface temperatures!  It looks to me as though surface temperatures will remain near (or above) 32 degrees throughout the precipitation event. I’d say small accumulations early Saturday will melt away during the day.  Then another minor accumulation Saturday night will melt away Sunday.  I don’t expect any road problems.

NOTE:  This is still a weak, developing system, so a lot of changes could happen over the next two days.  Updates will follow.

Climate update:

Even though the U.S. dropped out of the Paris Climate Agreement, we’re done a better job at carbon reduction than almost all the nations that did sign the agreement!.  U.S. carbon emissions were up a little last year, but we are 11% below our 2005 totals.  2005 is the “base” year for the carbon reduction goals.  Europe is also down a little, but the rest of the world continues to rapidly increase carbon emissions.  China and India are BY FAR the greatest contributors  to the increase.

Sudden Stratospheric Warming

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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!

Energy-packed atmosphere, but…

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Friday, July 20, 2018 Noon

…we’ll probably get lucky.

Unusually strong summer system is dropping southeast from the western Great Lakes and should trigger numerous strong-to-severe thunderstorms this afternoon/evening.

Morning rains set up the higher moisture, now the upper dynamics have plenty to work with.  Lucky thing for us is that the next big surge of upper energy is approaching rapidly and probably won’t get enough heat energy to kick off storms until it is either right over us or to our east.

Storms should start organizing between 2-3 P.M. near I-65 and move rapidly southeast.  Some scattered severe activity is possible in the I-65 corridor, but these storms will get better organized and much more dangerous east of I-65.  Widespread severe weather is likely over the eastern half of KY this afternoon/evening.

Luckily, most (if not all) of the damaging weather will be east of the Louisville metro.

Watch the skies this afternoon.

Timing update

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Thursday, May 31, 2018  5:45 P.M.

Development to our west is still slow.  Primary development, as expected, will stay south (where the energy is) with heaviest storms over western TN.  A weaker bit of energy may still work its way up the Ohio River tonight, but that looks like it’ll be later than I originally thought…probably arriving around 11 P.M. to Midnight.  No problems with this system, if it arrives.

Comment:  This has been a really bad month for Louisville area forecasters.  It’s only fitting that the  current NWS forecast seems destined to join the faulty list.  My guess is they haven’t taken into account the changes caused by this afternoon’s storm system.

Storms possible again tonight.

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Thursday, May 31, 2018 5 P.M.

Severe wind gusts ripped across the area this afternoon as winds gusted as high as 59 mph at Standiford Field.  Many reports of 50+ mph came in from around the state.  That cluster of strong storms is continuing to create trouble over southeastern KY.

Meanwhile, to our west what was expected to be the “big event” tonight is having a tough time organizing.  No surprise there.  This afternoon’s big cluster of storms has used a huge amount of the potential energy expected to fuel tonight’s storms.  So, no “big event” is likely tonight.  A line/cluster of thunderstorms could develop into our area around 9 P.M. until Midnight. But they won’t be very strong, even if they do reach us.  No additional severe weather is expected tonight  It appears that tonight’s outbreak may stay south of KY.  Lots more energy available over TN.

Two rounds of heavy thunderstorms possible today

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Thursday, May 31, 2018  Noon

After a largve production of heavy/severe thunderstorms in the central plains overnight, two distinct developments today as that energy moves east.

1).  A pulse of upper energy is moving rapidly eastward and is creating a developing strong cluster of storms over southern Illinois. This system is expected to expand eastward across southern Indiana and extreme northern Kentucky over the next few hours.  Some severe thunderstorms are likely this afternoon.  Primary threat will be brief, strong gusty winds.  Smaller threat will be hail.  If everything develops as expected, the cluster of storms will move through the Louisville area from about 2 P.M. to 3:30 P.M.

2).  The “main event” from the midwestern system is expected to develop later this afternoon and reach our area tonight.  Best time for us looks like 8 P.M. until Midnight.  Again, strong, gusty winds will be primary threat.  This time, however, the storms are expected to be more widespread.

NOTE:  How this afternoon’s storms play out could have a significant say in how tonight’s system develops. I’ll have an update on that later.

Update to rain chances

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3:30 P.M. 5/26/2018

Rain/thundershowers over southern IN have remained weak and are not showing any indication of dropping into KY.  So, there will still be a slight  chance for a shower later today or tonight, but most, if not all, of  the Louisville area will stay dry through the weekend.  But, it’ll be hot!  Have fun!

Hot Holiday Weekend

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Sat. May 26, 2018  12:30 P.M.

Up to an hour of rain and possible thunder late this afternoon appears to be the only weather disruption we’ll see this long weekend.  Memorial Day weekend is often referred to as the “unofficial beginning of summer.”  This year, however, it’ll be more like the middle of summer, especially tomorrow and Monday.

This afternoon, I expect a narrow line of showers/thunder to form over southern Indiana by around 2 P.M.  They will drift slowly southeastward through the Louisville metro between about 4 P.M. and 5:30 P.M.  It should not be a solid line, so not everyone will see rain.  Even those who receive rain won’t get much, probably less than a quarter inch.

The rest of the weekend will be hot, humid and dry.  Only a scant chance for a thunderstorm tomorrow and Monday.  Highs both days will be near 90 degrees.  (heat index: low 90’s)

Beautiful evening

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Tuesday, March 20, 2018

On my previous post I gave two reasons why I wasn’t expecting to see much snow tonight.  The second reason has been my downfall to getting this forecast correct.  The weak secondary upper has formed, BUT it formed too far east to disrupt the flow of wrap around moisture westward into Ohio Valley.  The result?  More snow than I expected.

As of 8 P.M. we already have two inches on the ground.  The snow should become very light over the next hour or two, then continue overnight.  Louisville area should have 2″ – 4″ by morning.  Deeper snows north and northeast of the city.  Lower totals south of the metro area.