Category Archives: forecast

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

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

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!

Storms possible again tonight.

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

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.

Hot Holiday Weekend

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

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.

Another close call

Sunday, March 11, 2018  4 P.M.

Majority of snow stays south of Louisville

As expected (at least by readers here), Friday’s weak Alberta Clipper failed to generate much snow around the metro area.  Today a strong Clipper is approaching our region and will pass through tonight.  This time, however, the storm has its eyes focused on central and southern Kentucky.  You guessed it…little, if any snow for the Louisville area.  Another missed opportunity in a winter highlighted by misses.

Once again, temperatures will play a big role in tonight’s weather.  Surface temperatures locally will stay above freezing during the precipitation event, so no problems are expected with area roads.  They will stay wet, even if we do get a small amount of snow.  In fact, most major roads will be dry before the morning rush hour.

But, let’s talk about central/southern KY

Starting about 20-30 miles south of I-64 on down to the Tennessee border, SNOW will be the primary factor.  Sloppy, wet snow (probably beginning as rain) appears likely for about 4-6 hours tonight.  Time frame should be roughly Midnight until 6 AM EDT.  Most of the southern two-thirds of KY should receive from 2″ to 4″ of snow – mostly on the grassy areas.  Some spots could get as much as 4-7″ of snow.  That would be enough for the heavy wet snow to break some tree limbs and/or power lines.

Louisville area summary

Light rain will move in during the evening.  Rain will mix with, or change to, snow around Midnight.  Precipitation should diminish by about 3-4 AM.  Snow accumulations, if any, should be less than one-half inch – on grassy areas only.  No traffic problems are anticipated.

Sloppy night ahead

Friday, March 9, 2012 6 P.M.

Rain and (mostly) white rain overnight

A weak Alberta Clipper system will work its way through the lower Ohio Valley tonight. First, we’ll see rain developing this evening.  Then, as a little colder air arrives, the rain will mix with snow.  We’ll also probably see all  snow for an hour or so.  The lower atmospheric temperatures will be the key as is often the case.

The models can’t agree on much.  But, two items are shared by all of them.  First, temperatures near the surface will stay several degrees or more above freezing during the precipitation event.  Second, the highest likelihood for accumulating snow will stay mostly north of I-65 AND, especially, east of Louisville.  Primary time for snow in the metro area will be from 1 A.M to 4 A.M.

Moisture is rapidly feeding into the system, but the majority of the moisture won’t arrive in time for significant snow west of I-65.  Areas from eastern Oldham and Shelby Cos to Georgetown may see 1-2″ of snow on grassy areas with isolated 3″-4″ amounts, but very little on roadways.  In Indiana, eastern Clark and Jefferson Counties may see 1″-3″.

Back home in the Louisville with temperatures up and smaller precipitation amounts expected, we should experience only a few, brief problems on the roads.  Otherwise, snowfall accumulations will be small – less than an inch on grassy areas.  Any minor accumulations on road surfaces will disappear by morning.

Oh yes…”White rain”

White rain is my definition for snow that essentially has the same effect as regular rain.

Narrow line of heavy snow approaching

Monday, Jan. 15, 2018 5 P.M.

After weakening all afternoon, the area of snow around us has developed a narrow line of moderate to heavy snow.  The line should pass through Jefferson County between 6 P.M. and 7 P.M. this evening.  This will cause roads to become snow-covered and icy, especially untreated roads.  This could give the county a quick 1/2″ to 1 1/2″ of new snow.  Flurries after that.

Snow system still fading

Monday, Jan. 15, 2018  2:30 P.M.

Model and radar trends are still weakening.  Light snow will continue until roughly 7 P.M. but roads will stay wet this afternoon.  Untreated roads will start getting icy after 4-5 P.M.  We will see just a small additional accumulation on grassy areas (less than one inch).  As snow moves southeast this evening continued light accumulations will occur, but still less than an inch.

Meanwhile, southern Indiana has seen light snow most of the afternoon with little accumulation.  The snow will fade by 5-6 P.M. with around 1″-2″ accumulation over the region north and west of the Ohio River.

But, everything will freeze hard again tonight as most of the area will see single-digit temperatures by morning.