It’s complicated…

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5 P.M. Monday, Jan. 30, 2023

General situation shows a large cold air mass over the midwest slowly dropping southward. Temperatures today have been slowly falling and will continue tonight as temperatures drop into the upper 20’s by morning. Meanwhile, a small upper level disturbance in the jet stream flow will move rapidly ENE over the area tonight. It’s not much of a system, but it does have enough moisture to bring us some icy weather tonight.

That’s where the forecast trouble starts. The lower atmosphere (up to 5,000 feet) is definitely cold enough to support an inch or two of snow overnight along the Ohio River. But, it’s not that simple.

There’s a pocket of slightly above freezing air roughly between 5,000 and 10,000 feet above us. That will be slowly cooling overnight but should still stay slightly above 32 degrees. That’s the fly in the ointment.

The primary consequence will be that some of the snow falling through this warm layer will melt, then refreeze into sleet before hitting the ground. That sets up a very subtle balancing act between snow and sleet for our overnight entertainment.

In general, the whole atmospheric column will be slowly cooling, so snow becomes the most likely result as time goes on. The onset is trickier. Everything depends upon just how thick that warmer air is and how much cooling it will get from evaporation of precipitation aloft.

The models are consistant on two things. First, the amount of moisture falling will be small. Probably between .1″ and .2″ of water. That would be a 1″-2″ snowfall but only about a quarter-inch of sleet. Second, the location of the maximum precipitation will be about roughly 30 miles north and south of the Ohio River.

After putting all those variables into a big pot and letting them simmer, here’s what I think will happen tonight. Precipitation should begin around 8 P.M. in Louisville. At first, it’ll be mostly sleet with a little snow mixed in. As the night goes on, the mix will gradually change to mostly snow with a little sleet mixed in. Any significant snow/sleet will end by 3-4 A.M. The Louisville area should end up with a snow/sleet total of up to one inch.

North of Louisville snow totals could get up to 1″-2″. South of Louisville will see a snow/sleet accumulation up to one-half inch.

By morning rush hour, treated roads should be in fairly good shape with icy spots. Meanwhile, non-treated roads should be mostly snow/ice covered.

Snow tonight

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Mon. Jan.30, 2023 12:30 P.M.

Forecast models are all over the place with tonight’s forecast. However. it now appears that we’ll see an accumulation of snow tonight. At this point it looks like an accumulation of about 1″ – 2″ around the Louisville metro area with slightly higher totals over southern Indiana.

If that pans out, school kids could see a free day tomorrow. However, as pointed out above, forecast models are unusually scattered for an event so near in time.

More later…there’s a lot to digest.

Snowball fight

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Today’s models can’t seem to agree on snow tonight, but rain is a sure bet.

First, a note on Sunday’s snowfall. Sunday’s weather events gave yet another reason why weather is so fascinating. Both the event itself and the (lack of) forecasting it. Rain was the models’ choice while also giving hints that there could be some snow at the start. But nothing like the 1″+ we had around the county. And that’s about the only place snow fell.

As the rain moved in, a sudden intensification of the precipation brought colder temperatures AND snow into Jefferson County and almost nowhere else.

Weather can be so much fun!

Tonight

Meanwhile, tonight’s system will be much stronger and almost all signs point to rain. This morning, the GFS was the only model predicting snow at the start with a quick change to rain. Now, other models are drawing closer to the snow start followed by rain. Temperatures with this system are about 3-5 degrees warmer than Sunday’s, so if any snow falls, it’ll melt quickly.

Snow and/or rain should begin around Midnight or shortly after. By 2-3A.M. any chance for snow will be gone. After that, periods of rain will continue during the morning then fade away by late afternoon. Winds will pick up during the afternoon with gusts probably topping 35 mph.

Snow flurries will be likely tomorrow night and Thursday.

Stuff:

The northernmost point of Brazil is closer to Canada than it is to the southernmost point of Brazil.

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11 P.M. UPDATE

Now looks like an hour or two of snow/sleet will be mixed in with the onset of rain around daybreak. Any minor accumulations on grassy areas will fade away during the morning.

Rainy Sunday

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Saturday, Jan.21, 2023 6 P.M.

I’ve been watching the models’ handling of the next two storms headed our way. Both have been indicating a cold rain for tomorrow and for Tuesday night/Wednesday. The second on will be much stronger (for us).

Yesterday, words like snow, sleet and freezing rain started entering the forecast. A deeper dive into the weather data made me believe those words shouldn’t be there. The atmospheric setup just isn’t cold enough.

A storm developing over Texas tonight will advance ENE over the Gulf Coastal states tonight and tomorrow before turning up the Atlantic Coast tomorrow night. With the storm staying so far to our south, we’ll be on the northern fringes, so rain totals will be on the light side.

Models agree that the rain/snow line will be at least 30 miles north of the Ohio River. So, don’t be surprised if we see a little wet snow mix in from time to time. Basically, though, we’re expecting just a cold, rainy morning. Then rain will slide eastward by early afternoon.

Models also point to another (mostly) rain event by midweek, so snow lovers are probably in for another disappointment with that system.

Meanwhile, global models are pointing toward below normal temperatures here for the next week or two. So, we’ll see additional snow chances ahead.

Snowy, blustery night ahead

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Thursday, Dec. 22, 2022  5 P.M.

The action begins this evening

If you’ve followed this blog recently,  you’ve heard about how very slow changes in the atmosphere can add up over time.  Also, we’re seeing today how these little changes can take you away from the original “solution” only to move back to the original forecast before the storm arrives.  Such as the evolution of the snow amount forecast from last week until today.

Last week, the early indications were for about 2″ to 4″ from the system arriving now.  By early this week the forecast for snow was down to about an inch or two.  Then, this morning, the forecasts started climbing. Now we’re up to about 2″-3″ for Louisville while 3″-6″ appear likely over southern Indiana.

Yesterday,  I mentioned that the changeover from rain to snow would be about an hour or two later than the previous estimate.  Too bad I didn’t think too much about that, because it seems to be the reason for the increased snowfall forecasts.  This is a developing storm.  It just recently got it’s act together and will intensify rapidly overnight. The extra time before the onset of the snow allows the storm to gather more moisture.  Little changes can make big differences.

Forecast summary

Rain this evening will change to snow around 8-9 P.M.  Winds  will increase to 20-30 mph with higher gusts overnight.  Temperatures will drop from the upper 40’s now to near zero by morning.  Louisville’s snow total from 2″ to 3″.  Areas north of the Ohio River could reach 6″ of snow.  Hazardous road conditions due to ice, snow and blowing snow.

Tomorrow will remain very cold as temperatures remain in the single digits in addition to strong winds continuing.  A mix of clouds and sunshine with flurries possible.

Christmas Eve and Christmas will remain quite cold.   High Saturday about 15 and 20 on Sunday.  Skies should be sunny to partly cloudy.

Merry Christmas!

Enjoy Saturnalia

 

Cold air, snow arrive tomorrow night

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Wed., Dec.21, 2022

Little change from yesterday.  Based on the latest model runs, only a few minor tweaks are needed.

Some light showers will develop tomorrow morning.  Southerly winds will warm us to the upper 40’s by mid afternoon.  More rain should arrive by late afternoon.  It appears the rain to snow changeover will be an hour or two later (8 to 9 P.M.).  Then temperatures drop about 20 degrees in two hours as stronger winds bring in the colder air.  Any appreciable snow should be over by Midnight to 1 A.M.

Snow accumulation stills looks to me to be 1″ to 2″.  But the models are trending lower.

Biggest concern is still the cold/wind.  Temperatures should drop to the low single digits by Friday morning then stay in the single digits all day.  Saturday should reach the mid teens and Christmas  will get all the way up to near 20.

Very Cold Air Still On The Way

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Tuesday, Dec. 20, 2022

Little change in the forecast since yesterday’s post.  The Super Christmas Storm of ’22 is still expected, but primary effects will cover the north central states from Colorado to northern Missouri to near Chicago.  The cold air behind the storm center will produce heavy lake effect snows across the Great Lakes Friday and Christmas Eve.

That part of the storm will make a lot of news through the weekend.  But, the main action will stay hundreds of miles away from us.  Nevertheless, we will not be spared from the storm entirely.  Rain will develop Thursday with temperatures in the 40’s.  The cold air sweeps rapidly into the area during the evening  (7 to 10 P.M. ?) as the rain changes to snow  for an hour or two.  An inch or two of snow is expected.

After Midnight, strong winds will be howling through the area over night…slowly diminishing Friday.  In addition, snow showers/flurries during the day could add an additional inch to our snow total.  The temperstures will slowly moderate through the weekend.  Friday’s high should be in the high single numbers rising to the mid teens Saturday and around 20 on Christmas.

Very Cold for Christmas Weekend

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Snow should be on the light side

Dec.19, 2022  4:30 P.M.

When I started forecasting weather for the Louisville area in 1969, I had one major point of emphasis about weather forecasting:  Don’t ever believe a weather forecast for more than 3 days ahead.  Weather forecasting has improved significantly since then, so,maybe, that could be extended by a day or two.  But the point is, we do not have perfect forecast models.  Nor can we measure weather parameters – humidity, temperature, winds, etc – precisely.  And, to make matters worse, when we measure our weather data, it’s at random spots on the Earth.  Forecast models are set to run on a precise computer grid.  The data is seldom measured at the grid points, so sophisticated smoothing systems have  been created to fit the data to the grid.

Thus, before forecast models even begin computing, we have three significant areas of known error sources within the system.  I am amazed at how well the longer range forecast models perform…most of the time.  But as good as the modern models are, they are not perfect!

So why do professional forecasters continue to believe them?   Why so much hype 7 to 10 days before an event is due to happen?

I can’t answer those questions, even after 50 years of trying.

This week

We are currently in one of those major “hype” situations.  The major outbreak of arctic air set to arrive Thursday night has been predicted to arrive “in 7-10 days” since before Thanksgiving.  So after many misfires it’s actually going to happen.  Since last week, the models have been predicting some pretty dire weather for much of the nation east of the Rockies.  The local outlook was for 4″-6″ of snow, very strong winds and a possible flash freeze in addition to frigid temperatures.  Keep in mind, this forecast was for at least 7 days ahead,

No matter!  The hype machine jumped into full gear.  By the weekend all the talk centered around a massive pre-Christmas storm of legendary proportions right here in Louisville.  But, as should be expected, the forecast models slowly made “adjustments” to the forecast.  Those incremental changes have greatly altered the forecast and possible consequences for us.  Even the most extravagent hypists should have it figured out by now.

This being Monday and the actual event is likely Thursday night, I expect more changes to occur during the days ahead.  Nevertheless, here’s what I’m currently expecting later this week:

Slowing warming temperatures tomorrow through Thursday midday.  Rain should move in Thursday afternoon and change over to snow Thursday evening.  Snow will last 2-3 hours with accumulations around 1″ – 2″.  Very windy, with temperatures dropping into the single digits by Friday morning.  Friday remains cloudy, windy and cold with snow showers and flurries.  Additional accumulation up to an inch.  Temperatures will reach only the lower teens.

Note: the possibility of a Flash freeze Thursday is much lower now than earlier thought.

Severe storm chance very low this evening

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Possible severe storms stay north of Louisville

Wed. June 8, 2022 5 P.M.

Storm Prediction Center did a good job of narrowing in on the severe storm threat area over southcentral and southeast Indiana.  However, they pushed their Tornado Watch box too far south.  Or did they?  More on that later,

Back to the current weather, the primary factors for severe storms have already moved east of I-65, so damaging weather threat is generally over for the Louisville area.  However, a weak wind shift line/cold front is trying to form over southern Indiana.  That will give us about a 30% chance for a thunderstorm around 7-8 P.M. tonight.  Then a little cooler, but much drier day tomorrow.

Tornado Watch?

As mentioned above the Storm Prediction Center pinpointed the severe threat today very well.  In fact the boundaries for the Watch they issued did not include extreme southern Indiana or  metro Louisville.  Their southern boundary was about 40 miles NORTH of the Ohio River near Louisville, where it should have been.

So what happened?  In recent years local Weather Service offices have been given the leeway to “alter” the SPC Watches.  So today they decided to change the prediction to include the Louisville area.  Seems to me we saw another case of CYA this afternoon.

To the uninitiated, CYA is a long-running acronym for “Cover Your A–”

Good job SPC!  Not so good, locals.