Cold air highlights the week ahead

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Monday, January 21, 2019

After Saturday’s Hall of Shame forecasting by the majority of local prognosticators, the cold air has settled in and calmed our weather for awhile.  Next system in line will be the remains of another large storm that blasted the Pacific northwest over weekend.  This system is diving into the southern  Rockies and then will slide eastward.  Unlike a couple of similar systems (the past two weekends), this one isn’t given much hope of regeneration.  The upper level parent trough is projected to remain, as we meteorologists say, positively tilted.  In this case, very strongly tilted.  That translates into normal people-talk as weak energy levels and very little development.

Tomorrow and Wednesday

The trough, however, will begin brisk southwesterly winds over the midwest and Ohio Valley tomorrow and transport moisture our way quickly.  Increasing clouds tomorrow with much warmer temperatures (into the 40’s).  Rain will return around midnight tomorrow night and continue into midday Wednesday.  Similar to Saturday night, the cold air behind this new system will be late to join the action.  In fact, the true blast of cold air won’t arrive until Thursday.  So there could be some snowflakes Wednesday afternoon, but no accumulation is expected.

Note:  The NWS is forecasting 1″-2″ of rain for us from this system.  That seems pretty high considering the upper support.  Probably closer to one inch than two.                                                                                                                                                                                                                   Later this week

With wintry air again dominating our weather, little active weather is anticipated.  Computer models are hinting at a couple of very weak Alberta Clippers drifting into the area Thu-Sat with periods of cloudiness, but not much chance for any significant snow.

Note:  The GFS is developing a strong Clipper into the western Great Lakes by early next week. Although not posing much of a rain and/or snow threat for us, the clipper is gathering a very potent cold air mass in its wake.  It might be the coldest air mass we’ll see this winter and probably bring along some light snow along with it.  Of course, that’s a week away – a lot of model changes can happen in that time.

Stuff

I see the Courier Journal has gotten even smaller.  The USA Today section has gone off the digital world.  So, there’ll be less paper in the “paper.”  At least the dimensions of the physical paper haven’t shrunk, as they have in recent years.

 

 

It’s all about the physics!

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Saturday, Jan. 19, 2019

Model snow solutions are far apart.

Weather forecast models…you rely on then, you love them and sometimes you hate them.  Today, I’m very confused by them.

A little background:  Models are an attempt to explain/predict the future weather conditions.  The atmosphere is extremely complicated and certainly not fully understood.  Nevertheless, we’ve taken various laws of physics and developed equations to explain the atmosphere’s behavior as best we can.  Then, we have problems with data collection (it’s far from perfect) and fitting the data to a three-dimensional grid.  So then we put the imperfect data into the imperfect physical model, adjust it to the forecast grid, and let the computer do its magic.  In spite of the weaknesses of the “initialization” the results are extremely good – most of the time.

We have have a lot of different models and model schemes.  They all have the same goal – a correct portrayal of the upcoming weather.  The two big workhorses of the National Weather Service (for forecasts of a few days) are the GFS (a global model) and the NAM (North American regional).  We have two very short term models that model 18-21 hours ahead.  These are the RAP and HRRR.  The GFS and NAM run every six hours while the higher resolution models run every hour

Different Physics Packages!

Each model has a different physics package at its core.  Sometimes the results match almost perfectly.  Other times, they don’t.  It’s up to the human forecasters to try to figure out what the best solution is.  Model differences are wide apart today.

Let’s get down to the nitty-gritty.  What we’re most interested in today is snow!  When and how much.  Last evening’s (7 P.M.) computer runs showed a wide divergence from earlier model runs.  All models increased their snow forecasts for tonight – some by several inches. (This much change is quite unusual so close to the weather system’s arrival.)  Since then, they’ve divided into two camps – the GFS/RAP are at the lower end of the spectrum with 1″ – 3″ inch forecasts while the NAM and HRRR are forecasting 4″-8″ overnight.  Quite a difference!

Since last night the GFS and (today) the RAP have been trending down while the NAM and HRRR have been trending upward.  Go figure!

So, what’s going to happen?

Good question.  I don’t know for sure, but I think I’ve got a pretty good idea.  Yesterday’s blog pointed out some problems I had with the NWS forecast.  The rain looks like it’ll end at the lower end of expectations.  The cold air system and the rain system have still not gotten together and it looks like the phasing of the two systems won’t happen until after midnght.  And, the falling temperatures this evening will take several hours – so no concern about the much-feared “flash freeze.”  Temperatures will fall.  Snow will fall.  Roads will become slick.  Just like always.

So, the GFS inspired forecast from yesterday has worked very well.  There are just more things I like about today’s GFS than the other models, so I’m sticking with it.  The GFS has upped its snow forecast from yesterday and seems quite reasonable to me. So…

Snow forecast:

1″ -2″ metro Louisville.  Up to 3″ north of the Ohio River.

Rain should change to snow around 9-10 P.M. and it will be quick – most of the snow should be over by 1-2 A.M.

Note:  This is my “best guess.”  The National Weather Service is at 3″ – 5″ and some of the model forecasts discussed above go even higher. This could turn out to be a snow-lovers dream.  I’m just not buying it, yet.

Think snow!

Wet and icy Saturday ahead.

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Colder weather by Saturday night

Models haven’t changed much since yesterday.  GFS is really playing down the snow for tomorrow while the NAM is still hinting at about 2″ along and north of the Ohio River.  The NAM was better last weekend, but that was unusual.  Both models have continued to lower their rain predictions with which I agree.  So, here’s my latest thinking…

Saturday

Rain moves in before daybreak and continues through about midday.  During the afternoon rain will diminish to light rain/drizzle.  Rain may even quit for a few hours.  Temperatures will likely reach the mid 40’s.  Rainfall totals should be in the .50″ to 1.25″ range – most of Louisville area will be an inch or less with the heavier totals south and east of us.

Saturday night

Around 6-7 P.M.  the cold air will make its entry.  Temperatures will drop quickly and drop below freezing by 9-10 P.M.  – on their way to near 20 by morning.  Winds will be very strong overnight with gusts over 30 mph.

The cold air will bring some moisture with it.  A quick rain to snow changeover will happen during the early evening.  Any snow should move out of the area before midnight.  There won’t be much snow – probably an inch or less.  But, over the years we’ve certainly learned that even a small amount of snow can create big road problems. Some icy spots are likely on area roads tomorrow night.

Sunday plus

Winds gradually diminish during the day, but it’ll still be a cloudy, cold day with temperatures remaining in the lower 20’s during the day.  Monday morning lows in the city will be in the low to mid teens, slightly colder in rural areas.

 

Another weekend…another storm

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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.

Snow is approaching!

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Friday, Jan.11, 2019

Snow overnight…sloppy tomorrow

Today the various models are in close agreement with only some minor differences.  The biggest difference is with snow totals where the GFS is slightly higher than the rest.  Without getting into the various interplays/interpretations that COULD happen, I’m just going to lay out what I THINK will happen.

Tonight

Snow should arrive in Louisville shortly before Midnight.  Most of our accumulation will occur between 1 A.M. and 5 A.M.  After that snow will be lighter and gradually end around sunrise.  By 8 A.M. most of the Louisville area will have a snow cover between 1″ and 2″.  North of the Ohio River, some areas (especially west of I-65) may have up to 3″.  Untreated roads will be snow-covered for a few hours.  Treated roads will be slushy and wet.

Tomorrow

There’s a chance for a rain/snow mix for a couple of hours late in the morning.  Snow cover should actually be decreasing by that time.  The afternoon  should be generally dry.  During that time roads will clean up and overnight snowfall will continue to melt.

Saturday night

Rain moves in during the evening and continues lightly until late night.

Sunday

During the morning light rain/drizzle will change back to light snow/flurries  Any precipitation will fade away by early afternoon.  No more than a “dusting” is expected.

Monday morning

There’s a chance (30% )that we could see some light snow/flurries for the morning rush.  Little, if any, accumulation is expected, but some slick spots could develop.

That’s  my thinking, now let’s see how it works out.

Think snow!

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.