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!

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.

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.

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.

Irma’s a Category 5

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.

Thursday, March 30, 2017

The atmosphere may, or may not, be primed for severe storms later this afternoon/evening.  The confusion was apparent yesterday as the GFS and NAM far apart in their solutions for today’s weather/thunderstorm possibilities – the GFS wasn’t too keen on severe thunderstorms while the NAM jumped on severe weather big time.  Today, the GFS and NAM are closer, but still at odds.  Meanwhile the short term models, while agreeing in general about how things will evolve, are also divergent about the expected strength of any thunderstorms.

Going with the suspicion that each model has something good to add to the discussion, here’s how I believe the weather will evolve this afternoon/evening:                                                                First, the amount of cloud cover that remains this afternoon is very important.  Remains from storms to our west overnight have been hanging around this morning.  We should get enough brakes in the clouds this afternoon to allow some sunshine to build up heat (and energy) for some storms.  More sunshine is likely over KY than IN.  Lack of sunshine will diminish the severe storm threat.  Satellite data shows the clouds thinning as of Noon.

Second,  we have strong upper air dynamics over the midwest working their way slowly eastward, but surface conditions are a mishmash ( a highly technical term) of ill-defined air masses, outflow boundaries, and, so-far, ill-fated attempts to form a surface low pressure center and a cold front.  It looks as though it’ll take 4-8 hours or longer for things to get more organized.  By that time, the main threat for severe weather will shift east of the I-65 corridor.

Third, with lack of coordination between the upper and lower levels, things are just going to happen in a seeming random fashion this afternoon.  Quick-moving thunderstorms should pop up in a “hit ‘n’ miss” fashion over western and central KY and (mostly)  IN.  Most of these will be strong with gusty winds and hail possible.  Some could even reach “severe” limits, though these are likely to be few and far between.  By 6-7 P.M. the majority of these pop-up storms should be east of the I-65 corridor.  By this time, any severe weather threat should be over for the Louisville area.  Primary threat for severe storms this afternoon will be over central and northern Indiana.

Four,  by 7-8 P.M. the surface part of this system will be better organized and is expected to create a large area of rain and thunderstorms (non-severe)  over western KY and IN.  This will bring us a very wet evening.  Even a little flash flooding is possible.  Rain should diminish shortly after Midnight.

Comment

I see from this morning’s CJ  that  Rick and Cal are the two highest paid college basketball coaches in the land.  But, the educational ratings of the schools they coach are low.  We should gain an important bit of knowledge from the first two sentences.

Monday, March 27, 2017  5:50 P.M.

Storms are fading fast as they advance quickly northeast.  Louisville metro will see weak thunderstorms between 6 and 7 P.M.  There is no threat for severe weather – just some brief gusty winds and heavy downpours.

I suspect the NWS will drop the Watch for our area soon.  However, even if they let the WATCH linger, the threat for severe storms is already over.