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.

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.

Sunday, Jan. 14, 2018  3:30 P.M.

Another Arctic blast coming…will it arrive with some snow?

Another bit of the so-called Polar Vortex is breaking away from the Arctic and will settle down over the western Great Lakes over the next 48 hours.  That keeps any heavy snow threat far to our north.  But, we’ll see two attempts at some light snow during the next 24 hours.

First, a weak warm front is moving east from Arkansas and Missouri and should pass overhead tonight.  It is currently creating some light snow west of the Mississippi.  However, as it comes east it’ll be hitting drier air.  Thus, the snow system will fade.  We may see some flurries or even a dusting of snow from the warm front, but nothing of any consequence is expected.

Second, a better chance for snow will come around midday tomorrow as the Arctic cold front comes quickly across our area .  There should be enough moisture to squeeze out some light snow and snow showers for a couple of hours.  With snow  showers in the mix a few isolated areas could get a quick inch (or so) of snow.  But most of us will probably get less than an inch of snow.  That’s not much, but even a small amount can create road problems.  Luckily there will be enough time to get roads back in shape by rush hour (for those who don’t get the holiday off).

Longer term…

Tomorrow’s shot of cold air will be the last for awhile.  Temperatures should warm significantly by late week with rain becoming our primary precipitation threat, probably Sunday,  In general it looks like the upper air pattern will shift to a  “western U.S. cold- eastern U.S. warm” pattern for at least two weeks.  Our January Thaw is on the way – right on schedule.

Thursday, Jan. 11, 2018  5 P.M.

Slide from rain to snow begins tomorrow morning

A couple of subtle changes in the forecast models point to some changes in how tomorrow’s winter storm will affect us.  First, the timing has accelerated so that the majority of the wintry mix will fall during the daylight hours.  That suggests lower snow/ice accumulations than previously expected.  Second, the storm development has been delayed.  Thus, the storm should not reach full classic cyclone status until tomorrow evening…after most of the snow has ended here.  This implies a shorter duration of the icy precipitation.

As usual the models show small differences between each other.  But, in general, they stand in pretty good agreement.  On the larger scale they have shifted the storm track just a little westward from yesterday.  You might think the general agreement among the models means that tomorrow’s weather is well defined.  Not so!  Freezing rain and sleet are extremely difficult to predict.  That’s because they are created only within VERY narrowly defined parameters.  Rain and snow can occur under a huge range of atmospheric conditions, but not sleet and freezing rain. In the lower 2000 to 3000 feet above the earth, one half of a degree(Celsius) of cooling can convert rain to freezing rain. Another half degree cooler and it can  change to sleet.  Another half degree and snow becomes dominant.  Computer forecast models are very good, but splitting hairs in near-surface temperatures is a little too much to ask.

So, it comes down to us humans to try figure it all out.  This human thinks it’ll work out something like this.  Rain showers this evening will become steady rain after midnight.  Temperatures fall into the 35-38 degree range by 7 A.M. Cold rain for the morning rush hour.  Sleet should begin  by late morning and change over to snow around 1-3 P.M.  Snow should taper off to flurries by 7-8 P.M.

That’s my timeline.  Here’re the results I expect:

Rush hour:  rain and cold                                                                                                                        Roads should get slushy/icy by Noon                                                                                         Afternoon rush hour:  Slick, icy roads, snow falling. Temperatures drop below freezing.       Night: Windy and cold with snow flurries.  Snow should end by midnight.                                  Total Snow/ice accumulation for Louisville area:  1″ – 3″  (Jefferson County and east closer to 1″-2″  while up to 3″ west of Louisville/southern IN)

Note:  I still expect a band of heavy snow from western KY northeast to Evansville, Indy and Ft. Wayne.  This swath of land should see a 4″ – 8″ layer of snow tomorrow.

Well, that’s what I think will happen tomorrow.  Now it’s time to settle back and wait to see what really happens!

Wed. Jan 10, 2018  5 P.M.

Heavy snow likely near Louisville

Today’s latest from the GFS products department…

Forecast for 12 hours ending at 7 A.M. Saturday.

Unfortunately for local snow fans, this is probably a little too optimistic for Louisville.

Yesterday there was a very wide range of computer solutions for the storm late this week.  Confidence is higher now as two changes have occurred in the past 24 hours.  First, the various models have converged in their solutions.  Second, the very unusual (and snowy) solution by the operational GFS has faded into a much more realistic-looking forecast today.

In general, my current expectation goes like this:  strengthening low pressure will develop over the northwest Gulf of Mexico and move northeastward tomorrow.  It will accelerate quickly along the spine of the Appalachians tomorrow night.  That storm track will be very important.  A little farther west than expected and we’ll see almost all rain with just a little snow at the end.  If the track moves a little east of current thought, we could be in for a heavy snow (5″-10″).

The highest probability, though, would be for the storm to follow the current projected path OR to the left (west) of the current prediction.  As usual, the NAM is a little more rambunctious with this system.  It almost always is more energetic than the GFS 48 hours in advance, but the GFS is almost always better in the end.

So, here’s what I expect – rain showers become likely by afternoon tomorrow. Rain continues tomorrow night and Friday morning.  Temperatures turn colder by Friday afternoon and the rain changes to snow by mid-to-late afternoon.  Temperatures will drop rapidly as the rain transitions to snow.  A “flash freeze” of roads will be possible.  Snow diminishes after midnight.  Total snow accumulation for the Louisville area:  1″ – 3″  Less snow will fall east of Louisville.  For instance, Lexington should see little more than flurries.

Note:  Very heavy snows are expected west and north of Louisville.  A swath of snow should fall over western TN, western KY, southwest and central IN.  Paducah, Evansville, and Indy could get as much as 6″-12″ Friday afternoon and night.