6 P.M. Sat., Feb 13, 2021

Models in closer agreement

Another day without sunshine and we probably won’t have much, if any, tomorrow.  Temperatures will probably remain in the 20’s all day.  But after that, snow enters the picture.  A  strong upper air system over the southwest today will cross the Rockies tonight and become better organized south of the Texas coast by late tomorrow.  Then it heads northeastward.  What the final path will be is still uncertain, but we should have a better idea tomorrow.

Currently, the GFS predicts a 4″-6″ snowfall for our area – higher over eastern KY.  The NAM has a 6″-8″ prediction.  Snowfall should begin before the Monday morning rush hour and continue through the day.  There is disagreement about when the snowfall ends.  Estimates run from Monday evening to Tuesday morning.  The longer duration of snowfall most likely would produce an even higher snow total.

The second storm expected next week has undergone more model changes.  Best guess now favors a freezing rain to rain scenario on Thursday.

Some doubt

Although at least some snowfall is likely Monday, the amounts are uncertain.  While most of the U.S. models are big on snow, the Euro, Canadian and Navy models carry everything farther east.  As a result, our snowfall totals would be much lower.

For now, I’ll go with a forecast somewhere between the two major themes  Let’s say something like 2″ – 4″ for the Louisville area.  Either way, higher snow totals east of Louisville, especially east of I-75.

I’m hopeful I’ll have a better handle on this tomorrow.

Tue., Feb 9, 2021  6 P.M.

Storm potential downgraded

Models are still having a debate at how the upcoming wintry weather system will play out.  In the short term a solution seems to be stepping forward.  But the GFS is still out on its own for the weekend.

Meanwhile, the models seem to be converging on an idea that the ice storm expected tomorrow will have its major impact over the southern two-thirds of KY.  Louisville area will have just a small amount during the day, but could see an increase in intensity tomorrow night.  I was happy to see the Weather Service downgrade Louisville’s threat assessment.  Outside of ever-slippery bridges/overpasses, tomorrow shouldn’t be too bad.  Even fewer problems over southern IN.

As colder air continues to slide southward, warmer air aloft will melt any snow trying to fall, so most of us will see freezing rain (some sleet also possible) probably beginning by mid morning.  Daytime heating should keep most of the roads wet with icy spots on the aforementioned bridges and elevated spots.  Wires, tree limbs, railings, sidewalks will probably get icy.  Luckily ice accumulations will be less than .1″

Freezing rain should pause during the afternoon, but resume again tomorrow night.  Once again, accumulations of ice should be small locally.  Also, the freezing rain should change to snow early Thursday.  Snow could accumulate an inch or two.

Although icing conditions are expected to be minor locally, this will be a MAJOR ice storm for the southern two-thirds of Kentucky.  Damaging ice conditions could accumulate to as much as .25″ to .50″.  That would be very damaging.

Mon., Feb. 8, 5:30 P.M.

Snow, sleet, freezing rain, and rain all likely this week

1).  The GFS model predicts we’ll have over 12″ of snow on the ground by Sunday afternoon.

2).  No other model has a prediction scenario anywhere near the GFS  ideas.

3).  We’ll see several chances for a variety of precipitation types this week…tonight, Wednesday into Thursday and Sat/Sun.

We’ll take a look at tonight and save the rest for later.  A weak upper air disturbance will pass over the region tonight and the Ohio River seems to be about the dividing line between rain/snow.  The Louisville area will be on the southern edge of the system.  We’ll most likely see some light rain/snow mix beginning late this evening.  The system will be bringing colder air, so a change from rain to snow should occur later tonight.  By morning, another light accumulation is likely.  Less than one inch here with even less snow south of town.

Meanwhile, over Indiana it’ll be mostly snow and more of it.  As you travel north of I-64 in IN and about 10-20 miles north of Louisville and north of eastern Oldham Co., Trimble and Carroll Cos., you’ll see rapidly increasing amounts of snow. Most of southern Indiana can expect 1″ to 3″ of snow by morning.  That 1″-3″ total also holds for northeastern KY.

Currently, Wednesday’s storm looks like it’ll be mostly ice.  More tomorrow.

Friday, Feb. 5, 2021  4:30 P.M.

Models keep delaying arrival date

Early this week the forecast high for Super Bowl Sunday (Feb. 7) for Louisville was 20 degrees.  Now the forecast is 32 deg. Yes, that’s cold.  But around here a high of 20 is quite a different situation.  So, what’s going on?

What’s going on is a common habit of the GFS model.  It (often) foresees a major pattern change or shift, but predicts it to happen too soon.  Such is the case this time.  Originally, the GFS brought the bitter cold air into the Ohio Valley tomorrow.  By midweek, the big arrival was pushed back until next Wed/Thu with only a small chunk of the colder air arriving Sunday.

Current thought is that another small surge of wintry air arrives about Tue/Wed.  Finally, the much anticipated “coldest air of the winter” makes it’s appearance Fri/Sat.

With the “Big Chill” still a week or so away,  the smaller air masses will still keep us in below normal temperatures next week.  Daytime highs will run from the upper 20’s to the 30’s.  Several weak upper air systems will probably bring some more small snows during that time.  The first chance will be tomorrow night into early Sunday.  Then, very light snow/flurries should be an almost daily occurrence next week.  Best chance for meaningful snowfall will be with the really cold air arrival late next week.

Sun. Jan. 31, 2021  6 P.M.

A weakening storm system which created large snowfalls over northern IL and IN yesterday gave us the overnight rain.  Today a very weak surface low (the remains of yesterday’s stronger storm) has been very slowly moving east over southern IN.  The  passage of the low has changed our winds to a westerly flow and brought in colder air.  As we’ve seen today, not much happens in the center of a low pressure system – especially a weakening one.

As the upper air system moves eastward to merge with the developing “Noreaster” along the east coast, we should see the added influx of energy allow the noreaster to become a major winter storm from the mid-Atlantic states to New England.  Very slow movement will keep this storm active over New England into Tuesday.

Meanwhile, as the upper air system moves east the so-called backlash part of the storm moves over us.  Basically, some of the moisture (from southerly winds) ahead of a storm becomes trapped in the lower atmosphere.  The counterclockwise flow around the storm takes this moisture northward, then pushes it westward, and finally southward again.  This wrap around effect takes the small supply of moisture into the colder air following the storm.  The cold air then squeezes the moisture out of the air.  Whether it’s rain or snow depends on temperatures.

Around a developed low pressure area the northwest quadrant pretty much promises two things.  1).  there will be precipitation, and 2). the amount of precipitation will be light.  Precipitation totals usually run about .02″-.03″ inches per six hours.

All that background to lead to tonight’s forecast…

Periods of light drizzle/rain this evening will change to light snow before midnight and continue overnight.  Temperatures will be slowly dropping to about 32 for the morning rush hour.  By that time, grassy areas will have less than an inch of snow.  Roadways will have little or no accumulation, so roads should be in good shape, mostly.  Possible exceptions, as always, will be bridges and overpasses.  If any icy conditions develop those areas are the most likely spots.

Additional light snow/flurries are possible tomorrow into tomorrow night.

COLD February!?

The U.S. has a forecast model, the coupled forecast system, version 2 (CFSv2) that is designed to detect weather/climate trends out to about six months ahead. For the past few months it has continuously predicted the whole country to have above  to much above normal temperatures for February.  As recently as last Tuesday, the warm February forecast covered most of the U.S.

Then, something strange happened.  Wednesday, the forecast changed to “near normal”.  Thursday, the forecast changed again.  Below normal temperatures covered about 2/3 of the country.  Just the southwest part of the U.S. stayed at near-to-above normal.

Today’s forecast continues the cold projection.  This model normally changes very little on even a weekly basis.  Even when it does, changes are slow.  But, a total forecast reversal in two days just doesn’t happen.  Until it does!

There has been some sudden fundamental change in the atmosphere that the CFSv2 has picked up on.  Could be a cold and stormy month lie ahead.  That would be fun for a change!

Tue., jan. 26, 2021

Afternoon model runs have been upping the snow forecast for late tomorrow.  Latest idea is for the snow total to be in the 1″ – 2″ range.