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.

Tuesday, Jan. 26, 2021  3:30 P.M.

The long term weather situation continues to strongly emphasize a mild weather pattern to continue over North America.  Had a little hope last week as the central Canadian upper low shifted eastward.  If the shift had held we’d be a a “cold” pattern for awhile.  But, the trough is re-intensifying over western Canada.  That signifies above normal temperatures along with wet conditions over the eastern U.S. for the next two weeks, at least.

Meanwhile, colder air is slowly shifting south over the central U.S. and we’ll see the results tomorrow.  A fairly strong upper air system is digging in over the midwest today and will move over the southern U.S. tomorrow.  Most of the system will be rain – from TN to the Gulf states.  However, the northern part of the precipitation will be snow.  Areas like MO, IL and western IN could see several inches of snow tomorrow because they will have more cold air and moisture.  As the system moves quickly eastward tomorrow, the primary energy will be streaking across the states to our south.

That leaves us in a situation with weakening upper energy and decreasing moisture.  Thus, nothing very exciting will be happening here.  But, with the way things have been this winter, even a small snow can be pretty exciting.

Tomorrow will be cloudy and cold – temperatures remaining in the mid (maybe upper) 30’s.  Light snow should move over the area from about 4 P.M. until 8-9 P.M.  As temperatures should remain above 32, roads should be wet for the rush hour although some bridges/overpasses could ice over.  So, no major road problems are expected.  Snow accumulation is likely on grassy areas.  Up to one inch of snow is likely there.

Thursday, January 14, 20216 P.M.

Lot’s of activity, but still lacking cold air

Temperatures have been mild this winter so far.  The short cold spell around Christmas is about the coldest we’ve been.  And, overall, the weather here has been rather quiet.  But, part of that equation is about to change.

Weather patterns are really expected to pick up over the next ten days as a major upper air trough over central is expected to expand and slowly move eastward.  That eastward shift opens up the opportunity to push some significant cold air south over the eastern U.S., but not until about 7-10 days from now.

Meanwhile, upper air patterns are going to start moving quickly across the country.  The first one will move over the northern Ohio Valley tonight and tomorrow.  Some scattered light showers will be likely this evening, but they will be of little consequence since the Gulf of Mexico is shut off from this system.  As colder air arrives tomorrow a few rain and/or snow showers will be possible.  Best chance for snow showers will be tomorrow night with accumulations up to one inch on grassy areas.  Temperatures should remain above freezing, so no major road problems are expected.   Some flurries could continue Saturday.

Sunday another disturbance will float over the area.  Once again Gulf moisture will be missing, so snow potential will be on the low side – probably up to a half-inch or so.

At least a couple more disturbances will hit the area next week, but there won’t be enough cold air to make snow…just cold rain.

It’s a long way off, but a storm expected next weekend should be quite strong and offer a rain-changing-to-snow situation.  It might be strong enough to push us into a “colder than normal” weather pattern.