Wednesday afternoon. 1/20/2016

Pretty, light and fluffy snow overnight and this morning left a coating of 3″ on my driveway and 4″ at the airport.  Similar totals around most of the area.  We’ve been talking about the main event this week being Friday’s expected storm, but today’s snow has raised the bar a bit.

There have been some interesting changes in the models since yesterday’s runs.  The most prominent one is that both the GFS and the NAM have dropped the system farther south.  Yesterday, they had the axis of heaviest snowfall right over the Ohio Valley while today they have the Ohio River just inside the northern edge of the snowfall shield.  There’s likely to be a sharp drop off in snow along the northern extreme of the precipitation area, so that’s a very important development.  Another interesting result from the morning’s runs is that, even though they’ve made the southern shift, the models haven’t changed their snow forecasts for us – generally 6″ – 10″.

To me,  that’s a very surprising development, one that doesn’t make a lot of sense.  There’s another problem – the storm diving over the Rockies is expected to eventually “cut off” from the main band of westerlies and drift slowly eastward and then get re-absorbed into the upper flow and become a huge east coast storm for the middle Atlantic states.  The time while it drifts over the southern states will be when it will have it’s greatest effects on us.  That drift was expected to be very slow, putting us in its path for a longer time.  The GFS is still predicting that, but the morning NAM ejects the system much quicker eastward, thus diminishing the duration of snow.

There’s no question that this storm will be able to tap into a vast supply of Gulf Moisture.  But, it seems the biggest question for us is “How far north will the moisture come?”

So, it’s obvious the Friday’s weather is still “up in the air” so to speak.  Tonight’s and tomorrow’s model runs should go a long way toward resolving the situation.  Until then, here’s my current thinking…I believe the shift to a more southerly storm track will, in general, hold.  I believe that the  GFS and NAM will come to a compromise over the evolution of the cut off low’s ejection eastward.  If it works that way, the axis of heaviest snowfall will be over southern KY/northern TN and go ENE from there.  thus the heaviest snows should fall from Nashville and Bowling Green to southeastern KY, West Virginia, northern MD, southern PA and New Jersey.  The western half of that area could see snows in the range of 6″-12″ while the eastern half could reach 12″-20″ or more.  That puts us on the northern side of the heavy snow axis, an area which should see rapidly diminishing snow totals northward from Bowling Green.  For the Louisville area, my current outlook would be in the 3″-6″ range (higher south and east, lower north and west).

That’s it for now.  I’ll be back tomorrow…probably with a completely different story.

11 P. M. Tuesday, Jan. 19,20016

Brief snow update

Evening data coming in is showing slightly higher precipitation totals for overnight and tomorrow morning.  Also, a slight change in timing.

Forecast update:  snow – 3 A.M. – 10 A.M.

snow accumulation:  2″ – 4″  (Louisville area)  higher totals south and west of                                                                                     Louisville.

Tuesday afternoon, January 19, 2016

Little change in the outlook today.  Models have done a flip-flop with the NAM now a little stronger than the GFS.  But, the system drifting toward us remains a weak one, so the biggest question remains, “How weak?”

Did you notice this morning that even though we had a clear, calm night and temperatures were down to about 10 degrees, there was no frost on rooftops or lawns.  That’s a testament to how dry our air is now.  The approaching system is coming from the WNW, so it’s not going be able to pick up pick Gulf moisture.  Luckily, the system does have a good supply of mid-level moisture to produce snow.  Unluckily, a lot of that snow will evaporate before it reaches the ground.  As that snow evaporates, however, it moistens the lower level air.  Eventually, the snow works its way to the ground.  And, that’s the key to tonight’s snow…how much snow will be left to fall after it finally starts reaching the surface?

We’ll probably start falling aloft over Louisville before midnight, but it looks like we won’t start seeing it hit the ground until around 4 A.M.  Snow is likely to continue until about 10 A.M., so that gives us roughly six hours of snow to work with.  Unfortunately, the models show a gradual weakening of the system overnight, so the snow we are going to miss (Mid-4 A.M.) should be more than the snow we will get later (8-10 A.M.).

One more thing to consider…that cold air.  That really changes the so-called snow ratios.  Under normal conditions (temperatures near 32 at surface and slightly warmer air aloft) the usual snow ratio is 10 to 1.  (One inch of water content will produce about a 10″ snowfall.)  Very wet snows can have ratios as low as 7 or 8 to 1 while very dry, fluffy snows can reach ratios as high as 20 to 1 (or higher).  This snow will have a high ratio.  So, a little moisture can go a long way.

So, for the next 24 hours, here’s what I expect…clouds roll in this evening with virga (that’s the snow aloft) showing up overhead (as seen on radar) before Midnight.  Snow starts around 4 A.M. and diminishes by 10-11 A.M.  Total snow accumulation: 2″- 3″ for the Louisville area.  Snow accumulations will gradually increase as you go south and west of Louisville.  The western third of the state should see 4″ – 6″ of snow.

Road conditions should be very messy (snow and ice) for morning rush hour but should return to near normal for the evening rush hour.

What about that late-week storm?
Good question, if I must say so myself.  All signs are still pointing toward a major winter weather event around the lower Ohio Valley Thursday night and Friday.  Models keep making adjustments to this storm as it begins to move over the northwestern states.  It’s strong enough to create havoc from coast to coast over the next 3-4 days.  But exactly what it’s going to bring us is still a question.  But, the most recent model runs still put us in line for some major snow.  The GFS has now upped it’s forecast to 8.2″.  But as close as 100 miles south of us, the forecast is for mostly rain.  And, trying to pinpoint something like that 2 to 3 days in advance is very difficult.  It has been my observation over the years that the GFS tends to be too far south initially with these systems and gradually brings them farther north with time.  As small a shift as 100 miles in the storm track over the next 48-72 hours could change a major snow into a cold winter rain.  It’s just too early to tell.  Stay tuned.

Monday afternoon, Jan. 18, 2016

There have been some changes since yesterday (see Sunday’s post) with the models, but nothing big enough to downplay our snow chances yet.

NAM and GFS are now closer together concerning the weak upper air disturbance crossing the midwest and Ohio Valley Tuesday night and Wednesday.  In fact, today’s runs have the NAM now more aggressive than the than the GFS.  Their current forecasts are now in the 2″-4″ for the NAM and 1″-3″ for the GFS.  More on this system tomorrow.

Meanwhile, both models continue to point toward Friday as this week’s MAIN EVENT.  A system developing over the southern Rockies is expected to develop into a large storm over the southcentral U.S. then travel over TN and up the Appalachians Friday.  That’s prime territory for deep snows for us.  It’s too early to predict an exact path, but this morning’s GFS is predicting 6.8″ of snow for Louisville.

Let’s wait and see!!!

Sunday,  Jan. 17, 2016

A few flurries arriving this afternoon along with another shot of Arctic air will set the stage for what could turn out to be a snowy week.  The first good chance will arrive Wednesday while the second seems to be on tap for Friday.  The current GFS model looks pretty impressive, but I’m always forced to use the disclaimer – A lot can change in a few days.  But, it’s always fun to speculate.  So here goes…

A weak to moderate disturbance will drift into the Ohio Valley by Wednesday.  It’ll be overriding the cold air mass arriving today, so surface moisture will be very limited.  Nevertheless, the GFS is trying very hard to generate its own moisture and is showing the potential for 2″-3″ of snow.  The NAM is much weaker with this system, but still shows the potential for an inch (possibly as much as two) of snow.

Friday’s system, at this point, looks to be stronger and have more moisture available.  Thus, the snow-making potential could support 4″ + accumulations.  But, there will be some hurdles to jump over before a deep snow can occur.  What happens Wednesday will go a long way toward determining what’s going to happen Friday.  If Wednesday’s system is as strong as the GFS suggests, it’ll drag in another surge of cold air and help support a larger snow on Friday.  The weaker NAM solution plays toward a rain/snow mix early Friday, then snow later.  Either way, it looks as though Friday’s system will be warmer, so it shouldn’t be as bad on the roads.

Of course, potential doesn’t often equal reality.  But, it looks pretty good at this time.  Check back for updates as the events draw closer.

Monday, Jan. 11, 2013

Another Winter Weather Advisory for the area.  Yesterday turned out different than I expected as temperatures dropped much faster than I was expecting, so there were plenty of road problems in spite of the less than an inch (.8″) that was recorded at the airport.

Tonight’s situation is entirely different…we’ll be on the tail end of what is commonly called an Alberta Clipper that will move through the Great Lakes late tonight and tomorrow.  There’s not usually too much to get excited about south of the clipper’s path, but this time may be a little different – at least the NWS seems to think so.  Me, I’m not so sure, but I do think we’ll get something tomorrow morning.

This evening and early tomorrow morning, we’ll probably see what appears to be lots of snow  on the radar, but don’t be fooled.  High levels will be producing snow, but the lower level air is too dry for it to reach the ground.  The result is called virga (falling precipitation that evaporates before reaching the ground).   It looks good on the radar, but the result is disappointing to snow lovers.

That virga over night will be from a weak upper air disturbance preceding the primary clipper system.  While it shouldn’t produce more than a few flakes of snow, it will serve to increase the low level moisture levels so that the primary system should have more chance to drop some snow.

As mentioned above, the major problems with the clipper will be far to our north, but the cold front trailing the system will come racing across Indiana and Kentucky tomorrow morning.  While the atmosphere is very cold right now, it’s hard to squeeze much moisture into the air.  But, it should be able produce a few hours of snow (probably between 6 and 10 A.M. in the Louisville area (earlier to our west and later to our east).

All the models I’ve seen are generating only small amounts of precipitation (less than .10″ liquid), so that doesn’t hint at much snow.  Also, temperatures are expected to remain in the lower 30’s tonight, so the roads should be able to handle it pretty well.

With the Winter Weather Advisory, the Weather Service (and most of our media sycophants) is predicting 1″-3″ of snow.  The indicators don’t look that strong to me.  It’s possible that a few scattered snow showers could produce a few isolated swaths of 1″-2″ of snow (especially over southern Indiana).  The vast majority of the area should see anywhere from a dusting to up to an inch of snow.

  Sat. Jan 8, 2016  9 P.M.

Quick look at the winter weather advisory for the area.  Seems to be a bit overdone.  Temperatures should remain above freezing during the time of expected snowfall.  Being it is night, there is a chance for some very sloppy accumulations on grassy areas after 4-5 A.M. but no problems with the roads.  Any accumulating snows should end by daybreak.  Cold and windy, possible flurries Sunday with falling temperatures into the 20’s.

Any snow accumulation on grassy areas should be less than one inch.  Road problems are not espected.

Monday, July 13, 2015 (3 P.M.)

Line of thunderstorms moving through Jefferson County and areas to the east have proven to be nothing more than typical old-fashioned summer afternoon “Toad stranglers”.  Once again, the brief heavy downpours may aggravate recent flash flood problems, but the rainfall has been much less than similar events recently.  Severe weather threat is pretty much over for Louisville area, for now.

On the bigger picture, the expected westward expansion and intensification process of the thunderstorm line over us looks as though it is finally underway.  If it continues, look for severe winds to hit many areas of southcentral and southeastern KY later this afternoon before reaching Tennessee by evening.  Currently, the strongest thunderstorms are concentrated along the I-75 corridor.

Later this afternoon, another cluster of severe thunderstorms is expected to break out over northern IL and IN.  This system should drop southeastward this evening and reach the Ohio River area by midnight or later.  This afternoon’s thunderstorm has taken a large amount of energy out of our atmosphere, so if this system moves as expected, any thunderstorms we get should be less of a threat than the current line – except for the heavy rain/flooding threat.