Midday Friday  (Feb.20)

I’ll have more details later, but here’s my current thoughts on weather tonight through tomorrow.  (There’s still a fairly large difference between the NAM and GFS, so there’s a pretty large “margin of error” this close to the event.)

1)  Increasing clouds this afternoon…high in mid 20’s.

2).  Periods of light snow begin after 7 P.M.  Snow becomes heavier after 10 P.M. with an accumulation of 2″-4″ by 3A.M.

3).  3A.M.-7A.M.  Sleet mixes with snow and eventually becomes all sleet (and possibly freezing rain.

4).  7A.M. – Noon    Temperatures warm to around 32 degrees around Noon.  Meanwhile sleet changes to freezing rain and then to liquid rain.  (Rain/freezing rain could be heavy at times, but no major (damaging)  ice accumulations expected.

5).  Afternoon:  Temperatures rise above freezing for several hours.  Rain continues, but lightens as time wears on.

6).  Some snow flurries are possible as temperatures drop below freezing again

5).

THURSDAY AFTERNOON

Unbelievable!!!  After a badly busted forecast of this morning’s lows, local weather authorities are poised to do it again tomorrow.  My guess is that they haven’t learned anything from this morning’s fiasco.  Anyway, they’re shooting for -11 tomorrow morning while four of their major forecast tools predict 3, zero, -2 and 5.  On average, slightly warmer than their forecasts for today.  This morning, the busted forecast was due to the winds.  Tonight it’ll be due to increasing clouds  after midnight.

NOTE:  Missing a temperature forecast by 9 degrees or more has become a real rarity these days.  I’d guess it happens less than 10 times a year here.  Coming with all the Watches and Warnings in place (dependent on the forecast), it was a real embarrassment for us forecasters.

Friday-Saturday storm

We’re getting close enough to the arrival of the next storm to be able to try to make some sense out of it (although a few doubts remain).

In general, the models are thinking along the same lines although the NAM is faster (and cooler) than the GFS models.  The upper trend is for another polar jet disturbance to sink southward over the western Plaines and Rockies.  Unlike the past several storms. this trough will hold back in the western U.S. and send us ripples of energy over the weekend.  But, the main part of the system does not play a major role in the weekend’s activities.

Meanwhile, the subtropical jet is available to send plenty of  moisture our way.  Here’s how it’s shaping up:  Increasing clouds begin tonight with a cloudy cold day Friday.  We could see some very light snow or flurries during the afternoon.  High near 24 degrees.  Temperatures continue rising tomorrow night as snow becomes heavier.  In fact, 2″-4″ of snow appears likely before a changeover to sleet and freezing rain Saturday morning.  By Saturday afternoon temperatures will rise above freezing so freezing rain will change to rain and begin a long cleanup.

Doubts:  models have backed off a bit on the 1″-2″ rain totals, so the prospect for flooding will be much lower.  HOWEVER , many urban streets/intersections will flood because the storm sewers will be blocked by snow.

Biggest question mark remaining is the duration of the sleet and freezing periods.  At this time, it looks like the freezing rain will be the biggest threat – a lot of ice is possible, especially if the NAM is better than the GFS.  More tomorrow.

Wednesday Afternoon

Zero is tomorrow’s record low.  From what I’ve been reading and hearing, breaking that record is a “no-brainer.”  Most of the forecasts locally have -5 to -10 as the low (the NWS says -11 for the city).  It very well may get that low, but I doubt it.  Two reasons: clouds and winds.

For the past several days, the forecast for Thursday morning has been around -10,  But, for the past two days the Models have made an abrupt change to forecasting a low just above zero.  Yes, the models know we have a deep snow cover, so that’s not the reason for the change.  But every forecast I’ve heard today has IGNORED what the models are trying to tell us.  I don’t think that’s wise.

To get extremely cold readings like -10 around here you need very cold air (we’ve got that), deep snow cover (we have that),  clear skies (iffy) and near-calm winds (very iffy).  So, it’s not a sure thing, and some of the temp/wind chill forecasts I’m hearing seem far too low.  First, the clouds.  Satellite/model trends have the clouds diminishing this evening and going clear after midnight.  So that should only retard the cooling a little.  The winds, however, will play a much more important roll in tonight’s low.  If the winds die down to less than 5 mph, we’ll see a good shot at -5 to -10.  However, the winds are predicted to remain 6 to 12 mph most of the night.  If that is correct, you can say goodbye to -10 and probably even -5!

By Louisville standards, it is extremely cold – and it’s going to stay this way for the next 36 hours.  But, most of the temperatures and winds chills being tossed around seem far too extreme!  I’ll go with a low in Louisville of 0 to -2 and wind chills about -15 to -20.  As usual, it’ll be colder in rural areas.

BIG MESS for Saturday

Storm shaping up in the Rockies will keep the winter weather coming.  Look for light snow developing Friday, then a changeover to freezing rain/sleet Friday night, and finally to liquid rain Saturday. Lot’s of flooding on city intersections due to clogged sewers Saturday.  More specifics tomorrow as the amounts/timing.

Tuesday afternoon

Another strong upper level disturbance will drop southward over the Great Lakes and the northern half of the Ohio Valley.  It has two things in store for us:  1).  The coldest air of the winter so far (Wed-Fri).  Before the cold comes snow late tonight.  This newest “clipper” is moisture-starved, but has plenty of energy.  The system should be able to squeeze out some snow for us, starting after Midnight and ending during rush hour.  Snow will be much less than the last one, but still should be on the order of 1″ to 2″ by morning.  Then, the COLD.

P.S. Could be a real mess brewing for Saturday!

Early Monday

Quick look at the evening run shows little change is needed to the forecast.  If anything, the evening runs of the NAM, RAP and GFS (new) are stronger than this morning’s runs.  Meanwhile, the odd man out is the old GFS which now carries the heaviest snows farther south.

So, as of midnight I’ll leave my projections the same as my previous blog which would be 8″ -12″ for metro Louisville.  (Even if the old GFS is correct, we’ll still have a significant snowfall.  But, totals would be 2″-3″ lower than I’m forecasting.)  The new GFS gives Louisville 9.3″ of snow.

Sunday afternoon

The system approaching us looked – 36 hours ago – like a puny attempt to get us some light snow.  Things have certainly changed!!!   The polar jet stream energy, which has long been predicted to be weak, has had an amazing increase in energy and now looks like it’ll be the perfect antidote to our mostly snow free winter (at least since November’s snow).  The southern jet stream has been the prime part of the forecast for days, but all indications were that it wouldn’t be strong enough to bring much moisture north into the colder air over the central U.S.  Then all of a sudden comes the polar jet’s energy.

That changes the whole game in a big way.  It will be able to bring plenty of moisture northward aloft, but still hold the surface cold air in place.  The result:  about a 200 mile northward shift of the major activity – right into the Ohio Valley.  It’s a setup for plenty of snow – let’s see if it happens!

Advancing snow tonight will have a hard time saturating the lower atmosphere, but some snow should begin in the Louisville area about 3-5 A.M. and we should have a messy rush with about an inch or two by rush hour.  Then the snow really takes off – heavy snow likely between 7 AM and 1 P.M. and slowly tapering off by evening.

How much snow?

Good question, but here’s my best guess –  Louisville area  8 “-10″

North of Louisville:  within about 30 miles of the river – 6″ 8″

South of Louisville:  8″ to 12″ north of the Parkway,  12” south of the parkway

NOTE:  Great snow for sledding, but too “dry” for snowballs and good snowmen.

Saturday

Little change in the outlook from yesterday.  Models still converging on a wet day tomorrow.  Here’s the outlook:

Thickening clouds this afternoon with highs in the 43-46 range.

Tonight:  A weak upper air system will push overhead tonight.  That will bring in higher low-level moisture and warmer air (especially aloft).  Systems like this often bring a little precipitation along.  If any precipitation falls, amounts should be very light – a trace to a couple of hundredths of an inch.  If it occurs, It’ll be mostly rain but some wet snow cloud mix in at the beginning.  No icy conditions expected as the temperature shouldn’t drop below 36 (with some slow rising overnight.  Chance for any precipitation is only 20%.  If it’s going to happen, it should be between 7 and 11 P.M. tonight

Tomorrow:  Cloudy with increasing chance for rain during the morning.  Rain likely during the afternoon with heaviest rains likely between Noon and 6 P.M.  High temperature should reach the upper 40’s.

Tomorrow night:  Much colder air arrives between 8 P.M. and Midnight.  Any lingering rain will change to snow and/or flurries.  Most of the area should see more more than a light dusting by Monday drive time, but snow showers/flurries should hang around at least through Noon.  Temperatures are likely to remain below 30 degrees all day Monday.

That’s it for now.  Think rain coats, not shovels.