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Another “iffy” March snow forecast

Tuesday, March 20, 2018  2 P.M.

Another big nor’easter is on track to pound the eastern U.S. from northern West Virginia, north Virginia and northern Maryland northward into New England.  4″ to 8″ of snow will be likely over a large area while some spots could record a foot of snow, or more.

Meanwhile, we’ll be on the back side of this big snow-maker.  The computer forecast models are predicting about a 2″ – 4″ snow in about a 100 mile wide swath from southern Indiana and extreme northern KY  northeastward toward Lake Erie. That swath could reach 6″ or more over east-central IN and northwestern Ohio.  The Louisville National Weather Service’s forecast includes Louisville in that 2″ – 4″ snow area.  But, don’t count on that much snow here.  I have two good reasons for predicting why our Louisville snowfall total should be lower.

First,  the western side of Northern Hemispheric storms is a weaker precipitation-maker than the warmer eastern side.  The northwest side of these systems has to “wrap around” moisture from the active eastern side of the storm. That’s a hard job to pull off. Nevertheless, it does work.  Whatever moisture that does make the wrap around is rather small, but efficient.  As it reaches the northwest quadrant of the storm, it encounters colder air which squeezes out some moisture.  Little, if any, moisture can get far enough around to reach the southwestern quadrant of the storm.  The problem here is that the Louisville area will be in the Southwestern quadrant of the system by Midnight-2 A.M.

Second,  several models are predicting a weak low pressure to form west of the primary storm center.  This development is expected over east KY and West Virginia.  When that happens this evening, it will interfere with the wrap around precipitation mechanism of the parent storm.  So, we have another problem with the potential snowfall here.

With all that to consider, here’s my forecast:  a light rain/snow mix will begin during the afternoon rush hour and quickly  turn over to snow this evening.  Periods of light snow will continue overnight changing to flurries by daybreak.   Temperatures will remain in the 30″s all night, so roads should remain mostly wet with just a few slick spots.

How much snow?

Louisville area: !” to 2″ on grassy areas

South of Louisville: less than 1″

Southern Indiana: 2″ to 4″ north of the Ohio River.  4″+ over south-central counties northeast to the Ohio border.


March 11 evening snow update

Significant changes in past few hours.

Models have been running the precipitation farther north this evening.  It now appears the southern one-quarter of KY will stay snow free.  Heaviest snow band looks to be between a few miles south of I-64 to southern KY.  Basically, Bullitt Co and south.

Also, models are predicting faster movement of the storm (should leave Louisville area by 3 AM.  Faster movement means lower precip. totals for us.

Another change:  Models are now predicting colder temperatures overnight.  That means slightly more accumulation of snow AND possible road problems for Louisville.

So, for Louisville area:  some rain, but mostly snow.  Louisville could see an inch of snow on grassy areas with some slush on roads.  Major roads, however, should have few problems

Today’s snow

Monday, Jan. 15, 2018

Not much to worry about this afternoon

A cold front pushing toward us has been producing some nice snow over southwestern IN this morning.  However, current short-term models are forecasting a considerable weakening of the snow field this afternoon as it passes through the I-65 corridor.  Plus, southerly winds have pushed temperatures to around 32 degrees and they should stay there this afternoon.

As a result, my forecast needs a little revision:

Light snow should begin around 1 P.M. and be mostly over by 5 P.M.  Flurries will continue overnight.  This afternoon’s snow will mostly melt on roadways, so this evening’s rush hour will only have a few slick spots.  As always, drivers will find those slick spots and we’ll have some accidents.  Overall, however, things should be pretty good considering holiday traffic will be lighter than usual.

Snow accumulations will be light.  Within a 30 mile radius of Louisville, the Ohio River will be a dividing line.  On the Kentucky side of the river, snow accumulations should run around 1″ on grassy areas (little, if any, on roads as discussed earlier).  South and east of Jefferson County snow totals will diminish to less than an inch.  On the Indiana side of the Ohio River, snow totals will be higher – 1″-2″ in the counties touching the Ohio.  Farther north and west, it’ll probably be more like 2″-3″.
NOTE:  I wasn’t surprised to see snow overnight.  However, the amount of snow really surprised me.  Best I thought nature could do was around .1″, maybe .2″  The half inch sure fooled me.  I’m hoping the prediction described above will be better.


Moisture increasing

Sunday, Jan. 14, 2018  11 P.M.

Evening models have all increased their forecasts for snow Monday.  Still a possible dusting overnight; then afternoon snow Monday should average around 1″ with some isolated spots perhaps as high as 2″.

Good news update!

Friday, Jan, 12, 2018

Icy weather takes a break

All of a sudden the freezing rain has quit and will not return for 2-3 hours.  As a result, the icy mess I talked about a couple of hours ago ISN’T GOING TO HAPPEN.

With this break, we’re back to a mostly snow situation.  Sleet and (mostly snow) will return by 4 P.M., just in time to foul up rush hour traffic.  Snow will continue through rush hour and gradually end before midnight.  Total snow accumulation: 1″-3″.

This sudden halt in the icy weather has given us a tremendous break!

Much worse than expected

Friday, Jan.12, 2018 11 A.M.

Sleet/freezing rain will cause more problems than snow.

This afternoon is going to be a real mess.  Yesterday, I discussed the quicker timing on the current weather pattern.  So far, that has worked okay…with one exception – cold air.  Temperatures were expected to remain in the 30’s until late afternoon.  But, the really cold air (20’s) has swept across the area much sooner than that.  It’s already here.  So, the consequence of that is much more trouble.

With temperatures aloft still well above freezing, rain will be the primary precipitation until late afternoon.  As that rain falls into the cold near-surface air we’ll see a 4 to 6 hour period of freezing rain gradually changing to sleet.  If freezing rain dominates, it could cause big problems with tree limbs, power lines, etc.  If sleet dominates the main problems will be with the roads.  Sleet should be the dominate precipitation, but a longer than expected period of freezing rain isn’t out of the question.

The snow part of the equation hasn’t changed.  The precipitation should change to snow by 3-5 P.M.  Snow will wind down this evening and end by midnight.  It’ll be hard to measure with all the ice already on the ground, but the Louisville area should see an accumulation of 1″ to 3″.  Higher snow totals are likely north and west of town.

Friday night snow?

Tuesday, Jan.9,2018  3 P.M.

GFS points to snow Friday night!

Here’s the latest prediction from the GFS 2.5 km model:

Looks exciting, doesn’t it?  But don’t get too excited yet.  This prediction is definitely an outlier, at least so far.  The GFS ensemble shows(a group of GFS models run under slightly different starting conditions) shows a wide range of possible solutions for this future storm.  The Euro and Canadian models also are much lower with their forecasts.  But, it’ll fun to see how it develops this week.



Quick update

Sun., Jan 7, 2018

The short term models have, as expected, all gone to a forecast for the Louisville area which consists of almost all rain tonight and tomorrow morning AND  a few periods of sleet/snow mixed in.  But, essentially we’re just looking a a rain situation locally as temperatures remain above freezing all night.

Doesn’t look like the NWS has given up on its icy prediction yet.

What’s going to happen tonight?

Sunday, January 7, 2018

Which precipitation type will dominate tonight?

Forecasts have been calling for snow and/or sleet and/or freezing rain and/or rain for tonight and Monday morning for several days now.  But, as we get closer to the event, the actual sequence of events seems to be coming into clearer focus.  The computer models are still quite varied – I’ve just looked at five different models and the results still are different.  One says mostly snow, another says mostly freezing rain/sleet, two say about a fifty-fifty split between icy types and rain, while another one predicts mostly plain old liquid rain.

So that aspect of the models doesn’t provide much help.  So maybe it’s time to put a little common sense human forecasting to work.  One thing the models do agree on is surface temperatures.  In general, they all hold surface temperatures above freezing overnight and tomorrow.  Thus, any icy precipitation that mixes in should melt on roadways.  Concrete sidewalks and roadways could get a bit icy late this evening.  Once precipitation begins this evening, temperatures will drop  few degrees for an hour or two.  During that time we’ll see our best chance for icy precipitation mixing in with rain.  After midnight, by far the dominant feature will be rain as temperatures rise into the mid to upper 30’s by morning.

So, summary, when all is over, this system should cause only a few, if any, problems for the Louisville area any all roads should be fine (although wet) for rush hour.  However, north and northeast of Louisville more ice will mix in, especially those areas which still have some snow on the ground.  Numerous road problems are likely in these areas.

Can Nate help us?

Friday, Oct. 6, 2017  11 A.M.

Recent changes cast doubt on current forecast.

This morning’s GFS model run has pushed Nate’s path farther east than the current forecast implies.  If this works out, and it likely will, our local hopes for some very beneficial rain this weekend are dimming.  Current official forecast calls for widespread 1″-2″ rainfall over our area late tomorrow into Sunday.  Forecast  changes this morning would indicate our rainfall will probably be less than half that of the current forecast.

As it looks now, we should get at least some rain this weekend, but not enough to take much of a bite out of our growing drought conditions.  A quarter to half an inch would be nice, but I’m getting the feeling I may be too optimistic.