Wednesday, Feb 6, 2019  11:30 A.M.

Lessening threat for flooding

Morning runs from the GFS and NAM both are lowering the rain estimates for the next 36 hours.  Since yesterday, radar rainfall estimates are under 1/2″ for southern Jefferson County rising to about .75″ along and north of the Ohio River.  Heaviest rain so far has been over southcentral IN.

Heaviest rain will shift into southern KY this afternoon as rain diminishes (for awhile) for northern KY and southern IN.  Periods of rain return tonight and tomorrow.  Now appears like the total will run between 1.5″ and 2″ for most of Louisville area with higher totals over southern KY.

Sat. Feb. 2, 2019

Early spring has arrived

We’ve now completed the cycle created by the Sudden Stratosphere Warming we began talking about about a month ago.  The breakoff vorticies from the polar jet stream have retreated northward to allow warmer air to take over.  The last segment of the polar vortex to hit the U.S. was extremely cold for the Great Lakes and northeast but moderated quickly as it pushed southward.  We didn’t even drop to zero ( 3 was the lowest), so it certainly wasn’t even close to “record breaking” as it was to our north and east.

With the polar jet now back home, the next few (maybe, many) systems to produce our weather will arrive via the Pacific Ocean, so they’ll be warmer.  And, with a little help from the Gulf of Mexico, probably wetter as well. The first will arrive Monday night.  Then, a large slow-moving system could provide periods of rain from Wednesday through Friday.

The GFS isn’t even hinting at decent snow chances for the next couple of weeks.  We’re going back to the West Coast Cold – Eastern U.S. Warm pattern that was prominent from late December to early January.  Get out your raincoat and put away the snow shovel for awhile.

The Groundhog

Punxsutawney Phil was rudely awakened from his hibernation around daybreak today.  His handler then read a statement “supposedly” from Phil.  The guy in the funny top hat announced that we’ll have an early spring.

The GFS and the seasonal model both say the same thing – early spring.  I consider that a far superior source for weather data.

Saturday, Jan. 26, 2019

Flurries tonight, Monday night is still a possibility

We’ve had some very light flurries early this morning, after sunrise, and again this afternoon.  Still, nothing to show for the effort.  But, this evening’s clipper may give us at least a dusting.

The weak clipper has be producing very light snow across southwestern Indiana this afternoon and is moving eastward.  It’s also weakening.  Very little snow (if any) will drop south of I-64 tonight, so this system will be mostly north of Louisville.  We’ll probably see some flurries twice this evening – centered around 6 and 11 P.M.  No more than a dusting is expected anywhere near Louisville.  Low tonight in the upper 20’s and not much increase tomorrow with highs about the mid 30’s.

Monday into Tuesday

For the past several  posts, I’ve been pointing toward a strong Alberta Clipper expected to move into the western Great Lakes early next week.  Models are now projecting the primary snow chance for us Monday evening.  South of Clipper Monday, we’ll see see strong southwesterly winds and a quick warming into the 40’s.  The cold front trailing the clipper will push across central IN/KY Monday evening.  That will bring us the coldest air mass of the season Tuesday through Thursday.  Temperatures should drop to the lower single digits a couple of days.

What about snow?

Yesterday I mentioned the (to me) unusually high amount of precipitation the GFS was projecting with that front.  The weather south of clippers is usually quite dry.  Today, the GFS forecast reduces the rain/snow totals considerably.  The NAM is also low.  That seems much more reasonable to me.  But, it also reduces the snow potential to less than an inch.  It’s early, things could change.

Jan. 21, 2019

Previous post accidentally described the next system to reach us as a negatively tilted trough.  That is incorrect.  Trough is positively tilted.  In general, positively tilted troughs produce weak weather systems.  Negative tilted troughs are far more energetic.

Sorry for the mistake.

Click on the corrected post (to the right).

Friday, July 20, 2018 Noon

…we’ll probably get lucky.

Unusually strong summer system is dropping southeast from the western Great Lakes and should trigger numerous strong-to-severe thunderstorms this afternoon/evening.

Morning rains set up the higher moisture, now the upper dynamics have plenty to work with.  Lucky thing for us is that the next big surge of upper energy is approaching rapidly and probably won’t get enough heat energy to kick off storms until it is either right over us or to our east.

Storms should start organizing between 2-3 P.M. near I-65 and move rapidly southeast.  Some scattered severe activity is possible in the I-65 corridor, but these storms will get better organized and much more dangerous east of I-65.  Widespread severe weather is likely over the eastern half of KY this afternoon/evening.

Luckily, most (if not all) of the damaging weather will be east of the Louisville metro.

Watch the skies this afternoon.

Thursday, May 31, 2018  5:45 P.M.

Development to our west is still slow.  Primary development, as expected, will stay south (where the energy is) with heaviest storms over western TN.  A weaker bit of energy may still work its way up the Ohio River tonight, but that looks like it’ll be later than I originally thought…probably arriving around 11 P.M. to Midnight.  No problems with this system, if it arrives.

Comment:  This has been a really bad month for Louisville area forecasters.  It’s only fitting that the  current NWS forecast seems destined to join the faulty list.  My guess is they haven’t taken into account the changes caused by this afternoon’s storm system.

3:30 P.M. 5/26/2018

Rain/thundershowers over southern IN have remained weak and are not showing any indication of dropping into KY.  So, there will still be a slight  chance for a shower later today or tonight, but most, if not all, of  the Louisville area will stay dry through the weekend.  But, it’ll be hot!  Have fun!

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.

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

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.