Southeast Ridge Retreating???

I've been studying those 500 millibar maps. They're not that hard to understand if you know what you're looking for.

Areas of red concentric circles indicates ridging, or areas of high pressure, and blue indicates troughing, or areas of low pressure.

Three outstanding features appear on the current 500 millibar map:

West coast ridging
SE ridge
Icelandic Low

The forecast maps show the SE ridge losing its influence on the U.S. over the next several days.

Colder air should have easier access to the region over the next several days.

Precipitation chances are harder to forecast, though. If we're going to get any exciting winter weather, we'll have to either hope for a robust clipper or a Southwest cutoff low ejecting out toward the Plains or southern U.S.

MS

Year-End Weather Outlook for Kentucky

First, our upcoming weather system looks wet and windy. This morning, I noticed the WPC has shifted an axis of heavy rain east that now encompasses areas along the Ohio River which could produce 3-day totals in excess of 4".

Long term outlook shows a persistent ridge off of the west coast of the U.S., which will keep them unusually dry for this time of the year. That could lead to some low snowpack and drought issues later on next year for many along the coast.

Another persistent feature includes a strengthening trough east of Iceland.

Our weather will include a variety of conditions. West-Southwest flow will be offset by periods of Northwest flow. I don't really see any significant winter storm affecting the region through the rest of the year.

Temperatures will be cold to mild, somewhat below normal to slightly above normal, but no Arctic outbreaks expected. Then again, no record breaking warmth expected after this weekend's storm event.

More on the possibility of flooding for parts of the region later....

MS

Models of a Snowstorm

Perhaps some of you more savvy worshipers of weather models have seen this before.

Since it has to do with our region and was a joint research project conducted by the NWS Louisville and Saint Louis University, I thought it would be a good read.

Unfortunately, the information is very technical. However, maps are provided as well; therefore, any of us non-technical people can download the current maps (for surface, 850mb temperatures, 300mb winds, and so forth) and compare them to the 'modeled' maps to see if we fall or will fall into one of the several types of models favoring a snowstorm.

And by the way, their estimation of a snowstorm counts as anything >=2", which may disappoint some of you. But, there was a map comparison of the January 1994 record snow and cold.

So, enjoy...

http://www.crh.noaa.gov/images/lmk/ResearchPapers/SnowComposites_OhioValley.pdf

How Does This Winter Stack Up Against Last Winter and Past Winters?

It's almost the middle of December. So far, Louisville Int'l has recorded 4 days with high temperatures of <=32 degrees this young winter season (November included). It appears the cold trend will continue, especially for the latter part of the month.

Last year, Louisville Int'l recorded only 6 days for the entire winter season with high temperatures <=32 degrees.

Although the recent cold spell has been relatively brutal, December's average temperature is nowhere near the top ten coldest December's on record for Louisville...yet. We are expecting a blast of winter cold for the period around Christmas, though. If the major block in Alaska continues, then storm systems will have to veer around that block by way of the Siberian and Arctic regions and spill chunks of that cold air into the Plains and Midwest. Therefore, you haven't felt winter's brutality yet.

Do you remember when...?

The year 2000 was the coldest December on record for Louisville and 2nd coldest for Lexington.

You want to see something eerie??? Check out this 500mb forecast for later this month...

Compare this map with the image just above this one. I see quite a few similarities of the winter 2000 brutal cold and the impending cold for later this month.

Snowfall has been variable for parts of the state. Louisville Int'l has received 5.8" as of this date. Lexington has received 2.0".

Last year, both sites had recorded only a trace of snow up to this date.

The winter season is still young but is already ripening as we head into the coldest part of the year in January.

MS

My Weather Today

Low temperature of 10 degrees at my house in Valley Station this morning.
According to NWS here in Louisville, snowfall could become a minor issue for Friday night-Saturday morning with up to an inch possible.
As of 4:00pm, snow depth here was 1".

MS

Overachiever?

At my location in Valley Station, only 0.6" accumulated here. However, timing could not have been worse. This was a low-end storm but high-impact event.

Yesterday, the NAM model reestablished itself after a mini-'vacation' during the last storm. It showed a stripe of heavier snow across southern IN possible.

Reports of 2-3" across southern IN and northern KY did exceed forecast totals. Also, the forecast based on this for Louisville was to be in the range of 0.2 - 0.8". Not too bad in terms of amounts.

As far as eastern and southeastern KY, amounts have verified for many. Latest reports I have seen so far is 1.5" in Pikeville and Prestonsburg as expected. However, within the last hour, a Winter Storm Warning was posted for Pikeville with accumulations forecast in a 3-5" range. Short-range models did show that Pikeville and Prestonsburg would be the 'winners' of this snow event.

To make a long story short, now, I would consider this storm to be a minor overachiever.

By the way, my snow depth is now at 3". I'll be updating my seasonal snow/sleet totals later. But, my total stands at 3.8" as of 8:30am.

MS

Stripe of Snow Possible UPDATED

5:15pm Update
I reviewed the RAP model and am satisfied by the results.
Looks like a weakening band of snow will approach the Ohio River after 4am
0.5 - 1.0" looks like a safe guess for southern IN
Louisville looks to get in on only a dusting to a 0.1" according to the latest run

SE Kentucky looks to get a little bit more snow than the rest of us. Basically from London to Pikeville, 1-3" will be possible, more closer to 1-2". However, cannot rule out upsloping; therefore, some amounts may exceed 2", especially near Pikeville.

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NAM model shows light snow entering southern IN and north central KY by 4-8 am time frame.
Amounts are forecast to be light but has been showing signs of increased lift which could produce a burst of moderate to heavy snow for areas especially in southern IN, with perhaps a quick inch or so.

Louisville area may only see anywhere between 0.2 - 0.8".

Nevertheless, needs to be monitored. I'll be looking at the RAP model later today. It only goes out to the 11pm hour as of this post, but it does show a stripe of snow developing to our west out across MO and IL streaking northeast toward IN.

MS

NOWCAST and RAP Model

At 4:05pm
Temp: 27 degrees
Wx: Lt to Mod Snow
Location: Home
Snow-covered roads here in the 'burbs
Accumulation has exceeded an inch; 1.3" of sleet and snow in Valley Station
This is on top of nearly 0.25" ice.
Getting reports of 3-7" across SW and southern Indiana

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At 3:15pm
Temp: 28 degrees
Wx: Lt to Mod Snow
Location: Home (see below)
Pavement sleet/snow covered; have not checked main roads; traffic cams downtown showing snow-covered to slushy roads.

Snow is now becoming the dominant precipitation in Louisville. Actually, downtown experienced changeover about an hour ago. I just saw my changeover within the past several minutes and now is snowing moderately.
Forecast is still for 2-4"; however, with earlier changeover, I wouldn't be surprised to see some higher totals.

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At 2:00pm
Temp: 29 degrees
Wx: Moderate sleet
Location: Home (see below)
Pavement slick; minor sleet accumulation
Total Ice Accumulation 0.25" or less

During the last hour, more sleet began mixing with rain; as of this writing, primary precipitation is sleet.
Pavement is becoming slick due to sleet accumulation; secondary roads becoming slick; treated roadways wet, except where sleet is falling more heavily.
Bloomington IN 7.5"
Bedford IN 5.0"
Princeton IN 7.0" (north of Evansville)
Mt Carmel IL 12.0"

Corydon IN experiencing changeover to sleet and snow during last hour.

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At  12:15pm
Temp: 30 degrees
Wx: Lt rain w/sleet
Location: Home (see below)
Wet pavement, additional icing since last report
Total Ice accumulation - 0.2"

During the last hour, sleet began mixing in with the rain in Valley Station; PRP mostly rain with some sleet trying to mix in.
6" snow near Bloomington IN
In Cadiz, near Hopkinsville I-24 reporting accidents due to icing

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At 9:45am:
Temp: 29 degrees
Wx: Very light rain
Location: Valley Station 1 mile north of Gene Snyder Freeway
Wet pavement, thin coating of ice on tree limbs (c. 0.1"), ice on windshields.

15z RAP (Rapid-Refresh Model):
For Louisville, changeover to snow by 3pm
Accumulations vary across county from 2.3" in south part of county to near 4" in northern part by 10pm.
Sleet may begin to become predominant precip between noon and 1:00pm

Snowing now in Covington, Bloomington.
Freezing rain in Evansville.
Moderate sleet in Tell City

Next update in an hour.

MS

NEW Call for Snowfall

Complicated weather for the next few days.
1st event:
Looking at data yesterday, I felt that more mixing of precipitation types would occur.

That may still be possible as NAM has been having issues deciphering between what falls in the air versus what actually could fall at the surface.

I've repeatedly noticed extraordinary amounts of snow for the region. However, when sleet is forecast, snow accumulations are still occurring, according to the latest runs.

Therefore, that 8-10" snow for Louisville could occur IF it was all snow. However, data suggests that a mix of rain, sleet, and snow will occur for a while before complete changeover here in Louisville.

Some icing may occur here in Louisville. Western KY looks to get significant amounts of ice.

You will notice that I have upped my snow amounts across the board as less amounts of mixing should happen.

Louisville  2-3" (perhaps some 4" amounts)
Lexington 1-2"
London  less than 0.5"
Jackson  less than 0.5"
Cincinnati  3-4"
Bloomington 4-5"
Salem 2-4"

If more mixing occurs, then snowfall amounts will be impacted, perhaps even back toward my original levels from the First Call.

MS

First Call for Snowfall

UPDATE 2:45pm EST
NWS conference call ended about 30 minutes ago.
Sounds like a snow maker to me for the first event here while a hydrologic issue just south.
I saw a recent NAM snowfall projection for Louisville 8-12"!
I say give it a few more runs and check back tomorrow.
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First, let's make one thing clear...this is for entertainment value only. And believe me, there's gonna be plenty of laughs going around as weather forecasters try and tackle the timing and precipitation types for the next 36-60 hours. Expect a lot of changes to the forecast.

I do think we may have a slightly better handle on precip types and possible accumulations within 24 hours of expected changeover to frozen precip.

While this forecast only projects snowfall amounts, don't be fooled by the totals. Wet surfaces, sleet accumulations, mix of p-types will affect these totals.

As far as ice potential with THIS system, I'm not as concerned about it here in Louisville and Lexington. Could be some nuisance icing on mailboxes and cars while a coating of ice could accumulate on tree limbs. Roadways will be warmer than other surfaces for a while. However, after dark, your typical bridges and overpasses will begin to freeze over. It will be difficult to treat wet roadways as rain will wash most of it away. But, I'm hoping that the heaviest rain will be exiting our region by the time temperatures go below freezing. Still, watch out for a brief period of heavy snow during the evening hours Friday.

Louisville  0.5 - 1.0" (some higher amounts possible)
Lexington  0.5 - 1.3" (some higher amounts possible)
Covington 1-3"
Bloomington 2-4"
Salem 1-3"
Jackson KY dusting to 0.5"
London KY dusting to 0.5"

I stress that some amounts may be higher if less sleet and rain mix in with the snow.
Ice accumulations for Louisville and Lexington should be on the order of 0.2" or less.
Again, all of this is subject to change.
As I finish writing this post, Winter Storm Watches are being posted for our region.
I will have an adjusted Call sometime tomorrow.

Otherwise, in conclusion, I'm more concerned about the possible icing that will affect parts of our region later this weekend. If temperatures are cold enough at and just above the surface, prolonged icing may occur as the cold, dense air could have a hard time getting scoured out. Right now, I'm planning for the worst case scenario.

MS

Analog For This Week

Looking at a GFS analog for later this week showed the number one date of the fifteen different analogs. It was December 15-16, 2008.

Conditions in Louisville were wet and mild initially. After frontal passage, temperatures tanked from a high near 60 to 24 degrees. The following day, temperatures struggled to reach the 32 degree mark. Snow showers accumulated across the region.

Louisville recorded 1.1"; Lexington reported 2.5".

This is just one analog, and it's the GFS, and it's a few days out. Take it for what it's worth.

Let's just say this system will need to be watched as we get closer to the event. Lots of rain is forecast on the front end while wintry precipitation is expected to make a quick appearance after frontal passage.

This reminds me of numerous past weather systems that are slow moving and have large temperature gradients over a small distance. With that said, I recall instances when heavy snow had set up a hundred miles or so north of the boundary.

We'll just have to wait for further refinements to the forecast to determine whether this will be a progressive or stationary event. Progressive means less snow and overall precip; stationary means more snow in the colder air and more overall precip for the rest of us near the boundary.

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UPDATE 12/02/2013
183800

I just viewed another analog worthy of mention...
The snow/ice storm of January 8-9 1999
Snowfall amounts of 4" in northern KY and southern IN; up to 8" in some areas
Freezing rain occurred over a large area of Kentucky.

Here is a weather map of that storm system
http://www.raymondcmartinjr.com/weather/1999/08-Jan-99-SurfaceMaps.html

Thanks for the map...
MS