Friday, February 20, 2015

NOWCAST Mode Sneetzing Rain

Okay, I know it's early in the morning. But what in the world is 'sneetzing rain'?

Snow, sleet, freezing rain, and just plain liquid rain.

I tried to make sneezing rain out of it, but I do think sleet will be a major factor in Louisville's precipitation type. However, that could change. That's why we call that nowcasting.

As the precipitation falls, we shall see how the upper levels of the atmosphere are responding between the diminishing Arctic influence and the surging 'warmth' from the Gulf of Mexico and make a better forecast based on the data.

And I guarantee you that will even change throughout the course of the next several hours. Just have to keep up and watch the forecast change many times even while precipitation is falling.

Therefore, I'll be posting from here for the next 24-36 hours. -- MS
---------------------------------

9:00am UPDATE

-32 near Richmond (Mesonet site) for a low temperature
-6 at Louisville Int'l airport
-18 at Lexington Bluegrass airport
-21 at Frankfort

These readings may be updated later.

Speaking of Lexington's Bluegrass airport, whatever happened about that heat-sensitive sensor issue during last summer? Their high of 7 with full sunshine yesterday compared favorably with the 6 degree Mesonet reading. Lexington could not even beat out Frankfort's official high of 8.

Lexington's snow and sleet total at 14.9" is good enough for 3rd snowiest February on record so far. The all-time snowiest February was 17.4" in 1998.

Also, if we called it quits right now, Lexington would have its 9th coldest February on record, replacing 2007's 9th place position.
------------------------------------

9:45am UPDATE

FWIW, Weather Prediction Center has from Louisville to Florence in a moderate shading for >= 4" snow.

The entire area south of Louisville has at least a slight risk of >= 0.25" ice accumulations.
------------------------------------

10:05am UPDATE

"There's one good thing about snow, it makes your lawn look as nice as your neighbors."--Clyde Moore

------------------------------------

11:05am UPDATE

14hr RAP model for midnight tonight shows snow and a mix moving into central and north-central KY. A mix and freezing rain in western KY. By 4:00am, snow north of Frankfort, mix for Louisville and Lexington, freezing rain in southwest KY and plain liquid rain and occasional mix for southern and south-central KY.

I will use the midnight and 4:00am time frame throughout the next successive runs of the RAP. I will update this in about 4 hours, the 18z run.
---------------------------------------               

11:20am UPDATE

Correspondingly, the latest NAM suite has freezing rain for much of Kentucky west of I-75 for the 1:00am time frame.
----------------------------------

2:40pm UPDATE

18z RAP model for midnight shows primarily a mix of snow and sleet moving into Louisville and heavy sleet by 4:00am. Heaviest snow confined to southern Indiana and northern KY like near Florence and Erlanger. Mix for most of the state with liquid rain in western KY also by 4am.

My thoughts - I've been leaning more toward a sleet storm here in Louisville and the RAP is picking up on this. Still, not a lock. The snow line is way too close for me to pull the trigger. Some portions of Louisville area could see a surprise big snow while others will see quite a bit of sleet.

After 4am, more of a heavy mix for Louisville. Tough to call which one will win out. I'm not used to having such a situation at the surface and diminishing Arctic influence while warmer air trying to win out. Since it does appear warmer air will eventually win out, I'm leaning more toward a sleet event through early Saturday morning.
---------------------------

Wednesday, February 18, 2015

Messy Weekend Coming Up

There's no technical way to say this. Simply, it will get messy this weekend.

After a harsh, deep freeze event preceded by more insulting, accumulating snows on top of an already deep snowpack, we look to the weekend and sigh, "What next?"

I hate to say it. But, a period of freezing rain appears likely. I'm not looking at the models yet to determine precipitation type. Just from watching similar setups, I am convinced that as warmer air aloft attempts to scour out the impressive cold at the surface, we will witness how stubborn cold air can be as the precipitation breaks out.

A best case scenario for surface temperatures at or below freezing, as absurd as it may sound, is for heavy rain to fall on the frozen surface. This will produce a two-fold result.

First, the heavy rain does not allow for ice to accumulate efficiently on limbs and power lines or even the pavement. True, some ice accretion will occur but would be preferred as to a lighter rain event over a long period of time that would allow for more efficient ice accretion on tree limbs and power lines, causing some potential issues.

Next, the heavier rain will bring down the warmer air from aloft more quickly to the surface thereby warming the surface. This works just the opposite when you can have sleet and snowflakes when the temperature at the surface is in the 40's, because the temperature above is so much colder thereby transferring the cold to the surface and dropping the temperatures.

The problem is...more than likely, it will not work out that way.

Therefore, it would be better for the precipitation to remain sleet for an extended period of time before transitioning to rain, perhaps freezing initially, then switching to good ole-fashioned liquid.

Well Mike, why not just to keep it all snow before changeover? The warmer air aloft will not allow the precipitation to remain as snow unless the cold air above is so dense that it resides well above 5,000 feet.

This does not mean we will not have a prolonged period of snow. Since the Arctic air in place has a lot of dry air, any moisture will cool the column of air all the way to the surface as it evaporates, slowly saturating the column. So, snow could be around a while for some of us.

Lastly, let me say I do have concerns about sheltered areas like valleys, especially toward Eastern Kentucky. Cold air has a propensity to become trapped in these areas making it difficult for warm air to scour out the cold air. Ice accumulations could become a major problem in these areas as the air warms all the way down to 2,000 feet but the cold air at the surface just cannot escape unless you have heavy rain, which does not appear likely as the temperatures are below freezing. The heavier rain should arrive mainly after we reach above 32 degrees. Ice accretion could become substantial in these areas, at least 0.25 to 0.50" and maybe more depending on how long it takes for the cold air to succumb to the warmer air.

MS

Tuesday, February 17, 2015

FeBRRRuary

Although I still think it is too early to tell how cold it will be later this week, it will still be very cold, so cold that it will put the BRRR in February.

I don't go by the models. Okay, look at this morning. Forecast lows were way off. The way cold air, calming conditions, snowpack, whatever, interacted with each other, produced some of the lowest readings in years. And yet...we may be looking at colder air than this.

I'll tell you what I have a problem with. Thursday morning wind chills will be brutal. However, those winds will help to offset the actual air temperature from plummeting too much. Yet, air temperatures are expected to be around -10 here at Louisville Int'l. Then, the following night, with calmer conditions, the overnight low is still expected to be -10.

Right now, and of course this is still subject to change, I'd be willing to go out on a limb and say that the ongoing forecast for these low temperatures for Louisville will change.

At this moment, for Thursday morning, I have Louisville Int'l at -6 with clouds and strong winds and wind chills of -20 to -25 degrees.

For Friday morning, with calming conditions and a significant snowpack, Louisville will see low temperatures of -11 to -13 actual air temperature. Perhaps -17 at my house in Valley Station.

Brrrr.

In the meantime, snow will accompany the leading edge of this upcoming Arctic air mass and give us a 1-3" possible accumulation.

Then, we turn our attention to this weekend system that could be quite dicey with the whole potpourri of wintry weather including rain.

Sheewww.

MS

Monday, February 16, 2015

NOWCAST February Big Snow 2015

Good morning....Valley Station right now at 1" with steadier snow moving in here at 5:30am.

Snowfall reports from west to east...

Mayfield................2.5"
Evansville..............1"
Madisonville..........2"
Central City KY...1.5"

I will be posting here periodically....MS

-----------------------

7:00am UPDATE

Snow really ramped up over the past hour in Valley Station. Now at 2.5".

Highview in Louisville.....2"
Greensburg........................2"
Lexington..........................2"
Rineyville..........................2"

In western KY, 2-4" reports are common.
---------------------------

8:00am UPDATE

Lighter snow last hour only yielded about 0.1". Valley Station total at 2.6". However, moderate to heavy snow bands on all sides of Evansville heading this way with more farther west. Expect heavier snow to pick up by 10am. May make slight adjustment in expected total for Louisville. My original forecast called for 7-10". But, that bust potential is getting closer to the Ohio River as I feared last night. Nevertheless, with some heavier bands around, 6-9" still looks good.

Reports of 5" amounts now in Brownsville, west of I-65 and south of Nolin Lake in Edmonson county.
---------------------------

9:15am UPDATE
3" in Valley Station...with moderate snow falling now.
Reports of 4-6" in western KY, including a 6.5" in Greenville KY in Muhlenberg County

2-4" in Jefferson County common.

4-6" south of Louisville in Breckinridge and Ohio counties.

---------------------------------

10:30am UPDATE
4.3" in Valley Station...moderate snow.
Moderate to heavy snow falling along the Ohio River back to Evansville then farther west into Cape Giradeau MO heading our way. After that, main accumulating snow begins to taper off.

My thinking is that Louisville or my part of Louisville in sw Jefferson county should end up with at least 7-8", again possibly more, depending on heavier bands.

Am seeing reports of 4-7" across the Louisville CWA. Far western KY seeing 8" while parts of Illinois have nearly 10"!
------------------------------------     

11:30am UPDATE
5.3" in Valley Station....snow had lightened for a brief moment but now picking up again.
On track to reach 7-8", perhaps higher if heavier bands develop.

Louisville Int'l has reached 5.2" during the last hour, good enough for a new daily snowfall record for this date. Our neighbor Lexington is on the verge of setting a new daily snowfall record for this date too.

Lots of 7" amounts being reported from E'town to Richmond and down in Taylor county near Campbellsville.

Looking at radar returns...could dry air be wrapping into this thing already? Out west, the moderate band is shrinking just near Evansville. Main accumulating snow may cut off here in a couple of hours. It's going to be a race for that 7" mark all of a sudden.
---------------------------------------

12:30pm UPDATE
9" reports coming in from Grayson county. 6-9" becoming more common around here in central KY.
I even read a report of 9" in Pleasure Ridge Park here in sw Jefferson county, an adjacent area just to my north. If that's the case, I'm jealous because I'm only getting 6.7" here in Valley Station.

-------------------------------------

2:30pm UPDATE
7.3" now in Valley Station, with much lighter snow over the past 2 hours. What about that band to the northwest of the area. Very heavy band of snow with that one.