Oklahoma Weather Discussion - January 2013

[venture]

00Z runs of the GFS and NAM are pulling rain amounts back a ton. Short term HRRR also showing the bulk of rain remaining in Texas.

GFS rainfall totals show roughly 0.5-1" over SW OK, less than a half inch everywhere else.

NAM rainfall is roughly < 0.5" Northern OK, 0.5 - 1" Central OK, and 1-2" Southern/SE OK.

We'll see what happens, but wanted to pass that part on.

GFS is also still latched on to the idea of snowfall on Monday. Mind you not all members of the GFS ensemble are in agreement with this.

[1972ford]

We will take anything we can get at this point just hope spring has lots of moisture in store for us

[SoonerDave]

Okay, Venture, here's a purely speculative question for you.

Rewind to Christmas, and we were all getting twitchy about the models showing another Snowmageddon for Christmas Eve/Christmas Day, but at seemingly the last moment (okay, last few hours), the models started pulling back and keeping the system farther south in Texas...

Now, back to now...last couple of days, we've been hearing about the models showing a pretty decent rainfall event for OK, but at seemingly the last moment (okay, last few hours), (stop if you've heard this...lol) the models started pulling back and keeping the system farther south in Texas...

So, is this purely a coincidence demonstrating the insufficiency of the models (despite the fact they accurately predicted snow/rain in the general area, but missed in the specific) in that they seem to have missed in these two forecasts in rather similar ways? Or is it indicative that maybe something else in the way these storms "spin out" (for lack of a technical term) that maybe we don't entirely understand?

I'm really just getting at what at least seems like a similar forecast, similar models, departing late-game into a keep-the-rain/snow-south projection, both at the same time, sure strikes me as an odd coincidence...

[Bunty]

Yeah, Dallas has a 100% of precipitation with "heavy rain" in the forecast this afternoon while OKC only has "showers" for tonight with a 90% chance.

[venture]

Okay, Venture, here's a purely speculative question for you....

Now, back to now...last couple of days, we've been hearing about the models showing a pretty decent rainfall event for OK, but at seemingly the last moment (okay, last few hours), (stop if you've heard this...lol) the models started pulling back and keeping the system farther south in Texas...

I think it is just a matter of marrying oneself to a model solution and refusing to deviate. You might remember even last week I mentioned it wasn't going to be a wash out. Rain amounts fluctuated, but Central OK was never on the high end. To me it really hasn't changed much.

Yeah, Dallas has a 100% of precipitation with "heavy rain" in the forecast this afternoon while OKC only has "showers" for tonight with a 90% chance.

Percentages only refer to area coverage, not amounts. 100% of the Dallas area will see precip. 90% of the OKC area will see precip. That how those should always be read.

[Anonymous.]

Actually the percentages used in the case of the poster above most likely refers to the dummied versions of percentiles. Those percentages are the probability or chance that precipitation will occur of the given area (in this case, Dallas or OKC).

Percentages like this, that the media gives out like "80% chance of rain on Monday" - does NOT mean 80% of the area, but rather the chance of the area receiving rain is 80%.

For sake of confusing the masses, media will often not move chance percentages concurrently with amounts. This is incorrect though, really. The real way to do a forecast is to explain to the viewers how it works. For instance, you can say there is a 100% chance of snow today - and the only thing that falls is snow flurries, this forecast was accurate - but since the common media has ruined our to view forecasting, people will think 100% chance of snow means A LOT of snow.

Hopefully this post makes sense, I have tried to explain these things in-person before, but have found it is rather difficult.

[SoonerDave]

I've always understood the POP figures to relate to the probability of a given amount of precipitation within a given distance of a designated point within a designated amount of time, eg 20% POP in OKC means a one-in-five chance of measurable rain within 3 miles of any given point within whatever boundary is implied by the designation of "OKC." Not so?

I've never taken those percentages to imply a particular intensity or coverage area.

[SoonerDave]

Okay, being too curious for my own good, I did some googling for NWS definitions on POP. Here's what I found from FAQ - What is the Meaning of

What does this "40 percent" mean? ...will it rain 40 percent of of the time? ...will it rain over 40 percent of the area?

The "Probability of Precipitation" (PoP) describes the chance of precipitation occurring at any point you select in the area.

How do forecasters arrive at this value?

Mathematically, PoP is defined as follows:
PoP = C x A where "C" = the confidence that precipitation will occur somewhere in the forecast area, and where "A" = the percent of the area that will receive measureable precipitation, if it occurs at all.

So... in the case of the forecast above, if the forecaster knows precipitation is sure to occur ( confidence is 100% ), he/she is expressing how much of the area will receive measurable rain. ( PoP = "C" x "A" or "1" times ".4" which equals .4 or 40%.)

But, most of the time, the forecaster is expressing a combination of degree of confidence and areal coverage. If the forecaster is only 50% sure that precipitation will occur, and expects that, if it does occur, it will produce measurable rain over about 80 percent of the area, the PoP (chance of rain) is 40%. ( PoP = .5 x .8 which equals .4 or 40%. )

In either event, the correct way to interpret the forecast is: there is a 40 percent chance that rain will occur at any given point in the area.

[venture]

Actually the percentages used in the case of the poster above most likely refers to the dummied versions of percentiles. Those percentages are the probability or chance that precipitation will occur of the given area (in this case, Dallas or OKC).

Percentages like this, that the media gives out like "80% chance of rain on Monday" - does NOT mean 80% of the area, but rather the chance of the area receiving rain is 80%.

For sake of confusing the masses, media will often not move chance percentages concurrently with amounts. This is incorrect though, really. The real way to do a forecast is to explain to the viewers how it works. For instance, you can say there is a 100% chance of snow today - and the only thing that falls is snow flurries, this forecast was accurate - but since the common media has ruined our to view forecasting, people will think 100% chance of snow means A LOT of snow.

Hopefully this post makes sense, I have tried to explain these things in-person before, but have found it is rather difficult.

Which highlights the differences in what percentages mean in weather forecasting. Neither of us are wrong, it comes down to the forecast area.

[Uncle Slayton]

So, are we going to get snow next week or not? Flurries or otherwise.

[Bunty]

On radar it looks like this system has spit in two as it moves north, leaving Oklahoma largely high and dry.

[OKCisOK4me]

Yep, its just spitting out there ;-)

[s00nr1]

The 00z NAM came in tonight with a bit of snow/sleet for Sat night-Sun am. Will need to keep an eye on this.

[Anonymous.]

As the Low is moving across S OK right now, some thunderstorms are trying to pop up. What an interesting weather situation. Warm air streaming from the south east, some clearing skies over OK with a strong Low scooting right over.

[venture]

My activity here is going to be pretty brief until the trojans are removed from the site. NAM and GFS in agreement with keeping the snow this weekend Northeast of Oklahoma for the most part.

[kelroy55]

Drove up to Joplin this afternoon for a funeral and hit decent rain from Tulsa on and still raining.

[Easy180]

Talking about a trace in the metro this afternoon...Sure we will only see it in the air, grass and rooftops

[venture]

Winter Wx Adv is up for some FRZ RN and Mix Precip...

URGENT - WINTER WEATHER MESSAGE
NATIONAL WEATHER SERVICE NORMAN OK
1052 AM CST SAT JAN 12 2013


OKZ008-012-013-018>020-024>026-029-030-130500-
/O.NEW.KOUN.WW.Y.0001.130112T1700Z-130113T0800Z/
KAY-GARFIELD-NOBLE-KINGFISHER-LOGAN-PAYNE-CANADIAN-OKLAHOMA-
LINCOLN-CLEVELAND-POTTAWATOMIE-
INCLUDING THE CITIES OF...PONCA CITY...ENID...PERRY...
KINGFISHER...GUTHRIE...STILLWATER...YUKON...EL RENO...MUSTANG...
OKLAHOMA CITY...CHANDLER...NORMAN...MOORE...SHAWNEE
1052 AM CST SAT JAN 12 2013


...WINTER WEATHER ADVISORY IN EFFECT UNTIL 2 AM CST SUNDAY...


THE NATIONAL WEATHER SERVICE IN NORMAN HAS ISSUED A WINTER
WEATHER ADVISORY FOR SNOW...SLEET AND FREEZING RAIN...WHICH IS IN
EFFECT UNTIL 2 AM CST SUNDAY.


* TIMING: LATE THIS MORNING THROUGH LATE TONIGHT. THE HEAVIEST
WINTRY PRECIPITATION IS EXPECTED LATE THIS AFTERNOON THROUGH
THIS EVENING.


* MAIN IMPACT: WINTRY PRECIPITATION WILL CONTINUE TO DEVELOP
THROUGHOUT TODAY ESPECIALLY ACROSS NORTHEAST AND CENTRAL
OKLAHOMA. A COMBINATION OF SNOW...SLEET..AND FREEZING RAIN IS
EXPECTED. SNOW AND SLEET ACCUMULATIONS AROUND 1 TO 3 INCHES WILL
OCCUR LATER TODAY ACROSS CENTRAL AND NORTHEASTERN OKLAHOMA. IN
ADDITION...FREEZING RAIN MAY ALSO RESULT IN ICE ACCUMULATIONS
AROUND ONE TENTH OF AN INCH.


* OTHER IMPACTS: SLICK ROADWAYS WILL DEVELOP ACROSS THE REGION
TODAY. INITIALLY...BRIDGES AND OVERPASSES WILL BECOME SLICK.
LATER THIS AFTERNOON AND EVENING AS COLDER AIR MOVES INTO THE
AREA...ALL OTHER ROADWAYS WILL ALSO BECOME SLICK. MOTORISTS ARE
URGED TO USE CAUTION TODAY AND TONIGHT.


PRECAUTIONARY/PREPAREDNESS ACTIONS...


BE CAREFUL IF YOU HAVE TO TRAVEL. EVEN SMALL AMOUNTS OF ICE AND
SNOW CAN MAKE ROADS AND SIDEWALKS SLICK AND DANGEROUS.

[venture]

Pretty good band of freezing rain and sleet now extends from Ponca to Perry to Guthrie to Mustang to Chickasha to Duncan. Movement is to the NNE.

[venture]

Light to moderate freezing rain in Norman right now. Areas mainly east of East 12th have a good glaze of ice on all elevated surfaces.

[ou48A]

Wow, its bone dry on the NW side Norman.

[kelroy55]

Looks like it's going to miss OKC to the east. I drove back from Joplin this afternoon and had rain most of the way until 50-60 miles from OKC

[Bunty]

Most of the ice and snow may be all over, assuming what's in the northwest part of the state doesn't maintain intensity and move this way.

[LocoAko]

Had a very light glaze on my car here in central Norman. Thundersnow (probably thundersleet) was reported in Shawnee just to our east.

[OKCMallen]

Aaron Tuttle posted a picture of a model projecting ~12" of snow on Wed/Thurs of this week.