General Weather Discussion - March 2015

[LocoAko]

What is this referring to the SREF runs and why the Yikes?

I don't understand your first question but the "yikes" was just because of the insane model spread (0-9", and fairly evenly across the spectrum... no clustering) for an event in the next 18 hours. Tough forecast that clearly isn't too stable in its solution.

HRRR and SREF...two models I don't hear much about. Would one of you with more experience mind breaking down the acronyms for these and their backgrounds?

Sure.

"HRRR" is the High-Resolution Rapid Refresh model. It runs every hour and only out to 15 hours. I'm not overly well versed on the model physics, but it is very high res (1 km) and is frequently used for its skill (sometimes lol) in forecasting radar evolution. Formerly called the RUC. http://ruc.noaa.gov/hrrr/

"SREF" is the Short-Range Ensemble Forecast. It is an ensemble of forecasts (initiated off the NAM I think) where there are three different physics schemes used (grouped by color -- ARW (pink), NMM (oranges), and NMB (blue)). Then amongst those, the initial conditions are also varied to get an idea of the sensitivity of the forecast to both the physics scheme used and the initial conditions. Clustering around a specific solution would imply a higher probability of that solution given assumed errors in model input, etc. Very often you'll see grouping by physics scheme which also shows a sensitivity to that. As you can see in the above forecast, the ARW members tend to be much higher than the rest, but otherwise there's a continuous range of possibilities along the spectrum that aren't particularly well defined or easy to pick out. What is usually posted here are the "plumes" for a given location, but traditional 2D "Weather maps" are also available -- they're just interpreted a bit differently since they are not deterministic forecasts but instead measures of spread in the solutions or the mean of all possible solutions.

Plumes - http://www.spc.noaa.gov/exper/sref/f...5&mTYP=roadmap

Maps - http://www.spc.noaa.gov/exper/sref/

[Anonymous.]

12Z GFS is clueless. Has ongoing precip. in the wrong places (placement too far SE), and is taking the Low almost due E/SE.

[Bobby821]

Hey Loco, the first part of my question was what was it referring to and I think I figured it out it is referring to snow depth. would be nice to see those 9" depths. verify.

[Easy180]

FWIW grounds temps are around 40 in the OKC area

[LocoAko]

MESOSCALE DISCUSSION 0113
NWS STORM PREDICTION CENTER NORMAN OK
1000 AM CST WED MAR 04 2015

AREAS AFFECTED...CENTRAL AND SOUTHWEST OKLAHOMA INTO PORTIONS OF THE
TEXAS PANHANDLE AND WESTERN NORTH TEXAS

CONCERNING...WINTER MIXED PRECIPITATION

VALID 041600Z - 042100Z

SUMMARY...MIXED WINTER PRECIPITATION WILL SPREAD EAST/NORTHEAST
ACROSS THE TEXAS PANHANDLE INTO SOUTHWEST AND CENTRAL OKLAHOMA OVER
THE NEXT SEVERAL HOURS. A BRIEF PERIOD OF FREEZING RAIN WILL BE
POSSIBLE BEFORE TRANSITIONING TO SLEET FOR MOST OF THE DAY.
EVENTUALLY...A TRANSITION TO SNOW IS EXPECTED...BUT NOT UNTIL LATE
AFTERNOON/EARLY EVENING. PRECIPITATION RATES SHOULD GENERALLY REMAIN
LIGHT...BUT MAY LEAD TO TRAVEL PROBLEMS.

DISCUSSION...MIXED WINTER PRECIPITATION WAS DEVELOPING IN WEAK WARM
AIR ADVECTION OVER A SOUTHWARD PROGRESSING COLD FRONT AND BAND OF
850 MB FRONTOGENESIS. THIS BAND OF PRECIPITATION STRETCHED FROM THE
TX PANHANDLE/SOUTH PLAINS NORTH/NORTHEAST TOWARD CENTRAL AND
NORTH-CENTRAL OK. SURFACE OBSERVATIONS SHOWED A MIXED BAG OF
PRECIPITATION TYPES INCLUDING SNOW...SLEET AND FREEZING RAIN. COLDER
AIR WILL CONTINUE TO OOZE SOUTHWARD THROUGH THE DAY AND ANY PERIOD
OF FREEZING RAIN SHOULD BE BRIEF AS VERTICAL TEMPERATURE PROFILES
COOL AND THE BOUNDARY LAYER SUB-FREEZING DEPTH INCREASES. AS
SUCH...A FAIRLY QUICK TRANSITION TO SLEET IS EXPECTED...BEFORE
FINALLY CHANGING TO SNOW LATE THIS AFTERNOON OR EVENING FROM CENTRAL
INTO SOUTHWEST OKLAHOMA AND WESTERN NORTH TEXAS. PRECIPITATION RATES
GENERALLY SHOULD BE LIGHT WITH PERHAPS BRIEF PERIODS OF MODERATE
INTENSITY.

[Anonymous.]

Hey they stole my technical drawing!

[mblackwell]

In this ever-changing situation, does this technical discussion hint at generally lower snow totals as opposed to the 2-4 inch predictions that have been floated out there for central OK over the last 24 hours?

[Anonymous.]

No, I would say 2-4 inches of snow is still a good bet for the area I mentioned earlier. But the air column isn't completely cooled way up top, so it will start as sleet, then switch to snow.

Looks like precip will begin falling consistently in the next hour for OKC.

[venture]

Those NE winds are definitely providing some neat streaking to the radar right now...

[BB37]

Sidenote: Don't let this weekend fool you, another powerful winter storm showing up around March 15th timeframe.

The biggest snowstorm I remember as a kid growing up in OKC was an 8+incher on/around the Ides of March (this was in 69 or 70, IIRC), so it IS possible.

[stratosphere]

No, I would say 2-4 inches of snow is still a good bet for the area I mentioned earlier. But the air column isn't completely cooled way up top, so it will start as sleet, then switch to snow.

Looks like precip will begin falling consistently in the next hour for OKC.

sleeting now in NW OKC

[Anonymous.]

Snow band in NW OK is looking really healthy. Ponca City to Enid to Elk City.

There is some weird dry-pocketing going on in C OK right now, so precip. keeps getting shut off. This should be overcome as the afternoon progresses, though.

[bradh]

looking like the metro is maybe missing the bulk of this, or is there more building to the SW that will show up later today?

I hate trying to figure this out and then determine what to do with my employees, who I know are just MF'ing me for not letting them go already.

[Tydude]

the roads will be fine for the rest of the day today

[bradh]

the roads will be fine for the rest of the day today

that's kinda what it's looking like

[Anonymous.]

Not a chance. The low is just churning away down in SW TX, all of these bands of precip will continue to evolve and I am still sticking with my guns and the image I posted on the previous page, saying I-40 and south, and along I-44 corridor will be the hotspot.

[OSUFan]

Sorry trying to follow along but am somewhat of a weather idiot but not a chance of what?

[LocoAko]

Sorry trying to follow along but am somewhat of a weather idiot but not a chance of what?

I think he means not a chance of roads remaining fine through this event.

Sleet/Freezing Rain mix in Norman but transitioning over to more sleet by the sounds of it.

[OSUFan]

Gotcha.

Also thanks to everyone in these threads. Really enjoy the info.

[Bobby821]

Getting some pretty good sleet now in NW Moore, ground looks like it is becoming damp and I can see sleet on Roofs across the street from me.

[venture]

Here is what we currently have.



Area in pink is the mix of sleet/snow and whatever else over us now. This small area has been growing some, but should focus most of its impact on the Southeastern half of the Metro area. For those that are new, when I say Metro or Metro area...I don't mean just Oklahoma City. I'm talking the entire 9-county metropolitan area. So the pink area is mostly going to impact those along/south of I-44...but also mostly south of I-40 until it gets east of Shawnee and continues to lift NE. Some areas could see some pretty moderate sleet or freezing rain in pockets - especially from Pauls Valley and south.

The next big feature is the massive snow band in blue (granted the southern half of this in Texas is actually rain, but it won't be for us). As the storm pushes east, so will this. I will say there are still some questions on just how much snow this will actually produce over the area. Looking at the latest runs of the short term models, they are all junk. They aren't handling on going precip very well at all. The main fly in the ointment here is going to be that area just to the east of the snow band - that is a lot of dry air. There are some isolated areas of precip attempting to saturate that area, so it might eventually fill in. It very well could eat up the snow band and keep things relatively calm.

With that said - are roads going to get terrible soon? I wouldn't say they'll be hazardous for the next couple hours as the dry slot is pushing in. Keep in mind that in these dry slots we can still get decent freezing drizzle that can ice things up decently. Just pay attention and if the road starts to appear a little wet, just ease off the gas a little and don't make any sudden lane changes or start/stops - especially on elevated surfaces.

[Anonymous.]

Yea the dry air destroyed the sleet bands all over SW to C OK in about two beam passes.

I think with the added lift when the storm system starts ramping up, we will see a period of heavy snow in this same area we have a dry pocket right now.

[mblackwell]

Yea the dry air destroyed the sleet bands all over SW to C OK in about two beam passes.

I think with the added lift when the storm system starts ramping up, we will see a period of heavy snow in this same area we have a dry pocket right now.

I love your wishful thinking.

[Anonymous.]

Haha, yea I will admit I have snow goggles, but I am also realistic in my thinking with this. I know it seems crazy now, but at 8PM we'll see who is smiling.

[bradh]

better shot at delayed starts tomorrow then right?