Feb. 18-20, 2012 Disco/Analysis

[Bevo]

This system will not produce snow from cold air in place, it will be with the dynamic cooling with the vort max coming in from the west.

Therefore if snow occurs, it will begin as rain except perhaps in the highest mountains. It looks pretty obvious that last night's Op Euro was an outlier- the surface low will probably take a more southerly track, we just need to hope the phasing occurs just barely west of here and the strength at 500mb is stronger more in line with the CMC. I agree with Lookout that GA is not looking very good for snow especially ATL south, there is a better chance in NC. However, we still have a ways to go, not giving up all hope yet.

Absolutely agree. When a system is upper level driven, you have to hope that the dynamics are great enough to generate the cold needed. Surface temps aren't my concern at the moment (upstate SC). Will it phase or not is the first dilemma...where it phases is the second.

[burgertime]

Saw Allan mentioned the Canadian here are some maps us NC folks will like

Granted it's ice....but with that heavy of rates could probably be snow

[RaleighWx]

Ok after perusing the 12z runs, my discussion for those interested

http://www.examiner.com/weather-in-raleigh/watching-snow-potential-for-this-weekend

[burgertime]

Ok after perusing the 12z runs, my discussion for those interested

http://www.examiner....or-this-weekend

Great write up. Just going to have to wait and see, but either way it's the best shot we've had all winter.

[griteater]

Ok after perusing the 12z runs, my discussion for those interested

http://www.examiner....or-this-weekend

Good write-up throughout Allan, but I thought this snippet was particularly spot on...

"In general the 50/50 low is not classic in that it is not very strong and it is only arriving in place as the southern stream system is moving in. The southern stream system is classic"

[Gastonwxman]

Ok after perusing the 12z runs, my discussion for those interested

http://www.examiner....or-this-weekend

Good write up and wholeheartedly agree. There will be plenty of variation in what solution we see based on how the overall set up is handled on the modeling so there is nothing definite at this point. Being that we're a few days away, this still gives us plenty of room to see improvement but if we are to see this look anything like what the 0z GFS had or the 12z CMC, at the latest it needs to start trending that way by say Thursday. Also I think that those who are panicking to death need to stop, relax, and consider the fact that there will be continuous waffling of some fashion (be it colder/wintry, warmer/wetter, etc.) until we get within the appropriate range to be sure of anything. It's the best potential threat we've had all winter and so can still hold promise toward something much more acceptable in the latter. How it plays out exactly is anyone's guess; for better or worse.

My suggestion: Just sit back and enjoy the ride.

[msuwx]

A few quick thoughts on the 12z model data....a lot of this will be shop talk.....keep that in mind.

12z Euro looked oh so close to a bombing phase around 108, but the phase was not terribly strong I think primarily due the orientation of the Great Lakes disturbance.

12z GFS still looks off to me, like the 6z. The entire orientation of the flow pattern at 500mb is different than most other modeling. It might score the coup though...who knows.

12z Canadian is nice for a chunk of NC. Pretty nice phasing, and because of that, a nice pulling sothward of the colder air aloft.

12z UKMET is weaker and farther south.

Here is what to take from this IMO. I see no trend in the modeling. What I see is each time a model is run, you get its latest interpretation of how a very chaotic 500mb pattern will look this weekend. There is no trend north or south....there is just varying positions and strengths of features.

For the upper Southeast to see a nice winter storm, we want some good phasing. Each model has taken turns showing this from time to time. That is needed to pull the colder air necessary for snow southward, and also get the precip rates heavy enough to overcome some marginal low level temps in some places.

Players remain on the field, and I am no more encouraged or discouraged than I was at this point yesterday.

[burgertime]

A few quick thoughts on the 12z model data....a lot of this will be shop talk.....keep that in mind.

Players remain on the field, and I am no more encouraged or discouraged than I was at this point yesterday.

Thanks for the info Matt! A good read as always.

[griteater]

HPC Disco...

12Z UPDATE... SOLNS REMAIN VARIED WITH THE ERN CONUS SYSTEM BUT

THE 12Z GFS/ECMWF SHOW FAVORABLE TRENDS TOWARD THE PREFERRED

COMPROMISE THRU EARLY DAY 5 SUN ALBEIT WITH THE GFS BECOMING MORE

SUPPRESSED THEREAFTER. BY LATE SUN THE 12Z CMC IS NOW THE

FARTHEST NWD WITH THE SFC LOW. THE UKMET STRAYS FROM CONSENSUS

WITH NRN STREAM FLOW IN THE SHORT RANGE PERIOD LEADING TO A VERY

FAST LEADING WRN ATLC WAVE AND SUPPRESSION OF A TRAILING WAVE IN

THE MEDR PERIOD. GEFS MEMBERS REMAIN SUFFICIENTLY DIVERSE FOR THE

MEAN TO BE VERY ILL-DEFINED WITH THE SFC REFLECTION. WITH THE

INCOMING WRN TROF ALOFT... THE 12Z ECMWF ALONG WITH OTHER MDLS

AGREE WITH FASTER TIMING THAN EARLIER ECMWF RUNS FOR THE INITIAL

SYSTEM NEARING THE PAC NW. THE GFS HAS TRENDED TOWARD THE PAST

COUPLE ECMWF RUNS THRU THE WEST INTO THE PLAINS EARLY NEXT WEEK...

BUT THE 12Z ECMWF BRINGS THE CORE OF MID LVL ENERGY AND ASSOC SFC

LOW INTO SRN CANADA INSTEAD OF THE CNTRL PLAINS. THE UKMET/CMC

BOTH SHOW AMPLIFIED SOLNS WITH THE WRN TROF AND THE CMC IS NOW ONE

OF THE SLOWER SOLNS WITH THE EMBEDDED CLOSED LOW.

THERE IS STILL CONSIDERABLE UNCERTAINTY IN THE COVERAGE/INTENSITY OF

RNFL FROM THE SRN PLAINS/GULF COAST INTO THE ERN STATES FRI-SUN...

WITH SOME SNOW PSBL IN THE NRN FRINGE OF THE PCPN SHIELD IF MSTR

REACHES FAR ENOUGH NWD. HOWEVER EVEN THE 00Z AND 12Z/13 ECMWF

RUNS SHOW FAIRLY WARM BNDRY LAYER TEMPS IN THE NRN PART OF THE

PCPN SHIELD SO WHAT SNOW OCCURS COULD END UP BEING CONFINED TO THE

APLCHNS OR AT THE VERY LEAST HAVE DIFFICULTY ACCUMULATING AT LOWER

ELEVS. HIGHEST POTENTIAL FOR LOCALLY HVY RNFL IS OVER THE GULF

COAST/EXTREME SERN CONUS/NRN FL.

[dsaur]

Thanks, Mets, for your ever informative, and calming input I was surprised at the vigor of the sleet I saw last night, and I expect I'll be surprised this weekend too. And if it's a ton of rain I get over this next 7 days, well, I can live with that. Tony

[beanskip]

This board needs people like me to shut up and people like Matt to post more -- this was one of the best synposis I have read on these boards in some time -- well done.

A few quick thoughts on the 12z model data....a lot of this will be shop talk.....keep that in mind.

12z Euro looked oh so close to a bombing phase around 108, but the phase was not terribly strong I think primarily due the orientation of the Great Lakes disturbance.

12z GFS still looks off to me, like the 6z. The entire orientation of the flow pattern at 500mb is different than most other modeling. It might score the coup though...who knows.

12z Canadian is nice for a chunk of NC. Pretty nice phasing, and because of that, a nice pulling sothward of the colder air aloft.

12z UKMET is weaker and farther south.

Here is what to take from this IMO. I see no trend in the modeling. What I see is each time a model is run, you get its latest interpretation of how a very chaotic 500mb pattern will look this weekend. There is no trend north or south....there is just varying positions and strengths of features.

For the upper Southeast to see a nice winter storm, we want some good phasing. Each model has taken turns showing this from time to time. That is needed to pull the colder air necessary for snow southward, and also get the precip rates heavy enough to overcome some marginal low level temps in some places.

Players remain on the field, and I am no more encouraged or discouraged than I was at this point yesterday.

[Rankin5150]

There must be a lot of cliff-diving in the Mid-ATL and NE threads right now

Seriously we cannot look at details yet- with phrasing streams it is a delicate balance and the models will continue to flop around for a while longer.

Now this is the BEST advice ALL DAY long (bolded). Thanks for keeping it real Cheez! I kind of laugh at the quote above, re cliff diving. LOL. We still have so many, many hours left to call this a done deal.

Thanks

[Brick Tamland]

A few quick thoughts on the 12z model data....a lot of this will be shop talk.....keep that in mind.

12z Euro looked oh so close to a bombing phase around 108, but the phase was not terribly strong I think primarily due the orientation of the Great Lakes disturbance.

12z GFS still looks off to me, like the 6z. The entire orientation of the flow pattern at 500mb is different than most other modeling. It might score the coup though...who knows.

12z Canadian is nice for a chunk of NC. Pretty nice phasing, and because of that, a nice pulling sothward of the colder air aloft.

12z UKMET is weaker and farther south.

Here is what to take from this IMO. I see no trend in the modeling. What I see is each time a model is run, you get its latest interpretation of how a very chaotic 500mb pattern will look this weekend. There is no trend north or south....there is just varying positions and strengths of features.

For the upper Southeast to see a nice winter storm, we want some good phasing. Each model has taken turns showing this from time to time. That is needed to pull the colder air necessary for snow southward, and also get the precip rates heavy enough to overcome some marginal low level temps in some places.

Players remain on the field, and I am no more encouraged or discouraged than I was at this point yesterday.

Thanks for the post. I like how you put it in layman's terms for those like me that just love following the weather, but have no idea how these models work.

[HKY_WX]

I honestly don't see a huge difference aloft on the euro versus 00z. The phasing is not as intense. The heavy precip pretty much avoids NC on this run. Overall the pattern remains very favorable here. Expect to see a lot more shifts until prob Friday.

[packfan98]

JMA looks like a good track. It looks warm to me based on the 540 line but I'm not an expert. There looks to be some sort of High pressure that moves from Michigan to NY with a CAD signature on the last frame. Anyone else with more experience with map reading, feel free to chime in.

http://grib2.com/jma/CONUS_JMA_1000-500_SLPTHKPRP_120HR.gif

http://grib2.com/jma/CONUS_JMA_1000-500_SLPTHKPRP_144HR.gif

[burgertime]

JMA looks like a good track. It looks warm to me based on the 540 line but I'm not an expert. There looks to be some sort of High pressure that moves from Michigan to NY with a CAD signature on the last frame. Anyone else with more experience with map reading, feel free to chime in.

I don't know man it looks to me like that low is trekking through the middle of GA...that probably wouldn't do anyone in the SE good outside of maybe TN. Hard to tell with the CAD setup but I would think WAA would overpower it.

[FallsLake]

RAH afternoon discussion (last part of Long Range):

Not good but not bad either

........FOR THIS WEEKEND...THE 12Z GFS AND ECMWF ARE IN BETTER AGREEMENT

COMPARED TO YESTERDAY...DEPICTING A COLD FRONT DRIVEN BY A NORTHERN

STREAM SHORT WAVE MOVING EAST AND MERGING WITH A SURFACE LOW DRIVEN

BY A SOUTHERN STREAM WAVE JUST OFF THE CAROLINA COAST BY LATE

SUNDAY. ALTHOUGH A SOUTHERN STREAM SYSTEM AND COASTAL LOW COULD

SUGGEST PRECIP-TYPE PROBLEMS FOR CENTRAL NC...BASED ON THE CURRENT

MODEL RUNS...IN THIS CASE THE NECESSARY HIGH PRESSURE AND COLDER AIR

TO OUR NORTH ARE NOT IN PLACE AT THE BEGINNING OF THE EVENT. THE

GUIDANCE CURRENTLY BUILDS IN THE CHILLY HIGH AFTER THE NORTHERN

STREAM FRONT PASSAGE...PERHAPS TOO LATE AND AFTER THE BULK OF THE

PRECIP MOVES ACROSS OUR AREA. AS SUCH...RIGHT NOW...THIS SYSTEM

APPEARS TO BE A RAIN-MAKER FOR OUR REGION THIS WEEKEND... AND THE

POTENTIAL FOR ANY WET SNOW MIXING IN WOULD OCCUR VERY BRIEFLY AT THE

END OF THE EVENT AS THE SYSTEM IS DEPARTING. GIVEN THE RECENT MODEL

DIFFICULTIES WITH THIS SYSTEM...FORECAST CONFIDENCE FOR THIS

WEEKENDS EVENT IS LOW. BUT IT DEFINITELY BEARS WATCHING AS THE EVENT

DRAWS NEAR. FOR NOW WILL FORECAST POPS INCREASING SATURDAY NIGHT AND

SUNDAY. TEMPS WILL BE WARM ON SATURDAY AHEAD OF THIS SYSTEM WITH

HIGHS IN THE MID-UPR 50S...THEN COOLER ON SUNDAY AND HIGHLY

DEPENDENT ON THE EVOLUTION OF THE AFOREMENTIONED SYSTEM.

-- End Changed Discussion --

[msuwx]

Haha....thanks. I was not trying to call you or anybody out.....was just kind of laying some thoughts out there. We will see how it plays out. Overall, odds will be fairly tough against us, but there's a chance.

This board needs people like me to shut up and people like Matt to post more -- this was one of the best synposis I have read on these boards in some time -- well done.

[packfan98]

I don't know man it looks to me like that low is trekking through the middle of GA...that probably wouldn't do anyone in the SE good outside of maybe TN. Hard to tell with the CAD setup but I would think WAA would overpower it.

I wasn't paying attention to the low when I posted it, just the precip field. I do believe that you are correct. It's weird that some of the models are flat and out to sea and others have a pretty sharp northeast track. I guess it's due to the phasing. One error with the JMA is that the low never looks to dig as far south as the other models. Most go down into the gulf but the JMA never gets down there. Oh well, I tried to bring some good news. I'll try again later if I can find any more potential silver linings.

[NavarreDon]

GSP afternoon....keeps the door open a bit:

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...

AS OF 205 PM TUESDAY...LOW AMPLITUDE RIDGING ALOFT WILL BEGIN TO

BREAK DOWN SAT WHILE THE ATTENDANT SFC HIGH WEAKENS AND MOVES

OFFSHORE. THIS WILL SET THE STAGE FOR THE NEXT SYSTEM DUE TO AFFECT

THE AREA LATE SAT THROUGH SUN. THE MODELS ARE IN SOME DECENT

AGREEMENT WITH THE 12Z GFS SIDING WITH THE MORE RUN TO RUN

CONSISTENT ECMWF. THE CMC IS THE OBVIOUS SLOW OUTLIER AND IT/S SOLNS

HAVE BEEN GIVEN LITTLE TO NO WEIGHT IN THIS FCST PKG. THE GEFS SFC

MSLP SPREAD ISN/T TOO GREAT UNTIL 00Z MON AND THE SPREAD CONSENSUS

IS ALIGNED TO THE NE OF THE SFC LOW...WHICH GIVES MORE CREDENCE TO

THE ECMWF AS WELL.

WITH THIS IN MIND...THE FCST HAS BEEN CONSTRUCTED WITH THE ECMWF

SYNOPTIC SOLN AS THE GENERAL GUIDELINE. CYCLOGENESIS SHOULD COMMENCE

ACROSS THE NRN GOM MID DAY SAT AND TRACK TO THE NE ACROSS CENTRAL GA

AND TOWARD THE CAROLINA COAST THROUGH 18Z SUN. THIS IS A RELATIVELY

WARM SCENARIO AS FAR AS WINTRY PRECIP IS CONCERNED...HOWEVER ACROSS

THE NC MTNS THERE WILL PROBABLY BE SOME MIXED -FZ/RA/IP DEVELOPING

ACROSS THE HIGHER ELEVATIONS. A MODEST WARM NOSE WILL DEVELOP AROUND

4.5 KFT TO 5 KFT WHILE SFC WETBULBS WILL ALLOW FOR AN ICY PRECIP MIX

ABOVE 4 KFT. RIGHT NOW THE VALLEYS LOOK TO WARM FOR MUCH OF AN

OVERNIGHT CHANGEOVER THREAT. TOO EARLY TO COMMENT ON ICE OR PRECIP

AMOUNTS ATTM AS MASS FIELDS COULD ADJUST SIGNIFICANTLY AS WE NEAR

THE EVENT.

[BrierCreekWx]

I think everyone is on top of this event - I especially agree with the thoughts of RaleighWx in his article. In looking at all the data, I think the best option for most of us, including central NC, is for the southern stream energy to slow down, and allow the northern stream energy to form the 50/50 low sooner, allowing high pressure to build in. The 12z Canadian somewhat does that, and at least half the event appears to be snow from RDU north, potentially upwards of 0.5" of liquid falling as snow, and probably pretty good rates at that.

In most events, it seems like the main energy always slows down with time, and a lot of times that is to our detriment as we already have a cold high in place and it's moving offshore. In this instance, it's the complete opposite, and the slower the southern stream is, probably the better because it will allow for a later phase, and for more cold air to become established. Right now, I am still fairly optimistic about this event, and I think the next 48 hours of model runs are going to be very interesting to watch. As others have mentioned, there really haven't been any legitimate trends established yet so I think all options are on the table still for NC.

[Rankin5150]

A few quick thoughts on the 12z model data....a lot of this will be shop talk.....keep that in mind.

Great post Matthew! We are blessed to have you here!

[nrgjeff]

In a nutshell the 12Z solutions converged except for the Canadian carpet snow bombing. The same issues remain regarding timing with the northern stream. My first did not mention the lead northern stream wave that I'll now call NE Friday wave, because I just assume it is a given and kind of took it for granted. Of course like Grit says (below) it is necessary to get cooler air down into the mid-South. I hesitate to say cold air. My discussion went into a smaller GL s/w originating in the Upper Midwest Saturday. THAT one is giving the models all kinds of trouble because it will help determine whether the southern system phases somewhat or just shears out to sea. Both slower might be helpful per Brier Creek post top of page. Agree with another post (not quoted) that one can't just punt the temp forecast this far out; that's a cop-out. However it is moot if the wave shears out into cold rain nada.

Hope that clears up my older post. Previous posts regarding northern stream action:

That's funny, I want to see the shortwaves and troughiness in the Great Lakes get out of there and into the NE prior to our southwest wave kicking east, for a colder setup. More like the UKMet and NAM look.

...but one can't just throw out the 06Z as rubbish. This far out it is perfectly acceptable for a human or a computer to be forecasting the Texas system behind the GL s/w which is what the 06Z does. That puts our system in subsidence behind the jet streak associated with the GL s/w. Short wave ridging is another way to put it. The 00Z GFS and Euro have our Texas system coming out with/ahead of the GL s/w which is at least neutral...

[HKY_WX]

Saw Allan mentioned the Canadian here are some maps us NC folks will like

Granted it's ice....but with that heavy of rates could probably be snow

It's interesting when you look at the color coding on the second image you can see how the snow is driven by dynamical cooling.

[burgertime]

18Z NAM @84 vs. 12z GFS @90

[WeSuck]

Wow. Huge difference! If only it wasn't the 84 hr NAM but it is a start!

[griteater]

The NAM looks better than any other model to me at this point (not just this run)....not it's strong suit outside of 48-54 hours though.

[BristowWx]

18Z NAM @84 vs. 12z GFS @90

What do you make of that? Less likely the N stream kills it?

[Southern Track]

The NAM looks better than any other model to me at this point (not just this run)....not it's strong suit outside of 48-54 hours though.

So would it be correct to assume that the DGEX this evening will probably look enticing with that look on the NAM at 84? Even though it's just for fun?

[BrierCreekWx]

To me, the 18z NAM looks really favorable for NC. It has the southern stream low in almost the identical position as the 12z CMC, and the northern stream looks better defined, with more confluence which could lead to a stronger high.