« Archives in February, 2014

Steady Eddy

There is no reason to change any of the outlines at this point.  I would like to reiterate the threat for significant power outages with widespread power outages likely from 1/4 to 1/2″ of ice with the potential for up to 3/4″, which would be debilitating.  If anything, the tendency would be to reduce snow/sleet totals and raise the freezing rain/ice totals.

We’re still nearly 48 hrs out from the event, so we have plenty of time to make refinements to the forecast.  But you all have time to take care of business and prep for a couple of days without power.  And while power outages can be more random than the weather, it’s better to be prepared than to be cold and eating Beenie-Weenies in your big coat!

More tomorrow.



Liquid Equivalent/QPF

Things continue on track for the main storm to arrive Wed.  We are experiencing a minor ‘flurry’ of activity now.  And we can expect the 2nd round of snow tomorrow, especially south of the Triangle into SC.  Probably very little if any accumulation with that this far north, but there will be accumulations south to the tune of a couple inches.

The headliner begins to spread precip in the Triangle late morning or just after lunch on Wednesday.  It will begin as snow, change to sleet and then to freezing rain.  The biggest question, which remains without an answer at this point, is how long does it precipitate in each form at any given location.  What is very clear at this point and the main point I’d like to drive home is that this storm will drop a lot of ‘something’.  What form that ‘something’ will take will be the debate.  In the met world we call this QPF (quantitative precipitation forecast) or liquid equivalent.  So even though there is uncertainty with how much of each p-type will occur in your backyard, what is more certain is there will be a lot of QPF.  And by a lot I mean over an inch of liquid equivalent.  Consensus among various models and ensembles of those models is centering in on between 1 and 1.5″ of liquid equivalent.  From the Triangle and to the west all this precip will be in some version of something frozen.  So anyway you look at it, it spells crippling winter storm.  Toward Winston-Salem through the Foothills down to Shelby looks confidently all snow.  Then points east of this line could begin to mix with sleet as the storm pulls in a mid-level warm tongue off the Atlantic.  And even farther east then there’s freezing rain to deal with.  Finally, along the eastern Sandhills and Coastal Plain the precip is likely to change to all rain.

Where all these transition zones line up will depend on the exact track of the surface low.  There is still wrestling going on with the track, but not by wide swings…more like quibbling over 100 miles…again, which makes a big difference inland.  Over the next 3-4 run cycles we’ll play these watch the track ebb back and forth, while hoping to get it nailed down.

I promised a map for this afternoon, but instead I’d like to offer a first guess for the Triangle and hold off on a map until tomorrow.  For the Triangle, we begin the real accumulating snow Wed near lunch.  We see 3 or 4 inches before changing to sleet and then add about 1/2″ of accrual of ice from freezing rain.  Then the mid-level cold pushes out the warm tongue on the backside of the low and we change back over to snow for a little more bonus accumulation.  Use this as a guideline to interpolate what you get.  As you go west, you add more snow and less ice.  So that in Winston-Salem they are looking at a foot.  As you go east and south, you get less snow and more ice and eventually a changeover to rain.

Bottom line is that now is the time to be making preparations.  You want to think about changing travel plans (all up the East Coast because this will ride up the coast).  You should also make preparations for loss of power.  1/2″ of ice would be crippling.

NWS is issuing Winter Storm Watches all around valid beginning Wed.

More to come…


The Haters Attack the Technical

First let’s be clear.  The previous post on ensembles was supposed to give broad brushed background information behind the mechanics of ensemble modeling.  That post was not intended to make any pronouncements on the upcoming storm, except to say the Euro is agreeing with itself.  Just information, for you in your next water cooler chat.

Now…what’s new with tonight’s models.  The NAM shows the Triangle as an ice rink. (I think it’s too far west with the low.)  The GFS gives a decent several inches with some sleet on top.  The Euro won’t be in until another hour or so.  But there is also support building in the shorter term US ensembles, the so called SREF.  The 21Z runs are trending totals of the ensemble means up quite impressively…10-12″ in Charlotte and 7-8″ in Raleigh.  Again, this is certainly not a forecast.  Just some interesting jockeying going on ahead of the main event.

Final word for tonight.  This will be a major disruptive event for NC.  Best 1st guess for Raleigh is a couple inches of snow followed by a layer of sleet followed by a glaze of the dreaded freezing rain.  Timing is questionable, but probably Wed AM to begin in the Triangle.  Areas near the SC border begin Tues.

Tomorrow you might begin thinking of changing your plans for Wed and Thus. I’ll have a full outline and a guess map tomorrow, early afternoon.

Ensembles for Dummies

I’ve gotten a lot of questions about ensemble models, so I thought this would be a good time to address.

There are the so-called deterministic versions of the models, which you can think of as the headliner versions.  These are supposedly the best resolution with the best physic schemes.  In addition to the deterministic models, each major global model runs ensemble versions.  There is a control run, which is a slightly dumbed down version of it’s big brother deterministic.  Then the rest of the ensemble suite is comprise of model runs, which are initial perturbed slightly.  The idea is to slightly alter the initial conditions in a manner that represents the inherent uncertainties with weather observation and subsequent reanalysis.  So, in the case of the ECMWF (Euro) there are 50 runs in addition to the control run.  The motivation here is to eliminate the iterative effects of chaos with extended timesteps in the modeling.  What you typically see, long to mid range out, is a wide ensemble spread.  As you approach the event, in the short term, your hope is that the ensemble members begin to look like each other.

Let’s look at an example with the current setup.  These are side by side comparisons from the ECMWF ensembles from 5 cycles ago and on the right from the current 12Z runs.

Euro Ensemble Comp

First off, I should say…don’t take these totals literally.  The Euro treats any frozen precip as “snow”.  So for our upcoming event, we are expecting snow and sleet and freezing rain.  The quick and dirty rule of thumb of 10:1 snow to liquid ratios will not be valid.  These charts show 10:1, chop them at least in half.  Again, what’s more important for this discussion is how the ensemble members have come into agreement.  (in the charts time moves from left to right, and each bar at the top is the snow accum for each of the 51 ensemble members…the graph at the bottom compares the deterministic snow accum to the ensemble mean.)  Note  how the deterministic was much above the ensemble mean 5 runs ago.  Now they match nicely.  Also, note the uniformity of pink on the right in the current run vs. lots of blue and variance on the left.  More confidence.  All this being said, there are still a lot of big questions.  Answers are coming.  I promise!

The new 0Z models are rolling in.  I’ll put some comments later.


The outline for a major Carolina winter storm is coming into better focus.  Finally, the various models are beginning to converge on a unified solution.  Notice I said beginning to…not that they’re there yet.  At issue are perturbations in the southern branch of the jet, their magnitudes and their timing.

Here’s the basic outline.  The arctic front will slip thru NC early tomorrow AM and the colder air will begin to filter in.  There will probably be a couple of snow showers late.  Then the first wave ripples along the front during the day on Tues.  It now appears that most of the associated precip will fall south of the Triangle during the day…south of a line from Greenville to Charlotte to Fayetteville to New Bern in the form of a rain/snow mix to the south, changing to all snow where it precipitates hard enough and on the north of the band where the colder air is.  If there is a shift north with this band, it would bring accumulating snows in earlier than the overnight Tues/Wed timeframe for the real storm. (latest 18Z NAM is hinting at earlier arrival)

Then Wed morning the major system approaches out of the Gulf and rides north along the coast and just offshore.  It appears to be a set up for a formidable storm with high QPF (precip) and extensive winter weather headaches over a large chunk of real estate.  Lots of snow and ice in the South, riding all the way up the Eastern Seaboard.  I like the looks of the 12Z Euro, but haven’t seen it’s ensembles yet.  The 12Z GFS is too far out to sea and whisks the storm away (altho it is now beginning to correct back west).  The 12Z Canadian is, well, very Canadian, eh.  Very snowy and a thumping from SC to Maine with a 961mb low off Cap Cod overnight Thursday.

As I said at the beginning, there are still many questions unanswered and hopefully these next two model run cycles will unify the message.  So, at this point, what does this mean for sensible weather?  It’s a classic NC winter setup with best chances for snow to the north and west and a transition zone to sleet then freezing rain, then all rain at the coast.  Right now it looks like the Triangle will see snow beginning Wed AM, changing to sleet and then possibly to freezing rain.  And you say, “what about accumulations?”  to which I say “that question really isn’t all that important”.  What is important is that there will be a lot of precip.  And the fact that it will all be something wintry is reason enough to say this will be a high impact event.  That’s the bottom line.  It will be a major event for most of the state and beyond.  We’ll fill in details about p-types and quantities over the next couple days.

So…stock up on the essentials: bread, milk, beer…and we’ll watch this evolve.

Complex Winter Weather Event(s) Next Week

It’s been a crazy day.  And while I’ve had time to look at a lot of data.  I haven’t had time to put two or three coherent sentences together until now.  And I’ve literally got to go now, but so may of you are asking for an update.  Here’s the skinny…

We are trying to predict a very complex situation for next week.  I’ll explain later, but here’s what we can say.  It is likely that NC will see winter weather.  There are good chances that the winter weather will be significant.  Timing is questionable, as are the number of systems.  Snow could arrive as early as Tues AM.  And there could be a prolonged duration to the precip.

A more detailed discussion tomorrow.  But if you’d like quicker brief updates, follow me on Twitter @trextrex14.

Buy the Skates!

A very quick post to say that the 12Z runs were very bullish on the a significant winter storm for central NC.  The Euro deterministic was very excited about a whole mixed bag of wintry mess…and a lot of it.  See the accumulated snowfall map (don’t read all of this as snow), which looks like a glacier.

Screen Shot 2014-02-06 at 5.47.25 PM

And not only that, there is great ensemble agreement in a wintry scene of some sort at RDU.  Nearly all the ensemble members print accumulating snow or ice.  See here…

Screen Shot 2014-02-06 at 5.47.01 PM

Of course this is a loooong time off.  At this point, we wait, watch and think about contingencies.

Oh yeah, and there might be a flurry tonight.  Enjoy.

Next Threat

It’s a crazy pattern that we’re in now with an active southern branch of the jet stream.  There are lots of little disturbances blipping by every couple days, and the fun is trying to figure out which one(s) will blow up into a decent storm.  And then figuring out even if it does mature into a surface cyclone whether or not it continues out to sea.

The best guess on the weekend is that a weak system sends a couple of flurries/sprinkles our way tonight.  Then the following system holds a better chance for some development on Saturday with a cold yuck rain…best chances from the Triangle and east.

But the more interesting event is mid next week.  Over the past couple of cycles, there’s been growing model and ensemble support for a significant winter weather event.  We’re 5-6 days out, so at this point it’s just something to watch as it comes better into focus.

Maps, charts and nerdy stuff to come…