A White Christmas for Many, but a Price to Pay

The Sunday-Sunday Night storm is shaping up to be a more dramatic system. Saturday night, winds will strengthen out of the SSE to 25-35, but with gusts to 45+ on the hilltops and along the L Erie shoreline. These winds will push temps up into the low/mid 50s by Sunday morning. Showers will increase later Sunday morning, and there may be a gusty tstorm as a sharp cold front crosses the region during early afternoon. SW winds will strengthen behind the front to at least 25-40 during the course of the Bills game, with gusts to over 45 by late afternoon. Precipitation will temporarily taper off as a "dry slot" behind the front takes over. Lake effect snow will gradually develop during the evening (if not very late afternoon) and pick up as some moisture gets back into the flow. The newest NAM model run suggests winds from 240 degrees much of the overnight, which would deliver much of the snow into the Northtowns (Amherst, Clarence), nrn Genesee, srn Orleans & southernmost Niagara Cos. The GFS seems to run more along a 250 vector, with a more rapid veering to 260 by and during the morning. 250 favors Buffalo.

Limiting factors: Wind shear at the outset, and dry air into early evening, before some more humidity returns later in the evening.

There is also some potential for Sunday afternoon & evening winds to go from being merely strong to High Winds (a severe weather term) which would pose the threat of localized property damage and increase shear. At this midday point, the High Wind looks like a 40 yes/60 no probability. The late night NAM will help with this factor.

Things May Get Interesting After All....

The last 3 runs of the NAM and, to a lesser extent, the 12z run of the GFS now display a better potential for some accumulating lake snow by Sunday evening. Following a cold frontal passage around midday Sunday, a tight pressure gradient will produce strong winds and cold advection into the evening. There are some signs the boundary layer winds will back to either SWly or WSWly for much of the evening, with temperatures at 5000'/850mb becoming sufficiently cold to bring about some lake effect. Now that Lk Erie is down to 36 degrees, the lapse rate in temperatures between 850mb and the lake surface has dropped off. Earlier in the season, nature was able to crank some lake effect with an 850mb temp of -7 (C). Now, it needs to be around -9 or -10. However, during Sunday evening some lift will be generated by an upper level low. Of course, it's still too early to determine precise boundary layer wind directions, and the GFS has drier air over us Sunday evening than does the NAM, which can dampen activity considerably.

Winds will eventually veer to a more Wly or WNWly orientation on Christmas Eve, but there will still be some snow showers and limited lake snow, the latter being mainly in Ski Country and the srn tier. It looks dry and seasonable for Christmas.

Weather Photos - News 4's Newstracker

Thank you to all the Newstrackers that submit your weather photos. They look great!

White Christmas Chances

We already had a thread on this topic, but it's buried further down now, so we'll start a new one. As of Monday night, there are indications a vigorous low will go by on Sunday, preceded by a significant warmup with rainshowers later Saturday evening into Sunday, followed by changeover to Snow Shwrs. The winds behind this frontal passage do show a southwesterly orientation, but it remains to be seen whether the boundary layer/lower atmosphere will get cold enough to generate lake effect. This morning's GFS model indicated it would remain too mild for anything significant, but the later (18z) run brings the temperatures at 850mb/5000 feet to be at least marginally cold enough for lake effect. Moisture availability remains marginal as well. Winds will veer to more northwesterly during Christmas Eve, so late Sunday/Sunday night in this 18z run would be our best chance for a fresh coat near the metro area. This far out, I hope you'll remember, lake snow with a quick moving storm system is something of a crapshoot.

Communicating Uncertainty to the Public

People want answers. How much is it going to snow in Orchard Park? Could the sleet make it up to Wheatfield by 9am tomorrow? Those kinds of answers. Sometimes we have those answers but many times we do not.

To start with, meteorology is a physical science which is--to say the least--inexact. We are on a spinning globe, 3/4 of which is covered in water and ice, being heated by a thermonuclear furnace 93 million miles away. We're dealing with fluids and gases and how they interact, along with differing land topography, plant cover, snow cover, & different reflectivity of the land (dark soil absorbs far more of the sun's heat, while ice and snow reflect much of it back toward space), to name a few of the changing variables. Sea surface temperatures, and where warmer or colder temperatures are located in the Pacific have a HUGE effect on weather as well. So, weather is not something akin to Leggo blocks where everything snaps neatly into place.

As for the issue of uncertainty, not all forecasts are created equally. I'm not referring to the training and experience of various Buffalo tv weathercasters and meteorologists--I'm referring to forecast confidence. Verification scores of forecasts generally show that competent meteorologist produce forecasts that are rather accurate 80% of the time for the first 36 hours. But that includes some relatively easy calls, such as when we're in a stagnant, stable weather pattern in which conditions will vary little for a few days. For the tougher calls, I'd venture a guess those probably register closer to 60% accuracy, which would still be pretty good, and getting better.

When meteorologists occur scientific conferences (for example, WIVB sends me to an American Meteorological Society once each year for continuing education), a great deal of time is spent by lecturing scientists on the necessity to communicate UNcertainty, in order that our public understands a particular forecast carries certain probabilities of not working out. The NWS uses probability percentages of precipitation as one way of communicating uncertainty. For myself, I've chosen not to use them in our on-air forecasts because my experience tells me many people don't understand the meaning of those percentages. A 30% chance of snow, for example, seems to mean to many that 30% of the area will have snow. That's not what it means, though. A 30% probability means that any given location in a forecast area has a 3 in 10 chance of having measurable snow. I've even seen a few meteorologists make this error. So, I use more informal means of communicating uncertainty, as you've seen on this blog prior to the weekend storm and on the air--letting folks know that computer models are at odds with one another. Sometimes it's in my inflection pattern and, I suppose, facial expression. If I had a paying client who wanted the most precise information possible, I would assign probability percentages to that forecast.

In any case, it's very important for you to know the uncertainty in a forecast or, for that matter, in environmental concerns and scientific controversies. Let's take it to a level where the stakes are higher; suppose you go to your internist with a worsening dull ache in your abdomen. After ordering tests, I think you'd want your doctor to give you the complete perspective on how certain or uncertain he or she is about your diagnosis before he begins treatment.

So, we're not going to present each and every forecast to you as if they were all created equally. Some are high confidence forecasts, and some are low, and you need to know that. Speaking of which, as of today, a forecast for a White Christmas with new snow is a lower confidence forecast.

Let's Get Another Storm Thread Going

The other one is simply too long.

At 2pm, drier air has moved into the srn tier, where little precip is falling. On the Niag Frontier, it now appears the moderate to occasionally heavy snow will continue much of the time into this evening. Still calling for anther 3-6" on top of what's fallen between now and 8pm, with another couple of inches possible overnight after that. As previously posted, heaviest amts will be to the north of Buffalo, especially Niag & Orl Cos. I stand corrected on a Wellsville report I've been forwarding on this blog. The automated observation there appears to be faulty (it's showing 49 at 2pm), since no other readings in that region are anywhere near as mild--so you can toss that out.

Surface pressure at the Airport was down to 29.15" at 1pm--quite low and still falling, as the parent/interior low passes by so close to us, and the coastal low undergoes significant deepening.
NE winds will back to NW and increase to 15-30 (just look at the Cleveland broadcast), with some gusts to over 30, producing occ'l near whiteouts later today and tonight--especially in open country.

These 2 areas of low pressure are occurring in what we call the synoptic or larger scale. But we also have to watch much smaller scale (mesoscale) features within the storms' circulations. Last night, a synoptic scale warm jet occurred just off the surface as the low moved so far west of us.
This was a feature our Super Microcast and the NWS NAM models were indicating in their output. Obviously, we're no longer under the influence of that feature. Another clue last night as to how far the low was moving to our west would have been to check the pattern of barometric pressure falls out ahead of the low. Generally, the deeper falls in pressure occur in a corridor-of-sorts, and provide something of a path of least resistance for the low to follow. Pressure falls, of course, can't be plotted until the storm exists--so that kind of hand and computer analysis could not have been done Thursday. Even on Friday, with the embryonic system still showing little at the surface, it really couldn't be done in a way which would have benefited our local forecast needs.