Post Christmas storm analysis

Forecast looked pretty good with a general 3-7 inches in the triangle with potential for higher accumulations. Accumulation was close to that conservative estimate with just a couple more inches on the high side. So a 4- 10 inch prediction with more toward the NE would've been perfect for the triangle. But still not bad at all. Timing was good as well with the significant snow arriving after midnight and arriving by lunch. I should've mentioned that NE sections of the triangle would do better than west sections, but I just didn't mention it. The NE sections and just to the east of the triangle did very well with 10 - 13 inches, so the intensity there was unexpected and aided by the fact that there were very little temp issues there and the storm was a wee bit stronger than anticipated.

Here's the map from RAH NWS:

11:00 AM Christmas day update`

Everything looks like a go for 3-7 inches of snow for the Triangle northeast through Williamsburg.

Some light snow may fall late this afternoon in Emporia and Williamsburg with little accumulation expect from this first batch.

The major batch of accumulating snow should come through the triangle late tonight. The RUC and the NAM first bring snow into the triangle by around 7:00 PM. This round is the snow falling in Western NC and down through northern Alabama. This band of precip should weaken as it enters the triangle... Late tonight expect a band of SE to NE oriented precip to move into the region. This will occur as the low deepens off the Georgia coast. This heavier batch of precip is well represented by the GFS and should arrive in the triangle after midnight and should last until about mid morning in the triangle. Up to 1 inch is possible in the triangle with the first batch and 1-2 inches possible north toward Emporia and Williamsburg and potentially higher amounts in Emporia. 3-7 inches is possible with the second round in the triangle. I expect the 2nd round of precip to have higher accumulation rates due to the more powdery nature of the snow. Locally higher amounts are possible.

The snow may mix with rain in the triangle if any falls this afternoon.

11:00 PM Update

Christmas night snow storm 2010:

A significant winter storm for the triangle now appears likely as a low pressure system moves across the gulf coast line tomorrow and eventually up the eastern seaboard off the North Carolina coast. 3-7 inches of snow is possible for the triangle by lunch time on Sunday with potentially higher amounts. Expect about the same amount in Emporia with potentially higher snowfall totals in Williamsburg possible but with less confidence that Williamsburg will see up to 3 inches.

While confidence is much higher at this time, things can still change and the forecast may need to be updated tomorrow morning. Expect the majority of the snow to fall after 5:00 PM Christmas night with a potential for heavy snow.

Significant winter storm appearing more and more likely

Both the GFS and the NAM continue to strengthen the southern energy associated with the storm, as well as phase the storm a bit sooner then earlier depicted. This is likely due to a small piece of energy shooting due south out of the Dakotas. This is causing the northern stream to catch up with the the stronger then earlier depicted southern energy. The RUC appears to be supporting this scenario as well. Even the NAM... which is further east and eventually out to sea... depicts warning criteria snow for the triangle. I need to see what the HPC says about any initialization errors... but right now I think at least a blending of the NAM and GFS makes sense. Will go ahead and up totals to reflect my earlier forecast. Taken literally the NAM is about 7" while the GFS is over 10"... It's the support of the RUC in keeping the southern vort strong that has me thinking the GFS may be on to something.

The snow/rain mix should start late Saturday afternoon with the bulk of accumulating snow falling at overnight/Sunday morning.

Right now I'll go with 3 - 7 inches for the triangle... maybe a bit more conservative for Emporia and Williamsburg at 2-6 inches.

Forecast confidence is still rather low and the storm has the potential to produce around a foot of snow.

I'll update again late tonight at around 11 or so after the next suite of models comes in.

Christmas night storm update:

Huge mess this afternoon.

The GFS came in much wetter laying down 6-10 inches of snow throughout central/eastern north carolina and southern Virginia. This is after showing maybe 1-3 inches at best in the last several runs. This is in disagreement with the NAM, which shows the surface pressure remaining open and broad and the upper features remaining positively tilted as the surface feature ascends up the Atlantic coast. HPC has stated that there were some initialization errors in both models, which is not good at all this late in the game. This is due to a shortwave disturbance in South Dakota... the models have not handled this feature well. HPC suggests to use 6z and 0z data to make the forecast, which is only slightly helpful. ECMWF is not a good short term model and seems to be struggling with short term conditions.

Will have to wait until the 18z models come in to adjust my forecast, but may have to adjust to warning criteria.

Christmas night storm update.

The latest model run show the system phasing late in the game and thus showing a weaker surface feature as well as a more eastern track.

The GFS and ECMWF are now in decent agreement with the surface features. The NAM is too suppressed.. will just throw that out for now.

Things can definitely still change... and in a dramatic way. If the system is a bit stronger and a bit closer to the coast, we could go from advisory criteria snow to a much more significant event. Will lower totals or the triangle to advisory criteria for now. Looking at an all snow event here with decent ratios should warrant at least 2 inches as of now. Will lower totals to reflect both Advisory and warning criteria potential. I may lower the totals tonight if the east trend continues but for now will just slowly taper back snow amounts. This is still a very fluid situation:

Christmas Day: A chance of snow after noon. Little or no accumulation expected

Christmas night: Snow likely. 1-4 inches of snow possible

Sunday: A chance of light snow before lunch. Little or no accumulation expected.

1-4 inches possible for the triangle.... 1-2 inches possible for Emporia

At this time a significant winter storm for the triangle is looking much less likely.

Christmas storm update # 3

The newest GFS model came in wetter and just a bit further west.

Storm total is showing about .8 inches of total precip. Will update the forecast snowfall total if this trend continues.

Still nowhere near as strong as the ECMWF, but a major winter storm nonetheless.

Christmas day/night storm 2010

A significant winter storm for the Triangle is looking more likely on Christmas day through the Sunday. The 12z GFS trended closer to the ECMWF with the ECMWF holding nearly steady... just a bit further west and stronger than 00z...

HPC prefers a 50/50 blend of the GFS/ECMWF with nam being a bit of an outlier at this time, which is not unusual in the 84 hr range. Agree with HPC to mix the GFS and ECMWF despite the impressive consistency of the ECMWF... But caution tells me to not side with a historic snow storm this early. A blending of the GFS/ECMWF is a great track for heavy snow fall in the triangle... A pure ECMWF solution shows a historic bombing low just of the coast dropping warning criteria snow for a large chunk of the deep south. GFS is further east and weaker and thus most of the precip stays along the coastlines.... although GFS likely under doing precip amounts to the NW of the low.

Accumulation rates will be on high side of a 10:1 ratio due to very cold temps aloft. Am thinking that high snowfall amounts is a good possibility. But at this time will stick with only warning criteria amounts for the triangle... will hold off on higher amounts due to model discontinuity this far in advance of the low... intensity and exact location are still in question. Taking qpf literally from the from the EURO gives the Triangle 2 feet of snow with blizzard conditions lasting through Sunday night! This has the potential to not only be a strong phased storm, but a slow mover as well.


Forecast:

Christmas Day: Cold with a slight chance of snow in the afternoon.

Christmas Night: Occasional Snow... the snow could be heavy at times...

Sunday: Snow likely... the snow could be heavy at times especially in the morning... Windy with frigid temps

Sunday night: A chance of snow... windy and very cold

Monday: Decreasing clouds and very cold.

Total accumulation 3 - 7 inches possible.... May forecast higher accumulation amounts as Christmas nears.

Christmas Day Storm 2010

The GFS and ECMWF have some major difference in the amplification of the system. The GFS closes the upper low over the lakes which helps to shear out the surface low in the deep south while ECMWF has the low bombing off the carolina coast. GFS is also a bit quicker with the system, and while it is mostly slow, it does not have much precip associated with it. A 1-3 inch snowfall is likely if the GFS is correct.

The ECMWF is a historic snow storm for most of North Carolina with over a foot possible in the triangle. The historic nature of this storm makes this scenario unlikely... however... with a strong parent high in a decent location (in the northeast quadrant of the great lakes) and supporting upper level dynamics... the ECMWF is a realistic scenario. Still pretty far out in advance of this storm and a more westerly track could even mean mostly rain or ice for the triangle. If the GFS pans out then could see just a minor snow storm. The GFS does seem to be trending toward the ECMWF which has been consistent the past 2 runs. Just to stress the historic nature of the current ECMWF run. It shows about 24 hours of snow, heavy at times, with very high winds... this would be a blizzard for the triangle.

There are legit reasons to support either model run right now, therefore will not support one with confidence this early in the forecast period. Instead I will just mention the incredibly large spread in my forecast to show how difficult it can be to forecast this far out:

Christmas Day: Occasional Snow... especially after noon, but maybe moreso before noon. The snow could be heavy at times or it may stay rather light. Total accumulations of 1 to 8 inches possible

Christmas night: Snow... or no snow. Total accumulation of 0 - 12 inches possible

Sunday: Frigid with a chance of snow in the morning.. Total of accumulation of 0-3 inches possible.

Total storm accumulation of 1-23 inches possible.


Final note: At this time the HPC does favor the ECMWF model, but just a bit weaker which would still likely be a blizzard scenario for the Triangle, but not quite as historic.

12/18 - 12/19

Still expect some mixing, but right now this could be a mostly snow event for the triangle.

Expect snow to begin around 3:00 PM and last till about 9:00 PM from SW to NE with the moderate snow ending sooner than that. Quick heavy bursts of snow have been reported in Charlotte and are possible in the triangle.

Forecast amounts of around an inch look ok for now with only around .25 inches of liquid precip expected.

12/18-12/19 Update

Just need to update the timing a bit on the precip by several hours. Am thinking precip moves in before sunset by around 2:ooPM w/ max intensity potential for snowfall will be between 7:oo and 10:00 PM and letting up around midnight.

NAM showed higher precip amounts especially between 5:00 and 9:00 PM with GFS remaining about the same.

Will keep qpf amounts the same for now.

Dec 18/19 update:

It appears as of now that this storm will produce some wintery weather for the triangle on Saturday night, however accumulation amounts look to be on the lighter side.

HPC prefers a blend of the 00z ECMWF and the 12z GFS. The GFS wraps moisture around a weak low pressure which will be located off the southeast coast Saturday night. WRF model data shows a weak 850 low skirting the S. Carolina/N. Carolina border helping to produce precip along the deformation zone axis. GFS shows about 1/4 inch of qpf for the triangle while the WRF actually spits out close to a half an inch. Expect the precip associated with these features to occur after sun set. The timing should help in regards to boundary level conditions, but I do think some mixing will occur through the event before ending as snow. Reasoning is due to potential warming aloft with southwesterly flow ahead of the 850 low. I only looked at the GFS bufkit sounding since this is what HPC prefers.

Not to get too detailed with the timing, but at this time it appears the best chance for moderate snow associated with the deform zone for the triangle will be between 8:00 PM and 2:00 AM with a potential isothermal layer setting up due to diabatic cooling processes. That's a 6 hour window of potential snowfall with the heaviest precip falling in the middle of that time frame. Expect rain to mix in when the snow is falling relatively light and perhaps remaining all snow during heavier precip. I do think mixing will occur through the event.

Because of this I have to predict only around an inch of snow possible for the triangle on Saturday night.

Will update tonight if there are any significant changes.

12/18 - 12/19 storm

Last night's GFS and NAM had the storm far to the east over the Atlantic and as an open wave, with little to no impact for the triangle.

Today's model runs are a different story with both the GFS and NAM showing the position of the low to be much closer to the coast, with a potential significant snow for the triangle. No reason to post any details until the models show some consistency. I'll do a 1st forecast tomorrow morning or afternoon for the Saturday afternoon/night storm.

Update on 12/16 storm

GFS - Light snow starts at 7:00 AM tomorrow morning, transitions to sleet at 10:00 - 11:00 and then freezing rain at 11:30ish before turning to rain at about 2:00 PM.. .3 qpf rain equivalent before change over to rain.

NAM - Light snow starts at 7:00 AM tomorrow morning, transitions to sleet/zr around 10:30 AM to all rain at noon. rain equivalent precip about .15 - .2 inches. frozen precip less than .1

HPC - Prefers a compromise with the GFS and the ECMWF which is basically a slightly more NWD solution of the GFS.

Forecast:

Tomorrow morning: Light snow starting at around 7:00 changing to a mix of sleet and freezing rain by 10:00... changing to all freezing rain by 11:oo before changing to all rain by noon. Snow accumulation less than an inch possible along with some light ice accumulation of less then a tenth of an inch.

Winter Weather Advisory will probably be issued by the Raleigh NWS office.



12/18 - 12/19 storm... Nice isothermal layer setup in the GFS bufkit soundings.

12/14 update for upcoming systems

12/16 storm:

As of now most of the moisture will be north of the triangle. NAM shows quite a bit of precip extending well out ahead of the surface low. Precip could start out as snow for an our or two before transitioning over to sleet and finally to rain. This looks like it will mainly be a light rain event based on soundings and lack of cold air aloft at approximately H85. Any frozen precip should stick and stay on the ground through rush hour so the morning commute could be troublesome if the precip arrives before the warm air aloft. With this in mind it is important to iterate that the warm air will be located aloft. Therefore expect surface temps to remain an issue until around lunch time.

The biggest issue with this storm is precip amount. Neither the GFS or NAM are showing much at all for the triangle. Most of the precip is to the north. Only .10 to .2 of an inch for the whole event is being shown by both models. Temps may be ok Thursday morning, but the lack of precip makes that irrelevant.

This could be a more significant event if the precip shield and associated dynamics shift significantly south. But as of now a chance of snow between 2-5 am Wed night transition to sleet and then to rain at around noon. This may not be a big snow event but sleet and freezing rain could be an issue during the Thursday morning commute. While this doesn't appear to be a major event at this time, you never know what can happen.

I do think there could be some accumulation and a winter weather advisory will maybe be issued by the NWS... sleet will be the predominant frozen precip type.


12/18 to 12/19 storm:

Potential for a major winter storm.. GFS and Euro coming into closer agreement on a potential major winter storm for the east coast. Cold air concerns exist with this storm due to a relatively weak surface high providing cold air ahead of the arrival of the surface low, which is predicted to track somewhere near or off the North Carolina coast. The Euro is beginning to show a more amplified with the gfs already showing a well amplified system which will undertake bombogenesis as it moves up the coast. This could be a historic blizzard for parts of New England if the GFS continues to amplify the sytem.

This type of set up has led to major snowfalls for the triangle. It's similar to the January 2-3 2002 winter storm which dropped a foot of snow in the triangle, but with one major difference. The strength of the parent high over the midwest is weaker. But the high over the midwest for the future system is a piece of a strong canadian high pressure and expect the low pressure to advect cold air from the north as it starts to move up the coast.

The bottom line is that the triangle could be in a position to get dumped on by the deformation band associated with this system. Several hours of heavy snow fall is possible. This will definitely be a storm to keep an eye on.

Update

Expect light snow to begin falling between 4 and 5. The heaviest snow (at most moderate) will fall this evening between 6 and 10 PM before it ends in a light mix by 1 AM

Up to an inch is possible.

12/4 - 12/5 snow even

An upper level disturbance with an associated surface low will through the triangle region this evening and tonight. Light precip is expected to fall between 6:00 PM through the early morning hours. GFS and NAM are in disagreement on total qpf. HPC actually prefers the ECMWF model at this time. I don't see any reason to disagree as these types of upper level systems typically move through the region quickly. So will go with middle ground qpf amounts.

I expect the surface low to quickly and lightly strengthen as it spins over the App mountains. This occurred with a similar system last year and is supported by theories in centrifugal force in relation to atmospheric spinning parcels. Because of this effect expect slight warm air advection ahead of the surface low which should cause the majority of the light precip to fall as rain or a rain snow mix over the triangle. When the low pressure is to the east of the triangle the precip should transition to snow however, moisture levels will quickly fall as substinance moves over the region.

ECMWF trended sw with the system which would put it closer to the southernmost NAM solution... this could mean a bit more snow than mix.. as warm air advection would not be nearly as strong with a more southern solution.

The ground is warmish but the precip will be falling at night which should enhance potential ground accumulation. A band of moderate snow could fall around and especially north of the triangle as part of the associated weak deformation band. Expect the potential for up to an inch of accumulation especially in the grass areas over this more moderate band of precip.

A dusting to an inch of snow is possible tonight in the triangle.