Major Update and Analysis.

After looking at the 12z data [and some of the 18z data], I will give you my latest thoughts on the system, as well as certain, specific details in the evolution of the system, and how I expect the system to impact us over the next several days.

Short Technical Discussion:

The 12z model suite came in rather well at a modest consensus among guidance. Nearly all guidance was tracking the storm-system from the lower Mississippi Valley and into Kentucky and South Central Ohio before rapidly deepening across the Northeast. There were still model differences, especially in the track and intensity of the system, but all in all it was nearly similar across the board. And because of this, I do think it is safe to conclude that parts of our area [N. Indiana and NW Ohio] will at least get clipped by the heaviest snow, if not rest in the axis of heaviest snowfall. Again, this is all dependent upon the actual development of the system. However, there is still evidence that the storm might shift paths ever so slightly and affect snowfall amounts. Today's 18z guidance [particularly the GFS and NAM] did not present such a "good" snowfall solution for us. In fact, the NAM trended much drier across the forecast area and moves the system out of the area much quicker than other guidance. For now, the NAM is seen as an outlier given its flat, progressive bias in amplified patterns [as evidenced by what happened with the last storm-system]. The bad news is that the GFS also followed suite, even though it kept the intensifying low and heavier precipitation back west [and we still got a decently heavy snow event]. At this point, I'm favoring the 12z guidance for two major reasons:

1.) The way the shortwave trough is amplifying currently, as well as short-range extrapolations of the shortwave indicate much more digging at the base of the trough AS WELL AS much more interaction of the primary shortwave [seen here over Montana and North Dakota] with a piece of the Polar Vortex farther north [which is ultimately going to be the factor which draws the intense Siberian air mass south into the United States behind the Arctic front]. All of this rules out the NAM solution as of now. We should be expecting a more amplified solution and it appears that models have not caught on quite yet [even the more amplified models]. On this point, the WPC and NWS IWX agree, and in this afternoon's AFD, the NWS did say that they were concerned that the entire storm-system could be stronger and farther northwest than currently predicted [as in the SREF solutions].

2.) The interaction of the strong clipper-system along the U.S./Canadian border currently and the cold-front which will be shifting through our area Saturday night will also allow a further west solution; the reason I say this is because of the fact that the cold front will rapidly slow down as the mean-flow above surface-frontal boundary becomes parallel to it. By this time, the shortwave will interact with the frontal boundary and produce another surface-trough, which, if the shortwave is oriented correctly, will rapidly develop into a 1004 MB low-pressure system by the time it reaches Central and Eastern Ohio. Due to the strong nature of the high-pressure system behind the front, a strong pressure gradient will also set-up. Regardless, I do not see this scenario reflected in the weaker guidance such as the 18z NAM, and hence why I do not believe it will come to fruition. However, better judgements can be made after the 00z guidance comes in tonight.

Now that I've cleared that up, I think we can quite confidently say that the 18z NAM [and possibly the 18z GFS] are both outliers. My own solution is in line with the ECMWF and CMC forecasts, although I believe a slight shift east or west is possible. A more substantial eastward shift is altogether unlikely but it is quite possible and not something to be dismissed at this time.




Now to the actual precipitation.

While snow-totals across the region will largely be dependent upon the track, speed and intensity of the low, another major factor which could affect snow-amounts is the moisture input into the area. Right now, we have too extremes/outliers in the guidance. On the one hand, the ensemble SREF mean is indicative of a very wet system over the area. Although it has a difficult time accurately printing out mean snow-totals that are realistic across the area, the amount of moisture that gets involved in the system [in the mean] is incredible and likely overdone. On the other-hand, we have the NAM and the high-res NAM which appear to be the "driest" solutions on the board. And the very reason why they are drier is for the very same reason that I described above; they do not amplify the shortwave aloft enough, and thus under-develops the surface-low, which in turn limits Gulf-return flow aloft. Even though moisture profiles will be less than ideal [mixing ratios only near 4 g/kg], I do believe we will see plentiful moisture from the Gulf of Mexico, and due to the anafrontal nature of the original wave, most of the precipitation will be behind the front [hence why we are seeing a major snowstorm].

Because of this, I believe QPF [Quantitative Precipitation Forecast] totals will exceed 0.5-0.6 inches across the entire area for the total event [Saturday night through Sunday evening], with localized higher amounts of 0.8-1 inches, especially along and southeast of the U.S. 24 corridor. Given that average snow-ratios will be around 16:1 or 17:1, snowfall totals should easily reach the 8-12" snowfall range especially along and southeast of the U.S. 24 corridor. However, if the cold-front does end up moving faster across the region and we see colder air, ratios could be as high as 20:1, which will enhance snowfall amounts.

Any other details regarding precipitation will have to be refined in now-casting and the use of mesoscale models, because right now it is extremely uncertain as to where heavier bands of snow will set up across the area, when and for how long. However, it is certainly possible that bands of 1"/hr could set up around the area and to our southeast, which could easily enhance snow totals.

NON-TECHNICAL DISCUSSION
In brief, here is what I expect from this winter storm across the area:

Snowfall totals will range from six inches in the northwest [especially in N. Central Indiana and SW Michigan] to as much as 12 inches along and southeast of the U.S. 24 corridor. However, this is subject to change [given what I discussed above], and especially if we see a stronger storm-system. If we see a weaker storm, snowfall amounts across the area will range from four inches in the NW to nearly eight inches in the east/southeast.

Blowing and drifting snow will be a major concern, especially after the snowfall ends as the storm "bombs" out to our east. However, as I discussed above, if we can get the storm to strengthen faster, we will likely see near blizzard conditions DURING the storm. Again, its very contingent upon a few seemingly minor details in the current upper-air analysis.

And because of this, we will have to also remain cautious about wind-chills, given that temperatures will fall down to about -11 Sunday-night after the storm passes through. Wind-chills with winds of 25 mph produces wind-chills of -30 to -40, which isn't pleasant for the human-body. Similar conditions will continue Monday into Tuesday and early Wednesday.

I will have more details tomorrow on this potentially crippling winter-storm.

**WINTER STORM UPDATE**

While I am still waiting on the rest of the 12z guidance to come out to get a full update, I think we have enough of a consensus this morning from the 00z guidance to have more confidence in the winter-storm solution. So I will release a brief update here and then another more detailed post later this afternoon detailing several potential factors in regards to the track of the system and its development.

First, several things need to be pointed out.

1.) Most, if not all of the 00z guidance came into agreement with the ECMWF [or at least close to it]. There are, however, still some disparity between the different tracks of the system which needs to be watched for the placement of the axis of heaviest snow.

2.) There is still large disagreement on final snow totals. While the global models seem "hell-bent" on producing 8-12" amounts [especially the GFS and ECMWF], the longer-range mesoscale models are showing much less snowfall [although the latest NAM was more bullish with snow amounts; however it hasn't been all that consistent]. This is largely due to the progressive nature of the storm on the NAM. However, I've already noticed some questionable features on the NAM's forecast that makes me doubt its weaker solution.

3.) Snow-ratios should begin around 11:1 on Saturday-night given the mini "heat-wave" that we will be seeing [temperatures in the upper 20's/lower 30's], with snow-ratios gradually increasing throughout the day Sunday as the Arctic front pushes through the area [possibly ratios of 16:1 or 17:1 during the heaviest snowfall]. This could enhance snow totals if we can see stronger banding and/or greater moisture transport into the system.

4.) Blowing and drifting snow will be a major concern, especially after the snow has ended. As the low bombs out over the NE and Southern Canada, winds should increase to the 20-25 mph range with higher gusts likely. This will lead to dangerous and nearly impassable roadways in the hours following the end of the storm. On top of that, temperatures will plummet into the -10's Sunday-night, which will prevent any melting of the snow on roadways. It will make it nearly impossible for snow-trucks to clear roads.

5.) Extreme cold will follow the winter-storm. Wind chills will likely drop into the -30's and -40's starting Sunday night and lasting through Tuesday, especially in the morning hours. Temperatures are not likely to make it above zero from Sunday-night through early Wednesday morning.

UPDATE: The NWS has issued a Winter-Storm Watch for the area, calling for 6-12" of snow areawide, with the potential for heavier snowfall along and  southeast of U.S. 24. 

WINTER-STORM POTENTIAL UPDATE

Okay, we have a bit more information on the upcoming winter-storm this Sunday. But first, a brief summary of today's storm.

As originally anticipated several days ago, snow totals ranged from 6-10" across the region, with the heaviest snow amounts across lower Michigan due to the clipper system on Tuesday-Tuesday night. However, because of the fluffy nature of the snow, there will be a lot of blowing and drifting this afternoon. And this won't even be the worst of it; with the decoupling of the boundary-layer tonight and under clearing skies, it appears that many areas will see temperatures rapidly falling below-zero tonight. If light winds hold on longer, we could see wind-chills as low as -15 to -20, which approaches dangerous criteria.

However, for the weekend-storm, we have a different scenario. As of now, model consensus seems to indicate that most of the area, especially across the east and southeast [east and southeast of Fort Wayne that is], will see a significant snowfall event. While the exact track of the storm and its intensity is still in question, confidence is growing in a major snowstorm for the area, especially if the ECMWF and CMC verify. Given that the 12z GFS and the 12z NAM are outliers compared to most guidance, it appears that the forecast will favor the ECMWF and CMC solutions right now. And both models are currently indicating snowfall amounts in the 10-12" range, based off of 10:1 ratios. And if the storm develops as quickly as guidance is currently indicating, it appears that we may see reduced visibilities and near blizzard conditions. However, this is not set in stone yet, and there is still some model variability [hence why the NWS will not issue any advisories, watches or warnings until Friday night or Saturday for this event] and hence some uncertainty. There is still the question of phasing and storm-track, which will definitely affect how much snow we get from the system.

As of now, I do not really have an anticipated range for snow accumulations, as there is still too much uncertainty, but I would venture to guess that 8-12" accumulations are not out of the question, but I'm willing to bet that a safer guess is going to be around 4-7" [but likely a lot more if the stronger-storm scenario verifies].

HOWEVER, what we do have more confidence in is the record-breaking cold that will follow the storm. Temperatures are likely to reach their maximums on early Monday morning before dipping below zero, which means early morning temperatures in the lower single digits. IF the cold-front blasts through as currently predicted, temperatures late Monday afternoon will be below-zero with gusty winds and possible lake-effect. This will cause wind-chills around -25 [thus the possibility of wind-chill warnings]. However, the coldest weather is expected Monday-night through Tuesday-night. High temperatures on Tuesday are expected to reach a maximum around -5 to -8 [according to WPC forecasted highs]. Lows Monday-night will dip down to about -16 to -19 across the area. By Wednesday, however, we should see temperatures rebounding to the upper single-digits [still well-below normal] and lower teens before another clipper-system moves through with the potential for more snowfall.

I will have more updates on this potentially significant event tomorrow morning.

***WINTER WEATHER UPDATE***

Here's a brief summary of what I expect to occur over the next few hours for the area:

1.) Light to moderate snow will continue into the late morning, possibly early-afternoon, before tapering off. Some periods of heavier snow and reduced visibilities are possible, especially as the surface-low moves to our east, and causes some heavier bands from our south to move northward. However, this period of heavier snow will be brief as the storm transfers to the coast.

2.) Snow-ratios are likely to increase as the day progresses, and especially as the snow becomes lighter later this morning. This will allow for a snow that can accumulate more than the small crystals that we saw last night and into this morning. At the same time, temperatures will likely be dropping as frigid Arctic-air sags in from the north. This in combination with gusty winds will cause blowing and drifting snow through the afternoon and evening hours. The cold temperatures will make it rather difficult for roads to melt as well, leading to nasty road conditions [even on the main highways].

3.) Additional snow accumulations of 2-3" are possible today, especially along and southeast of the U.S. 24 corridor. This will lead to storm-total accumulations of 6-10" area-wide [36-hour accumulations from Tuesday-night and Wednesday included].

POTENTIAL WINTER STORM

***POTENTIAL WINTER-STORM***

Since the holidays are almost over, I'll be making more weather-related posts here during the next few weeks. I do not expect to be absent and I should be able to provide you with the most up-to-date weather forecasts now. 

But for now, it appears that we have a potential winter-storm on our hands for the mid-week period. Right now, models have come to a general consensus on the formation and track of a low-pressure system from S. Colorado through the Southern Plains and into S. Ohio from Wednesday through Thursday. This same primary low will then weaken as an intense secondary-low develops off of the East Coast. Overall, depending upon the track of the storm, the intensity of the initial shortwave and the timing of secondary development, we could be seeing a major winter-storm, stretching from Iowa and Illinois through N. Indiana and Ohio and into the Northeast/New England. Due to the bombing nature of the secondary-low [due to CISK and its interaction with the baroclinic zone generated by the Gulf stream], an intense winter-storm is expected for areas farther east.

Several factors need to be monitored for snow accumulations with this storm-system.

1.) Moisture- Generally, Colorado-lows are not moisture-starved and have ample-access to Gulf-moisture. At this time, moisture does not appear to be a concern that will hamper snow accumulations.

2.) Snow-ratios/depth of cold air- Unlike the last winter storm [December 14th], this winter-storm is likely to bring much higher ratios. 850 MB temps during the height of the storm are only likely to be around -7 to -9 C and surface temperatures are likely to be in the upper-teens. This in combination with a deep DGZ layer [Dendritic Growth Zone] will likely produce snow-ratios on the order of 15:1 to as much as 18:1. However, this needs to be ironed out over the next few days, as it is notoriously difficult for models to get thermal profiles correct even one day out. However, in general, it is highly likely that snow-ratios will be higher for this event.

3.) Intensity/track of the primary-low: This is likely to be the trickiest detail to forecast as of now, and it will likely be the most significant factor in determining who receives the most snow from this system.

At this point, the NWS and WPC are both leaning towards the ECMWF solution, which shows a stronger primary low tracking into S. Ohio as a highly amplified short-wave induces cyclogenesis. The 00z run late last night and early this morning continued the trend of a more amplified primary short-wave, which leads me to believe that the primary low will be stronger. However, given that the shortwave appears to be more amplified, the primary-low is likely to track farther south than what the GFS and other models are currently predicting. IF this is the case, then I can definitely see higher snowfall amounts for the area. Because at this point, the GFS and long-range NAM both have the low-pressure system tracking farther north and bringing the heavier snow totals to areas in S. and Central Michigan.

Right now, the ECMWF appears to have a better handle on the system, but this needs to be watched. If the ECMWF solution verifies, its likely that most of us see 4-8"+, with the heavier snow totals falling north of U.S. 24. And because of this, the NWS has issued a Special Weather Statement for the entire area, detailing the potential for a winter-storm. I will continue to monitor this event over the next few days.

I will have a map out sometime this week [likely before Wednesday].