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.
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.
No comments:
Post a Comment