WINTER WEATHER UPDATE:
The NWS has issued a winter weather advisory for the entire area through noon tomorrow. This winter weather advisory was issued due to growing concerns for icing potential as well as snowfall potential. Here's the scoop.
The mesoscale models have been rather insistent on bringing in at least a period of moderate to heavy snowfall for one or two hours across the area, especially around 5 a.m. tomorrow morning. I'm rather doubtful that we see heavy snowfall tomorrow morning, due to the presence of dry air at the onset of the event, but it appears to be reasonable, given the potential for jet-streak induced low-level frontogenesis, and snow-banding, as well as the wet-bulb cooling effects, which will tighten the baroclinic zone. Also, it appears the system will take a further southeast track than originally indicated due to the strong blocking pattern to our north and east. This will then cause stronger forcing to clip the area (though not in the deformation zone, which will feature the heaviest farther west over the Mississippi Valley), potentially leading to more snowfall than originally indicated. Not only this, but NAM and RAP forecast soundings, when compared with actual soundings from this morning, were way off in regards to water vapor amounts in the mid-levels. Actual soundings were showing dew point depressions of 15-20 degrees, while forecast soundings were showing dew point depressions of 40 degrees, indicating that these models have an inherent dry bias. For this reason, I can see credibility going to a forecast of heavier precipitation tonight.
Another reason that I think that precipitation amounts will be higher is due to the fact that the strongest moisture flow is currently east of what was originally forecasted. In fact, the main heavy precipitation regions (snow, ice and rain) have shifted eastward, and are contributing to snow banding on the eastern edge of the warm-frontal system.
What are potential caveats and mishaps that may leave us with little more than a dusting of snow? One could be the fact that some of these mesoscale models usually have a slight bias towards higher QPF, Quantitative Precipitation Forecast. Because of this, they will tend to forecast heavier precipitation. So, the NAM's 0.3 to 0.5 inches of precipitation tonight may be an overestimation. On the otherhand, the RAP has an inherrent "dry" bias. It is showing less than 0.09 inches of precipitation tonight, which indicates that its inaccurate calculations of upper level forcing, as well as low level flow and moisture calculations are inaccurate. Another could be increased dry Canadian flow off of a strong high pressure system located to our northeast. If I somehow miscalculated the influence this high pressure system will have on our weather, then we may be in for a bit of a surprise when less precipitation falls tonight. Other factors could include the destruction of snow bands as they impinge upon the area (related to mid-level dry air, which at the time, does not seem apparent on WV imagery. But since WV imagery is quite obsolete with a thick overcast, its not a good idea to make an analysis from it), moisture flow which is diverted south and east of the area (due to the developing convection to our south.). As of this time, though, I believe these valid reasons will become obsolete, and probably have less effect on our weather tonight.
Here's a forecast reflectivity chart from the latest RAP. As you can see, it has a heavy band of precipitation (presumably snow) moving slowly north across far Eastern Indiana and Western Ohio. This could be a significant factor (if it verified. I believe it will because the RAP has been rather consistent with such a band of precipitation over the last four runs). The one problem I have with it though, is that the RAP is exhibiting its usual bias; it brings in the precipitation way too quickly. The time stamp says 06z Friday, which translates to 1 a.m. tomorrow morning. It's kind of obvious that its a few hours too early with this. On another note, based on the latest radar trends, it seems as if the NAM may be too slow with bringing in precipitation. So, I will go with a compromise, which leads me to believe that snow will begin lightly falling at about 11 p.m. southwest of Fort Wayne, 1 a.m. from Fort Wayne to Antwerp, and 2 a.m. farther east. The precipitation will begin intensifying and become heavier by about 5 a.m., before snow begins to mix with and change to freezing rain. This will lead to ice accretion upon roads and other surfaces, making for very hazardous driving during the morning commute. This will likely result in school delays (possibly closings, but I'm highly doubtful of the amount of ice that falls tomorrow).
As for my forecasted precipitation amounts, I believe they will end up in between 0.2 to 0.5 inches, with the higher amounts southwest of Fort Wayne. Some of this precipitation looks to remain as snowfall due to strong mid-level cooling from dynamics and evaporational cooling, while a significant portion could end up as icing accretion. This will lead to snowfall amounts of around 1-3 inches areawide, with corresponding icing amounts of 0.1 inches. Freezing drizzle/light snow mix will continue through the midday hours before tapering off. I'm expecting little or no liquid precipitation. If there is, I suspect that significant cooling from snow and ice will continue to allow for ice build-up.
Have a great evening everyone!
The NWS has issued a winter weather advisory for the entire area through noon tomorrow. This winter weather advisory was issued due to growing concerns for icing potential as well as snowfall potential. Here's the scoop.
The mesoscale models have been rather insistent on bringing in at least a period of moderate to heavy snowfall for one or two hours across the area, especially around 5 a.m. tomorrow morning. I'm rather doubtful that we see heavy snowfall tomorrow morning, due to the presence of dry air at the onset of the event, but it appears to be reasonable, given the potential for jet-streak induced low-level frontogenesis, and snow-banding, as well as the wet-bulb cooling effects, which will tighten the baroclinic zone. Also, it appears the system will take a further southeast track than originally indicated due to the strong blocking pattern to our north and east. This will then cause stronger forcing to clip the area (though not in the deformation zone, which will feature the heaviest farther west over the Mississippi Valley), potentially leading to more snowfall than originally indicated. Not only this, but NAM and RAP forecast soundings, when compared with actual soundings from this morning, were way off in regards to water vapor amounts in the mid-levels. Actual soundings were showing dew point depressions of 15-20 degrees, while forecast soundings were showing dew point depressions of 40 degrees, indicating that these models have an inherent dry bias. For this reason, I can see credibility going to a forecast of heavier precipitation tonight.
Another reason that I think that precipitation amounts will be higher is due to the fact that the strongest moisture flow is currently east of what was originally forecasted. In fact, the main heavy precipitation regions (snow, ice and rain) have shifted eastward, and are contributing to snow banding on the eastern edge of the warm-frontal system.
What are potential caveats and mishaps that may leave us with little more than a dusting of snow? One could be the fact that some of these mesoscale models usually have a slight bias towards higher QPF, Quantitative Precipitation Forecast. Because of this, they will tend to forecast heavier precipitation. So, the NAM's 0.3 to 0.5 inches of precipitation tonight may be an overestimation. On the otherhand, the RAP has an inherrent "dry" bias. It is showing less than 0.09 inches of precipitation tonight, which indicates that its inaccurate calculations of upper level forcing, as well as low level flow and moisture calculations are inaccurate. Another could be increased dry Canadian flow off of a strong high pressure system located to our northeast. If I somehow miscalculated the influence this high pressure system will have on our weather, then we may be in for a bit of a surprise when less precipitation falls tonight. Other factors could include the destruction of snow bands as they impinge upon the area (related to mid-level dry air, which at the time, does not seem apparent on WV imagery. But since WV imagery is quite obsolete with a thick overcast, its not a good idea to make an analysis from it), moisture flow which is diverted south and east of the area (due to the developing convection to our south.). As of this time, though, I believe these valid reasons will become obsolete, and probably have less effect on our weather tonight.
Here's a forecast reflectivity chart from the latest RAP. As you can see, it has a heavy band of precipitation (presumably snow) moving slowly north across far Eastern Indiana and Western Ohio. This could be a significant factor (if it verified. I believe it will because the RAP has been rather consistent with such a band of precipitation over the last four runs). The one problem I have with it though, is that the RAP is exhibiting its usual bias; it brings in the precipitation way too quickly. The time stamp says 06z Friday, which translates to 1 a.m. tomorrow morning. It's kind of obvious that its a few hours too early with this. On another note, based on the latest radar trends, it seems as if the NAM may be too slow with bringing in precipitation. So, I will go with a compromise, which leads me to believe that snow will begin lightly falling at about 11 p.m. southwest of Fort Wayne, 1 a.m. from Fort Wayne to Antwerp, and 2 a.m. farther east. The precipitation will begin intensifying and become heavier by about 5 a.m., before snow begins to mix with and change to freezing rain. This will lead to ice accretion upon roads and other surfaces, making for very hazardous driving during the morning commute. This will likely result in school delays (possibly closings, but I'm highly doubtful of the amount of ice that falls tomorrow).
As for my forecasted precipitation amounts, I believe they will end up in between 0.2 to 0.5 inches, with the higher amounts southwest of Fort Wayne. Some of this precipitation looks to remain as snowfall due to strong mid-level cooling from dynamics and evaporational cooling, while a significant portion could end up as icing accretion. This will lead to snowfall amounts of around 1-3 inches areawide, with corresponding icing amounts of 0.1 inches. Freezing drizzle/light snow mix will continue through the midday hours before tapering off. I'm expecting little or no liquid precipitation. If there is, I suspect that significant cooling from snow and ice will continue to allow for ice build-up.
Have a great evening everyone!
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