RNS and Erica's Winter Outlook 24 hours early>>>>
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The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or STORM2K.
The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or STORM2K.
nice descriptions of CSI. I've noticed recent work seems to highlight the sources of that mid-level frontogenesis. Apparently a component of the warm conveyor belt is wrapped around the nw side of the cyclone, and even without occlusion occuring, there can be a TROWEL...which, as you've said, can lead to heavy snow bands(given near 0 EPV and sufficient moisture).
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Stormsfury
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RNS wrote:Ah...notice how on the GFS (MRF) analysis for 0Z (in 2C incriments) 3/14/93...how there is a strong thermal gradient at H85 between the warm sector, and the very cold air thats being drawn in behind the low.
anytime one observes the tightening of the thermal gradient like that at any level, it usually indicates the presence of enhanced frontogenesis (which is a tightening of the thermal gradient over a particular area), in addition to enahncing precipitation, forntogenesis tends to prolong the life cycle of CSI.
the best overall set-up for this is one would want to have the symmetrically unstable layer above the sloping frontogenesis, in an environment which is sufficiently saturated.
Ahhh, yes ... very interesting that you bring this up ... this is the only time I can ever recall in Charleston that strong CAA (Cold air advection) was brought in on strong Southwest winds ...
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WEATHERGURU
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things like that can happen when you have systems which become this strong and take on an extreme negative tilt. the satrongest temperature advection occures in the warm sector on a southeast to east wind in conjunction with the triple point low between the cold and warm, and occluded frontal boundaries.
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WEATHERGURU
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nice descriptions of CSI. I've noticed recent work seems to highlight the sources of that mid-level frontogenesis. Apparently a component of the warm conveyor belt is wrapped around the nw side of the cyclone, and even without occlusion occuring, there can be a TROWEL...which, as you've said, can lead to heavy snow bands(given near 0 EPV and sufficient moisture).
near zero or slightly pos EPV is alright...but to be sure that a layer is symmetrically unstable i like to see -EPV. Its related to the thermally direct circulation (or DTC however one wants to refer to it) which has a trajectory up the warm side of the frontogenesis. lets not forget though that in addition to the forntogenesis, and sufficient moisture, one would also like to see strong negative omegas in conjunction with both of those factors.
i did a case study on CSI a little over a year ago (after the Jan 6, 2002 event...using that event as an example to prove some things)...and now that ive sparked this unrest abvout the subject i/ll try to get something together to post on here later tongiht or tomorrow so that everyone can understand it as it is quite a complicated meteorological process.
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weather guru,
here you go: (using DTX):
SNOWFALL (AVG 42): 45-50" mainly the product of a greater number of storms which track up along or just west of the applachains.
TEMPERATURE: -0.5 to -1.0F or slightly colder than normal. the best deviations below normal will be in the southeastern part of the country.
here you go: (using DTX):
SNOWFALL (AVG 42): 45-50" mainly the product of a greater number of storms which track up along or just west of the applachains.
TEMPERATURE: -0.5 to -1.0F or slightly colder than normal. the best deviations below normal will be in the southeastern part of the country.
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WEATHERGURU
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http://meted.ucar.edu/norlat/bandedsnow/
That's what refired my interest in this stuff lately. Yeah, isn't the omega at least mostly due to the frontogenesis? I remember them talking about the difference between purely convective snows due to CI, versus CSI. There you would have theta E surfaces tilted to it is just decreasing with height, as opposed to being tilted nearly vertical with a CSI situation. I would think much more thunder/lightning would occur in the CI situation with elevated convection...alot more fun IMO. Then again, CSI setup probably produces a more extended period of heavy snow. Also, They seem to think 0.25 EPV is the prime value, but as you say, I think that could be debated. What surprised me was the highlighting of this occuring in fairly weak systems. Complicated, but good stuff to know.
That's what refired my interest in this stuff lately. Yeah, isn't the omega at least mostly due to the frontogenesis? I remember them talking about the difference between purely convective snows due to CI, versus CSI. There you would have theta E surfaces tilted to it is just decreasing with height, as opposed to being tilted nearly vertical with a CSI situation. I would think much more thunder/lightning would occur in the CI situation with elevated convection...alot more fun IMO. Then again, CSI setup probably produces a more extended period of heavy snow. Also, They seem to think 0.25 EPV is the prime value, but as you say, I think that could be debated. What surprised me was the highlighting of this occuring in fairly weak systems. Complicated, but good stuff to know.
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EPV values of 0.25 are alright IMO for considering CSI, however one would need very strong frontogenesis below the symmetrically unstable layer in order to maintain it.
and yes...stronger frontogenesis would tend to enhance omega. however the best environement IMO for strong UVM is upper level divergence above surface convergence. also...sharp downstream ridging northeast of a cutoff low is usually a favorable environemnt for PSI (or CSI if RH/s are suitable), due to the fact that the absolute vorticity of the geostrophic flow underneath the ridge will normally be weaker...possibly telegraphing inertial instability. normally the stronger the vort max associated with the cutoff low...the weaker the absolute vorticity of the flow will be underneath the ridge, thus the better potential for inertial instability in that region.
IMO (and as i was taught)...using theta-e and momentum surfaces or for that matter slantwise CAPE to predict CSI is obscelete and somewhat unreliable. cross-sections of EPV, frontogeneis, omega, and RH are the best was to assess wither or not the environment is symmetrically unstable.
we/ll be dealing with these situations quite a bit this winter, but my advice (FWIW) would be to use cross-sections of EPV, frontogeneis, omega, and RH instead of comparing momentun surfaces and theta-e.
both CI and CSI were big factors in the extreme snowfall i received from the January 6 event. (in total i had 11 inches in 5 hours!!!)
and yes...stronger frontogenesis would tend to enhance omega. however the best environement IMO for strong UVM is upper level divergence above surface convergence. also...sharp downstream ridging northeast of a cutoff low is usually a favorable environemnt for PSI (or CSI if RH/s are suitable), due to the fact that the absolute vorticity of the geostrophic flow underneath the ridge will normally be weaker...possibly telegraphing inertial instability. normally the stronger the vort max associated with the cutoff low...the weaker the absolute vorticity of the flow will be underneath the ridge, thus the better potential for inertial instability in that region.
IMO (and as i was taught)...using theta-e and momentum surfaces or for that matter slantwise CAPE to predict CSI is obscelete and somewhat unreliable. cross-sections of EPV, frontogeneis, omega, and RH are the best was to assess wither or not the environment is symmetrically unstable.
we/ll be dealing with these situations quite a bit this winter, but my advice (FWIW) would be to use cross-sections of EPV, frontogeneis, omega, and RH instead of comparing momentun surfaces and theta-e.
both CI and CSI were big factors in the extreme snowfall i received from the January 6 event. (in total i had 11 inches in 5 hours!!!)
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ColdFront77
Stormsfury wrote:And interesting in March, during some of the stronger El Niño seasons, typically, the coldest winter month occur during this month. The March Superstorm was a pure aberration with the subtropical jet, the polar jet, and the arctic jet phasing (triple-phased storm) ...
For those that haven't read this write-up and viewed some of the reanalysis maps for the Superstorm 93 plus a 2 day Satellite loop ... here's your chance ...
The Superstorm began as a strong baroclinic leaf over the GOM and quickly and deepened rapidly eventually bottoming out at 960mb over Chesapeake Bay ...
In Early March 1993, the Chief Meteorologist at WBZ-TV 4, Boston (at the time) said that a low pressure that currently doesn't exist will develop rapidly and move up the east coast and could really be a blockbuster storm. Sure enough that is what happened... this is without any obvious indication of a low in the east-central Gulf of Mexico.
He mentioned that this low pressure development will be like throwing a pebble in a puddle of water and watching the rings radiant from the center of where the pebble hit.
..CI: Conditional Instability
CSI: Conditional Symmetric Instability
EPV: Ertel's Potential Vorticity
PSI: Potential Symmetric Instability
UVM: Upward Vertical Motion
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Stormsfury
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ColdFront77 wrote:Stormsfury wrote:And interesting in March, during some of the stronger El Niño seasons, typically, the coldest winter month occur during this month. The March Superstorm was a pure aberration with the subtropical jet, the polar jet, and the arctic jet phasing (triple-phased storm) ...
For those that haven't read this write-up and viewed some of the reanalysis maps for the Superstorm 93 plus a 2 day Satellite loop ... here's your chance ...
The Superstorm began as a strong baroclinic leaf over the GOM and quickly and deepened rapidly eventually bottoming out at 960mb over Chesapeake Bay ...
In Early March 1993, the Chief Meteorologist at WBZ-TV 4, Boston (at the time) said that a low pressure that currently doesn't exist will develop rapidly and move up the east coast and could really be a blockbuster storm. Sure enough that is what happened... this is without any obvious indication of a low in the east-central Gulf of Mexico.
He mentioned that this low pressure development will be like throwing a pebble in a puddle of water and watching the rings radiant from the center of where the pebble hit.
..CI: Conditional Instability
CSI: Conditional Symmetric Instability
EPV: Ertel's Potential Vorticity
PSI: Potential Symmetric Instability
UVM: Upward Vertical Motion
The Superstorm was well seen by the forecast model guidance ... the GFS depicted a big storm (but was much too high with the barometric pressures) ... DT (WxRisk.com) has a really nice writeup regarding the Superstorm and how many of the globals were handling the system days out from the event ...
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Stormsfury
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ColdFront77
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