Central PA/fringes of MD - December 2013 continued

[NeffsvilleWx]

is there a header for this? I would like to see what I am looking at.

 

thanks.

 

Date/hour    FHr  Wind    SfcT          Ptype       SR |Snow||Sleet|| FZRA|| QPF CumSR|TotSN||TotPL||TotZR|| TQPF   S%| I%| L%

----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---

131214/1500Z  51  10007KT  25.4F  SNOW   13:1| 0.4|| 0.00|| 0.00|| 0.031   13:1|  0.4|| 0.00|| 0.00|| 0.03  100|  0|  0

131214/1800Z  54  10009KT  26.3F  SNOW   13:1| 1.2|| 0.00|| 0.00|| 0.093   13:1|  1.6|| 0.00|| 0.00|| 0.12  100|  0|  0

131214/2100Z  57  09006KT  29.4F  SNOW   13:1| 1.9|| 0.00|| 0.00|| 0.149   13:1|  3.5|| 0.00|| 0.00|| 0.27  100|  0|  0

131215/0000Z  60  10008KT  31.5F SNZRPL   0:1| 0.0|| 0.27|| 0.14|| 0.269   13:1|  3.5|| 0.27|| 0.14|| 0.54   38| 12| 50

----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---

131215/0300Z  63  08006KT  33.2F  RAIN    0:1| 0.0|| 0.00|| 0.00|| 0.057   13:1|  3.5|| 0.27|| 0.14|| 0.60    0|  0|100

131215/0600Z  66  36003KT  33.2F    DZ    0:1| 0.0|| 0.00|| 0.00|| 0.019   13:1|  3.5|| 0.27|| 0.14|| 0.62    0|  0|100

[Eskimo Joe]

The issue with ratios is that it is based on the assumption on a static thermal profile throughout the event.  But in this case there is a wealth of warm air advecting into the cold air mass so you may start out with the standard 10:1 for a time, but eventually your rates fall as the snow growth zone becomes contaminated with warmer air.  Thus, a shrewd met. would undercut the standard 10:1 for the first snow forecast.

[Wmsptwx]

KIPT specialty is overrunning events so I'm guessing a solid 2 to 5 up this way!! If we bust I will eat the hat I referenced on Sunday!!

[NortheastPAWx]

GFS is bitter for next week.

 

131219/0300Z 159 28014KT 8.1F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131219/0600Z 162 28014KT 7.8F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131219/0900Z 165 28013KT 7.6F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131219/1200Z 168 28008KT 7.2F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131219/1500Z 171 29011KT 12.6F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131219/1800Z 174 29011KT 17.1F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131219/2100Z 177 28007KT 15.3F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131220/0000Z 180 26004KT 7.6F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0

[mappy]

The issue with ratios is that it is based on the assumption on a static thermal profile throughout the event.  But in this case there is a wealth of warm air advecting into the cold air mass so you may start out with the standard 10:1 for a time, but eventually your rates fall as the snow growth zone becomes contaminated with warmer air.  Thus, a shrewd met. would undercut the standard 10:1 for the first snow forecast.

 

Yup -- same reason why on Tuesday ratios were crappy compared to Sunday. Sunday was colder all the way down the column, while Tuesday wasn't.

[NeffsvilleWx]

The issue with ratios is that it is based on the assumption on a static thermal profile throughout the event.  But in this case there is a wealth of warm air advecting into the cold air mass so you may start out with the standard 10:1 for a time, but eventually your rates fall as the snow growth zone becomes contaminated with warmer air.  Thus, a shrewd met. would undercut the standard 10:1 for the first snow forecast.

 

I understand that, but I thought Cobb/coolwx (and other sites that give total stats) into account when crunching the numbers? On the 06Z GFS run, a warm air pocket was visible on the temp profile that coincided with a changeover from snow to fzra.

 

I would think that this method is more accurate than just looking at QPF and making an educated guess on ratios, but I'm just a hobbyist. If there is a more accurate way to interpret models, I'm all ears.

[CarlislePaWx]

I understand that, but I thought Cobb/coolwx (and other sites that give total stats) into account when crunching the numbers? On the 06Z GFS run, a warm air pocket was visible on the temp profile that coincided with a changeover from snow to fzra.

 

I would think that this method is more accurate than just looking at QPF and making an educated guess on ratios, but I'm just a hobbyist. If there is a more accurate way to interpret models, I'm all ears.

Ok Neff...I had no idea that you were referencing a different data source (coolwx) when you mentioned the .209" increase.  I assumed you were comparing the 6z cobb to the 12z cobb.  On coolwx it gives mdt a total qpf as snow of 0.55 which would be fantastic if it comes true. I'm getting a little bit confused with data references changing between posts.

[sauss06]

Ok Neff...I had no idea that you were referencing a different data source (coolwx) when you mentioned the .209" increase.  I assumed you were comparing the 6z cobb to the 12z cobb.  On coolwx it gives mdt a total qpf as snow of 0.55 which would be fantastic if it comes true. I'm getting a little bit confused with data references changing between posts.

i have only seen from .25 to .355 range for MDT

[NeffsvilleWx]

Ok Neff...I had no idea that you were referencing a different data source (coolwx) when you mentioned the .209" increase.  I assumed you were comparing the 6z cobb to the 12z cobb.  On coolwx it gives mdt a total qpf as snow of 0.55 which would be fantastic if it comes true. I'm getting a little bit confused with data references changing between posts.

 

My apologies. Only today did I realize that those snow calculations are just that, calculations. I guess it never clicked that they weren't taken verbatim from the model output   I've been trying to make sure I clarify, but I'm sure I missed some.

[djr5001]

12z euro looks to have a primary low move into ohio a little stronger than the 0z run... this allows for 850s to rise for southeast PA as the coastal low develops... really only main different between the two runs that I can see from initial look... slightly higher qpf before a projected changeover...

[NeffsvilleWx]

i wouldn't pay attention to anything that tries to predict ratios. its why those snow maps (regardless of where they come from) are hardly right. They all have their own ratios/algorithms they are using to "predict" how much snow actually falls. Which is really hard to narrow down exactly.

 

I only look at qpf values, then assume a 10:1 ratio, since that seems to be about where most snow events fall. Then if its higher than 10:1, you are pleasantly surprised!

 

Missed this, thanks mappy!

[heavy_wx]

Snow ratios depend a lot on the microphysical processes within the clouds and are different depending on the dominant snowflake type. These processes determine the snow ratio because they can affect the density of the snowflakes as they accumulate. Things like fragmentation (breaking snowflakes due to wind speed), aggregation and sublimation can all affect the snow-liquid ratio. Fragmentation tends to be most detrimental to snowflakes that are more fragile such as stellar crystals and stars. Aggregation can increase the density of a group of snowflakes at temperatures closer to freezing within the cloud, but in colder regions with more dendrites the density can actually decrease.

 

Surface temperatures may have some effect but this relationship could just be because surface temperatures are correlated with temperatures aloft (colder temperatures in the snow growth region usually mean colder temperatures at the surface). Warm ground temperatures can also affect the snow ratio, mostly the lowest few inches of snow closest to the ground and only if the ground is above freezing.

 

So you can use temperatures and moisture within the region of best lift to determine the dominant snowflake type and then try to estimate how those physical processes will affect that snowflake type.

 

This manuscript from meted is a good source of further  information.

http://www.meted.ucar.edu/norlat/snowdensity/from_mm_to_cm.pdf

[NeffsvilleWx]

Snow ratios depend a lot on the microphysical processes within the clouds and are different depending on the dominant snowflake type. These processes determine the snow ratio because they can affect the density of the snowflakes as they accumulate. Things like fragmentation (breaking snowflakes due to wind speed), aggregation and sublimation can all affect the snow-liquid ratio. Fragmentation tends to be most detrimental to snowflakes that are more fragile such as stellar crystals and stars. Aggregation can increase the density of a group of snowflakes at temperatures closer to freezing within the cloud, but in colder regions with more dendrites the density can actually decrease.

 

Surface temperatures may have some effect but this relationship could just be because surface temperatures are correlated with temperatures aloft (colder temperatures in the snow growth region usually mean colder temperatures at the surface). Warm ground temperatures can also affect the snow ratio, mostly the lowest few inches of snow closest to the ground and only if the ground is above freezing.

 

So you can use temperatures and moisture within the region of best lift to determine the dominant snowflake type and then try to estimate how those physical processes will affect that snowflake type.

 

This manuscript from meted is a good source of further  information.

http://www.meted.ucar.edu/norlat/snowdensity/from_mm_to_cm.pdf

 

Thanks!

[canderson]

Snow ratios depend a lot on the microphysical processes within the clouds and are different depending on the dominant snowflake type. These processes determine the snow ratio because they can affect the density of the snowflakes as they accumulate. Things like fragmentation (breaking snowflakes due to wind speed), aggregation and sublimation can all affect the snow-liquid ratio. Fragmentation tends to be most detrimental to snowflakes that are more fragile such as stellar crystals and stars. Aggregation can increase the density of a group of snowflakes at temperatures closer to freezing within the cloud, but in colder regions with more dendrites the density can actually decrease.

 

Surface temperatures may have some effect but this relationship could just be because surface temperatures are correlated with temperatures aloft (colder temperatures in the snow growth region usually mean colder temperatures at the surface). Warm ground temperatures can also affect the snow ratio, mostly the lowest few inches of snow closest to the ground and only if the ground is above freezing.

 

So you can use temperatures and moisture within the region of best lift to determine the dominant snowflake type and then try to estimate how those physical processes will affect that snowflake type.

 

This manuscript from meted is a good source of further  information.

http://www.meted.ucar.edu/norlat/snowdensity/from_mm_to_cm.pdf

Take your science talk outta here! (Just kidding, this is a great summary - thank you).

[djr5001]

12_12_13 12z EURO

2m temp © / 850mb temp © / surface pressure (mb) / surface relative humidity (%) / 700mb relative humidity (%) / 6-hour QPF (IN) / 500mb height (DM) / 1000-500mb thickness

 

IPT
SAT 12Z 14-DEC  -9.3    -9.5    1031      89      99    0.03     553     529   
SAT 18Z 14-DEC  -5.9    -8.3    1027      86     100    0.09     551     530   
SUN 00Z 15-DEC  -5.4    -5.8    1021      91      98    0.28     551     534   
SUN 06Z 15-DEC  -3.4    -1.3    1011      95      84    0.17     548     539   
SUN 12Z 15-DEC  -1.9    -3.8    1008      95      26    0.04     544     538   

 

UNV
SAT 12Z 14-DEC  -8.1    -8.0    1029      90      98    0.03     553     531   
SAT 18Z 14-DEC  -5.6    -6.0    1025      88      99    0.12     552     532   
SUN 00Z 15-DEC  -3.5    -5.0    1019      94      98    0.29     551     536   
SUN 06Z 15-DEC  -2.8    -0.2    1011      96      85    0.10     548     539   
SUN 12Z 15-DEC  -0.5    -5.3    1009      94      18    0.03     545     538   

 

MDT
SAT 12Z 14-DEC  -6.9    -6.9    1029      87      98    0.01     556     533   
SAT 18Z 14-DEC  -2.8    -5.3    1026      87      96    0.10     554     534   
SUN 00Z 15-DEC  -1.9    -3.6    1020      94      98    0.26     554     539   
SUN 06Z 15-DEC  -0.7     2.4    1010      94      47    0.25     552     544   
SUN 12Z 15-DEC  -0.9    -1.2    1008      96      49    0.00     547     541   

 

LNS
SAT 12Z 14-DEC  -6.4    -6.9    1030      84      98    0.00     556     533   
SAT 18Z 14-DEC  -2.8    -5.4    1026      89      97    0.09     555     534   
SUN 00Z 15-DEC  -2.0    -3.3    1020      95      98    0.24     555     539   
SUN 06Z 15-DEC  -0.4     2.9    1010      94      34    0.32     553     545   
SUN 12Z 15-DEC  -0.4    -0.1    1008      96      53    0.00     548     541   

 

THV
SAT 12Z 14-DEC  -6.0    -6.4    1029      86      98    0.01     556     534   
SAT 18Z 14-DEC  -1.7    -4.6    1025      87      95    0.11     555     535   
SUN 00Z 15-DEC  -0.5    -2.5    1019      97      98    0.26     555     540   
SUN 06Z 15-DEC   0.1     3.5    1010      95      37    0.24     553     545   
SUN 12Z 15-DEC  -0.7    -1.0    1009      96      51    0.00     548     541   

 

AOO
SAT 12Z 14-DEC  -6.7    -6.8    1028      89      98    0.03     555     533   
SAT 18Z 14-DEC  -4.6    -4.6    1024      92      98    0.15     553     534   
SUN 00Z 15-DEC  -2.1    -3.4    1018      97      97    0.36     552     538   
SUN 06Z 15-DEC  -1.2     0.3    1010      98      78    0.08     549     541   
SUN 12Z 15-DEC   0.0    -5.1    1010      91      17    0.02     546     539   

 

AVP
SAT 12Z 14-DEC -10.1   -10.2    1032      87      91    0.02     553     528   
SAT 18Z 14-DEC  -7.7    -8.7    1029      81     100    0.08     551     529   
SUN 00Z 15-DEC  -8.7    -5.0    1024      88      98    0.20     551     533   
SUN 06Z 15-DEC  -5.2    -0.1    1013      90      82    0.31     549     539   
SUN 12Z 15-DEC  -2.5    -2.5    1007      95      52    0.04     545     539   

[sauss06]

^^^^^ those qbf numbers went up for MDT now .62

[NeffsvilleWx]

^^^^^ those qbf numbers went up for MDT now .62

 

Yeah, looks like 0.25" or so will be fzra or pellets. At 06z on the 15th, 850 mb temp is 2.4º C

[djr5001]

^^^^^ those qbf numbers went up for MDT now .62

but also pushes 850mb temps above freezing... I still say it plays out similar to Sunday except with more snow north and west in terms of snow early and quick to move out before warm air gets far enough north... most precip through before a brief changeover late... my first guess is 1-3" with .01-.1 ice for our area and 2-4" with somewhere getting 3-5" north and west of us

[sauss06]

but also pushes 850mb temps above freezing... I still say it plays out similar to Sunday except with more snow north and west in terms of snow early and quick to move out before warm air gets far enough north... most precip through before a brief changeover late... my first guess is 1-3" with .01-.1 ice for our area and 2-4" with somewhere getting 3-5" north and west of us

thats fine, a little freshing up!

[JamieOber]

Sucky part here is that coolwx doesn't get data for KUNV.

It does for State College but I am not sure what the difference is. When it was for KUNV I swear to God it was for the radar location up on the Allegheny Front. 

[Mallow]

It does for State College but I am not sure what the difference is. When it was for KUNV I swear to God it was for the radar location up on the Allegheny Front. 

 

I've seen that point used for KUNV before, too. My theory is that it's actually the closest model gridpoint to KUNV, and it's just by chance that it happens to be near the radar.

[mappy]

Missed this, thanks mappy!

 

anytime!

[psuhoffman]

Point about the euro for south central PA, yes it pushes a warm layer in at 66 hours, but if you look at the temps at 60 hours...the 850 line still comfortably in MD while moderate precip rates are over the area...then at 66 hours after the precip has ended the warm layer has blasted well north...I think its implied that the warm layer comes in towards the tail end of the precip.  I think most of the precip is probably snow north of the turnpike and just ends as freezing drizzle. 

[mappy]

LWX seems like to accumulating snow near the PA/MD Line

 

ACCUMULATING SNOW IS LIKELY ACROSS MUCH OF THE AREA...ESPECIALLY
ACROSS THE NORTH AND WEST NEAR THE MASON-DIXON LINE WHERE LOW-LEVEL
COLD AIR WILL HANG ON THE LONGEST.

[NeffsvilleWx]

LWX seems like to accumulating snow near the PA/MD Line

 

ACCUMULATING SNOW IS LIKELY ACROSS MUCH OF THE AREA...ESPECIALLY

ACROSS THE NORTH AND WEST NEAR THE MASON-DIXON LINE WHERE LOW-LEVEL

COLD AIR WILL HANG ON THE LONGEST.

 

Coinciding with the snow already on the ground, no doubt.

[mappy]

Coinciding with the snow already on the ground, no doubt.

 

most definitely. still going to be a marginal event, temps hovering near freezing. much like tuesday. higher amounts will be where a band sets up. ratios won't be that good, then it will rain afterwards. but hey, snow is snow, right?

[NeffsvilleWx]

 snow is snow, right?

 

Sure is!

[sauss06]

most definitely. still going to be a marginal event, temps hovering near freezing. much like tuesday. higher amounts will be where a band sets up. ratios won't be that good, then it will rain afterwards. but hey, snow is snow, right?

thats my theory! i'll take whatever i can get, however i can get it! jsut freshin up the ground!

[Fozz]

most definitely. still going to be a marginal event, temps hovering near freezing. much like tuesday. higher amounts will be where a band sets up. ratios won't be that good, then it will rain afterwards. but hey, snow is snow, right?

 

that's when living at 700' comes in handy

[I-83 BLIZZARD]

Plenty of time to trend colder.