The "What To Title The Storm?" Thread - Dec 8-9

[mitchnick]

Now you are getting just downright greedy, have possibly our best event since Jan 2011 here and you want to also pick the start time.

if it wasn't going to be washed away I would be a little more excited

I'm hoping Tuesday works out because will last

[ravensrule]

if it wasn't going to be washed away I would be a little more excited

I'm hoping Tuesday works out because will last

You can't have everything. I would love 2" of snow followed by some sleet and then freezing rain.

[Heisy]

Mitch that 2nd storm is just a cold front associated with the ULL over the lakes, too warm ahead of it, besides the GFS being goofy it would just be rain followed by maybe some flurries, but thats about it. 

[snow.]

18z looks like a snow sounding to me.

 

barely but yes for DCA

 

[Bob Chill]

Mitch that 2nd storm is just a cold front associated with the ULL over the lakes, too warm ahead of it, besides the GFS being goofy it would just be rain followed by maybe some flurries, but thats about it. 

 

If you look at h5 and h7 it's more than just a cold front. There's a weak disturbance embedded in ul flow and decent moisture lift out in front. Not saying I expect anything out of it but it's worth watching. 

[SomeguyfromTakomaPark]

Not even that warm at the surface at 108, starting to think "mostly frozen".

[Amped]

Usually surface temps are slower to warm than expected in heavy CAD situations. It is possible the Shenandoah Valley gets an extended period of freezing rain.  This will probably extend up to Hagerstown and Harrisburg as well, since the Valley Technically extends that far north with the exception of a 500 yard gap in Harpers Ferry, WV where the Potomac cuts through.   We might still have a hard time changing to plain rain here in Frederick, but I don't think we'll get enough ZR to cause a major issue.  Hopefully we can get a good thump of snow first.

[H2O]

could be..I think we will see CAD show up more and more in the mid levels..this run is markedly better than last night's bad one in terms of that

 

THis is a great panel for NW VA

 

1pm sunday

 

18zcad.PNG

 

Seems that this is a benefit of the cold air being fairly fresh.  Granted it isn't super cold but you are talking about 12-18 hour window for it to come in and settle just as more precip comes over top of it.  Other cases of CAD are ones where it is cold for a couple days and slowly warming each day.

[Bob Chill]

Seems that this is a benefit of the cold air being fairly fresh.  Granted it isn't super cold but you are talking about 12-18 hour window for it to come in and settle just as more precip comes over top of it.  Other cases of CAD are ones where it is cold for a couple days and slowly warming each day.

 

This is a really good point and one to keep in the memory banks for future setups like this. I posted my thoughts some days back about hoping the first wave is more of a cutter for a larger cold air supply. This was flawed thinking because anything on the tail of a cutter's front is several days after frontal passage. I don't remember who corrected me though so I can't give them credit. 

 

In this case, it's a big positive that the overrunning is hitting as the fresh cold is pressing down rather than already ready to slide away. The cold does in fact slide away of course because of the surface low track and no serious blocking but you can see on the panels that the 850's are still moving south just as the precip is knocking on the door. Luckily 850's are down near NC at their furthest extent and not over Jebman's house. 

[winter_warlock]

 I was wondering if any of you  in mid atlantic can remember more then a few times weve had these CAD setups, when  the frozen precip whether it was snow or sleet or zr was forecasted to change over because of warm air eroding the cold eventually, only to have the cold air  never really retreat and it stay frozen, im not saying it weill be like that this time and im NOT wish casting, just sumthing I was thinking about, there were a lot of times  where the  precip never changed to rain like forecasted too,  anyone else remember those times?.

[winter_warlock]

This is a really good point and one to keep in the memory banks for future setups like this. I posted my thoughts some days back about hoping the first wave is more of a cutter for a larger cold air supply. This was flawed thinking because anything on the tail of a cutter's front is several days after frontal passage. I don't remember who corrected me though so I can't give them credit. 

 

In this case, it's a big positive that the overrunning is hitting as the fresh cold is pressing down rather than already ready to slide away. The cold does in fact slide away of course because of the surface low track and no serious blocking but you can see on the panels that the 850's are still moving south just as the precip is knocking on the door. Luckily 850's are down near NC at their furthest extent and not over Jebman's house. 

I agree it is a very good point,  fresh cold air is always   better for CAD situations then  stagnant  cold air that has been modified over a few days .  yes I believe there is a difference

[winter_warlock]

Anyone remember the times when the front end thump never happened?

yeah I do remember those days too lol

[Kevin Druff]

 I was wondering if any of you  in mid atlantic can remember more then a few times weve had these CAD setups, when  the frozen precip whether it was snow or sleet or zr was forecasted to change over because of warm air eroding the cold eventually, only to have the cold air  never really retreat and it stay frozen, im not saying it weill be like that this time and im NOT wish casting, just sumthing I was thinking about, there were a lot of times  where the  precip never changed to rain like forecasted too,  anyone else remember those times?.

 

While this does happen, I think it tends to happen more closer to the mountains than more on the plains like DCA, EZF, RIC. In areas like Charlottesville, Staunton, Winchester, Front Royal, even Leesburg to an extent, it can be VERY hard to erode the cold air all the way to ground level. The caveat being freezing rain at 31-32 isn't nearly as big a deal as ZR at 28-29 and the former is more often the case in these situations than the latter.

[Bob Chill]

 I was wondering if any of you  in mid atlantic can remember more then a few times weve had these CAD setups, when  the frozen precip whether it was snow or sleet or zr was forecasted to change over because of warm air eroding the cold eventually, only to have the cold air  never really retreat and it stay frozen, im not saying it weill be like that this time and im NOT wish casting, just sumthing I was thinking about, there were a lot of times  where the  precip never changed to rain like forecasted too,  anyone else remember those times?.

 

Definitely happens sometimes but we usually have a block locking the hp in place. We get lucky with a degree or 2 at onset and it holds on. Other times the precip simply shuts off faster than expected and it goes to drizzle mist after all the good rates remain snow/sleet. 

 

Those events are usually progged to be borderline changeovers and not have 850's soar like they will late sunday. Good favor on Sun will be having precip shutoff sooner. Latest trends are starting to favor that outcome to some extent. Especially out west. 

[winter_warlock]

Definitely happens sometimes but we usually have a block locking the hp in place. We get lucky with a degree or 2 at onset and it holds on. Other times the precip simply shuts off faster than expected and it goes to drizzle mist after all the good rates remain snow/sleet. 

 

Those events are usually progged to be borderline changeovers and not have 850's soar like they will late sunday. Good favor on Sun will be having precip shutoff sooner. Latest trends are starting to favor that outcome to some extent. Especially out west. 

Im hoping the dewpoint is very low,  evaporative cooling will drop temp at the onset even more,  the farther they fall the more they have to go to change

[usedtobe]

The "front end dump" is really tenuous.  The 18Z GFS run has the 15Z GSF temp at 800 mb above freezing but is only .5 with a dewpoint 0.2, if perfect probably snow,  if 0.5 warmer, maybe sleet.  Even at 12, the 800 temp is a tad above freezing but the dewpoint is low so it wouldn't matter. 

[DDweatherman]

Bob, your description of this event leading up to where we are has been excellent. The set-up is unique in that its actually a timing play, but not a thread the needle. We can succeed to an extent in set-ups where the storm moves in under already cold but somewhat moderating airmasses. However, as Matt has mentioned, the airmass is actually going to get colder through the morning on Sunday as the cold really entrenches itself over the area. Things are looking better and better for this one, hope the trends continue. Little by little for the next few days and we could really be looking at a nice event. 

[jnis]

 I was wondering if any of you  in mid atlantic can remember more then a few times weve had these CAD setups, when  the frozen precip whether it was snow or sleet or zr was forecasted to change over because of warm air eroding the cold eventually, only to have the cold air  never really retreat and it stay frozen, im not saying it weill be like that this time and im NOT wish casting, just sumthing I was thinking about, there were a lot of times  where the  precip never changed to rain like forecasted too,  anyone else remember those times?.

Yep, in 1994 we had an ice storm with temps in the upper teens and low twenties. The forecast was that temps would rise above freezing after a few hours of zr, but the temps hung tough. At some point there were temps in the low 50's in WV while it was still well below freezing east of the mountains.

[peribonca]

Yep, in 1994 we had an ice storm with temps in the upper teens and low twenties. The forecast was that temps would rise above freezing after a few hours of zr, but the temps hung tough. At some point there were temps in the low 50's in WV while it was still well below freezing east of the mountains.

I remember those 1994 ice storms really well. It was 55F in Fredericksburg at one point and 18F in Bethesda!

[Ian]

Bob, your description of this event leading up to where we are has been excellent. The set-up is unique in that its actually a timing play, but not a thread the needle. We can succeed to an extent in set-ups where the storm moves in under already cold but somewhat moderating airmasses. However, as Matt has mentioned, the airmass is actually going to get colder through the morning on Sunday as the cold really entrenches itself over the area. Things are looking better and better for this one, hope the trends continue. Little by little for the next few days and we could really be looking at a nice event. 

 

Think this is a dubious assumption still.  The high is already moving east by the time the precip arrives -- winds start to shift to off the ocean at least to the 95 corridor by 12z on both the Euro and GFS .  The main cooldown should come when precip starts. I'd be kinda surprised if we see any widespread cooling on Sunday otherwise. 

[DDweatherman]

Think this is a dubious assumption still.  The high is already moving east by the time the precip arrives -- winds start to shift to off the ocean at least to the 95 corridor by 12z on both the Euro and GFS .  The main cooldown should come when precip starts. I'd be kinda surprised if we see any widespread cooling on Sunday otherwise. 

Well Ian, I agree, but I feel like the CAD that has locked in as Matt was saying should be accompanied by temps cooling via the DPP around 10-15F in most locales. That means temps after the onset could drop to around 24-25 in some places, with 26-27 around the bay NAK up to APG. I don't want to be misunderstood, I don't expect widespread cooling. However, we could lose a degree or maybe two in certain spots depending on geographic influence. The high on some runs has started to exhibit a little slower eastward movement of late it seems compared to some of the "not-so-good" runs we've had. 

[WxUSAF]

Think this is a dubious assumption still.  The high is already moving east by the time the precip arrives -- winds start to shift to off the ocean at least to the 95 corridor by 12z on both the Euro and GFS .  The main cooldown should come when precip starts. I'd be kinda surprised if we see any widespread cooling on Sunday otherwise. 

I don't actually disagree with you RE: temps cooling on Sunday, but at what level are winds "off the ocean" at 12z?  Matt posted the 18z DCA sounding from the GFS above and you can see ~40-50deg wind vector at the surface.  Above that, winds are easterly or southeasterly. 

[Ian]

I don't actually disagree with you RE: temps cooling on Sunday, but at what level are winds "off the ocean" at 12z? Matt posted the 18z DCA sounding from the GFS above and you can see ~40-50deg wind vector at the surface. Above that, winds are easterly or southeasterly.

I was just looking at streamlines of sfc winds on Weatherbell. It's not due east or anything till about 0z but starts swinging that way by 12z at least on raw images. Not like a northeast wind instantly screws us anyway or something. I guess I lean on the warmer side of the envelop where a degree or two is more important than if it's like 27-28.

The CAD is nice and we all sorta saw that a few days ago but I'm not ready to assume it's going to keep getting colder till go time. It could.

[Bob Chill]

The "front end dump" is really tenuous. The 18Z GFS run has the 15Z GSF temp at 800 mb above freezing but is only .5 with a dewpoint 0.2, if perfect probably snow, if 0.5 warmer, maybe sleet. Even at 12, the 800 temp is a tad above freezing but the dewpoint is low so it wouldn't matter.

We're in an awesome place to walk the tightrope aren't we. It's always something. I think we've probobily already seen best and worst case model runs temp wise. Don't think there much room to improve or fall to pieces.

I feel pretty good at a shot for an inch or so of pure snow before the inevitable buffet. Am I being unreasonable?

[mitchnick]

OK mets, assume these numbers to be true at 99hrs imby on 18z GFS, snow, snow grains, sleet, or a mix?

1017.    72.    0.1   -0.0    64.0     4.2 1000.   212.   -0.4   -0.7    72.9     7.4  975.   414.   -1.0   -1.1    90.5    10.3  950.   622.   -0.9   -1.0   110.7    11.7  925.   835.   -0.6   -0.8   131.2    11.5  900.  1054.   -0.3   -0.6   155.7    11.5  850.  1512.    0.4   -0.0   196.2    14.7  800.  1999.    0.3   -0.0   216.5    20.7  750.  2516.   -0.8   -1.0   226.1    25.6  700.  3068.   -0.8   -1.0   238.5    31.8  650.  3660.   -2.5   -3.0   251.4    34.0  600.  4291.   -5.9   -7.0   255.6    34.4

[WxUSAF]

I'd say probably snow if precip is heavy, mostly pingers if it was light.  Certainly would get some riming on the flakes. 

[mitchnick]

I'd say probably snow if precip is heavy, mostly pingers if it was light.  Certainly would get some riming on the flakes. 

yep, that's what I figured    thanks

GFS puts down .41" up to that point so that's 4" of snow before change verbatim

[WxUSAF]

yep, that's what I figured    thanks

GFS puts down .41" up to that point so that's 4" of snow before change verbatim

Gonna revise and say mostly pingers.  Didn't see both 850 and 800 were a bit above.  But dews are still at or just below freezing.  Probably PLSN. 

[WVclimo]

yep, that's what I figured    thanks

GFS puts down .41" up to that point so that's 4" of snow before change verbatim

I don't think you can assume a 10:1 ratio, Mitch.

Cobb Bufkit Data has 8:1 ratios at MRB for the front end.  It also has 0.93" of freezing rain after that, most of that with temps below 30.

[ravensrule]

Here is the cobb for us Mitch, i will take their 3" and be tickled pink.

 

StnID: kbwi Profile Thermal Adjust: 0.0 Cloud RH threshold: 85% Average Hourly Sounding: NO

Date/hour FHr Wind SfcT Ptype SR |Snow||Sleet|| FZRA|| QPF CumSR|TotSN||TotPL||TotZR|| TQPF S%| I%| L%
============================================================================================================================
131204/2100Z 3 15005KT 50.8F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131205/0000Z 6 16005KT 49.4F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131205/0300Z 9 17005KT 50.1F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131205/0600Z 12 17006KT 50.8F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131205/0900Z 15 17006KT 51.3F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131205/1200Z 18 19007KT 52.1F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131205/1500Z 21 20009KT 54.4F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131205/1800Z 24 20011KT 59.8F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131205/2100Z 27 20011KT 61.2F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131206/0000Z 30 21011KT 58.5F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131206/0300Z 33 21009KT 59.4F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.009 0:1| 0.0|| 0.00|| 0.00|| 0.01 0| 0|100
131206/0600Z 36 21011KT 60.2F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.01 0| 0| 0
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131206/0900Z 39 27006KT 60.2F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.022 0:1| 0.0|| 0.00|| 0.00|| 0.03 0| 0|100
131206/1200Z 42 36015KT 47.9F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.045 0:1| 0.0|| 0.00|| 0.00|| 0.08 0| 0|100
131206/1500Z 45 01009KT 46.5F DZ 0:1| 0.0|| 0.00|| 0.00|| 0.008 0:1| 0.0|| 0.00|| 0.00|| 0.08 0| 0|100
131206/1800Z 48 36008KT 47.4F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.019 0:1| 0.0|| 0.00|| 0.00|| 0.10 0| 0|100
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131206/2100Z 51 03009KT 44.7F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.120 0:1| 0.0|| 0.00|| 0.00|| 0.22 0| 0|100
131207/0000Z 54 02010KT 43.4F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.085 0:1| 0.0|| 0.00|| 0.00|| 0.31 0| 0|100
131207/0300Z 57 04009KT 41.8F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.073 0:1| 0.0|| 0.00|| 0.00|| 0.38 0| 0|100
131207/0600Z 60 36011KT 40.2F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.133 0:1| 0.0|| 0.00|| 0.00|| 0.52 0| 0|100
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131207/0900Z 63 35012KT 38.4F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.025 0:1| 0.0|| 0.00|| 0.00|| 0.54 0| 0|100
131207/1200Z 66 35012KT 35.9F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.54 0| 0| 0
131207/1500Z 69 34013KT 37.7F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.54 0| 0| 0
131207/1800Z 72 34013KT 40.5F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131207/2100Z 75 35011KT 38.2F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131208/0000Z 78 36008KT 33.5F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131208/0300Z 81 01007KT 31.2F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0

131208/0600Z 84 02007KT 29.7F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131208/0900Z 87 03007KT 29.9F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131208/1200Z 90 06006KT 30.8F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131208/1500Z 93 06008KT 30.3F SNOW 6:1| 0.1|| 0.00|| 0.00|| 0.021 6:1| 0.1|| 0.00|| 0.00|| 0.02 100| 0| 0
131208/1800Z 96 07011KT 29.2F SNOW 10:1| 2.9|| 0.00|| 0.00|| 0.285 10:1| 3.0|| 0.00|| 0.00|| 0.31 100| 0| 0
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131208/2100Z 99 06009KT 32.8F RAPL 0:1| 0.0|| 0.00|| 0.00|| 0.121 10:1| 3.0|| 0.00|| 0.00|| 0.43 5| 36| 60
131209/0000Z 102 09010KT 35.3F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.091 10:1| 3.0|| 0.00|| 0.00|| 0.52 0| 0|100
131209/0300Z 105 10012KT 36.8F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.281 10:1| 3.0|| 0.00|| 0.00|| 0.80 0| 0|100
131209/0600Z 108 10006KT 39.1F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.104 10:1| 3.0|| 0.00|| 0.00|| 0.90 0| 0|100
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131209/0900Z 111 20005KT 40.2F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.147 10:1| 3.0|| 0.00|| 0.00|| 1.05 0| 0|100
131209/1200Z 114 21006KT 39.1F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.062 10:1| 3.0|| 0.00|| 0.00|| 1.11 0| 0|100
131209/1500Z 117 24006KT 39.5F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.027 10:1| 3.0|| 0.00|| 0.00|| 1.14 0| 0|100
131209/1800Z 120 28005KT 41.1F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.053 10:1| 3.0|| 0.00|| 0.00|| 1.19 0| 0|100
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131209/2100Z 123 32008KT 41.6F RAIN 0:1| 0.0|| 0.00|| 0.00|| 0.039 10:1| 3.0|| 0.00|| 0.00|| 1.23 0| 0|100
131210/0000Z 126 32013KT 41.4F 0:1| 0.0|| 0.00|| 0.00|| 0.000 10:1| 3.0|| 0.00|| 0.00|| 1.23 0| 0| 0
131210/0300Z 129 33012KT 38.2F 0:1| 0.0|| 0.00|| 0.00|| 0.000 10:1| 3.0|| 0.00|| 0.00|| 1.23 0| 0| 0
131210/0600Z 132 34008KT 35.7F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131210/0900Z 135 36007KT 33.5F 0:1| 0.0|| 0.00|| 0.00|| 0.000 0:1| 0.0|| 0.00|| 0.00|| 0.00 0| 0| 0
131210/1200Z 138 35006KT 35.0F RAPL 0:1| 0.0|| 0.00|| 0.00|| 0.057 0:1| 0.0|| 0.00|| 0.00|| 0.06 8| 4| 88
131210/1500Z 141 33005KT 34.8F RASN 0:1| 0.0|| 0.00|| 0.00|| 0.207 0:1| 0.0|| 0.00|| 0.00|| 0.26 29| 0| 71
131210/1800Z 144 30012KT 33.7F RASN 0:1| 0.0|| 0.00|| 0.00|| 0.138 0:1| 0.0|| 0.00|| 0.00|| 0.40 58| 0| 42