A look ahead at the the first week of december

[usedtobe]

Decided to add to Ji's depression by making a post about the 1st week in December. part of my reason for making such a post was clicking on Channel nine's winter forecast and seeing both mets calling for early dec snowstorm, one calling for Dec 3rd and another Dec 5th. The latter was probably based on the fluke that 4 or the last 8 dec 5ths have had snow on them. That may be true but, the climo for getting an inch of snow any day of the 1st seven days of dec is only 14.7%, it's only happened 18 times in the last 122 years.

Some might argue that having a strongly negative nao raises the odds and that may be true but the pattern shown on the progs still isn't a good one as the pacific and north Atlantic continue to battle. The 6-10 day mean forecasts of both the GFS and euro show two things that make the pattern less than stellar. Both show the strongest negative height anomaly over the U.S. still anchored in the west. That means that enough troughing should remain across that region to have the stronger low track to out north and west. They also show the 50 50 low around 10 degrees to far east for it to keep cold air across out region as it is far enough east to allow southwesterly or wswly flow to develop across the mid atlantic.

Our closest chance for snow might be Dec 1st with a wave that forms of the front but even that doesn't look good as the low actually tracks a little to far inland to help I95. I may offer Jon Jon snow (is he with this fourm?) After the Jan 1st, the next low really track north on both the gfs and euro and the gfs ensemble members support this idea. Look at the dec 5th low on the 240 hr ensembles

Not a pretty picture, the euro ensemble at that time still is holding the trough west promising above normal temps so it is supporting the low tracking north of us idea.

It even suggests that the 12Z gfs may still be a little early bringing in the cold air and certainly make it look like any storm before dec 7th is a real long shot.

Yes, the models have been all over the place but they've also been too aggressive in bringing cold into our region. The CPC D+11 top analog is Dec 1955, a month that averaged pretty cold relative to normal but didn't give us much snow. That doesn't mean, this year will have similar snow amounts . Just that the 1st week of December might not be that good.

[RIC Airport]

Thanks for the update, Wes. After all it's still very early and all it takes is a good couple weeks of a great pattern to make most of the MA happy for the season.

[Ian]

well it can't snow on dec 5th forever..

do you see a cold dec wes?

[usedtobe]

well it can't snow on dec 5th forever..

do you see a cold dec wes?

The 1955 analog says yes it will be a cold Dec and with all the blocking I don't see how we won't get some cold in Dec sometime after the 6th or 7th but I'm not very confident like I was comparatively speaking last year. I don;t like seeing the month start kind of warm as that's where all the skill is. The negative NAO is still a plus and as the month progressed probably ehlp us more and more providing it stays negative, that's a pretty big assumption.

[Midlo Snow Maker]

thanks for the update wes

[+SN]

Nice analisys, thanks.

[sauss06]

Good write up Wes

[MidlothianWX]

Thanks for the update Wes!

[Ender]

Taking a look at today's analogs we see the following DCA snow occurrences relative to the analog date (D+ is analog date +X days, D- is analog date -X days).

D+8 Analog dates:

11/27/73: 10.2” on D+19

11/30/50: 1.6” at D-5 and 3.2” on D+10

11/25/70:

11/30/05: 1.4” D+5 and 1.6” on D+9

11/20/65:

11/20/03: .9” at D+14, 1.7” at D+16 and 3.6” on D+24

11/24/61: .6” on D+15

12/21/68: .2” on D+15

12/16/55: .3” D+3

D+11 Analog dates (de-duped from the D+8 set):

12/24/65: .2” at D-4

11/29/66: 6.7” on D+14

12/05/54: .1” on D+0

12/06/68:

11/20/55: .2” on D-1

Juding by the pairs of color coded dates this is a pattern that apparently "likes to repeat" itself in 15 - 30 days.

The roll-forward on the D8 analogs shows a tendency for very cold -5C depatures by D+6 through D+12 (IOW, 14 - 20 days from now) centered from nothern OH through PA/NY/CT.

[Ender]

Having just seen the D10 EC from today it at least looks remotely interesting with the lingering energy in the four-corners region. Of course heights are about to start rising around here by D11 - 13 which doesn't bode well.

[usedtobe]

Taking a look at today's analogs we see the following DCA snow occurrences relative to the analog date (D+ is analog date +X days, D- is analog date -X days).

D+8 Analog dates:

11/27/73: 10.2” on D+19

11/30/50: 1.6” at D-5 and 3.2” on D+10

11/25/70:

11/30/05: 1.4” D+5 and 1.6” on D+9

11/20/65:

11/20/03: .9” at D+14, 1.7” at D+16 and 3.6” on D+24

11/24/61: .6” on D+15

12/21/68: .2” on D+15

12/16/55: .3” D+3

D+11 Analog dates (de-duped from the D+8 set):

12/24/65: .2” at D-4

11/29/66: 6.7” on D+14

12/05/54: .1” on D+0

12/06/68:

11/20/55: .2” on D-1

Juding by the pairs of color coded dates this is a pattern that apparently "likes to repeat" itself in 15 - 30 days.

The roll-forward on the D8 analogs shows a tendency for very cold -5C depatures by D+6 through D+12 (IOW, 14 - 20 days from now) centered from nothern OH through PA/NY/CT.

Interesting, not nearly as coherent a a signal as last year. All the days centered within the centered mean 5 day period look light which makes sense. The longer range D+14 and D+19 are interesting if indeed the pattern tends to repeat itself. I do like that the models seem to be trying to get a semblance of a nice vortex going south of the block. That could help us down the road. The 240 hour euro ens mean does not have a bad look to it.

[tombo82685]

Interesting, not nearly as coherent a a signal as last year. All the days centered within the centered mean 5 day period look light which makes sense. The longer range D+14 and D+19 are interesting if indeed the pattern tends to repeat itself. I do like that the models seem to be trying to get a semblance of a nice vortex going south of the block. That could help us down the road. The 240 hour euro ens mean does not have a bad look to it.

wes in that ens map, is that a pos epo ?

[usedtobe]

wes in that ens map, is that a pos epo ?

Tom, I think it more neutral than positive but note that Allan's site shows it weakly negative at 228 hours and weakly positive at 240 hours. I don't think it strong enough to negative the negative nao.

[tombo82685]

Tom, I think it more neutral than positive but note that Allan's site shows it weakly negative at 228 hours and weakly positive at 240 hours. I don't think it strong enough to negative the negative nao.

can i ask, do you have a map that shows a -epo or positive so i can figure out what it looks like on a map. I thought it was trof over alaska that made it a pos epo.

[usedtobe]

can i ask, do you have a map that shows a -epo or positive so i can figure out what it looks like on a map. I thought it was trof over alaska that made it a pos epo.

Here's the typical loading pattern for a positive epo, note the negative height anomalies with positive ones to the south.

Maybe one of the other mets has something better. I also have map with the 500 coorelations with the epo for Jan which puts a ridge in the east with a postive epo but the correlation is not that high.

[tombo82685]

Here's the typical loading pattern for a positive epo, note the negative height anomalies with positive ones to the south.

Maybe one of the other mets has something better. I also have map with the 500 coorelations with the epo for Jan which puts a ridge in the east with a postive epo but the correlation is not that high.

so going back to the ens map posted, it has the -hgt anamolies like you posted for a pos epo, but it doesnt have the higher hgts below that. Is that why its not a pos epo because it doesnt have the higher hgts?

[usedtobe]

so going back to the ens map posted, it has the -hgt anamolies like you posted for a pos epo, but it doesnt have the higher hgts below that. Is that why its not a pos epo because it doesnt have the higher hgts?

I think so but am not an expert on the index. Heck, it's not even used any more by CPC, they've changed it.

[tombo82685]

wes, this is from the 384 hr ggem ens, is this a good pos epo refrence, with the trof over alaska and higher heights cutting underneath?

[nzucker]

wes, this is from the 384 hr ggem ens, is this a good pos epo refrence, with the trof over alaska and higher heights cutting underneath?

That's definitely a +EPO.

December 2006 is another great example of the +EPO/Alaska vortex:

[tombo82685]

That's definitely a +EPO.

December 2006 is another great example of the +EPO/Alaska vortex:

is it possible to have a -epo and pos pna, that would have to be a massive ridge, or just short wavelengths.

[nzucker]

is it possible to have a -epo and pos pna, that would have to be a massive ridge, or just short wavelengths.

Oh yeah definitely...if a PNA ridge amplifies towards AK you could have that pattern. The arctic outbreak on January 16, 2009 looked like that I believe.

[Ender]

FWIW the analogs have dropped some of the poorer years (65, 70, 55) in favor of some better ones. It does seem like our first inch could be coming up here in the 8 - 14 day range (color coded duplicate years):

Day 8 Analogs:

11/25/50: D0 1.6” D+15 3.2”

12/07/81: D+8 1.7”

12/06/54: D-2 .2”

12/07/68

12/22/61: D+2 .5”, D+6 .1”

11/21/81:

11/30/66: D+13 6.7”

12/05/03: D-1 .9”, D+1 1.6”, D+9 3.6”

12/21/66: D-8 6.7”, D+1 .6”, D+3 7”, D+7 1.8”

12/06/50: D+4 3.2”

Day 11 Analogs (unique):

11/28/71: D-3 1.4”