December 2024 Observations and Discussion

.29" needed rain in the bucket. Low 40's all day.

36 here. Virga or whatever it is called. Sleety slushy kinda confectioner’s powder falling

48* in Solebury, dense fog, visibility barely even 150 yards.

Rainy and dreary blah. Looks like some intense rain and WA (most of the area) or HWW (eastern areas) winds tomorrow afternoon and evening. At least it is good for the drought.

I think snow is going to fly briefly Wednesday night along and to the NW I95. At least a trace and could be c-1". It's rapid temp crash but just won't be enough time for much more. If this had the slightest slow down on the frontal wave I believe 4"+ would've occurred. Rb was a a dime's width away from verifying IMO.

42 at 4:22 am. Play those numbers.

Rain is pitter-pattering. The dog, who wanted to go out, took one look outside and went back upstairs to bed.

58.5 strong southerly flow. Light rain with .25" in the bucket.

Latest 06Z GEFS. Won't be much snow but some is likely. Trace to a coating especially NW of 95.

Tremendous clash of air masses.

I thought it was so post very windy out !!!all my co workers are yelling at me

My guess is right around 9 PM NW I95 see's some snow.

Irish wrote:rb, how much snow are we getting today?    just having some fun, appreciate the work you put in here.

.....Somebody get this man a microphone and a stage

Nah, so, in all seriousness, I want to provide a quick synopsis on why I have been so reluctant about changing my ideas about today's snow. Unfortunately, I can't do a whole discussion, but I want to try to relatively briefly (emphasis on "relatively" LOL) demonstrate why I am STILL hesitant that this feature doesn't surprise people. Without going into too much detail, between the tropics and the Northern Hemisphere, we do have factors that bias cold for the eastern CONUS, most notably:

1. +PNA (ridging in the western U.S.)
2. -EPO (ridging over Alaska)
3. -WPO (overall neutral height anomalies poleward/north of negative height anomalies over the north-central Pacific)
4. -AO (ridging over the North Pole)
5. MJO acting more like a Phase 7/8 atmospherically (as discussed with mugsy in the other thread)
6. downturn of ~1ºC in the ocean water located in Niño region 1.2 ~2-3 weeks ago

The above factors are offset by:

1. +NAO (zonal/progressive pattern in the Atlantic domain, identified by ridging equatorward/south of troughing)
2. no 50N/50W low

^both factors highlighted by heehaw

3. no 70N/70E ridge
4. warm Gulf of Mexico/enhanced latent heat release
5. strong and sustained S.O.I. burst (indicating a change of pressure pattern between Tahiti and Darwin, Australia, which then imprints onto the atmosphere 7-10 days later)

Working within that background, I think that the biggest driving factor is the -WPO/-EPO/-AO/+PNA quadruplet, as that is strongly forcing truly arctic air southward, and, in my opinion, adds extra "oomph" to the background bias of a more aggressive cold push. However, I want to focus in on the details a bit, so here's an annotated image of the current situation:



-blue cold front: cold front at 850 mb, also approximate location of 0ºC line at this level, and what I am using as the approximate rain/snow line in this situation
-red line: 500 mb trough axis
-red circle: area of 500 mb vorticity advection (forcing for ascent)
-yellow circle: area of 300 mb forcing for ascent via jet dynamics
-(not added specifically here, but in green circle below): area of overlap of 500 mb vorticity advection and forcing for ascent from 300 mb jet dynamics

Let me now show you the same image valid for 4-5pm this evening:



The background of the first image wasn't important, however, on this one, it is. This annotation was made on a PWAT anomaly (precipitable water) anomaly chart, which basically depicts how much anomalous moisture could be forced out of the atmosphere if it was all condensed out. Now, Looking at this map, notice where the approximate cold front/0ºC line is - it's approaching the I-95 Corridor, and if I went to the next frame, it would be through it. So, that front is crossing around 6pm, give or take, which is only an hour or two at most after this image verbatim, but look at where the overlap (green circle) is located - that area of best synoptic forcing for ascent throughout the atmospheric column is still well to our southwest. Additionally, note the PWAT anomalies within that green circle, are still ~+.6" by eye, and this is backed up by data showing that the incoming dry air previously mentioned as a concern by a couple people, including heehaw, is lagging further behind the front and area of best synoptic forcing for ascent at various levels (700 mb, 500 mb). Within that green circle, you have very strong frontogenesis at the lower levels (925 mb, 850 mb, and 700 mb), beneath the 500 mb vorticity advection and increasing* jet dynamics as the system progresses, all while still being downstream of the main trough axis, which in itself is a favorable area for vertical motion. All of this leads me to think that the southwestern edge of the precipitation shield, especially behind the 850 mb front/rain-snow line, is still being poorly modeled, and is where I believe the "surprise factor" will come from with this system. Additionally, as the forcing for ascent continues to strengthen, we should see the advance of the low-level cold air accelerate; with more air being evacuated from above, that air has to be replaced from underneath it, which forces stronger convergence/frontogenesis. Now, as that cooling air is lifted, it only cools further, which should help to speed up the changeover process as that trailing forcing approaches.

Trying to remove any previous bias from myself in this analysis, I truly do not see a reason why the southwestern edge behind the front is so dry on modeling with regard to QPF output, and still see a period of a 2-4, maybe even 5 hours where we should be seeing frozen precipitation falling, and with such strong forcing mechanisms in play, can also see it being pretty heavy right up until it shuts down completely between 9-11pm.

I understand that I am on an island, I have absolutely no model support verbatim, and it may seem like I can't admit when I'm wrong, but this just doesn't make sense to me, so I am going to hold the line here and go down with my ship if (when) it sinks. I have no problem figuring out where I went wrong after the fact, as you all know I always like to do a post-mortem/verification, but right now, I have to go with my gut, and that's telling me to watch out for back-end snow. My cards are on the table, so now it's time to let Mother Nature show us her hand.

frank 638 wrote:I thought it was so post very windy out !!!all my co workers are yelling at me

Frank I am disappointed in you lol, the wind advisory is 12 noon to 10pm, and may only last 1-3 hours. Strongest winds from LI to central/eastern CT where there are HWW. I think strong gusts may be localized, this looks almost like a severe t-storm line coming though later.

docstox12 wrote:60 degrees, moderate rain, breezy.
Amazing plume of moisture extending from Florida up to Canada!

And it is all rain : (

62* with a steady rain. Some heavier lines to the west that may contain thunder as the frontal system begins to pass. Rain has turned to heavy snow across western PA as the cold air moves in behind the storm.
Looks like tomorrow and Friday will be a repeat of last Thursday and Friday with blustery cold temperatures and low wind chills tomorrow and more below normal temps on Friday. After a couple warm days, will probably feel even colder tomorrow.

While I would have preferred snow from this system, I believe we should be starting to put some of these drought concerns to rest with these last few rainstorms.

Absolutely torrential outside

Negatively tilted h5 troughs can be mischievous as Rb has pointed out. This tilt says the models might be shutting off the precip a bit too soon.

On current radar there is a substantial area of snow on the cold side of the front extending from about State College PA back to the PA/Ohio border. Will be interesting to see if this cold sector precip sticks together into NJ and gives us some surprise (not for rb) flakes on the backside of the storm.

64 for the high today. And steady rain that started about noon.(We had a 2 min downpour)...Son's school in RI want virtual for evening and stopped all shuttle and evening events.. he said there is heavy rain currently

60*, still sprinkling, 3/4 of an inch of rain so far in New Hope/Solebury

Kalleg, can you see the Raritan river from where you live? How is it running

I'm actually in PA, in Solebury, next to New Hope, across the Delaware River from Lambertville, NJ--about 4.5 miles, 8 minutes from the river. But since you asked about a river, here's the local news.

The Delaware, flowing as a border between PA and NJ, has been really low since the spring, given how little rain we've had--now at 1.7 ft , but is forecast to go up to 5.5 ft on Friday as creeks and small rivers drain from around here and the Poconos. And given where it is now, am thinking that level might be even higher. Good news!

Here's a link to track the flow
https://water.noaa.gov/gauges/nhpp1

Lol in the donut hole. ...rain all around us..this is funny

dropped 10 degrees in 25 minutes 49.5/49.3

.97" in the bucket