All signs point towards the possibility of a white Christmas

We’re in a stormy pattern (already referred to as the “storm train” in some media), and this just might mean a white Christmas for those of us in the mid-atlantic region. While anyone can point towards to the sway of the weather models back and forth between solutions, but something I see that is making me feel confident is the NAO. Specifically, a switch of the NAO from positive to negative.

Now, according to history, a negative NAO will typically mean a big Nor’easter, but I also am a firm believer that a change in the NAO (or any other teleconnection indicy) from positive to negative can bring about substantial weather. Here’s the latest:

The bottom two graphs are of the NAO; the left from the ESRL (Earth Science Research Lab), the right from NCEP. NCEP’s model is usually more trusted, and if you look along the time series, you will see that the changeover occurs right around Christmas. I’ll keep an eye on this, and I’m hoping for a white Christmas!

We just might get snow!

This situation has been looking pretty upsetting for the past few days… because I really just want to see some snow. But first, what’s been going on.

Verification!

Tues:

I said:

A strong warm front will move in… the low will be recorded around 1am or so as the front approaches… 7am it will be below freezing still, by mid-morning warm up to the mid-40s, and from there temperatures will start to plateau. Skies will be overcast all day and night…

What happened:

Temps rose all night; At 7am we were at 31; We didn’t rise too fast- only at 39 by noon; Max temp for the day was 48; skies were OVC all day, with a scattered/broken lower layer at some points

Not bad for a 0-day forecast.

Wednesday:

What I said:

Temps rise slowly throughout the day… possibly only four or five degrees from the low … We might hit 50 or even a few degrees higher. A mostly rainy day… most of the rain will be in the morning to mid-afternoon period. Winds will be moderate out of the south.

What happened:

We got up to 57! Wow! Rain all day. Winds were out of the south, then changing to out of the west, max sustained at 14 mph.

Now, what’s gone on today and tonight:

Lot’s of rain! The area is under a flood watch, and some parts of metro Philly are under flood warnings (but not flash flood warnings, meaning streams will slowly rise).

I’ve been very pessimistic about the possibility of snow tomorrow (Friday) morning and day, but I think we just might have a shot at a few flakes. I say this due to the fact that the latest NAM run has the 850 temps at -1 C at 7am. This could bring snow, since the snow will have (hopefully) not melted by the 850mb level. I still doubt any real accumulation, but a dusting isn’t out of the question- though I wouldn’t really call it a dusting… more like a layer of cool whip on top of the soaked ground.

Only time will tell!

Morning update – Early/Mid Dec East Coast event

Well there is certainly a lot going on today… severe weather in the south central US, Winter Storm Warnings in Michigan, and seemingly mild (but actually seasonal) temperatures here in Millersville.

WeatherTAP National Radar (Winter Mask) 12/09/2008 at 14:25z

Due to some technical problems, the Millersville Observations are not operational right now, but I’m using a few other local Personal Weather Stations (PWS) from Wunderground and other sites. From what I can tell on Wunderground’s Wundermap, temperatures are inching towards 40 in the mid-atlantic region as I write this, and they should be slowly but steadily rising up throughout the day, with a high around 49. Clouds are just about overcast now and I expect this not to change for a few days.

The Thursday night / Friday event seems to have all but disappeared from the latest (12z) NAM run (which, on the latest run, goes out till Friday evening), though the HPC’s forecast (issued very early this morning) still the idea of some sort of secondary low.  Last night’s GFS run is still showing the low forming south and moving up the coast. This solution, however, leads to a more east track. However, knowing how low the resolution of the GFS is (compared to the NAM and actual obs), this sort of difference isn’t too big of a variance 60+ hours out.

Upcoming complex system – a one-two punch

This upcoming system has a lot of things going on, and I couldn’t resist posting about it. In case this is your first time reading, I post mostly to keep track of what I think is going to happen, and see how I do. I figure some real world forecasting (and the ever-important verification) will somehow help me become a better meteorologist. At least that’s the goal!

Alright, back on topic: What’s in store for the Millersville/Lancaster/SE PA area over the rest of the week.

Tuesday: A strong warm front will move in… the low will be recorded around 1am or so as the front approaches… 7am it will be below freezing still, by mid-morning warm up to the mid-40s, and from there temperatures will start to plateau. Skies will be overcast all day and night… and that goes for the entire rest of the week, as well.

Tuesday Night: Temps will be in the mid to upper 40s throughout the night under overcast skies… moderate winds out of the southeast, turning south by day break. Possible isolated shower late.

Wednesday: Temps rise slowly throughout the day… possibly only four or five degrees from the low- this, of course, due to the overcast skies. We might hit 50 or even a few degrees higher. A mostly rainy day… most of the rain will be in the morning to mid-afternoon period. Winds will be moderate out of the south.

Wednesday night: The rain continues… we’ll probably receive over a half inch by late Wednesday night. I’d say about 0.8 inches total for this part of the storm. Winds will die down and begin to come out of the southwest. Temps will fall below freezing.

Thursday: Rain finally tapering off! Skies will be partly sunny to mostly sunny for the day, with a high struggling to reach 40 or so.

Friday: I’ll be back to update this… at first glance its looking like there is a chance of a coastal low riding up the east coast, which could spell snow! I’ll delve deeper tomorrow.