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What’s in a name? Winter Storm Watch/Warning/Advisory


The map is showing purple! And pink! And blue! Winter weather is on the way! Here are the areas under a Winter Storm Watch, a Winter Weather Warning, and a Winter Weather Advisory.


WHAT DOES THAT MEAN?! I’m just a person who looks up their forecast on the phone and sees snow and gets concerned. What is a Winter Storm Watch? How is it different from an Advisory? That’s great that there’s a difference, but I’ll be damned if I know what that difference is.

Stop posting those stupid multi-colored maps thinking what you’re doing is making any bit of difference. Make a snow accumulation map. Inform people on timing and intensity. Will there be ice, too? How much? When? How bad will the roads be?

Maps like the one above are mostly useless to the general public. Add information that people can actually understand and use to plan.

Of course, this is all part of the “we have too many ways to say it will snow” conversation, which I am all for consolidating all these Watches/Warnings/Advisories into something that’s much easier to ingest. But that’s another topic for another day.

Winter 2014-2015 (DJF) Forecast

I like to keep my seasonal forecasting short and sweet, so here it is:

– Latest model guidance and ENSO trends suggest DJF will likely be a weak El Nino.
– +PDO to support ridging in the western U.S. and troughing over the Midwest/eastern U.S.
– +AMO could help keep the Southeast milder (read: less cold).
– -QBO will allow for a greater chance for blocking in the Atlantic (-AO/-NAO) as well as stratospheric warming events. This would promote colder temperatures in the eastern half of the country.
– Drought conditions in the West will promote warmer and drier conditions there.

– The western U.S. could go warmer given favorable +PDO and long term drought.
– If -NAO/-AO becomes the main forcing mechanism for the U.S. weather pattern, it could bring colder air into the Midwest, Mid-Atlantic and Southeast while providing warm and wet risks in New England.
– If a moderate Nino develops, a stronger subtropical jet associated with it could allow for wetter conditions across the southern U.S. and Mid-Atlantic.

A note on my track record… I have been about 50/50 with long-range forecast skill since I started in 2010. There are many others out there with more long-range knowledge, reasoning and a better understanding of how the atmosphere works on a longer timescale. That said, nearly every forecast I have seen so far favors a warmer West and cooler East, so I’m not exactly breaking the mold with this forecast. It looks like we’re all in the same boat with this one. The only thing left to see is if we can sail to victory or go down with the ship in defeat.

As always, the forecast anomalies are based off the latest 30-year normals (1981-2010).

Winter 2012-2013 (DJF) Forecast – Update

My original forecast from August had to basically be thrown out due to a few key factors.

1. ENSO faltering. While the positive trends have recovered, there was a major misstep in the trend as the values for most of the ENSO regions started to fall. The latest data indicates that the positive trend has resumed, which led me to go with an ENSO value bordering on positive neutral and weak Nino for DJF. A new ENSO prediction means new analogs, which can be found at the end of the post.

2. Siberian snow cover. As you can see from the graphic below, significant gains have been made in Siberia compared to the start of the month. Studies show a correlation between positive snow cover trends over Siberia and cooler temperatures across eastern North America.

3. The North Atlantic Oscillation (NAO). The NAO has generally been negative since May, and it shows no signs of going positive any time soon. A -NAO helps pull cold air into the eastern U.S. during the winter months.

Along with this new data, I also used the PDO and AMO signals to help weight my analog years.

The monthly breakdown:

Winter 2012-2013:

in [year (weight)] format

1976-77 (more)
1958-59 (more)
1952-53 (more)
2003-04 (less)
1990-91 (less)
1979-80 (less)
1960-61 (less)

NOTE: Anomalies are against 1981-2010 normals.

Winter 2012-2013 (DJF) Forecast – First Look

The monthly breakdown:

Winter 2012-2013:


Looked at the possible/likely ENSO forecast (around +0.9 for DJF holding steady or fading slightly) and matched years within +/- 0.3 of this. Analogs that had negative ENSO anomalies the previous winter and near neutral ENSO during the summer were favored. I then took the previous summers’ temperature anomalies into consideration when weighing the analogs.

in [year (weight)] format

2006 (more)
2002 (normal)
1994 (normal)
1986 (normal)
1953 (less)

NOTE: Anomalies are against 1981-2010 normals.


– A persistent -PDO could keep the West Coast cooler.
– The +AMO could allow for warmer temperatures in the Southeast and southern Plains.
– The -QBO might trigger blocking earlier than expected and allow cooler temperatures to work into the north-central U.S.
– Drought conditions over the central U.S. might keep drier and warmer weather over the central Plains and southwestern Midwest.

Winter 2011-2012 forecast verification

This was an ugly forecast… pretty much the exact opposite of what actually happened. There was virtually no blocking this year (I was relying on blocking for the cold pattern), and a fairly persistent and strong trough over Alaska prevented any sort of real, long-lasting cold from entering the U.S.

DJF temperature forecast: F

December 2011: F

January 2012: F

February 2012: D-

DJF precipitation forecast: D

Christmas weekend snow thoughts and January update

UPDATE 12/22: Doesn’t look like it’s going to be a white Christmas unless you try to scrape out a little orographically-induced snow in the western Appalachians (which even then is a bit of a stretch unless the 500mb vort. from the northern stream intensifies like on the 12z GFS). I won’t put chances at 0% but it’s certainly very low.


There is still a lot of disagreement between the models concerning the potential Christmas Day winter storm. Right now the 12z Euro Op. is bringing front-end snow into the Mid-Atlantic followed by rain that lasts until the end of the event. While the Euro has trended northwestward with this system in recent runs, it is not worth looking into the trend too much at this range considering the high amount of uncertainty with this system and its ability to jump wildly in both position and time in ANY direction. It is my personal opinion that true run-to-run trends aren’t that telling of specific winter storm systems until we get within the 72 hour window.

This isn’t even bringing the GFS Op. into account, which over the last two runs has failed to produce a system even remotely like the Euro. The lack of support by the GFS is another good reason to dismiss any trends on the Euro at this stage of the game since there’s obviously a lot of different possibilities still on the table.

Having said all that, I have come to the conclusion that this potential storm needs to get “punted” for at least another day (more likely two days). There’s no reason to call for snow, rain, mix or whatever at this point since the models can’t even come up with similar enough solutions. Given what usually happens when there’s a huge disagreement between the models, I’m going to say that the GFS picks back up on the storm by the 00z Thursday run while the Euro starts to lose the “trend” it has displayed over the last couple of runs and become more random with its shifts. Right now the Euro typically has an edge on the GFS in sniffing out the general storm track and timing, so I’ll give the Euro a heavy lean for now, but by no means am I going to take it verbatim.


As far as January temperatures are concerned, I’m going to have to do a similar thing I did with December and basically flip my forecast around, resulting in a cool West and warm East. Aside from some blips in the stratosphere, there really isn’t anything to stop the eastern U.S. from “torching” in January. AO and NAO look to remain solidly positive going into the start of January as the PNA tries to shift negative (though I have a feeling it might stay neutral to slightly positive, which doesn’t have much an effect on the eastern U.S. given the much stronger AO/NAO signal). The forecast becomes a lot more uncertain heading into the second half of January, but confidence in a warm start to the month is higher than normal given what the medium range signals are forecast to be.

For the month as a whole, I currently have the East Coast around 2-3F above normal, but the first half of the month could easily be 3-5F above normal before any potential for a lasting period of cooler temperatures. I will post a U.S. forecast map for January at the end of the month.

Snowfall Verification for Dec 7-8

Quite a trying forecast, but overall it wasn’t a complete loss. Verified the mountain areas and highest totals fairly well, but the more heavily populated areas left much to be desired. Looking back, I could have been less generous with the 2-4 inch range in northern MD and southeastern PA, but other than that and bringing the 1 inch cut-off further north in MD I don’t see much that I could have done to change my overall thinking for this event.

The changeover from rain to snow was fairly messy east of the mountains, and most did not even transition to 100% snow. On top of that, the snowfall ended more abruptly and sooner than I had expected, which prevented the stronger cooling to make it to the surface in tandem with the back edge of the heavier precipitation. That slightly warmer boundary layer is what turned 1-4 inches into little to no accumulation.

Going to be a little generous and give myself a C- overall, though it wouldn’t take much convincing to push that to a D+ considering the bust in south-central/southeastern PA and MD and the western edge of the snowfall.

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