Computer Model Trends: St. Patrick’s Day Storm

Fred CampagnaMarch 14, 2014

UPDATE – 12Z ECMWF and CMC

Both models are much farther south than the 12Z NAM, which is an outlier from the model consensus at this point. However, I’m reluctant to totally throw in the towel on this one. We’ll see where the 00Z runs go, but it would not be a shocker if they trended north of the 12Z runs.

UPDATE – 12Z GFS

The 12Z GFS is a complete swing and a miss for snow in Southern New England. It has shifted south from the overnight runs and does not bring a flake of snow to SNE. Based on the way the winter has gone, I tend to lean toward the GFS miss instead of the NAM smash hit. Next up is the CMC then the ECMWF.

UPDATE – 12Z NAM

The 12Z NAM model is “robust” for Southern New England, and the timing of the storm is mainly Sunday night, which would help with accumulations. The model projects 8-12″ of snow for Southern New England. I’m very anxious to see what the 12Z GFS has to offer.

From Earlier Friday

An on again, off again Southern New England storm is more “on again” based on the latest computer model trends. While it has not risen above nuisance status, there is still potential for this storm to have an impact on travel in part of Southern New England on Monday. Keep in mind, there are lots of factors to consider with a snowstorm just before the start of spring. The snow needs to really come down during the midday hours if it is going to stick to the roads. Most of the big impact storms after March 15 have happened at night. This one is scheduled to come primarily during the day. The timing is not set in stone because the models are splitting the storm into two separate bundles of energy. If it ends up being one storm instead of two systems, that could change the timing, intensity and impact. Here is a look at some of the latest model trends as of the Thursday night and predawn Friday runs.

06Z GFS Bufkit data has a minor-moderate snow event in Southern New England. At this time of the year, it's unlikely this storm would have the impact of a 4" snowstorm in mid-winter. — 06Z GFS Bufkit data has a minor-moderate snow event in Southern New England. At this time of the year, it’s unlikely this storm would have the impact of a 4″ snowstorm in mid-winter.

The NAM has a higher impact scenario, with a decent snowstorm followed by sleet in the I-95 corridor. Farther inland, it brings a foot of snow to Worcester.

The Canadian model has been insistent on a minor/moderate storm on Monday. Other models were coming on board Thursday night.

The CMC ensemble mean looks decent for some impact in SNE

The JMA has a higher impact scenario similar to the NAM, but a bit farther south, so most likely all snow for I-95

The operational ECMWF has a minor event with the energy strung out through the Mid-Atlantic. Snow would have a tough time sticking to the roads because it would not be heavy.

ECMWF snow totals are highest in the Mid-Atlantic, with less than 2" for most of SNE. — ECMWF snow totals are highest in the Mid-Atlantic, with less than 2″ for most of SNE.

ECMWF ensemble mean indicates a better looking storm than the operational model.

06Z GFS with a minor event for SNE. Some accumulating snow, but primarily on the grass because of the light intensity and midday timing.

06Z GFS - also a strung out storm with some energy jumping into the Atlantic Ocean. Not a big deal for SNE. — 06Z GFS – also a strung out storm with some energy jumping into the Atlantic Ocean. Not a big deal for SNE.

GFS ensemble mean looks a lot like the CMC and ECMWF with a decent setup for some snow in the Mid-Atlantic and SNE.

ECWMF ensemble members - some are predicting a big storm for SNE, therefore the mean has more snow than the operational. — ECWMF ensemble members – some are predicting a big storm for SNE, therefore the mean has more snow than the operational.

Short Range Ensemble Forecast - predicting a moderate to high impact event for SNE. The SREF has not had a good winter so far, but we'll keep an eye on it. — Short Range Ensemble Forecast – predicting a moderate to high impact event for SNE. The SREF has not had a good winter so far, but we’ll keep an eye on it.

06Z NAM - without a doubt the highest impact scenario for the Mid-Atlantic and Northeast. We'll see if it backs off on Friday's runs. Keep in mind, this algorithm treats sleet as snow, and the totals would be lower than projected on this map from the coast to I-95 — 06Z NAM – without a doubt the highest impact scenario for the Mid-Atlantic and Northeast. We’ll see if it backs off on Friday’s runs. Keep in mind, this algorithm treats sleet as snow, and the totals would be lower than projected on this map from the coast to I-95

06Z NAM with a vigorous system bringing snow and a wintry mix to SNE on Monday

The Bottom Line

It looks like there will be some snow in SNE on St. Patty’s Day, but it is still unclear if it will be enough to cause major travel issues and potential school closures or delays. We will keep you posted throughout the weekend.

Fred Campagna

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