Monday, December 10, 2012

December 14-17 Potential Winter Storm

The models are converging on the potential for a winter storm during the December 14-17 timeframe.

We'll start off with the American's GFS model. This is the sea level pressure (SLP) anomaly forecast for hour 120, or 5 days' time. We can see this potential winter storm emerging from the Plains as a 1005 millibar storm system, cloaked in dark blue, signaling below normal height anomalies for the region (a.k.a. a low pressure system). A few things to note here, we can see two high pressure systems on either side of this system. We have a 1022 millibar high pressure system in the Southeast, as well as a high pressure system in Canada. The latter is shown in orange colors. These two high pressure systems could create a straining of the jet stream, which means the storm could squeeze through the Ohio Valley, in between the two areas of high pressure.

24 hours later, on the morning of December 16th, we see that our system has taken the path it should with two high pressure systems on either side. The storm system has moved into Ohio, with the central minimum pressure now at 1003 millibars, still fairly high for a storm system, indicating it is weak. At this point, it could go one of two ways- out to sea in a due-east path, or shoot north into Canada. It will come down to the placement of this 1027mb high pressure system in Canada. Personally, the more climatologically-favored path would be east and possibly up the New England coast, but we'll have to wait to see what future forecasts say.

Unlike the GFS model, the European's ECMWF model shows plain values of SLP, rather than anomalies. The ECMWF ejects this system from the West as a pretty strong 997 millibar system. It is also a bit further north than the GFS' 120 hour forecast (this ECMWF forecast is also for 5 days out), but the main issue is strength difference. We see two areas of high pressure to the east, one in the Mid Atlantic and one in Canada. The system has to go somewhere, and that 'somewhere' will be towards the weaker high pressure system.

The Hour 144 forecast from the ECMWF model has the system diverted to the northeast, because a storm system won't just hightail it right at the weaker high pressure system- it will still be diverted. This storm is now in southeast Wisconsin, with a minimum central pressure of 997 millibars, unchanged from the previous forecast. Obviously the ECMWF is further north than the GFS, but I don't want to mess with that right now.

Preferred Forecast: ECMWF
Confidence: 45%


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