Sunday, July 29, 2012

ECMWF Ensembles' Forecast On Par With Expected Winter Conditions

ECHAMA Precipitation Rate Anomaly

ECHAMF Temperature Forecast Anomaly

The ECMWF Ensemble forecasts for December-January-February (DJF) appears to be the most in line with having a reasonable forecast, over other forecast members of the NMME association. Here's why I chose the ECHAMA and ECHAMF, members of the ECMWF squad.

Ridge over Gulf of Alaska (GOA)
There were some models showing warmer than normal temperatures over Alaska, signifying a high pressure over the area. However, after viewing temperature forecasts on the same members, those members showed above normal precipitation for Alaska, not in line with a high pressure over the Gulf of Alaska. Thus, those members were ruled out.

Ridge over GOA + Cool East US
A ridge over the Gulf of Alaska will lead to cooler than normal conditions over the eastern US. Similarly, a low pressure system over the Gulf of Alaska will bring warmer than normal conditions over the eastern US, as was seen last winter. However, despite a warm Gulf of Alaska, a few members showed a warmer than normal Eastern US, disqualifying their reason into their forecasts.

Wet Conditions over the Eastern US
Due to an incoming El Nino, wetter than normal conditions are expected over the Gulf of Mexico coast as well as the East Coast. One or two members displayed below normal precipitation anomalies over the mentioned areas, practically ignoring the El Nino that will be present come winter-time.

All of that said, I find it probable that if a forecast of the NMME members were to verify, it would be the ECHAMA and ECHAMF forecast maps charted above as described above.

Andrew

ECMWF Digs Strong Disturbance; Accompanying Severe Threat Possible

The ECMWF continues to show the prospect for a potential severe weather event in the first week of August, projecting a deepening disturbance over the western Great Lakes area.

This ECMWF solution seems pretty solid. A strong high pressure ridge remains over much of the southwestern US, and this does not look to go away anytime soon. If anything, expansion eastward seems probable. At the same time, a negative NAO currently in place is likely to persist into August, bringing the likelihood of a disturbance swinging down into the Great Lakes/Northeast regions in accordance with the buckling of the jet stream as is typical in a negative NAO.

If such deepening of a disturbance were to occur, an area of instability would be potent over the Midwest as a cold front attached to the back end of the disturbance would likely swing south and may ignite some strong to severe storms across the Midwest area. However, let's not jump to that conclusion just yet. It remains unknown where any cold front may set up, and if any instability could fuel any thunderstorms. Further analysis of the ECMWF at the same forecast hour reveals lower level winds in place over the Midwest, signaling a favorable thunderstorm atmosphere. However, jet stream winds look to be displaced to the east, which would diminish a tornado threat.

Andrew

Atlantic Development May Increase Soon

Development potential in the Atlantic Ocean may increase in due time as the Madden-Julian Oscillation (MJO) cycles towards Phases 8 and 1. These phases are conductive to development as convection is enhanced over the region.
The model solutions still vary, with the ECMWF forecasting a Phase 1 or 2 situation, which wouldn't be too conductive for tropical cyclone development.

Andrew

Atlantic Development May Increase Soon

Development potential in the Atlantic Ocean may increase in due time as the Madden-Julian Oscillation (MJO) cycles towards Phases 8 and 1. These phases are conductive to development as convection is enhanced over the region.
The model solutions still vary, with the ECMWF forecasting a Phase 1 or 2 situation, which wouldn't be too conductive for tropical cyclone development.

Andrew

Negative NAO Shows No Signs of Letting Up

Sea Surface Temperatures (SST) continue to indicate that the negative NAO that has been in place for well over a month now will continue to stand its ground for at least the next couple weeks.
SST's show a large region of warmer than normal temperature anomalies in the waters surrounding Greenland and as far south as Nova Scotia, Canada. This large warm water anomaly gives a strong indication that a negative NAO is present in the area, with no signal that it is to let up soon.

The NAO ensemble forecasts show a continued negative NAO engagement through the next several days, further enhancing the potential for a disturbance to sweep down from Canada and strike the Northeast with potential severe implications. Whether that comes to fruition remains to be seen.
I feel that the ensemble forecasts are not in the most accurate of realms- yesterday they were displaying a trend to a positive NAO phase, whereas today the ensembles have shifted to a more negative phase. That said, I don't have too much confidence in the ensembles at this time, but I do believe that the forecast listed above is more likely to pan out than a positive NAO.

Of additional interest surrounding the NAO is what the stratosphere is saying in response. In recent weeks, the stratosphere has been warming to normal levels, while it had been near record low temperatures before the negative NAO stepped into the picture.
Because the stratosphere remains at near normal levels rather than cooler than normal, I believe that the negative NAO will remain in place for a while to come.

Is it possible for the negative NAO to stick around into winter? It's possible, but prolonged patterns are like trying to treat diseases with one type of medicine- the more you use that one type, the more potential the disease has to find a way around it and break down the medicine's effectiveness. In this case, the atmosphere could find a way to break through the negative NAO and intense high pressure regimes before winter. Accurate forecasting on those regimes, however, is not warranted at this time.

Andrew