Sunday, May 31, 2015

Heading Into June

Yesterday (May 30th) was the first 100 degree day at the NWS observing site at the airport - the high reached 102 F. May has been very mild and it has only been during the past few days that the air conditioner has been coming on during the afternoons - nice.

Andres has been a Category 2 hurricane since yesterday afternoon and is now heading northwestward toward cooler waters and its gradual demise. The above IR image is from 11 UTC this morning. A MIMIC blended PW analysis (below, for 08 UTC from CIMSS at the University of Wisconsin) shows very high PW south of 20 degrees north and an intrusion of values of just over an inch into the southern GoC. However, Andres position, and his associated PW field, are very much different than the global models long range predictions of a week and more ago, which took the storm much more to the north and east. The next tropical system is already developing, and the GFS is again spinning this second eastern Pacific system up earlier than is the ECMWF

Although Andres has provided a nice example of how very far off the long-range, global model forecasts can be, I'm going to venture into those waters again. There are interesting differences between the ECMWF and the GFS operational members at 168-hours from 00 UTC last evening. The 500 mb forecasts valid at 00 UTC on June 7th are shown above for ECMWF and below for the GFS. 

The two forecasts are fairly similar for the continental U.S., but the differences over the Southwest are enough to be significant. The closed low at 500 mb in the GFS forecast is south and west of the same feature in the ECMWF forecast. The anticyclone to the south and east of the lows are similarly located in different spots (GFS centered over the Big Bend and ECMWF centered over eastern Texas), with the GFS high being much more pronounced. The net result is that the ECMWF has dry, southwesterly flow over Arizona, while the GFS forecasts southerly winds over the state with a long fetch from low latitudes. The GFS forecast allows high PW values of an inch or more (see bottom graphic) to intrude into Arizona and southern California. So, the question will be whether the GFS forecasts are again over-forecasting a tropical moisture push to the north. 

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