Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 307 AM EDT Thu Jul 09 2020 Valid Jul 09/0000 UTC thru Jul 12/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation with Final Preferences/Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low moving east across south-central Canada through Friday... ...Associated cold front crossing the northern Plains Wednesday/Thursday and the Great Lakes Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/UKMET/12Z ECMWF mean Confidence: Average ...07Z update... The 00Z ECMWF remained similar to its previous 12Z cycle and the 00Z UKMET adjusted similar to the ECMWF. However, the 00Z CMC remains a bit slower and deeper with the base of the trough axis which moves east toward the Appalachians into Saturday morning which is largely unsupported. ...previous discussion follows... South of a mid-level closed low tracking across southern Canada, a shortwave trough will organize and move east across the Mississippi River through Friday morning. Differences with the evolution of this feature impact placement of a related cold front at the surface. The 12Z CMC is the most aggressive and slowest with the mid-level shortwave while the 00Z GFS appears to be the fastest. The 00Z NAM is also a bit slow while the 12Z UKMET is less defined by the end of the week. Mesoscale convective details make for differences with respect to synoptic evolution in each model which is typical this time of year and keeping confidence average at best. ...Low pressure moving northeast along Eastern Seaboard into this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/00Z ECMWF/12Z ECMWF mean blend Confidence: Average ...07Z update... The 00Z ECMWF's mid-level center of the East Coast low shifted farther away from the coast compared to its previous 12Z cycle, with its surface reflection also moving farther offshore, but with less displacement compared to the upper levels. The 00Z UKMET adjusted in the direction of the 00Z ECMWF but remains a bit farther south with its 850-500 mb low, as does the 00Z CMC. The preference is to be nearest to the average of the GEFS/ECMWF mean positions, which is in between the 00Z NAM and 00Z ECMWF, but closer to the ECMWF position...or between the 12Z and 00Z ECMWF cycles. ...previous discussion follows... The 00Z NAM and 00Z GFS are quicker to bring a surface low northward along the East Coast through the end of the week. The 00Z GFS is the fastest to move the low northward and deviates from the relatively good run to run consistency seen in the past 4 cycles of the ECMWF/GEFS/CMC ensemble scatter low plots. The somewhat slower 12Z ECMWF/CMC are a better match to the ensemble clustering over the next 36-60 hours while the 12Z UKMET becomes slower than most guidance. While the models are well initialized with the current surface feature at 00Z, with mid-level ridging to the north of the advancing low, there is some question with how quickly the low will advance. There are also uncertainties with the upstream (OH Valley) trough evolution and subsequent influences on the mid-upper level flow which keeps confidence in the preference only near average. ...Trough moving into the Pacific Northwest Thursday night, over-topping the ridge into the Upper Midwest by Sat and diving into the OH Valley by Sunday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The models show similarly with this system with only minor adjustments noted in the 00Z ECMWF/UKMET/CMC compared to their previous 12Z cycles. ...Larger scale trof dropping into Pacific NW Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average ...07Z update... No significant adjustments were noted in the 00Z ECMWF/UKMET/CMC compared to their previous 12Z cycles. ...previous discussion follows... Minor timing differences exist with the 00Z NAM and GEFS mean slightly slower to advance the trough axis eastward into the Pacific Northwest while the 12Z UKMET/CMC are faster. However, these differences in timing are small enough that a middle ground or general model blend appears reasonable across this area of the country. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml This product will terminate August 15, 2020 with the 21Z issuance: www.weather.gov/media/notification/pdf2/scn20-58pmdhmd_termination. pdf Otto