Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 312 AM EDT Fri Sep 13 2019 Valid Sep 13/0000 UTC thru Sep 16/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Northern Plains/Upper Midwest Closed Low and Approaching Shortwave... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Above average A closed low currently over the northern Plains will lift northeast and open up as it moves toward Ontario/Quebec this weekend. Through 36 hours, there are only subtle differences in the 500 mb heights and mass fields. A secondary shortwave behind the main wave then approaches the northern tier of the U.S. and southern Canada. The 00Z GFS is a bit deeper/amplified compared to the rest of the guidance. Otherwise, guidance is in fairly good agreement through the end of Day 3 and a general model blend is preferred. ...Closed Low Approaching Pacific Northwest Day 3... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Above average 07Z Update: The 00Z UKMET remains too fast with the digging trough over the Pacific Northwest, especially by Day 3. The rest of the models keep the trough axis offshore by the end of Day 3, while the UKMET is solidly across the interior portions of OR/WA. With this in mind, felt that it is too fast and should be excluded from the blend, especially for Day 2/3. ---previous discussion--- A broad and strong closed low is expected to drop southeast from the AK coast toward the Pacific Northwest by the end of Day 3. There is above average support from the deterministic and ensemble guidance with the evolution of this system such that a general model blend of the available guidance is preferred at this time. The 12Z UKMET is perhaps a tad faster than the rest of the guidance but its differences are not significant enough to be excluded at this time. ...Potential Tropical Cyclone Nine... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Official NHC Forecast Confidence: Much below average 07Z Update: The rest of the 00Z guidance trended toward the east similarly to the GFS/NAM, with pretty much all the guidance now taking the low well off the FL/GA coastline by Day 3, although there is considerable differences in terms of strength/intensity. This is a below average forecast, particularly beyond 24-36 hours. The latest official NHC track lies similar to a NAM/CMC/ECMWF blend but users should see the official advisory for the latest information regarding Potential Tropical Cyclone Nine. ---previous discussion--- See the latest official NHC advisory on Potential Tropical Cyclone Nine. Satellite imagery continues to show blossoming convective cloud tops around Potential Tropical Cyclone 9 located over the southeastern Bahamas. There is a growing consensus in the cyclone developing into a Tropical Storm as it approaches the east coast of Florida in the next couple of days. The track however remains uncertain. The 00Z GFS did trend toward the other non-NCEP guidance and shifted eastward, although it remains the western outlier with its surface low moving toward Tampa and then turning northeast toward Lake City. Meanwhile, the 12Z UKMET/CMC/ECMWF all remained off the east coast of FL, although with varying degrees of intensity. A time trend analysis over the past 4 model cycles show the GEFS members trending eastward toward the ECENS and CMCE solutions. The 00Z NAM also offers some utility as its track is fairly similar to the official. For now, based on the latest advisory, the best proxy is a consensus of the ECENS/CMCE with some inclusion of the NAM through Day 3. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Taylor