Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 237 AM EDT Tue Sep 11 2018 Valid Sep 11/0000 UTC thru Sep 14/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Gulf of Mexico Wave... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z NAM/UKMET/ECMWF blend Confidence: Average 07z update: Little change with the remaining 00z solutions...the CMC remains fast (and a bit more deep/closed), while the UKMET/ECMWF continue to match best with the NAM...so just replacing the 12z runs with the 00z runs in the NAM/UKMET/ECMWF blend at average confidence. Generally modest but high amplitude ridging will dominate the east from the Lower MS River Valley to New England in advance of Florence and this appears fairly agreed upon and strong within the ensemble suite/deterministic runs with small differences at the fringes (Nova Scotia/Gulf of Mexico). In the Gulf, a tropical wave will traverse the Yucatan Wed into the Western Gulf with some solid indication of amplification potentially into a tropical cyclone by late Thurs/Fri as it approaches the TX coast. The 00z GFS continues to be the weakest/least amplified solution even less than the GEFS mean and the 12z CMC is clearly fast. While the 00z NAM looks a bit off axis with the trof compared to the UKMET/ECMWF, there is some useful signal toward a compromise for its inclusion. As such a 00z NAM and 12z ECMWF/UKMET solution is preferred in the Gulf by late week at average confidence. ...Pacific Northwest/Northern Plains/Canada... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/ECWMF/UKMET blend Confidence: Average 07z update: The 12z ECMWF further slowed sharpened the northern stream wave and remains similar to the GFS/12z ECMWF, initial preference. It also favorably flattened the lead height falls/energy from the closed low. The 00z CMC continues to be very strong/sharp with this wave across central Canada...and remains unfavorable. The 00z UKMET, while not as sharp/west as the ECMWF... has further sharpened to provide a bit more confidence toward the initial preference and its full inclusion at this point. Confidence remains average overall in a GFS/ECMWF/UKMET blend. Two streams begin to phase/grow upscale into a larger scale/global scale trof toward Thurs. The middle stream/closed low along the BC coast will slowly drop south and potentially shed energy eastward across the Rockies, as the northern stream trof sharpens under strong cold air advection from cross-polar jet off the NW Canadian Arctic Sea. The increased spread in model solution is directly related to: 1) amount of the mid-stream wave shedding east and 2) the angle, ie leading, phased or delayed to the digging northern stream trof. Here, the 00z NAM continues to lead with greater amount of the wave lifting. The 00z GFS sheds a modest amount eastward but the bulk of the closed low remains phased and languishes waiting for main height falls over BC upstream. The 12z ECMWF is a mix of the two, having shed more of the wave east BUT also shows a much stronger/slower digging northern stream trof; as such it stands out in the ensemble spaghetti cycle to cycle analysis plots, but seems plausible. The 12z CMC, is most like the ECMWF, but is very strong with the wave into central Canada messing up the otherwise good positioning of the stationary frontal zone bisecting the northern plains. All in all, the 00z NAM and 12z CMC look most out of place with most unfavorable sensible weather evolution/timing across the Pacific NW and Northern Plains, and as such a 00z GFS/12z ECMWF blend is preferred with lower weighted inclusion of the UKMET, confidence is average given all the internal wave interactions and differences that have the potential to unfold... though large scale the trof placement/orientation look solid. ...Hurricane Florence... ~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: See NHC forecast discussion Best Proxy: 10/12z UKMET 07z update: The 00z GEFS mean and CMC continue to shift eastward with the stalling/anticyclonic loop, near or offshore of the Outer Banks, The 00z ECMWF and UKMET keep their tracks but at 84hrs both show signs of stalling, bringing greater certainty for the slow/stalled solution but less for the precise location/latitude of landfall. So, the UKMET remains best proxy for 03z NHC forecast but not past 78hrs as it is stalled near/along the coast than plunging inland further. As such the 10/12z UKMET remains best proxy to NHC. Models are in fairly strong agreement with the track and now much better in timing through the first 66hrs with respect to Florence. As the hurricane reaches the Gulf Stream, timing/tracks rapidly diverge into a strong weakness 'col' in the flow. The stronger ridge solutions (ECMWF/UKMET) continue to press the cyclone ashore, with the ECMWF and a bulk of its members further south and further ashore. The GFS/GEFS/NAM and CMC solutions are very slow/even stall starting to make an anticyclonic loop near or just ashore of NC. Either way very heavy rainfall is expected with some beyond extreme totals possible (especially with tighter, near coastal loop solutions), so please refer to WPC QPF forecasts and Excessive Rainfall Discussions. All in all, the 03z NHC official forecast is very close to the 12z UKMET solution and can be used as a solid proxy for the official forecast. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina