Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1123 AM EST Sat Nov 23 2019 Valid Nov 23/1200 UTC thru Nov 27/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Phasing northern/southern shortwaves across Great Lakes and associated Western Appalachian surface low transferring to coastal low by Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The pieces all appear to be on the board, ie within the RAOB network, that different data assimilation schemes appear to have resolved detail differences to come into a much stronger consensus in the deterministic, as well as within the ensemble suites. The trend toward a stronger, more westward track has become much more evident starting with the 00z suite. This should bring higher moisture while deepening allowing for increased wintry mix through the northern Mid-Atlantic into New England. The consensus brings higher confidence in a general model blend, but given the dynamic deepening/cooling and rather broad shift west, confidence is not absolute. The key on duration, and deepening appears to be the well upstream shortwave/jet speed max crossing southern Canada into the Great Lakes Saturday. This is much faster/sharper with the interaction, which may still not be fully resolved. Still, confidence is slightly above average given the evolution presented in a general model blend. ...Shortwave racing through Canadian Rockies Sunday before supporting Northern Tier surface wave Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Average The fast Pacific flow continues to press the parade of low amplitude shortwave/jet speed maxima through Sat into early Sunday. The last will help break the zonal flow pattern as it amplifies across the Southern Prairies of Canada into the Northern Tier by early Monday. This will support a strong Clipper system. Given the flat/zonal flow, there is expected small timing differences that lead to latitudinal differences as it amplifies. The is most noted in the NAM and GFS a bit further north than the CMC/ECMWF/UKMET. However, the NAM being a bit stronger and slower is effectively well on the northern fridge of solutions, particularly with eh surface low track and QPF swath. All considered, a Non-NAM blend appears appropriate at average confidence (given fast/flat flow regime). ...Developing broad global trof over Northwestern North America... ...Lead shortwave in Great Basin Monday, shifting to Central Plains by Tuesday... ...Secondary broad shortwave digging along West Coast Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECMWF/CMC blend and 06 GEFS/00z ECENS mean Confidence: Below Average In the wake of the last zonal shortwave, the overall large scale pattern starts its phase of amplification centered around Alberta after midday Monday. A strong leading jet and associated shortwave rips through the Great Basin and by 12z Tuesday is sharpening over the CO Rockies, developing a strong Central Plains surface low. Upstream, another broad shortwave hugging the Panhandle of AK will drop south along the Coast, starting to buckle into a larger closed low feature just after the period. The model spread is driven mainly by the spacing between systems. The UKMET is most dramatic with the shortest wave length/spacing. This also allows for great upper level diffluence to support rapid cyclogenesis along the leading edge of the secondary wave, even supporting a sub 976mb low by 27.00z. This solution is enhanced by the 12z GFS, which has flip-flopped with evolution between the 00z, 06z and back on the 12z run. Though the 12z GFS is a bit faster with the lead wave compared to the UKMET. Both provide reduced confidence in the overall solution, as it is clearly plausible for these solutions to manifest (based mainly on the downstream shortwave ridging/divergence aloft). The GEFS/ECENS and CMCE solutions would suggest that the stronger solutions may be a bit too far out of tolerance at this point. The ECMWF/CMC along with the GEFS appear to be a more consistent solution for preference. The 12z NAM, is quite agreeable for the lead wave, through the Rockies into the Plains, but the secondary shortwave is very weak and more driven through the northern stream energy/cold push through the Western states than the shortwave evolution out of the Pacific stream. As such there is hesitation for its inclusion in the blend along the Pacific Coast on Day 3. While the 00z CMC shows the next shortest wavelength, it is only on the edge of the remaining ensemble suite to support a stronger wave. So, it is solid to include it in the blend to help account for the stronger/deeper solution. So all considered both shortwaves, a 00z ECMWF/CMC blend with inclusion of the GEFS/ECENS is preferred. The 12z NAM could be blended in the leading shortwave, but should be excluded along the Pacific Coast with the second system. Confidence is below average, particularly for the second wave. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina