Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1234 PM EDT Mon Apr 01 2019 Valid Apr 01/1200 UTC thru Apr 05/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Cyclogenesis Tuesday off Southeast US...Moving Up East Coast Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECMWF/ECENS, 06z GEFS mean, 12z GFS Confidence: Average An upper level shortwave trough currently over Texas will continue moving east toward the Southeast US through Tuesday. This energy will initiate cyclogenesis off the GA/SC coast Tuesday morning. This low will then deepen and race northeast, brushing the NC Outer Banks before moving up the East Coast. A time trend analysis shows the latest 12z guidance trending slightly westward as well as a tad faster. The 12z NAM is furthest west, at least through 00z Wednesday, and is closely aligned with the latest GFS as well. Through about 00z Wednesday, the models are in fairly good agreement spatially and temporally. The QPF maximum through 00z Wednesday will skirt the Outer Banks, with the GFS and NAM showing the most QPF falling onshore, owing to its western shift this cycle. After 00z Wednesday, solutions diverge, where the ECMWF/CMC/GFS are faster than the NAM and also on the western side of the model consensus. The 00z UKMET is fairly similar to the NAM but differ on how deep the low gets off Cape Cod through 00z Thursday. It's not until the northern stream energy coming from southern Canada Thursday that the whole system deepens again with the surface low falling into the 980s mb. By this point however the QPF will be offshore and much of the eastern seaboard will be in northwest flow. Looking at the ensemble guidance, the operational ECMWF is very close its ensemble mean while the new GFS is again left of the 06z GEFS mean. With this in mind and looking at the QPF fields, a blend of the ECMWF/GFS (with their respective means) is preferred through the forecast period. Additionally, some inclusion of the CMC would be reasonable as well. ...Western US trough, southern/central Plains system mid/late week... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 04.00z GFS/ECMWF blend after 04.00z Confidence: Slightly above average Another shortwave trough will approach the western US coast late Monday into early Tuesday, centered mostly on central/northern California. This wave will quickly eject through the Rockies and move into the southern/central Plains by mid/late week. A weak surface low develops in response over OK/TX. Here, the latest GFS is a tad faster than the rest of the guidance by 00z Thursday. The 12z NAM is also more progressive with the surface low, taking it to central AR by 18z Thursday while most of the other guidance is back across northern TX/southern OK. The 00z UKMET is a bit more amplified, but overall the guidance is fairly good agreement with the mass fields. By the end of the forecast period, a stronger shortwave trough will move closer to the Pacific Northwest. The bulk of the system will push onshore after the current forecast period, but there is considerable spread in the 500 mb heights tilt/orientation. The GFS is the fastest solution and also further north (brings the trough into WA State) while the ECMWF/UKMET (and NAM to some degree) are further south over northern CA. The CMC is an outlier showing most of its energy rotating into B.C. Canada. The initial preference will be a general model blend through about 04.00z then lean on a blend of the GFS/ECMWF afterwards. The greatest model uncertainty is across the Pacific Northwest late in the forecast period where perhaps some inclusion of the UKMET is possible as well. ...Shortwave trough across Midwest Tuesday/Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Impressive northern stream energy will brush the northern Plains and Upper Midwest by mid-week. There is reasonably good model agreement with this feature as it moves across and for the mass fields, a general model blend will suffice at this time. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Taylor