Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1214 AM EDT Mon May 13 2019 Valid May 13/0000 UTC thru May 16/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Great Lakes Closed Low slowly wobbles through New England Tues/Wed with associated coastal surface low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend to 14/06z; Non-CMC afterward Confidence: Above average Models are in solid agreement with the slow progression of the closed low through the Great Lakes into New England including the initial development of the coastal surface low off the Delmarva the slides NNE toward the benchmark 14/06z. At this point, the 12z CMC becomes broader and weaker shifting the track east. As such will eliminate it from the preference after this time period, but otherwise confidence is quite high. ...Small shortwave potentially sharpening through Eastern Great Lakes/Mid-Atlantic Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend (weighted to UKMET/ECMWF) Confidence: Average In the wake of the closed low wobbling into SE Canada, the northern stream starts to dip across the Great Lakes with a speed max moving into the mid-level weakness. The slightly faster solutions ejecting the closed low, the UKMET/NAM and GFS all amplify this wave substantially, the 18z GFS most dramatically. The 00z GFS while still quite amplified took a more sensible approach matching the 00z NAM. The 12z CMC being less favored with the positioning with the downstream closed low leaves it undesired handling this situation. The 12z ECMWF however, being a bit flatter with the wave has the support of the bulk of the ensemble suite including a majority of GEFS members (even though some are even more dramatic with the wound up closed low than the operational GFS). The UKMET is more middle ground and would support that with the ECMWF as preference. Inclusion of the more amplified 00z GFS/NAM is preferred as well but at lower percentage. Confidence is average given the spread and uncertainty built in by small differences in timing from the downstream closed low. ...North Mexico closed low into TX Late Mon/Tues before shearing across central Gulf Coast Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The closed low across northern Mexico is expected to cross into S TX and starts to shear quickly. The difference in guidance is completely affected by convective up-growth to keep the wave compact or weaken slightly to be faster toward shearing into confluent flow across the Gulf Coast. Surprisingly, the CMC is fastest weaken followed by the UKMET. The GFS/NAM are slower with the ECMWF slowest. Timing differences/QPF axis differences are fairly small to support a general model blend at slightly above average confidence. ...Initial broad shortwave/jet streak entering Pac NW Tues, sliding atop the ridge clipping the Northern Plains Wed/Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/12z ECMWF blend Confidence: Average to slightly below average Along the periphery of larger west Gulf of AK vortex, confluent stream flow from the central Pacific and northern Pacific enhance a jet streak and associated shortwave around 50N 130W that slides east into the Pacific NW late Monday into early Tuesday. Given confluence and distant proximity to the larger scale features there is modest to high model spread in timing of the wave. The 12z UKMET is fastest accompanied uncharacteristically with a fairly compact ECMWF solution. The 12z CMC is timed well with the slower 00z GFS and NAM but is much weaker...and this continues through the remainder of the forecast period as the wave runs the gap between the Arctic Vortex in NW Territories and the broad ridge over the Central US. The compact nature of the ECMWF slows it and allows for better timing with the GFS/NAM after forming a lee surface cyclone in Alberta early Wed. The UKMET continues to outpace all other guidance, though the evolution looks more middle ground, not too amplified with the surface wave crossing southern Canada toward N MN but also not too weak/opening into a SW to NE inverted trof like the ECMWF becomes Thurs. Though the ensembles including the 21z SREF/18z GEFS and 12z ECENS mean all generally match the ECMWF. The 00z NAM/GFS both are compact moving through the southern Canada squeeze and support deeper surface reflections, the NAM well north and east of any other solution/ensemble member. To compromise a blend between the 12z ECMWF/00z GFS seems best with some inclusion of the ensemble means. Confidence is average to slightly below average given moderate to high spread especially in timing, but also contingency of strength/placement of the Arctic vortex and the ridge itself. ...Latitudinal stretching of Eastern Pacific Trof with surface low off CA by late Wed into Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/12z CMC blend Confidence: Average As a larger scale trough develops/stretches latitudinally toward late Tuesday/Wed in the wake of the initial shortwave into the NW, there is modest model spread. Ensemble trends over the last four cycles depict a fairly steady state of the ECMWF and ECENS members which are much stronger and further south overall. Recent ensemble and deterministic solutions from the other guidance has slowly drifted toward a deeper solution but not as deep. Still, the 12z ECMWF went much stronger compact and closes off the wave off the CA coast by 12z Thursday, driven by a 165+kt 250mb supergeostrophic jet west of 130W late Wed. This is nearly 15/20kts stronger than the remaining guidance. While the 00z GFS/NAM and 12z CMC feature this strong jet up to 150kts, the shape/strength of the ECMWF calls it into question. The 00z NAM, a bit weaker and initially sharper, leads to a northward close-off and the weaker/slower 12z UKMET, leads to a southward close off. While the ECMWF may be deep, the surface low evolution looks good placement-wise and the 12z CMC is a very good proxy for a weaker evolution and is favored in the WPC preference. The 00z GFS trended this way as well, providing additional confidence, matching the ensemble suite. Confidence is average in a 00z GFS/12z CMC blend. Some inclusion of the ECENS mean/GEFS mean in the blend may help stabilize the moderate spread/hold continuity better. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina