Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 236 PM EDT Tue Jun 05 2018 Valid Jun 05/1200 UTC thru Jun 09/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation including preferences and forecast confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low/upper trough over southern Quebec sliding thru the Northeast today... ...Associated surface low moving through southern Quebec and redeveloping over SE New England today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Solutions continue to converge on common solutions for the upper trof swinging through the Northeast with the associated redevelopment off the SE New England coast late tonight into tomorrow morning, as well as the exiting surface low SE of Nova Scotia. Minor differences remain as the 12z GFS is showing typical fast bias (especially with the exiting low off Nova Scotia, but this also allows for the upstream trof/surface low to shift faster comparatively. As such the GFS is a bit north and left of track with the surface wave as it lift north into Day 3 as well, but these remaining differences small enough to be smoothed out by using a general model blend with higher confidence in the resultant mass fields. Confidence is slightly above to above average in this blend. 19z update: Slightly faster/westward shifts were noted with the 12z ECMWF/UKMET/CMC tightening the cluster to the 12z GFS for both surface waves. The upper/mid-level patterns were also better aligned to have above average confidence in a general model blend. ...Lower MS valley shortwave advancing southeastward and stalling in the NE Gulf thru Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average While the feature is generally weak and stretching into the base of weak troughing along the east coast, models continue to be fairly agreeable with the placement/depth and timing. The 12z NAM shows some smaller scale internal maxima associated with convection and higher-resolution of the model but still acceptable. The 00z CMC is the only minor displacement, as it generally shed the bulk of s/w energy into the east coast trof allowing the remaining energy to be progressed further southeast across the Eastern Gulf, sufficiently to be an outlier. As such above average confidence is given in a non-CMC blend. 19z update: The 12z CMC slowed initially, retaining similar amounts of mid-level energy into the Eastern Gulf, like the remaining guidance. As such a general model blend can be supported at above average confidence. ...Mid-level shortwave moving across southern Canada through Thursday with accompanying surface low/front eventually the Northeast Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The 12z NAM/GFS continue with continuity and strong model alignment in depth/shape and timing as the shortwave crosses the NW high plains into southern Canada. Surface response is also quite agreeable with the associated low translating across S Canada and the inverted trof/cold front through the Dakotas into the Upper Midwest. This continues through Ontario/Quebec toward the Northeast Thurs into Fri, respectfully; the only minor departures is a slight lagging of the 00z UKMET with the placement of the surface wave in Canada, but the frontal zone remains well timed through 00z Sat. As such above average confidence can be given to a general model blend, with perhaps a Non-UKMET blend in Canada on Thurs. 19z update: Little overall change with the exception of the UKMET coming back to strong low level mass agreement. As such a general model blend can be supported through the entire domain at above average confidence. ...Weakly amplified shortwave off CA coast Wed...lifts through Intermountain West supporting "ridge-rider" MCSs in Northern/Central Plains Thurs night and Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly below average Trailing shortwave energy at the tail end of the wave described in section above, is able to amplify slightly in the weakness between system and slowly drift ashore central CA by midday Wed. The amplification is sufficient to allow for increased downstream broadening/diffluent flow to support return 'upslope' flow and spark convective complex(s) from MT to CO along the lee trof. Here, mass fields are in good agreement with only small differences in timing (CMC slow) yet the mass fields are in fairly good agreement. The differences remain in the thermal profile and convergence along the SW exiting frontal zone through the Midwest which in turn, change focus of convective development into Fri. The ECMWF/UKMET are both a bit warmer in the lower to mid-levels across IA/IL which limits convective development here and shifts forcing further north to the next MCS rolling through SD into MN. The 12z GFS/NAM and CMC are a bit cooler and allow for more development in IA/N IL/S WI and slightly reduce convection across SD, shifting to best height-falls/forcing in MT/ND by late Fri. With respect to mass fields, no guidance member tips the scale toward a preference and therefore confidence is slightly below average, but will support a general model blend as either solution is plausible, and thermodynamic differences will be driven by cloud cover/differential heating. At least the timing of the larger scale wave is good strong enough to have some confidence in the likelihood of MCS development. 19z update: The ECMWF tempered a bit on cap strength while the UKMET remains a bit stronger, this does not lead to significant mass differences or changes from 00z convective complex tracks/locations to help increased overall confidence in the general model blend preference. ...Large closed low off of the British Columbia coast through the end of the week... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Large scale closed low in the Southeast Gulf of Alaska will wobble and expand through Thursday and eventually start the southward and eastward wobble toward Fri corralling a south side skirting shortwave toward the Pacific Northwest coast by 00z Sat. Overall the models are very agreeable and while there are small differences in timing due to small differences in amplification of this under-cutting shortwave reaching the coast (ECMWF/UKMET/GFS fast while the NAM/CMC are slower and more amplified), however this is minor and enough to support a general model blend at slightly above average confidence. 19z update: Little changes were noted in the 12z ECMWF/UKMET with the CMC perhaps a bit slower/more amplified at the end of Day 3, but given this is still fairly minor at this forecast tau, a general model blend can still be supported at slightly above average confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina