Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 253 AM EDT Fri May 03 2019 Valid May 03/0000 UTC thru May 06/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Southern stream trough/wave activity over the South... ...Energy lifting northeast toward the Mid-Atlantic... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM/UKMET/ECMWF Confidence: Slightly above average A series of southern stream shortwave impulses will continue to lift northeast from the southern Plains up across the OH/TN Valleys and into the Mid-Atlantic region going into the weekend. This will allow multiple waves of low pressure to lift up along a frontal zone draped across the region. The current MCV and associated low center currently moving into the lower OH Valley will move to the central Mid-Atlantic region by Friday evening as another weak wave farther north crosses the lower Great Lakes region and moves into the interior of the Northeast. The models are in good agreement overall with the mass field details of these two waves, and the combination of both surface waves will drive a cold front gradually southeast back across New England and the Mid-Atlantic states by early Saturday. The front will then extend back to the southwest down across the TN and lower MS Valleys where there will be another shortwave impulse lifting northeast from the southern Plains that will interact with the front and support a new wave of low pressure. This low center will then lift northeast and across toward the central Mid-Atlantic region by late Saturday night and early Sunday. The 00Z ECMWF/CMC solutions still track this surface wave north of the 00Z NAM/GFS/UKMET solutions, but it should be noted that the ECMWF and CMC did shift farther south with the low track. The 00Z GFS though becomes the most progressive solution in taking the surface wave east across the Mid-Atlantic by early Sunday. The 12Z ECENS mean now shows better support for the 00Z ECMWF/CMC solutions, but the CMC still overall appears to be too strong. The 00Z GEFS mean supports a low evolution that is slower than what the 00Z GFS depicts, and it would appear that the GFS becomes a progressive outlier. Accounting for the CMC being too strong, and the GFS too fast, the remaining guidance as a consensus offers a reasonable solution. Thus, will prefer a blend of the 00Z NAM/UKMET/ECMWF solutions which would in effect equate also to a compromise between the 12Z ECENS mean and 00Z GEFS mean. ...Low to mid-level trough impacting the FL Peninsula... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average The models take a low to mid-level trough moving across the FL Peninsula gradually north and then northeast over the next couple of days as the system rounds the western periphery of a weakening subtropical ridge off the Southeast coast. Most of the guidance does support the development of a weak surface low, but the 00Z CMC in time becomes a bit of a deeper outlier with this system. Any low center is expected to gradually merge with a frontal zone dropping southeast off the Mid-Atlantic states by Saturday. Will prefer a non-CMC blend with this system. ...Southern stream closed low approaching CA... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 72 hours Non-NAM blend...after 72 hours Confidence: Above average The guidance allows for a southern stream closed low to approach central/southern CA by late Saturday and into Sunday. The models are well clustered with the timing and depth of this system through about 72 hours. Thereafter, the 00Z NAM begins to drop the closed low a bit south of the model consensus. Will prefer a general model blend through 72 hours, and then a non-NAM blend thereafter. ...Height falls traversing the northern Plains/Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 48 hours Blend of the 00Z UKMET/ECMWF...after 48 hours Confidence: Slightly above average A series of northern stream troughs will cross the northern Plains and upper Midwest through the period. There is good agreement with the shortwave impulse that crosses the northern Plains and upper Midwest on Friday. Then the guidance supports a closed low feature crossing southern Canada on Saturday and Sunday which will allow drive a cold front southeast down across the Midwest. The 00Z GFS supports stronger shortwave energy trailing its closed low feature. The better model clustering at this point remains generally with the 00Z UKMET/ECMWF solutions and has reasonable support from the 12Z ECENS mean and 00Z GEFS mean. So, based on this, will prefer a general model blend through 48 hours, followed by a blend of the 00Z UKMET/ECMWF solutions. ...Trough digging into the northern Rockies by Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM/UKMET/ECMWF Confidence: Slightly above average The models support a shortwave trough amplifying somewhat into the northern Rockies by Monday. The 00Z GFS and to a lesser extent the 00Z NAM are the most amplified solutions. The entire non-NCEP suite of guidance is relatively flatter and this is supported by the 12Z ECENS mean, however, the 00Z non-NCEP suite did trend just a tad stronger. The 00Z GEFS mean favors a bit more amplitude like the 00Z GFS/NAM solutions. The amplitude of this shortwave will be dictated largely be the degree of upstream ridging over the Gulf of AK and far western Canada. For now, a compromise solution will be preferred via a blend of the 00Z NAM/UKMET/ECMWF solutions. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Orrison