Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1227 AM EDT Thu Apr 04 2019 Valid Apr 04/0000 UTC thru Apr 07/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave/surface low crossing the Ohio Valley Friday... ...Potential surface low developing along the Southeast coast Fri night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend excluding the 12z CMC Confidence: Average to slightly above average The trend for a weaker shortwave crossing Central Plains currently will reach the Ohio Valley / Mid-Atlantic by Friday continues with the latest model cycle. The biggest model differences noted so far is the much weaker but also faster CMC solution which has the wave nearly off the east coast by 12z Friday while the rest of the operational models remain further west over the spine of the Appalachians. There is fairly good agreement between the GFS/ECMWF/NAM/UKMET through the forecast period that a general model blend, excluding the CMC, can be incorporated across this area. Some of the models still hint at a weak surface low developing off the SC/NC coast late Friday night into Saturday. The ECMWF/UKMET have this feature the most while the NAM is faster and show some weak surface reflection further out to sea. The ensemble means lean toward less of a surface low forming but whatever does appears to be on the weak side at best. Overall, a general model blend outside of the CMC is preferred. ...Active Pacific upper-level jet reaching the West Coast with series of embedded shortwaves... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 00Z Sat ECMWF/UKMET blend after 00Z Sat Confidence: Average through 00Z Sat, below average after 00Z Sat An increasingly active pattern will evolve over the Pacific Northwest through the next few days. The first in a series of shortwaves will push into the region late Thursday night into Friday followed a few more through this weekend. The biggest differences begin to develop more on Day 3 (Saturday into Sunday) with respect to a stronger shortwave moving into either Washington State or southern B.C. The GFS and NAM (and some degree the CMC) show an amplified wave and subsequently a much deeper surface low moving into the region (along with higher QPF). Meanwhile the ECMWF/UKMET are flatter with the upper level pattern and much more delayed (and further south) with the potential surface low moving into the area. Given the fast bias of the GFS and NAM, will lean on the ECMWF/UKMET solutions for now but overall forecast confidence drops to below average beyond Saturday morning. ...Southern stream shortwave crossing the Southwest Fri and reaching the central U.S. Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: GFS/ECMWF/UKMET through 00z Saturday ECMWF/UKMET after 00z Saturday Confidence: Average through 00Z Sat, below average after 00Z Sat A couple shortwave troughs crossing through the Southwest US and Four Corners region through Saturday will then push into the south-central Plains. The initial wave reaches portions of Texas by Saturday afternoon then lifts northeast into OK/KS/MO, where a general model blend would appear to be sufficient and preferred. Quick on its heels is another shortwave that originates more from Pacific / Rockies. The degree of phasing between these shortwaves (along with more northern stream energy) is the main model difference, mainly after 00z Saturday. The GFS and NAM are much more phased from the northern stream to southern stream and subsequently have the trough axis through the whole central Plains. The ECMWF and UKMET are more separate with the southern stream energy further south into Texas. The trend from the previous model cycles seems to have less phasing initially and more separation between the two, more like the ECMWF/UKMET solutions. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Taylor