Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1235 PM EDT Mon Apr 13 2020 Valid Apr 13/1200 UTC thru Apr 17/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Overall CONUS pattern ~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS/00z ECMWF blend (NAM inclusion, ok in West) Confidence: Slightly above average Average to slightly below average off West Coast Day 3 Eastern half of CONUS ----------------------- Extremely deep surface cyclone is lifting out of the northern Great Lakes with centroid of deeper global scale trof with it. The extremely strong warm conveyor belt and cold front will press through the Northeast without significant difference in the mass fields to support a general model blend; though the trailing frontal zone through the Southeast will become stationary by Tuesday. A subtle shortwave out of the West in fast moving westerly flow will eventually support a weak surface wave in GA/SC or along the Gulf stream by late Tues/early Wed. As the shortwave reaches the confluent region of the eastern portion of the large scale trof, there is some amplification as it lifts north along the Gulf stream and eventually toward Cape Race by late Thursday. There is sizable model differences with its timing/placement along the front with the UKMET lagging and the NAM a bit left of ensemble suite, enough to suggest less preference there. In the northern stream, reinforcing shortwaves round and help to elongate the global trof before it slides eastward through the Great Lakes Wed before swinging through the Northeast Thursday. The 12z NAM is a bit stronger/amplified, in line with deepening the aforementioned offshore surface low. The 00z CMC also appears to be very compact strong with this wave too, but also a tad slower...so will push a bit further away from this solution too. Western US/Rockies -------------------- A highly amplified ridge exists in the Eastern Pacific through the Gulf of AK... this block presents a lower predictability forecast for a compact shortwave that will plow through the northern portion of it on Tues before descending south just off shore. Weak flow and small variation can lead to larger downstream differences. This is clearly the case with the 00z UKMET, which is smaller/more compact and slower getting through the ridge. The CMC also is coming out in fractional pieces which doesn't look correct as well. A northern stream trough currently in central AK will also drop between the ridge and the larger scale trof and enter the US Rockies Wed. The wave in the general weakness between the larger scale trof begins to broaden/amplify across the Great Basin by the end of the forecast period. This will bring it closer to interacting with the aforementioned off-shore low. The ensemble suite is solid with the placement between the two, and the 12z GFS (though a tad fast) and the 00z ECMWF (though a tad slow) are the best representations within the guidance suite. All together, will suggest a 12z GFS/00z ECMWF blend, though the NAM maybe useful in the West/Rockies. Confidence is slightly above average with exception to the closed low off the West coast which is average to slightly below average. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina