Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 244 PM EDT Mon May 25 2020 Valid May 25/1200 UTC thru May 29/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Weakening long wave trough crossing the Northern Plains through Tue Short wave energy in the northern stream tracking across the Northern Plains Wed ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/12Z ECMWF blend Confidence: Slightly above average Both the 12Z NAM/GFS are close to the consensus with the initial long wave trough over the northern High Plains weakening across the Northern Plains Tue as it encounters mid level ridging building northwestward from the northern Mid Atlantic/southern New England. Both models are close to the consensus with short wave energy coming across the British Columbia coast early Tue, which then moves along the International Border into early Wed. After that time, the 12Z NAM slows with the evolving feature, as the 12Z UKMET/CMC remain flatter with the mid level wave. Almost all models have slowed with this feature in the last three model runs, though the 12Z GFS/12Z ECMWF have been the most consistent with its during that time. These models also have the support of their respective ensemble mean solution. Based on this, a 12Z GFS/12Z ECWMF blend is preferred. In the fast flow, there is bound to be some timing issues until we get closer to the event, but for now forecast confidence remains slightly above average. Full latitude over the Rockies evolving into closed low over Southern Plains/Lower and Mid MS Valley ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 12Z CMC blend Confidence: Slightly above average The 12Z NAM/GFS are close to the model consensus as short wave energy over the Southwest drops into the base of the developing full latitude trough across the western High Plains through 26/00Z. The 12Z NAM becomes faster with the feature as it crosses the Southern Plains into the Lower MS Valley, as it is not as sharp with the ridge over the Central Rockies. However, the 12Z UKMET has sped up its solution, and along with the 12Z ECMWF, forms a better consensus with the remaining guidance placing the closed mid level low over southern MO/northern AR. While the 12Z NAM remains a but faster with the mid level trough (and does not close off the mid level system), it is now close enough to the consenuss to include in the blend. Mid-level trough and weak surface lows impacting Florida/Southeast ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/12Z ECMWF blend Confidence: Average The 12Z NAM/GFS show the mid level short wave energy over the central Gulf of Mexico early in the period, which is close to the model consensus. However, the mid level feature becomes more difficult to discern with time as it tracks toward Tue morning, with another mid level short wave crossing the Bahamas. Both the 12Z NAM/GFS are close to the consensus with this feature as well. While the 12Z NAM/GFS are close on the subtle wave forming along the middle FL east coast before 12Z Tue. While there is good ensemble agreement that the wave tracks toward GA/SC, the 12Z NAM seems too strong with its surface low as it crosses the SC coast near 27/12Z. The 12Z GFS/12Z ECMWF have ensemble support bringing the weak surface wave into GA/western SC during this time. Since there is better agreement with this feature among these solutions, the 12Z GFS/12Z ECMWF blend was preferred, but given the spread in the track of the surface low, forecast confidence is only average. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hayes