Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1244 PM EDT Sat May 23 2020 Valid May 23/1200 UTC thru May 27/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Initial Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Cut-Off Low exiting the Northeast U.S. by Saturday night ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: High A weak upper low currently south of Long Island is sustaining a surface low that will emerge offshore tonight and then gradually slow down in forward motion by Sunday and into Monday, as the upper low evolves into an open wave. Given the near-term evolution and track of this feature, there is enough model agreement to merit the use of a multi-deterministic model blend. Southern stream trough from Intermountain West to Southern Plains ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 48 hours, then 6Z GEFS mean/00Z EC mean blend Confidence: Limited-Moderate The latest guidance shows very good agreement in bringing a new large scale upper trough and associated closed low in across the Intermountain West this weekend. By Monday, the models support a deep trough edging toward the Plains with one closed low center exiting the northern Rockies and crossing the northern High Plains by then. Meanwhile, a second closed low will be attempting to focus over the central Rockies, and by Tuesday the guidance is in reasonably good agreement on the idea of this closed low becoming better defined out across the southern High Plains. This will result in a corresponding surface low, and with this feature there is a fair degree of model mass field spread. The 00Z CMC has a weaker and northerly tracking low center up over southwest Missouri at the end of the period versus the 00Z UKMET, which is the strongest solution and has it down over southwest Oklahoma owing to the stronger ridge across the east-central U.S. compared to the other guidance. A general model blend should generally suffice with this entire mass field evolution through 48 hours, but thereafter as the deep trough/closed low ejects out across the Plains, a blend of the latest GEFS mean and ECENS mean will be preferred as a starting point in the forecast process given the large spread in the details of surface cyclogenesis. Shortwave/closed low crossing the Midwest through Saturday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 12Z Monday, then non-UKMET blend Confidence: Moderate-High A rather compact mid-upper level low has been tracking across the central Plains and is now over Iowa. This low will be advancing northeast across Minnesota and Wisconsin through Saturday night, and then gradually weakening over the northern Great Lakes on Sunday as it tracks around the northern periphery of the building Southeast U.S. upper ridge. The model guidance is in good agreement overall with this system through 12Z Monday, after which the 00Z UKMET depicts a somewhat stronger trough that exits the Great Lakes and moves across northern New England for early in the week. Given good clustering in the guidance otherwise, a non-UKMET blend will be preferred for this region. Shortwave lifting northeast across the southern Plains on Sunday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Moderate As the deep trough and associated closed low evolves across the West this weekend and slowly encroaches on the High Plains, there will be a weak shortwave trough pivoting around the base of that and lifting northeast across Texas through Sunday night, and this is expected to support the development of an MCS across portions of southern Texas. Based on the latest trends and deterministic clustering, a general model blend will be preferred. Mid-level trough impacting Florida early in the week ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/NAM/00Z EC mean Confidence: Moderate As a strong subtropical ridge builds over the Southeast and the Mid-Atlantic region going into the beginning of the week, there will be a mid-level trough axis lifting north from the Yucatan Peninsula and western Caribbean Sea to the southern Gulf of Mexico. This energy is expected to elongate and cross areas of southern Florida by late Monday and into Tuesday. There will likely be an inverted surface trough that accompanies this as well. The UKMET is stronger with the building ridge to the north and loses ensemble support, and there has been a multi-model trend to focus a stronger mid-level trough a bit farther north over the southeast Gulf of Mexico and southern Florida for Monday and Tuesday. The 00Z ECMWF appears much heavier with the QPF across the region compared to the other guidance, owing largely to higher instability over land with its solution. Taking these factors into account, the preference at this time will be for a blend of the 12Z GFS/NAM/00Z EC mean. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick