Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1210 PM EDT Sat Mar 23 2019 Valid Mar 23/1200 UTC thru Mar 27/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation With Preferences/Confidence Intervals ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Plains closed Low shearing into Ohio Valley early Mon across Southeast Tues ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Slightly above average Models continue good agreement with the closed low trekking through the Plains today into the Midwest by 00z Mon. However, after this point, there is some model difference in the magnitude of influence/shearing with respect to the larger scale vortex dropping across the eastern Great Lakes and Northeast. The 12z NAM appears most influenced, favoring a faster southward press of the cold air/vortex helping to accelerate the shearing process and enhancing the deformation zone across the Ohio Valley, and therefore mass fields show this most near the 7H level. The 12z GFS continues to be weaker with the convection along the cold front/dry line advancing eastward allowing for increased moisture flux into the Ohio Valley for and enhanced band of QPF, but this seems to be in line with a typical negative bias. The remainder of the 12z GFS mass fields are in line with the remaining guidance even as the wave elongates into a stretched positive tilt trof along the Southeast Coast Mon to Tuesday. This suggests a Non-NAM blend is best preference at slightly above average confidence. Shortwave moving through the Great Basin/C Plains to Southeast Sun-late Tues ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z NAM and 00z UKMET/CMC blend Confidence: Average GOES-W WV suite depicts base-heavy neutral trof entering the Pacific Northwest with more concentric energy near N CA at this time. This wave is forecast to elongate NW to SE trekking through the Great Basin to Snake River Plain, given persistent large scale ridging trying to come back in the wake of the Plains closed low Sun into Mon. As such, there is moderate model spread in where the wave will break off a smaller vort to move through the ridge. The 00z ECMWF is most aggressive with a very strong/compact wave (mostly as it is the slowest initially) to eject this wave along the WY/CO boarder and given proximity to the W-E jet, accelerate it into the MS Valley by Tuesday, eventually filling out the base of the remaining positive tilt trof in the Southeast. On the other side of the spectrum, the 12z GFS is fastest lifting north today into tomorrow across OR, and does not shear much (if any) energy through the ridge, making it very weak and northern most of the guidance. The 12z NAM shows some potential upscale feedback from enhanced activity over SE OR/NW NV tonight into morning tomorrow (Sun) but enters the ridge and WNWLY flow in a more central position, much like the 00z UKMET/CMC. As such will favor the CMC/UKMET in a blend with the NAM, though there are limited impacts after exiting the West. Confidence is average in this blend. Large Pacific Gyre's First Wave Entering Northwest Mon; Main Core Nearing N CA by Late Tues ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS and 00z ECMWF/CMC blend Confidence: Average to slightly above average GOES-W WV suite depicts a very small compact closed low in the Southern Gulf of AK, with a southern stream trof phased along 145W at this time. The interaction between the two will build a larger Pacific Gyre between 130-140W by Monday. The southern stream wave will advance as the eastern portion of the gyre and bring a dual moisture stream flow into Central to Northern CA Monday. The 00z UKMET and 12z NAM both are very strong with this wave, while the NAM is well timed with the remaining GFS/CMC/ECMWF, the UKMET is out of phase, slower and by 00z Tues, both have developed deep surface reflections. The ECMWF is the weakest overall with this initial wave, and so is a bit off balanced (favoring the northern closed low). As the northern system, rounds the western portion of the gyre to the southern portion, the ECMWF is stronger and lags the CMC/GFS slightly...but come into better phase timing approaching the 40N130W benchmark by 84hrs (00z Wed). As such, the overall setup and ensemble suite suggest that the 12z GFS along with the 00z CMC/ECMWF blend is strong providing average to slightly above average confidence throughout the forecast period. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina