Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Sat Mar 16 2019 Valid 12Z Tue Mar 19 2019 - 12Z Sat Mar 23 2019 ...Overview... Models and ensembles show a blocking mid/upper-level ridge initially centered from the Pacific Northwest to western Canada early next week drifting slowly eastward through the forecast period. Downstream from this ridge expect a mean upper-level trough initially across the Great Lakes/Northeast to lift out before deeper troughing may amplify into New England around next Fri-Sat. Meanwhile a shortwave over the northern Plains should progress southeastward through the eastern U.S. early-mid period. Guidance continues to depict strong North Central Pacific westerly flow splitting as it approaches the western coast of North America. Some of this energy will form a system crossing the southwestern U.S. while the rest flows into the higher latitudes of Canada. Stronger height falls may approach the central/northern West Coast by next Fri-Sat as the CONUS portion of the mean ridge shifts far enough eastward. ...Guidance Assessment/Preferences... The updated forecast emphasizes the 00Z ECMWF/UKMET/CMC (with a small 00Z NAEFS mean component) from day 3 Tue into day 5 Thu and then adjusts to an even model/mean blend consisting of the ECMWF/CMC and ECMWF/NAEFS means. This cluster represents the current majority for the trough/upper low expected to track into the southwestern U.S. and the Rockies mid-late week while depicting an intermediate timing for the shortwave dropping southeastward from the northern plains. For the system coming into the West, latest GFS/GEFS mean runs have backed off somewhat from yesterday's fast timing but not yet to the point of joining consensus. That said, the ECMWF has trended a tad faster over the past day so the slowest solutions (the 00Z CMC mean in today's case) may not be ideal either. The 06Z FV3 GFS compares much better to the favored blend than the operational GFS runs. Forecasts to the southeast of closed highs--such as the one over southwestern Canada as of early Tue--are notoriously difficult so it is not exactly surprising to see the great spread and run to run variability seen thus far for the shortwave energy progressing from the northern Plains through the East. Guidance trends have generally been in the direction of UKMET/CMC ideas from the past couple days so it seems reasonable to account for those runs and similar ECMWF. This cluster is a good midpoint between the fast 00Z GFS and slow 06Z GFS. During the latter half of the period the models/means are more agreeable than average with height falls reaching the West Coast, favoring a model/mean blend. The 06Z FV3 GFS is quite deep/sharp versus other guidance for upper troughing that amplifies into the northeastern U.S. The 06Z GFS may be a little too amplified with the southwestern part of the trough but other models/means agree fairly well. ...Weather Highlights and Hazards... The Pacific system tracking into California should spread rain and high elevation snow into the Sierra Nevada, Great Basin, and central/southern Rockies by next Wed-Fri. Some localized enhancement of precipitation over favored terrain will be possible. By Fri-Sat expect moisture to increase ahead of the system, supporting greater coverage/intensity of showers and thunderstorms over portions of the Southern Plains with locally heavy rain possible. Also in that time frame the stronger height falls aloft and a cold front approaching the Pacific Northwest and northern California may bring a return of rain/mountain snow to that area. Expect widespread and potentially heavy rain over the southern half of the Florida Peninsula on Tue and perhaps into Tue night-Wed as a wave of low pressure moves along a surface front stalled south of the state. Some rainfall of mostly light-moderate intensity will be possible from the central Plains eastward Tue-Thu in association with an upper shortwave and weak surface wave/frontal system. By late in the week locations near the coast of the Carolinas may see a brief period of rainfall as low pressure develops off the southeastern coast but then tracks rapidly farther offshore. Northern parts of the East should be fairly dry except for light late week/early weekend snow over favored terrain of New England behind a cold front that drops southeastward from Canada. A majority of the West should see above normal morning lows during the period (plus 10-15F anomalies at some locations) while the system crossing the southern half of the West will keep highs near to below normal over affected areas after Tue. The southern High Plains will tend to be on the cool side versus normal during the period but the northern-central Plains will likely see near to above normal temperatures as warmth spreads from the West. The eastern U.S. will be 5-10F below normal Tue-Wed but moderate toward normal thereafter. A frontal passage could bring cool and breezy conditions to the Northeast by next Sat though. Rausch/Ryan Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml