Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 AM EST Sat Mar 2 2019 Valid 12Z Tue Mar 5 2019 - 12Z Sat Mar 9 2019 Weather Pattern Overview ~~~~~~~~~~~~~~~~~~~~~~~~ A return to a more amplified upper level flow pattern is expected across the continental U.S. for the early to middle part of next week. The passage of a strong cold front across the eastern U.S. by Monday will herald a much colder airmass across the central and eastern U.S., accompanied by a pronounced upper level trough and sprawling surface high from Canada. The presence of the eastern U.S./Canada trough supports a broad upper ridge across the Rockies and High Plains by midweek, which gradually flattens out towards the end of the forecast period as the flow returns more quasi-zonal with some shortwave perturbations passing through. An unsettled weather pattern is expected to return across the West Coast region as multiple Pacific disturbances move inland, with a large scale trough expected across the Intermountain West by the end of the week. Model Guidance Evaluation and Preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The deterministic model guidance is in above average agreement for the Tuesday and early Wednesday time period owing largely to the amplified flow. This especially holds true for the large scale upper level trough anchored over the eastern half of the nation through midweek. The main forecast challenge, similar to yesterday, resides over the West Coast region beginning on Wednesday with the development of a rex block over the northeast Pacific. The UKMET is indicating a track north of the model consensus with the next storm to affect California, and reasonably good agreement among the other guidance. More noticeable differences are evident as this feature crosses the Rockies and emerges over the High Plains on Friday, with the operational GFS well to the north of the model consensus, so more of the FV3 model was incorporated in place of the GFS. The forecast was primarily derived with a blend of the latest deterministic solutions (ECMWF/GFS/FV3/CMC) as a starting point for the Tuesday through Thursday time period. For Friday and Saturday, the GEFS and EC means along with smaller percentages of the FV3 and ECMWF were incorporated into the forecast process. No major changes from previous WPC continuity were warranted. Sensible Weather and Potential Hazards ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Much colder weather will be making headlines at the beginning of this forecast period after the passage of a strong cold front on Monday. A massive arctic surface high will encompass all of the central and eastern U.S. through the middle of the week, and reaching well into eastern Mexico. The projected departures from early March climatology will be impressive, with high temperatures on Tuesday on the order of 20 to 35 degrees below normal across much of the Plains and extending eastward across the Midwest and Ohio Valley. This equates to widespread subzero and single digit low, and highs only in the teens and low 20s for many of those areas. There will likely be numerous daily record lows to be established with this arctic airmass, with the greatest potential for this on Tuesday morning. Temperatures only slowly moderate through midweek with anomalies of 15 to 30 degrees below normal, and this will extend eastward towards the Mid-Atlantic and Northeast. Although the magnitude of the cold temperatures will abate some by the end of the week, below normal temperatures will be the rule for the entire forecast period. Heavy rain and mountain snow are expected to make a return to the western U.S. by Tuesday night as an atmospheric river event accompanies a strong Pacific low headed towards California. The Sierra Nevada will likely get hammered by very heavy snow, thus adding to its extensive snow pack. Significant snow is forecast for the central and northern Rockies by Wednesday and Thursday as the moisture plume advects inland, albeit not to the same degree as California. Heavy rainfall across the lower elevations of California may lead to some flooding problems, and future excessive rainfall outlooks will have additional information as this event enters the short range forecast period. D. Hamrick 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