Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Sat Apr 02 2022 Valid 12Z Tue Apr 05 2022 - 12Z Sat Apr 09 2022 ...Heavy rainfall/convection and runoff threat to extend into the Southeast next Tuesday... ...Overview... Guidance continues to agree upon the transition of the upper level pattern to an amplified and slowly evolving regime consisting of a trough drifting over the central-eastern U.S. (containing a northern Plains into Great Lakes low) and ridge building over the West. An upstream Pacific trough should reach the West Coast by around next Saturday, pushing the ridge axis into the northern Plains through southern Rockies. Ahead of the amplifying upper trough, southern tier convection producing some heavy rainfall expected to be already in progress at the start of the period early Tuesday should extend through the Southeast and vicinity Tuesday-Tuesday night, helped along by a Lower Mississippi Valley through Mid-Atlantic surface wave. The system more directly associated with the upper trough will also produce precipitation across the eastern half of the country mid-late week with potential for some areas of enhanced totals. The upper ridge building into the West will bring another period of unseasonably warm temperatures that should peak around Thursday-Friday. ...Guidance Evaluation/Predictability Assessment... For the most part the models and ensembles remain in good agreement for the overall evolution of the amplified central-eastern U.S. upper trough and associated surface evolution, with fairly typical scattering of individual solutions. Reviewing runs through the 12Z/18Z cycles, the GFS/GEFS continued their recent tendency to be a little on the southern/southeastern side of the full spread for the portion of the upper low track over the northern Plains/Upper Mississippi Valley and then a bit faster with northeastward progression of the surface reflection over the East. Preference remained with an intermediate approach fairly close to continuity. The new 00Z GFS offers favorable trends in both regards. By days 6-7 Friday-Saturday, the details within the core of the upper trough become more ambiguous as solutions vary with where the initial upper low may track and whether separate energy could yield another low center. Meanwhile the Tuesday-Wednesday wave tracking from the Lower Mississippi Valley through Mid-Atlantic displays typical scatter but good continuity for the overall consensus. Guidance has been showing some difficulty in resolving the details of Pacific flow pushing into the western ridge late in the period, as demonstrated by a widening ensemble spread over the eastern Pacific/western U.S. by Friday-Saturday. Through the 12Z/18Z cycles, the ensemble means and 12Z ECMWF represented the majority scenario of keeping the western ridge fairly strong into Friday while a Pacific trough reaches near the West Coast around early Saturday. The 18Z GFS was somewhat slower while the past couple CMC runs have been somewhat fast/amplified with the trough. The new 00Z GFS has adjusted closer to the means/12Z ECMWF. Model/ensemble comparisons and continuity led to favoring an operational model blend during the first half of the period and then a transition to a model/mean mix with the increase of detail uncertainty. This yielded a 60-70 percent tilt toward the ECMWF cluster where differences existed and the new 00Z GFS adds support for leaning away from some specifics of earlier GFS cycles. ...Weather Highlights/Threats... A leading central-eastern U.S. shortwave and Lower Mississippi Valley through Mid-Atlantic surface low will help to focus areas of heavy rainfall over the Southeast and vicinity Tuesday into Tuesday night, extending an event that should initiate farther westward in the short-range time frame. The deep upper low tracking over the northern Plains and Great Lakes will support a corresponding surface low while leading height falls will bring a front to the East Coast, with a triple point wave possibly becoming the dominant surface feature by the end of the week. Over the course of the period these features may produce some areas of heavy precipitation over the northern and eastern U.S. but with uncertainty over specifics at this time. Regions of potential interest include parts of the Midwest to Lake Superior with the parent system, portions of the Northeast where a coastal wave could focus moisture, and locations farther south along the trailing cold front. Check the Storm Prediction Center's latest outlooks for more information regarding severe threats across the southern tier. Extreme northern areas from the Upper Midwest into interior New England may see some precipitation fall in the form of snow. Over the West, the strong jet initially crossing the region should produce some light to moderate rain/high elevation snow during Tuesday. Then expect most of the region to be dry until late in the week when light precipitation may reach the Northwest ahead of an approaching upper trough. Expect the Southwest to see highs up to 10-15F above normal through the period. The upper ridge building into the West will expand coverage of above normal temperatures mid-late week, followed by some moderation on Saturday as the Pacific trough arrives. Much of California should see highs at least 10F above normal Wednesday and greatest anomalies (plus 10-20F and locally higher) will likely extend from California and southern Oregon into the Great Basin Thursday-Friday. Some daily records for highs/warm lows will be possible late in the week. Meanwhile cool air under the amplifying upper trough will bring highs down to 5-15F below normal over the northern Rockies on Tuesday, the central U.S. Wednesday-Thursday, and eastern states by Friday-Saturday. Flow ahead of the upper trough/surface system will bring a couple days of above normal readings (especially for morning lows) to the East around Wednesday-Thursday. Rausch Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml