Extended Forecast Discussion NWS Weather Prediction Center College Park MD 242 PM EST Tue Nov 5 2024 Valid 12Z Fri Nov 08 2024 - 12Z Tue Nov 12 2024 ...Watching T.S. Rafael as it tracks into the Gulf of Mexico toward the Central Gulf Coast... ...Four Corners upper low to bring lingering Rockies snow and areas of heavy rain and runoff issues to the South-central Plains late this week... 19Z Update: The 12Z model guidance suite features decent overall agreement among the UKMET/GFS/ECMWF guidance on Friday across the continental U.S., however the CMC already differs with the general pattern near the Pacific Northwest and also on the Ohio Valley with a lead shortwave crossing through the region. By Saturday, the 12Z CMC becomes much less amplified with the trough crossing the Pacific Northwest, and is not a favored WPC solution, whereas the 00Z CMC seemed to fit the pattern better, so some of the 00Z run was used in the model blend. In terms of the track for T.C. Rafael, the GFS remains to the right of the model guidance spread, whereas the ECMWF/UKMET solutions are to the left, and the CMC faster and weaker. The ICON and JMA are also closer to the ECMWF solution that suggests the storm will drift left across the Gulf before turning again to the north. The latest NHC track features a position between the GFS and UKMET solutions. Given increasing uncertainties by the latter half of the forecast period early next week, the ensemble means accounted for up to half of the model preferences, and dropped the 6Z GFS given its stronger solution with the trough across the Eastern U.S., which did not have much ensemble mean support. The previous discussion is appended below for reference. /Hamrick ---------------- ...Overview... Guidance has maintained good continuity with most aspects of the large scale pattern evolution aloft. An upper low will eject northeastward from New Mexico while persistent upper ridging over the western Atlantic extends a ridge into parts of the eastern U.S. into the weekend, with ridging also potentially filling in over the Gulf of Mexico as the mid-level reflection of Rafael weakens. Ejection of the upper low and its associated surface system/fronts will produce heavy rainfall over parts of the Plains and possibly over some locations farther eastward, with Rafael also potentially contributing some moisture as it reaches the northern Gulf. An amplifying upper trough pushing into the West will become the dominant feature early next week, spreading rain and high elevation snow across more of the West by then. Above normal temperatures will prevail over much of the East into the northern Plains, while the southern Rockies will be quite chilly late this week under the upper low. ...Guidance/Predictability Assessment... 12Z/18Z guidance provided numerous differences for significant features through the period. Solutions continue to show remarkable divergence for T.S. Rafael (forecast to reach hurricane strength for a time per 0300 UTC NHC advisory) after late this week, with machine learning (ML) guidance also varying considerably but as a whole not leaning as far west as latest ECMWF/UKMET runs or as fast to lift the system northward as GFS/CMC runs. Meanwhile the 18Z/00Z GFS strays somewhat fast for the upper low ejecting from New Mexico while it also dampens the Southeast ridge more than other guidance (pushing the cold front farther east/southeast versus consensus). Some GFS runs also show curious interactions between incoming Pacific energy and the upper low around the Great Lakes/southeastern Canada. Finally, most ML models favor a fairly amplified upper trough (more than ECMWF runs) reaching the West early next week with faster timing than the latest GFS runs. Consensus is slower than UKMET runs in particular for the preceding weaker shortwave. Guidance comparisons led to emphasizing the 12Z GFS/ECMWF early in the period with minor input from the 12Z UKMET, followed by removing the UKMET and tempering ECMWF input by mid-period while introducing the 18Z GEFS/12Z ECens means. Then the blend quickly shifted to mostly ensemble means by next Monday-Tuesday as they provided the best combination of western U.S. trough amplitude and timing compared to ML guidance. ...Weather/Hazards Highlights... The upper low expected to emerge from New Mexico and track northeastward may bring lingering potential for meaningful snow to parts of the Colorado/New Mexico Rockies into Friday but with lower totals than what may occur in the shorter term. A little snow could extend into the High Plains. Immediately to the east, some heavy rainfall should already be in progress over parts of the southern Plains at the start of the period. This activity should persist and expand somewhat through Friday-Friday night, favoring maintenance of the existing Slight Risk area in the Day 4 Excessive Rainfall Outlook with a modest broadening on the north side (yielding an area from northwestern Texas into south- central Kansas) to give some account for spread among the slower non-GFS guidance cluster. As the surface system continues eastward into Saturday, there is increasing spread for where heavy rainfall could focus depending on frontal progression and details of a potential axis of moisture anomalies extending northward from the Gulf of Mexico (suggesting a connection with some of Rafael's moisture). The Day 5 ERO introduces a Marginal Risk area from far eastern Texas into southern Kentucky where the best potential for moisture/frontal interaction exists among the non-GFS envelope, between the slower ECMWF/UKMET and faster CMC. The 0300 UTC National Hurricane Center track for Rafael would likely keep most of the enhanced rainfall directly around the system near or just south of the central Gulf Coast during the Days 4-5 ERO period. Expect rainfall of varying intensity to continue spreading eastward/northeastward across the eastern U.S. through Sunday. The forecast continues to show the Northwest trending wetter with high elevation snow from Friday onward due to a succession of systems. The leading one will bring moderate amounts of precipitation to the Pacific Northwest and far northern Rockies during Friday-Saturday. The next system should be stronger and more amplified, bringing higher totals along with expanding southeastward coverage into California and the Intermountain West/Rockies by the start of next week. There is still a fair amount of guidance spread for the exact timing and amplitude of the upper trough, tempering confidence for some aspects of precipitation magnitude and coverage at this time. The Four Corners states and southern High Plains will see anomalously chilly temperatures continue into Friday with some highs 15-25F below normal as the upper low drifts across the region. The weekend will bring a noticeable moderating trend as the upper low departs, though parts of the southern Rockies may not quite recover back to normal by early next week. The remainder of the West should trend to near normal readings during the weekend and generally into Monday. The amplifying upper trough forecast to reach the West by next Tuesday should bring fairly broad coverage of below normal readings, with anomalies determined by the trough's timing and depth. Meanwhile, aside from northern New England staying close to normal Friday-Sunday, the eastern U.S. plus the Upper Midwest/far northern Plains should see above normal temperatures through the period. The warmest anomalies of plus 15-20F or greater should be for morning lows over the Southeast Friday-Saturday (when some daily records for warm mows are possible) and then spreading north-northeast ahead of a front by Sunday-Monday. Highs will tend to be 5-15F above normal. The southern Plains may see some of this warmth early next week as well. 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 forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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 https://www.wpc.ncep.noaa.gov/#page=ovw