Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Wed Nov 6 2024 Valid 12Z Sat Nov 09 2024 - 12Z Wed Nov 13 2024 ...Watching Hurricane Rafael as it tracks into the Gulf of Mexico... ...Overview... The National Hurricane Center continues to issue advisories for Hurricane Rafael as it tracks across the Gulf this weekend into early next week while weakening as it interacts with a mean upper ridge stretching from the Bahamas. Models and the NHC forecast have trended farther south with Rafael, keeping it offshore well south of the central Gulf Coast while it weakens. But the combination of Rafael's moisture and a frontal system supported by an upper low ejecting northeast from the Plains may produce some areas of locally heavy rainfall from the Gulf Coast northward especially this weekend. Meanwhile, a series of Pacific systems will increase coverage of rain and higher elevation snow over the West from the weekend into early next week. Much of the East should see above normal temperatures through the period while the southern Rockies will start the weekend on the chilly side and cooler temperatures will spread across the West next week. ...Guidance/Predictability Assessment... For Hurricane Rafael, recent model runs have generally trended to the south, showing the surface low weakening over the Gulf rather than making landfall in the central Gulf Coast as some previous runs had showed. The 00Z ECMWF, UKMET, and many EC ensemble members were particularly aggressive with this southwestward shift as Rafael does not get picked up by the upper trough to track it northward. GFS runs are indicating this trend but not to the extent of the EC/UKMET that take Rafael so far south it goes into central Mexico. The 12Z CMC does have Rafael track north into the central Gulf Coast, along with some GEFS members and the bulk of the AI/ML models initialized at 00Z, so there remains uncertainty with this trend. Continue to monitor latest NHC products for additional information on Rafael. Farther north, the first system of note is a closed upper low starting the period Saturday atop the central High Plains and tracking northeast Sunday-Monday while opening up. Model guidance is rather agreeable with this feature especially over the weekend, but guidance has been more erratic with details of a shortwave that enters western North America during the weekend and may have some influence on the remaining upper low energy by early next week. The 00Z CMC in particular seemed like an eastern outlier with this shortwave for more interaction with the preexisting upper low/trough. This leads to lingering uncertainty for some details of the frontal system reaching the Northeast. There are continued timing and amplitude differences for the larger scale trough moving into/through the West early next week and toward the central U.S. by midweek, with GFS runs leaning slower and ECMWF faster. Latest ML models show a similar spread, arguing for a blend/compromise approach. This also mitigates issues for how energy may be distributed within the upper trough by the middle of next week, with individual solutions ranging between greater dynamics in the northern part of the trough, or farther south, to an evenly phased trough. A compromise also looks best for the next system that may come into the picture over the northeastern Pacific by next Wednesday. Overall a blend favoring the 06Z GFS and 00Z ECMWF with lesser portions of the UKMET and GEFS/EC ensemble means early in the period, with an increasing proportion of the ensemble means as the period progressed given increasing uncertainty. ...Weather/Hazards Highlights... The combination of the Plains system pushing into the Mississippi Valley and moisture from Rafael, which is forecast to be south of the central Gulf Coast by the weekend, will lead to the potential for some areas of heavy rainfall from the central Gulf Coast to the Ohio Valley this weekend. On Saturday, maintained the Marginal Risk in the ERO with generally minor changes from the previous forecast. By Sunday, good moisture and some limited instability should continue to spread into similar regions, shunted just a bit eastward. This forecast cycle, WPC has stretched the Marginal Risk well north across parts of the Lower Mississippi Valley to Mid- South to the Ohio Valley where moderate to heavy rainfall rates may train in the vicinity of the frontal system. The areal coverage may be able to shrink with time if models converge. Dry antecedent conditions in the Ohio Valley in particular may limit the extent of impacts of flash flooding from heavy rain, but a 5 percent risk (Marginal) seems warranted. Some rainfall may linger beyond Sunday but most of the East should trend drier by Monday-Tuesday. Also of note, a wave tracking from the southern Bahamas into the eastern Gulf may increase rainfall over Florida around Sunday-Monday. The West will see a wetter regime with high elevation snow, starting in the Pacific Northwest and then spreading farther south into parts of California and east into the Rockies. Highest totals should be in the Sunday-Monday time frame with a vigorous upper trough and frontal system approaching/reaching the area. While there is still a fair amount of spread for QPF magnitudes, first- guess guidance is showing enough of a signal to introduce a Marginal Risk area in the Day 5 ERO over parts of the Pacific Northwest where initial soil conditions are neutral to damp. Higher elevation snow is likely for the Cascades, Sierra Nevada, and northern/central Rockies. Another system is likely to bring additional focused precipitation to the Pacific Northwest next Wednesday. Depending on western upper trough progression, some rainfall may develop over the central U.S. by the middle of next week. Except for the Great Lakes into New England during the weekend, the eastern half of the country will likely see above normal temperatures through the period. Warmest anomalies should be for morning lows, reaching 20-25F above normal on one or more days over the South and extending a little farther northeastward at times. Coverage of plus 10-15F anomalies for highs should increase going from the weekend into the first half of next week. Corresponding to these relative anomalies, there will be better potential for some record warm lows versus more isolated records for daytime highs. The northern Plains will also be well above normal until a cooling trend Tuesday-Wednesday, while the southern Plains will be warmest early next week. Chilly temperatures over the southern Rockies/High Plains will gradually moderate while much of the West will be near normal during the weekend. Then the upper trough pushing into the West next week should expand the coverage of below normal temperatures from west to east. Tate/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