Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Fri Feb 21 2025 Valid 12Z Mon Feb 24 2025 - 12Z Fri Feb 28 2025 ...Wet Pacific Northwest pattern lasts into Monday... ...Overview... The upper flow pattern should remain rather progressive through much of the medium range period. By Monday, a northern stream shortwave will shift through the Northeast, with a southern stream wave through the Gulf and Florida. Meanwhile, a strong shortwave will move onshore in the Pacific Northwest on Tuesday, with guidance suggesting it eventually amplifies over the east by late next week. This in turn leads to an amplifying ridge over the West with a trough or cut off low reaching the West Coast by next Friday. The initial shortwave into the West will be associated with an ongoing Atmospheric River and heavy rain threat that lasts through about Monday. ...Guidance/Predictability Assessment... Models and ensembles show fairly good agreement on the large scale pattern through much of next week, though still considerable variability in the details of individual systems. There was enough agreement the first half of the period for a multi-model blend. Two areas of uncertainty to note the second half of next week. The first being uncertainty in stream flow separations and pattern amplification over the East late next week, which translates to considerable differences in the precipitation distribution and amounts in the East. The second area is out West with an approaching upper trough/cut off low next Thursday-Friday. The 18z GFS is considerably slower than the ECMWF and CMC, holding the upper low well offshore. WPCs forecast favored the ECMWF and CMC with the ensemble means, which resulted in a position over southern California next Friday. The new 00z guidance tonight (available after the WPC forecast went out) continues to show variability, with the GFS considerably faster and the ECMWF/CMC slower than their previous runs. WPC leaned more heavily towards the ensemble means late period. ...Weather/Hazards Highlights... A consistent feed of moisture will be ongoing into the Pacific Northwest as the period begins Monday, with moderate to heavy lower elevation rain and high elevation/mountain snows. Enhanced snows will also work inland over the northern Intermountain West/Rockies with downstream system translation. Expect highest precipitation totals over the favored terrain and coastal areas of western Washington/Oregon and into northwest California. The Day 4 WPC Excessive Rainfall Outlook valid for Monday continues a Marginal Risk threat area given the cumulative effect of the multi-day episode which begins in the short range period. The Northwest should trend drier midweek as a dynamic Monday- Tuesday system departs and upper ridging builds in. Downstream, shortwave energy over the Gulf and Florida may support periods of moderate rainfall across south Florida on Monday. Digging of northern stream shortwave energy into early next week will spread light precipitation (mostly snow) from the Great Lakes region through New England. Latest guidance is not too enthusiastic about potential for wrapback coastal low linkage over the Northeast to enhance activity early- mid next week, but it remains worth monitoring in future runs. Moderate cyclogenesis and frontogenesis may develop over the Plains/Mississippi Valley next Wednesday and work into the Eastern U.S. by Thursday and Friday. The warmer pattern by then should mostly favor an emerging area of moderate wrapping rains with return Gulf moisture flow aside from a little wintry weather on the far north cool side of the low. By early next week most, locations west of the Mississippi River will warm to much above normal with decent coverage of plus 10-25 degree anomalies. Best potential for highest anomalies will be near the northern Plains. The East should also warm to above normal early to mid week, before cooling off again back to normal (or slightly below) late week underneath of troughing. Santorelli 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