Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 AM EST Mon Feb 10 2025 Valid 12Z Thu Feb 13 2025 - 12Z Mon Feb 17 2025 ...Continued active weather pattern with periods of heavy rain and winter weather across parts of the West and the eastern half of the lower 48... ...Overview... The medium range period will feature a series of systems producing areas of significant rainfall and winter weather. The first system should track through the Northeast on Thursday with snow for northern New England at the same time a wet/snowy system reaches the West Coast, with heaviest precipitation focused over California. Continued progression of the West Coast system's upper trough will likely support low pressure reaching the East by Sunday and the Canadian Maritimes by Monday. This low should spread wintry weather from the Upper Midwest through the Northeast, with heavy rain farther south over some areas that may be affected by prior heavy rain. The next Pacific system will track farther north than the first one, confining the rain and higher elevation snow more to the Northwest from the weekend into early next week. Parts of the Plains will see the most pronounced cold anomalies, especially on Thursday and the weekend, while gradually increasing Pacific influence should help the West to moderate from its cold temperatures as of Thursday. The Southeast will tend to see above normal temperatures from late week through the weekend. ...Guidance/Predictability Assessment... The updated forecast based on 12Z/18Z guidance placed more emphasis on the 12Z ECMWF/18Z GFS relative to the 12Z CMC/UKMET early to mid period, followed by incorporation of 30-40 percent ensemble means (18Z GEFS/12Z ECens) while adjusting GFS input a little more toward the 12Z run and eliminating the 12Z CMC. Guidance consensus is fairly good for the system reaching the Northeast on Thursday, with some lingering differences for strength and the dynamical model average leaning a bit deeper than the average of machine learning (ML) models. There are some lingering differences for exact details of the upper trough, affecting cold frontal timing over the Southeast. GFS/ECMWF/UKMET runs, ensemble means, and most ML models clustered well in principle for the system reaching the West Coast late this week, but the 12Z CMC structure differed from the majority and was not favored. As this system reaches the East by the weekend, dynamical and ML models have differed somewhat on upper trough details and the resulting surface reflection. However there has been a consistent majority close to recent ECMWF/ECens mean runs for a surface low track over or a little east of the upper Ohio Valley as of early Sunday. GFS runs have waffled slower/faster (18Z/00Z runs faster), while the new 00Z ECMWF has nudged a little faster as well. Recent CMC/CMCens runs had strayed slow with the upper trough and weak/suppressed with the surface wave, but the new 00Z run has adjusted close to the 12Z ECMWF. ML models support fairly strong development of this storm as it reaches the Canadian Maritimes by next Monday (versus the weak 18Z GFS). Finally, dynamical guidance shows better than average agreement with the North Pacific system that should affect the Northwest by the weekend and early next week, with the surface low likely tracking toward or close to Vancouver Island. ML models show potential for a little more variation in timing/details of the upper trough, leaning a tad faster than the dynamical majority on average. ...Weather/Hazards Highlights... The system tracking through the Northeast on Thursday will bring meaningful snow to northern New England, while the trailing cold front will cross the Southeast. Recent guidance runs have been narrowing the spread for this front and its associated axis of moisture. Models show some instability with this front and potential for some locally heavy rainfall, mainly over parts of northern Florida into Georgia. However this region has dry antecedent conditions with very high flash flood guidance values. Thus the Day 4/Thursday Excessive Rainfall Outlook continues to depict no risk area for this activity. Will continue to monitor for any trends toward broader organized heavy rainfall on the higher end of the envelope. With fairly strong low pressure and associated frontal system reaching the West Coast Thursday into early Friday, guidance has maintained good continuity over the past day regarding favorable moisture anomalies/enhanced IVT values focusing heaviest rainfall and higher elevation snow over California. Therefore the new Day 4 ERO carrying over from yesterday's Day 5 outlook has made no changes at this time, with a Slight Risk area over a majority of coastal California and extending into favored terrain of the Sierra Nevada. This area reflects the best overlap of heaviest forecast rainfall and current sensitivities from either wet antecedent conditions or burn scars. Especially as shorter term guidance refines the best focus of heaviest rainfall, it is possible an eventual upgrade to a moderate risk may be needed across southern California and in particular the burn scar areas. The new Day 5 ERO introduces a Marginal Risk area along the far southern coast, with lingering moisture early in the day and the upper trough passing overhead to provide some possible instability. Continued progression of this system will spread areas of rain and heavy mountain snow farther inland, eastward to the Rockies. The upper trough will likely support surface low development over the eastern half of the country during the weekend. South-central areas that will already be sensitive due to prior heavy rainfall may see another episode of heavy rain, while areas from the Midwest into the Northeast will see the best potential for significant snow. A transition zone of wintry mix may separate the rain/snow areas. There may be a period of gusty winds over parts of the East behind this system. A farther northward track of the next Pacific system will favor the Northwest for the next round of rain and higher elevation snow from the weekend into early next week. Amounts should start out on the light to moderate side on Saturday but may trend somewhat heavier on Sunday. Expect moisture to spread farther eastward/southeastward into the Rockies By Monday. Parts of the central U.S. will see well below normal temperatures for most of the period, with some central-southern Plains locations 20-30F below normal for highs on Thursday followed by another cold surge bringing similar anomalies into the far northern Plains on Friday and extending farther southward during the weekend. Progression of an upper trough into the East will spread a modified form of this cold air eastward by next Monday with most of the northeastern quadrant of the lower 48 seeing highs 10-20F below normal. Cold air will also extend into the Northwest through late week but the West as a whole will gradually trend warmer as Pacific flow gains influence. The Four Corners states and vicinity may achieve above normal highs by the start of next week. Systems forecast to reach the East around Thursday and Sunday should pull some above normal temperatures northward from the Gulf Coast/Southeast. A few locations over the Florida Peninsula could challenge record highs on one or more days. 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