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FXUS06 KWBC 131931PMDMRDPrognostic Discussion for 6 to 10 and 8 to 14 day outlooksNWS Climate Prediction Center College Park, MD300 PM EDT Mon September 13 20216-10 DAY OUTLOOK FOR SEP 19 - 23 2021Today's ensemble mean solutions show very good agreement among the models onthe 500-hPa flow pattern over North America. An amplified ridge is forecastover the Aleutians. A 500-hPa trough stretches from northern Alaska to thenorthwest CONUS and mean ridging is favored over much of the remainder of theCONUS. The 500-hPa height blend features positive height anomalies over theAleutians and southwestern Mainland Alaska, negative height anomalies over mostof the remainder of Mainland Alaska, the Alaska Panhandle, and the northwesternCONUS. Positive height anomalies are favored over much of the remainder of theCONUS, underneath mean ridging.Amplified troughing over the Gulf of Alaska favors below-normal temperaturesfor much of Alaska and the western CONUS. Predicted 500-hPa ridging forecastover the southwestern CONUS and most of the eastern CONUS leads to enhancedchances of above-normal temperatures, with the highest probability (exceeding90%) over the eastern Midwest and much of the Mid-Atlantic and the Northeast.Along and west of the forecast mean trough axis, northeasterly surface flow ispredicted, increasing odds of below-normal precipitation over of southwesternMainland Alaska and the Aleutians. The forecast trough over the Gulf of Alaskafavors an active storm track and increased onshore flow across much of theremainder of Mainland Alaska, the Alaska Panhandle, and portions of thenorthwestern CONUS, leading to enhanced odds of above normal precipitation.Southeast of the predicted trough over the Gulf of Alaska, forecast surfacehigh pressure increases the likelihood of near to below-normal precipitationacross much of the southwestern CONUS from the High Plains to the West Coast.Ahead of the predicted trough, several storm systems with trailing frontalboundaries are forecast to sweep eastward, favoring above-normal precipitationfor much of the eastern half of the U.S. However, below normal precipitation isfavored over parts of the Northeast, consistent with the consolidation forecasttool.The official 6-10 day 500-hPa height blend consists of 15% of Today's 6z GFSEnsemble Mean centered on Day 8, 15% of Today's GFS Superensemble Mean centeredon Day 8, 10% of Today's operational 6z GFS centered on Day 8, 30% of Today's0z European Ensemble Mean centered on Day 8, 10% of Today's operational 0zECMWF centered on Day 8, and 20% of Today's 0z Canadian Ensemble Mean centeredon Day 8FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: Above average, 4 out of 5, due togood agreement among the ensemble models and tools in depicting a relativelyamplified pattern, offset by increasing uncertainty in the position andstrength of the forecast trough.8-14 DAY OUTLOOK FOR SEP 21 - 27 2021Heading into the Week-2 period, the 500-hPa pattern shows a slight progressionof the 6-10 day mean 500-hPa pattern, though the amplitude of most features isexpected to be lower due to increased uncertainty. Due to the pattern beingvery similar to the 6-10 day period, the Week-2 temperature and precipitationprobability forecasts are very similar as well. The potential for tropicalactivity during the Week-2 period increases the likelihood of above-normalprecipitation in the Southeast and along the Gulf Coast.The official 8-14 day 500-hPa height blend consists of: 15% of Today's 6z GFSEnsemble Mean centered on Day 11, 15% of Today's GFS Superensemble Meancentered on Day 11, 10% of Today's operational 6z GFS centered on Day 11, 40%of Today's 0z European Ensemble Mean centered on Day 11, and 20% of Today's 0zCanadian Ensemble Mean centered on Day 11FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: Average, 4 out of 5, due to goodagreement among the models and tools, and a relatively amplified and persistentpattern across the domain with good day-to-day consistency.FORECASTER: Y. FanNotes:Automated forecasABNT20 KNHC 132311TWOATTropical Weather OutlookNWS National Hurricane Center Miami FL800 PM EDT Mon Sep 13 2021For the North Atlantic...Caribbean Sea and the Gulf of Mexico:The National Hurricane Center is issuing advisories on TropicalStorm Nicholas, located near the central Texas coast.A tropical wave located over the far eastern tropical Atlantic isproducing an area of disorganized cloudiness and thunderstorms.Environmental conditions are forecast to be conducive for gradualdevelopment of this disturbance over the next several days, and atropical depression is likely to form by later this week while thesystem moves westward at about 15 mph across the eastern tropicalAtlantic Ocean.* Formation chance through 48 hours...medium...40 percent.* Formation chance through 5 days...high...80 percent.An area of low pressure is expected to form by midweek a couple ofhundred miles north of the southeastern or central Bahamas as atropical wave interacts with an upper-level trough. Some gradualdevelopment of this system is possible thereafter, and a tropicaldepression could form later this week while the system movesnorth-northwestward or northward across the western Atlantic.* Formation chance through 48 hours...low...10 percent.* Formation chance through 5 days...medium...50 percent.$$Forecaster Roberts