Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Sat May 13 2023 Valid 12Z Tue May 16 2023 - 12Z Sat May 20 2023 ...Warmer than average temperatures will persist across the Northwest... ...Overview... The overall weather pattern through next week will consist of an anomalously strong upper ridge over the western half of the U.S. and into western Canada that will be persistent aside from an upper low gradually shearing out/weakening atop the Northwest through around midweek. This pattern will maintain warm to hot temperatures across the Northwest and to a lesser extent over other parts of the West. Downstream, mean troughing is likely across eastern North America, with individual shortwaves supporting cold fronts that drop into the northern/eastern parts of the country. Meanwhile moist inflow continues into the southern Plains, maintaining some risk of excessive rainfall there, though the threat of widespread flash flooding should decrease through next week given less upper-level support compared to the near term and short range period. ...Guidance/Predictability Assessment... Model guidance continues to show good agreement for the large scale pattern while exhibiting some embedded detail differences/adjustments. Seemingly the main feature within the western ridge/eastern trough pattern to key on from a model diagnostics perspective is the potent shortwave with perhaps an embedded upper low tracking through south-central Canada along with a surface low reflection for Wednesday and beyond. The 12Z UKMET appeared to be a fast outlier with this, with other models/ensembles generally similar with their timing and track through around Friday until the 12Z ECMWF speeds up compared to the GFS/CMC. The incoming 00Z model cycle seems to be pretty consistent with the 12/18Z cycle that was available for this forecast issuance, though there may be a slightly faster trend with the cold frontal position by day 7/Saturday compared to the WPC forecast. The GFS sped up but the ECMWF slowed up a bit compared to its previous run, and the CMC remains on the slow side. Meanwhile there are still notable smaller scale differences aloft across the central U.S. and into the Southeast, with effects on QPF placement and amounts. The low predictability involved with such features will minimize confidence in any specific solution. The WPC forecast was based on a multi-model deterministic blend early in the period, phasing out the UKMET and lessening some other model components in favor of the GEFS and EC ensemble means to a little less than half by the end of the period. ...Weather/Hazards Highlights... Persistent moist inflow is likely to continue into the southern Plains through much of next week. Though rain amounts should not be as high as with recent events and in the short term across Texas, some rainfall continuing over what is likely to be extremely wet ground has led to Marginal Risks in the Excessive Rainfall Outlook continuing into Days 4-5/Tuesday-Wednesday, with some eastward shift for Wednesday compared to Tuesday. There is still a fair amount of model spread with placement of any heavier totals that may not be resolved until the short term or near term. One such uncertainty is the ECMWF model suite continuing to indicate moderate with perhaps pockets of heavy QPF extending farther west into New Mexico and even Arizona compared to other guidance, with higher precipitable water anomalies as well. With other models drier, limited the ERO areas mainly to Texas for now, but a monsoon-like pattern setting up farther west promoting some locally heavy rain amounts is not completely ruled out. Areas of rain farther north in a monsoonal type of pattern with moisture coming in underneath Great Basin ridging aloft are also uncertain in terms of placement and amounts. But by the latter part of next week, a low pressure system moving across southern Canada and possibly as far south as the Great Lakes should bring a cold front across much of the central U.S., serving to focus rain and thunderstorms along and ahead of it with slightly more predictability, with rain chances gradually progressing south and east with time coincident with the front's movement. This front could bring some upslope flow over parts of the south-central Rockies/High Plains, enhancing potential rainfall amounts there. Ahead of this cold front, some scattered showers and storms are possible across the Gulf Coast states through much of the week as moisture pools along a couple of west-east oriented fronts. The Northeast could see a round of rain on Tuesday but then is likely to see dry conditions until moisture is drawn into the East late week ahead of the central U.S. cold front. Temperature-wise, expect warm to hot temperatures to persist across the West as large scale upper ridging prevails on the whole. The Northwest (the Pacific Northwest into the Great Basin) is likely to see the highest temperature anomalies of 10-20 degrees above average persist through much of the week, though with perhaps some slight moderation late week for the Pacific Northwest while areas inland may slightly warm. The highest potential for record highs has now phased into the short range period, but record high minimum temperatures in the 50s and 60s could continue to be widespread through mid- and late week across the West, perhaps even challenging monthly records. The warming trend over the northern Great Basin by Friday-Saturday may once again reach record highs though. Farther south, highs in the 90s are likely in the California Central Valley with highs above 100F in the Desert Southwest (though the latter is not terribly anomalous for May). Warmer than average temperatures should expand across much of the northern tier early-mid week, followed by a cooling trend Thursday-Saturday after the frontal passage. The Northeast to Mid-Atlantic should see variable above or below normal temperatures depending on frontal progression. Currently anticipate the most notable anomalies being on the cool side of normal by 5-15F over the Northeast during Wednesday into early Thursday after a Tuesday frontal passage. The cloudy and rainy conditions over the southern High Plains should keep highs 5-15F below normal especially for the first half of the week, with more moderate readings likely thereafter. Tate 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, experimental excessive rainfall outlook, winter weather outlook probabilities and heat indices are at: 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