Extended Forecast Discussion NWS Weather Prediction Center College Park MD 246 AM EDT Fri Aug 26 2022 Valid 12Z Mon Aug 29 2022 - 12Z Fri Sep 02 2022 ...Overview... Across the CONUS during the period, the mean flow is expected to transition from nearly zonal/flat flow to a more amplified pattern featuring troughing over the eastern Pacific and eastern U.S. with a ridge extending through much of the western U.S. though by the end of next week, there are signals that troughing may push onshore the Pacific Northwest. The primary synoptic forcing for rainfall will be along a progressive cold front through the central to eastern U.S. next week and the greatest temperature anomalies will be found across the interior West underneath the amplifying upper ridge. ...Guidance Evaluation/Predictability Assessment... Shortwave energy moving across the Northwest this weekend is expected to reach the Northern Plains by the start of the medium range period and overall, the most recent deterministic guidance has come into better agreement with its progression and amplitude. The 18Z/12Z GFS showed some differences in the speed and magnitude, with the 12Z GFS being somewhat an outlier compared to the ECMWF and UKMET, having a slower progression and eventually closing off a low that drifts southward into the Plains. The 18Z (and new 00Z) GFS runs are more in line with the ECMWF, being progressive across the northern tier. That energy is expected to deepen a trough over the Great Lakes and push a cold front through much of the central to eastern U.S., reaching the Southeast and Gulf Coast later in the period. Sprawling Canadian high pressure in its wake will bring drier and seasonable temperatures to portions of the central/eastern CONUS. A weakness in the ridge over the Southern Plains may lead to a period of unsettled weather with a weak surface boundary in place interacting with Gulf moisture and the aforementioned frontal boundary. The GFS is more bullish showing this potential for more widespread precipitation compared to the ECMWF which shunts all the deeper moisture well to the coast. Toward the end of the period, model guidance is showing potential for another shortwave trough to approach the Pacific Northwest, with the typical timing biases showing up. Ahead of that feature, the upper ridge over the Southwest is forecast to build northward and strengthen. ...Weather/Hazards Highlights... Deeper moisture pooling along and ahead of an advancing cold front across portions of the central/eastern U.S. may lead to pockets of moderate to locally heavy rainfall at times next week. One area of focus for higher rainfall potential is across the Southern/Central Plains where interaction with Gulf moisture may boost rainfall intensity and amounts. Showers and thunderstorms are also likely to continue across portions of the South, including the Gulf Coast and Florida Peninsula where locally heavy rainfall is possible, but likely to be localized/isolated. Elsewhere, the Southwest monsoon activity should see a reprieve during the period with the better moisture shunted over to the east. With upper ridging building over the West, the greatest temperature anomalies are expected over the Pacific Northwest into the Northern Rockies with daytime highs next week 10-15 degrees above normal. A few places could challenge daily records for highs/warm lows. Elsewhere, slightly above normal temperatures are forecast for the Mid-Atlantic and Northeast early to mid week ahead of the approaching cold front while the central U.S. is expected to have near normal readings for late August. Taylor/Putnam 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