Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Tue Jun 11 2024 Valid 12Z Fri Jun 14 2024 - 12Z Tue Jun 18 2024 ...Heatwave to spread from the Southwest to parts of the central and eastern U.S. during the period... ...Excessive Rainfall Threat for Florida through late week and perhaps the central Gulf Coast early next week... ...Guidance/Predictability Assessment... The WPC medium range product suite was primarily derived from a composite blend of reasonably well clustered overall guidance from the 18 UTC GFS and 12 UTC ECMWF/Canadian/UKMET, the 01 UTC National Blend of Models and WPC continuity for Friday into Sunday in a pattern with average to above average predictability. Opted for smaller input from the models in lieu of more run to run consistent GEFS/ECMWF ensemble mean blending into early next week amid growing uncertainties, including in particular continued variances with local sensible weather/threat focus. The blending process tends to mitigate variance by limiting detail consistent with individual feature predictability. This also acts to maintain good WPC product continuity that remains generally in line with a similar blend of latest 12 UTC guidance. ...Weather/Hazards Highlights... A protracted period favorable for heavy rains should continue through later week for the Florida Peninsula as well above normal tropical/Caribbean moisture pools along and south of a wavy stalled front with aid from upper level impulses/energy back through an unsettled Gulf of Mexico. There remains high confidence in heavy rainfall in Florida with locally heavy rainfall rates, but lower confidence on placement of any extreme convective amounts on any particular day. Storm total rainfall (including what falls before the medium range period even starts) of 7-10 inches, with locally higher amounts to 15 inches, is forecast. WPC Excessive Rainfall Outlook Slight Risk areas remain in place for the central to southern Florida Peninsula into Day 4/Friday. Heavy rain may last into Saturday across Florida where a Day 5 Marginal Risk has been introduced via collaboration with local WFO offices for lingering activity. However, as the weekend progresses and into early next week, there is a growing guidance signal that moisture influx and possible heavy rainfall may refocus and increase into the central Gulf Coast and vicinity to monitor for runoff issues given the favorable deeply moist pattern. Meanwhile, leading and dynamic northern stream upper trough energy approach and passage is expected to fire convection along/ahead of a wavy/pooling surface front over the Northeast into Friday where a Marginal Risk area remains in place as the parallel upper flow and convective axis may lead to repeat cells and runoff issues. Elsewhere, an increasing convective precipitation threat will emerge across the central and northern Plains/Upper Midwest late week into the weekend as well defined southern stream troughing ejects northeastward toward the region from the Southwest to focus lift/instability. A WPC ERO Marginal Risk area remains in place for Day4/Friday from the southern High Plains to the central Plains, except for the Sandhills of Nebraska that are not as sensitive to heavy rain. A Day5/Saturday Marginal Risk area has been introduced from the central Plains to the Upper Midwest given system progression and continued unstable flow. As for anomalous temperatures, an amplified upper ridge slated to steadily/broadly shift from the Southwest through the south- central U.S. to the East will produce much warmer than average temperatures and the threat for some record heat into next week. The Climate Prediction Center continues a heat threat into week 2. Schichtel 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