Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 PM EDT Fri Jun 7 2024 Valid 12Z Mon Jun 10 2024 - 12Z Fri Jun 14 2024 ...Hot temperatures for the West/Southwest plod into next week... ...Overview... There is some general agreement in the guidance that an elongated upper low over southern-eastern Canada this weekend will split by the start of the medium range period on Monday, with a trough moving through the Northeast Monday-Tuesday and a compact closed low getting left behind over south-central Canada (or the far northern U.S.). This energy should linger for a day or two before becoming absorbed by an additional shortwave from western Canada. This progresses eastward mid-late week with troughing extending southward through the East. Additional southern stream energy embedded within will keep unsettled conditions and heavy rainfall potential across the southern Rockies-southern Plains early week, with an inherent stronger threat signal for a multi-day wet period across the Florida Peninsula starting on Tuesday. Behind this, upper ridging over the West will slide into the Central U.S. with continued heat, though likely moderated a bit compared to currently. Stronger troughing from an upper low south of the Gulf of Alaska looks to enter the West Coast later in the week. ...Guidance/Predictability Assessment... Overall, guidance has come into better agreement on the large scale pattern progression during the medium range period, but continue to struggle with the details, some of which have important implications on sensible weather. For the central-Canada compact upper low, models have flip-flopped the past few days between whether this lingers over Canada or rather drops through the Upper Midwest states, but the last few runs of guidance (including the new 12z guidance for today) seems to support the former. Still though, given the sensitivity of this small scale system to the strength of a trough in the East, it remains a low confidence forecast. Additional southern stream energy through the south- central Plains shows uncertainty and how this interacts with the northern stream will affect elongated troughing eventually over the East later in the week and availability/efficiency of moisture directed into Florida and interacting with a stalled frontal boundary. Otherwise, out West, there are still some timing differences with ridge progression into the Plains related to differences in troughing into the Northwest coast. With sufficient agreement, the WPC forecast was able to use a majority blend of the deterministic guidance for the first half of the period, with some additional weighting given to the ECMWF since it had a little better run to run continuity than other models. After this, ramped up inclusion of the ensemble means to 70 percent of the blend to help mitigate late period differences. Maintained some of the ECMWF through day 7 just for a little added system definition. On the large scale, this maintained good agreement with the previous WPC forecast. ...Weather/Hazards Highlights... Ample pooled moisture and instability with a wavy front that will tend to stall from the central Rockies to southern High Plains and vicinity may produce periods with heavy convection with potential for heavy rain rates, so a Marginal Risk area is delineated for Day 4/Monday. A weakening front lifting back into the south-central Plains may continue a threat for heavy rainfall into Day 5 across very waterlogged southeast Oklahoma to northeast Texas region. Added a marginal risk on the day 5 ERO to capture this. A multi- day period favorable for some heavy rains is then possible to develop across the Florida Peninsula starting Tuesday as well-above moisture pools along the stalling front with some aid from weak upper level impulses/energy. There is a lot of uncertainty in the details and much of the state is in a drought. Still, some threat for high rain rates exists, and its possible much of the threat remains confined to urbanized areas. Still, opted to expand the marginal risk on Day 5 to include much of the central and southern Peninsula to account for the uncertainty. The better moisture and heftier QPF should come in mid to late week anyways. Elsewhere, much of the country should be dry except for late week showers moving back in to the Rockies-central Plains along a frontal boundary. The mean ridge in the West/Southwest will continue to cause much warmer than average temperatures, but seemingly not quite as hot as in the short range period. The highest temperature anomalies of 10-20F above normal are forecast for the Great Basin, warming a bit and expanding eastward as the week progresses into the northern Rockies and Plains. Temperatures will also rise a few degrees in the Desert Southwest to bring some temperatures back above 110F, with heat risk threat levels mostly at moderate to major levels. Heat should build again across south to southwest Texas as well, with heat indices creeping back up to around 110 by the end of the week. Santorelli/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