039 FXUS21 KWNC 172126 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT June 17 2026 SYNOPSIS: Forecast mid-level high pressure over the southwestern contiguous U.S. (CONUS) is expected to promote above-normal temperatures with possible extreme heat conditions across the California Valley eastward into the lower Four Corners later next week. Enhanced subtropical high pressure over the Gulf of America and western Atlantic also brings an increased risk of heat over portions of Florida during week-2. Above-normal precipitation is predominately favored over much of the Midwest early in week-2, however there continues to be outlook uncertainty in regards to designating a corresponding heavy precipitation risk. HAZARDS Slight risk of extreme heat for parts of California Central Valley, Desert Southwest, Southern High Plains, Thu-Sun, Jun 25-28. Slight risk of extreme heat for Florida, Thu-Wed, Jun 25-Jul 1. DETAILED SUMMARY FOR SATURDAY JUNE 20 - WEDNESDAY JUNE 24: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR THURSDAY JUNE 25 - WEDNESDAY JULY 01: Towards the middle of next week, dynamical model 500-hPa height anomaly forecasts from the GEFS and ECMWF ensembles continue to be at odds with one another in regards to the shape and evolution of the mid-level pattern over the northwestern CONUS and eastern Pacific, contributing to increased uncertainty in the hazard outlook. Consistent with previous ensemble runs, the GEFS favors the development of shortwave troughing over the Pacific Northwest, whereas the ECMWF ensemble remains bullish in maintaining above-normal height departures, resulting in contrasting temperature responses over this part of the country early in week-2. Downstream, there is general model agreement featuring broadly weak mean longwave troughing east of the Rockies, with weaker subtropical ridging over the southern tier of the U.S. Both of these features are expected to bring cooler temperatures over parts of the Great Plains, Mississippi, Tennessee, and Ohio Valleys heading into the week-2 period, however parts of the eastern Gulf coast and Florida could struggle to experience relief from above-normal temperatures lingering from week-1. Tied to stronger shortwave troughing over the northwestern CONUS in the latest 0z GEFS, the corresponding raw and calibrated temperature tools indicate near to below normal daytime temperatures, along with a downtick in heat signals in the Probabilistic Extremes Tool (PET). While above-normal temperatures and heat conditions remain possible across this region as advertised by the ECMWF and Canadian ensembles, deterministic solutions from the ECWMF and GFS also point to the potential for shortwave development, resulting in insufficient confidence of maintaining a slight risk of extreme heat over parts of the Pacific Northwest and Northern Intermountain in the updated outlook. However, a slight risk of extreme heat remains posted further south across the portions of the California Valley and the lower Four Corners where there is better agreement in the mid-level height and temperature forecasts among the dynamical models. Within the highlighted region, both GEFS and ECMWF PETs indicate at least 20% chances for maximum temperatures exceeding the 85th climatological percentile, with similar chances for actual temperatures exceeding 100 (110) deg F in parts of the California Valley (Desert Southwest) early in week-2. The slight risk coverage is adjusted to remove parts of the Texas where cooler temperatures are forecast early in week-2, and is now valid through Jun 28 as the ridging aloft gradually deamplifies. Despite the cooler temperatures favored downstream, the PETs continue to highlight increased chances for maximum temperatures exceeding the 85th percentile over the Florida associated with persistent enhanced subtropical ridging over the Gulf and western Atlantic throughout the period. Therefore, a slight risk of extreme heat remains posted (Jun 25-Jul 1) with coverage limited to the Florida peninsula in the updated outlook. The National Blend of Models (NBM) also continues to depict a number of locations with near record high minimum temperatures over Florida later next week suggestive of little relief of potential heat during the overnight hours. Surface low development in the lee of the Rockies and associated enhanced likelihood of heavy precipitation is possible early in the period, however the GEFS and ECMWF differ in regards to the placement and strength of any discernible mean surface low. A more westerly solution of a mean low pressure center is found in the GEFS tied to the shortwave troughing upstream, whereas the ECMWF favors lowered mean surface pressure extending from the Great Plains to the Great Lakes with a robust precipitation reflection focused over the Middle Mississippi Valley in its precipitation tools. In particular, the uncalibrated ECMWF indicates 40% chances of 3-day amounts exceeding an inch over parts of Iowa, Missouri eastward to the Ohio Valley. This risk however is much less supported in the GEFS, GEFSAI and Canadian guidance precluding any corresponding precipitation hazards in the outlook. This potential will continue to be monitored in the coming days. Due to aforementioned disagreements in the height pattern among the dynamical models, no wind hazards are posted over the CONUS. Both GEFS and ECMWF PETs show increased chances for wind speeds exceeding the 85th percentile across the western CONUS, however there is little to no support for wind speeds exceeding hazard thresholds in the uncalibrated tools. FORECASTER: Nick Novella $$