660 FXUS21 KWNC 181816 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT June 18 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. Surface low development in the lee of the Rockies supports an increased risk of heavy precipitation mainly across parts of the Middle and Upper Mississippi Valley early in the period. HAZARDS Slight risk of extreme heat for parts of California Central Valley, Desert Southwest, Southern High Plains, Fri-Sun, Jun 26-28. Slight risk of extreme heat for parts of the Florida peninsula, Fri-Thu, Jun 26-Jul 2. Slight risk of heavy precipitation for parts of the eastern Central and Northern Plains, Upper and Middle Mississippi Valley, and parts of the western Ohio Valley and Great Lakes, Fri-Sun, Jun 26-28. DETAILED SUMMARY FOR SUNDAY JUNE 21 - THURSDAY JUNE 25: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR FRIDAY JUNE 26 - THURSDAY JULY 02: Compared to yesterday, 500-hPa height anomaly forecasts from the GEFS and ECMWF ensembles generally feature a less amplified pattern early in week-2, with the mean week-2 height fields depicting fairly muted positive height anomalies over portions of the CONUS. Perhaps the most meaningful change in the ensemble guidance resides in the ECMWF, which maintained an amplified ridge center over the northwestern CONUS over the past few days, but now favors a considerably more westward mean solution of this height feature over the eastern Pacific in the latest 0z run. This shift falls more in line with the GEFS, and could allow for more troughing over the northwestern CONUS and potentially force rising mid-level heights downstream later in the week-2 period. Over the lower latitudes, there continues to be good model agreement featuring enhanced subtropical ridging to increase chances for above-normal temperatures with possible heat conditions developing over the parts of the West Coast, lower Four Corners, and the Gulf States during the period. Analysis of ECMWF and GEFS 500-hPa height anomalies in standardized space continues shows a fairly strong height maxima centered over northwestern Mexico early in the period supportive of extreme heat risk. With Probabilistic Extreme Tools (PETs) also indicating at least 20% chances of daytime temperatures exceeding the 85th climatological percentile tied to this height feature, a slight risk of extreme heat remains posted for portions of the California Valley, Desert Southwest and parts of the Southern Plains, and remains valid through Jun 28 before the ridge center deamplifies. Within the highlighted hazard area, raw temperature tools continue to depict increased chances for maximum temperatures exceeding 105 deg F over parts of the California Valley, and over 110 deg F over the lower elevations of the Desert Southwest. Although near to below normal daytime temperatures are largely favored east of the Rockies, the PETs continue to highlight increased chances for maximum temperatures exceeding the 85th percentile across parts of 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 26-Jul 2) 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. Since yesterday, PETs also show a northward expansion of warm signals into the lower Eastern Seaboard beginning by days 9-10 (Jun 27-28). The GEFS is a bit more aggressive with this expansion compared to the ECMWF, but regardless, there is not much support for actual temperatures exceeding hazard thresholds based on the raw tools. Therefore, no adjustments are made to the area highlighted with a slight risk of extreme heat in today's outlook, however this potential will continue to be monitored in the coming days. For precipitation, models continue to point to potential surface low development in the lee of Rockies early in week-2, however ensemble solutions remain quite diffuse in regards to the location of development and the eventual track of surface low. Despite this, raw uncalibrated precipitation tools have come into better agreement converging on the greatest precipitation risk centered over the Upper and Middle Mississippi Valley with at least 20% chances for 3-day amounts exceeding an inch. Additionally, there is also better agreement in the GEFS and ECMWF PETs highlighting this part of the Midwest with 20% chances of 3-day amounts exceeding the 85th percentile and 1 inch, supporting the addition of a slight risk of heavy precipitation, valid for Jun 26-28 for this region. Due to the slight risk for excessive rainfall forecast during week-1 across parts of lower Missouri River and Ohio River basins, any heavy precipitation realized may trigger localized flooding during week-2. No hazards are posted over Alaska. Favored ridging aloft and warmer than normal conditions over parts of the Mainland may lead to increased air mass thunderstorm activity, supportive of fire weather during the period. FORECASTER: Nick Novella $$