615 FXUS21 KWNC 061857 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT June 06 2025 SYNOPSIS: Mid-level high pressure is favored over the eastern half of the Contiguous U.S. (CONUS) early in week-2, leading to the development of potentially hazardous heat over portions of the Midwest, Ohio Valley, and Mid-Atlantic. Soon thereafter, this area of mid-level high pressure and hazardous heat is predicted to concentrate over the Central Plains and Midwest. Surface high pressure over the North Atlantic favors abundant Gulf moisture to move over the Great Plains, leading to elevated heat indices and also fueling potentially heavy rainfall along the Gulf coast and also over portions of the coastal Southeast, Great Plains and Mississippi Valley. Mid-level low pressure over the Pacific Northwest at the outset of week-2 has the potential to bring periods of high winds to much of the northwestern CONUS through the middle of the forecast period. HAZARDS Moderate risk of extreme heat for parts of the Central Great Plains and Midwest, Sun-Tue, Jun 15-17. Slight risk of extreme heat for a larger portion of the Central Great Plains and Midwest, Sat-Wed, Jun 14-18. Slight risk of extreme heat for the Mid-Atlantic, Sat, Jun 14. Slight risk of episodic high winds for the northwestern CONUS, Sat-Mon, Jun 14-16. Slight risk of heavy precipitation for much of the eastern Great Plains and Mississippi Valley, Upper Great Lakes, and the Gulf and South Atlantic coasts, Sat-Mon, Jun 14-16. Possible flooding for much of the Middle to Lower Mississippi Valley and eastern Central and Southern Plains. DETAILED SUMMARY FOR MONDAY JUNE 09 - FRIDAY JUNE 13: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR SATURDAY JUNE 14 - FRIDAY JUNE 20: Model ensembles are in fairly good agreement with regard to a persistent mid-level ridge over areas east of the Rockies, with widespread 6-12 dm positive 500-hPa height anomalies early in week-2, with a predicted consolidation of the ridge over the north-central CONUS shortly thereafter. This favors anomalously warm temperatures which, when combined with high humidity (70 deg F or greater dew points) due to advection of Gulf moisture, results in potentially hazardous heat for much of the middle of the CONUS. Heat index values of 100-105 deg F fall just a bit short of hazardous thresholds for mid-June, but this is offset slightly by the longer (expected) duration of this event. The Probabilistic Extremes Tools (PETs) indicate at least a 20% chance of maximum temperatures exceeding the 85th percentile and at least 90 deg F for much of the Central Plains eastward across the Middle Mississippi Valley beginning on June 14th and extending through most of the forecast period. Similar thresholds are briefly reached for the Mid-Atlantic on June 14, therefore a slight risk of extreme heat is posted for these regions for the respective time periods indicated. The Mid-Atlantic heat event is considered marginal and is predicted to wane after the 14th of June, as the Midwestern ridge shifts westward and 500-hPa heights fall over the Northeast and Mid-Atlantic regions. Though slight risks of extreme heat are posted for both areas, even though air temperatures may fall a bit short of hazardous thresholds for mid-June, this heat event is expected to be the first of the season, last most of the week (for the Central Plains and Midwest), and be accompanied by high levels of humidity. In addition to these factors, dry soils and a slight amplification of the ECENS 500-hPa raw height anomalies late in week-2 favor a moderate risk of extreme heat for a smaller portion of the Central Plains and Midwest, June 15-17. This differs from the GEFS solution starting around day 12, which favors a weakening ridge predicted to retrograde to the Rocky Mountain states. The ECENS scenario is thought to be more likely than the GEFS scenario. Across the southern CONUS, temperatures are likely to be quite hot but hazard criteria are not likely to be met outside the regions discussed above. Ensemble means from the GEFS, ECENS, and CMCE for 500-hPa height anomalies depict an amplified trough situated over the West Coast during week-2, although this feature is favored to weaken throughout the forecast period. Associated with this is weak surface low pressure over the Great Basin, which along with strong surface high pressure over the North Pacific sets up a tight pressure gradient and resultant enhanced surface winds across the northwestern CONUS. This is supported by the Probabilistic Extremes Tools (PETs) from the ECMWF, which broad-brushes at least a 20% probability of 3-day maximum wind speeds exceeding the 85th climatological percentile for the first few days of the outlook period over this region. The CMCE and GEFS PETs are less bullish but still show some signal over these areas for at least a portion of the forecast period. Therefore a slight risk of high winds is posted for the Pacific Northwest, Great Basin, and Northern California for Jun 14-16. A strong Bermuda high is favored by the ensembles throughout week-2, setting up moist southeasterly flow off the Gulf and into the central CONUS. The models also indicate weak troughing east of the Rockies which is anticipated to pair up with the Gulf moisture and lead to significant daytime heating and potentially heavy precipitation for much of the eastern Great Plains, Mississippi Valley, Upper Great Lakes, and the Gulf and South Atlantic Coasts. This enhanced rainfall signal is well-supported by the ECMWF and GEFS PETs, which both indicate at least a 20% chance of 3-day precipitation totals exceeding the 85th percentile and at least 1 inch of precipitation for at least the first several days of the forecast period. Given this, a slight risk of heavy precipitation is posted for the regions noted above for Jun 14-16. Additionally, the Middle Mississippi Valley has been plagued by surplus precipitation and subsequent flooding during the spring and the ground has not had time to drain much, so new or renewed flooding is a concern, warranting the posting of a possible flood hazard for the region. Just north of the primary flood region of the Middle to Lower Mississippi Valley and eastern portions of the Central and Southern Plains is a relatively dry region (Iowa, northern Illinois, and far northern Missouri), which has reported low soil moisture (lowest one-third of the historical distribution) over the past 30-days. This region of relatively dry soils is being monitored for a potential ROD (Rapid Onset Drought) designation. Ice-bound rivers are slow to break up in the North Slope of Alaska. There is no associated hazard posted at this time but this situation will be closely monitored in the coming days and weeks as conditions can quickly change, leading to the potential for ice jams, aufeis (a sheet-like mass of layered ice that forms from successive flows of ground or river water during freezing temperatures), and associated flooding. FORECASTER: Anthony Artusa $$