239 FXUS21 KWNC 301803 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT June 30 2026 SYNOPSIS: Building mid-level high pressure over parts of the western and central contiguous U.S. (CONUS) supports above-normal summertime temperatures with an increased heat risk extending from the Desert Southwest into the upper Midwest early in week-2. Further south, enhanced subtropical high pressure also favors the potential for extreme heat conditions for parts of Florida during the period. Above the subtropical mid-level high pressure, there is better model support for surface low development and an accompanying heavy precipitation risk over parts of the Southeast and Mid-Atlantic. Over the West Coast, strengthening pressure gradients favored leads to increased chances for episodes of high winds across the Pacific Northwest and California for much of the period. HAZARDS Slight risk of extreme heat across much of the Great Basin, Northern Intermountain, Rockies, Southwest, and Great Plains, Wed-Fri, Jul 8-10. Slight risk of extreme heat for the eastern Gulf Coast and Florida Peninsula, Wed-Sun, Jul 8-12. Slight risk of heavy precipitation for parts of the Mid-Atlantic and the Southeast, Wed-Fri, Jul 8-10. Slight risk of episodic high winds for portions of California and the Pacific Northwest, Wed-Tue, Jul 8-14. DETAILED SUMMARY FOR FRIDAY JULY 03 - TUESDAY JULY 07: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR WEDNESDAY JULY 08 - TUESDAY JULY 14: A significant heat event remains favored for much of the central and eastern CONUS during week-1, with heat risks expected to shift westward and potentially linger into week-2 associated with a retrograding 500-hPa ridge by early next week. Mid-level height anomaly forecasts from the today's 0z GEFS and ECMWF ensembles are in good agreement by the outset of week-2 (Jul 8), both featuring a 594 dm height center over the Four Corners, with the strongest positive height departures focused over the Northern Plains and southcentral Canada. This mid-level pattern should allow for more mean northwesterly flow to bring cooler temperatures and heat relief for areas downstream mainly east of the Mississippi, however the greatest potential for continuing heat risk resides along this ridge axis extending from the southwestern CONUS into the Upper Midwest early in week-2. In addition, enhanced subtropical ridging remains a factor across the lower latitudes later next week. While the GEFS is relatively weaker with this potential, the ECMWF places a secondary 594 dm height center over the eastern Gulf of America. This translates to height anomalies that are greater than 3 standard deviations above normal, supportive of an increased heat risk over the eastern Gulf of America during the period. Over time, diverging mid-level height forecasts from GEFS and ECMWF result in increasingly varied temperature solutions. The GEFS favors a more stable ridge pattern over the Interior West with deeper troughing developing over the eastern CONUS, whereas the ECMWF reestablishes a height anomaly center over the Upper Midwest and Great Lakes leading to higher odds for above-normal temperatures and possible renewed heat risks over the northeastern CONUS. Based on good agreement among temperature tools among the models early in week-2, a slight risk of extreme heat remains issued extending from the southwestern CONUS northeastward to the Upper Midwest for in proximity to the ridge axis favored. Coverage has been adjusted to include more portions of the Interior West, and is now valid through Jul 10 before the ridging potentially deamplifies as advertised in the ECMWF ensemble. Within the highlighted slight risk area, Probabilistic Extreme Tools (PETs) indicate 10-40% chances of daytime temperatures exceeding the 85th percentile and raw temperature tools show the greatest signals for positive temperature departure from normal exceeding 5 and 10 deg F. With the hottest temperatures favored over the Desert Southwest, a moderate risk of extreme heat was considered based on stronger support in the GEFS PET and increasing heat signals in the NWS probabilistic heat risk tool, however, this risk is less supported in the ECMWF PET which shows less than 20% chances for maximum temperatures exceeding the 85th percentile over the lower Four Corners. The omission of a higher risk designation is also consistent with the National Blend of Models (NBM) which maintain daytime highs below 110, and ECMWF precipitation PET depicting wetter conditions associated with the Southwestern monsoon, where increased cloudiness and precipitation would keep any elevated heat potential at bay early in the period. By day 10 (Jul 10) and beyond, the diverging mid-level height solutions result in anomalous temperature patterns that nearly become out of phase with one another over the mid-latitudes. With the GEFS (ECMWF) PETs focusing the strongest signals for anomalous warmth and potential heat across the western (northeastern) CONUS, there is added uncertainty precluding any additional temperature related hazards being posted in the updated outlook. Tied to the strong subtropical ridging over the Gulf and western Atlantic, a slight risk of extreme heat is also posted over the eastern Gulf coast and Florida Peninsula where both PETs show increased chances for daytime temperatures exceeding the 85th percentile through the middle of week-2. This risk is also supported by the deterministic NBM depicting apparent temperatures above 100 deg F late next week, and very warm sea surface temperatures in the eastern Gulf, with anomalies registering upwards of 1.5 to 2 deg C above normal. The NBM also continues to show a number of locations with very warm nighttime lows approaching and/or breaking records along the Gulf coast through late next week. With more mid-level troughing favored over the eastern U.S. towards the middle of next week, there is growing ensemble support for surface low development potentially affecting parts of the Southeast and Mid-Atlantic. Strengthening low members over the lower eastern Seaboard and just offshore in western Atlantic are also reflected in probabilistic ECMWF and Google AI tropical cyclone development tools. As is often the case with these types of offshore lows, there is high uncertainty as to whether any low that develops will acquire tropical characteristics, but such a realization cannot be ruled out. Regardless, enhanced precipitation is favored to accompany any developing surface low and PETs are beginning to converge on an increased heavy precipitation risk over parts of the Mid-Atlantic and Southeast. Given this, as well as raw tools now favoring 20-40% chances for 3-day amounts exceeding an inch where PETs indicate growing signals in percentile space, a slight risk of heavy precipitation is issued for Jul 8-10. Within the highlighted slight risk area, localized urban flooding is possible. In addition to the aforementioned wet trend evident in the ECMWF PET over the Desert Southwest, the GEFS PET also shows increased chances for 3-day amounts exceeding the 85th percentile, but to a weaker extent. Even with these increased signals in both the PETs since yesterday, raw and calibrated mean precipitation amounts, as well as chances for amounts exceeding a half an inch still remain fairly low over the lower Four Corners, precluding a corresponding precipitation hazard at this time. Localized thunderstorms are still possible and this area will continue to be monitored with ensemble guidance indicating precipitable water increasing during the week-2 period. Surface high pressure off the West Coast along with thermally induced low pressure over the Great Basin and Desert Southwest increase chances for episodes of high winds during week-2. The GEFS and ECMWF PETs continue to indicate at least a 20 percent chance of wind speeds exceeding the 85th climatological percentile. Therefore, a slight risk of high winds remains posted across this region, Jul 8-14. It should be noted that any substantial increase in monsoonal moisture and precipitation will bring cooler temperatures, which is likely to break down the thermal low pressure and weaken this high wind potential during the period. FORECASTER: Nick Novella $$