


Prognostic Meteorological Discussion
Issued by NWS
Issued by NWS
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691 FXUS21 KWNC 251812 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT July 25 2025 SYNOPSIS: Developing mid-level low pressure over eastern North America late next week is expected to bring a welcomed cooldown for many parts of the central and eastern Contiguous U.S. (CONUS) experiencing extreme heat conditions. Potentially stalled frontal activity favored over the lower Eastern Seaboard supports an increased risk for heavy precipitation over the Gulf states and the Southeast. Associated with mid-level high (low) pressure favored over the Great Plains (West Coast), periods of elevated winds are possible over the western CONUS, as well as heavy precipitation over parts of the Great Plains and Mississippi Valley which could trigger localized flooding over parts of the lower Missouri River basin. HAZARDS Moderate risk of heavy precipitation for parts of the Southeast and lower Mid-Atlantic, Sat-Sun, Aug 2-3. Slight risk of heavy precipitation for parts of the Lower Mississippi Valley, Southeast, and Mid-Atlantic, Sat-Tue, Aug 2-5. Slight risk of heavy precipitation across parts of the Great Plains and Mississippi Valley, Sat-Sun, Aug 2-3. Slight risk of high winds for many parts of the western CONUS, Sat-Mon, Aug 2-4. Flooding possible over the lower Missouri River basin. DETAILED SUMMARY FOR MONDAY JULY 28 - FRIDAY AUGUST 01: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR SATURDAY AUGUST 02 - FRIDAY AUGUST 08: The week-2 hazards perspective remains on track, as dynamical models continue to favor an anomalous ridge center over central Canada, with a pair of mean troughs over eastern North America and over the northeastern Pacific heading into the first weekend of August. Over the past few days, the overall mid-level height pattern has trended negatively in anomaly space across the CONUS, which has resulted in a weaker and zonally narrow ridge axis across the central U.S, with broader mean troughing across the eastern U.S through the middle of the period. This latter mid-level feature looks to remain responsible for a welcomed cooldown to the extreme heat conditions favored during week-1, and likely keep any renewed heat risks at bay east mainly east of the Rockies in the outlook. Much of the cooling is expected to be underway leading into week-2 associated with a large frontal boundary extending from the Southern Plains into the western Atlantic on day 7 (Aug 1). By day 8, Probabilistic Extremes Tools (PETs) indicate weak chances for any lingering extreme heat, and the corresponding slight risk area is removed in the outlook. Later in the period, ensembles continue to point to the mean ridge retrograding into the Interior West along with a deamplification of the mean trough over the northeastern Pacific. This pattern shift being advertised has been somewhat dubious, given that the models have varied on the strength of the ridge and timing of this evolution in recent runs. Regardless, above-normal temperatures are favored to develop over much of the Interior West, where if any extreme heat conditions were to emerge, the Central California Valley, portions of the Great Basin, and the Desert Southwest would appear most likely based on the raw temperature tools. While PETs show increased chances for maximum temperatures exceeding the 85th percentile, there are only modest chances for actual temperatures exceeding hazard criteria and no associated heat hazards are issued. This potential will continue to be reassessed in upcoming outlooks. Tied to the aforementioned frontal boundary of the eastern CONUS, there continued model support for this feature to slowly advance over the southeastern CONUS, bringing a potentially prolonged period of enhanced precipitation to portions of the lower Eastern Seaboard and into the central and eastern Gulf states. The GEFS PET remains comparably weaker than the ECMWF, but both show 20-30% chances for 3-day amounts exceeding the 85th percentile, with the wettest signals along the coastal Southeast and just offshore in the Atlantic. The uncalibrated ECMWF remains the most robust with the heavy precipitation risk. This tool has slightly backed off of the threat over the coastal Carolinas, but now shows elevated chances (30-50%) of heavy precipitation further south into Georgia and into the Gulf region. Due to this uptick in potential, and continued agreement in regards to the evolution of this surface feature, a moderate risk of heavy precipitation remains issued with its coverage shifted southward, and valid through Aug 3. Even with soils expected to become drier associated with the heat event favored across parts of the southeastern CONUS during week-1, urban flash flooding is still possible with the highlighted moderate risk area. Consistent with recent rainfall events with this synoptic setup, surface low formation also remains possible along a stalled frontal boundary, which could gain tropical characteristics should any development occur offshore and this potential will continue to be monitored in upcoming outlooks. Along the northern periphery of the mean 500-hPa ridge over the central CONUS, episodic shower and thunderstorm activity may bring locally heavy precipitation amounts across the Great Plains and parts of the Mississippi Valley. This potential remains supported in the PETs through early week-2, with good consistency indicating increased chances for amounts exceeding three quarters to an inch across much of the Missouri River Basin. Therefore, a slight risk of heavy precipitation remains issued for the Central and Northern Plains and portions of the western Mississippi Valley, valid through Aug 3 before the mean ridging begins to slide westward. Due to high rainfall surpluses over the past few weeks (several areas have registered more than two to three times their normal rainfall accumulation over the past 14 days), as well as potentially heavy rainfall forecast during week-1 across the southern periphery of the slight risk area, a flooding possible hazard is added to the outlook over the lower Missouri River Basin for week-2. Upstream, enhanced onshore flow tied to a 500-hPa trough near the West Coast is anticipated to bring above-normal precipitation into much of the northwestern CONUS. Although there are elevated probabilities for 3-day amounts exceeding the 85th percentile in the PETs, actual totals are expected to remain below hazard thresholds. Periods of elevated winds are however, a concern at or near the base of the mean troughing aloft, and a slight risk of high winds is posted (Aug 2-4) for much of the western CONUS where PETs maintain increased signals for wind speeds exceeding the 85th percentile. The combination of elevated wind speeds, low humidity and high temperatures increases the risk for wildfire activity across parts of the West. The enhanced mid-tropospheric moisture tied to the mid-level troughing as well as a growing potential for renewed tropical cyclone activity favored in the eastern Pacific is expected to bring increased precipitation amounts into the southwestern CONUS towards the end of July. Based on the WPC week-1 QPF and week-2 precipitation tools that are trending drier, any heavy precipitation risk looks to have timed off into week-1, and the slight risk area for heavy precipitation is discontinued in the outlook over Arizona and New Mexico. No hazards are issued over Alaska. Although amplified troughing is favored over the Gulf of Alaska to promote increased winds and enhanced precipitation amounts over the Southeast, tools indicate amounts remaining below hazard thresholds. FORECASTER: Nick Novella $$