


Prognostic Meteorological Discussion
Issued by NWS
Issued by NWS
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646 FXUS21 KWNC 231812 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT July 23 2025 SYNOPSIS: There are continued model indications for developing mid-level low pressure over eastern North America, supporting cooler temperatures and lowering the risk for extreme heat across many parts of the central and eastern Contiguous U.S. (CONUS). Potentially stalled frontal activity favored over the southeastern CONUS supports an increased risk for heavy precipitation over the Gulf states and into the mid-Atlantic. 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 lower Four Corners and Great Plains. HAZARDS Slight risk of extreme heat for parts of the Great Plains, Mississippi, Tennessee and Ohio Valleys, Southeast, and the lower Mid-Atlantic, Thu-Fri, Jul 31-Aug 1. Slight risk of heavy precipitation for parts of the Lower Mississippi Valley, Southeast, and Mid-Atlantic, Fri-Mon, Aug 1-4. Slight risk of heavy precipitation across many parts of the Great Plains and Mississippi Valley, Thu-Mon, Jul 31-Aug 4. Slight risk of heavy precipitation for parts of the Desert Southwest, Thu-Mon, Jul 31-Aug 4. Slight risk of high winds for many parts of the western CONUS, Thu-Mon, Jul 31-Aug 4. DETAILED SUMMARY FOR SATURDAY JULY 26 - WEDNESDAY JULY 30: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR THURSDAY JULY 31 - WEDNESDAY AUGUST 06: Over the past few days, dynamical models continue to advertise a strengthening 500-hPa anomalous ridge center over central Canada, with more amplified troughing downstream over southeastern Canada and into the northeastern CONUS. The prevailing northwesterly flow tied to this trending mid-level pattern is expected to bring cooler summertime temperatures, and likely keep any widespread extreme heat risks at bay over many parts of the central and eastern CONUS later next week and into the first weekend of August. One exception remains the southcentral and southeastern CONUS where both raw and calibrated temperature tools maintain elevated odds for above normal temperatures early in the period. However, the latest ECMWF and GEFS Probabilistic Extremes Tools (PETs) differ on the location of greatest heat signals, with the former (latter) favoring a more easterly (westerly) solution across the southern tier. Given uncertainty associated with the extent of the mean surface high pressure behind an advancing frontal boundary over this part of the country, a moderate risk of extreme heat is discontinued in the updated outlook. However, a slight risk remains posted and valid through Aug 1 where PETs show at least 20% chances for daytime temperatures exceeding the 85th percentile, as temperatures could be slow to moderate. Later in the period, there is model support in the ensembles for anomalous ridging redeveloping across the Interior West. The GEFS indicates a modest warming response in its PET, though the ECMWF remains largely free of any heat signals beyond day 10 (Aug 2) throughout the CONUS. As a result, no additional temperature hazards are included in the outlook, but the potential for renewed heat will continue to be monitored this week. Tied to the aforementioned frontal boundary, raw model guidance suggests that this surface feature may stall over the southeastern CONUS and bring repeated chances for heavy precipitation along for the Gulf States and into the Mid-Atlantic through the middle of week-2. The PETs are in fair agreement with this potential, indicating increased chances for 3-day amounts exceeding the 85th percentile with the highest amounts focused along the coastal Carolinas, Delmarva region and just offshore. Notably, the uncalibrated ECMWF shows >40% chances for amounts exceeding an inch, supportive of a moderate risk designation for heavy precipitation. However, in deference to the drier GEFS, a slight risk remains issued (Aug 1-4) and is expanded westward to include the central and eastern Gulf states in the outlook. Consistent with recent rainfall events with this synoptic setup, additional surface low formation remains possible along a stalled frontal boundary, which could gain tropical characteristics should any development occur offshore. Probabilistic tropical cyclone genesis tools are weak with this realization, but this potential will continue to be monitored. 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 the middle of week-2, with model consistency indicating higher chances for amounts exceeding an inch into the Central Plains. Therefore, a slight risk of heavy precipitation remains issued and is expanded southward to include more of the lower Missouri River basin in the outlook. Upstream across the West, there is better model support for enhanced onshore flow with mid-tropspheric moisture overspreading the western CONUS associated with deeper troughing extending from the eastern Pacific into the West Coast. This is well reflected in the PETs, which indicate 20-60% chances for 3-day amounts exceeding the 85th percentile across portions of the Northern Intermountain, Rockies, and Great Basin, but amounts are not expected to exceed hazard criteria. 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 (Jul 31 to Aug 4) for much of the western CONUS where PETs show 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. Over the southwestern CONUS, the combination of deeper troughing in the West, as well as a renewed potential for tropical cyclone activity favored in the eastern Pacific, supports increased chances for above-normal and possibly heavy precipitation in the lower Four Corners. While the GEFS is comparably drier than the ECMWF, a slight risk of heavy precipitation is issued over parts of Arizona and New Mexico (Jul -31-Aug 4) based on a wet trend in the tools, increased chances for 3-day amounts exceeding the 85th percentile, along with higher chances for elevated dewpoint temperatures in the Desert Southwest. 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 $$