Composite Map Day 8-14

Experimental Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards Snow Hazards

Valid Wednesday April 30, 2025 to Tuesday May 06, 2025

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT April 22 2025

Synopsis: At the outset of week-2 surface low pressure is forecast to be departing across the Great Lakes and southeastern Canada, with a trailing cold front extending across the central and east-central contiguous U.S. (CONUS). This favors enhanced chances of heavy precipitation and thunderstorms continuing into the early part of week-2 across the Central and Southern Plains and Middle and Lower Mississippi, Tennessee, and Ohio Valleys. Broad mid-level high pressure is forecast to develop across the CONUS later in week-2, favoring increased chances for above-normal temperatures over many areas.

Hazards

• Slight risk of heavy precipitation for portions of the Central and Southern Plains and the Middle and Lower Mississippi, Tennessee, and Ohio Valleys, Wed, Apr 30.
• Possible flooding for the Lower Mississippi River.

Detailed Summary

For Friday April 25 - Tuesday April 29: WPC Days 3-7 U.S. Hazards

For Wednesday April 30 - Tuesday May 06: Late in week-1, surface low pressure is forecast to track across the Northern Plains and Upper Midwest. As this system departs, a trailing cold front is predicted to remain across parts of the Great Plains and Mississippi Valley early in week-2 serving as a focus for continued increased chances of heavy precipitation and thunderstorms. The uncalibrated 0z ECENS continues to depict a swath of heavy precipitation stretching from northeastern Texas into the Tennessee Valley on day-8 (Apr 30), with the 0z GEFS also showing a wetter solution over these areas compared to yesterday. The ECENS and GEFS Probabilistic Extremes Tools (PETs) depict these areas having at least a 20 percent chance precipitation totals exceed the 85th climatological percentile and 1-inch. As a result, a slight risk of heavy precipitation is posted across portions of the Central and Southern Plains and the Middle and Lower Mississippi, Tennessee, and Ohio Valleys, Apr 30. Thereafter, enhanced precipitation chances are forecast to shift into Texas and along the Gulf Coast. However, daily precipitation totals are generally low in the GEFS and ECENS ensembles (less than 0.5 inches), and the isolated, convective nature of the precipitation precludes extending the hazard.

The convective and sporadic nature of the precipitation during week-2 leads to less confidence in determining exact areas most at risk of additional flooding, although localized flooding is a concern over portions of the Central and Southern Plains that do receive heavy rainfall. A possible flooding hazard remains posted across the Lower Mississippi River given the potential for new and renewed rises in water levels during week-2 tied to any additional rainfall over the region as well as runoff from rainfall upstream. Main channels are already very high, and thus are unlikely to have large responses to additional precipitation. Regardless, tributaries and streams will continue to be susceptible to renewed flooding or flash flooding if additional rainfall occurs.

As the aforementioned surface low and associated mid-level trough exit the region early in week-2, there is some potential for elevated wind speeds across the northern CONUS. However, the signal in the PETs has diminished compared to yesterday, with much of the enhanced threat over the Northern Plains timing off. Probabilities in the GEFS and ECENS uncalibrated guidance for wind speeds exceeding 20-mph are generally weak (less than 20 percent) and confined to the Great Lakes and adjacent areas on day-8 (Apr 30). As a result, a slight risk for high winds is no longer indicated, but some higher wind gusts still cannot be ruled out, particularly across the Great Lakes in the wake of the frontal passage.

Anomalous ridging is forecast across the eastern CONUS at the beginning of the period. This favors a period of unseasonably warm temperatures over much of the East during the first half of week-2, with models trending warmer across the region compared to yesterday. The ECENS PET depicts parts of the Mid-Atlantic and Northeast having at least a 40 percent chance maximum temperatures exceed the 95th climatological percentile on day-8 (Apr 30), with daily records a possibility based on the National Blend of Models (NBM). This translates into actual temperatures potentially well into the 80s deg F over parts of the Mid-Atlantic, with relatively cooler temperatures (70s deg F) favored across the Northeast and Ohio Valley. While these temperatures are noteworthy by late-April and early-May standards, and for some areas could be the warmest temperatures of the year thus far, no heat related hazards are issued due to the time of year and lack of adverse impacts. A general trend toward more broad ridging and a pattern typical of late-Spring is forecast to emerge over much of the CONUS later in week-2.

Troughing forecast across Alaska favors increased chances for above-normal precipitation over the southeastern part of the state, with actual precipitation amounts not expected to reach hazards thresholds. Below-normal temperatures forecast over many areas favor a delay in seasonal river ice breakup. However, as temperatures continue to warm, the eventual river ice breakup may lead to ice jams and associated flooding in the coming weeks.

Forecaster: Thomas Collow

$$ Please consult local NWS Forecast Offices for short range forecasts and region-specific information.

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts