043 FXUS21 KWNC 151812 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT April 15 2026 SYNOPSIS: Mid-level low pressure forecast over the western contiguous U.S. (CONUS) and associated lee cyclogenesis supports the potential for episodes of high winds, high elevation heavy snow, along with an elevated risk of heavy precipitation focused over the Lower and Middle Mississippi Valley early in week-2. The favored eastward expansion of the heavy precipitation risk is expected to provide relief for many moisture starved portions of the Southeast. Over the upper Midwest, flooding is possible associated with persistent near to above-normal precipitation accelerating spring snowmelt over the next two weeks. HAZARDS Moderate risk of heavy precipitation for portions of the Southern Plains, Middle and Lower Mississippi, Tennessee and Ohio Valleys, Thu-Fri, Apr 23-24. Slight risk of heavy precipitation for portions of the eastern Great Plains, Mississippi, Tennessee, and Ohio Valleys, Appalachians, and Southeast, Thu-Sun, Apr 23-26. Slight risk of heavy snow for the Central Rockies, Thu-Sat, Apr 23-25. Slight risk of high winds for parts of the Great Basin, Southwest, Rockies, Great Plains, and Mississippi Valley, Thu-Sat, Apr 23-25. Possible flooding for parts of the Great Lakes region and Upper and Middle Mississippi Valley. DETAILED SUMMARY FOR SATURDAY APRIL 18 - WEDNESDAY APRIL 22: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR THURSDAY APRIL 23 - WEDNESDAY APRIL 29: During week-2, dynamical models continue to feature a transient 500-hPa height pattern, with the period starting off with anomalous troughing favored across the southwestern CONUS and a deamplifying ridge mainly east of the Mississippi. Over the past few days, both the GEFS and ECMWF ensembles depict a more amplified and deeper mean solution of this former mid-level feature by later next week, where associated surface low development in the lee of the Rockies, combined with ample return flow from the Gulf, is anticipated to bring a period of unsettled weather for much of the central third of the CONUS. Meanwhile, ensembles continue to favor the development of an amplified ridge centered near the Davis Strait consistent with a transition towards a negative North Atlantic Oscillation (-NAO) circulation. This pattern shift may be in response to a high amplitude Madden-Julian Oscillation (MJO) unfolding in the tropical western Pacific. With the potential for higher latitude blocking becoming established across Canada, ensemble guidance is increasingly favoring more negative height departures overspreading much of the CONUS, and feature a pair of mean negative height anomaly centers over the southwestern and northeastern CONUS later in week-2. As a result, this is anticipated to promote a predominantly cooler pattern for many parts of the CONUS towards late April. Tied to the stronger mid-level troughing over the southwestern CONUS early in week-2, both the GEFS and ECMWF ensembles continue to feature surface low development over western Nebraska and western Kansas, with a deeper mean low (now sub 1000-hPa) compared to yesterday. With ample lower-level moisture advection ahead of the mean low, the highest precipitation amounts remain primarily favored over the Lower and Middle Mississippi Valley. A moderate risk of heavy precipitation remains posted for this part of the country for Apr 23-24 and is slightly expanded where the uncalibrated GEFS and ECMWF show at least 40% chances of 3-day amounts exceeding one inch early in week-2. Similar to previous guidance, the ECMWF continues to depict a more southeasterly extension of the heavy precipitation potential into the Southeast which is likely due to a faster erosion of the ridging aloft compared to the GEFS early in week-2. While this does add to uncertainty in the outlook, the uncalibrated GEFS does show an uptick in the heavy precipitation signals over the Southeast a bit later in the period, and therefore the enveloping slight risk area of heavy precipitation is again expanded eastward to cover more of Mississippi, Alabama, and Georgia in the updated outlook, and valid through Apr 26. The adjusted slight risk coverage is also consistent with both the GEFS and ECMWF Probabilistic Extreme Tools (PETs) which indicate at least 20% chances for 3-day amounts exceeding the 85th percentile through the middle of week-2. Within the highlighted heavy precipitation risk areas, there is a threat of thunderstorm activity, where deterministic solutions show dewpoints reaching the upper 60s and lower 70s (deg F). Given this expanded heavy precipitation risk into the Southeast, the Rapid Onset Drought (ROD) risk is removed in the updated outlook. Despite week-1 remaining very dry and warm, there is growing support in the predicted 14-day precipitation anomalies flipping sign over the Southeast due to this heavy precipitation risk, as any enhanced precipitation is expected to mitigate antecedent dryness in the region. Upstream of the mean surface low, there is better model support for accumulating snowfall over the higher elevations of the Central Rockies. Although the uncalibrated GEFS features low probabilities for heavy snow, its calibrated Snow Water Equivalent (SWE) counterpart indicates at least 20% chances for values exceeding the 85th percentile, with the uncalibrated ECMWF depicting at least 20-50% chances for 3-day snowfall amounts exceeding 6 inches. Therefore, a slight risk of heavy snow is posted over the Front Range of Colorado and into the parts of Wyoming. The favored anomalous troughing also supports an increased risk of periods of elevated winds during week-2. A broad slight area of high winds remains issued for the higher elevations of the interior West eastward to the Mississippi Valley (Apr 23-25) where uncalibrated tools show increased chances for wind gusts exceeding 34kts (~40mph) through the middle of the week-2. A corresponding moderate risk area was considered over the Southern Rockies and Southern Plains ahead of the mean trough axis and where higher probabilities of exceedance are indicated in the raw tools, however, PET guidance remains less supportive of this higher risk designation. With above-normal snowpack and above-normal precipitation being registered for much of the Great Lakes, seasonal spring melt has led to saturated soils as well as widespread river flooding, thus any additional water in the river systems will not be easily accommodated. Much of the Great Lakes remains favored for near to above-normal precipitation during the next two weeks, which could result in accelerated snow melt exacerbating the flooding potential. A flooding possible hazard is posted for parts of the Great Lakes region and Upper and Middle Mississippi Valley, where the confluence of these parameters is greatest. However, the threat of flooding is not limited to these areas alone, as lingering snow remains on the ground over portions of the High Plains as well. No hazard is issued for the Red River of the North or other watercourses in the region, although river rises are likely as snow melts and localized flooding may occur. No hazards are issued over Alaska, but flooding can occur this time of year with little or no notice during river ice breakup season. The colder temperatures in the Week-2 Outlook increase the chances of delayed river breakup in Alaska and increase the chances of ice jam flooding. Check the Alaska Pacific River Forecast Center (https://www.weather.gov/aprfc/breakupMap) for the latest conditions or advisories. FORECASTER: Nick Novella $$