848 FXUS21 KWNC 251811 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT April 25 2026 SYNOPSIS: Early in week-2, a strong surface high pressure system and accompanying anomalously cold air is expected to settle into the central and eastern contiguous United States (CONUS). Much below normal temperatures with freezing and near freezing conditions are possible in some areas, potentially damaging early spring blooms. Later in week-2, redeveloping mid-level low pressure over the northeastern CONUS may bring the return of unseasonable cold air to portions of the Midwest, along with heavy precipitation across portions of the Plains and Mississippi Valley, but there is too much uncertainty to post any additional hazards at this time. HAZARDS Moderate risk of much below normal temperatures for portions of the Ohio Valley, Great Lakes, Appalachians, Mid-Atlantic, and Northeast, Sun, May 3. Slight risk of much below normal temperatures from portions of the eastern Great Plains, Mississippi, Tennessee and Ohio Valleys, Appalachians, northern areas of the Southeast, Mid-Atlantic and Northeast, Sun-Mon, May 3-4. Slight risk of high winds for much of the eastern U.S., Sun-Mon, May 3-4. DETAILED SUMMARY FOR TUESDAY APRIL 28 - SATURDAY MAY 02: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR SUNDAY MAY 03 - SATURDAY MAY 09: Dynamical model ensemble mean 500-hPa height forecasts from the GEFS and ECMWF remain consistent in favoring amplified troughing over the northeastern CONUS next weekend, where the pairing with a strong anomalous ridge center to the south of Greenland is consistent with a negative North American Oscillation (-NAO) pattern supportive for the advection of anomalous cold air into many parts of the central and eastern CONUS. A -NAO circulation is predominantly favored over eastern North America as the period progresses, and the latest ensemble means are beginning to show signs of a redeveloping mean trough towards the middle of week-2. Based on continued model differences in the height pattern upstream, it is unclear whether the dynamical forcing contributing to this redevelopment is southern or northern stream based, as the ECMWF (GEFS) continues to favor more ridging (troughing) across the western CONUS. But regardless, any reamplification of the troughing is expected to keep below normal temperatures entrenched over the eastern U.S. through early May, where periods of freezing and near freezing temperatures look to possibly threaten vulnerable springtime vegetation, particularly in areas that have experienced early growth due to antecedent warmth during April. In the wake of a large frontal boundary extending from northern Mexico to the western Atlantic late in week-1, guidance continues to feature a mean high pressure system settling over much of the Midwest. Ensembles maintain an eastward progression of the mean surface high center into the Ohio Valley by the start of week-2, with little change to its strength since yesterday. Though, both raw and calibrated temperatures tools have trended slightly colder, which is likely tied to a deeper surface low favored offshore in the Atlantic injecting a stronger northerly wind component into the northeastern CONUS. Both the uncalibrated GEFS and ECMWF now favor >60% chances for negative double digit temperature departures from the Ohio Valley to the Northeast, with Probabilistic Extreme Tools depicting 40-50% chances for minimum temperatures falling below the 15th climatological percentile focused over the southeastern quarter of the CONUS. While freezing temperatures are mostly likely to be confined to the north, there continues to be increased chances in tools for minimum temperatures falling below 38 F into the northern portions of the Lower Mississippi and Tennessee Valleys, and lower Mid-Atlantic to potentially impact spring vegetation. Spring leaf index anomalies from the National Phenology Network show a very early (10-20 days) emergence of growth focused over parts of the Central Plains, Middle and Upper Mississippi and Ohio Valleys, and Great Lakes. As a result, a moderate risk of much below normal temperature remains posted for May 3, with its spatial coverage shifted eastward to approximately the I-95 corridor where there are increased signals for low temperatures dipping below 38 deg F since yesterday. While the GEFS supports an extension of this moderate cold risk an additional day, the ECMWF is quick to moderate temperatures with the surface high weakening. Therefore, a slight risk of much below normal temperatures remains posted where PETs show at least 20% chances of minimum temperatures falling below the 15th percentile and below 40 deg F, and remains valid through May 4. The slight risk coverage is also adjusted to remove portions of the Upper Midwest where a moderation of temperatures are expected early in week-2, at least temporarily. In addition, a slight risk of high wind is issued (May 3-4) for much of the eastern U.S. associated with the strengthening mean pressure gradient between the aforementioned surface high and the deepening low offshore. The slight risk area for high winds is supported by stronger troughing favored aloft, as well as increased wind signals in the PETs and the potential for strong gusts in the uncalibrated tools. Later in week-2, temperature tools indicate a return of negative temperature departures over the Midwest associated with redeveloping troughing aloft. The potential renewal of a much below normal temperature risk is best supported in the ECMWF, favoring more northern stream shortwave energy to promote a southward expansion of cold signals from Canada, with increased chances of minimum temperatures falling below the 15th percentile over the Great Plains and Mississippi Valley in the PET by days 10-12 (May 5-7). By contrast, the GEFS is comparatively much more muted with this potential, precluding the issuance of any additional temperature hazards. However, given the favored persistence of a -NAO circulation, the renewed cold potential will continue to be closely monitored in the upcoming hazard outlooks. Tied to the troughing aloft by the middle of the period, both the GEFS and ECMWF show the return of increased precipitation amounts mainly over the southern tier of the U.S. in response to more return flow from the Gulf becoming established. There is some support in the raw tools for 3-day amounts exceeding an inch to suggest some of this precipitation may be heavy. However, the GEFS PET is absent of any heavy precipitation threat, and ensembles generally disagree in regards to a discernible surface forcing feature at this lead resulting in no corresponding precipitation hazards at this time. Over Alaska, models continue to favor mid-level troughing over the Bering Strait with ridging over the Mainland. An associated mean surface low centered over the Aleutians is expected to bring potentially strong winds and stormy conditions along the southern tier of the state early in week-2 before the pattern aloft deamplifies. At this time, conditions are expected to remain below hazard thresholds, and no corresponding wind or precipitation shapes are posted. Additionally, the typical peak of the river ice breakup season is approaching, and ice jam flooding can occur this time of year with little or no notice as conditions on frozen rivers can change quickly. Please check with the Alaska Pacific River Forecast Center for the latest conditions and advisories. FORECASTER: Nick Novella $$