Valid Thursday, February 28, 2019 to Monday, March 11, 2019

Summary of Forecasts and Hazards

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT April 01 2025

Synopsis: Mid-level low pressure is favored over eastern Canada and the U.S, with surface high pressure overspreading much of the central and eastern CONUS early in week-2. While this is expected to bring a period of welcomed dryness for areas affected by heavy precipitation in week-1, the synoptic setup favors elevated chances for much below normal temperatures which may adversely impact emerging springtime vegetation following a very warm March for much of the southeastern CONUS. Upstream, mean mid-level high pressure forecast is expected to keep much of the western CONUS free of weather related hazards, with any enhanced onshore flow limited to the higher elevations of western North America.

Hazards

• Moderate risk of much below normal temperatures for portions of the Southern Plains, Lower and Middle Mississippi, Tennessee, and Ohio Valleys, Appalachians, Mid-Atlantic, and Southeast, Wed, Apr 9.
• Slight risk of much below normal temperatures for much of central and eastern CONUS, Wed-Thu, Apr 9-10.
• Slight risk of high winds for the northeastern CONUS, Wed, Apr 9.

Detailed Summary

For Friday April 04 - Tuesday April 08: WPC Days 3-7 U.S. Hazards

For Wednesday April 09 - Tuesday April 15: There continues to be good consistency in the dynamical models advertising a large-scale pattern change, with amplified mean ridging (troughing) becoming established over western (eastern) North America by early next week. Tied to this latter mid-level feature, both the GEFS and ECWMF ensembles show the mean surface high pressure center shifting over the Tennessee Valley and the Appalachians behind a departing low pressure system over the Canadian Maritimes. Although the troughing is favored to deamplify by the middle of next week, a slight risk of high winds remains posted for portions of the Great Lakes, Ohio Valley, Mid-Atlantic and Northeast for Apr 9 based on lingering signals in the Probabilistic Extreme Tools (PETs). Any residual moisture being wrapped in the deepening low may lead to accumulating snowfall over parts of the Northeast and Appalachians, though models are unsupportive of any amounts exceeding heavy snow thresholds.

Accompanying the mean surface high pressure, the GEFS and ECMWF ensembles continue to show elevated chances (>50%) for negative double digit temperatures departures, with the strongest cold signals over the southeastern CONUS, with moderating temperatures upstream over parts of the Great Plains and Mississippi Valley by the outset of the period. This is well reflected in the GEFS and ECMWF PETs, depicting >30% chances for minimum temperatures falling below the 10th percentile and below 40 degrees F on day 8 (Apr 9). While these temperatures are well outside wintertime hazard criteria, such temperatures could be quite a shock following a very warm March in the lee of the Rockies, and potentially bring adverse impacts to emerging springtime vegetation across many parts of the southeastern CONUS. Therefore, a moderate risk of much below temperatures remains issued for Apr 9, with much of its coverage mainly confined to areas east of the Mississippi. A broader slight risk area of much below normal temperatures remains posted and valid through Apr 10 based on residual cold signals in the PETs with the mean surface high weakening and shifting offshore.

Later in week-2, ensembles continue to feature a reloading mean trough by days 10 and 11, implying a renewed hazardous cold risk for the eastern CONUS. In addition, there is increased support in guidance favoring surface low formation along the lower Eastern Seaboard at this lead. However, both raw and calibrated tools are not yet supportive to include any additional temperature and/or precipitation related hazards, but this potential will continue to be monitored in upcoming outlooks.

With the development of strong mid-level ridging favored over the western CONUS, unseasonably warmer and drier conditions are forecast compared to week-1, resulting in no weather related hazards for the western CONUS for week-2. Any enhanced onshore flow to promote above-normal and possibly heavy precipitation would most likely be limited to the higher latitudes of North America over extending from the upper Pacific Northwest to the southern Alaska Mainland. This is reflected in the PETs which depict increased chances for 3-day precipitation amounts exceeding the 85th percentile. However, actual totals do not presently meet hazard criteria, as heavy precipitation potential remains tenuous due to the favored weakening of mid-level troughing over the northeastern Pacific during week-2.

Forecaster: Nick Novella

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