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HOME> Expert Assessments>Hazards Outlook

For 3-7 day hazards see Weather Prediction Center's: WPC 3-7 Day Hazards

U.S. Week-2 Hazards Outlook - Made March 18, 2024 | About the Hazards Outlook

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Type and Period Temperature Precipitation Snow Wind Rapid Onset
Drought
Composite Days 8-14 Map No HazardsNo HazardsNo HazardsNo HazardsNo Hazards
Probabilistic Days 8-14 Map

Composite Map
Experimental Probabilistic Outlooks

Valid Tuesday March 26, 2024 to Monday April 01, 2024

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT March 18 2024

Synopsis: By early next week, a potentially potent low pressure system tracking across the Midwest leads to an increased risk for heavy precipitation across the Mississippi, Tennessee and Ohio Valleys, accumulating heavy snowfall, along with a widespread threat for episodes of high winds for much of the central and eastern U.S. In the wake of the low pressure system, anomalously cold air is favored to dive southeastward renewing the risk of early spring frost and/or freezes for many parts of the southeastern CONUS. Predicted mid-level low pressure returning across the West promotes the risk of high elevation heavy snow over parts of California and Oregon.

Hazards Detailed Summary

For Thursday March 21 - Monday March 25: WPC Days 3-7 U.S. Hazards

For Tuesday March 26 - Monday April 01: Early in week-2, dynamical models are in fair agreement featuring amplified ridging centered over the northeastern Pacific and Alaska, with deep troughing downstream consisting of a broad distribution of negative 500-hPa heights overspreading much of the western and central CONUS. In regards to the ridging upstream, both the GEFS and ECMWF ensembles have trended more towards a more amplified mean solution over the past few days, resulting in stronger northwesterly flow and the potential for anomalous cold air advection over the central CONUS by early next week. Additionally, lee cyclogenesis and a fairly potent low pressure system shifting into the Great Lakes remains favored in the ensembles, which is expected to sustain the increased risk of heavy precipitation across the southeastern CONUS, with the potential for accumulating heavy snowfall on the backside of the tracking low, along with the episodes of high winds.

Tied to the amplified troughing aloft by the outset of week-2, the GEFS, ECMWF and Canadian ensembles have been consistent with the timing and location of increased daily precipitation amounts in the warm sector of the predicted low pressure system. A slight risk of heavy precipitation is issued over portions of the Mississippi, Tennessee and Ohio Valleys and the Southeast, where Probabilistic Extremes Tools (PETs) show at least a 20% chance of 3-day accumulations exceeding the 85th percentile and 1 inch. A moderate risk was considered for issuance based on the ECMWF PET favoring higher chances (>40%) for meeting hazard criteria over parts of the eastern Gulf states, however this is much less supported in the uncalibrated daily guidance and GEFS PET. Localized flooding is also possible across parts of the Gulf states due to above-normal precipitation received during the past two weeks leaving several locations at minor flood stage, and enhanced precipitation favored in the region during week-1. Later in week-2, there is some support in the PETs for the heavy precipitation risk emerging over parts of the coastal Mid-Atlantic and Northeast associated with a secondary surface low developing over the Southeast in the ECMWF, though this is not well represented in the GEFS and Canadian. At the base of the eastward shifting troughing aloft, a slight risk of high winds is also posted over a broad area of the eastern CONUS for Mar 26-28 which is also supported by PETs.

In the wake of the predicted frontal system, the uncalibrated GEFS depicts stronger mean surface high pressure compared to previous runs, with negative temperature departures in the double digits (Deg F) over the Northern Plains and upper Midwest during the first few days of the period. These trends are also reflected in the PETs, which depict elevated chances (40-60%) for minimum temperatures falling below the 15th percentile over the upper Midwest. Despite these strong cold signals, no corresponding hazards are issued over this part of the country, as actual temperatures are not expected to reach hazard criteria (especially with higher sun angles later in March). However, as the troughing aloft shifts eastward with time, so does the anomalously cold air mass, where early spring frost and/or freezes may adversely impact emerging spring vegetation over parts of the Plains, Mississippi, Tennessee and Ohio Valleys and the Southeast. Weaker signals are depicted in the PETs as the cold air mixes southeastward by the middle of next week, but these tools maintain at least a 20% chance for minimum temperatures falling below the 15th percentile and 40 degrees F, supporting a slight risk of much below normal temperatures Mar 27-29. With the anomalous cold in place, accumulating snowfall looks increasingly likely on the backside of the low over north-central CONUS, as well as farther west across portions of the Rockies associated with upslope flow. Based on the uncalibrated ECMWF and the GEFS Snow Water Equivalent (SWE) PET, a slight risk of heavy snow is issued (Mar 26-27) from the Rockies to the Great Lakes and excludes parts of the Northern Plains where drier air is favored.

As much of the anomalous troughing weakens and begins to lift out by the middle of week-2 over the eastern CONUS, both the GEFS and ECMWF ensembles continue to feature additional 500-hPa troughing encroaching the West Coast. While much less amplified in comparison to the troughing downstream, additional shortwave activity is expected to promote the return of above-normal precipitation over the western CONUS, with potentially heavy precipitation over parts of California and the Pacific Northwest. Both the GEFS and ECWMF PETs are in agreement depicting a broad area with increased chances for 3-day amounts exceeding the 85th percentile with, with 30-40% chances over the central West Coast. However, the heaviest totals in the uncalibrated tools and PETs appear limited to the higher elevations of California and Oregon. As a result, no corresponding risk of heavy precipitation is issued, but a slight risk of high elevation snow is posted over these areas for Mar 27-30.

No hazards are issued over Alaska as much of the state is favored to be under the influence of a strong 500-hPa ridge. While this ridge is favored to gradually deamplify later in week-2, much of the Mainland and Southeast are expected to be unseasonably warm through late March. Enhanced wind speeds are possible associated with developing mean low pressure over the Bering Sea and Gulf of Alaska, though wind speeds are not expected to exceed hazard thresholds.

Forecaster: Nick Novella

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

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts