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Composite Map Day 8-14

Experimental Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards Snow Hazards

Valid Saturday February 11, 2023 to Friday February 17, 2023

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST February 03 2023

Synopsis: Mid-level low pressure with one or more surface storm systems could bring below (above)-normal temperatures (precipitation) to much of the West, with heavy precipitation possible across central and southern California, and heavy snowfall possible in the Sierra Nevada and some higher elevations in the Great Basin and Four Corners region. It should be noted that while surplus precipitation is anticipated in much of California, an extreme event like the ones seen earlier this winter appears unlikely at this time. Meanwhile, the storm systems have the potential to generate high winds at times over much of the central and western Contiguous United States (CONUS). To the east, one or more storm systems ejecting out of the Southwest and through the Great Lakes region could drop heavy snow on portions of the Upper Midwest and heavy rains across parts of the Southeast and the Mississippi, Ohio, and Tennessee Valleys.

Hazards

• Slight risk of heavy precipitation for parts of the Lower Mississippi, Ohio, and Tennessee Valleys and the Southeast, Mon-Fri, Feb 13-17.
• Slight risk of heavy precipitation for portions of California and adjacent Nevada, Sat-Wed, Feb 11-15.
• Slight risk of high winds for parts western CONUS and the central Plains, Sat-Fri, Feb 11-17.
• Slight risk of heavy snow for the higher elevations of the Sierra Nevada in California, Sat-Fri, Feb 11-17.
• Slight risk of heavy snow for parts of the higher elevations in the Four Corners and Great Basin, Sun-Thu, Feb 12-16.
• Slight risk of heavy snow in the Upper Midwest, Tue-Fri, Feb 14-17.

Detailed Summary

For Monday February 06 - Friday February 10: WPC Days 3-7 U.S. Hazards

For Saturday February 11 - Friday February 17: Tools are in better agreement than yesterday on the evolution of the mid-level pattern through week-2 as all ensemble means settle into a pattern featuring a strong anomalous ridge in the central North Pacific, a mid-level trough with its axis in the western CONUS, and another 500-hPa ridge over the eastern CONUS. The main area of disagreement is in eastern Canada. The European ensemble mean keeps above-normal 500-hPa heights in this region while the Canadian ensemble mean shows near- to below-normal heights in the region, especially toward the Davis Strait. The GEFS is a compromise of the other two ensemble means. This could impact temperatures in the eastern CONUS later week-2. If temperatures are high enough, snowmelt and ice jam flooding is possible across parts of New England, but confidence is not sufficient to post a hazard at this time. In any case, this pattern favors generally unsettled weather in much of the West through at least the middle of week-2, and a potential storm track from the southern High Plains through the Great Lakes could trigger hazards for wind, rain, and snow over parts of the interior CONUS.

Timing is uncertain, but for the middle and later part of week-2, the mid-level trough has the potential to trigger several hazards, particularly in central and southern sections of the western CONUS. Heavy precipitation is possible over central and southern California and adjacent Nevada, although an extreme event like those experienced earlier this winter seems unlikely at this time. With continued support in the reforecast tools, a slight risk of heavy precipitation remains posted for California for Feb 11-15, as well as a slight risk of heavy snow for the higher elevations of the State Feb 11-17. The same features bring a slight risk of heavy snow to the higher elevations of the Great Basin and western Four Corners Region for most of week-2 (Feb 12-16), and any individual surface impulses has the potential to bring high winds to parts of the central Plains and western CONUS. Therefore, a slight risk of high winds remains posted for this part of the country for the entirety of week-2 to capture the uncertainty in the timing of individual storm systems in the Southwest and their ejection northeastward across the central CONUS during the period.

After early week-2, most tools take a high surface pressure center from the eastern CONUS into the western North Atlantic. The resulting southerly surface winds to the west of the high pressure are expected to pull moist air from the Gulf of Mexico into much of the southeastern CONUS. Models are in better agreement today indicating this may be enhanced by a surface low pressure center or two tracking from southwestern Plains through the Great Lakes region during mid to late week-2. Regardless, the flow of moist, mild air over a weak surface front draped across the southeastern CONUS to the south of the storm track increases the chances for heavy precipitation from the lower Mississippi Valley across the interior Southeast and southern Appalachians. The GEFS and Canadian ensemble means drop about twice as much precipitation there as the European ensemble mean, although totals in the two wetter model means were slightly lower than yesterday, in the 1.5 to 2.0 inch range from central Mississippi through northern Georgia and the Tennessee Valley. The GEFS and European ensemble reforecast tools are more robust than yesterday with the chances for precipitation exceeding the 85th percentile over the lower Mississippi Valley and Southeast, but still appear lower than indicated by the raw ensemble mean precipitation outputs. But the anticipated southerly flow and the agreement on heavier precipitation in the Canadian ensemble mean prompts the slight chance for heavy precipitation later in week-2 (Feb 13-17). This is consistent with the slightly cyclonic mid-level flow expected from the trough centered farther to the west. Confidence is tempered by the inconsistency on the precipitation intensity among the tools, but there is somewhat better agreement than yesterday.

The increased potential for one or more storms tracking from the Southwest through the Great Lakes Region increases the risk for heavy snow to the north of the storm track through the Upper Midwest during the middle and later part of week-2, and for high winds farther west in the wake of these storms. The reforecast GEFS snow water equivalent tools and the raw precipitation output from many of the tools increases confidence in this development, but the uncertainty in the strength and timing of the storms tracking through the region tempers confidence somewhat for any particular location and time, and a slight risk of heavy snow is posted for Feb 14-17. .

Over Alaska, a strong storm system west of the Mainland early week-2 could produce heavy precipitation and high winds along parts of the southern tier near the Pacific Coast before the low pressure weakens, reducing the pressure gradient and therefore the high winds and moist Pacific inflow as well by the middle of week-2.

Forecaster: Rich Tinker

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

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts