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Composite Map Day 8-14

Experimental Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards Snow Hazards

Valid Friday February 03, 2023 to Thursday February 09, 2023

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST January 26 2023

Synopsis: Surface high pressure, with anomalously cold temperatures, is likely to shift eastward from the Great Plains and Midwest to the Northeast late next week. Enhanced onshore flow increases the risks of heavy precipitation, heavy snow, and high winds across the Pacific Northwest, northern California, and the northern to central Rockies from February 3 to 6. Later in week-2, a more zonal flow pattern is expected across the mid-latitudes which leads to higher forecast uncertainty.

Hazards

• Moderate risk of much below-normal temperatures for the Upper Mississippi Valley and Great Lakes, Fri, Feb 3.
• Slight risk of much below-normal temperatures for the Great Plains and Midwest, Fri-Sat, Feb 3-4.
• Moderate risk of much below-normal temperatures for parts of the Northeast, Fri-Sat, Feb 3-4.
• Slight risk of much below-normal temperatures for the Northeast and Mid-Atlantic, Fri-Sun, Feb 3-5.
• Slight risk of heavy precipitation for portions of California, Oregon, and Washington, Fri-Mon, Feb 3-6.
• Slight risk of heavy snow for northern Coastal Range, Cascade Range, Sierra Nevada Mountains, and Northern Rockies, Fri-Mon, Feb 3-6.
• Slight risk of high winds for portions of California, Oregon, and Washington, Fri-Mon, Feb 3-6.

Detailed Summary

For Sunday January 29 - Thursday February 02: WPC Days 3-7 U.S. Hazards

For Friday February 03 - Thursday February 09: The Arctic air outbreak across the Great Plains and Midwest is likely to peak prior to week-2, on Feb 1 and 2. However, the GEFS and ECMWF reforecast tools support a continuation of a slight (20%) and moderate (40%) risk of much-below normal temperatures (minimum temperatures reaching the lowest 15th percentile) for these areas through the beginning of week-2. As 500-hPa heights increase and the core of the Arctic air shifts northeastward beyond that time, moderating temperatures are forecast across the central U.S. by Feb 5.

A short-lived and transient outbreak of Arctic air is forecast for the Northeast early in week-2 with a deep anomalous 500-hPa trough rotating through southeastern Canada. On Feb 3 and 4, a moderate risk of much below-normal temperatures is posted for northern New York and New England where the reforecast tools depict minimum temperatures having a 40 percent chance of falling below the 15th percentile. Uncalibrated model solutions feature minimum temperatures below -10 degrees F in the outlined area for a moderate risk. A broader slight risk of much below-normal temperatures extends south to the Mid-Atlantic through Feb 4. Due to large model differences on how far south the anomalous cold spreads, the Southeast is not included in the slight risk.

Recent deterministic model runs, such as the ECMWF (0Z/Jan 26), have shown a wave of low pressure developing across the lower Mississippi Valley late next week with an eastward track to the Mid-Atlantic. This could occur with a shortwave trough separating from the full-latitude trough over the east-central CONUS. If this were to happen, accumulating snow may affect the central Appalachians and Mid-Atlantic. However, forecast confidence is low due to the lack of good model agreement/consistency and this type of winter weather event is difficult to predict at the week-2 time scale.

The GFS and ECMWF ensemble means remain consistent that a shortwave trough progresses eastward from the northeastern Pacific to the Pacific Northwest and northern Rockies early in week-2. This shortwave trough, reforecast tools, and uncalibrated model output support a slight risk of heavy precipitation and snow across the Pacific Northwest, northern California, and the northern Rockies from Feb 3-6. The integrated vapor transport tool for the GEFS and ECMWF ensemble indicate the most likely area for heavy precipitation to be from 40-45N along the West Coast. The enhanced onshore flow, associated with the shortwave trough, also results in a slight risk of high winds for the Pacific Northwest and northern California. Although model spread increases by the second week of February, the consensus is for the storm track to shift northward with the ECMWF and Canadian ensemble means predicting the development of a mean 500-hPa ridge near the West Coast.

The GEFS and ECMWF ensemble means are in poor agreement with the longwave pattern over Alaska. The GEFS is most bullish with anomalous cold, while the ECMWF reforecast tool favors near to above-normal temperatures during week-2. Therefore, no temperature hazards are posted. Above-normal precipitation is slightly favored for the Alaska Panhandle, but hazardous precipitation is unlikely.

Forecaster: Brad Pugh

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

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts