Home Site Map News Organization

Search:  

Composite Map Day 8-14

Experimental Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards Snow Hazards

Valid Thursday October 12, 2023 to Wednesday October 18, 2023

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT October 04 2023

Synopsis: Confidence is increasing regarding an active southern stream early in week-2, which favors enhanced precipitation chances across portions of the Southeast, particularly Florida. Today’s models are not depicting as much of a northward component compared to yesterday resulting in relatively lower precipitation amounts inland across the Tennessee Valley, allowing the Rapid Onset Drought (ROD) risk to remain in place. Toward the middle of week-2, interaction with northern stream energy may lead to the development of a surface low pressure system near the Northeast bringing enhanced chances for heavy precipitation up the Eastern Seaboard. While increased precipitation chances are still likely across the Pacific Northwest throughout week-2 due to mid-level low pressure over the Northeast Pacific, daily precipitation totals are not forecast to reach hazards thresholds.

Hazards

• Slight risk of heavy precipitation across portions of the central Gulf of Mexico coast, Florida, the Southeast, and the southern Mid-Atlantic, Thu-Sat, Oct 12-14.
• Slight risk of heavy precipitation across portions of the Mid-Atlantic and Northeast, Fri-Sun, Oct 13-15.
• Slight risk of much below normal temperatures across portions of western Mainland Alaska and the Alaska Peninsula, Thu-Sat, Oct 12-14.
• Rapid Onset Drought (ROD) risk over parts of the Lower Mississippi and Tennessee Valleys, and Southern Appalachians.

Detailed Summary

For Saturday October 07 - Wednesday October 11: WPC Days 3-7 U.S. Hazards

For Thursday October 12 - Wednesday October 18: Today’s dynamical models are depicting a more amplified 500-hPa height pattern during week-2 compared to yesterday, with troughing favored across the eastern CONUS, ridging over the western CONUS, and another trough over the eastern Pacific and Alaska. The trend toward more troughing in the East leads to increasing confidence for heavy precipitation. Additionally an active southern stream is forecast, with moisture from tropical systems in the Eastern Pacific being ejected eastward toward the Gulf of Mexico and Southeast by the start of week-2. By the middle of the period, interaction with the trough over the East may pull some of this moisture northward, with the 0z ECMWF ensemble favoring surface low pressure to develop across the Northeast around Oct 14 bringing a substantial precipitation event to parts of the region. The 0z GEFS is further offshore, and would spare the northeastern U.S. from the heaviest precipitation. The ECMWF and GEFS Probabilistic Extremes Tools (PETs) indicate at least a 20 percent chance 3-day precipitation totals exceed the 85th percentile and 1-inch extending from the Southeast up through parts of the Northeast, with higher probabilities in the ECMWF PET given the higher precipitation amounts forecast, particularly across Florida and the Northeast. Given the uncertainty regarding multiple interacting features, only slight risks of heavy precipitation are posted across the Eastern Seaboard. Further, around the New York Metropolitan area and southern New England heavy precipitation and flooding in the past week along with additional precipitation forecast during week-1 favor a sensitive area for additional precipitation in week-2. Two separate areas are highlighted to address the favored temporal progression. The first is across the Central Gulf of Mexico Coast, Southeast, and southern Mid-Atlantic for Oct 12-14, and the second extends northward through the remainder of the Mid-Atlantic and Northeast for Oct 13-15.

The potential system across the Southeast favors cutting back the Rapid Onset Drought (ROD) risk across the Southeast close to the Gulf of Mexico coast. However, both the ECMWF and GEFS ensembles do not bring much precipitation northward into the Tennessee Valley, instead sliding most of the moisture eastward across the Southeast and Florida, and then potentially up to the Northeast. Therefore, the Tennessee Valley is not forecast to have as much precipitation as points farther south and east, allowing the ROD risk to remain over this region.

Persistent mid-level troughing is forecast over the Northeast Pacific, which favors elevated chances for rounds of precipitation across the Pacific Northwest throughout week-2. The ECMWF PET has backed off its elevated probabilities for 3-day precipitation reaching the 85th climatological percentile early in the period, and while probabilities in the GEFS PET remain above 20 percent, precipitation totals in the uncalibrated guidance are not particularly noteworthy, and the strongest atmospheric river signal based on the GEFS and ECMWF Integrated Vapor Transport tool occurs during week-1. Due to these decreasing signals, the slight risks for heavy precipitation and high winds are discontinued across the Pacific Northwest. Although generally wet conditions are favored due to the onshore flow pattern, particularly across coastal Washington, it is less likely daily totals in week-2 reach hazards criteria.

Persistent mid-level troughing forecast across Alaska favors below-normal temperatures across much of the state. The ECMWF and GEFS PETs continue to indicate at least a 20 percent chance of minimum temperatures falling below the 15th climatological percentile and 20 deg F across much of western Mainland Alaska and the Alaska Peninsula, supporting a slight risk of much below normal temperatures, Oct 12-14. This could lead to increasing freeze-up of rivers and lakes. As this trough retrogrades later in week-2, chances for heavy precipitation are likely to increase across Southeast Alaska. However, hazards criteria is not forecast to be reached.

Forecaster: Thomas Collow

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

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts