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HOME> Expert Assessments>Hazards Outlook

U.S. Hazards Outlook - Made October 16, 2017

 Days 3-7Days 8-14Prob. Days 8-14
Precipitation No HazardsNot Available
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Categorical Outlooks
Experimental Probabilistic Outlooks (Information)

Valid Thursday October 19, 2017 to Monday October 30, 2017

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT October 16 2017

Synopsis: A surface low is expected to track from western to eastern Canada over week-1. Its trailing cold front is anticipated to sweep across the lower 48 states throughout the day 3 to 7 period into the beginning of week-2. Surface high pressure is forecast to build across much of the Contiguous U.S. ahead of and in the wake of the cold front. A series of surface low pressure systems are predicted to develop over parts of mainland Alaska as well as the Gulf of Alaska during the 3 to 7 day period. Some models favor amplified mid-level troughing throughout week-2 across the eastern half of the U.S. with the potential for a storm approaching the Aleutians, South Coast of Alaska, and the Alaska Panhandle.

Hazards Detailed Summary

For Thursday October 19 - Monday October 23: A surface low is predicted to form over Alberta, Canada at the start of the period and track eastward across Canada throughout the 3 to 7 day period. Its trailing cold front over the CONUS is expected to sweep across the lower 48 states throughout week-1, bringing heavy precipitation to parts of the country. At the beginning of the period, as the cold front stretches across the Pacific Northwest, parts of Northern California and the Pacific Northwest may receive heavy rain on Oct 19 and the Pacific Northwest Oct 21 to 22. Higher elevation areas in the Cascades may receive episodes of heavy snow Oct 19 to 22. Some models indicate the possibility of localized areas receiving 3 to 4 inches or greater of liquid equivalent in a 24-hour period. Additionally, parts of the Northern Rockies in Idaho may receive heavy snow Oct 20 to 21. Several inches of snow is possible across high elevation areas. Another surface low pressure is forecast to develop off the West coast of Canada. This feature supports high winds (40 knots or greater) across coastal parts of the Pacific Northwest Oct 19.
Strong surface high pressure is forecast to build across the western CONUS behind the cold front by Oct 21. This pattern may support a prolonged period of moderate to strong offshore winds across parts of southern California. These elevated wind speeds may lead to increased chances for wildfire risk throughout the weekend. Sustained wind speeds may reach 30 knots or greater.

As the aforementioned cold front traverses the CONUS, parts of the Central Plains, the Southern Plains, and the Mississippi Valley may receive heavy rainfall on Oct 21, followed by the Southeast, the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley on Oct 22. Localized areas may receive up to 2 inches or greater of rainfall in a 24-hour period.

A surface low is predicted to form over the South Coast of Alaska by Oct 22. This storm may bring heavy snow to parts of the Kenai Peninsula (liquid equivalent totals of 2 inches or greater in a 24-hour period).

For Tuesday October 24 - Monday October 30: In general, some models are indicating the development of a mid-level trough across the eastern half of the CONUS throughout week-2. This pattern may translate to much below normal temperatures across the southeastern quarter of the CONUS Oct 27 to 29. The 6Z GEFS shows a more amplified trough than the 0Z ECMWF Ensemble, leading to significant forecast uncertainty. The GEFS Reforecast Tool indicates a 20 percent chance of temperatures in the southeastern quadrant of the CONUS being in the lowest 15th percentile, with the minimum temperatures of some areas dipping into the 40s (Deg F). The GEFS Reforecast Tool also indicates increased chances for heavy rain across parts of Texas, Louisiana, the Lower Mississippi and Tennessee Valley Oct 24 to 26. This is attributed to the placement of the subtropical high pressure favoring strong southerly flow from the Gulf of Mexico into the CONUS, in addition to surface low pressure north of the Yucatan Peninsula. However, due to the 0Z ECMWF Ensemble having a less amplified trough, it does not indicate precipitation amounts as high as the GEFS. Due to these significant model differences, specific hazards areas are not highlighted at this time for week-2.

A strong storm system may approach the Aleutians at the beginning of week-2, tracking along the Gulf of Alaska throughout week-2. This storm may bring heavy precipitation to southwestern mainland Alaska, the South Coast of Alaska, and the Alaska Panhandle throughout week-2. The GEFS Reforecast Tool shows broad areas of 20 percent, localized areas of 40 percent of heavy precipitation. The 0Z ECMWF Ensemble favors a less intense storm, leading to lower expected precipitation amounts. This significant model difference precludes a related hazards area from being determined at this time but will be monitored in the upcoming days.

Forecaster: Melissa Ou


Click here to see a display of the GFS Ensemble Forecasts

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