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HOME> Expert Assessments>Hazards Outlook

U.S. Hazards Outlook - Made April 20, 2017

 Days 3-7Days 8-14Prob. Days 8-14
SoilsNot Available

Categorical OutlooksDay 3-7Day 8-14
8-14 Day Probabilistic OutlooksTemperature HazardsPrecipitation Hazards

Valid Sunday April 23, 2017 to Thursday May 04, 2017

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT April 20 2017

Synopsis: A surface low pressure system is forecast to move eastward across the southeastern quarter of the CONUS at the beginning of the period, exiting the Southeast coast by Apr 25. Meanwhile, a storm system is anticipated to form over the Northern Plains by April 24 and track across the northern tier, exiting the Great Lakes by Apr 26. An area of upper-level low pressure is expected to develop over the western U.S. early next week and persist through at least the early part of Week-2. Multiple surface low pressure systems are forecast to move across the Gulf of Alaska during the next two weeks.

Hazards Detailed Summary

For Sunday April 23 - Thursday April 27: A shortwave trough is forecast to advance east across the southeastern quarter of the CONUS this weekend into early next week. This feature may bring heavy rain (2 inches of rainfall or greater in a 24-hour period) to parts of the Southeast and the Mid-Atlantic on April 23.

An upper-level trough is likely to develop across the western U.S. next week. A relatively wet pattern can be expected next week throughout the Pacific Northwest, northern Great Basin, and north-central Rockies due to the trough aloft. An area across the Pacific Northwest is highlighted for potential for heavy rain and snow at the highest elevations for April 24 to 26. Localized areas may receive 2 inches or greater of liquid equivalent in a 24-hour period.

The amplifying upper-level trough and the development of multiple surface lows across the high Plains are forecast to result in periods of high winds (gusts above 40mph) for parts of the western U.S. and high Plains, April 24 to 25.

Deterministic model runs continue to indicate a shortwave trough ejecting onto the Great Plains by April 26, with lee side cyclogenesis. Locally heavy rain and high elevation snow (one inch or greater of liquid equivalent in 24-hours) is expected to develop across the Central Rockies and the Central Plains on April 26 as a low pressure system interacts with increasing low-level moisture from the Gulf of Mexico. The longwave pattern favors a multi-day outbreak of severe weather across the central U.S. next week. However, the Storm Prediction Center states that confidence is too low to define a specific area at this time.

Amplified mid-level troughing is forecast to build across the majority of the western half of the CONUS at the beginning of the period. This pattern supports increased chances for much above normal temperatures across portions of the desert Southwest on April 23. Maximum temperatures near or above 100 degrees F can be expected in the outlined area and these maximum temperatures are 10 to 15 degrees above-normal for late April. Much above-normal temperatures are expected to shift east to the southern Great Plains on April 25 and 26 as downslope flow results in maximum temperatures warming into the low to mid 90s (degrees F).

For Friday April 28 - Thursday May 04: Model guidance remains consistent with its forecast of an upper-level trough centered over the west-central U.S. at the beginning of Week-2. The position and amplitude of this upper-level trough coupled with enhanced moisture return from the Gulf of Mexico signal an increasing risk of heavy rainfall (1 to 2 inches, locally more) and the potential for severe thunderstorms across the central U.S. on April 28 and 29. The outlined hazard area for heavy rainfall is based on 48-hour precipitation amounts from the deterministic 0/6Z GFS and 0Z ECMWF models and their ensemble means which are in good agreement for days 8 and 9 as well as the GEFS Reforecast Tool. The GEFS Reforecast Tool indicates increased chances for potential heavy rain across the Lower Mississippi valley for the rest of week-2 as the mid-level trough shifts eastward. Models show the trough becoming less amplified toward the middle of week-2. This region will be monitored in the upcoming days. This trough also supports a slight risk of much below normal temperatures across parts of the western half of the CONUS April 28 to 30. The highlighted area indicates at least a 20 percent of freezing temperatures which could have an impact to sensitive vegetation.

Downstream of the amplified mid-level trough, amplified mid-level ridging is expected to build across the eastern half of the CONUS. This pattern supports a slight to moderate chance of much above normal temperatures across the Southern Plains April 28 to 29 and across the Southeast and Mid-Atlantic April 28 to 30. These areas may experience maximum temperatures reaching the 85th percentile and temperatures reaching 90 Deg F or greater.

Surface high pressure is predicted to develop across northern mainland Alaska from the beginning of week-2 until at least the middle of week-2. This supports a slight chance of much below normal temperatures across the North Slope of Alaska and the Northwest coast of Alaska April 28 to 30. The GEFS Reforecast Tool indicates the potential for this area experiencing minimum temperatures reaching the lowest 15th percentile and less than zero degrees F.

According to the U.S. Drought Monitor released on April 20th (using data through 8am Eastern time, April 18th), coverage of severe, or greater intensity, drought throughout the CONUS remains the same as last week (1.44 percent). This remains the lowest coverage of D2-D4 drought over the CONUS since Aug 2010.

Forecaster: Melissa Ou


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