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U.S. Week-2 Hazards Outlook - Made April 24, 2024 | About the Hazards Outlook
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| Composite Map Day 8-14 |
Experimental Probabilistic Outlooks |
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Valid Thursday May 02, 2024 to Wednesday May 08, 2024
US Hazards OutlookNWS Climate Prediction Center College Park MD
300 PM EDT April 24 2024
Synopsis: In week-2, heavy precipitation remains a concern across the central contiguous U.S. (CONUS) with mid-level low pressure forecast across the West and mid-level high pressure likely across the eastern CONUS. This will allow for a continued active pattern leading to chances for heavy rain and thunderstorms across the Plains and Mississippi Valley. The strongest chances for heavy rain have shifted north relative to the prior forecasts. Heavy rain is also expected in week-1, and additional precipitation in week-2 could cause localized flooding over portions of the Plains, Mississippi Valley, and western Great Lakes. Associated with mid-level low pressure over the West, chances for periodic high winds are possible for much of week-2 over much of the southwestern CONUS, Rockies, and Plains.
Hazards
- Moderate risk of heavy precipitation for portions of the Central Plains and Middle and Upper Mississippi Valley, Thu-Fri, May 2-3.
- Slight risk of heavy precipitation for portions of the Northern Rockies, Plains, Mississippi Valley, and western Great Lakes, Thu-Sun, May 2-5.
- Slight risk of high winds for much of the Southwest, Rockies, and Great Plains, Thu-Sun, May 2-5.
- Flooding possible for parts of the eastern Central and Southern Plains, Mississippi Valley, and parts of southwestern Great Lakes.
For Saturday April 27 - Wednesday May 01: WPC Days 3-7 U.S. Hazards
For Thursday May 02 - Wednesday May 08: The GEFS and ECMWF ensemble means are in good agreement indicating a fairly stagnant pattern featuring a moderately-amplified mean 500-hPa long-wave trough over or near western North America, and a downstream mid-level ridge with an axis over the eastern CONUS. The western trough looks likely to weaken and diminish by the middle of the week-2 period. However, a trough across Alaska may help to reestablish negative anomalies across the eastern Pacific Ocean at the end of the period.
The persistent mid-level trough in the West favors southerly surface flow bringing unusually moist air northward into the central CONUS, where cyclonically-curved divergent flow aloft is expected. This combination puts a large part of the central CONUS at increased risk for one or more episodes of heavy precipitation and localized thunderstorms. This quasi-stationary pattern is expected to persist into the middle of week-2 before weakening later in the period, keeping a slight risk of heavy precipitation in place through the early and middle parts of the period, May 2-5. Probabilistic Extremes Tools (PETs) from the GEFS and the ECENS are in less agreement relative to yesterday. The GEFS has lower precipitation amounts relative to the ECENS and this increases the uncertainty. Further, the heaviest precipitation totals are in areas that are currently experiencing moderate to severe long term drought. Nevertheless, raw tools from the GEFS and ECENS forecast at least a 30% chance of 1 day precipitation amounts exceeding 0.5 inches on days 8 and 9. Therefore, a moderate risk of heavy precipitation remains posted for May 2-3 across portions of the Central Plains and Middle and Upper Mississippi Valley. The risk has shifted north relative to yesterday to capture the strongest probabilities among the raw forecast guidance and the ECENS PET.
The heavy precipitation and thunderstorm activity anticipated during week-2 is not expected to be as intense as conditions in the short-term, but will exacerbate impacts related to excessive precipitation in week-1. The combined effects of two weeks of excessive precipitation support a flood risk near and downstream from areas where the greatest rainfall totals are expected including eastern portions of Kansas and Oklahoma and much of the Mississippi Valley according to the GEFS and ECMWF ensemble means. Runoff from heavy rainfall is expected to enhance the flood risk farther to the south and east (downstream) across the Lower Mississippi Valley.
The anticipated long-wave pattern also favors cyclogenesis near or to the lee of the Rockies, with higher surface pressures forecast farther east and west. The timing and strength of any surface low pressure system that forms is uncertain, so a large area from the Southwest and the Rockies eastward through the Great Plains has a slight risk for one or more episodes of high winds for May 2-5 until the mid-level trough across the West weakens by the end of week-2.
Farther north, models generally favor below normal 500-hPa heights across Alaska, with a trough axis near or west of the Mainland that favors stormy weather near the coast of south-central and southeastern Alaska. This pattern may support one or more periods of enhanced precipitation and winds, but conditions are not expected to reach hazardous criteria precluding associated hazards from being designated.
Forecaster: Ryan Bolt
$$ Please consult local NWS Forecast Offices for short range forecasts and region-specific information.
Resources
Week-2 Probabilistic Extremes Tool
GFS Ensemble Forecasts