Home Site Map News Organization

Search:  

Composite Map Day 8-14

Experimental Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards Snow Hazards

Valid Saturday May 04, 2024 to Friday May 10, 2024

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT April 26 2024

Synopsis: Early 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. 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. By the middle of the period the longwave height pattern may break down as more zonal flow is forecast, reducing risks for hazardous weather. Rapid onset drought may become a concern in parts of the Florida peninsula over the next few weeks.

Hazards

• Slight risk of heavy precipitation for portions of the Plains, Mississippi Valley, and western Great Lakes, Sat-Sun, May 4-5.
• Slight risk of high winds for much of the Southwest, Rockies, and Great Plains, Sat-Sun, May 4-5.
• Flooding possible for parts of the eastern Central and Southern Plains, Mississippi Valley, and parts of southwestern Great Lakes.
• Rapid Onset Drought risk for portions of central Florida.

Detailed Summary

For Monday April 29 - Friday May 03: WPC Days 3-7 U.S. Hazards

For Saturday May 04 - Friday May 10: The GEFS and ECMWF ensemble means are in good agreement across the eastern CONUS indicating a mid-level ridge early in the period. But upstream, the ensemble means disagree on the strength of a reloading mid-level trough near and along the West Coast. The ECENS maintains a much weaker trough at the end of week-1 and into week-2, whereas the GEFS has a much more pronounced trough for nearly the same period . However, this does not seem to have too big of an impact on the chances for hazardous weather across the CONUS at this time. A trough across Alaska early in week-2 is forecast to bring a renewed chance for negative 500hPa height anomalies and troughing across the West by the end of the period. At the same time, negative mid-level height departures are forecast to develop along and near the Northeast coast.

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 through the early part of week-2 before weakening later in the period, prompting a slight risk of heavy precipitation in place through the early part of the period, May 4-5. Probabilistic Extremes Tools (PETs) from the GEFS and the ECENS are in better agreement relative to yesterday, which both highlight a similar area across the Plains and Mississippi Valley with a 20% chance for precipitation to exceed the 85th climatological percentile or 1 inch of precipitation. Raw tools from the GEFS and ECENS are also in more agreement over this positioning with the ECENS remaining slightly more robust in its probabilities for exceeding an inch over a 3-day period..

The heavy precipitation and thunderstorm activity anticipated during early in week-2 may exacerbate impacts related to excessive precipitation in week-1. The combined effects of two weeks of excessive precipitation support a flooding possible risk near and downstream from areas where the greatest rainfall totals are expected including eastern portions of Kansas, 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 early in the period 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 4-5 until the mid-level trough across the West weakens by the end of week-2. Some of the raw ensemble model guidance is also indicating increased chances for high winds to become reestablished by the middle to end of the week-2 period. But uncertainty in the overall height pattern reduces confidence and no wind hazard is posted for later in the period at this time. This potential will continue to be monitored in upcoming outlooks.

In the Southeast, above-normal temperatures and near- to below-normal precipitation is forecast during weeks-1 & 2. In parts of the central Florida peninsula and the North Carolina piedmont soil moisture levels are declining due to limited precipitation in recent weeks and months. Recent weeks have seen areas of abnormal dryness (D0) developing and expanding across both of these regions. As we approach the middle of May, increasing sun angles and temperatures in the 80’s to 90’s deg F. could lead to rapid onset drought (ROD) across these regions. Therefore, an area of ROD has been added to parts of central Florida. However, in North Carolina, near-normal precipitation is favored in the week-2 forecast, therefore, no ROD hazard has been posted for this region at this time but interests should remain vigilant.

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 the wind is likely to be largely maritime across the Gulf of Alaska and land conditions are not expected to reach hazardous criteria. During week-2, river breakup will have commenced across many rivers across Alaska leading to chances for flooding hazards but uncertainty in the location of any potential impacts precludes any hazards at this time.

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