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Composite Map Day 8-14

Experimental Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards Snow Hazards

Valid Thursday May 09, 2024 to Wednesday May 15, 2024

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT May 01 2024

Synopsis: There is good agreement between multiple model ensemble means indicating amplified mid-level high pressure across the south-central and southeastern contiguous U.S. (CONUS) from the beginning to middle of week-2 gradually weakening by the end of the period. This pattern supports increased risk of excessive heat across portions of the Gulf Coast states and South Carolina at the beginning of week-2. Mid-level low pressure across the Interior West may support high winds across parts of the southwestern quadrant of the CONUS. Ahead of this mid-level low pressure, a fairly stationary front favors enhanced risk of periods of heavy precipitation across parts of the Central and Southern Plains, Middle and Lower Mississippi, Ohio, and Tennessee Valleys, and Southern Appalachians which could continue flood risk in some of these areas.

Hazards

• Moderate risk of excessive heat for parts of the Gulf Coast states and South Carolina, Thu-Fri, May 9-10.
• Slight risk of excessive heat for parts of the Gulf Coast states and South Carolina, Thu-Sat, May 9-11.
• Slight risk of periods of heavy precipitation across parts of the Central and Southern Plains, Middle and Lower Mississippi, Ohio, and Tennessee Valleys, and Southern Appalachians, Thu-Mon, May 9-13.
• Slight risk of episodes of high winds for parts of the southwestern quadrant of the CONUS, Thu-Sat, May 9-11.
• Possible flooding over parts of the Central and Southern Plains and Lower and Middle Mississippi Valley.
• Rapid onset drought risk over parts of the Florida Peninsula.

Detailed Summary

For Saturday May 04 - Wednesday May 08: WPC Days 3-7 U.S. Hazards

For Thursday May 09 - Wednesday May 15: The 0Z GEFS and ECENS are in good agreement today indicating amplified mid-level ridging across the south-central and southeastern CONUS from the beginning to middle of week-2. A slight risk of excessive heat continues to be highlighted across parts of the Gulf Coast states and South Carolina, May 9 to 11, where the GEFS and ECENS probabilistic extremes tools (PETs) show at least a 20% chance of maximum temperatures exceeding the 90th percentile, climatologically, and 90 Deg F (100 Deg F across southwestern Texas). An embedded area is designated with a moderate risk (40 to 60% chance), May 9-10, supported by both dry air temperature and heat index tools. The ECENS (GEFS) PET shows at least a 50% (40%) chance of maximum temperatures exceeding the 85th percentile across much of the moderate risk area. The National Blend of Models (NBM) shows relatively widespread potential for record high temperatures, May 9th, in the low to mid 90s across the Lower Mississippi Valley and Florida, with triple digits (deg F) across southwestern Texas.

There is better agreement today compared to yesterday between the GEFS and ECENS ensemble means regarding amplified mid-level troughing across the northwestern and north-central CONUS continuing from the end of week-1 into the beginning of week-2, gradually weakening by the latter portion of the period. An initial front is predicted extending southward from the Great Lakes followed by a surface low ejecting eastward from the lee of the Rockies ahead of the mid-level trough in the West. These disturbances support a slight risk for periods of heavy precipitation across parts of the Central and Southern Plains, Middle and Lower Mississippi, Ohio, and Tennessee Valleys, and Southern Appalachians, May 9 to 13. The GEFS and ECENS PETs indicate at least a 20% chance of 3-day precipitation totals exceeding the 85th percentile and one inch across the highlighted risk area. Recent deterministic GFS runs show enhanced convective available potential energy (CAPE) that could be conducive for thunderstorms in the highlighted risk area.

Saturated soils in addition to expected antecedent heavy rainfall during week-1 and predicted week-2 heavy rainfall supports increased likelihood for flooding for portions of the Central and Southern Plains and Lower and Middle Mississippi Valley. This highlighted flood risk area is based on where the National Water Center’s experimental flood outlook shows possible flooding during the 4-7 day period and where there is a slight risk of heavy precipitation during week-2.

A series of surface lows are anticipated to form over the southwestern CONUS at the beginning of week-2. These disturbances combined with adjacent surface high pressure over the North Pacific supports areas of tight pressure gradients and resultant increased chances for high winds across the southwestern CONUS. A slight risk of episodic high winds is designated across parts of the southwestern quadrant of the CONUS, May 9-11 based on where both the GEFS and ECENS PETs shows at least a 20% chance of wind speeds exceeding the 85th percentile and 20 mph across the highlighted risk area in addition to where recent deterministic model runs indicate enhanced wind speeds and surface low formation. Anticipated increased potential for high winds combined with dry soils and antecedent and expected dry conditions supports enhanced risk for wildfires, especially across the Big Bend of Texas, New Mexico, and Arizona, where the National Interagency Fire Center (NIFC) shows moderate risk of significant fire potential by the end of week-1.

In the Southeast, above-normal temperatures and near- to below-normal precipitation is forecast during weeks 1 and 2. In parts of the central Florida peninsula 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. As we approach the middle of May, increasing sun angle and temperatures in the 80-90 deg F could lead to further drying of soils and potentially lead to drought conditions across this region. Therefore, an area of rapid onset drought (ROD) is posted for portions of central Florida.

In Alaska, as we move into the middle of May snowmelt season is underway and frozen rivers will begin to break up in the near future. This leads to the potential for river flooding related to ice-jams. We continue to monitor the situation but currently there are no indications of impending major river break-ups so no flooding-related hazards are posted at this time.

Forecaster: Melissa Ou

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

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts