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Composite Map Day 8-14

Experimental Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards Snow Hazards

Valid Friday May 24, 2024 to Thursday May 30, 2024

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT May 16 2024

Synopsis: Mid-level high pressure is forecast across the Southern Tier of the contiguous U.S. (CONUS) during week-2. This favors increased chances for anomalously warm temperatures, and excessive heat conditions possibly affecting parts of the Southern Plains and the Florida Peninsula. Mid-level low pressure predicted across the northwestern and north-central CONUS early in the period could lead to a disturbance traversing the CONUS supporting increased likelihood for heavy precipitation across portions of the central and east-central CONUS, along with elevated wind speeds across the Four Corners and High Plains as this potential system ejects out of the Rockies early in week-2.

Hazards

• Moderate risk for excessive heat across southern Texas and the southern Florida Peninsula, Fri-Sat, May 24-25.
• Slight risk for excessive heat across portions of the Southern Plains and the Florida Peninsula, Fri-Tue, May 24-28.
• Slight risk for heavy precipitation across portions of the Great Plains, Mississippi, Tennessee, and Ohio Valleys, Great Lakes, Southeast and Mid-Atlantic, Fri-Sun, May 24-26.
• Slight risk for high winds across parts of the Four Corners and central and southern High Plains, Fri-Sun, May 24-26.
• Rapid onset drought risk across the southern Florida Peninsula and southern Texas.

Detailed Summary

For Sunday May 19 - Thursday May 23: WPC Days 3-7 U.S. Hazards

For Friday May 24 - Thursday May 30: Subtropical ridging is forecast across portions of the south-central CONUS during the week-2 period. This favors increasing chances for anomalously warm temperatures stretching from the Central and Southern Plains eastward to the southern Mid-Atlantic and Southeast coasts. Given the time of year, many areas away from the Gulf Coast are not expected to have temperatures reach excessive heat criteria. Stronger signals for excessive heat are across portions of Texas where the GEFS and ECENS Probabilistic Extremes Tools (PETs) depict at least a 20 percent chance of maximum temperatures exceeding the 85th climatological percentile and 95 deg F. The GEFS PET continues to show probabilities above 40 percent across portions of southern and southwestern Texas, although the ECENS PET generally depicts probabilities above 30% for temperatures to exceed the 85th percentile. The National Blend of Models (NBM) depicts record daily maximum temperatures across parts of south Texas (up to 105 deg F) early in week-2. Given the support from the NBM and the calibrated GEFS heat risk guidance, which indicates at least a 30 percent chance of heat indices exceeding the 95th climatological percentile or 110 deg F across parts of southern Texas, the moderate risk for excessive heat is maintained for May 24-25. A broader slight risk (20 to 40% chance) continues across much of the southern half of Texas and southeastern New Mexico for days 8-12. The slight risk is reduced relative to yesterday across the northern and eastern portions of the shape. Significantly rainfall is expected during week-1 in these areas and a shortwave trough looks like it may work into the Lower-Mississippi Valley during the middle for the period. This reduces the chances for excessive heat across these areas. For the western side of the slight risk area, excessive heat is likely to be temperature driven, but higher dew points favored across southeastern Texas may push heat indices above 105 deg F despite the relatively lower temperatures compared to those further west.

Across portions of southern Texas, above-normal temperatures continue to be strongly favored through at least week-2. Precipitation is also forecast to be below-normal during week-1 and 2 across portions of the region. There have been notable declines in soil moisture across southern Texas in recent weeks and abnormally dry conditions have expanded over the past few weeks. With continued expectations for warm and dry conditions, a rapid onset drought (ROD) risk has been introduced to the southern Texas region today.

The ECENS PET remains very robust bringing in hot temperatures across the Florida peninsula, with probabilities greater than 60 percent for maximum temperatures exceeding the 85th climatological percentile across parts of south Florida. There has also been an uptick in the signal in the GEFS PET compared to yesterday, with these same areas having probabilities above 40 percent. The NBM also depicts some parts of the peninsula reaching the mid-90s deg F, and combined with dew points above 70 deg F, would result in heat indices possibly greater than 105 deg F. Given these signals, the slight risk for excessive heat remains forecast for most of the Florida Peninsula for days 8-12, May 24-28. A moderate risk is highlighted across the southern Florida Peninsula from May 24-25 where there is the strongest signal among the GEFS and ECENS PET. Decreasing soil moisture and a warm and dry pattern predicted in week-2 lead to increased risk for rapid onset drought across parts of south Florida.

Troughing forecast across the northwestern and north-central CONUS favors below-normal temperatures across much of the West, extending into parts of the Northern and Central Plains, Upper and Middle Mississippi Valley, and Great Lakes. The ECENS and GEFS depict a shortwave disturbance moving across the CONUS early in week-2. Given the potential for a storm system to eject out of the Rockies, a slight risk of high winds is posted across parts of the Four Corners and central and southern High Plains for May 24-26. Deterministic runs from the 0z GFS and ECMWF depicting wind speeds exceeding 25-mph over these areas combined with the anomalously dry conditions could enhance the wildfire risk over the region.

Further east, the ECENS PET and uncalibrated ensemble indicate at least a 20 percent chance of 3-day precipitation totals exceeding the 85th climatological percentile and 1-inch across a broad area of the central and east-central CONUS. The GEFS PET is somewhat supportive of this risk across portions of the Mississippi and Ohio Valleys. The ECENS PET brings much stronger chances (>40% chance) of precipitation exceeding the 85th climatological percentile into portions of the Southeast but this is not supported by the corresponding raw tools or the GEFS PET. However, there is a slight expansion south and east of the forecast precipitation hazard from yesterday. Therefore, a slight risk for heavy precipitation is posted across portions of the Great Plains, Mississippi, Tennessee, and Ohio Valleys, Great Lakes, Southeast, and Mid-Atlantic for May 24-26. If the more robust scenario from the ECENS is correct, there could be increasing chances of heavy precipitation spreading into parts of the Northeast around the start of the Memorial Day weekend, but holding off on expanding the hazard due to less agreement from the GEFS.

No hazards are issued for Alaska, with near- to below-normal temperature probabilities favored for most of the state south of the Brooks Range. Snowmelt season is underway and frozen rivers are beginning to break up, leading to the potential for river flooding related to ice-jams. However, there are no indications of impending major river break-ups or serious threat of ice-jamming so no flooding-related hazards are posted at this time. Caution should continue to be exercised as river break-up can be unpredictable and local conditions can change quickly. Anomalous ridging over the north-central Pacific favors an enhanced storm track into western Mainland Alaska, although precipitation amounts are expected to remain low and not reach hazardous thresholds.

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