Composite Map Day 8-14

Experimental Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards Snow Hazards

Valid Saturday May 17, 2025 to Friday May 23, 2025

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT May 09 2025

Synopsis: An area of mid-level low pressure over the western Contiguous U.S. (CONUS) at the outset of week-2 is favored to shift eastward, leading to increased potential for heavy precipitation and new or renewed flooding over portions of the Southern Plains and Lower Mississippi Valley and the surrounding regions. Multiple days of anomalously warm temperatures may reach hazardous thresholds at times across parts of the Rio Grande Valley and parts of Florida beneath developing mid-level high pressure.

Hazards

• Slight risk of excessive heat for portions of the Rio Grande Valley, Sat-Mon, May 17-19.
• Slight risk of excessive heat for portions of Florida, Sat-Mon, May 17-19.
• Slight risk of heavy precipitation for portions of Southern Plains, Lower and Middle Mississippi, Lower Ohio, and Tennessee Valleys, Sat-Mon, May 17-19.
• Flooding Possible for portions of the Southern Plains and Lower Mississippi Valley.

Detailed Summary

For Monday May 12 - Friday May 16: WPC Days 3-7 U.S. Hazards

For Saturday May 17 - Friday May 23: Ensemble means from the GEFS, ECENS, and CMCE for 500-hPa heights depict an amplified trough coming ashore over the West Coast during week-1 and spreading over the western CONUS by the outset of week-2, along with lee cyclogenesis and a surface low over the Great Plains. This synoptic setup favors moist southerly flow off the Gulf and into the Southern Plains and Mississippi Valley, increasing the potential for heavy precipitation across a region repeatedly impacted by rounds of excessive rainfall. The GEFS, ECENS, and CMCE Probabilistic Extremes Tools (PETs) for heavy precipitation all indicate at least a 20% chance of 3-day precipitation totals exceeding the 85th climatological percentile and at least 1 inch for much of the forecast period across a portion of the Southern and Central Plains and into the Lower and Middle Mississippi Valley. Tools have generally shifted precipitation further northeast relative to yesterday. This would be welcomed across eastern Texas and Louisiana still dealing with ongoing flooding from the past week’s rainfall. However, the signals persist across much of Arkansas, northeast Texas and into Middle Mississippi, lower Ohio, and Tennessee Valleys. Therefore, a slight risk of heavy precipitation is posted for this region for May 17-19.

The southern portions of the highlighted slight risk of heavy precipitation have had widespread amounts of four or more inches of rain in the past seven days and eight or more in the last 30. The current 7 day QPF shows a dry period during week-1 which may allow time for soils to recover but another round of heavy precipitation could lead to renewed chances for flooding. Therefore, a flooding possible risk is forecast for parts of the Southern Plains and Lower Mississippi Valley.

Positive 500-hPa height anomalies are forecast to spread into the Southern Plains and across the Gulf by late week-1 and into week-2. Anomalously warm temperatures are indicated by multiple models for the lower Rio Grande Valley and in parts of Florida late in week-1 and extending into early week-2 as a result of this mid-level ridge. The maximum temperature PETs show a strong signal for anomalous warmth in percentile space, 30-50% chances of exceeding the 85th climatological percentile, across both Florida and the Rio Grande Valley. In southern Texas, the PETs also show 20-40% chances for temperatures to exceed 100 degF, approaching 105. The NWS heat risk tool indicates major heat risk developing along the Rio Grande at the end of week-1. Multiple days of temperatures near excessive heat thresholds may result in expanded heat risk by the beginning of week 2. In Florida, the GEFS depicts widespread 95 degF across Florida early in the week-2 period with bias-corrected apparent temperature tools showing 20-30% chances of apparent temperatures exceeding 100 degF. Therefore, slight risks of excessive heat are highlighted for portions of the Rio Grande Valley and Florida, May 17-19. Models are showing elevated dew points along the southern Texas Gulf Coast in addition to the building heat which may lead to elevated apparent temperatures in the area and so the excessive heat risk shape was expanded east to the Gulf Coast today. Parts of the southwestern and south-central CONUS will need to be monitored throughout week-2 as the ECENS and GEFS forecast a building mid-level ridge across the region by the end of week-2.

As spring continues and daily incoming solar radiation flux totals increase, ice-bound rivers are beginning to break up in Alaska. There is no associated hazard posted at this time but this situation will be closely monitored in the coming days and weeks as conditions can quickly change, leading to the potential for ice jams and associated flooding.

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