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U.S. Hazards Outlook - Made May 23, 2018
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Valid Saturday May 26, 2018 to Wednesday June 06, 2018
US Hazards OutlookNWS Climate Prediction Center College Park MD
300 PM EDT May 23 2018
Synopsis: An active pattern is expected to bring wet weather to much of the eastern U.S. during the forecast period and the highest rainfall is expected to be in the Southeast. A low pressure system with tropical origins is forecast to bring significant rainfall to the Southeast this weekend and residual rainfall is likely to spread to the mid-Atlantic by the beginning of next week. A series of upper-level low pressure systems will move through the Gulf of Alaska this week and could bring significant rainfall to the Alaskan Panhandle on Saturday.
Hazards
- Heavy rain across portions of the Southeast, the Southern Appalachians, the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley, Fri-Sat, May 25-May 26.
- Heavy rain across portions of the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Sun-Tue, May 27-May 29.
- Flooding possible across portions of the Mid-Atlantic, the Pacific Northwest, and the Upper Mississippi Valley.
- Flooding occurring or imminent across portions of the Northern Plains, the Northern Rockies, and the Northern Great Basin.
- Flooding likely across portions of the Northern Plains, the Northern Rockies, and the Northern Great Basin.
- Heavy rain across portions of the Alaska Panhandle, Sat, May 26.
- Slight risk of much above normal temperatures for portions of the Central Plains, the Central Rockies, the Lower Mississippi Valley, the Southern Rockies, the Southern Plains, and the Southwest, Thu-Sat, May 31-Jun 2.
- Moderate risk of much above normal temperatures for portions of the Southern Rockies, the Southern Plains, and the Southwest, Thu-Sat, May 31-Jun 2.
- Slight risk of heavy precipitation for portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Ohio Valley, Wed-Sun, May 30-Jun 3.
- Moderate risk of heavy precipitation for portions of the Southeast, the Mid-Atlantic, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Wed-Fri, May 30-Jun 1.
- Severe Drought across the Central Plains, the Central Rockies, the Central Great Basin, the Northern Plains, the Southern Rockies, California, the Southeast, the Southern Plains, and the Southwest.
For Saturday May 26 - Wednesday May 30: The upper-level pattern over the CONUS is forecast to feature two large troughs over the western and eastern U.S., leading to a likely unsettled pattern for much of the lower 48. The National Hurricane Center has upgraded the tropical system in the Gulf to a 60% chance of formation in the next 5 days. This tropical system is likely to bring heavy rain to the Southeast and Florida for the duration of the 3-7 day period, May 26-30. Most model guidance has continued to support the tropical low moving up the western side of the Florida peninsula, except for the deterministic GFS, which has the system moving up eastern side. Due to model agreement in the other models, the deterministic GFS solution was not favored in this forecast. The Gulf coast is likely to see the heaviest precipitation in the early part of the period, May 26-28, with localized totals possibly reaching up to 4 inches. As the tropical system moves over land, the region of heavy rain is forecast to expand northward to Tennessee and the Carolinas. Many of these regions have been impacted by heavy rain in the past few weeks, so continued heavy rain could elevate certain localized hazards.
Several surface low pressure systems are expected to transverse the central U.S. over the 3-7 day period. Heavy rain is likely in Nebraska in association with these systems, from May 28-29. Both GFS and ECMWF models show 24-hour rainfall totals from 1.5-2.5 inches for localized regions.
Upper-level ridging and southerly flow are expected to impact the central CONUS, causing widespread much above normal temperatures over the Plains, May 26-28. Several areas in the central Plains are forecast to break or tie daily temperature records with temperature anomalies up to 16 degrees F. Highs in these regions are expected to reach the upper 90’s, with localized areas surpassing 100 degrees F. Heat index values along the western Gulf Coast are forecast to reach 105 degrees F, with some regions in southern Texas reaching 110 degrees F on Monday.
Persistent upper-level troughing is expected for Alaska throughout days 3-7. At the start of the period, a storm system associated with an upper-level trough is forecast to move inland over the Panhandle from the Gulf of Alaska. This will bring heavy rainfall to the Alaskan South Coast and Panhandle. Although most of the South Coast rainfall should stay below our hazardous criteria, models indicate that isolated areas along the Panhandle could see more than 3 inches of rain on Saturday, May 26.
For Thursday May 31 - Wednesday June 06: Broad upper-level ridging is forecast over the CONUS for much of Week-2. This upper-level pattern is likely to continue warmer temperatures over the central and southern Plains in the early part of Week-2. A slight risk for much above normal temperatures has been issued for the southern Plains up through parts of Kansas for May 31-June 3. Southern Texas and parts of the Panhandle are likely to experience the warmest temperatures. Model guidance from the GEFS indicates a 40% chance that temperatures in these regions will surpass the climatological 85th percentile, so there is a moderate risk for much above normal temperatures in Southern Texas from May 31-June 2. Toward the end of the period, the upper-level pattern is forecast to weaken and begin to break down.
For the Southeast, a weak upper-level trough is likely over the region for the early part of Week-2. Heavy rainfall is expected to continue for the Southeast through the period. The GFS and ECMWF ensembles support heavy rain throughout the entire period, with a 20% chance of reaching the 85th percentile of the climatological normal. A slight risk of heavy precipitation is forecast for the region May 31-June 6. Model guidance shows the highest chances (above 40%) of reaching the 85th percentile mid-period, so a moderate risk of heavy precipitation has been issued from June 2-4 for the central Gulf Coast states.
Upper-level ridging is expected to replace most of the troughing from the day 3-7 period for Week-2 over Alaska. This will likely bring some warmer temperatures to interior Alaska, though none are currently forecast to reach above hazardous thresholds.
The US Drought Monitor, valid on May 15, indicates that the coverage of severe to exceptional drought increased slightly from 15.92 percent last week to 16.71 percent this week.
Forecaster: Christina Finan
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