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Climate Prediction Center

U.S. Hazards Outlook - Made Apr 24, 2015

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Day 3-7 Outlook Day 8-14 Outlook Day 8-14 Probabilistic Temperature Hazards

Valid Monday, April 27, 2015 to Friday, May 08, 2015

Summary of Forecasts and Hazards

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT April 24 2015

Synopsis: An area of upper-level low pressure is expected to develop over the east-central U.S. with a surface low progressing from the southern Great Plains to the Gulf Coast on Monday and Tuesday. An area of upper-level high pressure is forecast to build across the Rockies and high Plains by the end of April, while onshore flow returns to the Pacific Northwest. A surface low is expected to weaken over the eastern Gulf of Alaska early in the period.

Hazards
  • Heavy snow for parts of the mountains of southern Colorado, Mon, Apr 27.
  • Severe weather for parts of Louisiana and Texas, Mon, Apr 27.
  • Heavy rain shifting east from the southern Great Plains to the lower Mississippi Valley, Gulf Coast, and Florida, Mon-Tue, Apr 27-28.
  • Flooding occurring along the Choctawhatchee River in the Florida Panhandle.
  • Flooding occurring or imminent for parts of the Souris River in North Dakota due to water release from Lake Darling.
  • A slight risk of much above-normal temperatures for parts of the central and southern Great Plains, Sat-Sun, May 2-3.
  • Severe drought for the central and southern Great Plains, Southwest, Great Basin, California, the Pacific Northwest, southern Florida, and Hawaii.
Detailed Summary

For Monday April 27 - Friday May 01: A vigorous upper-level trough is forecast to eject from the Four Corners region by Monday. Heavy snow is expected to continue into Monday morning with snow levels potentially falling to around 6,500 feet for the mountains of southern Colorado. Total snowfall amounts through Monday with this spring storm are likely to range from 1 to 2 feet, locally higher, across the southern Colorado mountains.

On Monday, the approaching shortwave trough, along with sufficient shear and instability, is expected to result in the risk of severe thunderstorms across central/southeast Texas and southern Louisiana. Beyond Monday, the surface front is forecast to shift south into the northern Gulf of Mexico and decrease chances for severe weather.

Early next week, 500-hpa height falls, a nearly stationary front, and abundant moisture from the Gulf of Mexico favor heavy rainfall from the southern Great Plains southeast to the lower Mississippi Valley, Gulf Coast, and Florida. The high-resolution model runs are consistent with a broad 1 to 3 inches (locally more) across these areas on April 27 and 28.

Unseasonably cool temperatures are expected across the southern Great Plains and Southeast from Monday through Wednesday, but minimum temperatures are forecast to average only at or slightly below-normal. By Friday, building 500-hpa heights are expected to result in a significant warming trend across much of the west-central U.S.

Although the potential remains for a strong low pressure system to affect the mid-Atlantic and Northeast on April 30 and May 1, the majority of 12Z GFS ensemble members on April 24 indicate a surface low exiting the Southeast during mid-week and moving away from the East Coast during subsequent days.

Moderate flooding along the Choctawhatchee River in the Florida Panhandle is expected to persist through at least Monday. Heavy rainfall during the next week could prolong or trigger additional river flooding along the Gulf Coast.

No hazards are expected across Alaska as a surface low weakens across the eastern Gulf of Alaska by Monday.

For Saturday May 02 - Friday May 08: The 0Z GFS and 0Z ECMWF ensemble means on April 24 indicate a progressive flow pattern with a trough shifting offshore of the East Coast, a ridge centered over the Mississippi Valley, and a trough moving onshore to the West Coast. A drier pattern is expected across the Southeast during the first week of May. Severe weather chances are likely to increase across the central and southern Great Plains after the east Pacific trough moves inland into the western U.S.

The increase in 500-hpa heights and downslope flow result in a slight risk of much above-normal temperatures across parts of the central and southern Great Plains on May 2 and 3. This is consistent with guidance from the GEFS temperature tool and the high-resolution 0Z ECMWF and 12Z GFS models on April 24 indicating 850-hpa temperatures warming above 21 degrees C across southwest Kansas and the Oklahoma Panhandle.

The most recent U.S. Drought Monitor, valid on April 21, indicates a very slight decrease (from 19.14 to 18.97) in the percentage of the CONUS in severe to exceptional drought (D2-D4).

Forecaster: Brad Pugh

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Click here to see a display of the GFS Ensemble Forecasts

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


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