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HOME> Expert Assessments>Hazards Outlook

U.S. Hazards Outlook - Made July 28, 2017

 Days 3-7Days 8-14Prob. Days 8-14
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Categorical OutlooksDay 3-7Day 8-14
8-14 Day Probabilistic OutlooksTemperature HazardsPrecipitation Hazards

Valid Monday July 31, 2017 to Friday August 11, 2017

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT July 28 2017

Synopsis: At the start of the period, a frontal system is forecast to stall over central Florida, near the Gulf coast, and parts of the southern Plains. Mid-level high pressure is expected to strengthen over the western U.S. Surface low pressure is predicted over the Gulf of Alaska as its associated frontal system approaches the Alaska Panhandle. During week-2, mid-level low pressure over the eastern U.S. is forecast to weaken as mid-level high pressure moves to the interior western portions of the lower 48 states.

Hazards Detailed Summary

For Monday July 31 - Friday August 04: A frontal system is forecast to stall across central Florida, near the Gulf coast, and parts of the southern Plains. The front will act as a focusing mechanism for showers and thunderstorms leading to heavy rain (amounts in excess of 1 inch in 24 hours) for the central Florida peninsula Jul 31-Aug 1, the central and southern high Plains, and central and southern Rockies Jul 31-Aug 2,
and the southern Great Plains and parts of central and eastern Gulf coast, and northern Florida Aug 2-4. The heavy rainfall leads to the possibility of flash flooding for parts of the central and southern Rockies, and central and southern high Plains. Antecedent heavy rain leads to possible flooding for parts of the Mid-Atlantic and central Appalachians Jul 31.

A strong mid-level ridge over the western CONUS leads to much above-normal temperatures for parts of the northern Great Basin, Pacific Northwest, Northern Plains, and California Jul 31-Aug 4. Positive temperature anomalies could be near 20 degrees F over parts of the interior northwest CONUS which would bring actual temperatures into the mid-100's F for portions of the region.

Surface low pressure is forecast over the Gulf of Alaska during much of the period. A frontal system associated with this area of low pressure is expected to approach the Alaska Panhandle and heavy rain (amounts in excess of 2 inches in 24 hours) is anticipated for parts of the region Aug 1-2.

Tropical systems Hilary and Irwin in the eastern Pacific are expected to remain well west of the U.S. mainland. A west to northwest track for both systems is expected through the weekend and early next week.

Moderate to major flooding continues along multiple rivers across eastern Iowa, northern Illinois, and southern Wisconsin. River flooding is expected to slowly recede during the next few days due to drier weather.

For Saturday August 05 - Friday August 11: An amplified 500-hpa ridge is expected to persist across the western U.S. through at least the early part of Week-2. This ridge supports a slight risk of much above-normal temperatures for much of the western U.S. and northern Great Plains Aug 5-6, and a moderate risk of much-above normal temperatures for the Central Valley of California Aug 5. The moderate risk area posted for the Central Valley of California is based on: good consistency among the ensemble mean solutions for an amplified ridge, guidance from the GEFS reforecast temperature tool, and recent GFS ensemble means indicating temperatures averaging 8 degrees F or more above normal on Aug 5. As the trough over the northeastern CONUS weakens during week-2, there is a slight chance of much-above normal temperatures for parts of the northeast Aug 6-9.

A variable monsoon flow is expected across the southwestern U.S.as the axis of the subtropical ridge oscillates during early August. A factor in the moisture availability is likely to be east Pacific tropical cyclone activity. The CFS model indicates a robust atmospheric Kelvin Wave propagating east across the Western Hemisphere during the next week to ten days which would provide a favorable environment for additional tropical cyclone development across the east Pacific through mid-August. The risk of flash flooding is expected to be highest across parts of the desert Southwest, southern Great Basin, and Big Bend of Texas due to anomalous southeasterly flow and the potential for enhanced moisture associated with tropical cyclones across the east Pacific later in Week-2. If a trough develops along the West Coast and causes more westerly flow, a rapid drying trend would likely occur across the southwestern U.S.

The U.S. Drought Monitor valid on July 25 indicates that severe to exceptional (D2-D4) drought coverage increased to 5.18 percent across the continental U.S. This increase is related to an expansion of severe drought primarily across the northern Great Plains.

Forecaster: Randy Schechter

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