Valid Monday July 31, 2017 to Friday August 11, 2017
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT July 28 2017Synopsis
: 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
Detailed Summary For Monday
July 31 - Friday August 04:
- Heavy rain for the central Florida
peninsula, Mon-Tue, Jul 31-Aug 1.
- Heavy rain for the central and southern high Plains, and central and
southern Rockies, Mon-Wed, Jul 31-Aug 2.
- Heavy rain shifting southeast across the southern Great Plains, Wed-Fri,
- Heavy rain for parts of central and eastern Gulf coast, and northern
Florida, Wed-Fri, Aug 2-4.
- Heavy rain for parts of the Alaska Panhandle, Tue-Wed, Aug 1-2.
- Flooding possible for parts of the Mid-Atlantic and central Appalachians,
Mon, Jul 31.
- Flash flooding possible for parts of the central and southern Rockies, and
central and southern high Plains, Mon-Thu, Jul 31-Aug 3.
- Much above-normal temperatures for parts of the northern Great Basin,
Pacific Northwest, Northern Plains, and California, Mon-Fri, Jul 31- Aug 4.
- Flash flooding possible for parts of the southwestern U.S., Sat-Fri, Aug
- Moderate risk of much above-normal temperatures for the Central Valley of
California, Sat, Aug 5.
- Slight risk of much above-normal temperatures for much of the western U.S.
and northern Great Plains, Sat-Sun, Aug 5-6.
- Slight risk of much above-normal temperatures for parts of the northeast,
Sun-Wed, Aug 6-9.
- Flooding occurring, imminent, or likely for parts of the Midwest and Middle
- Severe Drought across parts of the Great Plains, Arizona, California, and
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
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
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.
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.