Valid Sunday July 30, 2017 to Thursday August 10, 2017
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT July 27 2017Synopsis
: An unseasonably strong mid-level low
is forecast to slowly exit the northern mid-Atlantic early in the period, while
a trailing front becomes stationary near the Gulf Coast. The tail end of this
front is expected to extend back towards the southern high Plains. Mid-level
high (low) pressure over the western U.S. (mainland Alaska) is likely to
persist through the beginning of August. Hazards
Detailed Summary For Sunday
July 30 - Thursday August 03:
rain for the eastern Big Bend of Florida along with northern and central parts
of the Florida peninsula, Sun-Wed, Jul 30-Aug 2.
- Heavy rain for the southern high Plains, Sun-Mon, Jul 30-31.
- Heavy rain shifting southeast to northern and central Texas, Tue-Wed, Aug
- Flash flooding possible for parts of the Southwest, Sun-Thu, Jul 30-Aug 3.
- Much above-normal temperatures for parts of the northern Great Basin,
northern Rockies, and Pacific Northwest, Tue-Thu, Aug 1-3.
- Flash flooding possible for parts of the southwestern U.S., Fri-Thu, Aug
- Slight risk of much above-normal temperatures for much of the western U.S.
and northern Great Plains, Fri-Sun, Aug 4-6.
- Flooding occurring, imminent, or possible for parts of the Midwest.
- Severe Drought across parts of the Great Plains, Arizona, California, and
A vigorous closed low at 500-hpa initially
over the mid-Atlantic, a pattern more typical during the cold season, is likely
to result in a cold front pushing south to the northern Gulf of Mexico and
Florida peninsula by July 30. The presence of this front, a trough aloft, and
ample moisture are likely to enhance the coverage of showers and thundershowers
across the eastern Big Bend of Florida along with the northern and central
Florida peninsula through August 2. Total rainfall amounts of 2 to 5 inches,
locally more, are expected in the outlined area for heavy rainfall.
The tail end of a front along with upslope low is likely to promote heavy
rainfall (total amounts locally exceeding 3 inches) across the southern high
Plains, continuing at least through August 1. The focus for heavy rainfall
(more than 1 inch per 24 hours) is expected to shift southeast to northern and
central Texas on August 2 and 3. The risk of flash flooding is likely to
remain high across parts of Colorado and New Mexico through August 1. Areas
with burn scars and locations with saturated soils will remain most vulnerable
to flash flooding.
As of July 27 at 8am PDT, Hurricane Hilary is located at 17.6/116W over the
east Pacific. Although the interaction between Hilary and Tropical Storm Irwin
remains uncertain, the model consensus favors a west to northwest track through
the weekend. The deterministic GFS model runs indicate an increase in
precipitable water values, partly associated with Hurricane Hilary, across the
desert Southwest this weekend. Therefore, a flash flooding hazard is posted for
An amplified ridge aloft is expected to result in much above-normal
temperatures, with maximum temperatures 10 to 15 degrees F above normal, across
parts of the northern Great Basin, northern Rockies, and Pacific Northwest. The
highest temperatures are forecast across eastern Washington where daily maximum
temperatures at or above 100 degrees F can be expected. This anomalous heat may
begin to expand east to the drought-stricken areas of the northern Great Plains
later 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 due to drier weather.
An upper-level trough is expected to promote scattered areas of rainfall
throughout mainland Alaska. Rainfall amounts are not expected to exceed hazards
criteria. For Friday August 04 - Thursday
Ensemble spread among the GFS and ECMWF members increases with
the amplitude of the western U.S. ridge during Week-2. Although their ensemble
means maintain above normal 500-hpa heights along the West Coast, the positive
anomalies are smaller compared to previous days. These smaller positive
anomalies are due to the increasing ensemble spread. Based on this increased
ensemble spread and poor continuity among the deterministic GFS model
solutions, the risk for much above-normal temperatures across the western U.S.
is limited to slight.
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 18 indicates that severe to
exceptional (D2-D4) drought coverage increased to 4.77 percent across the
continental U.S. This increase is related to an expansion of severe drought
across the northern Great Plains.
Forecaster: Brad Pugh
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.