Valid Sunday August 31, 2014 to Thursday September 11, 2014
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT August 28 2014Synopsis
: A surface low pressure system is
forecast to strengthen as it tracks towards the upper Mississippi Valley on
Sunday, while a strong cold front pushes east from the north-central Plains to
the Midwest. An area of upper-level low pressure is expected to develop across
the northwestern U.S. and persist into early September. Elsewhere, a
subtropical ridge of high pressure is forecast to build across the southern
Plains, lower Mississippi Valley, and Southeast. A series of weak low pressure
systems are expected to progress east from the Bering Sea and affect Alaska
during the next week. Hazards
Summary For Sunday August 31 - Thursday September
- Heavy rain shifting east
from the northern/central Great Plains to the Great Lakes, Sun-Mon, Aug 31-Sep
- Severe weather for parts of the northern/central Plains and upper
Mississippi Valley, Sun, Aug 31.
- Heavy rain for south Texas, Tue-Wed, Sep 2-3.
- River flooding is occurring, imminent, or possible across the Missouri
- Severe drought for the Central and Southern Great Plains, Southwest,
Pacific Northwest, Great Basin, and California.
A vigorous shortwave trough is forecast to reach the north-central
Great Plains by Sunday. This shortwave trough and anomalous low-level moisture
are likely to result in another round of heavy rainfall (1 to 2 inches, locally
more) across parts of the Great Lakes, upper Mississippi Valley, and Midwest on
Sunday and Monday. Due to recent heavy rainfall, this region is vulnerable to
flash flooding and isolated river flooding. Instability, abundant low-level
moisture, and favorable wind shear are predicted to favor severe thunderstorms
from the north-central Great Plains east to the Midwest on Sunday.
Thunderstorms are expected to continue into Monday across the upper Mississippi
Valley and Great Lakes, but lower instability may limit the coverage of severe
An upper-level trough is expected to bring relatively cool temperatures to
the northern Rockies during the Labor Day weekend. Maximum temperatures are
forecast to average 5 to 10 degrees F below-normal from Sunday through next
Tuesday across the northern Rockies. Although minimum temperatures are forecast
to remain above freezing across the lower elevations of the northern high
Plains, freezing temperatures are expected across the higher elevations of the
Early next week, a tropical wave originating from the eastern Caribbean Sea
is expected to enter the southwest Gulf of Mexico where conditions could become
more favorable for tropical cyclone development. The GFS model continues to
indicate more robust surface low development with this tropical wave than the
ECMWF model. Regardless of any tropical cyclone development, this tropical wave
along with easterly flow increase the potential for heavy rainfall across south
Texas next week.
Occasional rain is forecast to affect central/southern interior Alaska and
the Alaskan Panhandle throughout this period, while some snow is expected north
of the Brooks Range. Rain and snow amounts are likely to remain below hazardous
criteria. For Friday September 05 -
Thursday September 11:
The 0Z GFS and 0Z ECMWF ensemble means at 500-hpa
indicate a weak trough persisting across the northwestern U.S. with a broad
ridge over the east-central U.S. This longwave pattern is expected to yield a
continuation of relatively cool temperatures across the northern Rockies and
above-normal temperatures from the south-central conus to the East Coast.
Although an active pattern is expected across the Midwest and Great Lakes due
to the upstream trough, uncertainty on the timing of individual shortwave
troughs preclude designation of a heavy rain hazard for these areas at this
The most recent U.S. Drought Monitor, released on August 28, indicates the
percentage of CONUS in severe to exceptional drought decreasing very slightly
to 21.55 percent.
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.