Valid Sunday November 30, 2014 to Thursday December 11, 2014
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EST November 27 2014Synopsis
: An area of upper-level low
pressure is expected to slowly progress inland from the East Pacific next week.
A strong surface high is forecast to shift southeast from the Pacific Northwest
and northern Rockies on Sunday to the Midwest on Monday. Meanwhile, an
upper-level ridge of high pressure is forecast to build across the southeastern
U.S. in the beginning of December. A surface high is expected to persist across
northeast Alaska during the next week, while a low pressure system strengthens
as it moves into the Bering Sea this weekend. Hazards
Detailed Summary For Sunday November
30 - Thursday December 04:
- Much below normal temperatures expanding eastward across the Pacific
Northwest, northern Rockies, northern/central Great Plains, and Upper
Mississippi Valley, Sun-Mon, Nov 30-Dec 1.
- Periods of heavy snow for the Sierras of California, Sun-Tue, Nov 30-Dec 2.
- Periods of heavy rain for parts of northern/central California, Sun-Tue,
Nov 30-Dec 2.
- Heavy rain for southern California, Tue-Wed, Dec 2-3.
- Significant river flooding possible, likely, or occurring for parts of
- High winds for the Columbia River Gorge in the Pacific Northwest, Sun, Nov
- High winds for the Aleutians, Sun, Nov 30.
- Severe drought for the Central and Southern Great Plains, Southwest,
Southeast, Pacific Northwest, Great Basin, and California.
An upper-level trough is forecast to separate
from westerly flow across the northeast Pacific this weekend. The evolution of
this trough remains uncertain as model differences increase next week. The
high-resolution GFS model continues to be much more progressive with this
upper-level trough and is also a wetter solution compared to the
high-resolution ECMWF model. Due to large differences among the high-resolution
models, the location and timing of heavy precipitation hazards for California
are based primarily on the 0Z and 6Z GFS ensemble means. Several inches of
precipitation (liquid equivalent) are expected across the coastal ranges of
northern California and the Sierras from Sunday through at least Tuesday. Snow
levels around 7,000 feet are expected for the Sierras. Onshore flow and the
potential for tropical moisture to become entrained into the upper-level trough
increase prospects for locally heavy rain (more than 1 inch) across southern
California on December 2 and/or 3.
The 12Z GFS model indicates light precipitation spreading north into the
Pacific Northwest on Sunday and Monday ahead of the East Pacific trough. If
precipitation occurs, surface temperatures are expected to support freezing
rain across the Willamette Valley and Columbia River Gorge. Large model
differences on precipitation amounts preclude designation of a freezing rain
hazard at this time.
Forecast confidence for heavy precipitation across Arizona is lower today
due to large model differences upstream over the East Pacific. The past few
runs of the high-resolution GFS model indicate less precipitation for Arizona
with the shortwave trough becoming less amplified as it moves inland.
Meanwhile, a strong surface high building south from western Canada is
expected to enhance easterly winds through the Columbia River Gorge where a
high wind hazard is depicted. Heavy rainfall this week may trigger flooding
along the most flood-prone rivers along the western slopes of the northern
A 1036-ha surface high building south from Canada is likely to result in
much below-normal temperatures across parts of the Pacific Northwest, northern
Rockies, and northern/central Great Plains on Sunday. The much-below normal
temperatures are then expected to expand east into the Upper Mississippi Valley
on Monday. Subzero minimum temperatures could extend as far south as Nebraska
and Iowa by Monday morning.
A low pressure system is forecast to strengthen as it tracks into the
Bering Sea during the weekend. The high resolution 0/6Z GFS and 0Z ECMWF models
indicate a 968-hpa low across the Bering Sea later in the weekend. On Sunday,
high winds across the Aleutians are expected to accompany this low pressure
system. For Friday December 05 -
Thursday December 11:
Since model differences are large as early as Day 5,
no specific hazards can be defined during Week-2 except for the areas of
ongoing severe to exceptional drought.
The most recent U.S. drought monitor, released on November 27, indicates a
slight decrease in the areal coverage of severe to exceptional drought (D2 to
D4) from 17.13 percent to 16.81 percent across the continental U.S. This this
the lowest coverage of severe to exceptional drought since December
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.