Valid Friday, November 28, 2014 to Tuesday, December 09, 2014
Summary of Forecasts and Hazards
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EST November 25 2014Synopsis
: Onshore flow is forecast to shift
south along the West Coast during the next week. A strong area of high pressure
is expected to progress southeast from Canada into the Great Plains by this
weekend. Meanwhile, an upper-level ridge of high pressure is forecast to build
across the eastern U.S. at the beginning of December. A surface high is
expected to persist across eastern Alaska, while a low pressure system tracks
towards the Aleutians this weekend. Hazards
Detailed Summary For Friday November
28 - Tuesday December 02:
- Much below
normal temperatures for parts of the northern Rockies and northern Great
Plains, Sat-Sun, Nov 29-30.
- Heavy snow for parts of the Northern Rockies, Fri-Sat, Nov 28-29.
- Heavy snow for parts of the Cascades, Fri-Sat, Nov 28-29.
- Heavy snow for the Sierras of California, Sat-Mon, Nov 29-Dec 1.
- Heavy rain for southwest Oregon and parts of northern/central California,
Sat-Mon, Nov 29-Dec 1.
- Heavy rain for southern California, Mon-Tue, Dec 1-2.
- Significant river flooding likely for parts of Washington.
- Significant river flooding possible for parts of New York.
- A slight risk of much below-normal temperatures for parts of the northern
Great Plains, Wed-Thu, Dec 3-4.
- Severe drought for the Central and Southern Great Plains, Southwest,
Southeast, Tennessee Valley, Pacific Northwest, Great Basin, and California.
A pattern change is likely by the beginning of
December as an upper-level trough develops along the West Coast and 500-hpa
heights increase downstream across the southeastern conus. This pattern change
is expected to bring heavy rain along coastal areas of California and heavy
snow to the Sierras beginning on Saturday. Total precipitation amounts (liquid
equivalent) are expected to exceed 5 inches during this period across coastal
ranges of northern California and also across the northern Sierras. Although
timing differences continue among the models, a shortwave trough with
subtropical moisture in the southern stream is expected to bring heavy rainfall
to southern California early next week.
Precipitation amounts inland across Arizona next week are less certain due
to model differences on the depth and speed of the aforementioned shortwave
trough, precluding additional related hazards from being determined.
Meanwhile, across the Cascades and northern Rockies, heavy snow is expected
on Friday and Saturday. Snow levels could fall below to 1,500 feet or lower
across the southern Washington Cascades and Columbia Gorge by Saturday. Heavy
rainfall during the next few days may trigger flooding along the most
flood-prone rivers along the western slopes of the northern Washington
A strong area of high pressure is expected to shift south from Canada and
bring much below-normal temperatures to parts of the northern Rockies and
northern Great Plains on Saturday and Sunday. Minimum temperatures could fall
below -10 degrees F across the northern high Plains this weekend.
A 1036-hpa surface high is forecast to persist over eastern Alaska through
Friday before it shifts southeast. A low pressure system is expected to bring
inclement weather to the Aleutians beginning on Sunday, but rainfall amounts
and winds are expected to remain below hazards criteria at this time. For Wednesday
December 03 - Tuesday December 09:
Model differences increase at the
beginning of Week-2 regarding the depth and speed of the southern stream trough
that is forecast to cross southern California and the Southwest. The high
resolution 0Z ECMWF model solution, which is the slowest and more amplified
than other guidance, indicates that heavy rain and high-elevation snow could
continue into Week-2 for southern California and the Southwest. However, the
latest GFS model runs and many of its ensemble members favor drier weather for
Multiple days of return flow from the Gulf of Mexico are expected across
the east-central U.S. at the beginning of December. An increase in low-level
moisture interacting with the upper-level trough moving from the western conus
raises the risk of heavy rainfall across the middle/lower Mississippi and Ohio
Valleys during Week-2. However, due to uncertainty on timing, a heavy rain
hazard is not defined at this time.
A very strong temperature gradient is expected to develop from Canada south
into the Great Plains. Since shallow, arctic air may return again spread south
during the early part of Week-2, a slight risk of much below normal
temperatures is posted for December 3-4 for the Northern Great Plains.
The most recent U.S. drought monitor, released on November 20, indicates a
slight decrease in the areal coverage of severe to exceptional drought (D2 to
D4) from 17.27 percent to 17.13 percent across the Continental
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.