Valid Monday December 05, 2016 to Friday December 16, 2016
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EST December 02 2016Synopsis
: During week-1 a surface low
pressure system is forecast to lift northward through the Mississippi Valley
towards the Great Lakes. Another surface low pressure may form along the
Mid-Atlantic as the aforementioned system reaches the Great Lakes. Behind these
disturbances arctic air is expected to spill southward due to an unseasonably
strong surface high pressure expected to be positioned over the Yukon.
Unsettled conditions are anticipated in the North Pacific throughout Week-1.
During Week-2, mid-level high pressure is forecast along the Pacific coast with
low pressure expected over the Great Lakes. Hazards
Detailed Summary For Monday December
05 - Friday December 09:
- Severe weather across portions of the Southeast and the Lower
Mississippi Valley, Mon, Dec 5.
- Heavy rain across portions of the Lower Mississippi Valley, the Tennessee
Valley, the Mid-Atlantic, the Southern Appalachians, and the Southeast,
Mon-Tue, Dec 5-Dec 6.
- Flooding possible across portions of eastern Texas, Mon-Tue, Dec 5-6.
- Much below-normal temperatures across portions of the Northern and Central
Plains, the Rockies, the Great Basin, the Pacific Northwest, and the Southwest,
Tue-Wed, Dec 6-Dec 7.
- Heavy rain across western portions of California and Oregon, Thu, Dec 8.
- Much below-normal temperatures across portions of the Southwest, the Great
Basin, the Rockies, Great Plains, the Lower and Middle Mississippi Valley, the
Tennessee and Ohio Valleys, the Mid-Atlantic, the Central and Southern
Appalachians, and the Southeast, Thu-Fri, Dec 8-Dec 9.
- Much below normal temperatures across portions of the Alaska Panhandle and
mainland Alaska, Mon-Fri, Dec 5-Dec 9.
- High winds across portions of the Alaska Panhandle, Tue-Wed, Dec 6-Dec 7.
- Slight risk of much below-normal temperatures for portions of the Great
Plains, the Great Basin, the Northern and Central Rockies, the Upper and Middle
Mississippi Valley, and the Pacific Northwest, Sat-Thu, Dec 10-Dec 15.
- Moderate risk of much below-normal temperatures for portions of the Alaska
Panhandle, Sat-Sun, Dec 10-Dec 11.
- Slight risk of much below-normal temperatures for portions of the Alaska
Panhandle, mainland Alaska, and the Aleutians, Sat-Thu, Dec 10-Dec 15.
- Severe drought across parts of the eastern U.S., Great Plains, Missouri
River Valley, Central Rockies, Intermountain West, California and Hawaii.
As Week-1 begins a surface low pressure system is
forecast over the Lower Mississippi Valley associated with a negatively-tilted
trough at 500-hPa. Dynamical model guidance continues to forecast this system
to shift northward towards the Great Lakes, however, forecasts now portray a
secondary coastal system developing off the Mid-Atlantic by mid-week. This
secondary development would limit snow and wind potential across the
northeastern quarter of the country from either system. Instead an eastward
shifting heavy rain hazard (exceeding 1" in 24 h) is the most likely threat
across the southeastern U.S. on Mon-Tue, Dec 5-6. The Storm Prediction Center
also anticipates a 15% risk of severe weather adjacent to the Gulf of Mexico
associated with this system as locally severe winds and tornadoes could be
possible on Mon, Dec 5. Significant river flooding is possible associated with
this system across parts of southeastern Texas on Mon-Tue, Dec 5-6.
Northerly winds are anticipated on the back side of the aforementioned low
pressure system as it strengthens and moves northward. Strong surface high
pressure is also forecast in the Yukon during Week-1, that will further help
bring cold, arctic air southward over the CONUS. Much below-normal temperatures
are possible Mon-Tue, Dec 4-5 for the Great Basin, Rocky Mountains, and Great
Plains. Here minimum temperatures could be 12-20 degrees F below normal. The
much below-normal temperature hazard region is expected to push eastward into
the Southeast and Ohio and Tennessee Valleys for Thu-Fri, Dec 6-7.
Persistent surface low pressure is forecast in the Gulf of Alaska and North
Pacific late in Week-1. This setup favors onshore flow off the Pacific for much
of the West Coast. Heavy rain is possible for coastal portions of northern
California and Oregon on Fri, Dec 9 as the cold front associated with this
system is expected to be coming ashore.
Alaska is also forecast to be impacted by the anomalously cold weather, as
polar air is forecast to wrap westward around the base of surface high pressure
positioned over the Yukon. This setup results in a region of much below-normal
temperatures forecast across much of Alaska for Tue-Fri, Dec 6-9 where
anomalies could exceed -25 degrees F. Within this region the hazard is expected
to shift eastward and southeastward over the course of Week-1. This setup also
supports the potential development of easterly high winds (exceeding 50 mph)
for exposed areas across the Alaska Panhandle south of Yakutat on Tue-Wed, Dec
For Saturday December 10 - Friday December 16:
The anomalous 500-hPa
forecast pattern for Week-2 favors ridging along the Pacific Coast and Bering
Sea, with troughing over the Great Lakes. The biggest difference among the
ensemble mean fields lies in the treatment of the ridging in the Pacific, with
the GEFS more amplified than the weaker European solution which keeps ridging
along the Mexican border rather than extending northward into Canada. However,
the GEFS is less amplified than the ECMWF ensembles in the anomalous ridge over
the Bering Sea, which would result in less transport of Siberian air towards
North America. The European solution results in colder air across much of North
America, however both ensembles appear less bullish on the cold air potential
over North America than prior runs.
Given the somewhat warmer solutions in ensemble guidance today,
probabilities for much below-normal temperatures are damped relative to the
previous forecast. A slight risk of much below-normal temperatures is now
forecast for approximately the northwestern quarter of the CONUS for Sat-Thu,
Dec 10-15. Roughly the southern two-thirds of Alaska, with the exception of
most of the Aleutians, has a slight risk of much below-normal temperatures for
Sat-Mon, Dec 10-12, with this risk becoming focused along the Canadian border
and Alaska Panhandle over the course of the week. Within this region, parts of
the Alaska Panhandle have a moderate risk of much below-normal temperatures
Sat-Sun, Dec 10-11.
According to the latest U.S. Drought Monitor (USDM) valid on November 29,
the coverage of severe or greater drought for the CONUS decreased nearly a half
percent to 16.6%. Improvements were noted for portions of the Lower Mississippi
Valley and New York state. While the most recent USDM shows deterioration of
drought conditions in the Southeast, rains following the latest release may
yield improvement for the next publication.
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.