Valid Saturday February 25, 2017 to Wednesday March 08, 2017
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EST February 22 2017Synopsis
: A strong surface low is forecast
to exit the Great Lakes on Saturday, Feb 25. Another vigorous low pressure
system is expected to move inland into the western U.S. by early next week.
Surface low development is forecast to develop across the central Great Plains
on Tuesday, Feb 28 with a subsequent track northeast to the Great Lakes. A low
pressure system is forecast to cross the Bering Sea early in the period. During
Week-2, an area of upper-level low pressure is favored over the western U.S.
while an unseasonably strong area of upper-level high pressure remains anchored
over the southwest Atlantic. Hazards
Detailed Summary For Saturday February 25 - Wednesday March 01:
- Heavy precipitation
(rain and high-elevation snow) for parts of California, Sun-Mon, Feb 26-27.
- Heavy snow for the higher elevations of Arizona and Colorado, Mon-Tue, Feb
- High winds for parts of the southwestern U.S. and central/southern high
Plains, Mon-Tue, Feb 27-28.
- Heavy snow for parts of the upper Mississippi Valley and Great Lakes,
Tue-Wed, Feb 28-Mar 1.
- Heavy rain for parts of the Ohio and Tennessee Valleys and central
Appalachians, Tue-Wed, Feb 28-Mar 1.
- Heavy snow for parts of interior northwest Alaska and the Alaska Range,
Sat-Sun, Feb 25-26.
- A slight risk of much below-normal temperatures for much of the western
U.S. and parts of the northern and central Great Plains, Thu-Tue, Mar 2-7.
- A moderate risk of much below-normal temperatures for parts of the Pacific
Northwest, northern Great Basin, and northern Rockies, Thu-Sun, Mar 2-5.
- A slight risk of much below-normal temperatures for the Alaska Panhandle,
much of mainland Alaska, and parts of the Alaska Peninsula, Thu-Wed, Mar 2-8.
- A moderate risk of much below-normal temperatures for parts of southeastern
mainland Alaska and the Alaska Panhandle, Thu-Sun, Mar 2-5.
- Flooding possible across portions of the Upper and Middle Mississippi
- Flooding occurring, imminent, or likely across portions of California, the
Great Basin, and Pacific Northwest.
- Severe Drought across portions of central and southern California,
southwestern Arizona, Great Plains, Arkansas, Tennessee Valley, southern
Appalachians, and the Northeast.
shortwave trough with enhanced Pacific moisture is forecast to enter California
where heavy precipitation (rain and high-elevation snow) is most likely across
the Sierra Mountains along with central and southern California. Model guidance
indicates precipitation amounts ranging from 1 to 3 inches, liquid equivalent,
in the outlined hazard area on February 26 and 27. Snow levels are expected to
be relatively low over the Sierra Mountains. As the shortwave trough progresses
inland over the western U.S., heavy snow (6 inches or more) is forecast for the
higher elevations of Arizona and the Colorado Rockies on February 27 and 28.
Snow levels are expected to fall below 6,000 feet across Arizona by Tuesday,
Feb 28 with lowering 500-hpa heights. High winds (speeds above 35 knots) are
forecast to accompany the upper-level trough over the southwestern U.S. on Feb
27 and extend to the central and southern high Plains on Feb 28. The risk of
critical fire weather conditions returns to the central and southern high
Plains early next week and are expected to be posted on the hazards map later
Deterministic model solutions feature surface low development across the
central Great Plains by Feb 28. Although there remains model spread on the
strength and track of this surface low as it moves to the Great Lakes, forecast
confidence is increasing for a swath of heavy snow (4 to 8 inches, potentially
more) over the upper Mississippi Valley on Feb 28 and Mar 1. The deterministic
ECMWF model is the most bullish with the strength of the surface low.
Meanwhile, in the warm sector, robust Gulf inflow sets the stage for heavy rain
(more than 1 inch per 24 hours) ahead and along a cold front across the Ohio
and Tennessee Valleys and central Appalachians on Feb 28 and Mar 1. Severe
weather is also possible for these same areas, but model variability precludes
designation of a severe weather hazard at this time.
A deep low pressure system is forecast in the Bering Sea at the beginning
of Week-1 with heavy snow predicted for northwest interior Alaska. Sustained
winds do not appear likely to meet the region's hazard criteria (35 kt), but
periodic blizzard conditions (frequent gusts to 35 mph for 3 consecutive hours)
are possible with this system. A second area of heavy snow (total amounts
greater than 12 inches) is forecast for the western and northern slopes of the
Alaska Range on Feb 25 and 26. For Thursday March 02 -
Wednesday March 08:
The predicted longwave pattern during Week-2 continues
to feature a highly amplified ridge over the north Pacific with a downstream
trough over western North America. This upper-level pattern favors below-normal
temperatures across Alaska and the western U.S. Early in Week-2, the highest
odds for much below-normal temperatures exists across southeast mainland
Alaska, the Alaska Panhandle, and the northwestern U.S. where the GEFS
probabilistic extremes tool indicates a 40 percent or higher chance of minimum
temperatures below the 15th percentile compared to climatology.
The amplified ridge upstream across the north Pacific is expected to result
in a major pattern change with below-median precipitation favored for
California during early March.
Severe drought is currently noted over portions of the Central Plains, the
Mid-Atlantic, the Lower Mississippi Valley, the Tennessee Valley, the
Northeast, California, the Southeast, the Southern Appalachians, the Southern
Plains, and the Southwest. Coverage of severe, or greater intensity, drought
decreased to 3.17 percent of the CONUS. This is the lowest coverage of severe
to exceptional drought since October 2010.
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.