Valid Sunday, February 26, 2017 to Thursday, March 09, 2017
Summary of Forecasts and Hazards
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EST February 23 2017Synopsis
: An area of upper-level low
pressure is forecast over the western U.S. during the next week, while a
strengthening area of upper-level high pressure becomes centered over the
Florida peninsula. Surface low development is expected across the central Great
Plains by Tuesday, Feb 28. This surface low and its trailing front are forecast
to advance across the central and eastern U.S. during mid-week. A pattern
change is becoming more likely during Week-2 with a building ridge of high
pressure near the West Coast and a developing area of upper-level low pressure
over the east-central U.S. Hazards
Detailed Summary For
Sunday February 26 - Thursday March 02:
- Heavy snow for the
Sierra Mountains and parts of western Nevada, 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.
- Critical fire weather conditions for parts of the southern high Plains,
Tue, Feb 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.
- Much below-normal temperatures for the eastern interior of Alaska, Thu, Mar
- A slight risk of much below-normal temperatures for parts of the Pacific
Northwest, northern Great Basin, and northern Rockies, Fri-Sat, Mar 3-4.
- A slight risk of much below-normal temperatures for the Alaska Panhandle,
much of mainland Alaska, and parts of the Alaska Peninsula, Fri-Thu, Mar 3-9.
- A moderate risk of much below-normal temperatures for parts of southeastern
mainland Alaska and the Alaska Panhandle, Fri-Sun, Mar 3-5.
- Flooding possible across portions of the Upper and Middle Mississippi
Valley and along the Red River of the North.
- Flooding occurring or imminent across portions of Idaho and Oregon.
- Severe Drought across portions of southern California, southwestern
Arizona, Great Plains, Arkansas, Tennessee Valley, southern Appalachians, and
Spread among deterministic model
solutions is large at this time range, regarding a shortwave trough entering
the western U.S. this weekend, its downstream surface low development, and
associated precipitation amounts. The latest model guidance reduced
precipitation amounts across California early in the period as the shortwave
trough taps into subtropical moisture for a limited time if any. However, due
to relatively low snow levels, a heavy snow hazard is maintained for the Sierra
Mountains and western Nevada on Feb 26 and 27. As the mid-level trough shifts
inland, heavy snow (6 inches or more per 24 hours) is expected across the
higher elevations of Arizona and the Colorado Rockies on Feb 27 and 28. High
winds (speeds above 35 knots) are also forecast to develop across the
southwestern U.S. on Feb 27.
The deterministic 0Z ECMWF model is preferred next week due to its
consistency during the past two days. Lee side cyclogenesis on Feb 28 is
expected to promote high winds (speeds above 35 knots) and critical fire
weather conditions across the central and southern high Plains. Although
moderate to potentially heavy snow (4 to 8 inches) is expected along the
northwest side of a surface low tracking across the upper Mississippi Valley on
Feb 28 and Mar 1, confidence is tempered due to spread among deterministic
model runs. Robust gulf inflow is forecast to result in heavy rainfall
(48-hour totals locally exceeding 2 inches) across the Ohio and Tennessee
Valleys and central Appalachians on Feb 28 and Mar 1. Severe weather is also
possible across these same areas, but low predictability precludes designation
of a severe weather hazard at this time.
The latest model guidance indicates a weaker low pressure system crossing
the Bering Sea this weekend with lower precipitation amounts. Therefore, the
heavy snow hazards across Alaska from previous outlooks are removed. Arctic
high pressure is forecast to build into the northern two-thirds of Alaska. Much
below-normal temperatures are posted for eastern interior Alaska where the 6Z
GFS ensemble mean indicates temperatures averaging more than 20 degrees F below
normal. For Friday March 03 - Thursday
The latest ensemble means indicate a large change in the
longwave pattern across North America during Week-2 compared to the previous
few days of model runs. 500-hpa heights are now forecast to increase (decrease)
across the western (eastern) U.S. during early March. Given this large change
in today's models runs, the risk for much below-normal temperatures is reduced
to low across the northwestern U.S. and limited to only Mar 3 and 4. A slight
to moderate risk of much below-normal temperatures remains more likely across
parts of Alaska due to the amplified ridge upstream over the western Bering
Sea. There are signs in the latest ensemble means and deterministic model runs
that the evolving longwave pattern may become more conducive for much colder
temperatures to shift south from Canada into parts of the central and eastern
U.S. during early March.
The amplifying ridge near the West Coast is expected to result in a major
pattern change with below-median precipitation favored for California during
According to the U.S. Drought Monitor valid on February 21, severe drought
is designated across parts of California, Arizona, the Great Plains, Arkansas,
south Texas, and the eastern U.S. Coverage of severe, or greater intensity,
drought throughout the continental U.S. remained nearly steady at 3.31 percent.
California, to the north of Point Conception, is free of long-term severe
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.