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Climate Prediction Center

U.S. Hazards Outlook - Made Feb 23, 2017

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Day 3-7 Outlook Day 8-14 Outlook Day 8-14 Probabilistic Temperature Hazards

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
300 PM EST February 23 2017

Synopsis: 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.

  • 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 27-28.
  • 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 2.
  • 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 the Northeast.
Detailed Summary

For Sunday February 26 - Thursday March 02: 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 March 09: 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 Week-2.

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 drought.

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.

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