HOME> Expert Assessments>Hazards Outlook
U.S. Hazards Outlook - Made January 18, 2017
Valid Saturday January 21, 2017 to Wednesday February 01, 2017
US Hazards OutlookNWS Climate Prediction Center College Park MD
300 PM EST January 18 2017
Synopsis: A major pattern change is likely during the final week of January with an area of upper-level high (low) pressure developing near the West Coast (east-central U.S.). Prior to this pattern change, enhanced onshore flow is forecast to continue across the western U.S. through January 23. A strengthening surface low pressure system and trailing front are expected to progress across the eastern U.S. early in the period. A surface low is forecast to track from the central high Plains to the upper Mississippi Valley on January 24 and 25. Arctic high pressure is forecast to weaken over mainland Alaska early in the period, with multiple low pressure systems entering the Gulf of Alaska during Week-2.
Hazards
- Periods of heavy precipitation (rain and high-elevation snow) for parts of the western U.S., Sat-Mon, Jan 21-23.
- Periods of heavy snow for the San Juan Mountains of southwest Colorado, Sat-Tue, Jan 21-24.
- Periods of high winds for parts of western U.S. and central/southern Great Plains, Sat-Tue, Jan 21-24.
- Severe weather for parts of the Southeast, Sat-Sun, Jan 21-22.
- Heavy rain for parts of the Southeast and Tennessee Valley, Sat-Sun, Jan 21-22.
- Heavy rain shifting north from the Carolinas and southern Appalachians to the mid-Atlantic and southern New England, Sun-Mon, Jan 22-23.
- Heavy snow shifting northeast from the central Rockies and northern/central Great Plains to the upper Mississippi Valley and Great Lakes, Tue-Wed, Jan 24-25.
- Much below-normal temperatures for parts of the western U.S., Wed, Jan 25.
- Much below-normal temperatures for parts of mainland Alaska, Sat-Sun, Jan 21-22.
- High winds for the Aleutians, northern gulf coast of Alaska, and the Alaska Panhandle on Mon-Tue, Jan 23-24.
- Periods of heavy precipitation (rain and high-elevation snow) for southeast mainland Alaska and the Alaska Panhandle, Tue-Sun, Jan 24-29.
- Periods of high winds for southeast mainland Alaska and the Alaska Panhandle, Mon-Sun, Jan 23-29.
- A slight to moderate risk of much below-normal temperatures for parts of the western U.S., Thu-Sat, Jan 26-28.
- A slight risk of much below-normal temperatures for parts of the southeastern U.S., Sat-Tue, Jan 28-31.
- Flooding occurring or likely across parts of the middle Mississippi Valley and Oregon.
- Severe Drought across parts of the eastern and southern U.S., Great Plains, Arizona, California, and Colorado.
For Saturday January 21 - Wednesday January 25: An amplified trough progressing inland, strong onshore flow, and enhanced Pacific moisture are likely to result in periods of heavy precipitation (rain and high-elevation snow) across southwest Oregon, California, and the southwestern U.S. during this period. Deterministic model solutions indicate that the heaviest precipitation (5 inches or more, liquid equivalent) is likely across the orographically favored coastal ranges and Sierra Mountains of California from Jan 21 to 23. Snow levels are expected to lower below 5,000 feet across Arizona on January 21 and again on January 23 as 500-hpa heights decrease. Occasional heavy snow (6 inches or more per 24 hours) is forecast for the San Juan Mountains of southwest Colorado with each shortwave trough. Periods of high winds (gusts above 50 mph) are also expected from the western U.S east to the central and southern Great Plains through January 24.
On January 21, the exit region of a strong mid-level jet (90 to 110 knots) coinciding with sufficient instability and abundant low-level moisture is forecast to result in severe thunderstorms across parts of the lower Mississippi Valley and Southeast. This risk of severe thunderstorms is expected to persist through January 22 across parts of the Southeast as a surface low and trailing front move through the region.
Heavy rain (locally more than 3 inches) is initially expected to develop along a stationary front near the Gulf Coast on January 21. Heavy rain is then forecast to shift north from the southern Appalachians and Carolinas to the mid-Atlantic and southern New England on January 22 and 23 when a low pressure system lifts northeast. Due to anomalous low-level moisture and very strong lift, total rainfall amounts could exceed 3 inches across the outlined areas for heavy rainfall.
The deterministic model solutions remain in good agreement today with cyclogenesis across the central high Plains on Jan 24 with a subsequent track of the surface low to the upper Mississippi Valley on Jan 25. Heavy snow (4 inches or more) is expected on the northwest side of the surface low track, from the front range of the Colorado Rockies northeast to the upper Mississippi Valley and Great Lakes from Jan 24 to 25. The deterministic GFS model runs are consistent with 48-hour precipitation amounts of 0.5 to 1.25 inches, liquid equivalent.
A 1036-hpa surface high is expected to build into the western U.S. by Jan 25. A much below-normal temperature hazard covers areas where minimum temperatures are forecast to average 10 degrees or more below normal across the Great Basin, with freezing temperatures extending to the San Joaquin Valley of California.
Much below-normal temperatures are posted for mainland Alaska through Jan 22, where the 6z GFS ensemble mean indicates surface temperatures averaging more than 16 degrees F below normal. The deterministic models continue to indicate that a potent low pressure system (around 964-hpa) will enter the northern Gulf of Alaska and bring high winds (50 knots or greater) to the Aleutians, northern gulf coast of Alaska, and the Alaska Panhandle on Jan 23 and 24. Heavy precipitation (1.5 inches or more, liquid equivalent) is forecast for parts of southeast mainland Alaska and the Alaska Panhandle on Jan 24 and 25.
For Thursday January 26 - Wednesday February 01: The ensemble means are in good agreement with a major pattern change becoming established by the Week-2 period. The amplified ridge (trough) over western (eastern) North America favors a much drier pattern throughout the lower 48. However, the potential for cyclogenesis exists near the East Coast, depending on where the amplified trough axis is located. A trend towards more seasonal temperatures is expected across the eastern U.S. during Week-2.
Surface high pressure centered over the Great Basin and strong low-level inversions favor a moderate risk of much below-normal temperatures across the Great Basin through at least January 28. A slight risk of much below-normal temperatures is introduced today across the southeastern U.S. from Jan 28 to 31, where the GEFS reforecast tool indicates that minimum temperatures have a 20 percent chance of falling below the 15th percentile compared to climatology and subfreezing temperatures are most likely.
An upper-level trough, located south of the Aleutians, favors multiple low pressure systems with onshore flow affecting southeast Alaska and the Alaska Panhandle early in Week-2. Heavy precipitation (rain and high-elevation snow with amounts of more than 1.5 inches per 24 hours) and high winds (speeds greater than 50 knots) are posted for these areas through January 29.
According to the latest U.S. Drought Monitor (USDM) valid on January 10, the coverage of severe or greater drought for the CONUS decreased from 8.63 to 7.96%. One to two category improvements were made to the drought areas across parts of California and Nevada from the previous week.
Forecaster: Brad Pugh
$$