Valid Thursday, February 28, 2019 to Monday, March 11, 2019

Summary of Forecasts and Hazards

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST November 15 2025

Synopsis: *** Week-2 U.S. Hazards Outlook will be updated later this afternoon Eastern time ***

Mid-level high pressure over Alaska and mid-level low pressure over the western contiguous U.S. (CONUS) are both predicted to strengthen early in the week-2 forecast period. Mid-level high pressure is also forecast across the eastern CONUS. This mid-level pattern is expected to drive various hazards across the Lower 48 states during the week-two forecast, including an inflow of Arctic air, heavy mountain snow, and gusty winds for portions of the West. Parts of the central and eastern CONUS may be impacted by heavy precipitation, heavy snow, gusty winds, and flooding.

Hazards

• *** Week-2 U.S. Hazards Outlook will be updated later this afternoon Eastern time ***
• Slight risk of heavy precipitation for eastern portions of the Southern Plains, Middle and Lower Mississippi Valley, Ohio and Tennessee Valleys, and adjacent parts of the Southeast, Sat-Sun, Nov 22-23, and Thu-Fri, Nov 27-28.
• Slight risk of heavy snow for much of the mountainous West, Sat-Fri, Nov 22-28.
• Slight risk of heavy snow over much of the Northern Plains and Minnesota, Tue-Fri, Nov 25-28.
• Slight risk of much below-normal temperatures across much of the western half of the CONUS, Mon-Fri, Nov 24-28.
• Slight risk of high winds over much of the eastern CONUS, Sat-Sun, Nov 22-23.
• Slight risk of high winds from the West coast eastward across the Intermountain region and Rockies to the High Plains, Sat-Fri, Nov 22-28.
• Flooding possible in the general vicinity of the Arklatex.

Detailed Summary

For Tuesday November 18 - Saturday November 22: WPC Days 3-7 U.S. Hazards

For Sunday November 23 - Saturday November 29: *** Week-2 U.S. Hazards Outlook will be updated later this afternoon Eastern time ***

Early in the week-2 period, an amplifying mid-level ridge over Alaska is expected to contribute to the deepening of a mid-level trough downstream over the western CONUS. This scenario is predicted to bring anomalously warm air to Alaska and anomalously cold Arctic air to the western Lower 48 states. Significantly anomalously warm temperatures predicted in southwestern Alaska favors precipitation in the form of rain rather than snow for many areas, which could lead to a number of hazardous impacts including coastal erosion, flooding, and a decrease in the stability of ice on rivers and lakes. For the western CONUS, temperatures are expected to fall below 20 deg F in many areas, and a hard freeze (28 deg F) is a significant concern for near-coastal areas of the Pacific Northwest, including Seattle and Portland. These minimum temperatures could bring an end to the growing season across Oregon's Willamette Valley, and are supported by 0z runs of the ECENS and GEFS. A slight risk of much below-normal temperatures are favored across much of the western half of the CONUS, Nov 24-28.

As the mid-level trough deepens across the West and progresses slowly eastward, a slight risk for heavy snow is posted for much of the mountainous West, Nov 22-28. This is consistent with raw (uncalibrated) snowfall guidance from the ECENS and GEFS, with predicted snowfall totals in excess of 6 inches, and locally a foot or more in the highest elevations. Broad cyclonic curvature and cold air aloft is expected to maintain the necessary instability to generate significant snowfall across the West, significantly boosting mountain snowpacks in the process. In addition to the predicted arctic air and heavy snow hazards across the West, increased chances for gusty winds of 20-30 mph or more are indicated by the ECENS and GEFS Probabilistic Extremes Tools (PETs) wind guidance and further supported by forecast 10-meter wind speeds from the 0z ECENS ensemble mean, and the expectation of tighter surface pressure gradients. These tighter pressure gradients are expected to be near the southern edges of advancing arctic air masses surging southward across the West. Accordingly, a slight risk of high winds is favored across the Western CONUS for the duration of week-2.

Over the Central CONUS, leeside cyclogenesis is predicted by the GEFS and ECENS models, with several surface low pressure centers tracking from the vicinity of eastern Colorado towards the Upper Great Lakes region, which is a very common storm track for late November. A slight risk of heavy snow (>85th historical percentile and 4-6+ inches) is posted for the northern flank of one of these disturbances as it tracks towards the Upper Great Lakes region during the second half of the forecast period. The area expected to be most affected by this storm system includes the northern Great Plains and portions of the Upper Mississippi Valley. Surface high pressure off the Southeast coast favors an increase in moist southerly return flow and heavy precipitation across south-central and southeastern portions of the CONUS as far north as the Ohio Valley, on Nov 22-23. A second round of heavy precipitation is indicated by multiple numerical models on Nov 27-28, in response to another passing disturbance. Precipitation amounts of at least 1-inch are forecast (3-day period), and as much as 4-7 inches of precipitation are predicted for much of this same area during the preceding week-1 period. As a result, an area of possible flooding is deemed most likely in the Arklatex region.

In the East, dynamical models indicate a frontal system anticipated to pass through the region early in the period, accompanied by gusty northwesterly winds of 20-25 mph. Lake-enhanced precipitation is expected to be fairly light in the wake of this system. However, if the arctic air predicted to impact the western CONUS during week-2 moves across the eastern CONUS after the week-2 period, the colder air streaming over the relatively warm waters of the Great Lakes will most likely result in more substantial lake-effect precipitation for the typical climatological snowbelt areas downwind of the Lakes.

Forecaster: Anthony Artusa

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