Composite Map Day 8-14

Probabilistic Outlooks Temperature Hazards Precipitation Hazards Wind Hazards Snow Hazards

Valid Wednesday March 18, 2026 to Tuesday March 24, 2026

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT March 10 2026

Synopsis: Very strong mid-level high pressure is expected to develop over the Interior West to promote unseasonably warm temperatures for much of the western U.S next week., as well as increase the risk of Santa Ana winds for southern California. East of the Rockies, mid-level low pressure is favored to bring a brief round of colder than normal temperatures following a very warm week-1 period over the eastern U.S.. The potential for subfreezing temperatures may adversely impact emerging early spring vegetation for parts of the southeastern U.S. early in the period. There is a lingering potential for enhanced onshore flow over the Pacific Northwest, which may bring heavy precipitation amounts to portions of western Washington, along with periods of high winds for the Interior northwestern contiguous U.S. (CONUS). Persistent mid-level high pressure to the west of the Bering Strait is expected to bring a period below normal and potentially impactful temperatures, with this threat gradually easing for much of Alaska later in week-2.

Hazards

• Slight risk of heavy precipitation for the Pacific Northwest, Wed-Thu, Mar 18-19.
• Slight risk of high winds for portions of the coast of Washington and northwest Oregon, Wed-Thu, Mar 18-19.
• Slight risk of high winds over the Northern and Central Rockies and into the Great Plains, Wed-Thu, Mar 18-19.
• Slight risk of high winds for portions of southern California, Wed-Sat, Mar 18-21.
• Slight risk of much above-normal temperatures for much of the western CONUS, Wed-Sun, Mar 18-22.
• Slight risk of much below normal temperatures for portions of the Lower Mississippi and Tennessee Valleys, and the Southeast, Wed, Mar 18.
• Slight risk of much below normal temperatures over much of southern and western Mainland Alaska and parts of the Southeast, Wed-Sun, Mar 18-22.
• Slight risk of high winds over the southern coast of Alaska and Southeast Alaska, Wed-Sun, Mar 18-22.

Detailed Summary

For Friday March 13 - Tuesday March 17: WPC Days 3-7 U.S. Hazards

For Wednesday March 18 - Tuesday March 24: Since yesterday, there is good consistency in the dynamical model 500-hPa height forecasts featuring a highly amplified ridge centered over the Interior West, with a deep trough downstream that begins to lift out over the eastern U.S heading into the week-2 period. There are however a few notable discrepancies in the mid-level height pattern between the GEFS and ECMWF ensembles contributing to some uncertainty in the outlook over the CONUS. The first concerns the troughing across the east, where the ECMWF is quicker to deamplify this feature than the GEFS, resulting in a weaker and shorter period of anomalous cold across the southeastern U.S. early in the period. Secondly, more amplified ridging is favored in the ECMWF upstream across the Interior West where 591 dam heights peaking over the southwestern U.S. early in week-2 translates to nearly 3 standard deviations above climatology. With anomalies of near equal strength favored to persist for much of next week, there is a higher and more expansive coverage of positive surface temperature departures west of the Mississippi throughout the period than the GEFS. Across Alaska, there remains good model agreement featuring strong ridging situated to the west of the Bering Strait persisting throughout the period, where downstream northerly flow is expected to bring below normal temperatures throughout the period for the entire state.

In conjunction with 500-hPa troughing established over the Gulf of Alaska, the stronger ridging favored across the West is expected to shunt any of the enhanced onshore flow to the north closer to British Columbia. This is supported in both the raw and calibrated precipitation tools which depict the highest probabilities for locally heavy precipitation mainly north of the Canadian border. Although Integrated Vapor Transport (IVT) Tools continue to highlight elevated chances for amounts exceeding 250 kg/m/s focused further south over the Pacific Northwest, deference is given to the drier solutions in the precipitation tools which better aligns with the prevailing mid-level pattern. A slight risk of heavy precipitation remains issued over western Washington where both the GEFS and ECMWF show increased chances (10-30%) for 3-day amounts exceeding 2 inches. Any increased precipitation may keep streamflows elevated within the highlighted region. The slight risk of high elevation heavy snow is discontinued for the Cascades due to a lack of support in the raw snow tools for amounts exceeding 6 inches and no signal in the Snow Water Equivalent (SWE) PET for values exceeding the 85th percentile. However, a pair of slight risk areas for high winds remain posted (Mar 17-18) over coastal portions of Washington and Oregon, as well as over the downslope regions of the Northern and Central Rockies where the Probabilistic Extremes Tool (PET) maintain at least a 20% chance of wind speeds exceeding the 85th percentile. Later in week-2, both ECMWF and GEFS ensembles feature some eastward progression of the strong mid-level ridging over the West to allow for the troughing upstream to dig further south over the northeastern Pacific. As a result, increased precipitation is favored over parts of western Oregon and northern California by mid week-2, however amounts are not supportive of any corresponding hazards at this time.

The strong mid-level ridging centered over the Great Basin also supports an increased risk of offshore flow and Santa Ana winds for portions of southern California. Since yesterday, ensembles have become somewhat stronger with the development of surface high pressure over the Four Corners, and there are better indications for the development of thermally induced low pressure in the Sonoran Desert to support this setup. Therefore, a slight risk of high winds remains posted for portions of southern California and is extended through Mar 21 before the anomalous ridge center deamplifies and shifts eastward. Accompanying this wind potential is an increased likelihood for much above-normal temperatures for much of the southwestern CONUS. The National Blend of Models (NBM) continues to show a high number of locations nearing record breaking daytime temperatures across the Northern Intermountain, Rockies, Great Basin, California and the Desert Southwest. While actual temperatures are not quite warm enough (lower 100 deg F) in the Sonoran Desert to support an extreme heat hazard, the unseasonable warmth looks to contribute to an early onset of spring snowmelt over the higher elevations where snowpack has already been well below normal across the West. Snowmelt is expected to significantly increase this week and lead to increased flows and affected rivers. Therefore, a slight risk of much above normal temperatures is posted (Mar 18-22) for much of the western CONUS and is expanded northward relative to the previous outlook to include parts of the Northern Rockies where PETs show elevated chances for maximum temperatures exceeding the 98th percentile through the middle of week-2. A moderate risk area was considered for inclusion based on the ECMWF temperature guidance, however the comparably weaker height and temperature solutions from GEFS and Canadian preclude a higher risk designation at this time.

Tied to the deamplifying trough over the eastern U.S., the Weather Prediction Center (WPC) day 7 (Mar 17) surface analysis depicts strong surface high pressure and accompanying anomalous cold air becoming established over the Lower Mississippi and Tennessee Valleys. While the strongest negative temperature anomalies favored further north, PETs continue to show increased chances for near to subfreezing temperatures to the south over portions of the Lower Mississippi and Tennessee Valleys. While such temperatures are not expected to be extremely cold, such a cooldown follows a very warm week-1 across the southeastern CONUS, where the possible return of frost and freezes may be a shock to any emerging spring vegetation for the lower latitudes of the CONUS. Therefore, a slight risk of much below normal temperatures remains posted from the Lower Mississippi Valley to the Carolinas, but is now only valid for day 8 (Mar 18) based on a fast moderation of temperatures in the ECMWF.

Due to the predominately drier conditions favored during week-2 over the Ohio Valley with conditions expected to fall below flood stage in the region late in week-1, the flooding possible hazard is removed in the updated outlook. Notwithstanding, any additional rainfall over the White River Valley of Indiana may worsen saturated ground conditions as this region has registered more than 5 inches of precipitation during the week, with additional rainfall amounts forecast based on WPC week-1 QPF.

Over Alaska, anomalous 500-hPa ridging west of the Bering Strait with downstream troughing over the Mainland and Gulf of Alaska is favored to bring well below-normal temperatures for the state. Over time, ensembles show a gradual breakdown of the mid-level troughing over the state, where there are lowering chances for minimum temperatures falling below the 15th percentile in the PETs. Therefore, a slight risk of much below normal temperatures is maintained for much of Alaska, but is now valid through Mar 22. This mid-level transition also brings a less deep mean surface low in the Gulf of Alaska to induce high wind speeds, and the slight risk of high winds is also adjusted, now valid through Mar 22. Within the highlighted wind risk area, freezing sea spray remains a concern due to the colder temperatures favored during the period.

Over the Central Pacific, mid-level troughing and associated Kona low development are favored to bring potentially heavy rainfall to the Hawaiian islands during week-2, which is reflected in both the GEFS and ECMWF PETs. While actual 3-day totals have lessened in these tools compared to earlier guidance, this threat of heavy precipitation looks to persist with little indication of dryness later in March.

Forecaster: Nick Novella

$$ Please consult local NWS Forecast Offices for short range forecasts and region-specific information.

Resources

Week-2 Probabilistic Extremes Tool

GFS Ensemble Forecasts