Plateau Weather

Forecast Discussion

— Extended
Office: KWBC Issued: Mar 16, 2026 at 3:57 PM EDT PMD

Overview

An amplified upper level flow pattern will be in place through late week, shifting to more zonal early next week. A highly anomalous upper ridge will be in place across the Southwest as the period begins Thursday, bringing continued summerlike heat that should set numerous daily and scattered March temperature records for California, the Intermountain West, and spreading into the Plains. This region should gradually moderate but still remain warm into early next week. Just north of the ridge, the southern end of an atmospheric river could cause heavy rain in the Pacific Northwest especially through Thursday. Downstream, upper troughing will be in place in the East, with reloading energies in the Northeast and uncertain low pressure possibly causing rain and snow.

Guidance/Predictability Assessment

Model guidance remains in good agreement for the early part of the forecast period, including the upper high atop the Southwest reaching over 594dm at times. Downstream, the trough axis should slowly move across the East late week. Into next weekend, the initial trough should move into the Atlantic, but northern stream energy could affect the northeastern quadrant of the U.S. along with possible surface low pressure. These features are considerably more uncertain, with a lot of run to run inconsistency, so expect future forecast changes. The 06Z AIFS was among the strongest with the energy and surface low by Sunday, but the 12Z AIFS does not dig the energy quite as deep into the East. Deterministic models generally vary in timing and depth without a lot of consensus. Farther west, CMC runs start to become a little out of phase with indicating troughing in the Intermountain West by early next week and suppressing the Southwest ridge more than other guidance. The WPC forecast was based on a multi-model blend early, but ensemble means reached half the blend Day 6 and more Day 7 given the increasing model differences.

Weather/Hazards Highlights

Warm to hot temperatures are forecast to break March records across much of the southwestern U.S. mid to late week as a massive upper ridge builds in, peaking in intensity Thursday into Friday. Highs are forecast to soar past 100 degrees for the first time this season (and earliest on record) for the lower elevations of southern California (away from the coast) and Arizona. Numerous daily records will be broken by the middle to end of the week, and many monthly March records are also likely. Extreme Heat Warnings are already in effect to account for this and also for how early in the season this is. Widespread warmer than average temperatures by 20 to 30 degrees will also be a concern across much of the Intermountain West and the Plains into late week, with temperatures in the 80s into the central Great Basin and central Plains, and 90s in the southern Plains. Expect temperatures to stay above average across the western to south-central U.S. into early next week, but moderated compared to this week.

One more cold morning is expected in the Southeast on Thursday underneath a chilly surface high behind a cold front, leading to potential frost/freeze concerns in areas where vegetation could be sensitive. The Southeast should gradually warm up through the rest of the period to above average temperatures, but farther north upper troughing atop the northeastern U.S. will gradually lead to cooler temperatures. The exact timing of the trough(s) and related surface low/frontal systems are uncertain, but a pattern of rain and inland snow are possible across the Great Lakes and Mid- Atlantic/Northeast at times late this week into early next week.

In terms of excessive rainfall, the only concern will be the Pacific Northwest, where the southern side of an atmospheric river will affect Washington into Thursday and Thursday night. Continue to maintain a Day 4 Marginal Risk for flooding concerns especially after the already wet pattern in the short range. The AR should lessen in strength by Friday and beyond, but some additional precipitation is possible, reaching the northern Rockies as well. Other parts of the country should remain mostly dry.