Severe Weather Outlook

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Outlook for Saturday, May 30

Outlook Summary

Isolated severe thunderstorms are possible from the interior Pacific Northwest eastward/southeastward across the northern and central High Plains on Saturday.

Outlook Images

overview

any severe 5%

Detailed Outlook

SPC AC 280712

Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0212 AM CDT Thu May 28 2020

Valid 301200Z - 311200Z

THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE INTERIOR PACIFIC NORTHWEST EASTWARD/SOUTHEASTWARD ACROSS THE NORTHERN AND CENTRAL HIGH PLAINS

### SUMMARY

Isolated severe thunderstorms are possible from the interior Pacific Northwest eastward/southeastward across the northern and central High Plains on Saturday.

East Coast into the Southeast

At the beginning of the period, a cold front is forecast to extend from a surface low over far eastern Quebec southward to Delmarva then back southwestward to the central Gulf Coast then arc westward/northwestward to a low over the central High Plains. This front represents the leading edge of a dry and stable continental air mass that will build southeastward from the northern Plains through the MS Valley into the Southeast. Showers and thunderstorms are possible along and ahead of this front, with the highest coverage expected from the Carolinas into the FL Panhandle. However, weak vertical shear should preclude storm organization and minimize any severe potential across much of the region. The only exception is across eastern ME, where stronger vertical shear could support more organized storms and higher severe potential. However, uncertainty regarding frontal position and storm coverage precludes including any severe probabilities with this outlook.

Pacific Northwest into the High Plains

Farther west, compact cyclone over the northern CA coast early Saturday is expected to devolve into an open shortwave trough as it moves quickly northeastward through the interior Pacific Northwest and northern Rockies. Surface low attendant to this upper system is expected to deepen in the lee of the Cascades before moving into southern British Columbia early Sunday morning. Southeasterly surface winds will strengthen across the northern High Plains, contributing to aggressive northwestward low-level moisture advection. By late Saturday afternoon, mid 50s dewpoints could be in place across much of central and eastern MT. Dewpoints closer to 60 deg F could develop where less boundary-layer mixing takes place near the surface low over eastern WA.

All of these factors contribute to a fairly anomalous pattern for this part of the country. Warm temperatures aloft will keep the area capped until the late afternoon/early evening. Therefore, forcing for ascent near the surface low and shortwave trough is expected to result in thunderstorms. Given the environment, some of these storms may be severe. While guidance has been relatively consistent regarding this scenario, combination of factors needed to produce this environment (i.e. near 60s dewpoints, surface low location, late afternoon/early evening shortwave timing) are still uncertain enough at this forecast range to only introduce 5% severe probabilities.

Aforementioned moisture advection combined with a sharpening lee trough will likely result in scattered convective initiation along the northern and central High Plains. The deeply mixing boundary layer and veering wind profiles could contribute to a few stronger storms capable of strong wind gusts and hail.

..Mosier.. 05/28/2020

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NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z

National Risk Overview

Thursday, May 28
TORNADO: 2%
HAIL: 15%
WIND: 15%
Friday, May 29
TORNADO: 2%
HAIL: 5%
WIND: 15%
Saturday, May 30
ANY SEVERE: 5%
Sunday, May 31
ANY SEVERE: low / uncertain
Monday, June 1
ANY SEVERE: low / uncertain
Tuesday, June 2
ANY SEVERE: low / uncertain
Wednesday, June 3
ANY SEVERE: low / uncertain
Thursday, June 4
ANY SEVERE: low / uncertain

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