Severe Weather Outlook

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Outlook for Saturday, July 4

Outlook Summary

A couple of organized clusters of severe storms may develop across parts of the northern plains Saturday into Saturday night, posing a risk for strong wind gusts and large hail.

Outlook Images

overview

tornado low

wind 15%

hail 15%

Detailed Outlook

SPC AC 031742

Day 2 Convective Outlook CORR 1 NWS Storm Prediction Center Norman OK 1242 PM CDT Fri Jul 03 2020

Valid 041200Z - 051200Z

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SATURDAY INTO SATURDAY NIGHT ACROSS PARTS OF CENTRAL AND EASTERN NORTH DAKOTA INTO NORTHWESTERN MINNESOTA…AND ACROSS PARTS OF EASTERN MONTANA INTO ADJACENT PORTIONS OF NORTHWESTERN SOUTH DAKOTA AND WESTERN NORTH DAKOTA…

CORRECTED FOR TYPO AND WORDING

SUMMARY

A couple of organized clusters of severe storms may develop across parts of the northern plains Saturday into Saturday night, posing a risk for strong wind gusts and large hail.

Synopsis

Models suggest that there may be substantive weakening of prominent mid-level ridging (initially centered near the Southwestern international border through the southern high plains, and extending northeastward across much of the southern Rockies, plains and Upper Midwest) during this period. It appears that this may be largely due to the progression of significant troughing within the westerlies, northeast of the Canadian and northern U.S. Rockies into the Canadian Prairies by late Saturday night.

This may be preceded by a convectively induced or enhanced perturbation migrating eastward along the North Dakota and Minnesota international border area. A weaker trough in the westerlies may lag to the southwest, gradually turning inland of the Pacific Northwest coast, into the northern intermountain region. And stronger (30-50 kt around 500 mb) westerly mid-level flow may develop east-northeast of the northern Rockies, through North Dakota and northern Minnesota.

Downstream, another belt of stronger cyclonic mid-level flow (initially curving southeast of Hudson Bay through the Canadian Maritimes) may amplify southwestward through Quebec, toward the lower Great Lakes and New England. This probably will be accompanied by a reinforcing cold front, in the wake a preceding front which may advance southward/southwestward into parts of the Mid Atlantic.

Otherwise, deep-layer mean flow will remain generally weak across much of the nation, beneath the remnant ridging and weak, lingering downstream troughing across southeastern portions of plains and lower Mississippi Valley into the Southeast.

Seasonable moisture may contribute to destabilization supportive of scattered thunderstorm activity across parts of the southern Rockies and plains into the lower Mississippi Valley, Southeast and Mid Atlantic. Some of this activity could pose at least a risk for strong/potentially damaging wind gusts. However, coverage is expected to remain sparse, resulting in severe probabilities near or below 5 percent. Potential for organized severe storm development appears most probable across parts of the northern plains.

North Dakota into Minnesota

Seasonably moist boundary-layer conditions will be maintained within weak surface troughing, and perhaps along an effective warm frontal zone, beneath the northern periphery of a plume of warm elevated mixed-layer air. In the presence of steep lower/mid tropospheric lapse rates, models suggest that large CAPE on the order of 3000-4000+ J/kg will develop, as the convectively induced or enhanced perturbation progresses along the international border vicinity.

The extent of ongoing convection at the outset of the period associated with this feature remains unclear, but re-intensification of ongoing or new convective development seems probable. In the presence of at least moderately strong deep-layer shear, the environment seems likely to become conducive to organized convection. This may include isolated supercells initially, before convection grows upscale into an organizing cluster. Due to spread within the various model output, some uncertainty lingers concerning more precise time and location.

Eastern Montana into Dakotas

Relatively moist easterly low-level flow may contribute to moderately large mixed-layer CAPE by late Saturday afternoon, as the trough in the westerlies aids forcing for ascent and convective development across the mountains. Activity should develop off the higher terrain into the stronger instability and intensify in the presence of moderate to strong deep-layer shear. A few supercells are possible, with upscale convective growth possible as activity spreads across eastern Montana into adjacent portions of the Dakotas through Saturday evening.

..Kerr.. 07/03/2020

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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z

National Risk Overview

Friday, July 3
TORNADO: 2%
HAIL: 15%
WIND: 15%
Saturday, July 4
TORNADO: low
HAIL: 15%
WIND: 15%
Sunday, July 5
ANY SEVERE: 5%
Monday, July 6
ANY SEVERE: low / uncertain
Tuesday, July 7
ANY SEVERE: low / uncertain
Wednesday, July 8
ANY SEVERE: low / uncertain
Thursday, July 9
ANY SEVERE: low / uncertain
Friday, July 10
ANY SEVERE: low / uncertain

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