wdt hazardous weather outlook 5/12/2017 · day 1 threat regions map day 2 threat regions map wdt...

Threat LegendOrange – Strong to Severe Thunderstorms PossibleRed – Significant Severe Thunderstorm ThreatPurple – Severe Weather Outbreak (Day 1 and 2 Only)Green – Excessive Rainfall

Blue – Significant Snow/Ice

Day 1 Threat Regions Map Day 2 Threat Regions Map

WDT HAZARDOUS WEATHER OUTLOOK 5/12/2017

Days 1 – 2 (Short Term) Threat Summary

DAY 1

SOUTHEAST: SEVERE THUNDERSTORMS POSSIBLE

MONTANA: SEVERE THUNDERSTORMS POSSIBLE

MID-ATLANTIC: HEAVY TO EXCESSIVE RAINFALL POSSIBLE

DAY 2NORTHEAST: EXCESSIVE RAINFALL POSSIBLE

FLORIDA/GEORGIA: ISOLATED STRONG TO SEVERE THUNDERSTORMS POSSIBLE

Day 3

Day 6

WDT THREATS AT A GLANCE – Days 3 Through 7 5/12/2017

Day 4

Day 5



Day 7



Day 1 – Friday Threat Assessments and Morning Frontal Analysis Threat Region Discussion:

Southeast: Low pressure system that was in the Central Plains yesterday will track east-southeastwards into the Southeast on Friday. The lows associated cold front will also track eastwards throughout the day as well, tracking from the Arklatex region to the Southeast by Friday evening. During the morning hours, ongoing rain and thunderstorm activity in Arklatex will slowly be moving eastward and most if not all of this activity will be sub-severe in nature. Then as we get into the afternoon, daytime heating and ample moisture across portions of the deep south and the Southeast ahead of this cold front should lead to at least some modest instability, regardless of morning cloud cover in the region. This is forecast to result in a renewed threat for strong to severe thunderstorm activity across the region. At this time damaging wind gusts and large hail seem to be the primary hazards, however and isolated tornado or two cannot be ruled out either.

Montana: As an upper level disturbance tracks eastward across the Pacific Northwest, a cold front will track across Montana during the afternoon. With daytime heating creating some modest instability across the region and the front providing ample lift, scattered showers and thunderstorms are forecast to increase in coverage and intensity with a few of these storms becoming strong to severe. Large hail and maybe an isolated strong wind gust or two will be possible with any of the stronger storms.

Mid-Atlantic: A quasi-stationary boundary will remain draped across portions of the Southeast during the morning hours. As we get into the afternoon and evening hours a surface low is forecast to form just offshore the Carolinas along this boundary and track northeastwards continuing to bring ample moisture into the Mid-Atlantic and Southeast. With this low providing the lift and ample moisture in place, moderate to heavy rainfall will begin to increase in coverage across the Mid-Atlantic tonight as the low begins to strengthen. Current model guidance suggests that general rainfall amounts of 0.50 to 1.0 inches, locally 2.0+, will be possible. With the ground already saturated from the previous days rain, an increased risk of flash flooding and excessive runoff will be possible during the overnight hours.



Day 2 – Saturday Threat Assessments and Morning Frontal Analysis Threat Region Discussion:

Northeast: Low pressure system that had formed offshore the Carolinas last night will continue to track northeastwards towards the Gulf of Maine on Saturday, rapidly strengthening as it approaches the Northeast. As this occurs ample moisture from the Atlantic will filter into much of the Northeast resulting in heavy to excessive rainfall across the region. Forecast guidance suggests that general rainfall amounts of 1 to 2 inches, locally 3+, will be possible across the region with the heaviest amounts likely begin found along the coastline. This will result in an increased threat for flooding and excessive runoff across portions of the Northeast on Saturday. In addition to this heavy rain, strong winds along the coast could also increase the risk for downed trees and power lines as well.

Florida/Georgia: As a cold front approaches Florida and Georgia, ample low level moisture combined with some modest instability will lead to an increase in shower and thunderstorm activity just out ahead of the front Saturday afternoon and evening. Some of these storms could become strong to severe in nature with damaging wind gusts and some small hail being the primary hazards within any of the stronger thunderstorms.



Day 3 – Sunday Threat Assessments and Morning Frontal Analysis Threat Region Discussion:

New England: Strong low pressure system near Cape Cod will continue to track northeastwards towards the Canadian Maritimes Sunday into Monday. As this occurs heavyto excessive rainfall will fall across portions of New England on Sunday. Model guidance currently suggests that 1 to 2 inches locally 3+ will be possible across the threat region,resulting in and increased risk for flooding and excessive runoff.

Elsewhere given the slow moving nature of this system, scattered showers and overall general cloudiness across the rest of Northeast are forecast to continue on Sunday. Across the Southeast fair conditions are forecast as high pressure will be entrenched across the region. With this high pressure system in the Southeast, return flow will also begin to set up across the Great Plains on Sunday bringing warm moist air northwards.

Further west a large upper level trough will finally make its way to the West Coast and slowly begin to move eastwards. As this occurs multiple upper level disturbances will eject into the Intermountain West/High Plains Sunday night into Monday. With these disturbances moving across the region a new surface low will form near Montana Sunday night resulting in the possibility for some scattered showers across the Montana and North Dakota late Sunday.



Day 4 – Monday Threat Assessments and Morning Frontal Analysis No Threat Regions:

Low pressure out in the Intermountain West will slowly begin to track eastwards into the High Plains Monday into Tuesday. As this occurs a stationary boundary out to the east of this surface low will become a warm front and slowly begin to track eastwards as well. With moist air being brought northwards into the Upper Midwest and High Plains moderate to possibly heavy rainfall and some thunderstorms are forecast to form across the region. At this time rainfall amounts and thunderstorm activity are forecast to remain below excessive rainfall and severe criteria so no threat region has been outlined in the Upper Midwest, however, a threat region may be introduced across the Upper Midwest for excessive rainfall if model guidance continues to show heavy rainfall across the region. To the south of this warm front, southerly flow will continue to bring warm moist air northwards into the Southern and Central Plains, however, with no frontal boundary around the region to promote forcing little to no shower and thunderstorm activity is anticipated at this time across the Southern and Central Plains.



Day 5 – Tuesday Threat Assessments and Morning Frontal Analysis Threat Region Discussion:

Central/Southern Plains: A dryline is forecast to set up across western Nebraska southward into west Texas and move little throughout the day. Southerly flow out ahead of the dryline will continue to bring warm moist air into the region. With daytime heating creating ample instability and the dryline creating ample forcing, shower and thunderstorm activity is forecast to increase in intensity and coverage during the afternoon and evening hours with some of these storms becoming strong to severe in nature. At this time forecast guidance suggests that all severe weather hazards will be possible with any of the stronger storms.

Day 6 – Wednesday Threat Assessments and Morning Frontal Analysis

Discussion: Low pressure that had brought severe weather to the Plains yesterday will continue eastwards towards the Great Lakes. As this low tracks eastwards, early morning rain and thunderstorms will also track eastwards across eastern Oklahoma into the Arklatex region. Although none of this early morning activity is forecast to be severe in nature, daytime heating will create ample instability out ahead of these showers and storms creating a renewed threat for strong to severe thunderstorms late Wednesday. In addition to this severe weather threat, given the continuous rounds of rain and thunderstorms across the same region heavy to excessive rainfall will also be possible across Texas and Oklahoma on Wednesday. Further to the west mountain snow and valley rain will be possible as another low forms near the Four Corners region on Wednesday. By Thursday pretty benign conditions are forecast to set up across a majority of the country with just some light rain and mountain snowfall across portions of the Intermountain West and some scattered shower activity across Arklatex.

Day 7 – Thursday Threat Assessments and Morning Frontal Analysis

wdt hazardous weather outlook 5/12/2017 · day 1 threat regions map day 2 threat regions map wdt...

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