Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 281653 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1253 PM EDT Wed Jun 28 2017 .AVIATION...
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Upstream radar trends indicate showers and a few storms surviving the usual morning weakening pattern for nocturnal convection. Mid level moisture transport is strong enough to maintain at least scattered shower coverage that is expected to brush through MBS during late afternoon and early evening. This is projected to be VFR outside of thunderstorms, coverage of which will be monitored for possible inclusion in later updates. A new round of surface based storms will then develop over the Midwest today and move into lower Michigan overnight in a weakening phase. Coverage of showers will then combine with the advancing warm front and warm sector to make MVFR possible through Thursday morning. The strong low level jet during the night prior to the warm front passage continues to warrant mention of low level wind shear through mid Thursday morning. For DTW... Added a prob mention of weakening showers to the forecast for late tonight through mid Thursday morning. This activity could combine with the advancing warm front for ceiling below 5000 ft while MVFR is more likely farther north. //DTW THRESHOLD PROBABILITIES... Low for ceiling 5000 ft or less overnight into Thursday morning.
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&& .PREV DISCUSSION... Issued at 413 AM EDT Wed Jun 28 2017 DISCUSSION... Upper energy pushing from the Central Rockies into the Plains this morning will work across the Great Lakes tonight, at the nose of an upper jet streak. Strong area of diffluence ahead of this feature interacting with northeastward advancing warm front/surface low pressure, and strong surge of the low-level jet will allow complexes of thunderstorms to develop over the Plains and Upper Midwest today. This activity should then progress eastward into Michigan during the afternoon and evening. Best potential for activity to be sustained as it progresses into the State looks to be more over Northern Lower Michigan, where the nose of the 60+ knot low-level jet will work in. Forecast soundings for Southeast Michigan still signal the influence of the exiting area of high pressure and shortwave ridging, with warmer mid-levels and a fairly dry airmass that will require better forcing to overcome it and/or strong moisture transport before we can see much activity. Forecast is dry for the first half of the day before showers begin working into the area from upstream during the late afternoon and evening. Activity will likely be in a state of decay as it fights a more hostile airmass, leading to just shower chances mainly north of I-69 through 03Z/11PM. Temperatures today will moderate a little as weak warm air advection occurs on the northern periphery of high pressure over the Ohio Valley. This should boost max temps into the mid-upper 70s. Some forecast models still drop an occluded front southward through Lower Michigan during the overnight hours, while others at minimum show strong theta-e advection within the warm sector south of the warm front. Either could serve as a focus for renewed convection over Southern Michigan as mid-level lapse rates steepen and low- level jet core surges up through Central Michigan. Elevated instability will increase as a result, with NAM/GFS Showalter indices falling between -1 and -3C allowing thunderstorms to begin developing. Most of the activity looks to still be focused over Northern Michigan, potentially keeping areas near the Ohio border dry until Thursday. Severe threat tonight looks limited, as does coverage of convection overnight. Although 0-6km bulk shear values increase to 30-40 knots, CAPE density above the low-level inversion does not look too impressive for large hail. Elevated convection will also limit wind gust potential. Heavy rain could occur with thunderstorms, but fast storm motion and more limited coverage will mainly keep the heavy rain threat north of the forecast area. Convection forecast for the end of the week then become more uncertain as it will in part become reliant on placement/coverage of previous rounds of convection and recovery from them. General message is that rounds of rain/thunderstorms will be possible Thursday through at least Friday night. Low-level boundary will continue to drop south through Southern Michigan on Thursday as weak surface low lifts through the U.P. of Michigan. Better coverage of convection will be roughly south of I- 69 as drier air works into northern Michigan during the afternoon. SPC has areas south of I-69 in a marginal risk as instability builds ahead of the boundary and storms become surface-based. Other forecast themes for Thursday are breezy conditions, with warmer and more humid airmass as dewpoints rise into the 60s. Upper low over Alberta will be the next big player in our weather for the end of the week. This wave will drop into the Midwest on Friday, kicking surface low pressure across the Northern Great Lakes. Warm front will lift through Lower Michigan Friday, bringing another surge of warm air and moisture. Temps warming into the upper 70s to mid 80s with dewpoints well into the 60s should allow CAPE to build through the day, while 0-6km bulk shear values increase to as high as 40 knots in the proximity of the warm front. This will bring a slightly higher severe threat, with SPC Day 3 outlook including all of Southeast Michigan. Threat for showers/tstorms will continue into the overnight hours as a cold front pushes through the region. MARINE... Southerly winds will develop in the wake of high pressure this morning. A moderate increase in wind speed may lead to a brief period of gusts near 25 knots across Saginaw Bay this afternoon. Maintenance of a firm southerly breeze into tonight will then support a more definitive increase in gust potential, leading to small craft conditions across Saginaw Bay. The potential for thunderstorms will exist tonight, particular across central and northern sections of lake Huron. Moderate southerly wind will sustain a warm and unstable environment through the latter half of the week. This will maintain unsettled conditions, with the potential for thunderstorms Thursday through Friday night. HYDROLOGY... Low pressure tracking into the northern great lakes will bring the potential for rain and thunderstorms this evening and tonight. The greatest potential will exist north of I-69, where rainfall amounts between one quarter and one half inch will be possible through Thursday morning. Additional showers and thunderstorms may develop throughout Thursday and Thursday night as warm and increasingly humid air builds into the region. The threat for rainfall will tend to focus south of the I-69 corridor during this time as a frontal boundary sinks into the region. Average rainfall amounts generally less than one half inch, but localized higher amounts in excess of an inch will be possible within any more concentrated areas of thunderstorms. Another low pressure system tracking west of the region will maintain the threat for thunderstorms Friday and Friday night. Should a more focused region of heavy rainfall emerge, then the potential for a corresponding rise of area rivers and streams, as well as minor flooding will be possible. While river flooding continues to ease across central Lower Michigan, this corridor will be the most susceptible to flooding risks. && .DTX WATCHES/WARNINGS/ADVISORIES...
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MI...NONE. Lake Huron...Small Craft Advisory from 10 PM this evening to 10 PM EDT Thursday for LHZ421-422. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE.
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&& $$ AVIATION.....BT DISCUSSION...HLO MARINE.......MR HYDROLOGY....MR You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.

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