Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 171626 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1226 PM EDT Sat Mar 17 2018 .AVIATION...
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SKC with winds light northeasterly to variable wind today becoming calm to variable tonight. /DTW THRESHOLD PROBABILITIES... * None.
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&& .PREV DISCUSSION... Issued at 353 AM EDT Sat Mar 17 2018 DISCUSSION... A ridge of weakening and modifying surface high pressure will remain over Lower Michigan today while a low pressure system slides nearby to the south and a cold front stalls over the northern Great Lakes. Mid and high clouds will be the only sign of the Ohio Valley system over SE Michigan as they stream northward to at least the M-59 corridor, and possibly up to the I-69 corridor, before the system shears toward the Atlantic coast. These clouds will result in some decrease in surface heating initially while the Tri Cities and northern Thumb receive full sun to jump start daytime heating from morning lows in the teens. Even in the south, the timing of the cloud decrease is expected to produce a late bump in surface heating that will help high temperatures achieve guidance values in the lower to mid 40s. The exception will be in the Thumb region where onshore wind from Lake Huron and substantial snow cover will limit readings to the upper 30s. A broad region of high pressure over the Plains will edge into the Great Lakes tonight. This will keep the sky clear and the wind light for another round of efficient radiational cooling. Lows in the lower to mid 20s are preferred and at the cooler end of the guidance range across the area while readings in the upper teens will once again be likely in the typically colder Thumb locations. The front stalling over the northern Great Lakes today will be held there tonight as a weak wave of low pressure ripples along the boundary and within the northern stream upper level flow. The passage of this system through Ontario will then allow the front to move southward through Lake Huron and Lower Michigan but not before a mild day unfolds over most of SE Michigan. This will be primarily due to westerly low level flow and resulting warm advection on top of the already mild high pressure air mass in place over the region. As the surface low exits Georgian Bay, the cold front will release easily southward over the cold Lake Huron water during the afternoon but will otherwise leak more slowly through Lower Michigan under parallel flow aloft. It is also getting to be that time of year when differential heating between the land and water begin to play a substantial role in the shape of the surface pressure pattern, especially with shallow frontal boundaries. Higher resolution versions of the models all show this well and are in reasonable agreement on a late afternoon northeast wind shift in the Thumb and Tri Cities. That will put a halt to the warming trend there after highs in the mid to upper 40s. Moisture will be severely lacking with this system which will lead to just patchy clouds with the frontal passage and full sun to the south. The combination of low level warm advection ahead of the front and mid March surface heating will boost highs easily into the lower 50s with a few mid 50s possible toward the Ohio border. Passage of the front across the rest of Lower Michigan Sunday night will bring temperatures back down below normal by Monday, a trend that will last through the middle of next week. Highs in the 30s will appear solid each day as the larger scale upper air pattern trends out of the recent blocking pattern. The lower amplitude flow still has the Great Lakes under influence of the colder northern stream while the remnants of the Rockies upper low moves through the Ohio Valley, and possibly as far south as the Tennessee Valley. The farther south trend is shown in all of the global models which keeps Lower Michigan dry for now, a trend that will be monitored cautiously during the low predictability transition period in the larger scale pattern. MARINE... High pressure over the region will lead to fairly quiet conditions over the eastern lakes into next week. Winds will be primarily out of the northwest and stay below 20 knots through the weekend until a weak cold front drops through Sunday producing a wind shift to the northeast. High pressure returns quickly on Sunday from the northwest which will keep the northeast flow going into the new week. Though wind gusts look to remain below 25 knots Monday, the long fetch and persistent northeast flow may lead to elevated waves heights in the Lake Huron nearshore zones along the eastern Thumb Monday through midweek. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....JVC DISCUSSION...BT MARINE.......DRK You can obtain your latest National Weather Service forecasts online at is the U.S. government's official web portal to all federal, state and local government web resources and services.