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Displaying AFOS PIL: AFDDTX Received: 2017-08-22 07:42 UTC
298 FXUS63 KDTX 220742 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 342 AM EDT Tue Aug 22 2017 .DISCUSSION... Overall picture currently shows the placement of the surface low over the northern Great Lakes as it continues to trek eastward. The cold front associated with this system was laid out across WI and back into IA. This front will continue to slide east and will be the focus for rain/storms to Southeast Michigan this morning into the afternoon. A line of storms over southwest Michigan at issuance time will continue to push east/northeast through the morning hours and will provide another round of storms to the area around sunrise. Behind this initial line, a more expansive coverage area of rain/storms moves in. Area continues to be outlooked in general thunder for the day. A weakening trend is currently be seen with the initial line of storms as they push across lower Michigan. Working against the severe threat will be the timing of the front. The bulk of the activity will be during the morning/early afternoon hours, thus cutting into any increasing instability associated with diurnal heating as skies remain overcast. Better instability will stay to the south and east of the state which coincides with SPC's outlook of general thunder over much of the CWA and the slight risk off to the southeast. Dynamics are still there given the front itself and the area will continue to see rain and thunderstorms during this time with the main threats being heavy rainfall and gusty winds in the moisture rich environment. Rain and isolated storms will move into portions of the CWA in the next couple of hours. Current radar trend shows this line with a break in the rain before activity increases again just ahead of the front. Main frontal passage will take place later this afternoon with activity pushing off towards the east by 00Z Wednesday. CAA behind the front will bring in cooler and drier conditions this evening, bringing an end to the humidity that has been around the past few days. Temperatures will be more pleasant for the remainder of the week as highs stay in the lower to mid 70s with lower dewpoints in the upper 40 to low 50 degree range. As the gradient weakens and troughing pushes east towards the East Coast, high pressure starts building in. This high will set up across the Great Lakes area bringing quiet weather conditions to the area through the weekend. && .MARINE... Moderate southwest wind will continue over marine areas during the morning ahead of a strengthening low pressure system and cold front. Early morning observations over the southern Great Lakes indicate wind conditions holding below SCA thresholds leaving widespread showers and thunderstorms along and ahead of the front as the primary marine weather impact before the frontal passage. Saginaw Bay will be an area to watch for funneling of enhanced southwest flow that could produce gusts around 25 knots at times. Low pressure near the Straits during the morning will move toward James Bay and deepen considerably during the afternoon based on the latest model depictions. The stronger trend on this system now makes northwest gales likely over the open waters of northern Lake Huron beginning late afternoon through tonight and a gale warning is in effect during this time. Waves exceeding SCA threshold will brush the northern Thumb tonight where a SCA is in effect. Elsewhere, the wind pattern will be from the northwest enough to keep the highest waves offshore of the southern Lake Huron nearshore zones and generally in the 1 to 3 ft range on Saginaw Bay before the wind weakens Wednesday and then veers toward the north Thursday. As the wind diminishes, the incoming air mass will be cold enough to produce instability over the water adequate for marginal waterspout potential. && .HYDROLOGY... A low pressure system near the Straits during the morning will move into Canada while pulling a strong cold front through Lower Michigan today. Warm and humid air in place ahead of the front will fuel showers and thunderstorms beginning during the morning and lasting into early evening. Basin average rainfall totals remain projected in the 0.25 to 0.50 inch range today. Locally higher amounts of 1 to 2 inches are possible where lines of storms or multiple rounds of thunderstorms occur which will make localized flooding possible in prone areas. Otherwise, flooding potential will be limited by the fast movement of the associated cold front which is timed to exit eastward by early evening. && .PREV DISCUSSION... Issued at 1215 AM EDT Tue Aug 22 2017 AVIATION... Showers/storms upstream will shift into the area later tonight through morning within broad surge of higher theta-e air in advance of an approaching cold front. This front will sink through the region during the afternoon bringing a chance of one more round of scattered convection later in the day. A tightening pressure gradient and strong mixing will lead to rather gusty conditions with 25+ knot gusts expected at times during the afternoon. Clearing skies and weakening winds can then be expected by evening in the wake of this fropa. For DTW...Best chance for storms will come late tonight through the morning with a secondary chance along the cold front by afternoon. Wind gusts to 25 knots will be quite possible, generally in advance of front with a direction from 250-260 degrees during the mid afternoon peak. //DTW THRESHOLD PROBABILITIES... * Medium for a thunderstorm during the morning. * Medium for ceilings aob 5000 feet. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...Gale Warning from 5 PM this afternoon to 5 AM EDT Wednesday for LHZ361-362. Small Craft Advisory from 8 PM this evening to 5 AM EDT Wednesday for LHZ441. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ DISCUSSION...SP MARINE.......BT HYDROLOGY....BT AVIATION.....DG You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.