Scientific Forecaster Discussion
Area Forecast Discussion National Weather Service Detroit/Pontiac MI 600 AM EDT WED OCT 26 2016 .AVIATION... Steady increase in mid level moisture this morning well downstream of approaching low pressure. Increasing shower potential with an accompanying reduction in ceiling for the afternoon period, initially holding at VFR. Widespread rainfall with eventual MVFR conditions then develops post-sunset. Extensive MVFR stratus within persistent shower activity locked in right through early Thursday. Easterly winds strengthen through the day, holding firm at 10 to 15 knots into tonight. For DTW...Little evidence to suggest CIGS will drop below 5000 ft yet this morning. Greater confidence for these conditions to emerge this afternoon as moisture steady increases and ceilings lower with time. Easterly winds /070-090 direction/ will strengthen today, holding at the trajectory through tonight. Widespread rainfall in sub 5k ft ceilings solidly in place for tonight. //DTW Threshold Probabilities... * Low in ceilings below 5000 ft this morning. Moderate this afternoon. High after 00z. && .PREV DISCUSSION... Issued at 310 AM EDT Wed OCT 26 2016 DISCUSSION... Sharp Upper Level Trough working through the Northern Plains early this morning, on track to move through the Central Great Lakes Thursday Morning. Additional shortwave/PV energy diving southeast through the Southern Plains as well. Upper level Ridge near Four Corners Region to build during the end of the work week, with some of the warmer air (850 mb temps 8-12 C) spilling northeast into Southern Lower Michigan by Saturday. Today looks to be the coldest day of the week, as temperatures remain stuck in the 40s with a cold rain developing. Widespread rain still on track, as precipitation overspreads southeast Michigan with lead moisture advection, 850-700 MB FGEN and isentropic ascent progged lifting through for this afternoon. Still looks to be close call for some wet snow to mix in across Tri-Cities region. 00z raob out of dtx indicated an 850 mb temp of -2 C, with apx also checking in at -2 C, but drier and with more opportunity to wet bulb. However, with the precipitation arriving during the daytime hours and strengthening southeast flow off southern Lake Huron, should be hard pressed to see any snow and certainly no accumulations with surface temps expected to reside in the upper 30s. Model consensus is for low to track along the southern Michigan border Tonight, as fast moving shortwave/height falls currently along the southern Alberta/Saskatchewan border merges and tracks through the Northern Great Lakes on Thursday, helping to draw the surface low northeast into Eastern Great Lakes. Cold/cyclonic flow on the backside of the low, with 850 mb temps still progged to drop to around -4 C. Precipitation chances look to be limited by the Mid level (700 mb) dry slot rotating through far southern Lower Michigan Thursday morning. Still gotta believe there is enough moisture down low with the steep low level lapse rates to support at least Isolated-Scattered Light Showers, with graupel mixed in still possible as what little cape in place hovers around zero isotherm. The weekend forecast remains a bit in flux, but Euro/Canadian/GFS have converged somewhat with the handling of the upper level energy off the Pacific Northwest Coast. It now appears a single, stronger low will be tracking through Friday Night, but well north, over Ontario. Associated moisture challenged cold front then progged to clear the State Saturday Morning, but magnitude differences in amount of cold advection to follow, with the thermal profile issues lingering into Sunday. Whatever secondary low which tries to develop from the upper level energy off the California coast is now forecasted to track through the Ohio Valley and remain rather flat. At this point, expecting temperatures well into the 60s on Saturday, with 70+ degrees possible Detroit/South, with high temps falling back into the 50s for Sunday. MARINE... Easterly winds strengthen today downstream low pressure system ejecting toward the region. Strongest winds expected tonight into early Thursday as this low lifts across Lake Erie and deepens. Wind gusts peaking into the 30 knot range over portions of the Lake Huron open waters during this time. The combination of the gusty conditions and prolonged onshore flow will result in a period of small craft conditions along the nearshore waters. These condition will linger through the duration of the Thursday period, before conditions ease Thursday night with approaching high pressure. HYDROLOGY... Widespread rainfall event remains on track from late today through early Thursday as low pressure tracks across the northern Ohio Valley. Light rainfall will expand across the area through the afternoon, before increasing in both intensity and coverage tonight. The heaviest rainfall will occur through the overnight hours, before tapering off Thursday. This system will result in a broad area of rainfall with amounts around three quarters of an inch through Thursday. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...Small Craft Advisory from 4 PM this afternoon to 10 PM EDT Thursday FOR LHZ421-441>443. Small Craft Advisory from 4 PM this afternoon to 9 AM EDT Thursday FOR LHZ422. Lake St Clair...Small Craft Advisory from noon today to 4 AM EDT Thursday FOR LCZ460. Michigan waters of Lake Erie...Small Craft Advisory from noon today to 4 AM EDT Thursday FOR LEZ444. && $$ AVIATION.....MR DISCUSSION...SF MARINE.......MR HYDROLOGY....MR You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.