827 FXUS63 KDTX 300453 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1153 PM EST Thu Dec 29 2022 .AVIATION... MVFR stratus will remain in place overnight as moisture streams north in advance of approaching frontal boundary. A wave along this front will bring showers by Friday morning with cigs lowering to IFR at times. The northwest edge of this rain will align near KFNT with perhaps just a period of light drizzle along fropa at KMBS. A strong low level jet (40-50 knots around 2kft) will bring LLWS overnight into Friday with occasional gusts to 20 knots reaching the surface, especially into Friday morning when the strongest pressure gradient exists. DTW THRESHOLD PROBABILITIES... * High in ceilings below 5000 feet overnight into Friday. * High in precipitation being all rain Friday. && .PREV DISCUSSION... Issued at 400 PM EST Thu Dec 29 2022 DISCUSSION... Key Messages: -Anomalous ridge pattern supports above normal temperatures today and Friday. -Light rain or drizzle possible tonight, followed by steadier rainfall into Friday, especially across the Metro area. -Additional rainfall south of I-69 Saturday until a cold front clears through yielding mainly dry conditions Sunday and Monday morning. -Currently expect to be on the warm side of the next low pressure system Tuesday which provides additional rainfall and high temperatures approaching 60F. Amplified synoptic pattern situated across CONUS today nestles the Great Lakes within the upstream flank of a ridge axis extending through the Mid-Atlantic. Strong low-level dynamics in-place with highly confluent flow pumps Gulf-modified air northward as evidenced by a sharp jump in 925-850 mb ThetaE advection. Isentropic perspective reveals sustained upslope/ascent through the lowest portion of the maturing warm sector this afternoon maintaining expansive overcast stratocumulus deck. The KDTX 29.12Z RAOB highlights both the depth of the warmer airmass (10C at 760 mb) and the degree of drier anticyclonically curved flow through most of the 850-500 mb layer capping mixing ratios near 3 g/kg. Near-term forecast soundings are not overly aggressive with moistening above 3 kft AGL through the remainder of today which ensures mainly dry conditions, even with the weak lower column saturated ascent in place. Topic of interest through the rest of today tied to the impacts of boundary-layer thermodynamics on peak gusts and high temperatures. Even with 35-45 knot winds at 2 kft AGL, static stability below yields a poorly-mixed layer, thus capped gusts around 20 mph with plenty of sites currently reporting gust-free conditions. Also bumped up highs a bit to bring more locations AOA 50F. As of 3 PM, Monroe was at 53F and Dundee read 54F. 925 mb temps continue to climb overnight with sustained warm/moist advection resulting in the development of light rain or drizzle. Global models remain too aggressive with the saturation rate, therefore latest QPF is more in-line with HREF/ARW/RAP/HRRR outcomes of very light rainfall amidst minor/negligible height falls. Meanwhile, a shortwave trough rides the ridge up through the UP into the morning hours which leads to some shearing of the resident wave while also kicking a cold front southeastward. This sets up a sharper gradient for high temperatures as the earlier arrival keeps highs below 50F over the Tri-Cities as the frontal slope oozes into Saginaw before stalling. No longer expecting much in the way of precip from the northern wave leaving that region mainly dry through the next 48+ hours. Steadier and heavier rainfall then arrives Friday PM as an axis of FGEN forcing slides into position. Gradient in PWAT bisects the area with higher QPF located south of a line from Howell to Sanilac. The position of the jet axis will likely lead to a notable cut-off in realized rain totals given the quasi- stationary nature of the feature into Saturday. Inbound longwave trough compresses meridionally Saturday morning as it deamplifies, but left exit region jet dynamics are in-play Saturday for eastern communities. Rainfall continues into the afternoon for Metro Detroit until the trough departs. The surface cold front should make enough forward progress to generate perhaps a bit of cold rain or melting snowflakes north of I-69 Saturday morning as it spills into Ontario. Light gradient flow becomes northwesterly suggesting muted diurnal curves. Confidence has increased for highs closer to 40F, warmest near the Ohio border. Weak low over the Upper Midwest may clip the northern half of the CWA generating a bit of light precip late Sunday morning. P-type will be dependent on how rapidly the warmer downstream return flow can make it into Lower Michigan. Height rises then commence Sunday afternoon/evening as a Pacific wave digs into northwestern Mexico, amplifying central CONUS ridging. Diffuse surface pressure field locally ensures a dry and mild forecast Sunday afternoon through Monday morning. Major differences exist between the 00Z and 12Z ECMWF solutions in how the upcoming Vort Max, rate of cyclogenesis, and duration of rainfall plays out with the next system. Should a more westerly trajectory hold during the peak, Southeast Michigan should remain within the warm conveyor resulting in an initial all- rain scenario. An arc of concentrated CVA could lead to decent rainfall rates Tuesday morning before a transition to scattered coverage. Right now the 12Z ECMWF has the system occluding over southern Wisconsin while the GFS is far more progressive carrying a 982 mb low all the way up through Hudson Bay. There is some potential for wintry p-types on the back edge of the system should the ECMWF or CMC solutions play out. MARINE... Deep southerly flow of 15 to 20 knots is in place over the central Great Lakes region this afternoon in advance of northern Plains upper level trough. A frontal zone will become increasingly organized tonight before a surface low lifts along the boundary over Wisconsin late tonight. Surface wind directions will veer to the west southwest behind the cold front as it pushes across Southeast Michigan late Friday. A shallow depth to the cold air in combination with a relative weak wind field is expected to keep wind speeds in the cold air at 25 knots or less. The frontal system will then stall out over the Ohio Valley and in vicinity of Lake Erie before the next low pressure system lifts through the region Saturday. Winds behind the weekend system are again expected to be 25 knots or less. HYDROLOGY... Rain expands in coverage late tonight into Friday morning, becoming widespread south of I-69 by Friday afternoon as waves of low pressure track through the Ohio Valley. Potential exists for 0.50 to 0.75 inches of rainfall south of a line from Howell to Sanilac. Rises on area rivers can be expected, although flood potential ultimately rests on the extent of frozen ground and any ice blockages that may occur from this spell of mild temperatures since the rain will occur over an extended period of time. Additional rainfall likely arrives late Monday, possibly continuing into Wednesday. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....DG DISCUSSION...KK MARINE.......TF HYDROLOGY....KK You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.