422 FXUS63 KDTX 140418 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1218 AM EDT Sat Apr 14 2018 .AVIATION... A mass of showers and thunderstorms entering Indiana and Illinois at midnight is on the way toward Lower Michigan before sunrise. This activity will combine with stratus settling slowly over the region to maintain IFR conditions across the terminal corridor. IFR is expected to hold firm with some intervals of LIFR as rain becomes widespread and lasts through much of upcoming day. There could be an occasional short break into MVFR during the afternoon just due to the strong wind and incoming cold air. At the same time, that same cold air will introduce freezing rain and sleet first at MBS where a mix of snow could also occur for a few hours and then spreading southward to FNT by late morning. The onset time at PTK remains a little more uncertain with a potential start during early afternoon in mid April, however the strong northeast wind will be a force in driving the cold air southward. Sustained wind is expected to increase to around 25 knots with gusts around 35 knots during the afternoon, especially from PTK northward. A substantial break in precipitation is expected toward evening before a second round of freezing rain and sleet develops Saturday night. For DTW... Low stratus is settling slowly southward from PTK and will reach DTW near the start of the 06Z forecast. The clouds will combine with showers and thunderstorms expanding rapidly through Indiana and Illinois to maintain IFR through the upcoming day. Northeast wind increasing to gusts around 25 knots will be able to carry colder air into the area, but at this time temperatures are expected to remain above freezing until possibly after sunset Saturday evening. /DTW THRESHOLD PROBABILITIES... * High for ceiling 5000 ft or less tonight through Saturday evening. * Low for ceiling 200 ft or less. * Low for thunderstorms before sunrise. * High in precip type as rain through TAF period. && .PREV DISCUSSION... Issued at 932 PM EDT Fri Apr 13 2018 UPDATE... A quick update on the status of headlines for SE Michigan. A Winter Weather Advisory will be added for Livingston, Oakland, and Macomb counties as a mix of freezing rain and sleet is likely to develop over northern portions of these counties by early afternoon Saturday. The lakeshore flood watches will be upgraded to warnings for Bay, Tuscola, Wayne, and Monroe. In the case of Saginaw Bay, a strong northeast gale during Saturday is expected to push water level over warning threshold, especially with high wave action considered. Strong wind gusts will be included in this message instead of expanding the wind advisory from Huron county where no lakeshore headline is in effect. For western Lake Erie, the same wind and wave impacts are expected from Gibraltar down to Luna Pier. A lakeshore flood advisory will be issued for Macomb county for the strong northeast wind funneling into southern Lake St Clair where the undisturbed water level is already around 43 inches above chart datum. No changes to marine headlines. PREV DISCUSSION... Issued at 408 PM EDT Fri Apr 13 2018 DISCUSSION... Relatively little change in overall thinking for this weekend. This afternoon's forecast package features mainly cosmetic changes to the going forecast and an upgrade of the existing watch to a winter storm warning for freezing rain. Showers and a few thunderstorms, including a half inch hail report at Harbor Beach this afternoon, are ongoing over the far northern CWA and northern lower Michigan. Temperatures warmed up nicely today, largely owing to clear skies for the first half of the day south of the mid-level front. Even so, progression of the Canadian high over Ontario and incoming rain with the next round of mid-level forcing will be sufficient to push the baroclinic zone well to the south by morning. General consensus on a half inch to an inch in the 06-12z period late tonight with high res models keying in more on the conditionally unstable airmass and producing localized bands in excess of one inch. This is all reasonable. In addition, some thunder can be expected and the possibility for localized pea sized hail. Most of this is expected to fall prior to the influx of cold northeast flow forcing temperatures below freezing at the surface. Thus, the WSW does not start until 12z Sat morning. Little change in the synoptic and frontal scale environment through the first half of Saturday as fgen intensifies and moisture gathers in the strengthening mid-level deformation axis. Moderate to locally heavy rain is expected to persist through 18z Saturday as sub-freezing temps gradually sag south. With the 12z EC more supportive of recent aggressive NAM trends, but not terribly different from previous runs, confidence is sufficiently increased to expect ice accretion to begin Sat morning. Despite high QPF, high rates and antecedent wet conditions will serve as an initial mitigating factor. As forcing and the deformation axis shift east Saturday afternoon, the formidable inversion and shearwise forcing in the boundary layer will take over as the dominant forcing mechanism and will continue to contribute to light freezing rain or freezing drizzle for the remainder of the afternoon and into the evening in the warning area. This will likely be no less hazardous given the nature of fzra is that diminished rates are countered by more efficient accretion. The greatest uncertainty through Saturday will be the depth of cold air across the far north. It remains possible that locations north of M46 see a prolonged period of sleet which could result in a reduction in the total ice forecast there. As the upper low approaches and takes on a negative tilt, the warm conveyor will surge northward Saturday night against background of strong synoptic scale dynamic support. The warm nose will blow away any mid-level cold air, ensuring that sleet does not complicate matters the second time around. Conditional instability and PWATs around 1.2" will support widespread showers, heavy at times, yielding freezing rain in the warning area. It is within the realm of possibility that an advisory for freezing rain will be needed for the M59 counties, or at least for locations along/west of the glacial ridge. Increased ice accretion totals to a few hundredths along an Ann Arbor to Warren line and to over a tenth along/north of M59. Persistent strong northeast winds will be ongoing throughout this time. The 12z GLERL and NOS runs are strongly supportive of lakeshore flooding issues in Bay County and Monroe County, where the water level alone will likely meet lakeshore flood warning criteria, the additional inland penetration due to high wave action. Storm surge is also a threat create problems on the Saginaw River. Tuscola and Wayne Counties, oriented slightly more flow-parallel, appear more likely to only achieve advisory criteria at this time. In addition, gusty winds coming off Lake Huron will approach or exceed wind advisory criteria during the day Saturday along the Huron County shoreline prompting the issuance of a wind advisory beginning 8am Saturday. The expansive low pressure system will lift away from the region on Monday as colder air aloft on the backside of the low transitions the ptype for any lingering showers to snow/rain. Temperatures will remain well below average through the early part of next week with highs in the upper 30s to low 40s on Monday before slowly moderating on Tuesday as weak riding brings drier conditions. The next low pressure system is then progged to lift across the region midweek bringing another round of precipitation to the region Wednesday. Will need to monitor the track of this low but current indications favor a more northerly track allowing warmer air to surge north keeping highs in the mid 40s north to mid 50s south and rain as the predominant ptype. MARINE... An approaching low pressure system and strengthening pressure gradient will increase wind and wind gusts across the lakes and bay, specifically across Saginaw Bay into all of Lake Huron. ENE gusts between 30 - 40 knots will persist early Saturday morning into all the way through the bulk of Sunday. This will produce wave heights ranging between 10 - 14 feet across nearshore Lake Huron through this timeframe, with waves up to 5-6 feet possible in the inner Saginaw bay. Small craft advisories will remain in effect until at least 8 AM EDT Saturday, in addition to a gale watch that will be in effect from Saturday morning through Sunday afternoon. HYDROLOGY... An elevated frontal boundary will produce scattered rain showers across SE MI tonight, with coverage increasing to widespread showers overnight and throughout Saturday as low pressure approaches the state. This dynamic system is expected to have the bulk of precipitation fall as sleet, freezing rain, or a combination of the two across I69 north, while the Metro region is expected to remain on the warmer side, producing rain through at least Saturday afternoon. Uncertainty does remain regarding how far south the freezing line will extend late Saturday into Sunday, which could help introduce sleet/freezing rain chances to the northern Metro region. 2 - 3 inches of liquid precipitation is expected to fall over the next 48 hours, between Friday afternoon into Sunday afternoon. In addition to precipitation, strong ENE flow will bring the chance to see lakeshore flooding across Bay and Tuscola county, and down into Wayne and Monroe county. As a result, a lakeshore flood watch is in effect for the four counties. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Winter Storm Warning from 11 AM this morning to noon EDT Sunday for MIZ060>063. Winter Weather Advisory from 11 AM this morning to noon EDT Sunday for MIZ068>070. Lakeshore Flood Warning from 8 AM this morning to 8 AM EDT Sunday for MIZ048-054. Winter Storm Warning from 8 AM this morning to noon EDT Sunday for MIZ047>049-053>055. Wind Advisory from 5 AM early this morning to 4 PM EDT this afternoon for MIZ049. Lakeshore Flood Warning from 8 AM this morning to 4 PM EDT Sunday for MIZ076-083. Lakeshore Flood Advisory from 8 AM this morning to 8 AM EDT Sunday for MIZ070. Lake Huron...Gale Warning until 10 PM EDT Sunday for LHZ361>363-462. Gale Warning until 11 AM EDT Sunday for LHZ442-463. Gale Warning until 4 PM EDT Sunday for LHZ421-422-441. Small Craft Advisory until 5 AM EDT Monday for LHZ443. Lake St Clair...Small Craft Advisory from 8 AM this morning to 4 PM EDT Sunday for LCZ460. Michigan waters of Lake Erie...Small Craft Advisory from 8 AM this morning to 4 PM EDT Sunday for LEZ444. && $$ AVIATION.....BT UPDATE.......BT DISCUSSION...JVC/JD MARINE.......AM HYDROLOGY....AM You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.