Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 231053 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 553 AM EST Thu Feb 23 2017 .AVIATION...
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A weakening cold front will be pushing across Se Mi between 12Z and 15Z. This front is advecting drier low level air into Se Mi. The result of which has been a slow clearing trend. The airmass advecting into the area is not too dry. So diurnal heating may allow some redevelopment of some MVFR strato cu later this morning and afternoon. One item of concern is a low IFR deck which advected off Lake Mi and is fast approaching central Mi. There are concerns that this may impact MBS later this morning. Considering downslope and daytime heating, an optimistic MVFR strato cu field will be maintained at MBS. For DTW...The weakening of the surface front as it works across metro Detroit late this morning suggests the stratus may linger off an on through the morning. Otherwise, the southwest winds will veer to the west-northwest by early afternoon with the passage of the front. Wind speeds will weaken as the gradient relaxes, so crosswind concerns will not be an issue. //DTW THRESHOLD PROBABILITIES... * Medium in ceilings below 5000 ft this morning. Low this afternoon and early evening. High tonight. * Low in thunderstorms tonight.
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&& .PREV DISCUSSION...
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Issued at 357 AM EST Thu Feb 23 2017 DISCUSSION... Orphaned cold front currently stretching from Northern Lower through Chicago to just south of Kansas City will slow and veer out today as forcing diminishes and it becomes increasingly aligned with the flow. Low clouds are established beneath the frontal zone as evidence by low cloud observations stretching the Upper Midwest into APX`s CWA. These clouds will make inroads into the CWA early this morning, likely gradually eroding through the late morning as low- level convergence weakens and unfettered insolation takes its toll. As a result, suspect a mostly sunny character to the day will be in store south of I-69 with high clouds moving in late. High temperatures for the day have probably already been established across the north with current readings at 08z in the upper 50s with dewpoints near 60. Sun and decreased clouds will allow southern areas to increase back into the low 60s. Cool northeast flow will develop tonight as the front settles south, spelling overnight lows in the upper 30s, which is still near average high temperature values for late February. Attention then turns toward the energy digging into the 4-Corners region early this morning. Pressure falls have already commenced along the front range with a lee cyclogenesis episode anticipated this morning. Subsequent longwave feedback will establish a coupled jet and attendant broad low-level isentropic response late this afternoon through tonight as the surface low lifts toward the Quad- Cities, Iowa. Antecedent dry air will delay precip onset locally, even while stronger forcing allows showers to blossom to the west. Eventual saturation will bring showers to all of Southeast Michigan, mainly after 03z tonight. Surging 40-kt LLJ and steepening lapse rates aloft will likely bring elevated thunder and some locally heavy showers as the front lifts north. Warm frontal showers lift north during Friday morning, exposing a yet uncertain portion of the CWA to the system warm sector as the low lifts toward southern Lake Michigan by 00z Friday. Non-GFS guidance suggests the the southeastern half of the CWA making it into the warm sector. Lack of significant convection does increase confidence that the front won`t be shunted further south as it prone to happen in the warm season. Large scale forcing will increase dramatically over the western Great Lakes Friday afternoon into Friday evening as very strong PV advection allows the mid-level circulation to begin acquiring a negative tilt. Current forecast assumes a warm frontal location somewhere invof the M59 corridor during Friday afternoon, north of which the temperature will be suppressed in the 40s and 50s and south of which low 70s may be approached conditional on clearing. Pristine EML progged by the 00z ECMWF to begin spreading overhead as early as Friday morning, effectively capping the free warm sector as instability builds to 500 to 1000 j/kg in response to 7.5 C/KM or greater lapse rates aloft. As the LLJ translates east during peak heating, deep layer forcing for ascent will become maximized immediately in advance of the descending dry conveyor and within the pre-frontal trough. Deep layer bulk shear vectors oriented about 45 degrees to the initiating boundary within the strongly sheared environment may support an initial supercell mode over western Lower Michigan. 0-1km shear in excess of 30 kts and 0-6km in excess of 50kts will be adequate for maintaining any surface-based mesocyclones for a period of time. A tornado threat will present itself west of US 23 within the 0-1km EHI maximum (Livingston/Washtenaw/Lenawee) as either this activity encroaches on the area or with any preceding low-topped warm sector convection that pops up, the latter of which may be too shallow to produce thunder given 800mb cap strength. Tornadic showers certainly not unheard of in these parts. Tornado threat forecast to remain on the lower end of the spectrum given uncertainty in convective mode and overall weak instability. Strongly unidirectional wind profile and an abundance of mid-level dry air suggest a high likelihood of an eventual transition toward downdraft modulated convective modes carrying primarily a straight- line wind threat as storms speed from SW to NE at 50+mph. Some uncertainty in the magnitude of the wind threat as convection marches east owing to developing nocturnal inversion as well as a more pronounced lake shadow east of a Flint-Pontiac-Warren line. Suspect legitimate downdrafts would have no problem punching through the young nocturnal inversion further west, which includes the majority of the Detroit Metro area. All said, a marginal tornado and wind threat Friday afternoon is expected to transition to a straight- line wind threat with time after 00z. Convection exits east by 06z. Gusty WSW winds in the wake of the cold front drop high temperatures to seasonably mild readings in the low to mid 40s. Strong cold advection through a deep layer will bring the potential for a very gusty day. Attm, however, high quality moisture within the column is progged to limit mixing depths and cap gusts below 30 kts. MARINE... Low pressure will lift northeast of Lake Huron early this morning and will drive a cold front across the lake later this morning. The front will settle into Lake Erie this afternoon. The strength of the prefrontal southerly winds early this morning are being limited by strong over lake stability. Neutral to slightly unstable conditions will develop across Lake Huron during the day within post frontal cold air advection under north-northwest winds. These winds should primarily remain below 20 knots as the gradient relaxes. The cold front will push south of Lake Erie during the evening before lifting back north as a warm front late tonight into Friday. This will occur as low pressure lifts into the midwest. The easterly gradient will tighten to the north of the warm front, resulting in gusty winds across Lake Huron on Friday. There is high probability that easterly gusts across nrn and cntl Lake Huron will reach 30 knots Friday, with lower probabilities for a brief period of gusts to gale force. The low is forecast to weaken a little as it lifts across Lower Mi Friday night. This system will provide a good chance for thunderstorms, especially across Lakes St Clair and Erie within the warm sector. The departure of the low to the northeast on Saturday will bring colder air into the region within gusty west- southwest winds. The strongest winds are expected Sat night, where gusts to gale force are possible. CLIMATE... Record high low temperatures for February 23 DTW...43 (1930) FNT...47 (2000) MBS...42 (1930) Record high temperatures for February 24 DTW...59 (1976) FNT...57 (2002) MBS...60 (1930)
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&& .DTX WATCHES/WARNINGS/ADVISORIES...
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MI...NONE. Lake Huron...Dense Fog Advisory until 7 AM EST this morning for LHZ361>363. Small Craft Advisory from 4 AM to 10 PM EST Friday for LHZ421-441. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE.
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&& $$ AVIATION.....SC DISCUSSION...JVC MARINE.......SC CLIMATE......JVC You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.

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