Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 220456
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1156 PM EST Tue Feb 21 2017


.AVIATION...

Fog and low stratus has already expanded significantly KFNT/KMBS,
but stratus deck in the 4000-6000 foot layer has inhibited notable
fog develop so far KPTK south. Plenty of mid/upper clouds may keep
whole area from tanking overnight, but still expect a trend to
increasingly widespread and locally dense fog. Current divide from
north to south should also hold for the most part as KFNT/KMBS and
KPTK? drop to LIFR/VLIFR at times with I-94 terminals edging into
IFR and eventually LIFR late tonight. Gradual improvement will then
occur mid/late morning Wednesday as southwesterly winds increase to
10 knots or so.

For DTW...Stratus and fog will likely form to some degree overnight
as low level moisture increases again in light southerly flow. IFR
cigs/vsbys should become the norm overnight with some LIFR late
night into early Wednesday (09z-13z). These cig/vsby conditions will
improve by midday Wednesday as this low level moisture is mixed out
within increasing southwest flow.

//DTW THRESHOLD PROBABILITIES...

* High for ceilings below 5000 ft into Wednesday morning.

* Low in ceilings/visibilities below 200 ft and/or 1/4SM 09z-13z.

&&

.PREV DISCUSSION...
Issued at 1044 PM EST Tue Feb 21 2017

UPDATE...

Updated to issue a Dense Fog Advisory mainly from I-69 counties
north, but also extending into Livingston county. Fog has been
expanding throughout the evening and dense fog of one quarter of a
mile or less has become common where mid to upper clouds have
oscillated between partly to mostly cloudy. This veil of clouds may
impede further expansion of fog somewhat, but it appears there will
be enough break to allow for extensive fog overnight, especially as
low level moisture begins to increase on light southerly flow. An
expansion of the advisory southward is not completely out of the
question, but current stratus deck in the 4000-6000 foot layer will
limit dense fog development for the foreseeable further.

PREV DISCUSSION...
Issued at 343 PM EST Tue Feb 21 2017

DISCUSSION...

Mid level low is cutting off from the mean flow as the next strong
jet comes ashore out of the Pacific. Longwave trough/ridge pattern
takes on a low amplitude in the wake of the current shortwave
passage, with WSW flow extending from southern CA into the Great
Lakes. This will keep the above average temperatures going though
the end of the week as all fropas through this stretch are weak and
do little to displace the warm airmass in place. 850mb temps look to
hover around +5 to +10C through the end of the week with a couple
thermal ridges folding over through the region.

Tonight will feature some degree of fog as temperatures fall in the
wake of the front, but low level moisture hangs around. In addition,
the boundary laid out to our south will get pulled back north as a
warm front overnight which will bring about southerly flow once
again. Dewpoints should hold at least in the low 40s tonight before
climbing again toward morning. Depth of saturation and strength of
the inversion could also lead to some drizzle within the fog.

Model soundings show the low level saturation holding into the late
morning hours Wednesday. Increasing southwest winds will help mix
out the fog in the late morning Wednesday. We then turn our
attention to temperatures Wednesday when more records could be set.
Mixing depths will increase up toward 925mb where temperatures will
near 12C. With mostly sunny skies, mixing depths, temps starting off
in the mid 40s, and southwesterly flow, mid to upper 60s should be
attainable Wednesday. As mentioned in the previous discussion, all
time February highs could be in play which are:

DTW...70 (1999)
FNT...68 (1999)
MBS...67 (1930)

Early Thursday morning a weak cold front will lift through lower MI
as a shortwave embedded in the SW flow, and assoicated weak surface
reflection, skirts across northern MI. Can`t rule out a stray light
shower but forcing and moisture profile do not look favorable for
any widespread shower activity. The rest of Thursday will be fairly
quiet around SE MI with only a brief dip in temps from Wednesday,
down to around 60. Upstream is a different story as the west coast
trough releases eastward and cyclogenesis over the plains results in
a strong low that will lift through the Great Lakes Friday and Friday
night. The lead warm front will lift through Thursday night
producing widespread rain showers. Looks like there could be a chance
of thunder as well as elevated instability and steepening lapse
rates develop between about 700-500mb.

Friday continues to be not only bring well above normal
temperatures, but the potential for thunderstorms as a strong low
tracks across the Great Lakes region. Models are still on par with
Southeast Michigan remaining in the warm sector as the center of the
low tracks generally over western portions of the state. Current
model runs have the surface cold front moving through later Friday
followed by the upper level swinging across the area on Saturday.
Warm southerly winds ahead of the cold front on Friday will again
bring a chance to break high temp records, particularly in the
Detroit area, as highs look to get into the lower to middle 60s over
southern portions of the CWA. Gusty northwest winds behind the cold
front will bring in cooler air with highs for the upcoming weekend
staying closer to normal.

MARINE...
Relatively light to moderate southwesterly winds will continue into
Thursday before a front veers the flow to the northwest. Winds will
continue to veer to east Friday ahead of a spring like system that
will track into the Great Lakes.  A strong cold front will sweep
through Friday night with the potential for strong thunderstorms.
Arctic airmass will funnel in behind the front over the weekend
bringing potential gale force gusts over Lake Huron.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Dense Fog Advisory until 9 AM EST Wednesday for MIZ047>049-053>055-
     060>063-068.

Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....DG
UPDATE.......DG
DISCUSSION...DRK/SS
MARINE.......DRC


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