Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

586
FXUS63 KDTX 160501
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1201 AM EST Mon Jan 16 2017

.AVIATION...

Minor fog/haze trends are the only short term concern in the
aviation forecast for the rest of the night. High clouds thickening
considerably over the DTW corridor and wind holding around 5 knots
at MBS should ease early onset suggested by observations during the
evening. Plan to continue monitoring conditions for anything more
than brief dips into MVFR.

Clouds will thicken and lower during the day but remain VFR through
mid afternoon as the next low pressure system approaches. The
transition to MVFR/IFR/LIFR will then get underway during late in
the day. Expect radar to detect considerable coverage of virga
through the afternoon before precipitation is able to reach the
ground mainly after 21Z. Temperatures will remain close to or below
the freezing mark by then and a wintry mix is likely as the
precipitation pattern fills in from the west while spreading
northward over the region through Monday evening.

For DTW... Other than a brief MVFR restriction in fog/haze, there
are no concerns through the morning. High clouds just thicken and
lower ahead of the next low pressure system. A downward trend into
MVFR/IFR/LIFR is then expected during late afternoon into evening. A
period of wintry mix or freezing rain is likely at precipitation
onset as the temperature at DTW will be very close to the freezing
mark. The mix is expected to be brief and followed by a change over
to all rain as temperature rises more firmly above freezing during
Monday evening. The mention of freezing rain specifically in the TAF
will be left to later updates as surface temperature forecasts are
refined.

//DTW Threshold Probabilities...

* High for ceiling 5000 ft or less by mid afternoon through Monday
  night.

* Moderate for wintry mixed precipitation or freezing rain late
  afternoon.

&&

.PREV DISCUSSION...
Issued at 315 PM EST Sun Jan 15 2017

DISCUSSION...

Existing mid level confluent west-northwest flow gives way to an
increasing southern stream influence over the next 24 hours,
prompted by a building upper height field immediately downstream of
a closed low now ejecting into west Texas.  Extensive higher level
moisture anchored within this height gradient will begin to advance
northward and into the region tonight.  A more sizable window of
open sky with northward extent before thickening high cloud invades
overnight. This will again promote a solid radiational cooling
opportunity within the influence of lingering surface ridging and a
corresponding weak gradient flow. Early morning temperatures
bottoming out in the teens most locales along/north of the ridge
line, lower 20s for points south.

Surface high positioning holds southeast Michigan in dry low level
east to southeast flow for Monday.  Substantial component of
moisture advection well underway upstream, driven by standard deep
layer southwest flow within the eastern flank of the inbound
southern stream closed system.  The ensuing advancement of deeper
moisture into southeast Michigan a slower process initially, owing
to rather modest 700-500 mb forcing anchoring the lead arc of moist
ascent.  A poorly saturated profile across the lowest 5-6k ft prior
to 00z suggests simply a lower probability for light returns to
emerge during the mid-late afternoon.  Deep layer sub-freezing wet
bulb temps with saturation issues down low at this stage would leave
ptype as a simple light wintry mix through the onset period.

Period of strong moist isentropic ascent with a trailing notable
uptick in dynamic forcing as the wave pivots through translates into
a widespread precipitation event Monday night through early Tuesday.
Front end of this event still challenged by concerns with thermal
trends, particularly at the surface.  Concerns emerge immediately
Monday afternoon, as the diurnal temperature response struggles
against a prevailing easterly wind component and thick cloud cover.
ARW/NMM yield the coldest landscape at 21z, roughly 2-4 degrees
colder relative to the NAM/GFS.  ECMWF a touch warmer with late day
highs, a good compromise in depicting readings inching a degree or
two above freezing.  Retention of mid 20s dewpoints will then
translate into a solid evaporative cooling component as aggressive
deep column moistening commences early Monday night.  Sufficiently
warm mid level environment moves the ptype to all liquid once
saturation occurs.  A tenuously positioned temperature initially
hovering in the vicinity of freezing, under the backdrop of an
overall warming thermal profile, will dictate the occurrence/
duration of freezing rain Monday evening/night. Increasing
probability for a multi-hour period of freezing rain with northward
extent, allowing for some light amounts of ice accretion
/less than a tenth/.

Strong deep layer ascent carries into early Tuesday, the focus
turning to a combination of convergence/PVA as the mid level wave
and attendant low level jet pivot through.  Diminishing mid level
stability along the frontal occlusion will bring a greater
convective element during the mid-late morning hours, enough to
warrant a thunder mention for southern sections.  Diminishing rain
chances by afternoon upon entry of the mid level dry slot. Exiting
warm air advection transitioning briefly to neutral leaves milder
conditions for the day, with highs mainly in the 40s.  Colder air
wraps back in Tuesday night, aided by the arrival of a trailing
northern stream wave.  Chance for a few light rain/snow showers as
this process unfolds overnight.

Some lingering showers are possible early on Wednesday as a northern
stream wave crosses the southern Great Lakes region. Model solutions
continue to differ on how far south the northern wave will track
leading to lower confidence for shower chances on Wednesday.
Nevertheless, limited cold air on the back side of the low will
allow high temperatures to approach 40 on Wednesday. Ridging then
builds over much of the Eastern US through the end of the week
allowing a warming trend to continue through next weekend with
temperatures approaching 50 by Saturday. A shortwave trough ejecting
northward from the Southern Plains will bring the next chance of
rain to Lower Michigan during the Friday/Saturday timeframe.
Otherwise, conditions should remain calm and unseasonably mild
through next Sunday with broad southerly flow in place across the
Great Lakes.

MARINE...

Light winds this evening as high pressure slides through the Central
Great Lakes. Southwest winds increasing some tonight, but topping
out mainly around 20 knots as milder air takes hold on Monday
evening. Surface low tracking through the Western Great Lakes early
next week resulting in southeast winds up around 20 knots over Lake
Huron on Tuesday.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

AVIATION.....BT
DISCUSSION...MR/JD
MARINE.......JVC


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.