Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 230045
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
745 PM EST Mon Jan 22 2018


.AVIATION...

Difficult aviation forecast as the area is locked within the warm
sector of very large occluded low pressure system over central part
of United States. Two items of focus for this TAF period. The first
was to time potential convective showers that will push across the
area in the 02-04Z time window. The potential will exist for a
thunderstorm during that small time period especially at the Detroit
Taf sites, however, confidence is too low at this time. The second
item was to time the transition of rain to snow Tuesday morning and
Tuesday afternoon. At this time, confidence remains low on timing as
the overall setup suggests a high dependence on depth of saturation
and precipitation rates. Forecast soundings and some hi-res output
suggests that quality of moisture will be lacking on Tuesday.
Precipitation will ultimately hinge on convective response that will
occur with the vorticity maximum and remnant deformation axis that
will stripe across the area. The best potential snowfall
accumulations will be across the northern cwa.

For DTW...MVFR is expected to settle back down into IFR this evening
as nocturnal boundary layer cooling occurs. 02-04Z time window
appears set for a line of broken showers to lift up from the south,
or develop overhead. A thunderstorm will also be possible, but
confidence remains very low. A mix of rain and snow is forecasted by
late Tuesday morning. Lack of forcing, precipitation coverage, and
warm surface accumulations will limit any snowfall accumulations.

/DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less throughout the period.

* Low for Thunderstorm between 02-04Z this evening.

* High for rain as precipitation type tonight, transitioning to a
  rain snow mix by Tuesday afternoon.

&&

.PREV DISCUSSION...
Issued at 359 PM EST Mon Jan 22 2018


Mature dry slot has been fully entrained into the stacked cyclone
presently situated over Iowa at 20z. Diminishing forcing within the
lead warm conveyor is supporting light showers in the process of
exiting stage right at press time. With cold air still back over
Missouri, SE Michigan will be engulfed the resident warm airmass
until the predawn hours. In the meantime, encroaching dryslot will
scour out mid-level moisture shortly, leaving drizzle as the only
precip threat for the next several hours. Lead edge of the deeper
cold air and the convergent back edge of the dry slot currently
supporting thunderstorms over Illinois will rotate into the area
from the southwest after about 06z tonight. Just a high chc/low end
likely w a chc thunder during this time as convergence diminishes
with time. Stratiform light rain/snow and low clouds noted over mid-
Missouri this aftn will lift into the area by sunrise beneath the
core of upper level cold air. Northern periphery of this precip
shield may manifest as some light snow, but wet/warm surface and
light rates will ensure little to no accums. Surface trough will
pivot through during Tues aftn bringing a brief and more strongly
forced window for snow followed by temps falling through the 30s
into the upper 20s by evening. High pressure and climatologically
average temps for Wednesday while lingering low-level moisture
supportive of low stratus and high clouds streaming in ahead of the
next shortwave ensure cloud skies one way or another.

Upper level ridging will build into the region Thursday into Friday
bringing dry conditions and a warming trend as highs increase from
the mid 30s on Thursday to the mid 40s by Friday. An upper wave
dropping into the Northwest US will then support the development of
low pressure across the Northern Plains on Friday that will move
eastward along the Canadian border before lifting across Ontario on
Saturday. This low pressure system will bring the next chance for
precipitation to the region next weekend as moisture increases ahead
of a cold front that will slowly push east across the region through
Sunday. Model discrepancies continue regarding the timing of the
frontal passage and location of the increased moisture transport
ahead of it. The ECMWF currently favors a slower, wetter frontal
passage for SE Michigan while the GFS/CMC solutions show a quicker,
drier frontal passage. For now expect a period of rain showers ahead
of the frontal passage on Saturday with temperatures in the 40s
before a transition to rain/snow showers as temperatures fall into
the 30s on Sunday.

MARINE...

Low pressure over Iowa with a warm front extending across central
Michigan and Lake Huron is producing strong easterly flow across
northern Lake Huron. This front will remain nearly stationary with
lighter southernly flow to the south.  The low pressure will track
along the front across Lake Huron Tuesday afternoon. Gusts to near
gales or marginal gales will develop late Tuesday afternoon and
continue into Tuesday night across all of Lake Huron. Winds and
gusts will decrease by Wednesday and remain relatively light through
the rest of the week. Another increase in winds will come for the
weekend.

PREV DISCUSSION...
Issued at 343 PM EST Mon Jan 22 2018

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....CB
DISCUSSION...JVC/JD
MARINE.......JVC


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at www.weather.gov/detroit.


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