Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 211931

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
331 PM EDT Mon May 21 2018



As of 330 PM EDT...An area of low pressure currently situated near
the Quad Cities continues to slowly move northeast towards the
region, with a remnant early morning MCS/QG-forced rain shield out
ahead of it across lower Michigan. Much of the day so far has been
dry, as surface high pressure that built in from the north overnight
brought in dry low-level air that has taken the morning to saturate
the column. Increasing cloud cover throughout the day has limited
high temperatures, with highs topping out in the 60s for most areas.

The rain will continue to spread eastward over southeast Michigan
through the remainder of the afternoon and into the evening hours. A
mainly soaking rain is expected through the evening, as surface, and
to an extent, elevated instability will be lacking. Still, embedded
heavier showers will be capable of locally heavy downpours, which
may lead to ponding of water on roadways and some poor drainage
flooding concerns.

Hi-res guidance has been in generally good agreement that the best
chance for thunder will be from 00z-06z as elevated instability
increases as the low approaches. However, more widespread rain and
embedded thunder looks likely to be impinged by the system`s dry
slot during the early overnight period, which will likely act to
decrease convective coverage mainly south of the I-69 corridor.
Further north, midlevel frontal forcing will act to keep more
steadier rain ongoing through much of the night. The approach of
trailing midlevel energy should lead to redevelopment of scattered
showers and isolated storms for the latter part of tonight into
early Tuesday morning. The surface low track looks to basically pass
over southern lower Michigan, which will allow winds to decrease and
with rain/copious low-level moisture, patchy fog will be possible at
times late this evening through much of the night. Low temperatures
tonight will settle in the 50s.


The area of low pressure and trailing upper-level energy will
continue to slowly exit the region for much of the day Tuesday, with
showers possibly lingering into the afternoon hours before ending
from west to east as the cold front and midlevel dry punch swing
through. During the morning hours, dewpoints look to surge into the
lower 60s across southern areas which will help keep the shower
potential going through at least the first half of Tuesday. Embedded
thunder cannot be ruled out as well as Showalter indices dip below
0. Lingering cloud cover will keep temperatures at bay, with 60s
across most areas, with low to mid 70s possible Detroit metro and
locations south.

Confluent flow across the northeast CONUS and rising heights
downstream across the upper Midwest will allow high pressure to
build in at the surface Tuesday night. With decreasing winds and
lingering near surface moisture, fog will be possible, but
confidence is not quite there yet to include in the grids. Low
temperatures Tuesday night will settle into the mid 40s to mid 50s.

High pressure and stable upper-level northwest flow will lead to a
quiet and dry period of weather Wednesday and continuing through
Thursday night, as the upper ridge axis remains anchored over the
upper Midwest. With mostly clear skies during this period,
temperatures will rebound with highs Wednesday well into the 70s and
reaching into the lower and possibly mid 80s Thursday. The high will
slowly shift eastward Wednesday and Thursday, allowing for
southwesterly return flow to set up Thursday.


The high will continue sliding off to the east Friday with
southwesterly flow strengthening in between the departing high and
an area of low pressure approaching the upper Great Lakes. This area
of low pressure will be accompanied by pieces of northern stream
energy that will help to drive the low pressure system southward
towards the region during the weekend. A period of unsettled weather
will be possible over the weekend with scattered showers and storms,
although there still remains uncertainty in the amount of available
moisture to work with.

Temperatures will be warmest on Friday with the brisk southwesterly
flow, as most areas could see high temperatures reach into the mid
80s. Upper 70s to lower 80s temperatures will continue into the
Memorial Day holiday weekend.



High pressure over Lake Huron will depart to the east as a broad
area of low pressure tracks into southern Michigan tonight. A warm
front extending east from the low will lift across Lake Erie tonight
supporting light and variable winds and widespread showers.
Meanwhile light easterly flow will develop over Lake Huron tonight.
As the low tracks east away from the region, the flow will back from
northeast to north through the day on Tuesday across Lake Huron.
Waves are expected to remain below 2 feet through Tuesday. High
pressure will then build across the southern Great Lakes on
Wednesday causing winds to back from northwest to west across
northern Lake Huron while becoming light and variable elsewhere.



Widespread showers, locally heavy at times, will track across
Southeast Michigan late this afternoon and evening. Additional
scattered showers will then be possible through tonight along with a
few thunderstorms mainly south of Interstate 69. A widespread three
tenths to six tenths of rainfall is expected to fall from late this
afternoon through Tuesday morning across Southeast Michigan. A few
localized spots, mainly south of Interstate 69, could see rainfall
amounts approaching one inch through Tuesday morning.


Issued at 106 PM EDT Mon May 21 2018


Low pressure tracking east over northern Illinois will bring a
gradual increase in moisture to the area through the remainder of
the afternoon. Radar imagery shows a region of rainfall and a few
thunderstorms associated with this low that high-res guidance
indicates will track eastward across all terminals after 19Z. As the
rainfall overspreads the area, expect lowering ceilings and easterly
winds through the late afternoon before MVFR ceilings develop during
the evening. The best potential for isolated thunderstorms appears
to be focused during the late evening for the Metro Detroit
terminals from PTK southward where instability will increase with
southward extent. As the low tracks into the area overnight,
increasing low level moisture will bring low MVFR/IFR ceilings and
visibilities across much of the region as showers continue through
early Tuesday morning. Some improvement is then expected by late
Tuesday morning as the low tracks westward and ceilings rise back to
MVFR under lingering low level moisture.

For DTW...Light to moderate rainfall is expected to overspread the
terminal after 19Z and continue through 00Z. Elevated instability
will then increase ahead of the low during the evening bringing the
potential for isolated thunderstorms during the late evening and
continuing into the overnight. Increasing low level moisture as the
low approaches will cause ceilings and visibilities to fall to low
MVFR/IFR late tonight before improving Tuesday morning.


* Moderate in ceilings at or below 5000 late this afternoon. High

* Moderate in thunderstorms impacting the airport late this evening.


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



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