Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 241700
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
100 PM EDT TUE MAY 24 2016


.AVIATION...

Southwesterly flow around departing high pressure will bring a
gradual increase in moisture through taf period. Skies will remain
mostly clear the rest of the day with increasing mid and high level
clouds this evening/night from the west ahead of an approaching weak
cold front. This front will settle into MBS/FNT area over night then
washout/dissipate.  No precip is expected with this front but some
virga is possible from the mid and high level cloud deck. Increasing
moisture may lead to some few-sct diurnal cu 4-5kt Wed.  Winds will
vary from basically 200-250 and generally 10kts or less through taf
period.


//DTW Threshold Probabilities...

* None

&&

.PREV DISCUSSION...
Issued at 1136 AM EDT Tue May 24 2016

UPDATE...

The first forecast item is temperatures today. There is good
background forcing for deep column subsidence and overachievement
from compressional warming potential as a deep negative vorticity
signature will push directly through the cwa this afternoon. Throw
low dewpoints in the mix and conditions are very good for low to
middle 80s today. No changes are needed.

The second forecast item for today is ascertaining and monitoring
the potential for an elevated shower or isolated thunderstorm in
and near Saginaw Bay this evening. Raw output of QPF fields has
backed off on developed activity. The overall forcing is weak from
a synoptic scale perspective with persistent upper level ridging
and anticylonic flow trajectories. The potential sprouts from some
overlap of 700mb theta e plume advecting into central and
northern sections of lower Michigan from due west, with the
surface modification or moistening of 950mb theta e that is
depicted to occur over the western cwa very late this afternoon
from south to north. The real problem is the quality of this lower
column moisture quality as the air mass is of a modified arctic
origin and owns a serious moisture deficit. While the landscape
has greened up recently there is some major question as to whether
or not there is any active evapotranspiration. This seriously
calls into question some of the guidance which is calling for
middle 50 dewpoints this afternoon and 60 dewpoints by this
evening. The chance for the isolated shower and thunderstorm
across the northern cwa is one that is marginally supported by
thermodynamics with a steep lapse rate pocket between 8-12 kft agl
between approximately 02-08z. The 4km NAM output is probably more
on point with the potential thermodynamic profile which is even
less optimistic with instability...with perhaps as much as 250
J/kg MLCAPE or even MUCAPE due to limited surface moisture. Given
deep antecedent dry air, probably looking at more of a sprinkle or
virga situation with no thunderstorms. If a thunderstorm was to
survive this far eastward the very low end instability will serve
as the limitation to the activity.

The third forecast item is whether or not a small POP exists over
the far southern cwa between 09-12Z tonight. Earlier solutions
were depicting some modeled shower and thunderstorm convection
developing developing over far southern IL/IN and western KY
today. This activity was then modeled to make a run for the MI/OH
border very late tonight. Latest 24.12Z guidance has backed off
again suggesting the convection will remain trapped within the
ridge. Will likely go with a dry forecast late tonight and remove
any POPS that had crept into the forecast on preliminary
thinking.

PREV DISCUSSION...
Issued at 314 AM EDT Tue May 24 2016

DISCUSSION...

Very dry air mass still locked in over southeast Michigan...per
latest water vapor imagery and 00z DTX sounding. Still looking at
highs in the low to mid 80s today (increased confidence based on
yesterdays results at FNT/MBS) with strengthening low level
southwest flow ahead of a cold front...as 850 mb temps rise into the
the mid teens (00z apx and GRB both showed 15 c at 850 mb). Upper
wave/jet energy working through Minnesota this morning lifting
northeast into Lake Superior today and into Ontario this
evening...helping to flatten the upper level ridge in place
slightly...but still questionable whether we will see any
shower/thunderstorm activity tonight as the moisture axis/plume
folding over into the Central Great Lakes constricts and weakens.
Still...there is narrow ribbon of negative showalter values north of
M-59 with frontal boundary which supports low chance pops. low level
frontal boundary to hang up and wash out over the CWA on
Wednesday...with some semblance of upper level ridge re-establishing
itself during the day...tending to cap/suppress activity...and
probably will have to wait until Wednesday night when warm front and
better surge of moisture arrives from the Midwest to support
scattered-numerous shower and thunderstorm activity. With less
activity expected during the daytime...temperatures should have no
problem rising at least in the lower 80s...as 850 mb temps hover
near 15 C.

Southern Lower Michigan then looks to be caught in between upper
level ridge along the Eastern Seaboard with trough out over the
Rockies...leading to warm/unstable/moist southwest flow Thursday,
Friday, and right into the weekend...with daytime instability
becoming moderate...as MLCAPES advertised to reach between 1000-2000
j/kg per blend of GFS/Euro/Canadian models. To far out to access
possible caps/lake breezes and timing of upper level impulses as we
reside in the ring of fire around the outer fringe of the ridge
axis...but stand a good chance of seeing periodic showers and
thunderstorms during the Thursday-Sunday time frame with the ample
moisture in place. Not much change in air mass will support highs
in the low to mid 80s...but better coverage or early initiation
time of activity could lead to cooler highs.

MARINE...

Generally light southwest wind will develop today over marine areas
ahead of low pressure moving through northern Ontario and as high
pressure continues to exit the Great Lakes. This will bring milder
air into the region that will interact with a cold front and produce
scattered showers and thunderstorms as the front settles into
northern Lake Huron tonight. The front is expected to reach the
south end of Lake Huron by Wednesday evening and leave a light wind
shift to the north. The main concern with this boundary will be
expanding coverage of showers and thunderstorms Wednesday night as
low pressure develops in the plains and pulls the front back
northward while supplying increasingly warm and humid air. Light to
moderate southerly flow will then develop all areas during Thursday
as the front clears the north portion of Lake Huron. A persistent
light south wind will then maintain warm and humid air over the
region into the weekend.

HYDROLOGY...

Warm air with increasing humidity will produce a chance of rain over
SE Michigan beginning tonight and persisting through the Memorial
Day Weekend. The greatest coverage and intensity of showers and
thunderstorms is expected Wednesday night as a cold front settles
into the region, stalls, and then returns northward Thursday.
Rainfall amounts are expected to vary widely depending on
thunderstorm coverage but should average 0.25 to 0.5 inch for the
Wednesday night-Thursday period with locally higher totals near 1
inch possible in thunderstorms. Warm and humid air will then remain
in place to support shower and thunderstorm potential into the
weekend with lower probability until arrival of the next front
possibly by Saturday.

&&

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

$$

AVIATION.....DRC
UPDATE.......CB
DISCUSSION...SF
MARINE.......BT
HYDROLOGY....BT


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at www.weather.gov/detroit.



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