Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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593
FXUS63 KDTX 251927
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
327 PM EDT Sun Jun 25 2017

.DISCUSSION...

The train of embedded upper level waves/PV anomalies and re-
enforcing cold pools will continue through Monday evening. 12Z APX
raob checked in with an impressive -24 C temp at 500 MB, and based
off the SPC climo sounding site, appears to be record territory.
Fortunately, surface dew pts have lowered into the 45 to 50 degree
range (outside of where it has rained), which has limited surface
based instability to 500 J/kg or less and no Lightning detected so
far this afternoon over southeast Michigan.

The main/large circulation tracking through Lake Huron
this morning did touch off thunderstorms over Lake
Huron and eastern Thumb Region however. Meanwhile, A smaller
circulation over central Lower Michigan is advancing southeast,
allowing for some modest mid level moisture advection, and should
maintain some shower activity into early evening hours. Cool airmass
(mid single temps at 850 mb) and west-southwest flow behind this
feature tonight. Some lake Michigan enhancement showers appear
possible as 850 mb thermal trough swings east, as lapse rates in the
5-10 KFT (per RAP) layer appear sufficient to support isolated to
possibly low scattered activity working east overnight.

One last upper level wave/cold pool, currently near western Lake
Superior slowly dropping southeast, with 850 mb temps progged to
lower to 2 to 4 C Monday Evening. However, showers may be hard to
come by during the day as drying/850-700 MB Theta-E minimum
encompasses southeast Michigan. As been the case the past couple of
days, best chance  of activity will be toward Saginaw Bay, closest
to the mid level circulation/trough and the mild waters of Saginaw
Bay.

Upper level northwest confluent flow allowing for large anticyclone
to build into Midwest Monday night, and into the western Ohio Valley
during Tuesday. Late June insolation and westerly flow over southern
Lower Michigan should allow for good temp recovery, with highs
reaching into the mid 70s.

A surface high pressure and ridging aloft will keep conditions dry
across Michigan during the morning and afternoon hours as low level
clouds start to build into the region ahead of a low pressure
system. As the surface low moves from Minnesota into northern lower
Michigan Wednesday into Thursday, it will drag along a warm front
with it, bringing likely rain and thunderstorm chances to Southeast
Michigan. Confidence it moderate to borderline-high regarding seeing
scattered showers and storms throughout Thursday, however,
additional model runs will be needed to pinpoint timing, as the
ECMWF run brings the precipitation in late Wednesday into Thursday,
while the GFS and GEM runs hold off on precipitation until the early
to mid-morning hours on Thursday. This system will be something to
keep an eye on given the flooding and saturated conditions across
Central Michigan, as localized heavy rainfall will be possible with
storms that do develop, given the impressive moisture transport and
PW values averaging 1.6 inches.

Confidence is starting to rise regarding rain and thunderstorm
chances late Friday into Saturday as a weak surface low pushes
northeast from Iowa into lower Michigan, as seen in the ECMWF and
GEM runs. For comparison, the ECMWF run had this low coming through
Michigan throughout Friday during yesterday`s run, and it was absent
from the GEM run. The GFS fails to resolve a low pressure system
tracking into Michigan unlike the GEM/ECMWF, however, it holds a
weak low pressure system across the U.P, which would allow a warm
front to provide some lift for showers and thunderstorms. As the
expected low moves east out of Michigan by Saturday, rain chances
will diminish, especially as ridging aloft builds into the Midwest
early next week.

&&

.MARINE...

Fresh westerly breeze over nearshore zones will ease tonight
allowing the small craft advisories for Lakes Erie and Saint Clair
to expire on schedule. Resurgence of gusty west wind on Monday will
likely warrant another round of small craft advisories including at
least Saginaw Bay and Lake Erie. Light to moderate wind will then
dominate until the arrival of the next system Wednesday into
Thursday. Moderate southerly wind will transition to fresh
southeasterly during this time, the stable southerly fetch limiting
gustiness.

&&

.HYDROLOGY...

Scattered diurnal showers will continue this afternoon and again on
Monday. Though rain may briefly be heavy on a local basis, basin
average rainfall is expected to remain under one tenth of inch on
each day and no noteworthy response to area rivers and streams is
anticipated. The next chance for organized rainfall will be
Wednesday night into Thursday when up to one half inch of rain will
be possible. The Tittabawassee River crested Saturday evening and
remains in major flood stage at this time. However, river levels
continue to fall and flood waters will follow suit. Meanwhile, The
Saginaw River continues to slowly rise and will crest on Tuesday
morning at moderate flood stage.

&&

.PREV DISCUSSION...
Issued at 1244 PM EDT Sun Jun 25 2017

AVIATION...

Corridor of isentropic ascent will pivot through the area during
peak heating. Most focused ascent will reside PTK north where
mention of -shra remains in the forecast. Given drier low-levels and
low rain intensity, expect nothing worse than brief MVFR with any
showers. Further south, VFR cu dominate. Low potential for showers
to move into the Detroit area given weaker forcing and downsloping
contributing to more dry air in the lowest levels. A passing shower
is possible but confidence is too low to warrant carrying in the TAF.

For DTW...Cigs aob 5kft will be possible but downsloping within
westerly flow makes the forecast difficult given borderline upstream
obs. For now will carry a borderline BKN050 pending evidence for
sustained 060 or higher.

//DTW THRESHOLD PROBABILITIES...

* Low for cigs aob 5kft

* Low for winds reaching crosswind thresholds from 270 degrees


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory from 10 AM to 8 PM EDT Monday for LHZ421-422.

Lake St Clair...Small Craft Advisory from noon to 8 PM EDT Monday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from noon to 8 PM EDT Monday for LEZ444.

&&

$$

DISCUSSION...SF/AM
MARINE.......JVC
HYDROLOGY....JVC
AVIATION.....JVC


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



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