Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 261641
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1241 PM EDT Fri May 26 2017


.AVIATION...

Stratocu maintaining its integrity while slowly lifting in response
to diurnal heating. Expect all sites to improve to low MVFR during
the afternoon, approaching 4.5kft once NW flow diminishes after
about 21z. Further scattering expected upon onset of nocturnal
stabilization. MCV originating from tstorm activity over eastern
IA/western IL will track through Southern Lower roughly 04-07z
bringing a chance of higher based showers carrying minimal vsby
restriction. Just a brief MVFR period of cig possible with this
activity. Several hours of clearing in the wake of the MCV followed
by return of sub-5kft cigs during Sat morning in response to renewed
diurnal heating.

//DTW THRESHOLD PROBABILITIES...

* High for cigs aob 5kft through 00z. Low 00z-15z. High after 15z
  Saturday.

&&

.PREV DISCUSSION...
Issued at 424 AM EDT Fri May 26 2017

DISCUSSION...

Holiday Weekend - Forecast Package Highlights.

1. Went drier overall today and again Saturday, with less broad
brush precipitation mention in the forecast. A chance for rain
exists tonight south of the I 69 corridor.

2. High confidence in a relatively longer duration rain event
Sunday. Was aggressive in increasing PoPs. Appears a bulk of the
precipitation will fall prior to 18Z as a warm front lifts through
southeastern Michigan. Precipitation chances persist throughout the
afternoon as a chance for thunderstorm redevelopment will exist.

Inconspicuous as it is, a rather complex low level pattern exists at
the moment over much of the central United States. Sort of a 3 leaf
clover configuration with 3 separate, lower geopotential height
centroids at 850mb. The centers of the low height anomalies are over
the northeastern U.S., the Canadian prairie provinces including
North Dakota, and a much weaker one over KS/OK. This places
southeastern Michigan between them all, where a weak col exists. The
lack of any tangible advections within this col will keep the
weather fairly static this morning. As a result, decided to go with
a patchy drizzle mention this morning. Little conflicted on what to
do with the clouds, as the back edge continues to creep closer.
Given the continued cyclonic flow trajectories locally, and higher
likelihood to cu back up with daytime heating,  feeling it best to
err on the side of a cloudy forecast, although there is a shot at
some breaks at times.

For tonight, models are at odds with how to handle the KS/OK
circulation as geopotential heights at the hemispheric scale are
shown to rebound. This will occur as blocking is relieved downstream
and the N.E. Low pulls away very quickly. The GFS and WRF-ARW is far
and away the most aggressive in preserving a convective vorticity
maximum and MCS, now near Kansas City, across the midwest directly
into southeastern Michigan tonight. Rough comparison to GFS output
to radar upstream shows the GFS solution was too overdeveloped with
the MCS over the northern parts of the circulation. On the other
hand, the ECMWF has been too underdeveloped with its output thus
far. Rather, it depicts convective development later today over
portions of far eastern Iowa and Illinois before tracking it eastward
through Ohio tonight. RAP based guidance shows a deeper circulation
which sides more in line with the GFS/ARW. Do like the placement of
the circulation with respective to the orientation of the midlevel
theta e ridge and the amount of advection of instability. All signs
point to the circulation remaining nestled up against the midlevel
shortwave ridging axis that will preserve some cyclonic flow
influence. Still cannot totally buy in given higher stability in the
6-12 kft agl layer here in semich and will leave out thunder. This
is in agreement with the latest Swody1 that keeps much of general
thunder to the south. Obviously, there is some potential for forecast
refinement later today. Stable conditions at the surface brings
higher confidence in no severe weather threat tonight.

Very strong signal for amplifying shortwave ridge over Lower
Michigan on Saturday. This is complete with high consensus forecast
for mesoscale anticyclonic vorticity advection bubble tracking
across semich. Really not much to say except this will undoubtedly
be the best day of the upcoming holiday weekend. Expecting a fair
amount of sun with highs pushing into the middle 70s for much of
southeastern Michigan. Dewpoints are even expected to rise into the
upper 50s which will give it a more humid feel.

The Canadian Prairie lower height anomaly is shown to dig or drift
southward eventually exerting its influence on southeastern Michigan
by Sunday. Energy rotating around and ejecting out of the southern
portion of the developing closed low will tap into some baroclinicity
and lead to a widespread precipitation event over southeastern
Michigan on Sunday. Still some timing difference on when the warm
front will move through, the ECMWF was notably a little slower. For
now, went with a likely PoP throughout the day. The potential for
severe weather, will hinge on whether or not the warm front can move
through earlier in the day and allow for the atmosphere to
destabilize during the afternoon. At this stage it appears that 1500
J/KG of MLCAPE will be attainable under a fairly well developed left
exit region dynamics. Something to monitor in the next couple of
days. Latest Swody3 has much of southeastern Michigan in a marginal
risk for severe weather.

MARINE...

A ridge of high pressure will build into the Central Great Lakes
today, allowing northwest winds to become light and variable by this
evening. Ridging will be brief, however, as a weak area of low
pressure tracks across the Ohio Valley overnight. Winds will remain
fairly light, turning east by late tonight and continuing through
Saturday. Another area of low pressure will cross the region Sunday,
allowing conditions to turn unsettled again as thunderstorms become
possible very late Saturday night through Sunday. Wind speeds are
generally expected to remain around 10 knots or less through Sunday
night. An increase in southwest winds is expected on Monday, with
gusts potentially topping 20 knots.

&&

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

$$

AVIATION.....JVC
DISCUSSION...CB
MARINE.......HLO
HYDROLOGY....HLO


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