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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
1259 am EDT Thursday Aug 28 2014



Aviation...

//discussion...

Surface high pressure building into the Great Lakes will allow for
veered northeasterly flow to make inroads into southeastern Michigan
this morning. Recent infrared imagery supports what earlier models
solutions have been advertising in developing a VFR deck for The
Thumb down into the M59 corridor. Went decidedly more pessimistic at
all taf sites with these clouds for tonight into Thursday. Stratus
during the early morning is expected to lift and scatter out with
time by Thursday afternoon.

//Dtw threshold threats...

* high confidence in ceiling heights at or below 5000 feet above ground level.

&&

Previous discussion...issued 346 PM EDT Wednesday Aug 27 2014

Short term...

High pressure near Lake Superior will translate toward northern
lower Michigan overnight tonight due to persistence of confluent flow
aloft. Northward displacement of the high center will result in the
maintenance of a weak surface pressure gradient for the balance of
the overnight hours, calling decoupling potential into question. The
exception will be northern areas in closer proximity to the high
and, in particular, The Thumb which will see some local
reinforcement of high pressure thanks to Lake Huron. As a result,
expect the best cooling across the north where prospects for
decoupling will be best. Upper 40s will be possible on a local basis
north of I-69, but rather moist antecedent boundary layer
conditions, a modest gradient, and incoming high cloud debris
preclude dropping forecast lows to the widespread 40s advertised
across the north by the 12z met/mav. Locations south of M59 will
remain firmly in the middle to upper 50s. The only notable forecast is
lake stratus potential overnight. Higher resolution model forecasts
indicate a brief period of enhanced boundary layer convergence as
northerly flow comes onshore in The Thumb, typically a good signal
for stratus formation. However, with flow tending to back to a more
north-northwest direction with time, expect that the best prospects for marine
stratus will be in the eastern thumb into Port Huron. Did not hit
the potential too hard given the uncertainty inherent in the
scenario, but did opt to introduce at a moderate cloud fraction into
the grids.

Long term...Thursday through next Wednesday

High pressure will be in place on Thursday across Southeast
Michigan. Strong upper level ridging will keep conditions dry while
850 temperatures in the 8 to 12 degree range result in much cooler
temperatures /highs only in the middle 70s/. The high will slowly drift
eastward by Friday morning. A low pressure system will begin to
develop across the central to upper plains as a shortwave trough
digs across the Central Plains on Friday. As the low tracks
northeastward it will send a warm front across lower Michigan on
Friday night. The warm front will bring an increased chance for rain
showers across the County Warning Area. Model agreement is a bit uncertain with the
timing of this frontal boundary. GFS model is keeping most of Friday
dry until Friday night when the warm front pushes into the area.
However...European model (ecmwf) model is showing precipitation to begin by Friday
afternoon and continue through Friday night. With the uncertainty
in timing on Friday afternoon...have kept only chance probability of precipitation /30 to 40
percent/ for the County Warning Area. However...precipitation seems fairly certain
for Friday night and have bumped up precipitation chances to likely probability of precipitation
for Friday night across the northern County Warning Area and high chance probability of precipitation for
the southern County Warning Area. Plenty of warm air advection will result in high
temperatures on Friday to jump back up into the upper 70s and low 80s.

Potentially active Labor Day weekend in store with a moist airmass
in place and periodic disturbances traversing the local area. Upper
air pattern will feature an amplifying trough advancing from the
Pacific northwest to the upper Midwest while an upper ridge holds
firm over the southeastern US. There is also a good signal of a feed
of Gulf moisture into the upper Midwest this weekend. 12z suite depicts a
deamplifying shortwave working through the local area in
southwesterly flow with enough confidence to go with likely probability of precipitation
Sat/Sat night. Models have also trended faster with the main upper
longwave trough/cold front working through by Monday/Monday
night...though more run-to-run consistency is needed before probability of precipitation are
bumped up in that timeframe. However...gave a nod to this solution
by keeping Tuesday/Wednesday dry in the wake of the potential
frontal passage.

Marine...

High pressure will continue to build over the area tonight and
remain over the Great Lakes region through Friday morning. Rain
showers and thunderstorms will return on Friday night as a warm
front tracks across Southeast Michigan. This warm front will stall
over Southeast Michigan allowing rain showers to continue through
Saturday. A low pressure system will then track across western
Michigan and drag a cold front across the region on Saturday night
and into Sunday...keeping rain chances around through the end of the
weekend.

&&

DTX watches/warnings/advisories...
Michigan...none.
Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.

&&

$$

Aviation.....Cb
short term...jvc
long term....rk/dt
marine.......rk



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