Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 152007
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
407 PM EDT Thu Jun 15 2017

.DISCUSSION...

Weak shear/marginal instability exists outside of our windows this
afternoon as MLCAPES will encroach the 750 to 1000 J/KG range.
Convective inhibition in the 2000-6000 ft agl layer has largely
eroded suggested by both synthesized analyses and just overall
behavior of agitated cumulus/lake breeze showers on radar recently.

The last of the upper level ridging will deflate this afternoon as
geopotential heights fall and an entrance region to an upper level
jet streaks snaps into place over the Great Lakes. Previous forecast
reasoning provided in earlier forecast discussion remains valid. The
setup appears ripe for the development of numerous showers and
thunderstorms with time as outflows from prior convection will
likely serve to triggering additional development. Latest
observational trends, most important being relatively low convective
depths on radar, suggests that less instability will be available
than previously thought. There is still some potential, but it looks
increasingly problematic to see storm tops routinely reach 30 kft
agl. Bulk of the activity is expected to occur between 19-01Z. A
marginal risk for severe weather exists this afternoon for all of
southeastern Michigan with the primary threats being an isolated
wind gust to 50 mph along with heavy downpours.

A fairly pronounced dry line feature is forecasted to push across
southeastern Michigan during the early evening hours tonight. Not
really a cold front, but the feature is very pronounced in the lower
level equivalent potential temperature progs. Model soundings show
the drying that takes place in the 2.5 to 6.0 kft agl layer will be
very efficient in developing a stable air mass over southeastern
Michigan. With no steep lapse rates of significance, confidence is
high for quiet and dry weather prevailing during the overnight.
Conditions tonight will remain relatively balmy with dewpoints
holding in the lower 60s.

The broad upper level low over Canada will continue to suppress
heights, firmly establishing zonal westerlies by Friday morning. A
slightly drier near surface thermodynamic profile along with the
introduction of some better mechanical mixing will provide for a
sneaky setup favorable for compressional warming  Friday. Questions
exist with amount of cloud cover, but thinking favors plenty of
early sunshine off a quiet start to the day. Went aggressive with
warmth with temperatures reaching the middle to upper 80s for much
of the area. Models have also arrived more robust with a lower
tropospheric anticyclonic circulation tracking along the Ohio and
Michigan border late tonight early Friday. Theta e advection is
forecasted to backfill behind the anticyclonic circulation in the
southwesterly return flow. Increasing moisture and humidity will
lead to increasing chance for isolated to scattered showers and
thunderstorms Friday afternoon. Attm, it appears that marginal
instability will limit convective vigor Friday afternoon.

A strong upper level jet streak is shown to push into the upper
Mississippi River Valley and Great Lakes region this weekend. Model
data has been progressively getting stronger and more organized with
the feature, with a bulk of the evidence pointing to an increase in
more active weather. Big item for Saturday evening will be the exit
region of the jet max pushing in vicinity of southeastern Michigan.
Models are suggesting a robust trough deepening response on the
cyclonic shear side of the jet axis which will evoke down stream
ridge amplification. Southeastern Michigan will likely be in the
sweet spot for upper level diffluence and increasing anticylonic flow
trajectories out of the exit region. This will lead to a high amount
of deep layer ascent developing due rapidly increasing warm
conveyor. Some question about where it will occur but looking at
likely PoPs developing Saturday evening. Increasing deeper moisture
and humidity potentially yielding CAPES of up to 2000 J/kg with
suggests Saturday will be worth monitoring for severe thunderstorm
potential.

Strongest of the PV advection is currently timed to lift northward
Saturday night along Lake Michigan during the nocturnal minimum.
Regardless, a significant increase in kinematics will exist compared
to what has been in place recently. Will need to watch for timing of
associated cold front and entrance region dynamics, but a severe
potential for damaging wind gusts will be possible Sunday afternoon.

A cold front will finally push across the area on Sunday, as the
surface low pushes up towards the Hudson Bay.  This frontal passage
will bring a relief to the warmer temps as highs drop back into the
upper 70s for the upcoming week.  Any rain/storms on Sunday will
slowly move east with the front as cooler air works in behind.  With
the northwesterly flow behind the front and the region remaining in
longwave troughing , slight chances for showers will exist
throughout the week.

&&

.MARINE...
Over all winds will remain relatively light and with a southerly
component through Sunday which is when a strong cold front will
swing through the Great Lakes veering winds to the west. There will
be the chance for showers and thunderstorms until the front passes
Sunday.

&&

.PREV DISCUSSION...
Issued at 1245 PM EDT Thu Jun 15 2017

AVIATION...

Weak surface front over Lake Michigan will push through southeast
Michigan in about the 18-00z time frame. Abundant sunshine so far
today is building instability for scattered shower and thunderstorm
development.  Sct-bkn cu in the 4-6kft range expected to develop
during the afternoon with brief lower ceilings possible during
showers/thunderstorms.  Coverage is expected to be scattered with a
more concentration PTK-MBS.  Any activity will dissipate/move east
by 03z.  Expected quiet conditions tonight with mainly skc-bkn mid
level clouds.  Most nocturnal convection should remain west of
terminals with a slight chc for some weak activity to survive
eastward around the 12z time frame. Expect Friday morning to remain
precip free with mostly bkn mid level cloud deck. Winds will remain
wsw under 10kts with brief wind shifts during any convection.

For DTW...VFR conditions through forecast period with exception
during any convection.  Best chances 18-00z and then again after 15z
Friday.  Winds will remain relatively light wsw becoming more south
Fri afternoon.  Brief wind shifts possible with any convection.

//DTW THRESHOLD PROBABILITIES...

* Moderate for thunderstorms this afternoon and evening.

* Moderate for ceilings below 5000 ft this afternoon and evening.


&&

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

$$

DISCUSSION...CB/SP
MARINE.......CB
AVIATION.....DRC


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