Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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801
FXUS63 KDTX 291426
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1026 AM EDT SUN MAY 29 2016

.UPDATE...

Warm sector destabilization is underway across Lower Michigan
ahead of a sfc cold front, moving into western Lake Michigan as of
14Z. Se Mi currently resides on the western edge of a dense high
cloud deck. These clouds will slide to the east very slowly today.
There will still be adequate afternoon destabilization west of
this cloud deck, which will advect into the forecast area under
good ssw flow today. There are however a few obstacles to
overcome in order to achieve deep convection today. First off,
large scale ascent via the mid level height falls, upper jet
support and convergence along the sfc front will not be terribly
strong. There is an axis of low level moisture extending from nrn
Indiana into Se Mi. Model soundings however suggest this moisture
is shallow, so there is a concern that diurnal mixing may reduce
boundary layer moisture to such a degree as to hinder deep
convection. The 12Z DTX sounding also showed some capping in the
900 to 800mb layer, which may also inhibit deep convective
initiation this afternoon. Given these factors, just chance type
pops for afternoon showers/thunderstorms will be maintained in the
forecast. Various hi res solutions suggest the most probable
locations for thunderstorm development will be across the thumb
into Port Huron in the 19Z to 23Z time frame.

If deep convection can materialize, strong to severe storms will
still be a concern. Despite rather marginal deep layer shear of 25
to 30 knots, if 0-1km MLCAPE can reach 1k to 1500 j/kg, model
soundings indicate somewhat good cape density, supportive of gusty
winds and hail. The degree of mid level dry air and steep low
level lapse rates would also support strong convective downbursts.
For these reasons all of Se Mi remains in a marginal risk for
severe storms this afternoon and early evening. A special 18Z DTX
sounding is being planned to better asses afternoon convective
potential.

&&

.PREV DISCUSSION...
Issued at 544 AM EDT Sun May 29 2016

AVIATION...

Warm and humid air mass will sustain chances for showers and
thunderstorms today. A few showers, perhaps even a thunderstorm,
will continue to develop through the morning and early afternoon as
the low-level jet continues to feed moisture into the area. Onset of
diurnal heating will allow lower VFR cu deck to fill in, although
presence of high/mid clouds this morning may delay it until 15-17Z.
Approaching pre-frontal trough and cold front should allow for a
more organized area of showers and storms during the mid to late
afternoon (west to east moving between 17-23Z). These storms will
carry a low potential to become severe, and may also contain brief
periods of heavy rainfall and low visibility. Southwest winds may
become a little gusty this afternoon ahead of the front, but gusts
are expected to remain below 25 kts. Modest westerly wind shift will
accompany the front this evening, with arrival of drier air ending
chances for showers/thunderstorms and allowing skies to clear
overnight.

FOR DTW...A few light showers may impact the airspace this morning.
Best window for thunderstorms looks between 19Z and 23Z today
preceding a cold frontal passage. Otherwise, latest model data
supports ceilings just above 5000 feet by 17Z with deeper mixing
helping to raise ceiling heights. VFR conditions are expected
tonight and early Monday.

//DTW Threshold Probabilities...

* Low for ceilings at or below 5000 FT through this evening.

* Low for thunderstorms affecting DTW/D21 airspace today.

PREV DISCUSSION...
Issued at 257 AM EDT Sun May 29 2016

DISCUSSION...

A weak cold front will progress west to east through lower Michigan
late today as a vigorous shortwave lifts from the upper Mississippi
Valley into the northern Great Lakes. A surface trough will precede
this front during the afternoon/early evening hours, providing focus
for scattered convection as moderately unstable conditions develop
within the warm/humid airmass that has overspread the region during
the past few days.

Mid level WSW flow in the 25 to 30 knot range will provide enough
bulk shear to allow for at least minimal convective organization
within the unstable warm sector. Generally expect a few multi-
cellular clusters with overall convective coverage remaining rather
scattered. Timing of the pre-frontal trough actually suggests most
convective initiation will occur over the area during the mid to
late afternoon with this activity then being swept east out of lower
Michigan by 00z or so. During this 4 or 5 hour window, expect a few
storms to at least approach severe limits with isolated large hail
and/or damaging wind gusts. This seems most likely over the Thumb
region where lake breeze convergence will most likely enhance the
updrafts that form along passing trough axis.

Several quiet days will follow as high pressure builds across the
central Great Lakes early in the upcoming week in the wake of this
cold front. While temperatures will still climb into the 80s in most
locations during this time frame, humidity levels will be lower as
the dew point temperatures in the lower/mid 60s of late will be
replaced by readings in the mid/upper 50s. This will also allow for
cooler overnight temperatures in the 50s to around 60.

Warm/humid conditions will briefly build back into the region during
the middle of the week as upper level heights build in advance of
the next shortwave trough as it eject slowly ENE along the US and
Canadian border region. This system will bring an increased chance
of showers and a few thunderstorms from Wednesday into Thursday
before the cold front associated with this upper level trough moves
through the region and brings a cooler/drier weather pattern heading
into next weekend as upper trough becomes established over the
Great Lakes late in this forecast period. Temperatures of 70 to 75
by day and 50 to 55 by night will become common from Friday on into
the weekend.

MARINE...

Areas of fog...potentially dense...will remain possible over Lake
Huron into this afternoon before south winds increasing to 10 to 15
kts ahead of a cold front allows any fog to mix out. The front will
push across the region late this afternoon and evening as low
pressure tracks across Ontario. Showers and thunderstorms will be
possible as the front slides through a warm and humid airmass...with
a few storms becoming strong or possibly even severe during the
afternoon and evening. The biggest threats will be damaging wind
gusts to 50 kts and hail to 1" in diameter. Light westerly flow and
dry weather are expected behind the front for Memorial Day.

&&

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

$$

UPDATE.......SC
AVIATION.....HLO
DISCUSSION...DG
MARINE.......HLO


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