Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 181046
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
646 AM EDT Tue Apr 18 2017

.AVIATION...

Maintenance of a dry and stable low level environment under the
lingering influence of high pressure will ensure VFR conditions hold
through the daylight period.  Limited late day diurnal cumulus
coverage within this environment, with plenty of clear sky expected
across the lowest 5 kft.  A firm 12-15kt southeast wind today may
briefly turn gusty /20 kts/ at the height of peak heating this
afternoon.  Benign aviation conditions through a good portion of the
night, only issue may be a marginal case of low level wind shear as
southwest flow across the 1500-2000 ft layer near 40 kts.  No
explicit inclusion at this time.  Moisture will increase upon the
approach of a cold front by Wednesday morning.  Mixed model signal
yet on the degree of low level moistening and subsequent lower cloud
and shower development during this time, warranting a conservative
approach to lowering cigs and possible vsby restrictions in showers
at this introductory stage.  Very low probability for embedded
thunderstorms with any activity.

//DTW THRESHOLD PROBABILITIES...

* Low for cigs at or below 5000 ft late tonight into Wednesday
  morning

* Low for thunderstorm occurrence Wednesday morning.

&&

.PREV DISCUSSION...
Issued at 346 AM EDT Tue Apr 18 2017

DISCUSSION...

Compact low lifting through the Dakotas early this morning will
continue to track ENE through today, crossing Lake Superior and
entering northwest Ontario late this evening into tonight.
Baroclinic zone is beginning to take shape nicely over the Front
Range while the nocturnal low-level jet supports disorganized
convection. SE flow will veer to southerly this evening as high
pressure is forced east. Expect a healthy west-east gradient in
temperature with lake shadowed areas remaining in the low 60s while
locations west of US-23 approach 70. By tonight, the bulk of the
forcing with this wave passes well north of the area. However, at
least the northern half of the CWA is modeled to be clipped by the
tail end of the veering LLJ. Enhanced low-level convergence within
the increasingly moist environment will support a mention of high
chc showers, higher pops precluded by uncertainty regarding
organization of showers.

Front sags south and becomes stationary invof the MI/OH border as
forcing departs and the boundary orients roughly parallel with the
mean flow. Expectation at this time is that fropa will bring a
chance of showers to all areas early Wednesday, but the general
character of the day will be dry as the surface front remains well
to the south. Nearer the Ohio border, forecast soundings indicate a
weakly capped environment. This may be just enough for solenoidal
forcing along the front to generate periods of showers/t-storms
mainly south of 8 Mile during the day Wednesday. Confidence in
coverage and duration across the far south remains low at this time.
Severe potential along the front on Wednesday will be limited by a
lack of better mid-level lapse rates. Limited updraft intensity
notwithstanding, locally enhanced shear along the front may support
a few rotating showers capable of producing an isolated weak tornado
near the southern state border. General expectation, however, is for
episodes of low impact showers possibly containing thunder to
periodically affect this area during Wednesday.

Wave presently well off the California coast will induce
cyclogenesis over the Front Range by Wednesday, the resultant
downstream isentropic ascent over Lower Michigan increasing markedly
along the resident stationary front after 00z Wednesday. Coverage of
showers and t-storms will increase as the boundary assumes a warm
front character and lifts through the area through Wednesday night.
Any concern for an isolated tornado becomes increasingly limited
given mid-April nocturnal boundary layer effects, but the
approaching LLJ axis beneath steepening lapse rates aloft will pose
some concern for a transient window of sub-severe or marginally
severe hail with any more vigorous updrafts along the warm front.

Strong consensus among 00z global model suite that warm sector
instability will build to 500-1000 j/kg MLCAPE during the first half
of Wednesday. Respectable forcing ahead of the cold front within the
highly sheared environment will be supportive of a line of strong to
severe storms transiting SE michigan during the afternoon. Progged
thermodynamic profiles not particularly impressive, supporting
nothing more than borderline severe wind gusts and 1 inch hail.
Nonetheless, strongly forced low-levels could yield a fairly
widespread, albeit low end, threat.

MARINE...

An increase in southeast winds today as high pressure exits to the
east.  Strongest response noted across northern Lake Huron, where a
period of 20 knot sustained winds may gust in excess of 25 knots
from late this afternoon through early tonight.   Winds then ease
again late tonight into Wednesday as a cold front slides through.  A
period of northerly winds immediately behind this front will remain
modest during the day.   The approach of strong low pressure will
then bring an increase in northeast winds Wednesday night and
Thursday across portions of lake Huron.  The wind and wave forecast
still carries some uncertainty during this time, with dependence on
the low track and strength.  There will be the potential for gusts
to reach near gales over north-central Lake Huron.  In addition,
small craft conditions appear likely for higher waves along the
nearshore waters and Saginaw Bay.  An unsettled period Wednesday
through Thursday with several rounds of showers and thunderstorms
possible.

HYDROLOGY...

Unsettled weather will return Wednesday and Thursday with periods of
showers and thunderstorms. Thursday is expected to be the wetter
day, as strong low tracks near or through southeast Michigan.
Rainfall amounts in excess of 1 inch are likely north of the low
track, but the exact location remains uncertain.  The potential for
some minor flooding will exist, particularly given the wetter than
average conditions noted in recent weeks.

&&

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

$$

AVIATION.....MR
DISCUSSION...JVC
MARINE.......MR
HYDROLOGY....MR


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