Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

000 
FXUS63 KDTX 291043
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
643 AM EDT Thu Jun 29 2017

.AVIATION...

Lingering remnants of an earlier convective complex exits eastward 
within the next couple hours.  A period of deep layer stability left 
in it's wake will likely act to limit renewed convective development 
through at least early afternoon.  Uncertainty in the degree and 
pace of the diurnal recovery as this stability relents under daytime 
heating casts doubt on thunderstorm prospects mid afternoon through 
the evening period.  Placement of the greater moisture content near 
or just south of the area suggests the Pontiac and Detroit corridors 
will reside at the northern extent of any late day development. 
Thus, confidence remains too low to provide a definitive at this 
time.  Strong south-southwest flow just off the surface this morning 
will translate into a gusty conditions today as the mixed layer 
deepens. Gusts reaching over 25 knots at times. 

For DTW...Low confidence in the potential and possible timing of 
thunderstorms late today and tonight.  Coverage this 
afternoon/evening may ultimately prove very limited.  Intermittent 
ceilings near 5000 ft this morning, with improving potential for 
cigs at or just below this level this afternoon as diurnal heating 
improves.  

//DTW THRESHOLD PROBABILITIES... 

* Low for ceiling 5000 ft or less this morning. Moderate this 
  afternoon. 

* Low in thunderstorms this afternoon and tonight.

&&

.PREV DISCUSSION...
Issued at 419 AM EDT Thu Jun 29 2017 

DISCUSSION...

Longwave trough will reside over the northern U.S. and Canada 
through the end of the week, while shortwave troughs embedded within 
the larger feature pass through the Great Lakes. This will keep 
unsettled weather over the area into the first part of the weekend.

The first upper wave is currently working into the northern Great 
Lakes, and will push an area of surface low pressure across the U.P. 
today into tonight. A couple of MCVs from upstream convection that 
occurred over IA/WI/IL yesterday evening are working across the area 
along with strong theta-e advection early this morning, bringing 
showers and a few thunderstorms (mainly north of M-59). The activity 
has been weakening as it moves towards Southeast Michigan and 
encounters a drier and more stable airmass. Idea is that this area 
of showers/tstorms will move east this morning, with subsidence 
behind the upper waves and mid-level drying over Central Michigan 
then yielding quieter weather for the middle part of the day. 
Recovery of the airmass then becomes the deciding factor in whether 
additional development of showers/tstorms occurs during the late 
afternoon and evening. Hi-res models are split with solutions. Best 
chance for redevelopment will be south of the I-69 corridor and 
especially towards the Ohio border where deeper moisture will 
reside. Warm and humid conditions are expected today, with max temps 
in the low/mid 80s and dewpoints surging well into the 60s this 
afternoon. Should also see a good pop of winds once we decouple late 
this morning, with mixed layer supporting gusts to 35, or even 40 
mph, per RAP/HRRR/NAM forecast soundings. Gusts should decrease by 
mid afternoon however as low-level jet axis and stronger winds aloft 
slide to our east. Severe weather potential this afternoon/evening 
will hinge on airmass recovery following morning showers/tstorms and 
clouds. Modestly strong wind field will exist over Southern Michigan 
on the south side upper wave and surface low over the Northern Great 
Lakes, with 30-35 knots of bulk shear in the afternoon per GFS/NAM. 
If we can build enough ML CAPE, could see a few severe storms in the 
afternoon/evening, with large hail and damaging winds the main 
threat. Heavy downpours will also be possible.

Next round of convection to watch will likely occur overnight as 
complexes of storms that develop late this afternoon/evening over 
IA/MO move towards southern Michigan. Nocturnal resurgence of the 
low-level jet stretching from the central Plains through the Ohio 
Valley will help to maintain this activity to some degree, with up 
to 1500 J/kg of CAPE keeping severe threat into the late night 
hours. Other concern for convective development, including a few 
severe storms, will be as a secondary warm front lifts into Southern 
Michigan, potentially allowing storms to become surface based while 
low-level shear increases, but CAPE should fall to less than 800 
J/kg, again limiting threat and coverage of severe weather. Other 
noteworthy item in the forecast tonight is the expectation of a warm 
and humid night, with low temps only falling into the upper 60s to 
near 70.

Next of the larger synoptic waves embedded within the longwave 
trough that will impact Michigan now dropping through the Pacific 
Northwest and will track into the Upper Midwest Friday, allowing 
surface low pressure to lift up through Michigan. Secondary warm 
front will continue lifting northward through the area during the 
day, ushering in additional warm air and moisture. Severe storms 
will again be possible, with strong flow once again residing over 
the area and a potentially better build-up of instability during the 
day. This will once again depend on overnight and early day 
convection, which could again limit instability.

MARINE...

The region will remain under a moderate southerly wind today, as low 
pressure slowly tracks across the upper peninsula.  These speed will 
be magnified over Saginaw Bay and over western Lake Erie, where 
channeling and alongshore flow respectively will enhance gusts. 
Small craft advisories are in effect through this evening for these 
areas as well as for Port Austin to Harbor Beach around the tip of 
the Thumb. This wind pattern will bring in warmer and more unstable 
air into the region before easing tonight into Friday. The warmer 
air will fuel increased thunderstorm activity as low pressure over 
the northern Great Lakes drags a diffuse surface trough through the 
region Friday into Saturday.

HYDROLOGY...

Lingering remnants of a weakening thunderstorm complex will maintain 
the potential for lighter showers/isolated thunderstorms through the 
morning period.  Rainfall amounts thus far largely arriving as 
forecast, with totals generally ranging between one quarter and one 
half inch where more widespread coverage was noted.  

Greater stability in the wake of this complex does cast doubt in the 
prospects for renewed thunderstorm development through the remainder 
of the daylight period.  Expectations remain that any additional 
development today will tend to focus south of the I-69 corridor, 
with the greatest potential closer to the Ohio border.  Once again, 
average rainfall amounts of less than half an inch are anticipated, 
but localized higher amounts in excess of an inch area possible 
should more concentrated areas of thunderstorms materialize this 
afternoon and evening.  Potentially active period for showers and 
thunderstorms will exist tonight through Friday night, although 
placement of the more concentrated development remains less certain. 
 
The potential for flooding will be dependent on the cumulative 
rainfall totals during this active period. Should a more focused 
region of heavy rainfall emerge, then the potential for a 
corresponding rise of area rivers and streams, as well as minor 
flooding will be possible. Central Lower Michigan will remain most 
susceptible as the area continues to recover from recent flooding.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through this evening for MIZ049.

Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422-
     441>443.

Lake St Clair...Small Craft Advisory until 10 PM EDT this evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EDT this evening for LEZ444.

&&

$$

AVIATION.....MR
DISCUSSION...HLO
MARINE.......MR

National Weather Service Glossary of Abbreviations