Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 171153
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
753 AM EDT Tue Oct 17 2017


.AVIATION...

Surface ridge in control over southeastern Michigan as parent
anticyclone pushest through the Ohio River Valley. Midlevel warm air
advection occuring over a very dry lower tropospheric environment
maintain high stability throughout the TAF Period. Only item of note
is southwest flow of 15 to 25 knots today. Confidence is high that
southwest flow operations will be supported.

//DTW THRESHOLD PROBABILITIES...

* None.

&&

.PREV DISCUSSION...
Issued at 356 AM EDT Tue Oct 17 2017

DISCUSSION...

Near Term / Through 6 PM Tuesday evening

As of 355 AM EDT...Quiet weather night across the region with dry
weather and clear skies. Surface high pressure is located across the
Ohio River Valley, with the close proximity leading to light and
variable winds across southeast Michigan. Despite the boundary layer
decoupling, temps have largely remained steady through the night, as
low-level warm air advection is beginning as the flow shifts to the
southwest. Still, low temps will reach the upper 30s to mid 40s early
this morning, coldest in rural areas of Monroe, Lenawee, and
Washtenaw counties.

Through daybreak, dry weather will continue under clear skies, with
high-level cirrus creeping in across northern areas mainly north of
I-69 as a low pressure system moves across northern Ontario.
Building upper-level ridge will limit the extent of the cirrus cover
due to increasing subsidence, with coverage less than scattered.

For today, aforementioned low-level warm air advection will continue
in earnest, with warmer southwest flow prevailing. With subsidence
from high pressure nearby and a WAA regime, boundary layer heights
will be limited to about 3 kft, but tightened pressure gradient with
the high to the southeast and low pressure across northern Ontario
coupled with plenty of thermal mixing will help compensate.
Southwest winds will occasionally be breezy at times at 15-25 mph,
especially in the Thumb region aided by a deeper marine boundary
layer and stronger marine winds off Saginaw Bay. An overall
stable/dry atmospheric profile (PWATs around 0.50 inch) will lead to
abundant sunshine and dry conditions, with high temperatures
reaching into the mid and upper 60s. Weak 925-850 hPa theta-e ridge
builds into the region, but will have little consequence other than
possibly helping to squeeze out a few boundary layer cumulus.

Short Term / 6 PM Tuesday evening through Thursday

High pressure remains in control through the short term period,
anchored over the southeast CONUS. Dry weather continues with
abundant sunshine. Upper-level heights will gradually build through
the period along with increasing low and midlevel thicknesses.
Return flow around the surface high will keep a general southwest
flow in place, occasionally breezy at times during the daytime hours
with a relatively tight pressure gradient in place with the high to
the southeast and another deep low pressure system moving well to
the north across Canada. A weak shortwave trough embedded in the
flat/slightly meridional midlevel ridging will move across the
region late Wednesday into Thursday coinciding with a dry cold
frontal passage. Just a slight increase in high cloud cover will
accompany these features before sunnier skies return later in the
day Thursday. With the low-level southwest flow and increasing
thicknesses, temperatures will be above normal, with highs in the
upper 60s to near 70 Wednesday and Thursday, with lows generally in
the 40s.

Long Term / Friday through Monday

In the wake of the passing weak shortwave trough Thursday, high
pressure will build again across the region, this time a few
millibars higher than the high earlier in the week. Pronounced upper-
level ridging will be in place as incoming potent Pacific energy
digs into the western CONUS and leads to an increasingly-enhanced
meridional flow pattern. Dry weather and sunny skies will prevail on
Friday, with highs reaching into the upper 60s to lower 70s for most
areas.

Heading into the weekend, the weather will become more unsettled, as
the Pacific energy digs a deep longwave trough across the central
Plains, with increasing clouds for Saturday. Latest runs of the GFS
and ECMWF introduce heightened forecast uncertainty for the weekend,
largely due to the fact that the guidance often struggles handling
the evolution of Pacific energy in the 5-7 day period. The latest
GFS shears out the trough and brings a cold front through the region
Sunday with a period of showers, while the ECMWF develops a closed
upper-level low over Texas, with the region sandwiched in a split
flow regime. With the timeframe being late October, the potential
for cutoff systems increases as northern stream PV and the southern
stream jet become more active, so will need to monitor trends over
the coming days, but a low confidence forecast for the weekend
outlook at this time. Temperatures over the weekend will ultimately
depend on the synoptic evolution, but above normal temps at the very
least will still be in place.

MARINE...

Surface high pressure will build in across the Ohio River Valley and
southeastern US as another low pressure system to our north pass
through northern Ontario. Michigan will be placed in between these
two system and it allow the gradient flow to strengthen out of the
southwest today. A long fetch of gusty winds out of the southwest at
20-30 knots will set up for much of Lake Huron basin and Saginaw
Bay. These winds should persist over the next couple of days as
gradient winds will remain elevated within this regime. Small craft
advisories are in effect for Saginaw Bay and the nearshore waters of
Lake Huron from Port Austin to Harbor Beach.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 6 PM EDT this evening for LHZ421-422-441.

Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....CB
DISCUSSION...IRL
MARINE.......CB


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at www.weather.gov/detroit.



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