Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
340 PM EDT Tuesday Aug 23 2016
Shortwave ridge supporting mostly clear skies and average
temperatures over the area this afternoon. Arrival of the ridge axis
overnight will open up area skies to cirrus and mid cloud
infiltrating from the west. Current visible over the MS valley is
not impressive with regard to cloud coverage, but ongoing convection
should result in expanding cirrus that will gradually work into the
area overnight. Mostly clear skies for much of the night are
therefore expected to allow overnight lows to settle near currently
observed dewpoints near 60 degrees.
Uncertainty in shower/tstorm potential for tomorrow remains
uncharacteristically high for this lead time. Nocturnal jet is
progged to set up along a line from roughly the Texas Panhandle to the
Quad Cities tonight coincident with lower amplitude energy ejecting
out of the SW United States. Convectively enhanced shortwave will
lift to the northeast, transiting mainly northern portions of the
County Warning Area during the day Wednesday as support from a waning nocturnally
enhanced jet diminishes. Therefore, have tightened the pop gradient
for the afternoon, confining likely to the northwest two thirds and chc to
the southeast third of the area. Corridor of Theta-E advection around the
periphery of the large southeast US high will support continuance of chc
pops into the late evening/overnight over the far southern County Warning Area while
lack of forcing elsewhere warrants removal of pops by 03z north of
Theta-E ridge fostering tomorrow's convective chances will bring a
rise in dewpoints as surface flow veers southwesterly. Muggy
conditions through Thursday as tds hover near 70 degrees, limiting
overnight lows to similar values. Clouds will cap daytime highs in
the low to mid 80s Wednesday and again on Thursday as a weak frontal
wave ripples across the deep baroclinic zone present within the
narrow corridor of SW flow across the Great Lakes. Limited
instability forcing may ultimately limit coverage, so chc pops
appropriate everywhere except the far south - where likelies are in
place - attm.
Quiet weather expected Fri/Sat with anticyclonic upper-level flow
and surface high pressure. Model consensus then depicts a
deamplifying upper wave tracking across the northern Great Lakes.
Moisture return in advance of this feature necessitates entry-level
chance pops Sunday despite better forcing located well to the north.
Some semblance of a frontal passage late Sunday, but baroclinic zone
may be close enough to warrant continued low pops into early next
week. Temperatures Friday through early next week expected to be
near to above normal.
A warm front will move through the lakes Wednesday afternoon/evening
bringing scattered showers and thunderstorms. A cold front will
follow shortly behind the warm front across Northern Lake Huron and
slowly drop southeastward during the day Thursday and clear to the
east and south by early Thursday night. More scattered showers and
thunderstorms are likely with the cold front. Winds will be modest
from a southerly direction ahead of the warm front then tone down a
bit after passage. Winds will become northwesterly Friday behind
cold frontal passage. High pressure will bring light and variable
winds Saturday then more southerly Sunday as it moves off to the
east and a cold front approaches from the west. This front may
bring showers activity across Lake Huron Sunday afternoon.
issued at 112 PM EDT Tue Aug 23 2016
Surface high pressure ridging over the area will pull off to the
east this afternoon while a warm front approaches the area on
Wednesday. Southerly flow will continue across the area through the
period. Scattered to occasional broken diurnal cu will occur this
afternoon in the 4-6k ft range as surface dewpoints slowly increase.
Models have some difference in timing of warm front and associated
precip with it Wednesday. Timing seems to range from late morning
to late afternoon. Will carry a prob 30 towards the end of taf
period for all sites. Bases with ceilings should remain VFR.
For dtw...mainly scattered to possibly broken cu 4-6k ft this
afternoon dissipating with loss of daytime heating. Mid to high
level clouds will advect in around 12z. Models differs slightly
with warm front arrival and associated precip from late morning to
later afternoon. Consensus past few days has been later so will
carry tempo group of showers and thunderstorms late afternoon with a
prob30 for some early arrival of some rogue showers.
//Dtw threshold probabilities...
* low for ceilings aob 5kft today. Medium Wednesday afternoon.
* Medium for thunderstorms Thursday afternoon.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
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