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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
1157 am EST Monday Nov 30 2015


Middle clouds streaming into mbs this afternoon...otherwise clear skies
(below 12 kft) will give way to rapid increase in low level
moisture/clouds late this evening...with MVFR ceilings by midnight
lowering into IFR category overnight ahead of an occlusion...which
should help focus light rain/drizzle. LIFR ceilings are expected by
12z across southern taf sites...which could expand farther north.
Little if any improvement expected during the first half of the
day on Tuesday...with light easterly winds this afternoon
gradually coming around to the southeast and then south tomorrow.

For dtw...

Clear skies this afternoon are expected to quickly give way to
developing low clouds (mvfr/ifr) this evening...with light rain and
LIFR ceilings overspreading by sunrise Tuesday. LIFR/IFR will likely
persist for much of Tuesday...before dry slot and winds shifting to
the southwest late in the day allows for improving aviation

//Dtw threshold probabilities...

* high confidence in ceilings at or below 5000 feet tonight through
Tuesday afternoon.

* High potential/confidence for rain as precipitation type tonight
into Tuesday.


Previous discussion...issued 347 am EST Monday Nov 30 2015

Short and tonight

Surface high pressure will become centered over the New England
states today while keeping a foothold in Southeast Michigan. This means dry
conditions through the day with a mixture of cloud cover. The
easterly low level flow will help supply stratus from lakes Huron
and Erie to portions of the region during the morning while high
clouds thicken ahead of the low pressure system moving from the
plains toward the Midwest. This system will pull a surge of rain
into the area later tonight.

Early morning satellite imagery indicates broken coverage of stratus
off Lake Huron into The Thumb. These clouds are getting a boost from
the lake but also have origins over southern Ontario and Lake
Ontario and will continue to move over the region while boundary
layer flow is from the southeast during the morning. The southeast
flow will also bring clouds from Lake Erie over south sections of
our area. The 00z DTX sounding and model forecast soundings
illustrate a favorable temperature profile for the clouds to expand
within a shallow layer between inversions before possibly being
disrupted by dry air from Ohio and Pennsylvania. The exchange of low
clouds for increasing higher variety should allow enough surface
heating for maximum temperatures in the lower to middle 40s over Southeast Michigan...and
even a few upper 40s Detroit to the Ohio border where greater
thickness warming will occur.

The 00z and model soundings also indicate the substantial amount of
dry air below 700 mb that is in place which will have to be overcome
and displaced northward before rain begins tonight. A maturing middle
level Theta-E ridge ahead of the upper low around 700 mb will
struggle to overcome the dry low levels as it slides overhead during
the evening. This will result in thickening cloud cover and maybe
some sprinkles toward midnight. Coverage of showers will then ramp
up after midnight as deeper isentropic lift develops with origins in
the warm sector over the Tennessee Valley. The associated stronger
moisture transport is producing a large area of showers over Iowa
and Illinois during the morning. Evolution of the low level
occlusion will pull the moisture axis westward initially but then a
band of showers will surge northward over lower Michigan after
midnight. Just a cold rain is expected as temperatures will be
steady or rising from the middle 30s in The Thumb to lower 40s Detroit
area through sunrise Tuesday.

Long term...Tuesday through Sunday

Attention through middle week is on the stacked closed low drifting
across the Great Lakes. Split upper level flow will then set back up
over North America by the end of the week providing fairly pleasant
weather through the weekend. Models show the western ridge expanding
into central Canada before westerly flow in the split flow advects
that air into the Great Lakes. A couple upper level impulses may
break off the main branch of the northern stream but remain
disconnected to the surface by the expansive and strengthening surface

By Tuesday morning...the closed low will located over the upper MS
valley. The main ribbon of Theta-E between the elevated warm front
and the occluded front will be draped across the state so rain will
likely be ongoing to start the period. Main questions will really be
the timing of the exiting rain band and then timing the occluded
front lifting N/NE. With such a strong and closed low...the trend of
a slower solution seems legit. A slower solution in this case means
the dry slot and left exit region of the jet will surge northward to
our west...thus the occluded front will align parallel to the flow
and take a bit longer to get through Southeast Michigan. A frontal passage around 18z will
allow the warm air to reside in the region long enough to keep high
temperatures elevated in the upper 40s...around 50 Detroit
southward...before the colder air moves in. The dry slot will shut
down the rain for the afternoon but strong ll lapse rates with cold air advection
will perk a low strato cumulus field which may result in some dz into the
early evening.

Could see a few showers Tuesday night...moreso west of i75...due to
cold air advection and lake effect processes. Better chance of additional showers
will come on Wednesday as the moisture wrapping around the
backside of the system passes over lower Michigan. The low track will be
centered through middle Michigan but as the low phases with the southern
stream of the jet...the greatest height falls will pass through
the Ohio Valley keeping a portion of the cold pool over southern
Michigan. Thermal profile suggests a rain snow mix but with wet bulb
zero temperatures at or below the freezing mark throughout model
soundings...could see an all snow scenario. At this point will
keep a rain/snow mention as daytime surface temperatures warrant...keeping in
mind any heavier showers/bursts may change over to all snow
temporarily. Little to no snow accumulation is expected. Ridging
aloft and at the surface will then build into the area Thursday


High pressure will hold over the region today keeping favorable
marine conditions across the waters. Light southerly winds will
increase while backing to the east tonight and Tuesday ahead of the
next low pressure system lifting northeast toward Lake Michigan. The
elevated easterly flow will increase wave heights along the Lake
Huron shoreline but looks to remain below Small Craft Advisory
criteria. This system will slowly pass through the central Great
Lakes Tuesday and Wednesday while pulling a cold front through the
region Tuesday afternoon. Winds will turn westerly behind the cold
front but even with the cooler air moving in...a weak pressure
gradient will keep winds minimized. High pressure will build back
into the region Thursday.


DTX watches/warnings/advisories...
Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.


long term....drk

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