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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
1252 PM EST Friday Mar 6 2015

Aviation...

Increasing southwest wind and mixed high clouds are precursor to
milder air moving into the Great Lakes during the weekend. The
beginning of the process will be tied to a warm front forming over
the Midwest during the evening. MVFR ceiling will be developing with
time as a warm front organizes and moves toward Southeast Michigan. There
is good agreement in model output on the development of the cloud
pattern but timing will not allow much evaluation from observations.
Trends will then be monitored for potential updates on coverage and
duration through the terminal corridor during the evening. Once in
place...the clouds will tend to linger through Saturday as the
milder air flows over the expanse of snow cover east of the
Mississippi River. Regarding precipitation with the front...expect
plenty of virga to appear on area radars but no more than a flurry
reaching the ground during the evening followed by dry conditions
through Saturday morning. Saturday afternoon will present a better
chance of snow with the next low pressure system.

//Dtw threshold probabilities...

* moderate for ceiling below 5 kft during the evening. High
overnight through Saturday.

&&

Previous discussion...issued 305 am EST Friday Mar 6 2015

Short term...today and tonight

High pressure draped across the southeast United States coupled with
low amplitude northwest flow aloft will facilitate persistence of
dry conditions through the forecast period and a continuation of
southwest gradient flow. Ongoing light warm advection will warm
925mb temperatures by 10 or more degrees over the next 24 hours,
ensuring high temperatures in the middle 20s, or about 5 to 10 degrees
warmer than yesterday. More potent energy located well upstream will
encroach on the Great Lakes overnight. Strengthening southwest
gradient will force a gradual rise in temperatures overnight. No
arguments from 00z guidance that indicate temperatures bottoming out
around 20 early before rising back into the middle 20s by sunrise
Saturday. Nothing more than episodic middle/high clouds expected
through the daylight hours before better low-level moisture lowers
the cloud deck after sunset.

Long term...

Lower amplitude middle level northwest flow will define conditions
locally through the upcoming weekend. Weak shortwave energy
originating from the Gulf of Alaska will shear into this flow over
the next 48 hours...translating across Southeast Michigan on Saturday.
Corridor of warm air advection will emerge immediately in advance
of the height falls...prompting a solid upward adjustment in
temperatures relative to today. Extensive cloud cover will dampen
the response to some degree...but a modestly mixed environment
through 925 mb /-2 to -3c/ supports highs of middle-upper 30s. Brief
shot of isentropic ascent on the front end and a late day cold
frontal passage warrants a low end pop mention throughout the
day...but the limited moisture quality and lackluster forcing will
seemingly restrict precipitation chances. Ensuing weak cold air
advection into Saturday night...the process perhaps yielding a few
flurries as moisture briefly deepens with the passing 850-925 mb
frontal slope. This frontal zone will temporarily settle just to
the south by Sunday morning...providing a window of opportunity
for some clearing overnight. Going forecast leaning toward the
colder end of guidance for lows Sunday morning...latest model
evidence providing little evidence to move away from this position
/upper teens to lower 20s/.

Frontal zone will wash back eastward and across Southeast Michigan on
Sunday as the mass fields reorient again with the approach of
another weak shortwave. Clouds will likely remain problematic
accounting for both the frontal passage and a brief uptick in cva with the
shortwave itself. Once again...moisture will be lacking to suggest
anything more than a lower end probability for a few snow showers to
develop. A moderating thermal profile will again support highs of
middle 30s.

The existing troughing will ease early next week...increasing depth
to the low level west-southwest flow establishing a firm period of
warm air advection. The magnitude and duration of this warm up
still carries some uncertainty yet at this time scale...00z GFS
considerably more progressive with the next inbound height fall
center and stronger frontal passage /Wednesday/ relative to the
European model (ecmwf) and Canadian /following weekend/. Regardless...looking at a
stretch of seasonable conditions through at least the midweek
period.

Marine...

Southwest flow will strengthen today throughout the central Great
Lakes. A firm southwest gradient reaching 25 to 30 knots will exist
across portions of Central Lake Huron this afternoon and early
evening. This will bring the potential for a brief period of
gales. However...the combination of a limited duration...marginal
magnitude and the fact that a majority of the lake remains ice
covered will preclude the issuance of a Gale Warning for today.
Pressure gradient will ease into tonight...with the arrival of
warmer air providing an increasing stable environment heading into
the weekend. Modest southwest flow in place Saturday in advance of
a cold front. Weak surface ridging then yields a weaker westerly
flow for Sunday.

&&

DTX watches/warnings/advisories...

Michigan...none.
Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
&&

$$

Aviation.....Bt
short term...jvc
long term....mr
marine.......mr



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