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Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1200 am EDT Friday Apr 25 2014
Middle and high clouds will continue to stream into the region ahead of
a low pressure system approaching the western Great Lakes. Models
continue to bring the system in late tonight and early Friday
morning...therefore VFR conditions are expected through 12z Friday.
A period of rain is expected roughly 12-18z. A dip into IFR
ceilings/visible is possible during this time frame...especially from
ptk southward...however upstream observations indicate this dip is
very brief and transient.
For dtw...VFR conditions will prevail through tonight with
east-southeast winds around 10 knots. A period of rain is expected
after 12z Friday...with ceilings and visible dropping into the MVFR
range...and possibly IFR between 14-18z. Conditions will improve
after 18z as the low pressure system moves eastward.
//Dtw threshold threats...
* high confidence in ceilings dropping below 5000 feet 12-18z Friday.
Previous discussion...issued 353 PM EDT Thursday Apr 24 2014
Short term...through midday Friday
Current water vapor imagery depicts a strong...neutrally tilted
shortwave over the Southern Plains...as well as a negatively tilted
shortwave over the Dakotas. At the surface...a 1002 mb low was
analyzed over eastern MO. Closer to home...scattered to broken middle
and high level clouds were streaming into Michigan...with very dry
air noted at the surface. Some virga was noted on radar...but it
stands no chance of reaching the ground. The pressure gradient will
be maintained or increase slightly overnight allowing for modest
southeasterly flow to continue. The wind...combined with increasing
cloud cover late...will keep lows tonight in the low to mid-40s.
The interaction...or lack therof...between the two
shortwaves has been a source of uncertainty in recent nwp
runs...with today/S 00z and 12z runs continuing to trend slower.
However...model-to-model agreement is generally good. The northern
wave will stall out over The Arrowhead of Minnesota tomorrow
morning...while the southern wave will remain strong and
progressive. Models generally agree on taking the surface low from
eastern Illinois to central Ohio from 06-18z tomorrow. Due to the copious
dry low level air in place...and lack of large scale forcing...the
precipitation should mostly hold off until after 12z tomorrow. During the
12z to 18z period...the southeastern half of the County Warning Area will be in the
favorable northwest quadrant of the cyclone...with good fgen and
deformation in the 500 mb to 700 mb layer. Precipitable waters will increase to 1"+ as
well. The result appears to be around 0.25-0.50" rain in our
southeastern half...with less than 0.25" elsewhere. Confidence in
precipitation amounts is a bit lower in the northwest half due to wide
discrepancies in precipitation amounts between the NAM /less than 0.1"/ and
GFS /greater than 0... the European model (ecmwf) appears to be a good middle
The dominant feature of the long term period will be the significant
baroclinic zone that will take shape south of the area late this
week and play a primary role in regional weather through next week.
Significant jet energy already evident immediately south of the
Aleutian island chain is prognosticated to dig aggressively into the
southwest United States late this week and result in significant
downstream ridge amplification through the weekend. Located well
downstream of the developing ridge axis, the Great Lakes will see
another round of northern stream height falls late Friday through
Saturday. This will shunt a cold front through the state Friday
night resulting in cooler temperatures that will only struggle into
the low/middle 50s on Saturday. Sprawling Canadian anticyclone will
expand into the Great Lakes in its wake providing cool easterly flow
from Sunday Onward. In the meantime, the amplifying upstream pattern
will result in warm advection and significant moisture return across
the central United States, effectively compressing the pre-existing
Theta-E gradient from the upper Midwest to the Ohio Valley. Late
Friday through Sunday, perhaps even Monday, will be largely
characterized by dry and cool conditions as Southeast Michigan is prognosticated to
remain firmly north of the baroclinic zone. A few showers will be
possible across the southwestern third of the County Warning Area during this time
as a weak jet streak provides some middle-level fgen, but potential is
too low to warrant a schc mention at this stage.
The upstream cyclone is prognosticated to eventually begin cutting off
upstream early next week, which will result in increasing cloud
cover, the potential northward migration of the baroclinic zone, and
subsequently wetter weather lasting through the end of the long term
Winds will ramp up a bit late tonight and early Friday morning as a
low pressure system slides through the southern Great Lakes. Waves
will pile up along the shoreline but a short residence time of
moderate flow looks to circumvent the need for small crafts. Winds
will quickly shift to the west Friday afternoon behind a weak
front...ramping up late Friday night and veering northwesterly as a
stronger cold front moves through the Great Lakes. At this time it
appears that gusts will stay below gale and small craft criteria.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).
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