Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
332 am EDT Sat Apr 19 2014
Short term...today and tonight
First things first...fog/stratus potential early this morning. There
is a narrow band of stratus extending from Jackson to Detroit and
and up through Mount Clemens. This band is on the edge of the 925mb
Theta-E boundary that sank south through the area last evening and
stalled over that area. Ceilings have slowly been increasing as dry air
takes its toll on the limited moisture. There is still a possibility
for patchy fog to develop...mainly in The Thumb as onshore flow
advects moist air below a strengthening inversion. Observation have not been
too favorable thus far keeping a dewpoint depression around 2-5
degrees for the most part but there are some dipping to around a
degree. With models showing improving conditions for a brief window
early this morning will keep the mention of patchy fog in the
forecast for now. Sunrise will quickly put an end to any fog that
does try to form.
The rest of the day will be pleasant with temperatures about 5
degrees below normal for more locations...especially the Lake
Huron/Erie shoreline area. Surface high pressure system centered over
northern Ontario will continue its March eastward through the day
reaching the East Coast by Sunday...while a middle level ridge axis
will pass over Michigan /around 00z Sunday/. Southeast Michigan will fall on the
southern periphery of this dome of high pressure resulting in
easterly/northeasterly flow off the lakes through the day. With lake
temperatures still in the low 40s...this onshore flow will prevent
typical surface heating from the middle April sun even with clear skies.
Question is how far inland does this marine influence make it?
Current thinking is that area west of I-75 will get a bit more
influence form the sun allowing them to reach into the upper 50s.
Split flow pattern developing in the longwave pattern will begin to
advect warmer air into the region tonight which will combat the
early radiational cooling keeping temperatures in the middle 30s.
Long term...Sunday through next Friday
A vigorous shortwave will track east along polar jet stream across
southern Canada...reaching James Bay by Sunday evening. With no
southern stream companion to this wave...expect the cold front that
pushes south in the wake of this system to hang up just north of the
area late this weekend as zonal upper flow remains in place over the
Great Lakes. This will limit rain shower chances to the Saginaw
Valley and thumb late Sunday/Sunday night...where probability of precipitation will be
A second polar shortwave will follow in behind this initial system
and phase to some degree with a well defined shortwave lifting from
the southwest Continental U.S. Into the Central Plains. Timing on the evolution
of this system...as portrayed by the 00z model suite...has slowed
slightly. This will allow the area to remain in the warm sector into
a large portion of Monday and will up temperatures into the lower
70s as nam12/ECMWF/GFS are all rather consistent in the
positioning of the upper trough axis...west of the County Warning Area through
00z. Will also have to back off on the higher shower chances over
much of the area until Sunday afternoon/evening...and with
additional daytime heating and destabilization...a mention of
thunder is now warranted as Li/S drop to 0c or below and sbcapes
are forecast nearing 500 j/kg...at least by the nam12.
With a greater degree of northern/southern stream phasing as this
system evolves...and the resultant deeper upper trough hanging back
over the Great Lakes...relatively cool weather will linger through
the middle of next week as highs top out in the 50s on average from
Tuesday through Thursday and lows drop into the 30s. A second well
phased storm system will then develop over the Dakotas/upper Midwest
and wobble into the area as it occludes late in the forecast period.
This will bring increased rain chances and milder temperatures into
at least parts of Friday. Notably colder air is then expected to
filter back into the area just beyond the forecast period through
next weekend...which was consistently forecast by medium range
models 24 hours ago as well.
Conditions will remain reasonably quiet into tonight as light east
flow...averaging 10 knots or so...continues to filter off of strong
high pressure centered to the north/northeast. Two low pressure
systems will then pass near the area late this weekend into early
next week. The first will track across Ontario on Sunday...dropping
a cold front down into Northern Lake Huron. The front will remain
quasi-stationary over this area until the second low pressure system
draws it southward Monday and Monday night. Stronger north winds are
then possible across the area late Monday night into Tuesday behind
the front as colder air filters back into the area.
Aviation...issued 1159 PM EDT Friday Apr 18 2014
High pressure will gradually build across Northern Lake Huron
through Saturday. This will provide favorable aviation conditions
in modest northeast flow through this time. Small window for a
brief MVFR fog/low stratus given the flow off Lake Huron early this
morning...but the limited probability and low confidence will
preclude a specific mention. Mostly clear skies with winds
gradually veering with time /NE to east/ on Saturday.
//Dtw threshold threats...
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).