Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
727 am EDT Thursday may 28 2015
Thin layer of fog developed early this morning but fluctuated quite
a bit across the region. Any residual fog will burn off over the
next hour or so. This will result in VFR conditions through the rest
of the period as high pressure both at the surface and aloft take
over the region. Winds this afternoon will gust to around 15 knots
from the south. There is a small chance that an isolated
shower/tstorm could develop near mbs but chances are too low to
include in the taf.
//Dtw threshold probabilities...
Previous discussion...issued 425 am EDT Thursday may 28 2015
Short term...today and tonight
High pressure both at the surface and alot will result in mostly clear
skies with high temperatures climbing into the low 80s for most
locations. The middle level ridge axis will pass to the east of lower
Michigan early this afternoon allowing for deep swerly flow to re-
establish itself over the area once again...albeit much weaker then
the last few days. This combined with plenty of sun will allow for
temperatures to reach 80 degrees today. Mixing depths will approach 700mb
this afternoon but wind speeds through the layer may only reach 15-
20 knots which will keep afternoon gusts minimal.
The forecast is not all sun and warmth though as there is an outside
chance that an isolated cell or two could try to initiate over the
Saginaw Valley this afternoon. A lingering weak surface trough draped
across northern lower in addition to forecast lake breeze
development could result in an agitated cumulus field and some isolated
showers and thunderstorms. Increased heights will have a better hold
as one heads south but due to proximity to the lower heights and surface
trough...some activity could leak south into the Saginaw Valley
region. This is low probability thus just went with 20 probability of precipitation.
Tonight...skies will remain mostly clear under the western edge of
the eastward drifting surface ridge. Dewpoints in the low 50s will allow
a decent bit of cooling back down to the upper 50s. Even with the
recent rainfall keeping surface moisture elevated...model soundings show
the airmass to be too dry to develop much if any fog. Anything that
tries to develop will be very shallow.
Strong frontal system to bring wet and unsettled weather late Friday
and Saturday before Canadian high pressure builds aggressively into
the region for Sunday.
Model consensus for days has been calling for a dynamic synoptic
scale cold front to impact the Great Lakes region this weekend. A
number of factors appear to be aligning to generate the Stout low to
midlevel dynamics. That is...the Idaho upper level circulation will
work under then be kicked ahead of a very strong potential vorticity
anomaly that will dive southward out of northern
Saskatchewan/Manitoba on Friday. Timing looks to be perfect for weak
jet energy attendant to the plains circulation to create a pseudo
jet entrance region over portions of Lake Superior/southern
Ontario Friday night. Sheared absolute vorticity ejecting
northeastward will then aid a rapidly developing ageostrophic
response over northern Wisconsin/Upper Peninsula of Michigan in
organizing a strong low level thermal gradient. This gradient will
then be driven rapidly southeastward by a large area of 1000-500mb
Friday...have been highlighting the past few days and will continue
to do so...timing of precipitation is the big question. Latest
model data...specifically the European model (ecmwf)...has backed off a little on
coverage of quantitative precipitation forecast for the Friday and Friday evening period. Models
are having difficulty here with the lack of capping. With the low
to midlevel ridge axis still over southeastern
Michigan...anticyclonic flow trajectories...and complete lack of
jet energy aloft overhead still do not want to deviate from chance
probability of precipitation for Friday. Total lack of wind in the column supports a pulse
type storm behavior with 0-6km bulk shear at less than 25 knots.
Latest swody2 has southeastern Michigan in a marginal designation.
The difference noted in the 28.00z suite was to dissipate the first
axis of midlevel deformation along the front over portions of
Northern Lake Michigan...northern lower Michigan early
Saturday...then redeveloping the dominant 850-700mb deformation axis
over southeastern Michigan Saturday afternoon. Don/T feel this is a
huge deal...but it does possibly signify that models still have not
dialed in on some large scale governing dynamics. Model cross
sections still depict a very good frontal support with upright
ascent by Saturday afternoon. At this time...severe weather threat appears
to be low for Saturday with a total void of midlevel lapse rates.
Rather...moisture profiles and forecast precipitable waters suggest heavy rainfall
could be the main threat.
Dry conditions are expected today as high pressure settles over the
area. These conditions will continue into Friday before the chance
of showers and thunderstorms return late in the day on into Friday
night and Saturday. A strong cold front will pass through the region
on Saturday bringing strong northeasterly winds to the area to close
out the weekend. Northeasterly winds will become quite strong
Saturday night and Sunday...with a long duration of windspeeds
ranging 20 to 30 knots.
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).