Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
1230 PM EDT Friday may 24 2013
Aviation...
//discussion...
12z DTX sounding showed a real strong inversion around 4000
feet...which allowed cold northerly flow off Lake Huron to support
solid stratus deck...which is currently in the process of mixing
out. Once this occurs (mid afternoon)...clear skies should be
the rule into tonight. Low levels should be warm enough and flow
backed to the west-northwest not to support a repeat performance of the low
clouds tonight. There will be some middle/high clouds arriving overnight
however...with just a bit of diurnal cumulus developing tomorrow (5000
feet). Marginally gusty northwest winds (around 20 knots) early this
afternoon diminishing...with light and variable winds tonight into
tomorrow.
//Dtw threshold threats...
* low confidence in ceilings below 5000 feet 18-20z.
&&
Previous discussion...issued 340 am EDT Friday may 24 2013
Short term...today and tonight
The weather up for discussion is the prospects for overcast skies
today as an opaque blanket of 030-035 feet stratus is aggressively
diving southward across Lake Huron. Trajectory of cloud deck in
addition to the orientation of the western edge aligns well with the
axis of maximum 925-850mb cold air advection and the depression of
the longwave trough axis. Nwp data is virtually void of cloud...a
result of inadequate vertical resolution within the models. While
the cloud is completely opaque it is undoubtedly a shallow layer of
moisture that is likely trapped within the base of the inversion
at/around 900-890mb. RUC soundings show saturation at this
zone...but the sounding structure itself does not inspire much
confidence as it is the wrong profile. Given the true northerly
trajectory...have decided to introduce overcast conditions for much
of the County Warning Area through the morning hours. It will be difficult to
pinpoint any west edge of the clouds given degree of dry air
immediately to the west. Pattern recognition suggests entrainment at
the edge should aid diurnal mixing to force stratus to go broken by
late morning...eventually clearing out for the afternoon.
Lowered maximum temperatures for many areas due to the cloud and steady
cold air advection. Expect temperatures to eventually reach 60-61
degrees across the south and Saginaw Valley very late in the day.
Otherwise temperatures are going to struggle to reach the lower 50s
in The Thumb.
For tonight...the compact vorticity over northern Manitoba will get
squeezed with a rogue vorticity streamer off of the pacnw anomaly
merging over the western Great Lakes. This will occur down the front
edge of the central Continental U.S. Ridge...allowing for a very healthy
ageostrophic response and stripe of frontogenesis very late. Any
significant temperature gradient will reside well west of lower
Michigan which is where the precipitation response will occur.
Regardless...increasing clouds late will establish a floor on
minimum temperatures tonight.
Long term...Saturday through Thursday
The overall pattern across North America this weekend will feature a
quasi Omega block. Short wave energy now shown rotating into northern
Manitoba is forecast to track across the eastern Great Lakes and middle
Atlantic early Saturday...leading to deepening of an upper low
rotating across New England. Lower Michigan will be located between this
system and amplifying middle level ridging across the northern plains/upper
MS valley. This will place the forecast area within a strongly
confluent upper flow with persistent high pressure at the surface.
The resident airmass across the Great Lakes will be cool and very
dry. Temperatures on Saturday should only rise to the low 60s over much of
the forecast area with 850mb temperatures hovering around +2c. The airmass
will moderate during the course of the weekend...with highs expected
to be around 70 by Memorial Day. Given the dry airmass and light
winds...nighttime lows will be quite chilly this weekend /30s and
40s/.
A seasonally strong 140+ knot upper jet is forecast dive into the
Pacific northwest early next week...leading to long wave trough
amplification across the western US and a building subtropical ridge
across the southeastern US. This will allow the middle level ridge to become
more progressive and pass east of lower Michigan toward midweek...allowing
a surface warm front to lift across the region from the southwest. This
warm front will advect a warm...moist and unstable airmass into the
forecast area. The GFS continues to bring this warm front through
faster than the other model solutions /suggesting convection as
early as Monday night/. The GFS has some obvious convective feedback
issues due to potential mesoscale convective system development over the plains. The GFS is
also less amplified with the long wave trough over the western US. Given
the strength of the polar jet and potential phasing with the
subtropical jet...the more amplified European model (ecmwf) remains the preferred
solution. This suggests the better chances for convection will hold
off until the Tuesday night/Wednesday time frame. Despite this uncertainty...
the overall trend next week will be for warmer and more humid
conditions with increasing chances for thunderstorms.
Marine...
Unseasonable conditions are in place over the central Great Lakes
today as cold air advection is ongoing within a deep trough axis.
Efficient northerly flow and a long fetch over the waters will
sustain high wave activity from Saginaw Bay down to Port Huron.
Recent water temperature readings from the buoys suggests that
conditions will be solidly in the neutral regime out over the Open
Lake which is atypical for late may. In fact...conditions are
unstable for Saginaw Bay with water temperature readings suggesting
lsts are at around 13 to 14 c vs an 850mb temperature that will be
dipping down to -4c by 12z this morning. Will expand the advisory to
include inner Saginaw. Conditions are more marginal on Lake St Clair
and Lake Erie. Will give respect to peak of the cold air advection
that will occur this morning for the southern zones and extend the
small craft for them as well. The stable surface anticyclone will
build into the central Great Lakes tonight bringing a return of much
more familiar stable season marine weather.
&&
DTX watches/warnings/advisories...
Michigan...none.
Lake Huron...
Small Craft Advisory...nearshore waters from Port Austin to Port
Huron...until 8 PM Friday.
Small Craft Advisory...outer Saginaw Bay...until 6 PM Friday.
Lake St Clair...
Small Craft Advisory...until 4 PM Friday.
Michigan waters of Lake Erie...
Small Craft Advisory...until 4 PM Friday.
&&
$$
Aviation.....Sf
short term...cumulonimbus
long term....SC
marine.......cb
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at www.Weather.Gov/Detroit (all lower case).
