Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
557 PM EST sun Feb 7 2016
Middle clouds will give way to lower VFR/MVFR overnight into Monday
morning as low pressures digs southeast into the central Great Lakes. Gusty
SW flow will ease considerably as the forecast begins early this
evening...and remain 10 knots or less into Sunday...veering to the
west as the aforementioned low settles to Lake Huron. While -shra or
-shsn will become more likely late in the forecast...coverage still
looks rather iffy...so will leave out of the forecast at this time.
At dtw...a band of light showers will develop...likely just east of
the terminal this evening as dry low levels below 5kft or so
maintain dry surface conditions long enough to limit any precipitation to
sprinkles. Ceilings will trend below 5kft later this evening and then
MVFR overnight...fluctuating near 4-5kft into Monday.
//Dtw threshold probabilities...
* high for ceilings at or below overnight into Monday early Monday
morning...then medium thereafter.
Previous discussion...issued 349 PM EST sun Feb 7 2016
The amplification and eventual broadening of an upper level trough
over southeastern Michigan is resulting in a very challenging
forecast for the early week period. Specifically...there is low
predictability in the integrity and timing of individual shortwave
energy that will be harbored within the upper level trough axis.
Distinct upper level absolute vorticity centers are digging
southeastward out of the northern plains this afternoon. Forecast
data supports the lead edge or gradient of the parent pv anomaly to
push across Lake Michigan and to impinge upon western lower Michigan
prior to 00z this evening. Models are strongly in favor of a
relatively messy jet evolution during the next 6-12 hours where a
disorganized upper level jet stream element will rapidly become
anticyclonic in curvature and become phased within the entrance
region of the much more dominant NE U.S. Jet branch. The net result
is for some decent to strong right entrance region dynamics
developing over southeastern Michigan. What is likely more favorable
from a dynamical standpoint is the convergence boundary/front that
will become sharper this evening along the pv gradient where forcing
will be maximized due to the mass adjustment caused by the
tropopause fold arrival. Numerical output supports a corridor of
light rain shower development (warm surface temperatures) over much of
southeastern Michigan between 01-04z. Pretty inconsequential...with
very light quantitative precipitation forecast amounts of a couple hundredths of quantitative precipitation forecast or less.
The low predictability then begins in earnest already late tonight
as intra-inter model continuity has been extremely poor with regards
to amount of low level moisture that will saturate/develop over the
extreme southeastern sections of the County Warning Area...near Detroit River/Lake
St Clair. Earlier deterministic and hires solutions showed an
increasing low level moisture plume and precipitation during the 10-
12z timeframe across sections of south central lower Michigan and
over the far Western Lake Erie Basin. The new 07.12z iterations of
these same models arrived and backed way off. Preference sides with
a drier solution for the Monday morning commute time for a couple of
reasons...1. There is no low level jet feature driving
advection...2. Low level saturation while being aided by right
entrance region dynamics aloft is still likely dependent on a good
amount of precipitation/hydrometeor production this evening. The NAM
is showing a minimum corridor of 850-700mb specific humidity
directly in place at 12z Monday.
The model solutions now support the corridor of light
precipitationprogressing east of lower Michigan for the Monday
period setting up what should be fairly widespread dry conditions.
While a classic midlevel dry slot is not resolved for
Monday...there is a good amount of dry air entrained within the
midlevel trough axis. Additionally...model data supports neutral
to isentropic downglide over southeastern Michigan. Carrying a low
chance for snow showers in many areas. The one item to watch for
is some possible convective shower development along a secondary
cold front/gradient feature that will push into the far western
County Warning Area/Saginaw Valley between 21- 24z Monday. No tangible height
rises will support very little cold advection on Monday.
Preference sides with warmer temperatures in the upper 30s to near
The model trend today has been for more of a southward solution with
the main vorticity energy within the trough axis by Tuesday. This
suggests possibly more of an eastward leak to the surface
low/reflection than what was earlier advertised. The best cva would
shift south and east of the County Warning Area which would take the main dynamical
support for precipitation with it. What remains over southeastern
Michigan is more in the way of northwesterly flow which is a dry one
for the area. The lake effect potential still remains for Tuesday
and Wednesday with very cold temperatures of -12 to -20c 850mb
expanding across the area. The one item of particular interest is a
potential lake aggregate trough which could lead to a good potential
for shovel-able snows over portions of The Thumb...primarily on
There is growing confidence that we will see some of the coldest air
of the season so far late next week into next weekend. 12z GFS/gefs
mean/European model (ecmwf) continue to highlight -15 to -20c 850 mb temperatures Wed/Thu.
Potential for even colder air next weekend with the Arctic closed
low sweeping into southeast Canada. Still some uncertainty with the
magnitude of cold air as it looks to be a glancing blow with The
Heart of the cold air over the northeast US...but even a glancing
blow would likely put 850 mb temperatures near -20 to -25c which would be
the coldest airmass so far this Winter. Lake effect snow shower
activity will be around...especially Wednesday...but likely on a
diminishing trend into the end of the week as colder...drier northwest flow
Moderate south-southwest of 15 to 25 knots winds will continue into
this evening before diminishing considerably tonight into Tuesday as
expansive low pressure settles across the Great Lakes. Winds will
back to northwesterly by late Tuesday into Wednesday and increase as
low pressure departs during the midweek period. Gusts of 25 to 30
knots are anticipated over Southern Lake Huron...along with snow
squalls...as much colder filters into the Great Lakes region over
the upcoming week.
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).