Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
552 am EST Wednesday Jan 28 2015
High pressure will bring VFR conditions today...but clouds
will increase tonight as this high shifts east and low pressure
approaches from the west. Ceilings should remain at or above 10kft or so much of
the night...but MVFR ceilings/visibilities will likely develop kmbs/kfnt after
09z-10z as -sn br work into the area with this system.
For dtw...light snow and MVFR conditions should hold off until after
//Dtw threshold probabilities...
* low in ceilings at or below 5000 feet late tonight...with higher confidence
Previous discussion...issued 309 am EST Wednesday Jan 28 2015
Short term...today and tonight
After a chilly start...temperatures will rebound to near 30 degrees
today as southerly winds increase in advance of an approaching wave
of low pressure. Mostly sunny skies will give way to increasing high
cloudiness as the leading edge of moisture associated with the wave
overspreads the area.
Clouds will then thicken and lower gradually into tonight as this
system moves into the central Great Lakes with light snow likely
developing late tonight over parts of the area. Accumulations will
be minimal prior to 12z with just a few tenths of an inch at most.
Temperatures...meanwhile...will remain relatively mild as clouds
increase with lows holding in the lower 20s.
Upper jet will intensify over northern Canada today as east Pacific
ridging builds toward digging high-latitude energy over northern
Alaska and the northwest territories at 07z this morning. This jet
enhancement will help to amplify a northern stream trough that will
absorb the shortwave over southern Alberta/Saskatchewan this morning
by late tonight into early Thursday. The digging trough will also
steer the remnant Baja California energy over Wyoming across the Ohio Valley.
Meridionally oriented surface trough will transit the state on
Thursday, anchored on both ends by weak low pressure centers tied to
northern & southern forcing maxima accordingly. As noted in the
previous forecast package, it is reasonable to respect model
solutions leaning toward a stronger southern wave given limited
upstream static stability that will favor stronger large scale
ascent. The 00z GFS has, in fact, trended in this direction. The
European model (ecmwf) has shown little change and depicts a more open surface
circulation, but still stronger than the remaining guidance. Respect
is given to the 00z GFS, but as a 4+mb outlier at this rather short
lead time, decided against a full buy-in.
Expectations for general evolution remain largely unchanged
regardless. Low-level jet response will develop over the middle
Mississippi Valley within broader southerly flow regime today before
progressing east across the area 6-12z tonight. Warming of the middle-
levels will bring brief but well-defined window for freezing rain
across southern areas during the morning. Ongoing surface warm
advection and diurnal heating will jeopardize snow chances south of
at least I-94 for the next several hours where midday conditions
will be strongly dependent on the strength of the surface low. North
of I-69, weak deformation and more favorable thermodynamic profiles
should help translate 0.25" quantitative precipitation forecast into 2-3" of snow accumulation. In
between, mainly snow is expected between roughly I-696/M59, although
a deep layer of temperatures decidedly warmer than -10c through the
lowest 10kft will significantly reduce snow ratios. Here,
accumulations are forecast to range from 0.5 to 1.5". The best shot
of accumulating snow for the southern 2/3 of the area will most
likely be immediately in the wake of the surface cold front after
20z, when cooling thermal profiles will support better dendrite
production prior to the exit of the deeper moisture.
Digging high-latitude energy will push a strong cold front through
the area from northwest to southeast Thursday night. This shot of cold advection
will drop 925mb temperatures from a peak of near 0c during Thursday
afternoon to -17c Friday morning. Northwest fetch should deflect any
lake effect to the southwest, but both lake clouds and les look to
be hard to come by given model depictions of rapidly building high
pressure Thursday night. Highs Friday will be limited to the
middle/upper teens in most spots despite prospects for mostly sunny
skies. Quick rebound of the height field downstream of Pacific energy
streaming into the western U.S. Will help temperatures recover into the middle
20s on Saturday.
Finally, model consensus is increasing that a wide swath of
accumulating snow will develop over the Ohio Valley and Great Lakes
Saturday night into Sunday night. This will occur as a northern wave
digs into the Western Plains and entrains a highly uncertain
percentage of energy from a closed low over the 4 corners. Broad
region of northward moisture transport and strong large scale right
entrance jet support favor retaining the entry-level likely probability of precipitation
introduced by the blended extended grids.
Fresh to strong southerly winds will develop late tonight into
Thursday morning as a weak low pressure system traverses the Great
Lakes. Stable southerly flow regime will limit the potential for
wind gusts. Therefore...while an isolated gust to gale force is
possible over Lake Huron...coverage and duration will meet gale
criteria. A strong cold front will then surge across the waters on
Thursday night. Much colder northwest flow will support widespread
gusts to strong gales across all of Lake Huron including the
nearshore waters. Significant wave heights will exceed 12 feet over
the southern half of Lake Huron by late Thursday night. Winds and
waves will subside Friday into Friday night.
Lake Huron...gale watch from Thursday evening through Friday morning for
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).