Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
723 PM EDT Monday Mar 10 2014
Gusty winds subsiding with the onset of surface layer cooling.
Otherwise...high clouds will spread over the region this evening and
maintain integrity through the day Tuesday. Winds will veer into
the northwestern quadrant as a surface trough settles south across
the lower peninsula. The excess moisture from today/S snowmelt
should help contribute to some minor restrictions to visibility
toward daybreak. Winds will remain manageable Tuesday with the weak
boundary stalls out just south of the state line. Impacts from the
next winter storm are beyond the current window.
//Dtw threshold threats...
Previous discussion...issued 331 PM EDT Monday Mar 10 2014
Short term...through tonight
18z surface analysis depicts 993 hpa low at the northern tip of Lake
Superior within the left exit region of a 100+ knots upper jet
straddling the international border from Manitoba to northern lower
Michigan. Decent surface pressure gradient between the surface low
and a high over the Gulf Coast is contributing to some breezy
conditions over the upper Midwest. Temperatures still in the
middle/upper 40s and lack of frequent gusts are signifying limited
mixing over our County Warning Area...though still think we could make a run at 50
from I-69 southward given continuing low-level warm air advection.
Cloud cover will be limited to high passing cirrus.
Winds will weaken after sunset as mixing ceases and surface low
lifts northeast causing pressure gradient to slacken. 850 mb
temperature advection turns negative after 00z as elevated frontal
zone eases southward into the region. Midlevel clouds will increase
overnight but ascent and low level moisture will continue to be
lacking so will maintain dry forecast. Cloud cover is expected to
keep min temperatures near freezing.
Upper level trough/wave has just come onshore of the Pacific
northwest this morning...and timing with the northern stream upper
wave/trough dropping southeast from central Canada remains highly
sensitive...which will dictate which intense fgen zone will be most
active. Phasing looks to be occurring right as the system sweeps
through the Ohio River valley. A surface low track right along the
Ohio River to Pittsburgh PA is ideal for arb-dtw. Unfortunately...a
model consensus track has not emerged....as 12z NAM and Canadian
have made big jumps to the north. Convection developing over the
southern Ohio Valley will be a key player...and NAM is still not
sufficiently warm enough with our surface temperatures tomorrow...so the
surface front over the Ohio Valley will probably not be as tight
as NAM suggests. Tough call on which fgen zone will be most
active...850 mb vs 700 mb...but expectations is the 850 mb zone
will be the main show...along with the convection developing over
the southern Ohio Valley. With that in mind...the forecast will be
skewed toward the farther south UKMET/GFS solutions which is real
close to the previous mention benchmark track. However...even
those solutions appear over-ally aggressive...as 12z Euro is even
farther south. Will blend the forecast with Euro/GFS...and will
thus issue a Winter Storm Watch...focused generally along an
Adrian-Warren-Port Huron line and points south...for snowfall
amounts potentially around 6 inches. Amounts will drop off sharply
to the north as dry Arctic air takes hold during Wednesday.
Wedge of 4 g/kg of specific humidity between 850-700 mb in place
Tuesday evening south of M-59. 850-700 mb average temperatures will
rapidly fall Tuesday night into Wednesday...as Arctic air surges
into the central Great Lakes. Thus...snow to liquid ratios will be
varying significantly from start to finish...as we will need to
relay on wet bulbing effects and cold advection to allow for rain to
changeover to snow initially Tuesday evening (coming off highs in
the lower 40s). Maximum middle level fgen looks to be near the
Ohio/Michigan border early Wednesday morning. Cross sections
utilizing epv shows impressive and deep instability above frontal
circulation...and intense snowfall rates in excess of 1 inch per
hour are possible. North-northeast winds gusting to 30 miles per hour or
better during Wednesday will cause blowing and drifting
snow...especially as the snow becomes more powdery in nature
toward the end of the event.
Once the snow tapers off Wednesday....the cold air will be the
weather story as the strong north-northeast winds slowly slacken off
Wednesday night with ridge of high pressure building into western
lower Michigan. With the fresh snow cover...no big complaints with
mav guidance...lows dropping to around zero...based on the
Assumption winds will decouple near sunrise Thursday.
Well below normal temperatures will prevail from the middle week period
into Thursday as the departure of the strengthening low pressure
system funnels Arctic air into the eastern Great Lakes region. A
fast moving northern stream wave originating from the Gulf of
Alaska is forecast to undergo some amplification as it traverses the
Great Lakes on Friday. There is actually reasonable agreement among
the 12z model suite in timing and amplitude of this feature...all of
which suggest ample low level warm air advection preceding the middle
level trough on Friday...supportive of highs back into the 40s.
Rather low moisture content within the warm sector will support a
continued dry forecast for Friday. Long wave amplification continues
to be shown by the medium range suite toward the end of the forecast
period. This will be characterized by a building ridge over the western
US which in turn will force the eastern Canadian polar low to drop into
Ontario and southern Quebec. The corresponding intrusion of more Arctic
air into the Great Lakes will trend temperatures well below normal toward
the later half of the weekend into early next week.
A weak frontal boundary will slowly drop south through the central
Great Lakes tonight into tomorrow...leading to light winds.
Northeast winds will then rapidly increasing Tuesday night into
Wednesday as a deepening low tracks along the Ohio River and into
the middle Atlantic. A gale watch as been issued for the majority of
Southern Lake Huron...as well as Lake St Clair and Western Lake
Erie. The period of gales looks rather brief and marginal however.
High pressure and lighter winds will return Wednesday night into
Michigan...Winter Storm Watch...miz063-miz069-miz070-miz075-miz076-miz082-
miz083...from midnight Wednesday to 4 PM Wednesday.
lhz464...from 8 am Wednesday to 8 PM Wednesday.
Lake St Clair...
gale watch...from 10 am Wednesday to 6 PM Wednesday.
Michigan waters of Lake Erie...
gale watch...from 10 am Wednesday to 6 PM Wednesday.
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