Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
400 PM EST sun Feb 1 2015
Short term... storm term through tonight
The main forecast adjustments for the afternoon package include
bumping the M-59 corridor into the 10 to 14 inch range for storm
total accumulation...and adding Sanilac County to the Winter Storm
Storm total accumulation in the 10 to 14 inch range...with locally
higher amounts...remains firmly in play heading into the peak of the
event during the late afternoon through the evening. Event totals so
far today are up to 6 inches generally along and south of the I-94
corridor and up to 4 inches as far north as the M-59 corridor at
press time. These totals represent the high end of the range across
the area and are ahead of schedule heading into the peak of the
event that will see rates double to around 1 inch per hour...making
another 6-8 inches attainable by midnight south of M-59...and 8-10
to the north through the I-69 corridor and east toward Port Huron.
Cold and dry air north of Lake Huron...single digit surface temperatures
and below zero dewpoint...will maintain a sharp gradient in
accumulation and keep the advisory area below 8 inches for the 24
hour event total.
Afternoon radar composite indicates middle level warm frontogenesis
intensifying a broad band of heavy snow from northern Illinois all
the way across the south 1/4 of lower Michigan and into Lake
Erie/Northern Ohio. A notable increase in the strength of radar
returns through the band is indicative of higher snowfall rates due
to stronger forcing and better dendrite production. The low pressure
circulation will now slide along the frontal zone and bring steeper
middle level lapse rates and a strong dynamic contribution to lift
associated with the middle level trowal. It is during this phase of the
event that storm totals will tend to even out from south to north
over the warning area. Expect the trowal/deformation axis will
contract and move toward the I-69 corridor which will allow rates to
diminish...but not end...over the Detroit area to the Ohio border.
The trailing deformation will then put the finishing touches on
storm totals through the eastern portion of the I-69 corridor to
Port Huron and south of M-46 in Sanilac County. The latest storm
total snow map reorients the band of maximum accumulation into more of
SW to NE configuration. This captures a farther north penetration of
the trowal axis inflection point and the extra accumulation under
the trailing deformation axis before it shrivels eastward toward
Long term... Monday through Friday
With the big weekend system on its way out...a low amplitude upper
level pattern will take over with ridging over the West Coast and
troughing holding over the east. It will be a fairly active pattern
as there is an alaskan low releasing short waves into the jet
stream...and all the while a series of pv anomalies will rotate
around the dominate polar low over north/central Canada and down
through the Great Lakes. Though the bulk of the shortwave activity
will dive just west and south of lower Michigan...there will be a chance
at some minor snow accumulations through the week. An additional
concern will be cold temperatures as these Arctic fronts usher in
some cold air over the fresh and deep snowpack.
First issue we will have to deal with is the back edge of the
exiting winter storm Monday morning over our eastern counties. The
system has been trending a bit slower today and there is a chance
that the middle level deformation band will still be working through
the eastern portions of our County Warning Area between 12-15z. Should be a sharp
cutoff to the snow through the morning as very dry air rushes in
behind the system. Forecast soundings show the airmass completely
drying out in the matter of about 2-3 hours. In addition to the
deformation band snow...models have been hinting at a lake effect
band setting up over The Thumb for a few hours in the morning as
winds back from NE to northwest. Though The Thumb might see a few hours of
extra cloud cover and flurries...thinking is that the incoming
airmass will just be too dry and will not allow deep enough
inversions depths to produce any real le band. We saw a similar
signature with an Arctic front last week that resulting in only
flurries in Huron County. The bigger concern for Monday looks to be
temperatures as the Arctic front drops through the state. 850mb
temperatures will fall to around -15c and with a fresh blanket of deep snow
the mostly sunny skies will do little to help boost temperatures.
Highs should hold in the middle teens with lows Monday night dropping
to near 0f. With northwest winds around 10mph through the afternoon
hours...wind chill values will reside mostly below 0f for all of Southeast
Michigan through the day and down toward -10f Monday night.
Chance of snow returns on Tuesday as a clipper dives across Southern
Lower Michigan just ahead of a shearing out pv filament along an Arctic
front that will drop through the region Wednesday. Models have been
very consistent over the last few runs with this clipper. Quantitative precipitation forecast has
been right around 0.1-0.15 inches amounting to a swath of 1-2 inches
of snow. The main difference from previous runs has been to slow it
down a bit which mean Tuesday will be mostly dry with the bulk of
snow occurring overnight. The thing to watch will be the placement
and orientation of the Arctic front behind the clipper. Models have
had it residing just south of the Michigan border for a couple days now
but a slight jog north could bring some additional accums to the
The rest of the week into the weekend look fairly quiet...but on the
cool side... as the Arctic front on Wednesday Ushers in the next
Canadian high pressure system and associated trough of Arctic air.
850mb temperatures will fall to near -25c Wednesday night and into Thursday
before ridging noses back into the western Great Lakes providing
some relief as heights moderate. Highs will only be in the low teens
on Thursday but rebound to near 30 for the weekend.
Northeast winds will strengthen this evening and tonight across the
region as a strong winter storm tracks through the Ohio Valley and
lower Great Lakes. Winds will begin gusting to gale force across the
southern half of Lake Huron...including Saginaw Bay...this evening
and into Monday morning as the tighter pressure gradient lifts north
over the eastern lakes and colder less stable air filters southward
from Canada. Gale force gusts will remain too infrequent across the
Michigan waters of Lake Erie and will hold with gusts to 30 knots at
this time. Winds will relax on Monday as high pressure builds into
the region behind the departing storm.
Aviation...issued 110 PM EST sun Feb 1 2015
A broad band of snow will significantly affect the terminal corridor
for the rest of today through tonight before tapering off toward
sunrise Monday. LIFR visibility restriction will persist into the
early overnight with vlifr around 1/4sm during the peak of the event
roughly in the 21z-03z timeframe. While visibility will not be much
different than earlier in the event...this is when accumulation rate
will reach 1 inch per hour or briefly higher at times. Northeast
wind gusting around 25 knots will also present considerable blowing
and drifting to hamper operations. The snow will be replaced by MVFR
ceiling during Monday morning with diminishing wind followed by VFR
late morning into Monday afternoon.
At dtw... LIFR/vlifr visibility will persist for the rest of the
afternoon into the early overnight...but snowfall rate will peak
around 1 inch per hour during the 21-03z period...and then diminish
after midnight. Storm total accumulation of snow with a cold/fluffy
consistency near 12 inches remains on target.
//Dtw threshold probabilities...
* high for ceiling below 5000 feet through the taf period.
* High for precipitation type of snow.
* High for visibility of 1/4sm in snow and blowing snow during the
late afternoon and evening.
Michigan...Winter Storm Warning until 7 am EST Monday for miz055-060>063-
Winter Weather Advisory until 7 am EST Monday for miz047>049-053-
Lake Huron...heavy freezing spray warning from 7 PM this evening to 10 am EST
Monday for lhz362-363-462-463.
Gale Warning from 7 PM this evening to 10 am EST Monday for lhz363-
Gale Warning until 4 am EST Monday for lhz421-422.
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).