Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
622 am EST sun Nov 23 2014
Conditions today look to be a bit variable...low VFR vs MVFR
ceilings...as backing surface winds out of the southeast will tend
to dry out the low levels...while areas of showers working through
the area will tend to moisten and suppress ceilings back down into
MVFR category. Higher confidence in the forecast this evening and
tonight with increasing low level moisture and moderate rain leading
to IFR conditions through majority of the night...as deepening low
pressure tracks west of Southeast Michigan. As the low tracks
through the northern Great Lakes tomorrow...winds will shift to the
southwest and become strong during the afternoon hours...likely
gusting above 35 knots.
//Dtw threshold threats...
* high confidence in ceilings below 5000 feet.
* High confidence in rain as precipitation type
Previous discussion...issued 320 am EST sun Nov 23 2014
Short term... today and tonight
Copious amount of upper level energy/pv working through The Rockies
this morning. Moisture laden upper level wave over eastern Texas
already becoming absorbed/captured within the strengthening
southwest flow over the central consus. Impressive 12 hour height fall
center (-18 dam) will move over western Ohio Valley by 12z
Monday...supporting good cyclogensis moving into the central Great
Lakes. This will assure a soaking rain tonight...with strong low
level jet/good overrunning set up/large scale ascent...and 850 mb
dew points of 7-8 c to work with. Rainfall totals around 1 inch will
likely be common. A quick look at 6 hour flood guidance shows 2
inch thresholds...and do think the ground will thaw out enough
today to be able to handle this rainfall...and not planning on
issuing a Flood Watch despite the 3+ Standard anomaly with respect
to precipitable water vales.
A mild start to the day...as temperature are currently in the middle
40s to around 50 degrees. However...with the surface/near surface
winds backing out of the southeast today...would not expect much
more of a rise (lower 50s)...with temperatures hovering in the upper 40s
to lower 50s tonight with renewed surge of warm air arriving.
Long term... Monday through Saturday
Dynamic middle level wave locked onto the exit region of an active
upper jet of North Pacific origin will quickly lift into the Great
Lakes on Monday...immediately behind the lead system working through
tonight. Some degree of interaction between these pv features and
attendant upper jet coupling will result in a steady strengthening
of the associated surface low tracking from Southern Lake Michigan
to just north of The Straits through Monday. There remains some
variability yet within the 00z model guidance in terms of both the
strength and forward momentem of the key low level features heading
into Monday. However the guidance envelop continues to contract
with each progressive model cycle...lending increasing confidence in
the details through this time.
Brief window of deeper pre-frontal southwest flow in place Monday
morning...temperatures likely peaking in the lower 50s during this
time. Brief subsidence suggests a small pause in shower development
middle morning...before the inbound middle level wave works across late
morning/early afternoon. Strong signal of frontal convergence
tucked beneath favorable upper jet dynamics and a period of good cva
points to an increase in shower coverage through this time.
Diminishing stability through the column could yield a few rumbles
of thunder as well. Main forecast element of interest remains the
wind potential as strong cold air advection ensues from middle
afternoon into the evening hours. Strong Post-frontal southwest
gradient takes hold during this time...sustained speeds increasing
into the 25 miles per hour range. Gust potential will capitilize on a period
of strong 280-285k isentropic descent and at least weak mixing
potential as lapse rates steepen with the advective process. Recent
guidance maintains wind speeds in the 40 knot range at 925 mb. This
would indicate gusts close to or at a low end advisory /40 to 45
mph/...greatest gusts centered 21z-02z.
Aggressive cold air advection brings temperatures back into the 30s
by early evening...a plummeting freezing level reintroducing the
potential for snow showers to mix in during this time. Modest Lake
Michigan response initially /lake induced equilibrium levels below
5000 feet/ with the strength of the wind field likely contributing to
a lack of better downstream organization. The main shortwave
anchoring the primary height fall axis will settle through
overnight...which may help augment the moisture flux in generating
some light snowers with minor accumulation. Low temperatures bottom
out within the 25 to 30 degree range.
Extended stretch of below normal temperatures starting Tuesday...
lingering low level thermal trough /-12c at 850 mb/ and plenty of
cloud cover ensuring highs arrive within a couple degree of
freezing. Low level flow veers to a westerly component during the
day...a more favorable trajectory for greater downstream advancement
of the Lake Michigan moisture plume and some localized convergence.
This will maintain a chance for snow showers through the diurnal
Dry and cold into Wednesday under lower amplitude ridging. Clipper
system on track to lift across the Great Lakes Wednesday night and
early Thursday. Modest moisture recovery immediately in advance of
this system would support a light accumulating snowfall as the
compact middle level dynamics sweep across during this time. Daytime
highs in the lower 30s both Wednesday and Thursday.
Moderate southerly winds will remain in place today and tonight as
strengthening low pressure lifts into the Great Lakes. The arrival
of warmer air in advance of this system will contain the gust
potential...with winds generally at 15 to 25 knots through this
The low pressure system will lift across the western and northern
Great Lakes through Monday...sending a strong cold front across the
area Monday afternoon. Gale force winds look likely behind the cold
front Monday and Monday night as a tight pressure gradient develops
and much colder air rushes into the area...with gusts potential in
excess of 45 knots. There is still some uncertainty with how much
this system will deepen and the exact track it will take across the
Great Lakes. Further adjustment to the forecast is possible. If the
system deepens further than currently anticipated...storm force wind
gusts could develop over portions of Lake Huron. Those with
interests in the Great Lakes Monday and Monday night should follow
changes in the forecast closely. A storm watch is now in effect for
Central Lake Huron...while a gale watch remains in effect Monday and
Monday night for all other marine areas.
Lake Huron...gale watch from Monday morning through Tuesday morning for lhz361-
Storm watch from Monday morning through Tuesday morning for lhz362-
Lake St Clair...gale watch from Monday morning through Tuesday morning for lcz460.
Michigan waters of Lake Erie...gale watch from Monday morning through Tuesday morning for lez444.
You can obtain your latest National Weather Service forecasts online
at www.Weather.Gov/Detroit (all lower case).