Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 201805
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
105 PM EST Mon Feb 20 2017
High amplitude upper level ridging will remain in place over the
central Great Lakes through the next 12 hours, but the surface
ridge axis aligned under greater geopotential height rises will
retreat out of the state more quickly. Models show a definitive
cold, stable lake aggregate response late this afternoon and early
evening, bringing with it a greater easterly flow this afternoon.
Have already been seeing this signal in surface observations. Dry
air will remain entrenched in the lowest 20 kft agl, bringing no
cloud considerations this afternoon and tonight. LLWS remains a
concern for tonight as the lead edge of low level jet axis pushes
towards southeastern Michigan. Followed the lead of the inherited
tafs which errs on the side of greater gradient flow at the surface.
Otherwise, the main change in this taf issuance was to push back
timing of prevailing showers. Narrowing ribbon of moisture in the
700- 600mb layer will not arrive over the Saginaw Valley until after
12Z, not over the Detroit terminals until as late as 17Z. Given
weakening dynamics and narrow deep moisture, the Tuesday event is
appearing to be a short duration one, with perhaps a 3 hour window
for rain shower chances.
For DTW...Daytime heating and an increasing, stable lake aggregate
response will lock wind directions in the 110 to 120 deg fetch with
high confidence flow of 10 knots. This will increase probabilities
for northeast flow operations.
//DTW THRESHOLD PROBABILITIES...
Issued at 242 AM EST Mon Feb 20 2017
Longwave trough emerging over the front range this morning exists as
a result of a brief phased period between lower amplitude Pacific
jet energy and the wave that came onshore in California a couple of
days ago. Through mid-day today, this spells downstream ridge
amplification overhead and light southeast flow at the surface in
the wake of departing high pressure. Cirrus will spill across the
ridge axis providing the only cloud cover on an otherwise clear day.
Easterly flow will limit mixing depths and provide some marine
modification in lake shadows that will limit highs near the water to
the 40s. Elsewhere 50s to near 60 are likely, particularly in the
Saginaw Valley where marine influence will be nil and downsloping
will aid afternoon warming. The record high of 62 (1930) at MBS is
not out of reach, particularly if cirrus is sufficiently thin to
allow stronger insolation during peak heating.
Showers and thunderstorms extending from northeast Mexico into
Kansas this morning as moisture is transported north in association
with the strengthening nocturnal LLJ. Phasing is too tenuous to
survive incoming Pacific jet, which will force the bulk of the
energy to close off over the southern US. This will effectively cut
off moisture transport early this afternoon, leaving the northern
branch with sufficient, but not particularly impressive, moisture as
it lifts northwest of the area late tonight into Tuesday. A band of
showers is modeled to be sustained by a weak prefrontal trough
associated with the weakening low-level jet axis. Pops gradually
diminish from northwest to southeast Tuesday morning into Tuesday
afternoon as low-level support weakens. Daytime timing for rainfall
will limit high temperatures to sub-record values in the mid to
A new round of records at one or more climate sites possible
Wednesday as a compact wave translates to our northwest against a
background of height rises over the Great Lakes. Stout southwest
gradient in advance of the cold front will push 925mb temps into the
low teens by Wednesday afternoon. 00z Mex guidance leads the pack in
terms of warmth with a solution nearing 70 degrees at Flint. Along
with surrounding offices, bumped temps up well into the 60s south of
the I-69 corridor. Antecedent dry air looks to limit any precip
potential along the cold front as it settles south of the Michigan
border and becomes increasingly parallel to the deep layer flow
Wednesday night, setting the stage for a significant late week
system begins to lift into the western Great Lakes Friday into
Friday night. NWP consensus remains strong on a track well to the
west of the CWA while the 00z ECMWF holds firm on severe weather
potential in the nocturnal warm sector with several hundred j/kg
elevated CAPE and 60+kts 0-6km bulk shear.
East-southeast winds will be on the increase today into Tuesday
morning as strong high pressure expands across the eastern Great
Lakes, while a frontal boundary approaches the western Great Lakes.
Warm air above the cold lake surface will keep fairly stable
conditions. Nonetheless, the gradient increase and long trajectory
over the lakes suggest winds will become rather gusty late today
into tonight. Gusts up to 30s knots appear likely across much of
Lake Huron tonight. There will be a brief window where gusts may
reach gale force on Lake Huron around daybreak Tuesday. The brevity
in the period of potential gales will not warrant a gale
watch/warning. The frontal boundary will slowly move across Lower Mi
and Lake Huron on Tuesday. There will be substantial weakening in
the winds as the broad frontal boundary moves into the region.
Further weakening of the post frontal gradient will support light
and variable winds Tues night. Modest southwest winds are then
forecast to develop on Wednesday.
Lake Huron...Small Craft Advisory from 10 PM this evening to noon EST Tuesday
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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