Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 201059
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
559 AM EST Mon Feb 20 2017


.AVIATION...

High pressure expanding across the eastern Great Lakes will
establish a strengthening east-southeast flow during the course of
the day. This will result in light southeast winds (8-12 knots
during the afternoon). Dry air associated with this high will
provide nothing more than high clouds during the day. Overnight,
winds will strengthen atop a shallow nocturnal stable layer with the
approach of a sfc front. This raises some concerns for low level
wind shear. There is concern that the boundary layer may not
decouple as strongly as suggested by model soundings, which would
thus support stronger sfc winds and less potential for LLWS.

For DTW...Daytime heating and an increased easterly gradient should
result in winds at 110 to 120 deg increasing above 7 knots around
16Z. This will increase probabilities for northeast flow operations.

//DTW THRESHOLD PROBABILITIES...

* None

&&

.PREV DISCUSSION...
Issued at 242 AM EST Mon Feb 20 2017

DISCUSSION...

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
upper 50s.

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.

MARINE...

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.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....SC
DISCUSSION...JVC
MARINE.......SC


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