Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 171748
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
148 PM EDT Wed May 17 2017


.AVIATION...

Main concern through the TAF period will be strong gusty winds from
the southwest, both this afternoon and again tomorrow. Tight
pressure gradient will be maintained between high pressure over the
Atlantic and low pressure lifting from the Central Plains to the
Northern Great Lakes. Mixed layer will continue to support gusts in
the 30-35 knot range through early evening before gusts subside as
the boundary layer shrinks. Strengthening low-level jet will then
provide a layer of low-level wind shear overnight and through early
Thursday morning. Winds and gusts will increase again by mid-morning
Thursday as daytime heating once again deepens the boundary layer.
Winds look slightly stronger than today, with gusts during at least
the first part of the day possibly reaching 35 to 40 knots.

Scattered 5000-6000 foot cloud layer this afternoon will decrease in
coverage this afternoon as drier air is entrained into Lower
Michigan. Chances for showers and thunderstorms will then exist late
tonight and again tomorrow afternoon. Axis of better moisture and
weak lift will cross the area after about 04Z tonight. This will
provide only a slight chance for showers and thunderstorms. Next
chance will be tomorrow afternoon as a cold front begins to drop
through the region, although lift may not be strong enough to
overcome a stable layer, and the afternoon could remain dry. If
storms do develop ahead of this boundary, they could be on the
strong to severe side from PTK southward.

//DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms late tonight. Low for thunderstorms tomorrow
  during the late afternoon and evening.

&&

.PREV DISCUSSION...
Issued at 340 AM EDT Wed May 17 2017

DISCUSSION...

Temperatures range from 65 to 73 across the CWA at press time,
impressive considering average highs for the date are right around
70 degrees. No noteworthy changes to forecast reasoning for this
package. Resident airmass remains largely unchanged from
yesterday`s, the key changes being better mixing behind the ridge
axis and a strong southwest gradient that will advect warm temps
into the Thumb. Convective debris is already spilling into the area
this morning, a trend that is forecast to continue through the day.
This will slightly suppress high temperature potential, but still no
arguments with 00z guidance indicating mid to upper 80s. Wind gusts
will be noticeably stronger than yesterday, 30+kts, in response to
boundary layer growth into the gradually strengthening wind field.

Southwest gradient will continue through tonight as the low lifts
toward the U.P. Clouds and mixed conditions at the surface will once
again contain lows to values closer to average highs. Forecast
soundings indicate a strongly capped environment through tonight.
Nonetheless, the dry currently progressing through central Texas and
Oklahoma will continue to work north and east, eventually bringing a
period legitimate forcing across the CWA after 06z. Suspect some of
the elevated instability will be realized under this scenario and
have maintained low chc for thunder.

Thursday essentially a redux, with substantial boundary layer
growth up to at least 5kft once again supporting highs in the 80s
and wind gusts around 30 kts. As noted in the previous forecast
package, MLCAPE over 1000 j/kg and adequate shear will be supportive
of a conditional severe threat. However, forcing will be rapidly
lifting northeast and flow becoming increasingly boundary parallel.
Abundance of dry air suggests primarily a wind threat. No argument
with SPC Day 3 Marginal.

Impressive temperature fall by Friday as marine-modified northerly
flow builds into the area in advance of approaching Canadian high
pressure. Strongly anticyclonic flow around the 1030+mb high should
erode any post-frontal low clouds, saving the area from highs in the
50s. Going forecast of low to mid 60s appears on target. The
exception will the Thumb where upper 40s/low 50s appear increasingly
likely.

MARINE...

Small Craft Advisories have been issued for the nearshore waters as
well mixed environment with decent pressure gradient will lead to
wind gusts of 30 knots or more over the land. While a stable layer
will exist over the marine layer, these wind gusts should be able to
penetrate offshore to some extent.

Similar wind conditions can be expected on Thursday. In fact, wind
gusts may be a bit stronger during the first part of the day as the
pressure gradient tightens in advance of approaching cold front as
it oozes in from the northwest as low pressure passes through the
northern Great Lakes. So, headlines are again possible.

This system will bring a chance of showers and thunderstorms from
Thursday into Thursday night. This will be especially true for the
northern half of Lake Huron as low tracks through the region.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 8 PM EDT this evening for LHZ421-422-
     441>443.

Lake St Clair...Small Craft Advisory until 8 PM EDT this evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 8 PM EDT this evening for LEZ444.

&&

$$

AVIATION.....HLO
DISCUSSION...JVC
MARINE.......DG


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