Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 170740

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
340 AM EDT Wed May 17 2017


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



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.


Issued at 1158 PM EDT Tue May 16 2017


High amplitude ridging will remain in place over the central Great
Lakes, including southeastern Michigan, throughout the next 24
hours. Active subsidence in the midlevels and a dry, ambient near
surface environment will keep any prospects for precipitation
extremely low. Increasing gradient flow developing along
northwestern periphery of subtropical ridge will make southwesterly
surface winds the story tonight and Wednesday. Maintained the
inherited non-convective low level wind shear mention. With daytime
heating and low humidity on Wednesday, mixing heights will rise
substantially leading to gusty winds. Very high confidence exists,
particularly south and east of the glacial terrain, that sw surface
wind gusts will reach and exceed 30 knots.


* None


Lake Huron...Small Craft Advisory from 10 AM this morning to 8 PM EDT this
     evening for LHZ421-422-441>443.

Lake St Clair...Small Craft Advisory from 10 AM this morning to 8 PM EDT this
     evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 10 AM this morning to 8 PM EDT this
     evening for LEZ444.




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