Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 171952

Area Forecast Discussion
National Weather Service Marquette MI
352 PM EDT Wed May 17 2017

.SHORT TERM...(This evening through Thursday)
Issued at 352 PM EDT WED MAY 17 2017

The main forecast concern this evening will be the potential for
flooding across the west and portions of central Upper Michigan, and
then the threat for strong to severe storms this evening. The strong
to severe storms should remain confined along the Wisconsin/Michigan
border, especially across south central portions of the area. The
main threats, other than flooding, will be damaging winds and hail.

Ongoing convection that developed down across northern Iowa and
southern Minnesota has taken advantage of the instability gradient
draped across Wisconsin and up into south central Upper Michigan.
Based on the current RAP analysis and comparing it to the 1800Z GRB
RAOB, it looks like the instability may be underplayed a bit within
the RAP. Given the orientation of the CAPE gradient along the
surface trough, prefer the HRRR solution as it takes the ongoing
convection right up along the instability axis across central Upper
Michigan. While instability isn`t great, the shear is rather stout
with 0-6km shear values of 50-60 knots. Also, based on the
unidirectional shear on the GRB 1800Z hodograph, we could see a few
splitting storms, which will further complicate how convection
evolves over the next few hours. The main severe weather hazard for
this evening will be damaging winds and hail, especially across
south central portions of Upper Michigan. As the storms continue to
push northeast across the area this evening, they may still be
strong; however, they will eventually out run the better instability
and should begin weaken. With PWATs running around 1.5 inches across
the area, heavy rain will also be a threat with localized flooding
concerns based on high rain fall rates. Have not made any
adjustments to the Flash Flood Watch across the west and portions of
central Upper Michigan, as even more rainfall looks on track for
later tonight into Thursday morning as the main upper-level trough
lifts north across the area and brings another shot of widespread
heavy rain overnight into Thursday.

Overnight, with elevated instability running a couple hundred J/kg,
wouldn`t be surprised if a few strong storms develop/intensity
across central and eastern Upper Michigan. While locations across
western Upper Michigan are not expected to see strong to severe
storms tonight, precipitation will become more widespread with heavy
rain being the dominant threat. As the above mentioned upper-level
wave lifts across the area, surface troughing will slowly push
northeast across central and eastern Upper Michigan, allowing colder
air to filter south. By Thursday morning temperatures are expected
to drop into the upper 30s across the west, while only dropping into
the lower 50s across the east and south central. Lingering rain
showers will continue across much of the area through the morning
hours; however, things will continue to dry out through the
afternoon hours as the cooler, drier air mass advects south across
the area. Accompanying this drier and cooler air, will the
increasing northerly winds across the area. Momentum transport
values from BUFKIT soundings even show a few locations gusting up
into the 30-40mph range.

.LONG TERM...(Thursday night through Wednesday)
Issued at 251 PM EDT WED MAY 17 2017

Nam shows a 500 mb trough over the upper Great Lakes 00z Fri with a
closed low over the central Rockies and a ridge over the northern
plains. This ridge moves into the upper Great Lakes 00z Sat. The
closed low moves into the northern plains 00z Sun. Nam shows 850-500
mb q-vector convergence with deeper moisture moving in on Sat. Looks
to be quiet through Fri night and then have chance pops Sat morning
over the west half and have likely pops over the west half in the
afternoon and a chance of pops over the east half in the afternoon.
Overall, did not make too many changes to the going forecast.

In the extended, GFS and ECMWF show a closed 500 mb low and trough
near the upper Great Lakes 12z Sun. This trough remains over the
area through Wed with some colder air returning and a cold front
that moves through on Tue. Temperatures look to remain below normal
for this forecast period.

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 138 PM EDT WED MAY 17 2017

Challenging aviation forecast this afternoon as periodic rain
showers continue to lift across the area allowing visibilities to
fluctuation from LIFR to MVFR across the west. Expect KIWD/KCMX to
remain fairly socked in the cloud cover this afternoon, visibilities
will likely improve as daytime heating continues and winds begin to
back slightly. However, expect the LIFR/IFR ceilings to persist.
Additional rain chances will arrive later this afternoon and
overnight. Heavy rain may limit visibilities at time. Conditions
will gradually improve through the morning/afternoon hours on
Thursday as drier air begins to move into the region, but winds will
become rather gusty.

Fog came onshore much earlier than anticipated at KSAW; therefore,
KSAW has been socked in LIFR conditions through much of the day so
far. Current satellite trends show a pocket of clearing just to the
south of KSAW. Difficult to say if the advection off the lake will
hold strong enough to keep the lower ceilings and visibilities. If
the clearing does start to lift north across KSAW, visibilities very
well may drop down to VLIFR briefly. Multiple rounds of showers and
possibly a few embedded thunderstorms are expected to move across
KSAW bringing heavy rain and possibly gusty winds.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 325 AM EDT WED MAY 17 2017

Northeast winds will increase in speed to gales of 40 to 45 knots
across the west and central tonight, before shifting over the
eastern half through the morning hours on Thursday. Winds will begin
to relax to around 10 to 20 knots across the west and central, while
20 to 30 knot winds will still be possible across the east by the
evening hours on Thursday.  Winds of 10 to 20 knots are expected
through the end of the work week and beginning of the weekend. This
weekend, winds will increase to 20 to 30 knots as another storm
system lifts out of the Plains across the Upper Great Lakes. Early
next week, 10 to 20 knot winds will persist over much of the lake.

Lingering fog will begin to diminish from west to east across the
lake tonight into the morning hours on Thursday as drier air begins
to filter eastward across the lake. However, at this time dense fog
will still be possible.


Upper Michigan...
  Flash Flood Watch through Thursday afternoon for MIZ002-004-009-

Lake Superior...
  Gale Warning from 8 AM to 8 PM EDT Thursday for LSZ267.

  Gale Warning from 4 AM to 4 PM EDT Thursday for LSZ265-266.

  Gale Warning from 11 PM EDT /10 PM CDT/ this evening to 11 AM
     EDT /10 AM CDT/ Thursday for LSZ162.

  Gale Warning from 11 PM this evening to 2 PM EDT Thursday for

  Gale Warning from 1 AM EDT /midnight CDT/ to 10 AM EDT /9 AM
     CDT/ Thursday for LSZ240-241.

  Gale Warning from 1 AM to 11 AM EDT Thursday for LSZ242-243.

Lake Michigan...


SHORT TERM...Ritzman
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