Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 250842
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
442 AM EDT Fri May 25 2018

.SHORT TERM...(Today and tonight)
Issued at 441 AM EDT FRI MAY 25 2018

Early this morning, as a subtle shortwave lifted across the region a
35 to 45 knot low-level jet ushered in additional low-level
moisture, providing additional lift and elevated instability for
convection tracking across Upper Michigan to work with. Upstream of
the region an elongated upper-level trough continued to slowly track
across the Northern Plains and into the Upper Mississippi Valley
with multiple shortwaves notable on water vapor imagery, including
the main shortwave moving across North Dakota. The main forecast
concern today is the chance for strong to severe thunderstorms this
afternoon and evening. Anyone with outdoor activities planned for
today through early tonight should keep a close eye on the weather.

We`re looking at another very warm and muggy day across much of
Upper Michigan today, with temperatures expected to climb into the
80s across the west half and 70s across the east half. Depending on
how cloud cover evolves through the late morning hours, we could see
a few locations approach the 90 degree mark this afternoon where
southwest flow would aid in downslope warming. Closer to Lake
Michigan, southwest flow off Lake Michigan should keep temperatures
in the upper 60s. With dewpoints this morning already in the low to
mid 60s, don`t expect moisture to be a concern for convection later
today. The combination of a humid airmass, diurnal heating, and
remnants of an elevated mixed layer steepening mid-level lapse rates
later today should allow for ample instability to setup across the
region. Shear on the other hand looks on the marginal side, with
deep layer shear approaching 25-30 knots at best. With a modest
cape, low shear setup today, expect storms to be pulsey. A few
storms may remain somewhat organized initially, but as cold pools
interact and the main shortwave moves across the area, expect
convection to congeal into a line as cells moves west to east across
the area. While wet-bulb freezing heights are around 10kft, thinking
the lack of shear should will limit the potential for large hail.
However, if we do see temperatures reach the mid to upper 80s across
the west half, the presence of inverted-v soundings and the
potential for collapsing updrafts should lead to the potential for
microbursts, and thus damaging winds. Along with damaging winds,
heavy rain will be a potential threat as storms will not be moving
fast and cell mergers may promote training of showers and
thunderstorms.

Right now, confidence is highest that convection will initiation
during the early-mid afternoon across the central portions of Upper
Michigan and across far western Upper Michigan. As we progress into
the late afternoon-evening hours expect convection to slowly move
eastward as the moisture transport veers west-southwest. Stronger
showers and thunderstorms will gradually diminish as we loose
insolation tonight, but with a couple trailing shortwaves progged to
dig south across the area, can`t rule out additional chances for
lingering showers and thunderstorms overnight.

.LONG TERM...(Friday night through Thursday)
Issued at 333 PM EDT THU MAY 24 2018

Above normal temperatures expected to continue through the extended
forecast along with scattered showers and thunderstorms through much
of the Memorial Day weekend.

Saturday: A shortwave is set to slide across the area Saturday
morning into the early afternoon hours, helping mlcape values reach
to around 1000J/kg. Models are showing that 0-6km deep layer shear
may be up to around 30 knots; however, with the shortwave set to
slide east of the area by the late afternoon hours. If enough
sunshine breaks out during the morning hours, then instability could
be enhanced enough to allow for some organization in the
thunderstorm activity across the area. There will be a conditional
risk for at least some isolated severe thunderstorms for late
Saturday morning into the afternoon for the central and eastern
U.P.with the increased shear values.

Sunday: There may be a few rain showers and possibly a thunderstorm
on Sunday morning; however, coverage and intensity will likely be
much more muted as the lingering shortwave will continue to slide to
the east. During the afternoon hours, under very weak pressure
gradient, convergent lake breeze boundaries may touch off a few
showers and a remote chance of an afternoon thunderstorm across the
area. Overall coverage will be minimal and mainly confined to the
central and eastern U.P.

Monday: There is a hint that a subtle shortwave may try to slide
through the Upper Great Lakes by Monday afternoon. This will help to
increase CAPE values a bit, probably in the 500 - 1000 J/kg range by
Monday afternoon. The instability along with lake breeze boundaries
under light flow, will lead to a few pop up afternoon showers across
the area, with a couple rumbles of thunder possible.

Tuesday through early Wednesday: Fairly quiet weather will be in
place for Tuesday and early Wednesday as high pressure slides
through the area and temperatures will continue to be above normal
for this time of year, by about 15 to 20 degrees.

Wednesday afternoon through Thursday: A deepening upper-level trough
is progged to approach the Upper Great Lakes region Wednesday
afternoon and slide through the area Wednesday night into Thursday.
This will be basically the same time frame that the associated low
pressure system and cold front slides through the area. Instability
is progged to be increased with the moisture advection into the area
and steepening lapse rates; therefore, there will likely be
thunderstorms ahead of the cold front. Shear looks marginally
favorable for severe weather; however, exact details will be ironed
out as we get closer to this time period and models converge on the
details.
&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 141 AM EDT FRI MAY 25 2018

Scattered showers and isolated thunderstorms will move through the
area off and on, although VFR conditions should prevail. LLWS will
continue at all sites overnight. Timing the onset of showers
and thunderstorms will be difficult.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 441 AM EDT FRI MAY 25 2018

Winds less than 20 kts are expected through the middle of next week.
Expect areas of fog to develop and linger at times into the weekend
as multiple rounds of rain are expected over the lake and the humid
airmass lingers. Fog may be dense at times, especially this morning
across the far west half. Thunderstorms are possible today through
Saturday night, and then again early next week.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Dense Fog Advisory until 11 AM EDT /10 AM CDT/ this morning for
     LSZ162.

Lake Michigan...
None.
&&

$$

SHORT TERM...Ritzman
LONG TERM...KEC
AVIATION...07
MARINE...Ritzman


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