Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 240520

Area Forecast Discussion
National Weather Service Marquette MI
120 AM EDT Sat Jun 24 2017

.SHORT TERM...(This evening through Saturday)
Issued at 350 PM EDT FRI JUN 23 2017

Tonight: As a shortwave shifts to the east of the area this evening
and daytime instability decreases, expect any of the few lingering
showers to diminish. This will lead to a mainly dry night across
much of Upper Michigan. There is a small chance that a few showers
may form late tonight over the northwest half of the area as a weak
surface trough approaches from the north. Thunder should not be an
issue overnight; however, as instability remain low. Would not
really expect too much more than a trace of rain over the
northwestern U.P. late tonight.

Saturday: The aforementioned surface trough will linger across the
area throughout the day as another/stronger upper-level disturbance
slides just south of the U.P. This added forcing from the surface
trough, along with steeper lapse rates, will allow scattered showers
and thunderstorms to develop across the U.P. The boundary being
nearly overhead will allow cloud cover to increase and showers to
develop earlier in the day; however, the coverage is expected to
become more widespread during the peak heating of the afternoon.
Some of the showers and thunderstorms may drop some heavy rain over
a short period of time, mainly over the south central and the
eastern portions of the U.P. Saturday afternoon. Severe weather
threat is expected to be margingal; however, the south central and
eastern portions of the U.P. could see some small hail from any
stronger thunderstorms that develop. This is largely due to
increased instability over those area along with freezing levels
dropping to around 6kt. Not much shear at all and the MUCAPE is only
around 600 - 1000 J/kg over the south central and east, so not
expecting anything more than the occasion pulsing thunderstorm with
small hail potential.

.LONG TERM...(Saturday night through Friday)
Issued at 416 PM EDT FRI JUN 23 2017

Mean mid-level positive height anomalies over western N America for
the next 7 to 10 days will support downstream troffing over eastern
N America. However, moving thru days 7-10, positive height anomalies
will shift toward n central Canada, resulting in the downstream trof
realigning from eastern Canada into the northern Plains. This large
scale pattern will support cool conditions/blo normal temps for the
Upper Lakes on most days. Coolest conditions will occur over the
next 2-3 days as negative 500mb height anomalies max out at 150-180m
over the Great Lakes region. There will be warming in the mid to
late week period next week as a rather strong shortwave cutting thru
the western ridge early next week goes on to set up troffing from
eastern Canada to the northern Rockies, backing flow downstream.
Temps will trend normal to above normal for a time. A return to
cooler conditions will occur next weekend as the upstream trof
reaches the Upper Lakes. As for pcpn, mid-level trof over the Great
Lakes for the next 2-3 days will be very conducive for sct to nmrs
shra due to combination of cyclonic flow, shortwaves and cold pool
aloft being worked on by max sun angle of the year. Shra coverage
should diminish on Mon as mid level trof begins to shift e. Will
likely be able to slip in a dry day on Tue with high pres ridge
passing. Another active period will then setup mid to late week
ahead of the trof extending from eastern Canada to the northern

Beginning Sat night thru Sun night, expansion of shra that occur Sat
aftn will tend to diminish Sat night with loss of daytime heating.
More persistent deep layer forcing lingering over the e may support
better coverage of shra in that area during the overnight. Approach
of another shortwave on Sun combined with daytime heating will yield
nmrs aftn shra inland from Lake Superior. Coverage should be least
over the eastern part of the fcst area due to greater stabilization
from flow off Lake Superior in that area. With mlcape into the 500-
900j/kg range, expect at least isold-sct tstms as well. Low wetbulb
zero heights in the 5.5-6.5kft range suggest there could be a lot of
cells producing small hail Sun aftn. Shra will again diminish Sun
night with loss of daytime heating. Highs on Sun will be in the 60s,
coolest near Lake Superior.

On Mon, heights will begin to rise as mid-level trof begins to shift
e. However, lingering cold pool aloft and some build up of
instability, though not nearly as much as Sun, should yield isold to
sct -shra inland from Lake Superior, especially over the s central
where the more limited mlcape will be centered. Temps should be a
little higher than Sun.

Tue should be a pleasant day as high pres ridge passes. Under mostly
sunny skies, temps will rise into the 70s across the area, locally
cooler along the Great Lakes.

Wed thru Fri looks to be an active period as trof developing into
the northern Rockies slowly shifts e. WSW flow and at least a couple
of shortwaves ejecting from the trof to the Great Lakes will
generate shra/tstms with probably some risk of svr storms. At the
moment, there is reasonable model agreement for a better potential
of shra/tstms Wed/Wed night. Agreement diminishes drastically
thereafter, but it appears there will be another round of shra/tstms
at some point Fri/Sat.

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 120 AM EDT SAT JUN 24 2017

Late tonight through Saturday morning, a weak surface trough and
upper level disturbance will approach the area. This will bring
increasing rain chances and cigs dropping into the MVFR range.
However, visbility should remain VFR even under some of the rain

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 350 PM EDT FRI JUN 23 2017

Winds will increase to 15 to 25 knots this evening, then decreasing
during the overnight hours into Saturday morning to around 10 to 15
knots. Winds of 10 to 15 knots are expected to continue into early
next week as the pressure gradient decreases and high pressure
builds in for the first part of the work week.

Upper Michigan...
Lake Superior...
Lake Michigan...


LONG TERM...Rolfson
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