Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 221142

Area Forecast Discussion
National Weather Service Marquette MI
742 AM EDT Mon May 22 2017

.SHORT TERM...(Today and tonight)
Issued at 513 AM EDT MON MAY 22 2017

Latest WV imagery and RAP analysis indicated a closed low over
Ontario north of Lake Superior early this morning. Q-vector
convergence out ahead of a shortwave rotating around the southern
periphery of the low was supporting sct showers over central Upper
Mi early this morning, especially over the east half of the U.P.

Today, with continued q-vector convergence ahead of the shortwave
moving through the Upper Lakes, expect numerous shower coverage over
the east half of the cwa this morning. Even with some expected
drying in the wake of the departing shortwave this afternoon,
diurnal heating/weak instability with the mid level trough still in
place over the area may still be enough to support some inland
sct/isold -shra development. Expect highs in the mainly in the 50s,
except for lower 60s far south central.

Tonight, any lingering instability showers should end early evening
with loss of diurnal heating. As closed low lifts from Ontario east
into Quebec, weak mid-level ridging setting up over the area should
ensure mostly dry conditions tonight as noted by models. Min temps
will range from the upper 30s inland to the lower to mid 40s near
the Great Lakes shorelines.

.LONG TERM...(Tuesday through Sunday)
Issued at 401 AM EDT MON MAY 22 2017

No high impact weather on the horizon this week. Rainfall chances
stay frequent through midweek and there are additional chances
next weekend, but total amounts should stay below 1 inch into
next weekend. RH values could be low to end the week (maybe as
early as Wed aftn far west but most likely on Thu) but with the
recent wetter weather pattern and light winds expected, a dry day
or two should not too much concern for fire weather. As a sfc high
pressure ridge crosses area late in the week, may have one or two
nights where temperatures inland would be low enough to support
mention of frost.

Upper low over the region slides to Quebec on Tue while secondary
trough lingers over middle Conus to the western Great Lakes. At the
sfc, main sfc low will head to Quebec while weaker sfc low pressure
wave drifts across western Great Lakes then drops to the northern
Ohio Valley by Wed where lower heights in the mean trough focus by
that time. Still appears that a shortwave or two affecting region
along with sufficient moisture blo h7 could lead to scattered light
showers over mainly west half of Upper Michigan on Tue. Some of that
rain may also try to affect southern and eastern forecast area on
Tue night on northern edge of sfc-h85 low and in area of weaker
upper level forcing. Overall though the forcing in lower and upper
levels remains weak so not expecting much in way of rainfall Tue
through Tue night. GFS most aggressive with showers lingering over
east on Wed in area of mainly mid level moisture/forcing. Other
models have that idea but keep focus either south or east of eastern
forecast area. Consensus keeps chance low for now which is reasonable
given the model differences and overall weak forcing.

That trough will only slowly give way to ridging aloft by Thu,
though GEM and to certain extent ECMWF indicate slower departure of
the trough. Since sfc low should be well south or east of forecast
area think risk of additional precip will be low, though the GEM
which has stronger secondary upper low over Upper Michigan would
point to some precip for a few runs now. Since the GEM is outlier
with strength of the upper low kept pops only at slight chance.
Farther west over west and central forecast area better chance of
sfc ridge building across so lowered min temps more in line with
bias corrected guidance sets which show interior west seeing lows
Wed night at least down into the mid 30s if not lower 30s. With the
lower temps have a mention for frost that night. Sfc ridge sliding
across on Thu night could lead to another night with temps down
into the 30s inland and some frost.

Once upper level ridging arrives Thu night into Fri it will not stay
around long as large upstream trough over scntrl Canada Thu night
will already be spinning a shortwave toward the Upper Great Lakes as
early as Fri aftn. Mid clouds should increase west to east but with
warming h85 temps, raised highs into the low 70s over interior west
which is more in line with last couple runs of GFS MOS extended
(MEX) guidance. Main sfc low stays closer to upper trough but sfc
trough tied to the low swings across Upper Great Lakes on Fri
night. Kept consensus low chances for showers over the west half.
Could be tsra as well over west in the evening with SI/s falling
blo 0C. Best chance for tsra will be upstream during the aftn in
MN with some sfc based CAPE indicated during peak heating. Rest of
weekend looks unsettled with chances for showers and possible
tsra as upper level troughing with embedded shortwaves affect
region. Could be rain on Sat, but better chance for rain probably
end up later Sat into Sun as better defined sfc trough moves in
from the northern Plains and there is potential for stronger
shortwave to move through.

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 737 AM EDT MON MAY 22 2017

Low IFR/LIFR cigs early this morning at IWD and CMX will improve
to MVFR late this morning/early afternoon with diurnal mixing and
to VFR late this afternoon. MVFR stratus clouds could redevelop
at IWD and CMX overnight. With sw downslope winds at SAW, MVFR
cigs will improve to VFR late this afternoon. &&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 513 AM EDT MON MAY 22 2017

A low pres trough lingering over the area will maintain fairly light
winds across the lake into tonight. Winds under 20 kts should then
be the rule Tue into Fri as a relatively flat pres gradient
dominates the Upper Lakes.

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


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