Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 210842

Area Forecast Discussion
National Weather Service Marquette MI
442 AM EDT Sun May 21 2017

.SHORT TERM...(Today and tonight)
Issued at 442 AM EDT SUN MAY 21 2017

08Z WV imagery and RAP analysis indicated a well-defined negative-
tilt shortwave lifting ne through ern IA. At the surface, low
pressure was located over southern MN with an occluded front through
central WI. Despite weak to moderate q-vector convergence ahead of
shortwave lifting ne through the Midwest, mid-level dry slot over
the area has limited pcpn so far this morning to dz or isolated

Today, as stronger qvector convergence ahead of approaching
shortwave and steeper mid level lapse rates greater than 7c/km move
across the area, models indicate another round of shra will move
across Upper Mi from approximately 10-16z with the potential for
isold tsra. The pcpn should then diminish later in the morning into
the afternoon as mid-level drying moves over the area. However, some
additional wrap-around shra may move into the west late. Expect
temps generally in the mid to upper 50s.

Tonight, the presence of the mid-upper low over the area and
continued cyclonic flow could sustain isold to sct showers across
the area tonight despite lingering mid-level dry air over the area
so wl maintain low chc pops for showers. Expect min temps in the low
to mid 40s under cloudy skies.

.LONG TERM...(Monday through Saturday)
Issued at 322 AM EDT SUN MAY 21 2017

Upper low over the Upper Mississippi River Valley slowly lifts
across northern Ontario and the Upper Great Lakes through Monday.
Main sfc low near Minneapolis this morning should lift north of Lk
Superior on Monday. Though majority of precipitation should be in
warm conveyor belt wrapping around the sfc low, low-level moisture
and cyclonic flow should allow for some lighter showers across most
of forecast area on Monday, especially if there are any shortwaves
working through around the base of the upper level trough.

Even as this upper low center moves to Quebec by Tue more troughing
fills back in over the Upper Great Lakes through at least Wednesday.
Indication that shortwave moving from SD on Monday aftn moves to WI
on Tue. Wave of sfc low pressure should track close enough to bring
some showers over at least south central Upper Michigan on Tuesday
with some models indicating precip over much of the central and
eastern forecast area. As the stronger portion of the upper trough
that is overhead for midweek affects the Upper Great Lakes late Tue
into Tue night, could see another episode of rain with best chances
over east half of forecast area. Later Wednesday, appears sfc ridge
and dry air finally begins to win out over the western forecast
area. Lingering moisture blo h7 should keep potential for light
showers or drizzle going much of the day over north central forecast
area where northeast winds between the sfc ridge and departing low
pressure system provide additional upslope lifting. Even with
occasional chances for rain, total rain amounts through Wed look on
the light side with most areas staying under 1.00 inch. With the
upper low in the vcnty and winds off of Lk Superior expect a few
days of cool conditions, especially near Lk Superior where highs
will only top out in the upper 40s to lower 50s. Highs farther
inland and near Lk Michigan away from flow off Lk Superior should
reach lower 60s. Plenty of clouds even when it is not raining will
keep min temps from falling too much.

As the upper low drifts toward New England Thursday into Friday,
upper ridging briefly moves across the Great Lakes downstream of
another upper low expanding from the Pacific Northwest to south
central Canada. The ridging and less cloud cover will allow temps to
rebound well into the 60s, though with the high building in from the
north, shoreline of Lk Superior will see temps stay in the 50s.

Once the upper ridge moves out of the area to the east, approaching
upper low shouls bring unsettled weather pattern back to the region
for next weekend. Main sfc front should be hung up well to south of
Upper Great Lakes, but approaching sfc trough may help to to produce
some showers. Recent model runs keep lowest showalter indices (SI/s)
to the south of here so will keep tsra out of forecast attm. Only
other primary issue in the long term is potential for frost. Western
forecast area would see greater chances of frost on Wed night with
all of the interior forecast area seeing more of risk Thu night.
Since the sfc ridge is just beginning to exit on Sat morning suppose
there could also be risk of frost over at least the interior eastern
area Fri night as well.

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 152 AM EDT SUN MAY 21 2017

Scattered rain showers will continue across the area with
lingering low pressure. Conditions will stay IFR through much of
the forecast period and perhaps fall to LIFR at a few sites this
morning. KSAW will be the exception by Sun evening as sw
downslope flow allows low MVFR conditions to set up.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 442 AM EDT SUN MAY 21 2017

As the low pres area moving across Lake Superior this afternoon and
evening will result in diminishing winds and shift in wind direction
from e-ne to w-sw late tonight. Winds under 20 kts should then be
the rule Mon into Wed as a relatively flat pres gradient dominates
the Upper Lakes.

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


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