Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 191559

Area Forecast Discussion
National Weather Service Grand Rapids MI
1159 AM EDT Sat Aug 19 2017


Issued at 330 AM EDT Sat Aug 19 2017

Clouds and scattered showers will exit this morning and high
pressure will provide a sunny and warm weekend. A slow moving
cold front will bring periodic showers and thunderstorms Monday
and Tuesday, followed by several days of dry and comfortable
weather as canadian high pressure gradually settles into the


.SHORT TERM...(Today through Monday)
Issued at 330 AM EDT Sat Aug 19 2017

Shower coverage associated with shortwave currently passing
through the region has been quite limited so far and will carry
just isolated showers in the fcst early on. While thunder
probabilities are not zero, risk seems too low to keep in the
fcst. Latest RAP MUCape progs indicate if thunder did occur it
would be near and south of I-94.

Otherwise partly sunny skies this morning trending toward more
sunshine than clouds this afternoon with subsidence behind the
departing shortwave. Remaining mostly clear through Sunday, with
warmer high temps in the mid 80s as waa develops on periphery of
sfc high slipping south toward the Ohio valley region.

Risk for showers and a few tstms will develop late Sunday night
mainly north and west of GRR as leading edge of higher PWATs over
1.5 inches and H8 theta-e ridge nudges into the region. Convective
risk expands over the entire area on Monday with zonal flow
regime aloft and southwesterly low level jet of 25-35 kts ahead of
approaching frontal boundary aimed into the area. Currently not
looking good for eclipse viewing with considerable cloudiness
expected, although timing of shortwaves/mcvs and potential
convective clusters within zonal flow is low confidence at this

.LONG TERM...(Monday night through Friday)
Issued at 330 AM EDT Sat Aug 19 2017

Forecast concerns deal with convective trends Monday night and
Tuesday with the passage of a moderately strong cold front.

Both the ecmwf and gfs have been advertising a cold front to move
across the Great Lakes early next week. There may be a small window
in which strong to severe storms could develop Tuesday afternoon
across the far southern cwa. GFS progs shear values in the 40-50 kt
range. Several short waves are progd to accompany the front, so we
may see several rounds of showers as the frontal boundary
approaches. The extensive cloud cover may limit instability, so the
potential for severe storms is still in question.

A strong shot of cooler air will flow in behind the front for the
latter part of the week. Dewpoints will finally fall from the 60s to
the the upper 40s/lower 50s late in the week. Lows in the 40s are
possible Thursday night and highs in the lower to mid 70s are
expected from Wednesday through Friday.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1159 AM EDT Sat Aug 19 2017

VFR conditions are expected into this evening then some MVFR
fog/mist early Sunday morning only to become VFR once again after

There is an upper trough/shortwave moving east of the
area as I write this. There is unstable air assoicated with that
trough but since it is already east of here, I would think any
convection from it would be east of I-75 (for the most part). This
can be seen on the the VIS satellite loops over MI with the
enhanced CU in the Thumb are to near western Lake Erie. The area
from the Thumb to near Jackson will have around 500 j/kg of most
unstable cap this afternoon. So, east of Jackson a storm is

Tonight high pressure moves overhead and winds should be near calm
at the surface with clear skies so light fog is expected. Tomorrow
the upper ridge moves through the area and surface winds turn to
the south so it should be solid VFR once the morning fog mixes


Issued at 330 AM EDT Sat Aug 19 2017

Looks like a fairly tranquil period on Lake Michigan through
Monday, then a threat for frequent tstms Monday night and Tuesday.
Next significant wind and wave event appears to be later Tuesday
into Wednesday with strong NNW flow behind a strong cold front.


Issued at 329 PM EDT Thu Aug 17 2017

Rivers continue running well within their banks and that is the
expectation this weekend as well. The flows at most sites are near
to below normal. Rises on at least the small rivers and streams look
possible for the middle of next week based on medium range guidance
QPF. An inch or more of rainfall is certainly a possibility Monday
night into Tuesday night.




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