Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 242352
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
752 PM EDT Wed May 24 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EDT Wed May 24 2017

An area of low pressure lifting north from the Ohio Valley will
bring chances for showers tonight along with a few storms this
evening. Showers remain in the forecast for Thursday, although the
trend will be towards drying out in the afternoon. Friday through
Saturday there may be a few showers around but these forecast
periods look fairly dry as well. Temperatures will be near normals
for this time of year through Saturday

&&

.SHORT TERM...(This evening through Friday night)
Issued at 330 PM EDT Wed May 24 2017

Main forecast challenge in the short term is in regard to
precipitation chances and extent. Main upper trough is clearly seen
in the water vapor imagery this afternoon from the Great Lakes to
the Gulf Coast. Distinct shortwaves are seen pivoting through the
upper trough. Our main weather maker for tonight is a shortwave
centered northeast of Louisville KY, moving northward toward our
area. Showers and a few thunderstorms have broken out well in
advance of this feature over Southern Lower Michigan this afternoon.
Expecting a continued push of showers into our area tonight with any
thunderstorms ending this evening with the loss of instability.
Instability at this point has remained on the meager side with
MUCAPE values on the order of 500-1000 J/KG. A better push of
moderate rain may try to make it into Southern Lower Michigan
tonight, but overall expecting a tapering of precipitation overnight
with the loss of heating/instability.

Thursday we are still expecting some showers to affect the area with
the upper trough still nearby. Thunder chances look fairly low with
limited if any CAPE. Plenty of moisture remain so expecting
considerable clouds based on deep layer RH and BUFKIT overviews.

Precipitation should taper off for Thursday night into Friday with a
dry forecast expected much of that time. Models are hinting at a
weak low moving through the Ohio Valley Friday night which may
spread some light rain showers up our way. Our thinking though is
that it will likely remain dry given how far north we are from the
low.

.LONG TERM...(Saturday through Wednesday)
Issued at 330 PM EDT Wed May 24 2017

Confidence remains relatively high that Saturday will be the nicest
day of the Holiday weekend with highs in the mid to upper 70s and
light winds. Subsidence/NVA aloft should keep things dry with partly
to mostly sunny skies.

Actually Sunday could be pretty decent as well across SW MI due to a
stable westerly low level flow. Plus the next upper low will still
be off to our northwest. Some chilly lakeshore readings in the 60s
should occur with the onshore flow, but mid 70s still seem possible
farther inland.

Guidance has be very consistent in showing the next upper low/trough
dropping down into the area on Memorial Day. The cold front
associated with the lead shortwave in the digging longwave trough
could trigger some tstms, and wouldn`t rule out some stronger storms
for the holiday.

Then we return to the familiar pattern of below normal temps and
occasional showers Tuesday into Wednesday with the upper trough and
low level cyclonic flow in place.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 743 PM EDT Wed May 24 2017

The instability has diminished considerably...thus the TAFS will
not feature any thunder tonight. An axis of showers was pivoting
westward from near KLAN through KJXN. These showers may have the
potential for brief IFR as the track westward this evening. Then
the models are trying to expand the IFR currently in far SE Lower
MI...northwestward with time. This makes some sense since it will
rain over the TAF sites over the next couple of hours...leaving
cooler temps and abundant low level moisture. So what I did was to
feature some IFR before 06z for most TAF sites.

The atmosphere destabilizes mid to late afternoon on Thursday.
This could support a brief thunderstorm prior to 00z Friday.



&&

.MARINE...
Issued at 330 PM EDT Wed May 24 2017

Northerly winds are expected tonight into Thursday night on Lake
Michigan. Waves will build into the 2 to 4 foot range at times, but
we are expecting to remain below Small Craft Advisory criteria for
the most part in the nearshore waters. Out on the open waters winds
will likely rise into the 15 to 25 knot range, but we will remain a
bit lower in the nearshore waters. Winds and waves tone down
considerably for Friday into Saturday with light winds expected.


&&

.HYDROLOGY...
Issued at 1259 PM EDT Wed May 24 2017

Rivers over the southern portion of the forecast area (south and
east of Grand Rapids) continue to run above normal. Southern
sites will be the main concern for any flood potential over the
next several days.

Precipitation forecasts for today have trended downward slightly.
The greatest totals are expected near Lansing and Jackson, where
amounts will range from 0.50-0.70 of an inch. Amounts will trend
downward further north and west.

Long term precipitation forecasts bring waves of precipitation
through late this weekend into next week. The current pattern
would suggest that amounts could vary widely from point to point
with any adjustment in timing and placement. In addition,
scattered convection could play a role in locally heavy rainfall
at times. Therefore, immediate flood concerns have decreased with
the latest trends in forecast qpf. The upcoming week may need
to be monitored with respect to sites that are experiencing higher
than normal river levels.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...Meade
AVIATION...MJS
HYDROLOGY...JAM
MARINE...Duke



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