Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 261817

Area Forecast Discussion
National Weather Service Grand Rapids MI
217 PM EDT Fri May 26 2017


Issued at 330 AM EDT Fri May 26 2017

A narrow high pressure ridge crosses the area into the mid day
hours resulting in partly sunny skies and highs in the lower 70s
inland. A frontal wave passing off to our south tonight and may
bring a few showers into southern sections prior to midnight.
Saturday will be the warmest day in the next 7 days with highs
near 80 inland. A frontal system moves across the area Sunday and
that brings the chance of showers and thunderstorms. The storm
that brought the front trough stalls over Hudson Bay early next
week so we stay in northwest flow around that system keeping it
unseasonably cool for most of this coming week. Expect scattered
showers from time to time into the middle of next week as we
remain cool unstable air due to the stalled system over Hudson


Issued at 1134 AM EDT Fri May 26 2017

Tweak POPs upward over the far SW corner of the CWA for late
afternoon/early evening. Added 40/50 POPs over Allegan and Van
Buren Counties. The MCS over Eastern IA late this morning is
expected to be maintained and continue east. It will have
favorable jet dynamics throughout the day and should arrive into
the SW corner of Lower Michigan between 21Z and 23Z. Best dynamics
and instability remains to our south, so severe threat will
remain south.


.SHORT TERM...(Today through Sunday)
Issued at 330 AM EDT Fri May 26 2017

There are several issues with this forecast. The first is the
frontal wave that will pass off to our south early tonight. There
is an MCV that is seen well on the waver vapor loops and is
initialized well in the upper air maps of the RAP and HRRR plus
the GFS but not so much in the NAM. Given that satellite image
loops look good when matched with the HRRR and RAP model 850, 700,
500 mb and various other features I believe the GFS is to weak
(the NAM does not even have the precipitation assoicated with it
this morning). So I am favoring the more southern track that is
shown by the HRRR and RAP models for this feature. That would take
the majority of the convection south of our CWA this evening.
Still one never really knows for sure so I do have chance pops
over our CWA this evening just in case.

The next feature is the next upstream system which has both a
southern stream and northern stream component to it. This moves
across our area Sunday. The models continue to be all over the
place with this so chance pops seem good at this point.

Saturday will likely be the warmest day in the next 7 days as we
get good southerly flow ahead of the approaching system and our
1000/925 mb thickness warm enough to suggest highs should be near
80 inland. So I adjusted our forecast highs up a few degrees to
show that. Our rex block upper air system stalled over Hudson Bay
most of the first half of next week will keep us cool with
scattered showers from time to time which is why Saturday will be
the warmest day at least till the following weekend.

.LONG TERM...(Sunday night through Thursday)
Issued at 330 AM EDT Fri May 26 2017

A cooler and unsettled wx pattern will develop early next week as
the upper level trough digs and amplifies over the Great Lakes

High temperatures Monday and Tuesday will reach the 60`s with fairly
extensive diurnal cloud cover and scattered instability rain
showers. Showers will be enhanced from time to time by several
shortwaves that will rotate around the base of the upper trough.

Temperatures should moderate a bit toward late next week as the
upper trough axis moves east of our region and h8 temps moderate.
High temperatures should reach the lower to perhaps middle 70`s by
Thursday. A high pressure ridge will build in and bring fair wx
late in the week.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 150 PM EDT Fri May 26 2017

VFR conditions will prevail through the afternoon then an area of
showers and a few thunderstorms will be arriving around 00Z. This
will bring areas of MVFR across southern Lower Michigan generally
south of MKG to GRR to LAN. The rain should taper off and end
around midnight with MVFR and patchy IFR lingering into Saturday
morning from AZO to JXN.


Issued at 330 AM EDT Fri May 26 2017

No much going on worth a headline as winds will be on the light
side until the cold air comes in behind the frontal system later


Issued at 217 PM EDT Fri May 26 2017

River levels in the upper Grand and the Kalamazoo basins are
running above normal for late May while elsewhere the levels are
closer to normal. Rain totals generally under a half inch in
Southern Michigan Friday night, then across much of the area on
Sunday, will likely not be enough to produce flooding.




LONG TERM...Laurens
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