Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 261535
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1135 AM EDT Fri May 26 2017

LATEST UPDATE...
Update

.SYNOPSIS...
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
Bay.

&&

.UPDATE...
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.

UPDATE Issued at 1135 AM EDT Fri May 26 2017

Two issues, first dense fog is spreading mostly in the BTL/AZO
area and along the lake shore north of Muskegon. Mid clouds are
coming in so I think the fog should be gone to soon for it to make
much sense out of putting out some sort of fog advisory.

Second that complex of thunderstorms assoicated with that MCV
over MO and SE IA continues to be shown by the ESRL HRRR to be
heading more toward SW Lower Michigan while the WPC version keeps
it south of Michigan, that is the strong storms but now even that
venison gives us some showers this evening. So, I updated the
grids and zones to have slightly higher pop as far north as GRR.

&&

.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
region.

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 12Z TAFS through 12Z Saturday morning)
Issued at 737 AM EDT Fri May 26 2017

This is a tricky forecast since the winds have finally let up some
just as the sky was clearing. The GOES16 fog loop showed the fog
rapidly expanding (centered on the AZO/BTL) area. However mid
clouds are already crossing the lake so I think the fog will be
history by 15z or so.

The next issue is the MCV over southern IA and eastern MO (1130z)
heading easterly (more or less). The HRRRX has it moving north of
CHI around 00z which the operational HRRR has it going south of
CHI. At GFS two runs in a row has it crossing southern Lower
Michigan and now the NAMNEST looks a lot like the HRRRX. So given
all of that I decided to allow for some showers in our TAFs this
evening and allow stratus to spread out after the rain ends.


&&

.MARINE...
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
Sunday.


&&

.HYDROLOGY...
Issued at 158 PM EDT Thu May 25 2017

An active pattern will set up across the Central U.S. over the
holiday weekend. The heaviest rainfall is expected to stay south
of Lower Michigan, stretching from Texas, northeast through the
Ohio Valley. Lower Michigan seems to stay north of the heaviest
precipitation amounts. Any appreciable precipitation should
remain light and be rather short in duration.

Despite low risk for additional flooding, elevated river levels
over southern portions of Lower Michigan will remain sensitive to
heavier rainfall. Any deviation in the current forecast could
impact river levels. Anyone planning activity on/or near rivers
this weekend should pay attention to updated forecasts.

&&

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

$$

UPDATE...JK
SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...Laurens
AVIATION...WDM
HYDROLOGY...JAM
MARINE...WDM



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