Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 191146
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
746 AM EDT Fri May 19 2017

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 306 AM EDT Fri May 19 2017

A low pressure system developing in Texas will track north
northeast through the weekend. As a result...this system will
spread increasing amounts of moisture into the Great Lakes region.
Clouds will thicken up today and showers may begin arriving from
the south in the afternoon. Then...wet weather is expected through
Saturday night.  The showers will come to an end on Sunday.

&&

.UPDATE...
Issued at 743 AM EDT Fri May 19 2017

The approaching area of showers...currently in Illinois was only
slowly dissipating. Thus it looks like more in the way of shower
activity can be expected this afternoon for southern parts of the
CWA. I also lowered temperatures slightly given more in the way of
clouds along with some possible showers.

&&

.SHORT TERM...(Today through Sunday)
Issued at 306 AM EDT Fri May 19 2017

The main challenge is whether it will rain today. I ended up
introducing POPs to the afternoon forecast for southwest
locations.

Most of the models now support bringing some showers in from the
southwest this afternoon. The warm front located south of the
region will lift northward through tonight. Moisture will be on
the increase through tonight. The initially dry airmass this
morning is shown to give way to deeper moisture by evening. A mid
level shortwave in IA...tracks northeast during the day. Moisture
advection ahead of this feature is fairly strong...so it should be
able to saturate the atmosphere later in the day...enough for some
rain. We may need to increase POPs even further this afternoon if
this feature holds together as it moves in.

Tonight through Saturday Night...several waves of rain are
expected. The shortwave that moves in this evening...should have
some showers with it. Then another arrives Saturday morning. This
one will have elevated instability to work with. As a result I
added thunder to the forecast for much of the region for Saturday
am. Then with an unseasonably moist airmass in place...featuring
deep moisture...a cold front approaches from the west Saturday
afternoon into Saturday night. This system will squeeze the
moisture in place leading to abundant showers and some
thunderstorms. Mid level lapse rates do steepen up during the
night and deep layer shear increases...so stronger is possible
then. Rainfall could be heavy as  well.

.LONG TERM...(Sunday night through Thursday)
Issued at 306 AM EDT Fri May 19 2017

We are looking at one main system that is expected to impact the
area in the long term. This will likely be around the area from Mon
night through Wed night/early Thu.

We will see drier weather for Sun night and Mon compared to the wet
first half of the weekend. The front should be well east of the area
by Sun night, and it looks like the upper low and clouds/pcpn with
it should stay west and north of the area, leaving us in the dry
slot.

The break in the weather will be brief as it looks like rain chances
will increase Mon night and linger through Wed Night. A large upper
low complex over Ontario will drive another strong short wave down
over the area from the NW. As the associated sfc low approaches and
strengthens, some Gulf moisture will advect north ahead of it. Being
on the warm side of the low on Tue, there will be a thunder threat.

Widespread rain will shift east of the area Tue night as the sfc low
moves east. We will then develop a more showery pattern for Wed and
Wed night as the upper low slowly rotates east/southeast. Cooler
temperatures can be expected during this time also with the cold
pool aloft with the low overhead.

There is good agreement that we should see conditions improve on
Thursday. The upper low/trough axis shifts east of the area at that
time. Skies should clear out, and temperatures should moderate
some.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 645 AM EDT Fri May 19 2017

MVFR cloud cover will be around for a few hours this morning
before dissipating later this morning or early this afternoon.
Meanwhile mid level moisture will be on the increase today....and
showers may arrive from the southwest this afternoon. At this time
the low level moisture looks limited for impact this afternoon or
evening.


&&

.MARINE...
Issued at 306 AM EDT Fri May 19 2017

Decided to extend the small craft advisory through most of the
morning. Waves remain elevated...and they are forecasted to only
slowly subside this am. Around Holland and Muskegon...the slight
offshore component will support low wave heights there within a
mile or so...but bigger waves will persist further out this
morning.


&&

.HYDROLOGY...
Issued at 355 PM EDT Thu May 18 2017

A large number of sites continue to have near normal streamflow.
A couple of places have actually dropped slightly below normal,
which reflects on how dry we have been recently.

Wet weather will come into play again late Friday into the early
half of Sunday. Additional rounds of precipitation will move
through over the course of next week. Though multiple waves of
rain are possible, it does not look like widespread heavy rain is
likely with breaks between each event. Runoff should have time to
work through streams and river with each round, so long as
nothing too heavy falls.

Overall rainfall amounts over the next 5 days may approach an
inch in some places. Within bank rises are likely, while concerns
for bankfull conditions to be reassessed as the forecast pans out
this week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 11 AM EDT this morning for LMZ844>849.

&&

$$

UPDATE...MJS
SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...NJJ
AVIATION...MJS
HYDROLOGY...JAM
MARINE...MJS



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