Area Forecast Discussion
Issued by NWS Grand Rapids, MI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

123
FXUS63 KGRR 260056
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
856 PM EDT SUN SEP 25 2016

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 324 PM EDT Sun Sep 25 2016

A strong cold front will move across the state tonight and set the
stage for much cooler weather for this week. Showers and storms are
possible tonight through Wednesday. Highs will remain mostly in the
lower to mid 60s through Wednesday before climbing to around 70 for
the rest of the week.

&&

.UPDATE...
Issued at 856 PM EDT Sun Sep 25 2016

Based on a generic lack of instability (see SPC SREF) I had
decided to (after consulting with others in the office) to
expunge most of the mention of thunderstorms from the zones
tonight. I did leave it along the lake shore for a few hours since
there is still some instability over Lake Michigan but none of
the models take any of that inland significantly.

Also there will be two periods of showers. The first is coming
through now and the second will be well after midnight. That
second one is associated with the jet entrance region getting
close enough to allow lift over our during that time.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 324 PM EDT Sun Sep 25 2016

For several days the models have had a decent handle on the cold
front that will move through the cwa tonight. Latest sfc analysis
shows the cold front extending from near DLH south to near the Quad
Cities. A couple of broken lines of showers and storms accompany
this front and we`ll see them move over the cwa tonight.
Precipitable water values increase to nearly 2 inches this evening
so a few of the stronger storms may produce heavy rainfall.

Much cooler air will flow over the lakes tonight through Tuesday.
The core of the cold air aloft moves over the lake Tuesday night and
we could see a few storms develop as lapse rates steepen quite a
bit. Lake effect showers will be possible through the short term as
h8 temps fall to around 2c and water temps are in the lower 20s c.

.LONG TERM...(Wednesday through Sunday)
Issued at 324 PM EDT Sun Sep 25 2016

Models remain in decent agreement in showing the mid level low
dropping southward through the CWA on Wednesday morning.  Given that
the airmass will be cold enough for lake enhanced moisture feeding
into the system...showers will continue to be around the region. The
low convergence is the greatest over southwest parts of the CWA
which is where I will keep the POPs the highest.  Well below normal
temperatures are expected with a cold core system overhead.

The potential for showers is expected to diminish Wednesday night
through Thursday as the flow becomes offshore and heights rise. Will
keep temperatures fairly close to normal values.

Bigger differences in the models show up for Friday into Sunday. The
GFS keeps the mid level low far enough east of the CWA to support a
dry forecast.  The new High Res Euro lifts the mid level low
northward back into the CWA...which would be very unusual.  I
somewhat favor the GFS...but will hold onto the low risk for a few
showers in that period.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 740 PM EDT Sun Sep 25 2016

There will be two periods of showers this evening. The fist is
well ahead of the cold front and should cross the GRR TAF sites
between 02z and 06z. Near the Lake Michigan shore should be
enough instability due to the warmth of Lake Michigan to allow
Thunderstorms prior to 06z. This may impact the MKG and GRR TAF
sites. A second band of showers will come with the cold front,
that will mostly be in the 06z to 12z time frame. Expect MVFR
ceilings with the second period of showers later this evening.

A period of clearing, typical behind and occluded front, will
move into the TAF sites in the 12z to 18z time frame. After that
the cold air comes in with VFR cigs by mid to late afternoon.


&&

.MARINE...
Issued at 324 PM EDT Sun Sep 25 2016

A strong cold front will move across the lake tonight. The colder
air coupled with stronger winds will create hazardous conditions for
small craft tonight through Tuesday and a small craft advisory was
issued.


&&

.HYDROLOGY...
Issued at 102 PM EDT Sun Sep 25 2016

River levels are around normal for this time of year. Showers and
thunderstorms are expected tonight and lake effect rain showers are
possible Monday into Wednesday. Through Wednesday, over an inch of
rain is possible to the north and west of Grand Rapids with less
than a half inch to the south and east. Rivers and streams should
remain below bankfull through the week.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...Small Craft Advisory from midnight tonight to 9 PM EDT Tuesday
     for LMZ844>849.

&&

$$

UPDATE...WDM
SYNOPSIS...04
SHORT TERM...04
LONG TERM...MJS
AVIATION...WDM
HYDROLOGY...63
MARINE...04



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.