Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 232343
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
743 PM EDT FRI SEP 23 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 315 PM EDT Fri Sep 23 2016

Fair weather will return tonight through Saturday and most of Sunday
with seasonably mild temperatures. A cold front will bring rain and
perhaps a few thunderstorms Sunday night into early Monday. A cooler
airmass will move in behind the front from Monday night
through Wednesday.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 315 PM EDT Fri Sep 23 2016

Primary short term fcst concerns involve timing rain into our fcst
area Sunday night.

An isolated light rain shower or sprinkle is still possible into
this evening mainly along the I-94 corridor closer to the nearly
stationary frontal boundary that extends across far northern IN/OH.
Otherwise quite a bit of cloud cover will linger overnight and some
patchy fog may develop during the early morning hours Saturday.

High pressure anchored to the northeast of our region will bring
fair weather Saturday through most of Sunday. It will be
seasonably mild in spite of easterly winds Saturday with high
temperatures reaching the middle 60s to lower 70s. It will be a
bit milder Sunday as winds veer to the southeast to south. This in
conjunction with some sun will help to boost max temps into the
lower to middle 70s.

The cold front approaching from the west will bring rain showers
Sunday evening that will become more widespread late Sunday night.
Convective potential late Sunday night is fairly low due largely to
frontal timing and weak instability.

.LONG TERM...(Monday through Friday)
Issued at 315 PM EDT Fri Sep 23 2016

Models are in decent agreement in showing the cold front moving east
of the forecast area Monday morning.  Less of a risk for
thunderstorms exists as the main instability axis will be ahead of
this front.  With a post frontal airmass moving in during the day on
Monday the highest potential for measurable rain will be in the
morning.

Some differences show up for Monday night into Tuesday.  The GFS
wraps around considerably more moisture behind the departing system.
This occurs partly because the GFS is much cooler and the lakes add
moisture to this low pressure system.  The new High Res Euro is
still dry as it is not as cool and it keeps the low further north.
Will hold onto the low risk for showers Monday night into Tuesday
given the spread in the models.

Ridging moves in for Wednesday into Friday.  Thus any risk for rain
looks minimal.  A moderating trend to the temperatures will occur as
the ridge builds east for the end of the week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 742 PM EDT Fri Sep 23 2016

This is a questionable forecast at best (just how fast the skies
will clear tonight). The current trend is toward clearing of the
lower clouds. Both MKG and GRR have had celling improve low MVFR
to VFR within the past hour. Similarly the BTL and AZO have gone
from IFR to low MVFR during the past hour. Both the RAP model and
NAM show the low level RH in the 1000 to 3000 ft layer drying out
but the RAP model is much slower showing the MVFR/IFR cigs holding
all night and not mixing out for the I-94 tafs sites till around
15z. Given the current trend I went for a quicker clearing but
time will tell how great of an idea that was.

Another issue is fog for the I-94 taf sites. BUFKIT profiles
suggest fog possible fog those taf sites. However the RAP and NAM
fog forecast does not show any fog tonight. I help on to the idea
of fog in the TAF for continuity I am on the fence with this. If
the sky can clear by 06z or so down by the I-94 taf sites I would
think the chance for fog is greater. If the low clouds hold that I
would think only MVFR fog is likely.

&&

.MARINE...
Issued at 315 PM EDT Fri Sep 23 2016

Northeast to east winds in the 5 to 15 kt range through Saturday
will result in minimal wave heights mainly in the 1 to 2 foot
range. Winds will veer to the se to south and strengthen somewhat on
Sunday out ahead of an approaching cold front. This will result in
building wave heights to at least 2 to 4 feet and potential for
wave heights to flirt with small craft criteria by Sunday
afternoon.


&&

.HYDROLOGY...
Issued at 1032 AM EDT Fri Sep 23 2016

Hydro concerns are minimal through the weekend, as little rain is
expected and river levels are around normal for the time of year.
Showers and thunderstorms are expected Sunday into Monday night with
additional rain possible Tuesday into Wednesday. Around 1 inch of
rain is expected and therefore rivers and streams should remain
below bankfull through the week.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...None.
&&

$$

SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...MJS
AVIATION...WDM
HYDROLOGY...63
MARINE...Laurens


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