Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 150730
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 AM EDT Tue Aug 15 2017

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine

.SYNOPSIS...
Issued at 330 AM EDT Tue Aug 15 2017

A weak cold front will produce scattered showers this morning
before moving south of the area this afternoon. High pressure
provides dry weather tonight and Wednesday, then humid conditions
with showers and thunderstorms are expected on Thursday as a low
pressure system tracks across Wisconsin.

&&

.SHORT TERM...(Today through Thursday)
Issued at 330 AM EDT Tue Aug 15 2017

Shortwave passes through early this morning taking most of the
ongoing shower activity with it. However lingering sfc convergence
and a dew point boundary may result in some new isolated diurnal
convection developing from mid morning through mid afternoon for
the I-94 corridor east of AZO. Some thunder would be possible if
this occurs since latest RAP guidance has SB Capes 500-1000 J/KG
developing near JXN by noon although dry air and subsidence
eventually ends that threat by 21Z or so.

Model trends have been for a slower solution with the mid week
system. Current expectation is for arrival of warm advection
showers and storms from the southwest very late Wednesday night,
then fairly widespread showers and tstms on Thursday with the
approach of the shortwave trough and the sfc cold front. PWATs
near 2 inches and sfc dew pts around 70 support the possibility of
some locally heavy rainfall, although the svr threat is
questionable due to the likelihood of considerable cloud cover.
Still, if any pockets of heating can occur, capes could reach
over 1500 J/Kg and deep layer shear of 30-35 knots would support
the possibility of some stronger/organized convection developing.


.LONG TERM...(Thursday night through Monday)
Issued at 330 AM EDT Tue Aug 15 2017

Showers and thunderstorms will linger into Thursday evening before
ending once the cold front moves through. Some strong to potentially
severe convection is possible into Thursday evening given favorable
cold frontal timing and potential for moderate instability to
develop along and just ahead of the front.

Severe potential is mitigated by several factors including stronger
upper level forcing staying north of our area. A consensus of latest
medium range guidance suggests sfc based cape values will stay near
or below 2000 j/kg. Stronger instability will likely develop south
of our area. So the overall severe wx threat Thursday evening
looks rather marginal.

Fair wx will return Friday and a cooler and drier airmass will
advect in behind the front.  In fact high temperatures Friday will
only reach the 70`s.

An upper level disturbance will move in from the west and bring a
few showers Saturday.  Fair wx will return Sunday and Monday as
another high pressure ridge builds in.  Temperatures by then will
undergo a gradual moderating trend to slightly above normal for this
time of year. Above normal temperatures are then anticipated through
the rest of next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1155 PM EDT Mon Aug 14 2017

VFR conditions at all the terminals at the moment will slowly
deteriorate to mvfr during the early morning hours Tuesday as
scattered showers and thunderstorms develop and lower cigs
develop.

Conditions will improve back to vfr by mid to late Tuesday morning
as scattered showers and storms gradually move east of all the
terminals and cigs improve. Conditions will then remain vfr
Tuesday afternoon through Tuesday evening.


&&

.MARINE...
Issued at 330 AM EDT Tue Aug 15 2017

A brief period of stronger northerly winds this afternoon into
the early evening should promote choppy 2-3 ft seas, particularly
near big and little sable points and south of South Haven.
Otherwise relatively tranquil conditions on Lk MI.

&&

.HYDROLOGY...
Issued at 1144 AM EDT Mon Aug 14 2017

Isolated to scattered showers may result in a brief dampening of
the ground in localized spots this afternoon. Better chances for
rain will come in overnight tonight and early Tuesday morning.
Measurable rainfall of around one-tenth of an inch may fall. Some
locations could receive a couple of tenths of beneficial rainfall.

A more active pattern is expected to setup for the midweek period
as a result of a strengthening wave that passes over the Great
Lakes Region. A deepening trough may result in showery activity
toward next weekend. It is possible for 5-7 day totals to approach
an inch or more in spots. Given recent dry weather, growing
moisture deficits, and near/below normal river levels, flood
concerns remain low.

&&

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

$$

SYNOPSIS...Meade
SHORT TERM...Meade
LONG TERM...Laurens
AVIATION...Laurens
HYDROLOGY...JAM
MARINE...Meade



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