Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 250225
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1025 PM EDT WED AUG 24 2016

LATEST UPDATE...
Update/Marine

.SYNOPSIS...
Issued at 330 PM EDT Wed Aug 24 2016

A low pressure system moving slowly through the Great Lakes region
will bring scattered showers and a few thunderstorms through
Thursday afternoon. High pressure will build in and bring fair
weather Thursday night through Friday night. The next chance for
showers and thunderstorms will come late Saturday through Sunday.

&&

.UPDATE...
Issued at 1025 PM EDT Wed Aug 24 2016

Areas of clearing have developed this evening, particularly south
and east of GRR. Light winds and sfc dew points in the lower 70s
should lead to some stratus/fog developing so have added patchy
fog to the fcst. Showers are expected to become more numerous
after 4 or 5 am as Iowa shortwave/vort max approaches from the
southwest. A few tstms will be possible with this as well as RUC
MU Cape progs show around 500-900 J/KG at that time.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 330 PM EDT Wed Aug 24 2016

Primary short term fcst concerns involve determining potential for
convection late this afternoon through Thursday afternoon.

18Z mesoscale analysis indicates weak instability over our fcst
area with ml cape values aob 500 j/kg. This is the main reason
convection has not developed and ir sat trends and sfc obs continue
to show rather extensive cloud cover across most of our area.

A few thunderstorms could develop late this afternoon and evening if
more breaks in cloud cover develop allowing instability to increase
a bit. However a consensus of latest short range guidance suggests
much stronger instability will stay well sw to south of our fcst
area.

The vast majority of convection and severe weather will stay south
of our fcst area across portions of IL/IN/OH late this afternoon and
evening. However the chance for showers and a few storms remains in
our fcst overnight though due to forcing from the cold front that
will move into our nw fcst area very late tonight.

The cold front will only very slowly move se across the remainder of
our fcst area Thursday and will bring scattered showers and a few
thunderstorms. The relatively best chc for convection Thursday will
be over our se fcst area given the cold frontal timing. Sb/ml cape
values could potentially reach around 1000 j/kg over toward KJXN
tomorrow aftn prior to fropa. Deep layer shear values are also
favorable at around 40-45 kts.

So a strong to potentially severe storm seems possible over our se
fcst area tomorrow aftn depending largely on the degree of
destabilization prior to fropa. However short range guidance
consensus suggests that greater instability and the primary threat
for severe wx will stay se of our fcst area.

High pressure will build in to produce fair weather Thursday night
through Friday night.

.LONG TERM...(Saturday through Wednesday)
Issued at 330 PM EDT Wed Aug 24 2016

Sfc high retreats to the northeast on Saturday with return flow
moistening and some warm advection showers encroaching on the
western zones in the morning, spreading east in the afternoon. A
weak shortwave trough is damping out as it tops the upper high
centered over the Mid-Atlantic states.

Showers and thunderstorms will be tapering off on Monday, as weak
sfc ridging builds in. Generally zonal flow or flat ridging for
Tuesday and Wednesday with weak impulses moving through and bringing
some isolated showers at times.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 800 PM EDT Wed Aug 24 2016

Generally VFR conditions are expected this evening although some
ocnl MVFR cigs are possible for the next couple hours in the
vicinity of the scattered rain showers south and east of GRR.

The soupy air mass now in place with sfc dew points in the lower
70s and subsidence in between short waves should lead to the
development of some stratus and fog overnight. Medium confidence
exists that IFR or lower conditions will impact much of the area
between roughly 09z and 13z Thursday.

Widespread rain showers are expected to arrive from the southwest
around 12z Thursday morning, which should mix out the low stratus
and fog by 14z, but will result in numerous MVFR cigs and vsbys
lingering through at least 18z. The rain should be moving
out/dissipating after 18z Thursday but tstms could redevelop
around JXN 18z-22z.


&&

.MARINE...
Issued at 1025 PM EDT Wed Aug 24 2016

Winds and waves have already diminished so have cancelled the
Small Craft Advisory and Beach Hazard Statement a bit early.

&&

.HYDROLOGY...
Issued at 121 PM EDT Wed Aug 24 2016

A Flood Warning remains in effect for the Portage River near
Vicksburg into the weekend. More rain is expected for this area and
river levels will be slow to fall. River levels are above normal
across the area but falling. Additional rainfall may bring levels
near bankfull, but new river flooding is not expected through the
weekend.

&&

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

$$

UPDATE...Meade
SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...Ostuno
AVIATION...Meade
HYDROLOGY...63
MARINE...Meade



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