Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 251743
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
143 PM EDT Thu May 25 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 326 AM EDT Thu May 25 2017

Expect scattered showers and isolated thunderstorms today as the
storm system that brought the showers recently departs from
northern Kentucky as it heads for redevelops into a strong East
Coast storm centered over Long Island New York by early Friday
morning. That will allow a high pressure ridge to cross our area
Friday. This will allow for partly sunny skies and pleasant
temperatures. Our next system comes at us from the Southern
Plains but does not get here till Sunday. This will mean a warmer
day Saturday with partly sunny skies.

The next system combines with a Canadian system on Memorial Day
and that brings a strong cold front through the area on Memorial
Day. This would mean more showers and possibility thunderstorms.
Beyond that it will be cooler than normal but most likely dry for
most of next week.

&&

.SHORT TERM...(Today through Saturday)
Issued at 326 AM EDT Thu May 25 2017

The overall trend in our weather will be toward drier and slightly
warmer temperatures into Saturday before the next system brings
the cold air and showers back to the area by Sunday.

The pattern of closed upper lows moving through the Great Lakes
will continue through next week (may see a break in this pattern
by the end of next week). The current upper level low at
midnight was centered over Northern Mississippi (which is why the
heavy rain is missing us to the east) and it will rotate
northeast toward Newfoundland by early in the weekend. That system
is being booted out by yet another digging upper low on the
northern stream, currently near British Columbia. The British
Columbia system digs into the Great Lakes by early next week and
creates a rex block by Monday causing the entire upper air
pattern to stall for most of this coming week over North America.

As for today, with the surface and upper air system lifting
northeastward (south of Michigan) we are on the northwest side of
the storm circulation but still in the storms circulation. This
will allow for instability showers this afternoon but it will
take the systems showers east of our area by midday. There is just
enough cold air aloft thanks to being in the circulation of the
upper low today that we will have enough vertical instability to
allow for afternoon heating type showers. What really will help
the cause is the lake breeze convergence boundary. Nearly all of
the high resolution models show a convergence boundary from near
MKG to near AZO by late afternoon. That will help to focus
convection. The NAMNEST shows this best. I actually played that up
in our pop and QPF grids this afternoon by showing an enhanced
area of convection near US-131 that does not go away till early to
mid evening.

The sky may try to clear tonight as the system moves away but
there will be light winds and considerable low level moisture
around so I would expect fog do develop by midnight and areas
where the sky really does clear.

Saturday for the most part should be dry and warmer as weak system
tracks east well to our south. It is not out of the question there
would be an isolated shower or thunderstorms near and south of
I-94 during the afternoon.

.LONG TERM...(Saturday night through Wednesday)
Issued at 326 AM EDT Thu May 25 2017

The wx pattern will become a little more unsettled Saturday night
into Sunday as a low pressure system moves through the lower Great
Lakes/Ohio Valley regions.

Most of the convection with this system should stay south of our
area but there may be sufficient enough instability for some
convective development over our fcst area Saturday night into
Sunday. However it is noted that 00z ecmwf guidance continues to
suggest that most pcpn with this system would stay further south of
our area while the gfs looks much wetter.

Relatively cooler wx is forecast for the early to middle portion of
next week as an upper level trough will move into the Great Lakes
region. High temperatures will reach the 60`s early to midweek along
with some scattered diurnally driven rain showers as a result of
some instability from daytime heating and with relatively cooler air
aloft in association with the upper trough.

$$

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 143 PM EDT Thu May 25 2017

IFR cigs were persisting southeast of a line from AZO to LAN
early this afternoon while improvement to MVFR has taken place
elsewhere. While cigs are expected to slightly improve through
early evening, they are expected to lower again tonight.

Confidence is high that widespread IFR/LIFR will redevelop and
impact the area late tonight /06Z-12Z/, with gradual improvement
to MVFR/VFR following after 12Z Friday. Lingering isolated showers
this afternoon are not expected to have a significant impact on
visibilities and would be of brief duration.

&&

.MARINE...
Issued at 326 AM EDT Thu May 25 2017

Winds will for the most part be light so I would not expect any
marine headlines through the weekend. Possibly lake fog could be
an issue but it is to early to say much about that now.


&&

.HYDROLOGY...
Issued at 1259 PM EDT Wed May 24 2017

Rivers over the southern portion of the forecast area (south and
east of Grand Rapids) continue to run above normal. Southern
sites will be the main concern for any flood potential over the
next several days.

Precipitation forecasts for today have trended downward slightly.
The greatest totals are expected near Lansing and Jackson, where
amounts will range from 0.50-0.70 of an inch. Amounts will trend
downward further north and west.

Long term precipitation forecasts bring waves of precipitation
through late this weekend into next week. The current pattern
would suggest that amounts could vary widely from point to point
with any adjustment in timing and placement. In addition,
scattered convection could play a role in locally heavy rainfall
at times. Therefore, immediate flood concerns have decreased with
the latest trends in forecast qpf. The upcoming week may need
to be monitored with respect to sites that are experiencing higher
than normal river levels.

&&

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

$$

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



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