Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 192351
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
751 PM EDT Fri May 19 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 325 PM EDT Fri May 19 2017

A low pressure system moving northeast from the southern Plains
states will bring some showers tonight. Showers will become more
widespread Saturday through Saturday night and a few thunderstorms
are possible as well Saturday afternoon through Saturday night.
The showers will come to an end Sunday.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 325 PM EDT Fri May 19 2017

Primary short term fcst concerns involve determining convective
potential Saturday through Saturday night.

Scattered showers will continue to develop late this afternoon
into early this evening as a result of several mesoscale
convective vortices which were moving through the lower great
lakes region. A consensus of short range guidance and rgnl radar
trends suggest that showers should end late this evening and
overnight.

However showers will redevelop from southwest to northeast
Saturday morning and afternoon as the plains states low pressure
system continues to move northeast into the western great lakes
region and the warm front lifts north out ahead of it.

To the north of the warm front elevated instability will increase
tomorrow as h8 li/s fall to -1 to -2 as suggested by 12z gfs/nam
guidance by aftn/eve. Therefore in addition to showers increasing
in coverage later tomorrow we also expect isolated to scattered
convection to develop in the aftn/eve.

Some showers will linger into Sunday morning before ending once
fropa occurs. A drier airmass will advect in Sunday afternoon
through Sunday night with seasonably cool temps for Sunday night.

.LONG TERM...(Monday through Friday)
Issued at 325 PM EDT Fri May 19 2017

The long term period will begin unsettled with an upper low centered
over the northern Great Lakes and troughing located over Lower
Michigan. The regime of upper troughing continues for much of the
long term with a digging shortwave deepening the trough overhead
into Tuesday. The upper trough is squarely overhead on Wednesday
before it slowly meanders off to the east Thursday and especially
into Friday.

Showers are possible from Monday right into Thursday given the upper
pattern. The ECMWF even hints at some showers on Friday, but the GFS
has some weak ridging. Bottom line the long term looks showery, with
the highest chances for rain being Tuesday into Wednesday.

Temperatures will likely end up being below normal for much of the
period, with highs expected in the 60s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 750 PM EDT Fri May 19 2017

ceilings will be around 1500 feet across far southern Lower
Michigan including AZO through Saturday. Elsewhere, VFR
conditions will prevail through the evening then ceilings will
lower to 1500 to 2500 feet on Saturday.

Winds will be east around 10 knots overnight with gusts over 20
knots on Saturday.

&&

.MARINE...
Issued at 325 PM EDT Fri May 19 2017

Wave heights will remain below sca criteria tonight through
Saturday with east winds of 10 to 20 kts through Saturday
evening. Some gusts to near 25 kts are possible mainly Saturday
afternoon. Scattered thunderstorms could pose a hazard to mariners
Saturday through Saturday night.


&&

.HYDROLOGY...
Issued at 1131 AM EDT Fri May 19 2017

Rivers levels have returned to near normal. Expecting rain totals
ranging from a half inch in Central Lower Michigan to over an inch
in Southern Lower Michigan today through Sunday with locally higher
totals possible. Another stretch of precipitation is possible Monday
night through Friday. Some river rises are likely with this rain,
but not expecting flooding at this time. Smaller streams and rivers
may need to be watched for above bankfull rises. Main stem rivers
should be able to handle this rainfall fine unless guidance trends
upward.

&&

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

$$

SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...Duke
AVIATION...Ostuno
HYDROLOGY...63
MARINE...Laurens


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