Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 270320
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1120 PM EDT THU MAY 26 2016

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 320 PM EDT Thu May 26 2016

The warm humid airmass will continue through Sunday after which a
cold front will move across Lower Michigan and bring in drier and
cooler air. Highs through the weekend will be in the lower to mid
80s and scattered showers and thunderstorms are also possible.
Memorial Day will be mostly dry with highs around 80.

&&

.UPDATE...
Issued at 1120 PM EDT Thu May 26 2016

Removed precipitation from the forecast tonight as instability has
decreased significantly. Surface based CAPE values have fallen
below 1000 J/KG. There are no triggers the remainder of the night
and the LLJ is positioned well west of the forecast area. Multiple
runs of the HRRR show dry conditions prevailing as well.

Introduced some patchy fog into the forecast as we are expecting
some light fog to develop after the 200am-300am time frame.

It will be a warm night by May standards with lows in the low to
mid 60s in most areas. Normal lows are in the upper 40s to around
50.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 320 PM EDT Thu May 26 2016

Forecast concerns deal with convective trends through the period.
Latest vis loop shows enhanced cu from far southwest Kent county
through central Montcalm county. We`ve seen pulse storms develop and
quickly dissipate along the line. Mesoanalysis shows 1500 j/kg
MLCAPE and LIs near -6c. Aloft we`re moving into a brief period of
NVA which may keep a lid on the storms. Shear is marginal, around 25
knots and unless that increases, any storms that develop should be
sub severe. That said, decent drying in the lowest layers from
latest AMDAR soundings suggest the potential for gusty winds and
small hail. Coverage and intensity of the storms should diminish this
evening as instability decreases.

Another weak short wave will approach around 06z and since we`ll
still be in a soupy airmass we should see convection develop again.
The LLJ increases to 35 knots Friday afternoon and that could keep
convection going through the evening. We have highest pops Friday
afternoon and then diminishing Friday night and Saturday.

Scattered showers and thunderstorms will be possible Saturday and
Saturday night as low pressure moves from the southern Plains into
the upper Mississippi Valley. We`ll remain on the east side of
the system which means high moisture content and decent instability.

Precipitable water values from Friday afternoon through Saturday
night will be near 1.5 inches. Thus any storms that develop will be
capable of locally heavy rain.

.LONG TERM...(Sunday through Thursday)
Issued at 320 PM EDT Thu May 26 2016

The main challenge in the long term deals with the potential for
storms over the later half of the holiday weekend.  The trend is for
less in the way of rainfall on Memorial Day.

Models are showing the mid level trough passing through the forecast
area on Sunday.  This will act to keep the risk for showers and
thunderstorms going then.  This feature loses amplitude as it goes
by. Low level wind fields on Sunday are still elevated and
instability will be present...but mid and upper level winds are
forecasted to decrease.  So if we do end up with storms...the risk
for severe weather looks low at this time.

A weak surface high pressure system is shown to move in for Memorial
Day. This would keep the risk for any shower and thunderstorm
activity low. Given the weakening nature of the mid level wave that
tracks through on Sunday...it is still not certain how much dry air
will move in for Memorial Day. The GFS actually is developing
thunderstorms across WI on the backside of this weak high. The GFS
has been forecasting too much instability lately...thus the more
stable High Res Euro seems better.  Will only feature a very low pop.

More in the way of a dynamic system is shown to move in for the
middle part of the week.  Thus a higher probability of storms will
exist then...with some possibly strong.

Will keep the trend of above normal temperatures going.  The brunt
of any cool airmass is forecast to stay in Canada.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 836 PM EDT Thu May 26 2016

VFR conditions are in place area wide with a few showers
diminishing towards Saginaw Bay. There may be an isolated shower
or storms through 03z, but for the most part expecting dry
conditions tonight.

Main concern tonight is the development of fog. Expecting MVFR
visibilities dropping into the IFR category in most places. We
will likely see some MVFR ceilings as well develop towards the I-94
TAF sites.

VFR conditions should return by 15z at all of the TAF sites.
Thunderstorms will likely develop Friday afternoon becoming more
numerous towards sunset.


&&

.MARINE...
Issued at 320 PM EDT Thu May 26 2016

A weak pressure gradient will result in low winds and wave heights
tonight and friday. High dewpoints however will cause fog to
continue and may become locally dense.


&&

.HYDROLOGY...
Issued at 320 PM EDT Thu May 26 2016

Many areas received rain last night on the order of a quarter inch
all the way up to locally 2 inches across Van Buren County. This has
created some rises on the Black River. Convection through the
weekend will produce mainly localized heavy rainfall so basin
average amounts will be limited...only around a half inch to three
quarters of an inch. Rises will mainly be confined to smaller creeks
and streams though rises on main stem rivers are possible if broader
areas of convection move over larger reaches of the respective
basins.

&&

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

$$

UPDATE...Duke
SYNOPSIS...04
SHORT TERM...04
LONG TERM...MJS
AVIATION...Duke
HYDROLOGY...Hoving
MARINE...04


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