Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 261919
AFDGRR

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

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

.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.

&&

.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 18Z TAFS through 18Z Friday afternoon)
Issued at 131 PM EDT Thu May 26 2016

The atmosphere has become rather unstable at this time...and will
remain unstable through the afternoon. A few thunderstorms look
likely to develop. The stronger storms will create ifr and lower
conditions. I was not confident enough to put such values in the
taf sites...and will need to monitor trends closely. I do feature
a several hr period of thunderstorms when I thought the best risk
was.

The risk for thunderstorms is not zero tonight...but the better
focus looks west of the taf sites. Fog could become an issue...and
will keep ifr and lower conditions going. As the morning
progresses...the fog should lift into a broken mvfr deck.


&&

.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.
&&

$$

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



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