Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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611
FXUS63 KGRR 261756
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
156 PM EDT Wed Jul 26 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 328 AM EDT Wed Jul 26 2017

A cold front will bring scattered showers and thunderstorms today
and into tonight then fair weather will return on Thursday as high
pressure builds in.

&&

.UPDATE...
Issued at 1112 AM EDT Wed Jul 26 2017

We have tweaked the forecast a little to account for current radar
trends. This was mainly to up rain chances a bit across the
northern row of counties with the weak band of storms expected to
move through up there over the next few hours.

The storms extending from Green Bay to Sheboygan WI are being
supported by a 35 knot low level jet/moisture transport still
ongoing this morning. This low level jet/moisture transport is
expected to sustain itself into the afternoon before moving NE of
the area later this afternoon.

The current track of the storms will take it along the U.S.-10
corridor. There is 500-1000 j/kg of MU CAPE up there resulting
from the influx of moisture. This instability is all elevated, so
severe weather threat is quite limited.

We can not rule out a shower/storm popping up later along any
possible outflow boundaries. All of the convection allowing models
show we should see a min in activity after the line moves through.
All models show limited instability also with plenty of mid-high
clouds shrouding the area.

&&

.SHORT TERM...(Today through Friday)
Issued at 328 AM EDT Wed Jul 26 2017

Main forecast challenge in the near term is coverage of POPs and
chance of strong thunderstorms this afternoon and overnight.
Forecast soundings show marginal sfc based instability along with
25 to 30 knots of 0 to 6 km shear this afternoon as mesoscale
models have storms moving into the northwest zones. Once again it
looks like the bulk of the stronger convection remains off to our
southwest, but the chance for thunderstorms with some heavy rains
continues through tonight as the front slowly sags south.

P-wat values are around 1.5 to 1.75 inches so heavy rain threat
exists where storms are able to persist, although the storm motion
should be a mitigating factor.

The front clears the southern zones by Thursday afternoon with
fair weather returning for Friday and beyond.

.LONG TERM...(Friday night through Tuesday)
Issued at 328 AM EDT Wed Jul 26 2017

High pressure will build in from the north and bring fair wx with
seasonable temperatures Friday night through the weekend. High temps
this weekend will reach the lower to perhaps middle 80`s with low
temperatures mainly in the 50`s except in the 40`s in typically
cooler locations.

A weak cold front will move in from the northwest early next week.
This system will have limited moisture to work with so there is only
a small chance for a shower or thunderstorm mainly on Monday. The
overall wx pattern continues to look quite dry however through the
middle of next week as another high pressure ridge will build in and
bring fair wx with seasonable temps.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 156 PM EDT Wed Jul 26 2017

Expect VFR conditions to prevail through at least midnight at all
of our TAF sites. The complex of thunderstorms moving east, north
of I-96 early this afternoon will not impact any of the TAF sites
this afternoon.

Since there is a cold front slowly working it`s way south across
Lower Michigan tonight into Thursday morning, it is not out of the
question there could be a few showers or thunderstorms near the
front. However, the case for these storms impacting any of our TAF
sites is weak at best, so I did not put VCTS in any of the TAF`s
expect MKG. I did have VCTS at MKG based on the HRRR showing a
band of thunderstorm (west to east) developing near MKG during the
early evening, that tracking east this evening. Even so those
storms do not get to GRR, AZO, BTL, LAN or JXN. Still be aware
this is still possible tonight.

On Thursday I would think there should be an area of MVFR cigs
behind the front. I did not bring the low clouds to JXN since by
the time the front gets that far south is midday and I am thinking
there will be enough mixing to prevent that.

So, bottom line, VFR till near sunrise Thursday, then expect MVFR
cigs.

&&

.MARINE...
Issued at 328 AM EDT Wed Jul 26 2017

Some strong thunderstorms are possible this afternoon and evening.
Winds in thunderstorms could gust over 30 knots. Fairly quiet
conditions expected on thursday but winds will pick up from the
north on Thursday night and conditions could become hazardous to
small craft.


&&

.HYDROLOGY...
Issued at 1055 AM EDT Tue Jul 25 2017

With near- to drier-than-normal conditions lately and a dry pattern
setting up for the next week, scattered showers and thunderstorms
Wed and Thu will be a welcomed sight to those looking for rain.
This does not look like a guarantee for everyone to get appreciable
rainfall amounts. But with 1.5 to 2.0 PW values nosing in and
relatively slow storm cell movement, it`s possible for some
locations to receive over an inch or two of rain in a couple hours.
Excessive rainfall to the point of flooding does not appear likely
due to a questionable storm coverage extent over the area.

&&

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

$$

UPDATE...NJJ
SYNOPSIS...Ostuno
SHORT TERM...Ostuno
LONG TERM...Laurens
AVIATION...WDM
HYDROLOGY...CAS
MARINE...Ostuno



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