Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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363
FXUS63 KGRR 281929
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
329 PM EDT Wed Jun 28 2017

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

.SYNOPSIS...
Issued at 329 PM EDT Wed Jun 28 2017

A risk of showers and thunderstorms will exist through the rest of
the work week.  However peak times for rain should occur tonight,
and Thursday night, and Friday afternoon and evening.  Humidity
levels will increase on Thursday and remain muggy into Friday.  It
will warm each day, with highs in the upper 70s to mid 80s.

It appears we will dry out by the weekend, but more rain chances
return by Monday and Monday night, and again Wednesday.  High
temperatures this weekend and into mid week should mainly remain
from 80 to 85.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 329 PM EDT Wed Jun 28 2017

A wet and stormy pattern is in store through Friday night.  It will
also turn much more humid and warm.

The general pattern is somewhat zonal across the Great Lakes through
the short term, but upper lows over Canada will continue to bring a
series of short waves that will bring periodic showers and storms.
With precipitable water values occasionally in the 1.5 to 2.0 inch
range, some localized rains can be expected.  We will also see an
occasional bouts with severe storms.

We continue to see the MCV over Central Lake MI move east and
weaken.  This will bring a few dieing showers to areas mainly north
of I-96 into the evening.  Meanwhile the that is over SW WI is
producing more storms across IA, IL and WI.  This jet will head
toward the NW portion of the GRR CWA late tonight and will bring
another surge of pcpn mainly to areas along and north of I-96.
Instability will be a bit questionable tonight, so not expect much
risk of severe storms.  With the LLJ nosing the NW CWA expect the
heaviest rains to occur there tonight, with half to three quarters
of an inch possible.

The pcpn will exit Thursday morning, only to see another surge
arrive late afternoon/early evening.  We should be able to recover
the instability in the mid day lull making severe weather possible.
Another LLJ, along with solid upper divergence from the upper jet,
arrives by late afternoon/early evening.  Bulk shear also looks
favorable, around 30 knots, to anticipate organized storms. Damaging
wind and large hail will be the main threats, but we can not rule
out an isolated tornado with favorable shear in the lowest 1km.
Seems that the highest threat will be over eastern half of the CWA,
and south of Mt. Pleasant.  The severe threat winds down after
midnight as the jet dynamics exits.  The heaviest rain Thursday
night should be south of I-96.

Friday and Friday will also see bouts of showers and storms.  The
possibility of severe also exists late afternoon/early evening
especially over the SW CWA where yet another short wave and LLJ and
upper jet moves in.  Once again the heaviest rain threat appears to
along and south of I-96.

All told expect we will see some areas pick up over two inches of
rain mainly south of I-96.  The rain soaked Central Lower MI should
see it`s steadiest rains tonight, with lesser amounts after that.
Most areas north of I-96 should see a half an inch to an inch of
rain through Friday night.

.LONG TERM...(Saturday through Wednesday)
Issued at 329 PM EDT Wed Jun 28 2017

The main challenge in the long term deals with the timing of any
showers or thunderstorms.

The long term period will start off with a mid level low across the
Canadian Prairies that will be dropping southeast into the Great
Lakes region on Sunday.  The associated height falls along with some
diurnal instability may lead to a few showers or perhaps
thunderstorms.  The axis of deeper moisture shifts east on Sunday so
the main period for precipitation would be on Saturday. Temperatures
will likely end up being close to normal during the day but a little
below normal at night.

Then a positively tilted mid level shortwave slowly drops into the
Lower Ohio or Middle Mississippi Valley for Monday into Tuesday.  We
will be on the north side of this system. It will tap some gulf
moisture supporting better instability.  Mid to upper level winds
will weaken with time.  Thus any storms that do form could be slow
moving.  As a result...there could be a heavy rain risk with them.
Will feature scattered thunderstorms for the period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 140 PM EDT Wed Jun 28 2017

A moist and increasingly unstable airmass will be overspreading
the TAF sites during the forecast period. Impacts at this time
look to be local and temporary. For now I included only VCTS
during parts of the forecast period given the uncertainty on the
exact location of any storms. Where any storms occur brief IFR
will be possible. Increasing low level moisture may support MVFR
clouds...mainly over the KMKG TAF site.

Impacts from the winds are expected. All sites should see some
gusts over 25 knots...with local 35 knots not out of the question.

&&

.MARINE...
Issued at 329 PM EDT Wed Jun 28 2017

Will continue the marine headlines, with improvement not expected
until Thursday afternoon.

&&

.HYDROLOGY...
Issued at 223 PM EDT Wed Jun 28 2017

River levels continue to fall and should continue falling into
tonight. There could be some minor rises by Thursday as a quarter
to three quarters of an inch of rain is expected tonight into
Thursday morning. Another half inch to an inch of rain is expected
on Friday, causing more moderate rises by Saturday.

During both these periods of expected rainfall there will be the
chance for thunderstorms with heavier amounts of rain. This could
cause sharp rises, especially where soils are still saturated such
as along the Muskegon, Chippewa and Pine Rivers.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through Thursday afternoon for MIZ037-
     043-050-056-064-071.

LM...Small Craft Advisory until 2 PM EDT Thursday for LMZ844>849.

&&

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...MJS
AVIATION...MJS
HYDROLOGY...Ostuno
MARINE...JK



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