Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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998
FXUS63 KGRR 201746
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
146 PM EDT WED JUL 20 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 1024 AM EDT Wed Jul 20 2016

High pressure will move east today with temperatures and humidity
increasing into the weekend. There will be a chance for showers
and thunderstorms after midnight tonight. Another round of
thunderstorms will be possible Thursday night. These storms could
produce damaging winds. Friday will be hot with highs well into
the 90s. After another round of showers and thunderstorms
Saturday night into Sunday...next week should feature somewhat more
seasonal temperatures with highs in the 80s.

&&

.UPDATE...
Issued at 1024 AM EDT Wed Jul 20 2016

An increasing number of convection allowing models advertise
thunderstorms moving south into the forecast area overnight and
persisting much of the day Thursday...
09Z HRRRX - http://go.usa.gov/xaQaP
NCAR WRF Ensemble - http://goo.gl/3s0vPT

Please reference the Hazardous Weather Outlook for further
details. We see a couple possible scenarios during the day
Thursday:

1) Storms persist into Thursday afternoon, mitigating afternoon
heat impacts.

2) Storms do not materialize, allowing hazardous heat
conditions to develop in the afternoon.

Even if storms occur Thursday, we still anticipate a severe threat
Thursday night as a seasonably strong low level jet will provide
enough low level theta-e advection to recharge the atmosphere.

These factors will be the main forecast concerns moving forward
this afternoon.

&&

.SHORT TERM...(Today through Friday)
Issued at 328 AM EDT Wed Jul 20 2016

Forecast concern in the near term is the potential for strong to
severe storms Thursday night. There is fairly good model
consensus for an MCS to drop south through Lower Michigan, which
the synoptic pattern would be favorable for. Forecast soundings
are impressive with CAPEs over 2000 and lifted indices minus 5 to
minus 7 overnight. Shear profiles are not as impressive with 25 to
30 knots of 0 to 6 km shear across southwest Lower Michigan.

The extent of the convection will also have a large bearing on the
max temperature forecast for Friday. We will go with maxes close
to the superblend guidance in the 90 to 94 range, but this could
go higher without convection...or be lowered by more extensive
clouds and rain along with a lingering cold pool of outflow.

.LONG TERM...(Friday night through Tuesday)
Issued at 328 AM EDT Wed Jul 20 2016

Saturday night looks like an active period across Lower Michigan.
Low pressure over the upper Mississippi Valley will move east and
push a warm front north across the cwa. We`ll likely see showers and
storms develop near this front. At the same time, a cold front
moving east across Wisconsin will also generate some storms. Li`s
near -5c coupled with shear values in the 35-40kt range suggest some
organization is possible. Models suggest the pcpn may linger through
Sunday. The ECMWF and GFS show the cold front exiting the cwa Sunday
evening. Cooler and drier air will filter into the cwa Monday and
Tuesday.

Saturday will be a hot day with highs in the lower 90s and then near
90 Sunday but then dropping to the mid 80s Monday and Tuesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 146 PM EDT Wed Jul 20 2016

VFR weather is expected this afternoon and tonight. FEW/SCT
cumulus development is possible this afternoon with bases around
5000ft. Otherwise, the only cloud will be some cirrus debris
clouds from upstream thunderstorms through this evening. The
cirrus will have bases at or above 18,000ft.

Tonight upstream thunderstorms may lower and thicken the cloud
cover at times, but VFR conditions will continue. The weather may
become more active Thursday morning when some model data indicate
a few showers and storms drifting southeast through the area.
Confidence is not high in this precipitation so only have VCSH in
the TAF for Thursday morning (14z-18z).

&&

.MARINE...
Issued at 328 AM EDT Wed Jul 20 2016

Winds and waves will be increasing today and tonight and may come
close to being hazardous to small craft on Thursday. There will be
a slight chance of thunderstorms through Thursday with a better
chance Thursday night. There is a chance of severe weather
Thursday night.


&&

.HYDROLOGY...
Issued at 330 PM EDT Tue Jul 19 2016

With chances for thunderstorms the latter half of the week and into
the weekend, but low confidence in timing and coverage, the pattern
will likely continue to support many locations not getting enough
rain and some locations getting too much too quickly. WPC basin-
average QPF is advertising a range between a half inch to nearly 2
inches across the CWA through Friday evening, with greater amounts
favored toward the south and west. But as is typical with weakly
forced summer convection, rainfall totals will probably vary
substantially over short distances.

&&

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

$$

UPDATE...TJT
SYNOPSIS...TJT
SHORT TERM...Ostuno
LONG TERM...04
AVIATION...Duke
HYDROLOGY...CAS
MARINE...Ostuno



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