Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 211924

Area Forecast Discussion
National Weather Service Grand Rapids MI
324 PM EDT Sun May 21 2017

Synopsis/Short Term/Long Term/Marine

Issued at 324 PM EDT Sun May 21 2017

A large upper trough will camp out over the Great Lakes much of this
week keeping the threat of showers and thunderstorms in the
forecast. Temperatures will remain a bit below normal However, by
the end of the week, the trough will move east and temperatures will
rise as we head into the holiday weekend.


.SHORT TERM...(This evening through Tuesday night)
Issued at 324 PM EDT Sun May 21 2017

Forecast concerns deal with pcpn trends through the period.

The occluded front pushed through this afternoon and we`re seeing
clearing behind the front. We should see dry weather through Monday
before a short wave rotates around the bottom of the upper trough.
That will bring scattered showers to the cwa Monday night and the
threat of pcpn will remain through Tuesday night.

Thunder is a possibility Tuesday. Both SBCAPE and MUCAPE ARE in the
500-1k j/kg range during this time frame. Both the sfc low and upper
reflection will move closer to Lower Michigan Tuesday/Tuesday night.
Shear values are progd to increase to 40-45kts Tuesday afternoon, so
we may be looking at a few stronger storms as they begin organizing.

.LONG TERM...(Wednesday through Sunday)
Issued at 324 PM EDT Sun May 21 2017

Intermittent showers and below normal temperatures will continue
Wednesday and Thursday beneath a slow moving upper low. Once this
feature finally departs, a warm front lifts north toward the area
and brings another risk of showers for later Friday into early
Saturday. Confidence is low regarding the timing/coverage of this
pcpn potential given uncertainty in how quick and how far north the
warm front gets, as well as the timing of a shortwave in the
southwest flow aloft.

As we move into the holiday weekend, guidance currently shows yet
another upper low just north of North Dakota on Saturday. This
feature is progged to track slowly east along the U.S./Canadian
border over the weekend. Since we will be south of this next upper
low, a warmer air mass and temperatures near normal are anticipated.
Pops are challenging next weekend though with the possibility of a
few shortwaves in the southwest flow aloft kicking off a round or
two of showers or tstms.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 155 PM EDT Sun May 21 2017

Showers and isolated tstms are now exiting to the east with a
cold frontal passage. Rapid improvement of cigs, from IFR/LIFR to
MVFR/VFR, takes place behind the front along with a wind shift to

For tonight more clouds rotate in from the west with more MVFR
cigs possible. Those clouds lift out of the area on Monday
morning, leading to VFR but breezy conditions for the rest of the
day. Winds on Monday will be from the southwest at 15-25 kts.


Issued at 324 PM EDT Sun May 21 2017

Issued a small craft advisory for tonight through Monday evening.
Winds and waves will increase as the pressure gradient tightens.
Waves will build to 3 to 5 feet after midnight and decrease Monday


Issued at 159 PM EDT Sun May 21 2017

Rivers levels have returned to near normal, but recent rain is
expected to bring rising levels to river systems in Southern Lower
Michigan. Additional precipitation is possible Monday night through
Friday. The Portage River near Vicksburg is in minor flood. Smaller
streams and rivers may need to be watched for above bankfull rises.
Main stem rivers should be able to handle this rainfall fine unless
guidance trends upward.


LM...Small Craft Advisory from 8 PM this evening to 10 PM EDT Monday
     for LMZ844>849.



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