Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 092335
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
735 PM EDT Thu Apr 9 2020

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 204 PM EDT Thu Apr 9 2020

- Fair weather through Saturday afternoon

- Very strong winds possible Sunday night and Monday

- Lake effect snow possible Monday night into Tuesday.

- Well below normal temperatures Tuesday through Friday

&&

.DISCUSSION...(This evening through next Thursday)
Issued at 204 PM EDT Thu Apr 9 2020

- Fair weather through Saturday afternoon

A ridge of high pressure will build over the region late tonight
into tomorrow. That will slacken any remaining gusty winds.
The cooler northwesterly flow will keep temperatures below normal
tomorrow into Saturday. Skies will be cloudy in the morning but
clear as the day continues. Temperatures will moderate to normal
Saturday.

A warm frontal boundary will be slowly moving into the region
Saturday afternoon and evening. There will be an increase in
clouds and maximum temperatures on Saturday will moderate back to
normal. There is a chance for showers Saturday evening into
Sunday as a deepening upper level trough rings the moisture from
the south. That upper level trough will continue to dig into the
midwest. The models have a good consensus for an 850 MB clouds low
trekking through the Great lakes with above normal PWATs
associated with it.

 While the heaviest areas of moisture are further south and east
of the area, The PWATS based on moisture advection should bring
periods of heavy showers to southwestern Michigan.

- Very strong winds possible Sunday night and Monday

Concern continues to increase in regard to a potential strong
wind/high wave/lakeshore flood event early next week. Both the
GFS and ECWMF operational and ensembles show a deepening low pivoting
out of Colorado across the plains on Sunday, then northeast from
the Mid Mississippi Valley through the Eastern Great Lakes Sunday
night through Monday night. The low is quite deep for this time of
year and is more rival that of a Gales of November type of storm.

At this point the depth of the system in all of the models at least
makes it into the 980`s, but some are showing 970`s mb depth. A lot needs
to come together for this system to materialize with a cut off low
in the desert southwest being picked up by a northern stream trough.
The wave phases and deepens as it goes negative tilt through our
area. Right now the depth of the low in the models is between 972-985mb`s.
This depth of low when combined with a 1030mb high in the plains will
create a strong pressure gradient across the Great Lakes. So, we will
be watching this system from run to run for consistency and our
concern will increase if it remains steady in the models.

- Lake effect snow possible Monday night into Tuesday.

The current runs of the EC and GFS continue to track the upper
and mid level lows over Hudson Bay. As this low pulls to the
northeast cold air will fill into the region in is wake. Latest
850mb Temperatures are in the -12C by Tuesday with the cold air
advection continuing through the week.
 A deformation zone sets up Monday night into Tuesday which,
coupled with a strong pressure gradient across the lake, could set
up for some lake effect snow showers with light accumulations
possible Monday night into Tuesday.

- Well below normal temperatures next Tuesday through Friday

 This cold and unsettled pattern will continue through the week.
showers could be possible midweek but current progs keep
precipitation just north of the area. Temperatures are tracking
to be 10 to 15 degrees below normal throughout the week with high
temperatures in the upper 30s to low 40s and lows in the 20`s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 733 PM EDT Thu Apr 9 2020

The rather strong showers will diminish into the evening. The most
likely location for impacts is KLAN. They have one more decent
snow shower headed their way. The gusty winds will also settle
down gradually into the evening as the temperature cools off.
While a few isolated showers could pop up on Friday they are
expected to be be few and far between. The winds should also be
lower than Thursdays winds.



&&

.MARINE...
Issued at 300 PM EDT Thu Apr 9 2020

In terms of impacts wind gusts of 50+ mph appear possible in all
areas with the strongest along the Lake Michigan shore. Waves on
Lake Michigan will easily top 10 feet and likely push to around
15 feet if the 970`s mb system verifies. Lakeshore flooding will
be likely with water being pushed up over the beach in some areas
and back up into river mouths. The flooding would be rival that of
what we saw in some of the systems from last October/November. Finally,
beach and dune erosion would be significant. The flooding and erosion
threat increases if the track of the low comes up through the
Lake Huron region. This track will create strong easterly winds
for a time through the Straits of Mackinac which can push a significant
amount of water into Lake Michigan adding to the flooding/erosion
threats by raising lake levels. This occurred during a system around
Dec 1st of last year and created some of the highest water levels ever
recorded at the NOS Water Level gages at Ludington and Holland.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Lakeshore Flood Advisory until 8 AM EDT Friday for MIZ037-043-
     050-056-064-071.

LM...Gale Warning until 8 AM EDT Friday for LMZ844>849.

&&

$$

SYNOPSIS...Ceru
DISCUSSION...Ceru/Duke
AVIATION...MJS
MARINE...Duke



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