Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 161134
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
734 AM EDT Mon Apr 16 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 325 AM EDT Mon Apr 16 2018

Our Slow moving storm system has moved to our east so now we are
in the cold wrap around phase of the system. This means snow
showers into Tuesday morning. Briefly A high pressure system moves
across the area later Tuesday into Wednesday but that is quickly
followed by yet another storm for later Wednesday into Thursday.
This will be a rain to snow event. Temperatures will run about 10
to 20 degrees below normal through Thursday. Then a warm up begins
late in the week and continues into the weekend.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 325 AM EDT Mon Apr 16 2018

Expect snow showers with only minor accumulations (mostly west of
US-131) into Tuesday morning and temperatures running 20 to 25
degrees below normal into Wednesday morning. Then we get another
rain to snow event later Wednesday into early Thursday.

A 2 way omega block (Upper low south of Greenland, upper ridge
along the east coast, upper low over the Great Lakes, upper ridge
over the central Plain, then another upper low over the western
CONUS) has got our upper air pattern seriously stalled. That
delays the total departure of our current system till later
Tuesday when a southerns stream wave from the North Pacific cuts
through the western part of the upper level block to finally force
a more progressive pattern. The system later on Wednesday into
Thursday is the system that breaks through all that blocking and
finally leads to a more zonal upper level flow pattern later in
the week.

In the shorter term, our system has finally moved far enough to
the east to put Southwest Michigan on the western side of the
system. This brings very cold air for this time of year today
through Tuesday. Since we have cyclonic flow till Tuesday
afternoon and the upper jet does not get overhead or east of here
till then. we will be in a great setup for lake enhanced snow
showers into Tuesday morning. This also leads to inversion heights
that rise to over 10000 ft by tonight. Also the DGZ becomes
saturated by midday today. Add to that a shortwave rotating around
the upper low coming into the area later today and we have all we
need for snow showers into Tuesday morning.

We do break out of this by midday Tuesday as we get shortwave
ridging between the departing system and the next one coming in
off the Pacific into the Central Plains. Thanks to our blocking
high over eastern Canada the next system must go south of us. Even
so we do get a warm advection precipitation event later Wednesday.
This leads to slightly milder temperatures but still well below
normal for this time of year.

.LONG TERM...(Wednesday night through Sunday)
Issued at 325 AM EDT Mon Apr 16 2018

We continue to focus on one system in the long term that looks to
occur during the Wed night into Thu time frame. A fairly amplified
upper trough will emerge from the Rockies and close off over the
Plains as it goes negative tilt.

It continues to look like mainly rain in the short term will
transition to snow Wed night with strong dynamics with the closed
low and cooler nocturnal temps. Some accumulations will be likely by
Thu morning. Exact amounts and location of accums are still a bit
uncertain. We expect rain will mix back on during the day on Thu
before the pcpn comes to an end.

We then look to get into a much quieter and gradually warmer period
from Thu night through next weekend. Another upper low will move
east across the CONUS, but will be a bit slower and further south.
This low will force a fairly amplified upper ridge over our area,
with gradually warming temps aloft. Temps will likely be around 50
on Thu, and should warm to hit 60 next weekend with dry
conditions.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 735 AM EDT Mon Apr 16 2018

Expect snow showers with MVFR to IFR conditions through tonight.
As typical of snow showers the ceilings and visibilities will vary
considerably from time to time. There is a shortwave that comes
through the area this evening so I would think the lowest
condition at that TAF sites will be between 21z and 06z.
Conditions should improve during the day tomorrow. Skies may
actually clear tomorrow night.

&&

.MARINE...
Issued at 325 AM EDT Mon Apr 16 2018

With our slow moving storm system and very cold air coming in
around the system, naturally we will have a decent amount of
northwest winds for the next 60 hours or so. So, I extended the
Small Craft Advisory till Tuesday evening.


&&

.HYDROLOGY...
Issued at 330 PM EDT Sun Apr 15 2018

As precipitation continues across the region, river levels are
around normal but rising. Precipitation totals will range from over
an inch and a half to around three inches from this past Friday
into Monday. This could lead to river flooding, but at this time
only the Muskegon River at Bridgeton is forecast to rise to near
flood stage. Stay tuned, as more flood warnings may be on the way if
all of the precipitation is realized.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 8 PM EDT Tuesday for LMZ844>849.

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...NJJ
AVIATION...WDM
HYDROLOGY...63
MARINE...WDM



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