Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 171753
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
153 PM EDT Tue Apr 17 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 321 AM EDT Tue Apr 17 2018

Snow showers will diminish through the day as high pressure moves
over the region by late in the day. We will see one last day today
of much below average temperatures with highs only in the 30s once
again.

After a break tonight and early Wednesday, rain will spread over the
region Wednesday afternoon as the next system moves through the
region. Rain will turn to snow Wednesday evening, with some
accumulations of an inch or so possible mainly on grassy areas. Snow
will come to an end Thursday morning.

Much quieter weather is then expected to move in later Thursday, and
hold over the area through the weekend and into early next week.
Temperatures will warm up, with 60 likely this weekend, and warmer
temperatures possible early next week.

&&

.SHORT TERM...(Today through Thursday)
Issued at 321 AM EDT Tue Apr 17 2018

Our main focus in the short term is on the Wed afternoon and Wed
night system, and potential snow accumulations with it. Right now,
this event looks like it should not produce significant impacts for
the area.

We have ongoing snow showers this morning across much of the area,
with limited accumulations only under the heavier snow showers. One
short wave can be seen moving into Nrn Indiana, while the main upper
low is dropping into toward the tip of the mitt. The snow showers
will keep going as is through daybreak as the deeper moisture and
lift ahead of the upper low will help the cause. Delta t/s over the
lake of around the mid-upper teens C will also continue to help the
cause early this morning.

We will see the snow showers come to an end this afternoon/early
this evening. The lift and better moisture depth will come down with
the passage of the upper low just after 12z. Upper cyclonic flow
will hold until later this afternoon when the upper jet core and
shear axis lifts NE of the area. This will bring ridging overhead,
and allow for some clearing to take place.

The break in the pcpn will occur from tonight and through Wed
morning, before pcpn chances increase from SW to NE Wed afternoon.
We will see strong moisture transport take place out ahead of the
incoming long wave trough that closes off as it emerges over the
Plains. Enough warm air from diurnal heating for the first half of
Wed and the warm air advection will allow just about all of the pcpn
to fall as rain prior to 00z Thu. We can not rule out some thunder
across the srn half of the area, as some weak elevated instability
is shown by the models.

Pcpn appears to change over to snow then fairly quickly after 00z
Thu with some lighter snow accumulations expected. This occurs as
the sfc low quickly moves SE of the area, and colder air advects in
behind it. There is some decent fgen in the mid levels that comes
through due to the deformation zone of the upper low slipping by to
our south.

Better snow accumulations look to be limited by relatively warm
ground temps from Wed. Also, the mid level fgen/deformation looks to
weaken quite a bit as it translates into the area from our west.
This is because the upper trough to our NNE will absorb the incoming
upper low, and the deformation zone dissipates. Also, the phasing of
the upper low/trough will take the initial upper low through the
area quick, not allowing it to do too much damage. We are looking at
most accumulations around an inch on grassy areas. Roads may slicken
up quick if a heavier burst moves through and overcomes the warmer
ground temps.

Most, if not all of the pcpn should move out of the area by 12z Thu.
We will see upper ridging build in Thu afternoon, allowing skies to
clear out through Thu.

.LONG TERM...(Thursday night through Monday)
Issued at 321 AM EDT Tue Apr 17 2018

Upper level low pressure over the Eastern Great Lakes and New
England will exit east Thursday night. Upper ridging will build into
the Plains and then Ohio Valley through the early part of the
weekend, break early in the weekend, then rebuild for Sunday and
Monday. This will position surface high pressure over Michigan late
Thursday night through Monday. Weak shortwave will drop through
Michigan Saturday as the ridge breaks, bringing an increase to
mid/high clouds. Otherwise, the weather will be very quiet with more
sun than clouds Friday and Sunday/Monday.

Temperatures will gradually warm Friday through Monday, reaching
close to normal by Monday (which is around 60).

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 153 PM EDT Tue Apr 17 2018

Snow showers will be diminishing and ceilings will range from 2500
to 3500 feet AGL through this evening. Winds will be west to
northwest around 15 knots gusting over 20 knots. Winds will go
east overnight and decrease to 10 knots or less.

&&

.MARINE...
Issued at 321 AM EDT Tue Apr 17 2018

The Small Craft Advisory will remain in effect through this
afternoon. Northwest winds will remain gusty into this afternoon
before they diminish. Waves will take until 00z tonight or so to
drop below the 4 ft criteria. Once winds diminish today, the next
period of possible marine headlines looks likely for Wed night
through Thu night.


&&

.HYDROLOGY...
Issued at 1122 AM EDT Tue Apr 17 2018

River levels are above normal in Southern Lower Michigan and around
normal in Central Lower Michigan. The significant precipitation over
the weekend has led to rising river levels across the area. With
only a few tenths of precipitation expected Wednesday into Wednesday
night and nothing else until next week, rises are still expected to
continue for the next several days. Minor flooding near river banks
is still possible.

&&

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

&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...HLO
AVIATION...Ostuno
HYDROLOGY...63
MARINE...NJJ


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