Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 192028
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
328 PM EST Fri Jan 19 2018

LATEST UPDATE...
Synopsis/Short Term/Long Term/Hydro

.SYNOPSIS...
Issued at 328 PM EST Fri Jan 19 2018

It will remain mild and quiet through Sunday morning. High
temperatures both Saturday and Sunday will be in the upper 30s to
lower 40s.  Light rain will hold off until Sunday afternoon or
Sunday night, but it will eventually become steady by late Sunday
night.  Areas north of Big Rapids and Mt. Pleasant could see a
wintry mix into Sunday night.

Monday will be another mild day with highs in the 40s, then we
should see temperatures drop to 30 to 35 for the middle of next
week, before another warm up starts Friday.  The precipitation will
continue Monday and Tuesday, but will change to snow late Monday
night into Tuesday.  The rest of the work week appears quieter.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 328 PM EST Fri Jan 19 2018

Mild air will hold in place through the short term with highs of 40
to 45, and lows 30 to 35.  Rain arrives Sunday afternoon or night.
However northern interior areas may see some freezing rain Sunday
night.

A slow moving boundary will cross WI over the next 36 hours keeping
MI within the warm sector.  Temps will remain 10 to 15 degrees above
normal.  Normals are near the lowest of the entire year in this time
frame.  The windy conditions tonight will lessen through the rest of
the short term.

With the boundary to our northwest slowly inching toward us, we will
gradually see deeper boundary layer moisture arrive.  We may see
patchy fog Saturday afternoon due to increasing dew points.  And
eventually we will develop stratus from south to north Saturday
evening into Saturday night.  However the moisture appears too
shallow to produce pcpn, so expect we will stay dry through noon
Sunday.

Into Sunday afternoon and Sunday night the surface boundary sags
into Lower MI as low pressure moves to about Kansas City by daybreak
Monday. Moisture depth will increase and rain will increase in
coverage, especially into Sunday night.  The warm air arrives aloft
first across Central Lower, and some areas of shallow cold air could
hang on.  For now I have a mix of rain and freezing rain over the
interior areas, north of Big Rapids and Mt. Pleasant.

.LONG TERM...(Monday through Friday)
Issued at 328 PM EST Fri Jan 19 2018

There is little question we will get a decent rain event (.75" to
1.25" in 12 hours) Monday. The cold air then wraps in behind the
system so we get lake enhanced snow showers Tue into Wed but most of
the snow will occur on Tuesday.

Looking at the "Big Picture" we have switched from a northern stream
dominant pattern (2nd half December into early January) to a
southern stream dominated pattern. It seems this pattern will
continue into next week and likely beyond that. It seems the MJO
going into phase 4 and being a strong phase 4 is a good part of the
reason for this change (we were in the cold phases of 8 through 2
late December into early January when the northern stream
dominated). In any event model forecasts suggest we will not get
back into a cold phase for 3 weeks. The MJO has to progress through
phase 7 to get back into a cold phase for Michigan. So this means we
should expect an active southern stream at least for the next 2
weeks for sure.  Both the ECMWF and the GFS and both models
ensembles support this idea too.

We are seeing an omega block developing then really strengthening
mid week. This locks the low in the Gulf of Alaska in place.  Even
so, southern stream upper wave energy continues to progress through
that southern part of that pattern. So the first system we get,
Monday goes negative tilt at upper levels Sunday afternoon as it
pulls out of the Southern Plains. As it reaches Michigan (Monday) it
then phases with the northern stream which helps deepen the storm
even more. This also helps pull in cold air from Canada  which is
what allows for the lake enhanced snow event Tuesday into midday
Wednesday.

Now the glitch, both the GFS and ECMWF continue to show the track of
the storm farther south and west, even the 12z run is significantly
farther south and west than the 00z run was which was farther south
and west than the 12z run on Thursday.  Given this trend, I wonder
if that real track will be even farther south than what we are
seeing now.  At this point there is still enough warm air to mean
all rain over the entire CWA as the main system comes out. However,
if this trend continues we may start to see freezing rain /sleet in
our northern zones and this would not be a trivial amount of those
either. For now I will stay the course with all rain but we will
need to watch this closely.

This creates a problem for the temperature forecast for Monday. Any
place where the warm front come through will get well into the 50s
but if the warm front does not get through, that place may stay in
the upper 30s or lower 40s with a sift east wind. Not being sure
where the warm front will be, I did not change our highs Monday.

So the bottom line is expect rain, heavy at times Monday morning
with a fair amount of wind. Then the cold front comes through, winds
turn southwest and the cold air comes back.  We will get into the
wrap around snow showers Monday night and those will be going strong
Tuesday morning into Tuesday afternoon. Ridging follows mid week. So
expect quiet weather with a warm up.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1240 PM EST Fri Jan 19 2018

VFR conditions prevail across the GRR TAF SITES at 18z. I expect
only high clouds for all of them through at least 06z tonight. The
NAM and GFS suggest low clouds will move in by sunrise at most, if
not all of the TAF sites, so that is how I played the TAFs.
However it should be noted the ECMWF suggests the low clouds do
not actually come in till Sunday morning. Clearly we will be
watching this issue.

&&

.HYDROLOGY...
Issued at 328 PM EST Fri Jan 19 2018

The latest update from the Muskegon River ice jam in Mecosta County
is that slow improvement continues. Chunks of ice remain in the
river, but are stable at this point with slowly falling river
levels. Minor flooding is ongoing immediately along the river bank
in low lying areas.

A limited snowmelt will occur Friday and Saturday as high
temperatures climb to around 40, then a more rapid melting of the
snow cover is likely Sunday and Monday as dewpoints climb above 32
degrees and winds increase. The snowmelt will be more complete in
southern Michigan where warmer air and higher dewpoints will be in
place for longer. Water contained within the snow is in the ballpark
of a quarter inch. Rainfall on Monday will likely range from a half
to one inch. Much of this water will efficiently run off into rivers
and streams due to frozen soil.

The combination of ice jams and runoff will increase the risk of
river flooding next week. Nuisance flooding in the typical flood-
prone spots is a good bet. Flooding encroaching on vulnerable homes
and businesses is less certain but will have to be monitored.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...WDM
AVIATION...WDM
HYDROLOGY...JK


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