Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 191740
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1240 PM EST Fri Jan 19 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 258 AM EST Fri Jan 19 2018

Fair weather with moderating temperatures will continue into
Saturday then rain will move in on Sunday and Monday. Colder air
with snow and snow showers will arrive Monday night into
Wednesday.

&&

.SHORT TERM...(Today through Sunday)
Issued at 258 AM EST Fri Jan 19 2018

Forecast issues are for timing and p-type early Sunday as area of
isentropic ascent and deeper moisture advecting in from the south
brings the chance patchy freezing rain at the outset. Temps and
dew points are at or near freezing across the southern zones
around midnight when the precip is expected to begin so there
could be a brief period of fzra and this is mentioned in the
forecast.

Model soundings also show the potential for some snow across the
northern tier, especially the higher elevations into Sunday
afternoon before the column goes above freezing with all liquid
expected by late afternoon and evening.

.LONG TERM...(Sunday night through Thursday)
Issued at 258 AM EST Fri Jan 19 2018

Strong isentropic upglide and increasing moisture north of the warm
front will result in widespread rain showers Sunday night. Rain will
continue Monday as the strong low pressure system moves northeast
into the Great Lakes region.

Patchy fog is also expected due to the high boundary layer moisture
and melting of any lingering snow cover. It is not completely out of
the question that a few thunderstorms may develop along and just
ahead of the sfc low/cold front. We left it out of the fcst at this
time mainly due to weak instability.

Colder air will move in on the back side of the departing system and
in conjunction with wrap around moisture behind the departing low
will cause rain showers to change over to snow showers Monday night.
Snow showers will continue Tuesday with potential for light
accumulations of around 1 to 3 inches as suggested by a consensus of
latest medium range guidance.

A high pressure ridge will then build in from the west and bring
fair wx Wednesday and Thursday. Temperatures will average near
normal for this time of year Tuesday through Thursday.

&&

.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 302 PM EST Thu Jan 18 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 warming trend through the weekend will result in snowmelt.
Existing snow depths generally contain 0.2" to 0.5" of liquid.
Precipitation amounts of 0.5" to 1.00" are possible through early
Tuesday. This will most certainly lead to some rising rivers with
minor flooding possible next week, especially on smaller streams.

Highs in the 40s and lows in the mid-20s to around 30 degrees may
not be quite warm enough to drastically weak ice on all rivers. This
may mitigate some of the impact. However, ice jams are nearly
unpredictable. Residents living near rivers in flood prone areas
should remain vigilant late this weekend and next week should ice
jams develop.

&&

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

$$

SYNOPSIS...Ostuno
SHORT TERM...Ostuno
LONG TERM...Laurens
AVIATION...WDM
HYDROLOGY...JAM



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